https://www.scipedia.com/sitemaps/year/2021?offset=1200 https://www.scipedia.com/public/Abdella_et_al_2017b Sun, 21 Mar 2021 12:26:03 +0100 https://www.scipedia.com/public/Abdella_et_al_2017b Investigation of the variation in different soil types and origins is an essential task for Geotechnical engineers. To overcome the effects of this change, the Geotechnical engineers, as well as other professionals, attempted to develop empirical equations unique to a region and soil type to use the soil for its intended purpose. However, these empirical equations are more reliable for the kind of soil where there is a strong relationship of parameters is developed. Hence, it is good practice to develop empirical equations that best fit the soil available in the location that we can access. On the flexible pavement, the subgrade is considered to be an ideal layer to resist wheel load, and its CBR value is considered as the strength measuring a parameter. Conducting a CBR test is an expensive and time-consuming procedure. Also, it is challenging to mold the sample at a desired in-situ density in the laboratory. Furthermore, if the available soil is of poor quality, suitable additives are mixed with soil, and the resulting strength of the soil is assessed by the CBR value which is cumbersome. To overcome such a problem, statistical approaches such as regression-based models are used. This can be used for quick and easily determined parameters. Relative to this, the study has been conducted to develop an equation to show the relationship between the index properties and CBR values precisely located along WelkiteArekit –Hosanna Road of about 121km stretches. It was carried out using thirty samples retrieved from this road and tested in a laboratory. The test result of the regression-based statistical analysis was used to develop the predetermined relationship. The relationship development was performed in the form of an equation of CBR as a function of grain size parameters, Atterberg’s liquid limits, and compaction parameters by considering the effect of individual soil properties as well as the effect of a combination of soil properties on the CBR value. Based on the results of the study for both linear and multiple linear regression analyses, it was revealed that there was a relatively fair relationship obtained by combining plasticity index, the percentage of fine content, and maximum dry density which are strength determinants of fine-grained soils. Also, the results showed that the coefficient of determination for multiple linear regression is R2=0. 731, while for single linear regression is R2=0. 682. Therefore, it is concluded that the index properties of soils are sufficiently accurate in determining the CBR values, of which it can be utilized for preliminary characterization.

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2017g Sun, 21 Mar 2021 12:20:02 +0100 https://www.scipedia.com/public/Quezon_2017g A road traffic accident was one of the severe problems which are affecting once’s a country and leading to death, injuries and property damage resulted in economic loss. The objective of this research was to investigate the effects of Human behaviors and Geometric factors in road traffic accidents along the road of Sululta-Fiche, which is located in the Northern Shewa of the Oromia region. Both probability sampling and non-probability sampling techniques were applied. The primary data were obtained from site observation of blackspot locations. While the secondary source of data was taken from records compiled by the North Shewa traffic office and Oromia Special Zone Surrounding Finfinne traffic Office. Descriptive and analytical design methods were used in this research, while the results were displayed by graphs, tables, and pie charts. From the study, the status of road traffic accidents showed that there were dramatically increase in accidents every year within the study period. A total of 830 crashes occurred in the past three years. From this, 237 accidents happened in 2012, 279 accidents in 2013, and 314 accidents in 2015. From the traffic police report analysis, there were 41 locations in Sululta Town, and 70 locations in Sululta Wereda, where those accidents happened. Based on the results of this research using the priority value approach, there were 12 selected locations in Sululta Town and 10 chosen locations in Sululta Wereda. Therefore, it is concluded that the significant factor in traffic accidents along Sululta –Fiche road was the driver errors such as over-speeding, night driving, and driving without attention, and it was followed by the geometric factors. These road deficiencies contributory to some errors of the drivers, which were inadequate road width, insufficient sight distance, and narrow bridge at sag curves, and improper intersection design. Based on the findings of the study, some of the countermeasures recommended reducing the road traffic accidents are the provision of speed limit signs to forewarn drivers, installation of speed barkers and rumble strips, widening the lane width of pavement, maintenance of the deteriorated road, repair of the road signs and provision of adequate sight visibility for drivers.

]]> Emer T. Quezon https://www.scipedia.com/public/Gurara_et_al_2017a Sun, 21 Mar 2021 12:11:03 +0100 https://www.scipedia.com/public/Gurara_et_al_2017a The research is concerned with the Effectiveness of geosynthetic to improve the performance of the pavement. It has been done on road construction projects under Addis Ababa Road Authority. Results indicated that the performance of bottom pavements structures constructed on poor subgrades with CBR values not greater than 4% was significantly enhanced using geosynthetic material. An increase of bearing capacity for subgrade and can improve the subgrade quality without excavating and filling of select material only by using geomembrane. Geosynthetic reinforcement in pavement design and construction should be widespread. Geosynthetic reinforcements are incorporated into permanent, paved roads either as base (or subbase) reinforcement - in flexible pavements to aid in the support of vehicular loads over the life of the pavement; or as subgrade restraint for construction of flexible or rigid roadways over weak subgrade conditions to aid in support of equipment loads on the unpaved base, or subbase, course during construction. Clearly, both base reinforcement and subgrade restraint with geosynthetics are proven techniques for use in pavement design and construction effectively.

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2016h Sun, 21 Mar 2021 12:00:03 +0100 https://www.scipedia.com/public/Quezon_2016h Road construction projects have been implemented all over Ethiopia as part of the national development plan. Roads are one of the country’s basic infrastructural facilities where high amounts of the budget allocated every fiscal year planning period. Since the cost comprises of a large portion of government investment, a careful evaluation of the alternatives is of utmost importance to make the right choice for a particular project. In the history of Ethiopia's road development program, almost all of the road pavements are flexible, and it demands high foreign currency for asphalt material importing from abroad. In addition, flexible pavement needs to be maintained and rehabilitated within a few years after its initial construction. In view of the emerging cement factories and the availability of cement in Ethiopia, it is practical to consider rigid pavement as one of the alternatives. Relative to this, the research project was conducted with the main objective of identifying the cost and benefit of rigid and flexible pavements at the Chancho-Derba-Becho road project, North Showa Zone in Oromia. The research work had been focused on the specific objectives to determine and compare the life cycle costs of rigid and flexible pavements and to investigate all other qualitative merits of rigid and flexible pavement. To achieve these objectives, a review of related literature, design and specifications, observations and investigations of the actual pavement construction projects, evaluation of life cycle costs, the future value of money and present worth calculation were undertaken with an analysis period of 40 years. While the data considered was gathered through investigation at the actual rigid and flexible pavement projects, an examination of specifications, drawings and pavement design, Ethiopian Road Authority manuals, rehabilitation, and maintenance strategy. In this regard, the cost parameters investigated are initial construction cost, maintenance cost, rehabilitation cost, user’s cost, and salvage value, in addition to other qualitative and quantitative data. Based on the results of the research project, it revealed that the initial cost of rigid pavement was almost twice of the flexible pavement, but in the long run, the cost of flexible pavement per kilometer was found out to have 7.9 Million ETB more than the rigid pavement because of the incurring costs of maintenance through its design life. Therefore, it is suggested that Portland Cement Concrete Pavement (PCCP) shall be used in pavement construction to cater to local material requirements. 

]]> Emer T. Quezon https://www.scipedia.com/public/Dunffa_et_al_2017a Sun, 21 Mar 2021 11:38:02 +0100 https://www.scipedia.com/public/Dunffa_et_al_2017a The construction of physical infrastructure is contributory to poverty alleviation in every country. The road is one of the major components which is very significant in Ethiopia due to the lack of highly developed infrastructure, particularly in the rural road sector. Selection of the appropriate road construction and maintenance methods such as a labor-based method or machine-based method is necessary to be financially viable. Most rural road construction projects usually suffer from the problem of selecting the appropriate technology for the proposed project and implementation of the chosen technology. In Ethiopia, Universal Rural Road Access Program (URRAP) is an employment-intensive program for employment purposes as a first step, out of poverty using labor-based road construction. However, there are problems, constraints, and challenges encountered when implementing labor-based methods leading to enforce the mobilization of machines. The aim of this research study is to carry out the comparative analysis of ongoing and finished rural road projects in Jimma Zone and to establish qualitative and quantitative merit of various technologies used in rural road construction and maintenance. Results showed from financial cost comparison, the labor-based method was 47% cheaper than a machine-based method to carry out the same tasks. On the other hand, the share of unskilled average direct labor cost comprised an astounding 65% more of the total direct cost of a labor-based method. Also, the labor-based method directly employed 300 unskilled laborers per workday for a month to complete a 1.0 km section of a rural road.

]]> Emer T. Quezon https://www.scipedia.com/public/Mamuye_et_al_Select a yeara Sun, 21 Mar 2021 11:34:03 +0100 https://www.scipedia.com/public/Mamuye_et_al_Select a yeara At the time of industrial development, the production of large amounts of wastage required proper disposal. To reduce the disposal problem, utilization of wastage in construction works is a very important aspect. The reuse of industrial waste had gained high momentum for achieving sustainable waste management locally and globally. Keeping this in mind, research carried out to assess the utilization of molasses, lime, and molasses-lime for improving natural gravel for sub-base and base course construction from the Jimma Jiren quarry site. The natural gravel from this quarry site is known to have poor quality since it did not satisfy the ERA standard specification for sub-base and base course construction. To use Jiren natural gravel as a sub-base or base course construction material, it is necessary to improve its engineering properties. The laboratory test matrix in each test plan included variations in additive type, additive content, and curing period. It was established 8% cane molasses by weight of dry soil as the maximum for effective stabilization of natural gravel for sub-base construction, but not suitable for a base course layer. Results indicated that the natural gravel specimens from the Jiren quarry site stabilized with lime provided higher CBR values than molasses used alone. On the other hand, replacing 50% of lime content with molasses indicated better results than the performance of either individual additive. Therefore, the natural gravel blended with the molasses-lime combination is much better when it used for sub-base and base course construction to treat such an inferior quality of natural aggregates.

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2017f Sun, 21 Mar 2021 11:28:02 +0100 https://www.scipedia.com/public/Quezon_2017f There were several slides and associated ground subsidence which brought significant impact on the cracking of walls and floor of several private and governmental buildings in Bonga Town. The principal and secondary roads were also affected by subsidence with vertical displacement up to 1m which hampered the traffic in the town. Water pipelines along the road were disturbed by the sliding which was later repaired. Cracking of the walls and floor of more than 120 private residences and more than 10 government buildings were recorded. The main highway that connects Bonga-TepiMasha via Alamo and Gatiba has been disrupted at four locations. This resulted in hampering traffic for several days. This research aimed to evaluate the cause and failure mechanism as well as the stability condition of the landslides. The study involved the investigation of the Geotechnical parameters of soil and the terrain characteristics to be used for the stability analysis of the slope, including distribution and characteristics of soils, the groundwater table, and the depth and geometry of the failures. The Slope stability analysis is supplemented by using Geo-studio 2004 software. Soil samples were collected and were tested for grain size analysis, distribution analysis (sieve & hydrometer) plastic limit, liquid limit, plasticity index, water content, unit weight of soil, specific gravity, and shear strength parameters following the ASTM procedures. Based on the findings, the landslides were triggered by heavy rainfall. Therefore, the main factors controlling the stability of the slope are soil type and characteristics, slope angle, water (surface and groundwater), and slope steepness. The design of the retaining wall is recommended to mitigate the impact of landslides in the study area. 

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2017e Sun, 21 Mar 2021 11:23:02 +0100 https://www.scipedia.com/public/Quezon_2017e Soil vibration may also cause by the movement of heavy vehicles and train, which affect adjacent structures along the route. The response of soils for incoming vibration from the train is measured by the dynamic properties of soils such as shear modulus and damping ratio. These soil parameters are very significant to study the ground motion as well as the site response of soil deposits under cyclic loading and soil-structure interaction. About this, the research study has been sought to give some information about the condition, specifically the shear modulus and damping ratio of the soil along the Addis Ababa light rail transit route from Megenagna to Hayat road. Also, this study was dealt with soil distribution along the route, which was conducted to determine soil properties. The sand replacement method was also utilized to investigate the controlling factors for the dynamic soil properties. From related literature, it was known that the dynamic soil properties are influenced by soil types and location of the soil profile. Five Test pits, designated A, B, C, D & E, were considered randomly for soil sampling to determine the properties of soil. The soil samples were taken from a depth of 2.5m below the surface of the roadside. Aside from the soil laboratory testing for common tests, another test was performed using a simple cyclic shear test for the representative samples. The values of normalized shear modulus and damping ratio are compared with already known curves from literature. The research study found out that the values of normalized shear modulus G/Gmax plotted against the shear strain, showed scattered points when it was compared with the curves of Seed and Idriss. Likewise, for the wet clay from the study area, all measured points were close to the known curve of the plot. On the other hand, the values of damping ratio were also compared to curves provided by Seed and Idriss. The Soil properties from all test pits had almost closer values as seen in the plot. However, the sample collected from test Pit D has the highest value of G/Gmax only, while samples from test Pit C has high values both for Gmax and Damping ratio. Test Pit C showed values of Dry density and liquid limit higher than the other test pits. Based on the comparison of the sand; for the strain less than 1%, all measured points of G/Gmax lying close to the extended curve given by Seed and Idriss. The strain of 0.2%, measured points of G/Gmax is closed to curve plot within the boundary, and it was below the curve given by Seed and Idriss. Likewise, for saturated clay, the measured points are close to the curve of Seed and Idriss. The values of damping ratio obtained for strain less than 1% obtained within the range of either the curves given by Seed and Idriss considers sand or clay soils. For strain, less than and equal to 1% the points lie within a range of clay. Therefore, the controlling factor that affects dynamic soil properties from a comparison of shear modulus and damping ratio curves based on consolidation pressure is the confining pressure, which shows high influence on the values of shear modulus and damping ratio based on the test results of the shear strain amplitudes. Index Terms—Damping Ratio, Dynamic Properties, Index property, Normalized Shear Modulus, Sand Replacement, Shear Modulus, Shear Strain Amplitude, Simple Cyclic Shear Test.

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2017d Sun, 21 Mar 2021 11:17:02 +0100 https://www.scipedia.com/public/Quezon_2017d Construction delay considered as one of the most recurring problems in the implementation of construction projects. It is widely known to have an adverse impact on project success in terms of time, quality, and cost. The effect of construction delay is not only confined to the construction industry but also its influence on the overall economy of a country like Ethiopia. This research was conducted to assess the causes of excessive delays in the completion of road projects during the construction phase due to the failures of Employer, Consultant, and Contractor in Addis Ababa City Road Authority projects. Spearman rank correlation coefficient from the Relative Importance Index (RII) analysis was used to test the agreement between different groups of respondents who participated in the questionnaire survey and to rank the three construction parties according to their responsibility area and importance as perceived by the respondents which factor causing the delay of road projects. This research identified sixty-five (65) causes of delay. There were fifty-one (51) valid questionnaires received back from Contractors, Consultants, and Employer (AACRA). Based on the results, the contractors have the highest percentage of responsibility area that causes the delay of about 40%. While the second was on the part of the Employer, which comprised 26.15%, and the consultant which placed third of 23.08%. On the other hand, there were 10.77% of the respondents attested that the Shared groups (3-parties) have the responsibility area which causes project delay during the implementation phase. About this, the research study identified and ranked the top ten factors causing delays of construction projects in Addis Ababa City Road Authority. Poor financial control of the project ranked 1st with Relative Importance Index (RII) of 0.905. Difficulties in financing projects by contractors ranked 2nd with the Relative Importance Index (RII) of 0.854. Type of project bidding and award (lowest bidder) ranked 3rd with an RII of 0.850. Poor site management and supervision of contractors ranked 4th with an RII of 0.839. Selecting inappropriate contractors ranked 5th with an RII of 0.823. Lack of high-technology mechanical equipment ranked 6th with an RII of 0.819. Inaccurate initial project scope estimate and Ineffective project scheduling ranked 7th and 8th with an RII of 0.803. Weak control of the project progress ranked 9th with an RII of 0.788. And the Contractor’s staff is not adequately trained in professional construction management techniques ranked 10th with an RII of 0.784. Therefore, it concluded that the main party Contractor did not perform properly his duties and obligations leading to the main contributory factor causing the failure of the project. 

]]> Emer T. Quezon https://www.scipedia.com/public/Achalu_et_al_Select a yeara Sun, 21 Mar 2021 11:08:03 +0100 https://www.scipedia.com/public/Achalu_et_al_Select a yeara Many years ago, consolidation accomplished by laborers wielding a variety of spades, tampers, and similar tools. In Ethiopia, there is no enough knowledge by the laborers, while the site engineers ignored the correct application due to some constraints. The agreement of acceptable vibration level in fresh concrete to which tamping time duration is optimum is an issue to obtain the desired specific compressive strength. This research study aims to evaluate the maximum time length and techniques used to Vibrating or Tamping fresh concrete and its effect on the compressive strength of C-25 Concrete through internal Rodding. Therefore, to study the effects of the period by vibrating or tamping, the needle-type internal vibrator was used to test new concrete cubes based on ACI309R-96. The quality of concrete is important to make physical tests on materials used before any actual experiments to perform. The fresh concrete samples tested by using internal vibration methods and techniques of compaction with different time duration of 1sec, 2sec, 3sec, 4sec, and 5sec. These tests performed by using steel rod in fresh concrete to know the Optimum time of compaction by internal vibration on the cube test of new concrete. Laboratory experiments had been conducted to check the methods and techniques applied to construction sites, as well as site observation on the effects of the vibration time of fresh concrete on the compressive strength and flexural strength of C-25 Concrete with varying vibration time duration and steel rod tamping. Based on the results of cube tests of compressive strength of Concrete Samples have been checked on the 3rd day, 7th day, and 28th day. This research study found out that the Optimum period of compaction was 3sec to produce an acceptable right quality of the concrete mix. Likewise, the flexural strength of the Concrete Sample, when it tested in the laboratory on the 7th day and 28th day, results revealed that the flexural strength improved when vibration time increased, but the amount of water has to be reduced to obtain the desired strength. Finally, Tamping is needed to place fresh concrete in the mold correctly. Furthermore, new concrete produced should match the properties and avoid improper tamping or vibration applications. This situation must not cause differences in the compressive strength of concrete.

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2016g Sun, 21 Mar 2021 11:02:02 +0100 https://www.scipedia.com/public/Quezon_2016g Contract claims are an inevitable fact of life in the construction industry. Contract claims are one of the problems that construction projects may face. Claims might cause many effects such as payment delay, an extension of time, and work suspension. The main aim of this research was an analysis of contract claims on building construction projects in Addis Ababa, Yeka Sub City by investigating the causes of contract claims and determining the factors to be considered in the selection of appropriate methodology for contract claims analysis. Literature and survey-based studies were made to provide an overview of the different contribution effects of contract claim analysis on building construction projects at the selected site. Interviews were also conducted with the three parties which have direct involvement in construction activities to get concrete ideas on the subject matter. A total of 75 questionnaires was distributed to respondents in Addis Ababa, Yeka Sub City building construction projects. Out of these 12 for client representatives, 35 for contractors representatives, 20 for consultant representatives, and 8 for other companies in order to identify claim causes that occurred in the study area. The quantitative data were analyzed using Excel and SPSS version 20 software, while qualitative data were analyzed by content analysis. The main factors of contact claim cause in the study area were identified. These factors further categorized into four groups; client-related, contract document-related, contractor related and consultant-related factors. While types of delays, knowing the strength and weakness of the project (project complexity) and conditions of the contract were identified as the factor to be considered in the selection of appropriate methodology for contract claim analysis. It is recommended that the three main contracting parties (Owner, Contractor, and Consultant) have responsibility for the effective accomplishment of the project. So each party would take part in their homework on time by developing technical knowledge about the effects of Contract claims on the progressive construction projects. Index Terms— causes, claim analysis, Contract claims, construction project, and risks.

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2016f Sun, 21 Mar 2021 10:52:02 +0100 https://www.scipedia.com/public/Quezon_2016f The construction industry has been seen as one of the hazardous industries. This is because the industry has a poor health and safety performance record compared to other industries all over the world. Labor law in every nation provides that it is the duty of an employer to ensure that every worker employed works under satisfactory, safe and healthy conditions. The research is focused on evaluating the health and safety issues in building construction projects in Addis Ababa, Ethiopia. The roles of the Client, Consultant and Contractor in health and safety consideration during project implementation were examined. It also determined the factors affecting health and safety performance of laborers. Whether, safety is used as criteria in selecting a contractor during the prequalification phase of public bidding was also identified. Building Construction Companies were involved in the sampling. All the information that could help in attaining the study objectives were collected, reviewed and formalized from the literature review. Data were collected and evaluated and the Relative Importance Index for each factor affecting health and safety was determined. The study determined the practical situation of building construction projects in consideration of health and safety, which was evaluated as low to medium. Relative Importance (RII) index of 12 factors affecting health and safety performance of labors were calculated. The top three factors identified were: (1) Non availability of a clear company Health and safety policy (0.85); (2) Inadequate enforcement of the existing building rules and regulations (0.82); and (3) Safety awareness of the company's top management (0.80). To improve the safety and health performance of building construction projects, the following major recommendations were proposed: each building, construction projects should have their own safety and health policy; include safety as a pay item in contract document; and allocate budget and time frames for health and safety in the contract document. Index Terms— Addis Ababa, Company Policies, Hazards, Health and Safety Practices, Rules and Regulations .

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2016e Sun, 21 Mar 2021 10:44:02 +0100 https://www.scipedia.com/public/Quezon_2016e Road construction in Ethiopia is in high demand to meet its short and long-term goals in infrastructure development programs. The road network is constructed radiating outwards North-South and East-West direction of the Capital City. Some projects are experiencing weather malady due to changing weather conditions in project locations. The study area of this research was focused on some selected projects in Addis Ababa and Oromia. The research had been addressed the effects of changes in weather in the three project planning phases, namely conception planning, design planning, and construction planning. A quantitative research design was used in this study. A literature review was undertaken and the result of which showed that the effects of weather changes are not extensively researched in the construction industry and there are limited references on the effects of weather change within the road construction industry. Sample data were obtained from sixty-three (63) construction practitioners through questionnaires, which were mailed to prospective respondents to assess their opinions. Questions were subdivided into three relevant areas covering demographics, experience with weather change factors, and the effects of weather change on road construction project planning. The study found that the effects of weather change on road construction project planning are similar to those found in other construction industries. The effects of weather change factors on road project planning vary with planning phases. These weather change factors as well as their effects were listed and ranked based on their frequency of occurrence and mean score. An independent sample t-test was used to compare respondents’ opinions on weather change effects between the two sample groups taken in Addis Ababa and part of Oromia. A partial correlation was also employed to identify the relationship between weather change factors and their effect on road construction project planning using SPSS-20. Delay of site preparation activities as a result of weather change on road project conception planning phase has a mean score of 4.30 Addis Ababa and 4.00 in for Oromia, while the influence of weather change on the selection and specification of construction materials for road project design planning phase has the highest mean score of 4.23 for Addis Ababa and 4.03 for Oromia. The effect of weather change on road workers' physiological comfort and quality of work for the road project construction planning phase has the highest mean score of 4.80 and 4.58 in Addis Ababa and Oromia, respectively. The study concludes with recommendations for potential research and with useful information and considerations on the effects of weather change on road construction project planning for construction professionals and project managers.

]]> Emer T. Quezon https://www.scipedia.com/public/Ganjealivand_et_al_2021b Fri, 19 Mar 2021 22:57:03 +0100 https://www.scipedia.com/public/Ganjealivand_et_al_2021b In this article, two parameter estimation using penalized likelihood method in the linear mixed model is proposed. In addition, by considering the stochastic linear restriction for the vector of fixed effects parameters we are introduced the stochastic restricted two parameter estimation. Methods are proposed for estimating variance parameters when unknown. Also, the superiority conditions of the two parameter estimator over the best linear unbiased estimator, and the stochastic restricted two parameter estimator over the stochastic restricted best linear unbiased estimator are obtained under the mean square error matrix sense. Methods are proposed for estimating of the biasing parameters. Finally, a simulation study and a numerical example are given to evaluate the proposed estimators.

]]> Fatemeh Ghapani https://www.scipedia.com/public/Gutierrez_Romero_et_al_2021a Tue, 16 Mar 2021 10:43:10 +0100 https://www.scipedia.com/public/Gutierrez_Romero_et_al_2021a Photogrammetry data-sets corresponding to the model basin experiments carried out within the NICESHIP project.

]]> Scipedia content https://www.scipedia.com/public/Quezon_Quezon_2019a Sun, 14 Mar 2021 19:15:03 +0100 https://www.scipedia.com/public/Quezon_Quezon_2019a Compaction is one of the essential engineering techniques, performed to assure the stability of soils based on specified strength. However, in most construction projects such as large-scale projects, obtaining the desired compaction characteristics, namely optimum moisture content (OMC) and maximum dry density (MDD), becomes time-consuming. In this case, predicting the compaction characteristics from the Atterberg's limits that involve a more straightforward and quicker method of testing becomes a vital task. This study focused on obtaining valid correlations between Atterberg's limit parameters and compaction characteristics of fine-grained soils. A series of laboratory tests for 50 samples conducted for the investigation. Statistical relationships of all the parameters were analyzed. The laboratory test results indicated that both OMC and MDD showed a strong correlation with LL and PL together using multiple linear regressions than with single parameters from single linear regression. Therefore, the study concluded that during the prediction of OMC and MDD from Atterberg's limits, the combined parameters of Atterberg's limits should be used rather than single parameters. It is recommended, the result of this research could be applied in different civil engineering practices, directly related to the parameters to be known.

]]> Emer T. Quezon https://www.scipedia.com/public/Quezon_2016d Sun, 14 Mar 2021 18:44:02 +0100 https://www.scipedia.com/public/Quezon_2016d Construction industry participants have started recognizing that accepting the least bid price does not guarantee maximum value. Continuous problems of inferior quality of constructing facilities, high incidence of claims and litigation, frequent cost overruns, and use of poor quality of materials have become the main features of Ethiopian’s public construction work contracts. This research was undertaken to evaluate the performance of publicly owned construction projects awarded on a lowest bid awarding system, to determine the effect of advance payment on the contractor’s performance, compare lowest and average bid systems, and check the quality of local construction materials use by lowest price won contracts. A literature review was carried out to identify different practices and floated questionnaire survey and laboratory test was conducted for selected and expected materials. Two alternative bid evaluation methods were discussed and suggested the better one from a performance point of view. The questionnaire was distributed to contractors, clients, consultants, and other related professionals. Additionally, interviews were conducted with them. A total of 88 questionnaires were distributed, including laboratory test results for selected and expected materials found in Jimma town. The data were collected and 80 valid questionnaires were analyzed by using SPSS-20, Excel, and laboratory test results requirement. The study identified that the causes of the poor performance of contractors were won projects with the lowest price; therefore more of the respondents do not like the lowest bidding method. Advance payment is the main solution to support the financial problems of contractors, but instead of paying in cash, purchasing the necessary construction materials is seen as an alternative to protect contractors from using the money for other uses. Obviously known that in the current bid awarding method of Ethiopia, most of the time, in order to be the winner of the bid price should be lesser. This leads the bidder not to get adequate profit, this pushes them to use poor quality of local construction materials. Finally, this work provides valuable information to the Ethiopian government, clients, consultants and contractors, and other stakeholders who desire to improve bidding methods; usage of advance payment; ways to improve performance of contractors, and to protect the project from contractors using poor quality of construction materials. 

]]> Emer T. Quezon https://www.scipedia.com/public/Kulyabko_2021a Fri, 12 Mar 2021 10:13:11 +0100 https://www.scipedia.com/public/Kulyabko_2021a The paper considers the features of nonlinear modeling of problems of dynamics of structures at different stages: design, testing and operation. Recommendations are given for nonlinear dynamic calculations and dynamic diagnostics (certification, identification of structural defects, etc.).

]]> Scipedia content https://www.scipedia.com/public/Ferrero_et_al_2021a Fri, 12 Mar 2021 09:55:48 +0100 https://www.scipedia.com/public/Ferrero_et_al_2021a Scipedia content https://www.scipedia.com/public/Vankan_et_al_2021a Thu, 11 Mar 2021 17:49:10 +0100 https://www.scipedia.com/public/Vankan_et_al_2021a Against the background of the big environmental and societal challenges as formulated for example in Flightpath 2050, current developments in aircraft design are aiming at further emission reduction through integrated, unconventional propulsion, systems and airframe innovations. This requires the further integration of methods for multidisciplinary modelling, analysis and optimization for aircraft design, but also for propulsion and system level designs. Moreover, experimental validation of the methods and physical testing of critical unconventional propulsion and system designs are prerequisites for industrially relevant development processes. This paper presents some key technologies for computationally efficient collaborative MDO (multidisciplinary design and optimization) frameworks for multidisciplinary design and validation of advanced aeronautic products like aircraft and propulsion systems.

]]> Scipedia content https://www.scipedia.com/public/Liu_2021a Thu, 11 Mar 2021 17:49:03 +0100 https://www.scipedia.com/public/Liu_2021a In this paper, we introduce a bi-fidelity stochastic collocation (SC) method for the linear transport equation with diffusive scaling and high-dimensional random inputs characterized by random variables. For the high-fidelity linear transport model, the asymptotic-preserving Discontinuous Galerkin implicit-explicit method in the micro-macro decomposition framework is used. We discuss different choices of low-fidelity models and conduct the corresponding uniform error estimates for the bi-fidelity method. Extensive numerical tests are presented to validate our bi-fidelity SC method.

]]> Scipedia content https://www.scipedia.com/public/Grubert_et_al_2021a Thu, 11 Mar 2021 17:48:55 +0100 https://www.scipedia.com/public/Grubert_et_al_2021a De-icing of general aviation aircraft is usually realized by chemical or thermal processes. These lead to an increase in fuel consumption or usage of electrical energy. Mechanical de-icing is a way to significantly reduce this consumption. In mechanical de-icing, a surface is deformed so that the required failure mechanisms are induced in the ice, causing it to detach. In this paper, the release behavior of ice on a CFRP layer is investigated. The CFRP layer consists of two plies, each 0.3 mm thick. A numerical calculation is performed to determine the natural frequency and the required amplitudes of the vibration. In addition, the relationship between the various failure mechanisms of ice and the ice layer thickness, as well as the control values are determined. Tests are also being conducted to demonstrate the feasibility of mechanical de-icing. For this purpose, the surface of a CFRP layer is iced with water in a climate chamber at -20°C. A modal shaker is connected to the CFRP and generates the required displacements at desired frequencies to observe the detachment of the ice.

]]> Scipedia content https://www.scipedia.com/public/Garcia-Banales_et_al_2021a Thu, 11 Mar 2021 17:48:47 +0100 https://www.scipedia.com/public/Garcia-Banales_et_al_2021a Soft materials, and especially soft biological tissues, have a complex highly nonlinear behavior both for quasielastic (slow) and viscous loading. In partiular, the cyclic behavior is different depending on the loading speed, number of cycles, and their magnitude. Furthermore, different soft materials and soft tissues have different particularities in their behavior. Therefore, a phenomenological proposal capable of accurately capturing all these singularities with few, easy to obtain parameters based on experimental data, is valuable. In this study, a visco-hyperelastic one-dimensional formulation to characterize different biological tissues is proposed, which has proven to be capable of capturing the response of numerous soft biological tissues (brain tissue, coronary arteries, tendons, tongue tissues, abdominal muscle, cells...) under pure and combined loading modes, including tension, compression, simple shear and the combination of the latter one with tension and compression. One of the main advantages of the proposed model is its simplicity, being that the formulation is calibrated with four simple parameters (two of them for the hyperelastic component and four for dealing with the different viscous aspects) obtained from the uniaxial loading. The formulation, based on a combination of Maxwell and Kelvin-Voigt rheological models has proven to represent to very good accuracy the behavior of a wide range of materials under different types of loadings, including effects like preconditioning and cycle stabilization. In all these cases, under different monotonic and cyclic loading, all aspects of the viscous and elastic behavior are accurately captured. Thanks to its structure, this model incorporates strain-level dependent nonequilibrium viscoelasticity and it may be easily incorporated to 3D nonlinear finite strains formulations.

]]> Scipedia content https://www.scipedia.com/public/Zank_2021a Thu, 11 Mar 2021 17:48:40 +0100 https://www.scipedia.com/public/Zank_2021a We consider a space-time variational formulation of the second-order wave equation, where integration by parts is also applied with respect to the time variable. Conforming tensor-product finite element discretisations with piecewise polynomials of this space-time variational formulation require a CFL condition to ensure stability. To overcome this restriction in the case of piecewise multilinear, continuous ansatz and test functions, a stabilisation is well-known, which leads to an unconditionally stable space-time finite element method. In this work, we generalise this stabilisation idea from the lowestorder case to the higher-order case, i.e. to an arbitrary polynomial degree. We give numerical examples for a one-dimensional spatial domain, where the unconditional stability and optimal convergence rates in space-time norms are illustrated.

]]> Scipedia content https://www.scipedia.com/public/Benitez-Aguilar_et_al_2021 Thu, 11 Mar 2021 17:48:32 +0100 https://www.scipedia.com/public/Benitez-Aguilar_et_al_2021 The study of tumoral cells behaviour through computational models is arising. The movement of these cells is governed by physical laws; therefore, the different forces exerted between them need to be implemented. Nevertheless, biological criteria should be also considered since other factors, as oxygen level or cellular density, are decisive in the real movement. These phenomena are captured by probabilistic models such as the Agent Based Model (ABM). Following this research line, the present paper outlines a numerical model that tries to join both criteria with the aim of reproducing the behaviour of the cells that are part of a brain tumor: Glioblastoma Multiforme (GBM). The study has been carried out by the implementation of the different force equations in a Smoothed-Particle Hydrodynamic (SPH) framework. The SPH method is a meshfree lagrangian method based on the discretization of the study domain into finite particles which carry their own information, as tumoral cells do. Cohesive, viscous and pressure forces have been taking into account. Also, the possible attraction or repulsiveness between cells is considered through the implementation of a mechanical force formulation that combines the Maxwell and KelvinVoigt viscoelastic models. In addition to this forces approach, an energetic model is proposed to consider the results provided by an ABM. It evaluates the energy consumption and the associated extra-force that the cell needs to reach the ABM position, which is considered the biologically optimal one. The model has been tested under different sets of parameters, getting the logical outcome. Successful results have also been found in the evaluation of the energy consumption and, therefore, of the extra-force, finding a formulation that joins both criteria.

]]> Scipedia content https://www.scipedia.com/public/Draft_Content_898328458 Thu, 11 Mar 2021 17:48:24 +0100 https://www.scipedia.com/public/Draft_Content_898328458 We present an application on springback of an anisotropic elastoplastic finite strain model. The computational procedure allows the sole use of internal elastic variables as it is fully hyperelastic. Based on the Lee-type multiplicative decomposition, which permits an additive solution in a logarithmic strain approach, it resolves the 'rate issue' by the employment of a corrector rate of elastic strains and its algorithmic implementation [1]. The associative nature and Clausius-Duhem inequality recover the formulation of Simo's isotropic strain-hardening particular case. Its application to metal and soft materials has been corroborated as it is also valid for anisotropic yield functions and for any anisotropic stored energy (linear and nonlinear in logarithmic strains) [2]. The computation of the stress-point algorithm is done using a simple backward-Euler scheme. Its validation has been performed by the implementation of the procedure into a subroutine which allows the user to compute benchmark models in the commercial program ADINA [3]. This permits to explore its usefulness in application for the numerical prediction of springback in thin sheet metal forming processes. The results are compared with both experimental and other authors' results. Moreover, many simulations were performed such as the draw-bending test, the unconstrained bending problem, the square cup or the 3DS warping benchmark.

]]> Scipedia content https://www.scipedia.com/public/Sotiropoulos_et_al_2021a Thu, 11 Mar 2021 17:48:14 +0100 https://www.scipedia.com/public/Sotiropoulos_et_al_2021a Structural optimization over the past decades matured from an academic theoretical field, to an important tool in the design procedure in various engineering disciplines. Some commercial software applications provide some suites with optimization solutions, but they are focused mostly in the aeronautics, automotive and aerospace industry. High Performance Optimization Computing Platform (HP-OCP) is a software developed by the ISAAR-NTUA and provides a holistic optimization approach for civil engineering structures. More precisely, HPOCP is a computational suite that has the ability to integrate with several structural analysis and design software and provide optimization solutions. Structural optimization is mainly divided in three groups, sizing (or parametric), shape and topology optimization. All of them are integrated in HP-OCP and the appropriate algorithms are provided in each category. Considering size and shape optimization, the parametric optimization module is developed, in which the design variables of the mathematical formulation can be the dimension of the section properties, the quality of the material, the coordinates of the nodes etc. In this module plenty of derivativebased and derivative-free algorithms are provided like the Projected Quasi-Newton, Constrained Optimization by Linear Approximation, Latin Hypercube Sampling etc. [1]. Considering the topology optimization module [2], the SIMP method is applied and the mathematical algorithms that are implemented are the Optimality Criteria and Method of Moving Asymptotes. HP-OCP was developed in C# programming language, making it a powerful suite that can be integrated with any commercial software that provide Application Programming Interface, batch analysis via XML files or any other type of data exchange format. In the current work the integration of HP-OCP with the SAP2000, ETABS and SCIA Engineering software is presented. Several examples considering parametric and topology optimization problems are examined. Remarkable cost reduction is succeeded in real-world structures, validating in this way the usefulness of HP-OCP not only in the research field but also in applied civil engineering problems.

]]> Scipedia content https://www.scipedia.com/public/Garcia-Modet_et_al_2021a Thu, 11 Mar 2021 17:48:05 +0100 https://www.scipedia.com/public/Garcia-Modet_et_al_2021a Topology optimization has undergone tremendous development since its introduction by Bendsøe and Kikuci in 1988, especially in recent years, due to its involvement in revolutionary generative design techniques. This paper aims to lay the foundations of a generative design methodology powered by an alternative approach to the well-known density methods. Based on finite element analysis, the objective is to develop an optimization algorithm with the Young modulus of the elements as design variables. That way, while previous studies have focused on void/solid distributions, this study searches for a distribution of different E values that could be manufactured due to progress in metamaterials and additive manufacturing. A mimetic metamaterial was also developed to be coupled with the topological optimization, but will not be included in this paper. To assess the optimization algorithm, several analyses have been carried out under different load and boundary conditions. The outcome shows correlation with our initial hypothesis: elements under higher strains increase their stiffness value, while the opposite occurs for those under minor stresses. Consequently, the results present a structure with a Young modulus distribution that optimizes the strain energy, and therefore, reduces the displacements.

]]> Scipedia content https://www.scipedia.com/public/Gonzalez_et_al_2021a Thu, 11 Mar 2021 17:47:56 +0100 https://www.scipedia.com/public/Gonzalez_et_al_2021a Metamaterials research and, moreover, their obtaining by additive manufacturing is trendy because of their potential industrial applications, since lattice structures can save weight when integrated in larger parts. For this reason, it is important to draw these new material properties in order to compare them with traditional structures obtained by classic manufacturing methods. In this work we present a numerical procedure to determine the mechanical properties of a metamaterial based on periodic cells. To date, for these materials there are no standard procedures to test and validate their structural properties, and specifically to determine their mechanical bending behaviour. We apply a virtual testing procedure using finite elements to determine the homogeneous elastic modulus, Young's modulus and shear modulus, using a set of modified bending virtual test, based on the three point bending and the four point bending test [1]. Theses physical testing procedures are common in sandwich composite materials [2], and can be apply to metamaterial testing taking into account some geometrical and material aspects to determine the proper parameters for testing. The results obtained are macroscopically independent on the number of elemental cells used in the metamaterial, and permit us to consider the intrinsic defects that may appear in the 3D additive manufacturing materials.

]]> Scipedia content https://www.scipedia.com/public/Logo_et_al_2021a Thu, 11 Mar 2021 17:47:48 +0100 https://www.scipedia.com/public/Logo_et_al_2021a The highly automated driving research is one of the most remarkable developments in the automotive world. Still, ordinary people can also realize the milestones facing more and more built-in vehicle assistant services brought by the new car manufacturers. The navigation system is also part of the 'success story' because the maps are currently high-resolution 3D databases, and permanently better visualization supports the drivers. The creation of these map databases relies on cutting-edge field data capture techniques, like aerial surveys. The paper presents a technology based on aerial photographs' evaluation done by human operators. The captured photographs were transformed into distortion-free orthophotos; then, skilled humans evaluated the expected database elements: road and lane segments. The map creation procedure aimed to serve the content fully compatible with the standards of the industry. This evaluation procedure resulted in a road and a lane-level graph, clearly in harmony with the traffic rules. The CAD-drawings of each operator form an excellent starting point to start new artificial intelligence developments.

]]> Scipedia content https://www.scipedia.com/public/Bonizzoni_Pradovera_2021a Thu, 11 Mar 2021 17:47:40 +0100 https://www.scipedia.com/public/Bonizzoni_Pradovera_2021a We study a PDE-constrained optimization problem, where the shape and liner material of the nacelle of an aircraft engine are optimized in order to minimize the noise radiated by the engine. More precisely, the acoustic problem is modeled by the Helmholtz equation with varying wavenumber kon an exterior domain. A model reduction strategy is employed to alleviate the cost of the design optimization: the minimal rational interpolation technique is used to construct a surrogate (w.r.t. k) for the quantity of interest at fixed shape/material parameter values, and a parametric model order reduction approach is employed to combine surrogates at different shape/material designs, resulting in a nonintrusivemethodology. Numerical experiments for shape and shape/material optimization are provided, to showcase the effectiveness of the presented methodology.

]]> Scipedia content https://www.scipedia.com/public/Conceicao_et_al_2021a Thu, 11 Mar 2021 17:47:31 +0100 https://www.scipedia.com/public/Conceicao_et_al_2021a This article presents a study on the grid generation and heat transfer in a complex topology maritime pine tree in a forest fire environment. The numerical model of the maritime pine tree thermal behaviour is developed and applied. This numerical model is based on energy balance integral equations for the maritime pine tree elements. These equations are obtained for the heat exchanges by conduction within the maritime pine tree elements, by convection between the external maritime pine tree surfaces and the environment, and by radiation between the external maritime pine tree surfaces and the fire front. The geometry of the virtual maritime pine maritime pine tree was here developed applying mesh generation, which is used to evaluate the view factors. In turn, these view factors are used to calculate the heat exchanges by radiation between the virtual maritime pine tree and the fire front. The virtual maritime pine tree geometry is constituted by 8863 cylindrical elements, which represent their trunks, branches and leaves, and it is divided into four levels. The input data considered in the numerical simulation are the mean flame temperature of 500ºC, the air temperature of 20ºC, the wind speed of 10 m/s and the air relative humidity around the pine tree of 50%. The numerical simulation results are the view factors and the evolution of the surface temperature of the maritime pine tree elements obtained in a transient regime. The values of the view factors and the surface temperature of the maritime pine tree elements decrease from the first level, near the ground, to the last level, at the top of the maritime pine tree. The stabilization time of the surface temperatures of the maritime pine tree elements decreases according to the increase of the height to which these elements are located.

]]> Scipedia content https://www.scipedia.com/public/Balcazar_et_al_2021a Thu, 11 Mar 2021 17:47:23 +0100 https://www.scipedia.com/public/Balcazar_et_al_2021a A novel conservative level-set method for saturated liquid-vapor phase change on unstructured meshes is introduced. Transport equations are discretized by the finite-volume method on collocated unstructured grids. Mass transfer promoted by thermal phase change is computed using the energy jump condition at the interface, as a function of the temperature gradient. The fractional-step projection method is used for solving the pressure-velocity coupling, convective terms are discretized by unstructured flux-limiter schemes, central difference scheme is used for discretization of diffusive terms. Verification and validation cases have been undertaken to prove the accuracy and robustness of the numerical methods, including simulation of the Stefan problem, and film boiling on a cylindrical surface. Excellent agreement between numerical solutions against analytical solution and empirical correlations from the literature is reported.

]]> Scipedia content https://www.scipedia.com/public/Nikl_et_al_2021a Thu, 11 Mar 2021 17:47:15 +0100 https://www.scipedia.com/public/Nikl_et_al_2021a The magneto-hydrodynamic model is widely used for description of magnetized fluids in plasma dynamics, microfluidics, astrophysics and many other applications. In terms of modelling, the Lagrangian formulation is favourable for the rapid expansion during laser­target interaction for example. This is the case for inertial fusion and laboratory astrophysics applications, which are our primary interest. However, the proposed numerical method remains general and can be applied elsewhere. The conservation properties and divergence-free magnetic field are crucial aspects, which are not satisfied by the traditional numerical schemes. Here, the Lagrangian hydrodynamics using curvilinear finite elements is extended to the resistive magneto-hydrodynamics. An energy-conserving numerical scheme is formulated maintaining divergence-free magnetic field. The mixed finite element formulation provides theoretically arbitrary order of the spatial convergence and application on unstructured Lagrangian grids in multiple dimensions. An example of a physically relevant numerical simulation is presented.

]]> Scipedia content https://www.scipedia.com/public/Kozubskaya_et_al_2021a Thu, 11 Mar 2021 17:47:07 +0100 https://www.scipedia.com/public/Kozubskaya_et_al_2021a The paper presents a method for simulating the flow of a viscous compressible gas around a moving obstacle, specified by the immersed boundary method on a simply connected unstructured mesh, and the features of its application for bodies of different configuration. An advantage of the developed moving-mesh method is that it keeps the topology of an initial mesh and provides an anisotropic mesh refinement to the 'immersed' surface of a streamlined body. The position and shape of the body are determined by the interpolation grid, which stores the distance and normal to the body surface. The paper also describes a special technique to improve the efficiency of adaptation. The technique is based on the prediction of the body location in some automatically chosen time. This trick allows to find the coordinates of mesh vertices during the predicted time interval by interpolation. The integral strategy combining the immersed boundary method with the developed moving-mesh adaptation is tested on several model cases in twoand three-dimensional formulations. However, the paper does not consider the numerical results of the cases, it is mostly targeted at the meshing details.

]]> Scipedia content https://www.scipedia.com/public/Settati_et_al_2021a Thu, 11 Mar 2021 17:46:59 +0100 https://www.scipedia.com/public/Settati_et_al_2021a This study focuses on investigating the effect of protruding branching duct on laminar fluid field in 90◦ dividing pipe junction of mini heat exchanger. The ducts under study, main and branch side, are of minichannel scale where the corresponding diameters are 3.96 and 1.6 mm respectively. First, numerical validations are given based on the experimental measurements of Cho et al. [1] for the case of non-protruding branching duct (h=0, β ≠0) and also comparing with Poiseuille flow for nonprotruding case with no flow in the branch side (h=0, β=0) where good agreements were found in each case. Second, the degree of protrusion in pipe branching duct is characterized studying and analyzing two cases of protrusions (h = D₁/4 and h = D₁/2). The effects of branching flow rate ratio β on local pressure changes and the velocity profile are presented and examined in both main and branching ducts. Finally, the influence of the extent of protruded branch on velocity field and the local pressure drop are documented as expected. The results shown a strong effect of protrusion on hydrodynamic flow

]]> Scipedia content https://www.scipedia.com/public/Materna_2021a Thu, 11 Mar 2021 17:46:52 +0100 https://www.scipedia.com/public/Materna_2021a In this contribution a method for the prediction of the change in a quantity of interest due to structural modifications is considered. The approach is based on a goal-oriented method by using the primal and dual problems. The method can be used in order to reduce the overall computational cost in the numerical simulation. Furthermore, the proposed method is easily to implement in existing finite element programs, because no derivatives with respect to the design variables are necessary.

]]> Scipedia content https://www.scipedia.com/public/Bikkanahally_et_al_2021a Thu, 11 Mar 2021 17:46:44 +0100 https://www.scipedia.com/public/Bikkanahally_et_al_2021a Natural convection,Hybrid RANS-LES,Turbulence modeling Transient,buoyancy-affected flows play a major role in some industries,for instance in the design of nuclear power plants or the under-hood space of automobiles. In order to avoid expensive experiments,promote rapid design,development,it is quintessential to employ efficient,robust,accurate CFD models to simulate such flows. With the aim of being cost-effective,retaining the ability to capture the necessary transient phenomena,the industry standard of using RANS models alone does not suffice,whereas LES is as of yet not affordable for industrial configurations. In this context,a Hybrid RANS-LES model based on temporal filtering,called Hybrid Temporal Large Eddy Simulation (HTLES) is developed,thus reducing computational costs by switching to RANS in the near-wall regions while being able to predict a large part of the turbulent scales in regions where it is necessary. The present work is based on the HTLES model developed for iso-thermal configurations [1],with the hybridisation applied to the standard k SST model. The extension to natural convection flows is carried out using the DNS database of a differentially heated square cavity [2]. The test case is characterised by the three non-dimensional numbers viz. Rayleigh number(Ra = 10 ),Prandtl number(Pr = 0.71),aspect ratio(A = L /L = 1),features a stratified core with a spatially developing buoyant boundary layer. The study reveals that the HTLES model is able to predict the mean profiles of temperature,velocity satisfactorily. Comparisons with URANS show that the HTLES model predicts the kinetic energy profiles more accurately,especially when considering coarser grids. However,it is noted that the current definition of the shielding function (used to enforce RANS close to the walls based on the Kolmogorov length scale) is inadvertently modifying the energy ratio far from the wall due to fluctuations in the dissipation rate,. This is further confirmed by way of a priori tests using the DNS database. It is essential to have a shielding function that is only effective in the near-wall regions. Therefore,to ward off this issue,a shielding function based on the Elliptic blending framework is developed. For the validation of the approach,flows in a differentially heated vertical channel [3],a 4:1 cavity [4] are considered,in order to investigate the ability of the model to reproduce natural convection flows with very different stratification.

]]> Scipedia content https://www.scipedia.com/public/Menshykov_et_al_2021a Thu, 11 Mar 2021 17:46:36 +0100 https://www.scipedia.com/public/Menshykov_et_al_2021a The linear crack between two dissimilar elastic isotropic half-spaces under normal harmonic shear loading is considered. To take the crack faces interaction into account we assumed that the contact satisfies the Signorini constraints and the Coulomb friction law. The problem is solved numerically using the iterative process ­ the solution changes until the distribution of physical values satisfying the contact constraints is found. The numerical convergence of the method with respect to the number of the Fourier coefficients and mesh size is analysed. The effects of material properties and values of the friction coefficient on the distribution of displacements and contact forces are presented and analysed. Special attention is paid to the size of the contact zone and the results are compared with the classical model solutions obtained for the static problems with and without friction.

]]> Scipedia content https://www.scipedia.com/public/Azua-Gonzalez_et_al_2021a Thu, 11 Mar 2021 17:46:28 +0100 https://www.scipedia.com/public/Azua-Gonzalez_et_al_2021a A novel multiscale variational method for modelling fracture propagation is proposed. The
method employs strong discontinuity kinematics enhancement, enabling macroscopic cracks to be modelled explicitly, while minimum remeshing is ensured. In addition, the response of quadrature points in the bulk is up-scaled using a Micromechanical continua, which enables the evolution of directional
micro-defects (e.g. microcracks) without venturing into prohibitive computational burden. Noticeably,
the method allows the Micromechanical continua to interact with macroscopic cracks. The framework is
conveniently formulated as a variational setting to provide a minimum energy solution. The new computational framework has been found to diagnose realistic failure mechanisms in quasi-brittle materials.

]]> Scipedia content https://www.scipedia.com/public/Ali_Ma_2021a Thu, 11 Mar 2021 17:46:20 +0100 https://www.scipedia.com/public/Ali_Ma_2021a This paper presents some results for PDE-based and solution-dependent parameterization of computational domains for isogeometric analysis (IGA) using non-uniform rational B-splines (NURBS). The final parameterization is produced based on the solution of a partial differential equation (PDE) that is solved using isogeometric collocation method (IGA-C) with Dirichlet boundary condition being the input boundary of the final desired computational domain for IGA, namely the IGA-C-PDE method for domain parameterization. The theory of PDE guarantees that the mapping between physical and transformed region will be one-to-one. In addition, we also apply intuitive position and ratio constraints while solving the PDE to achieve solution-dependent parameterization. While one may use any general PDE with any constraint, the PDEs and additional constraints selected in our case are such that the resulting solution can be efficiently solved through a system of linear equations with or without additional linear constraints. This approach is different from typical existing parameterization methods in IGA that are often solved through an expensive nonlinear optimization processes. The results show that the proposed method can efficiently produce satisfactory analysis-suitable parameterization.

]]> Scipedia content https://www.scipedia.com/public/Curto_et_al_2021a Thu, 11 Mar 2021 17:46:11 +0100 https://www.scipedia.com/public/Curto_et_al_2021a Fruit packaging is highly impactful in temperature and humidity distribution for post-harvest fresh fruit cooling and conservation. It is also the most flexible part on fruit production and should be able to increase shelf-life by deterring adverse conditions. However, packaging thermal performance during cold storage where it is displayed to the internal airflow is influenced by the size and position of vent-holes. In this study airflow inside the fruit box and fruits thermal behaviour are evaluated in order to determine differences between three prototype package models. Models differ from each other by the holes' configuration and size. Furthermore, models' performance is compared to a commercially available box of similar dimensions. Experimental tests were carried out in three stacked boxes, equipped with temperature and humidity sensors, and placed inside a refrigeration chamber with forced air cooling. Packaging box CFD models of each prototype wall were developed to predict the airflow and heat transfer during storage in a refrigeration chamber. Models predictions were validated by experiments results. According with simulation results, all prototypes have better thermal performance than the commercial model. However, significant performance differences between prototype walls were found. Fewer, larger and strategically distributed vent-holes allow a better result in terms of temperature homogeneity inside the box and significant reduction in fruit cooling times.

]]> Scipedia content https://www.scipedia.com/public/Anders_et_al_2021a Thu, 11 Mar 2021 17:46:03 +0100 https://www.scipedia.com/public/Anders_et_al_2021a Injection molding is undoubtedly one of the most widely used manufacturing process for polymers [1]. Due to its advantages over other processing techniques in terms of good surface finish, the ability to process complex parts without the need of secondary operations and low cost for mass production, injection molding has found its way into various branches of industry [2]. In order to implement process optimization a thorough understanding of the material behaviour, the filling process as well as the underlying physical phenomena is necessary. A suitable way to address this issue is the application of numerical simulation of the injection molding process. In this contribution the authors present a comparative numerical study for the mold filling of an exemplary thin-walled mold geometry. For the numerical simulation the commercial CFD software packages Cadmould 3D-F and ANSYS CFX are employed. Both software packages make use of different simulation strategies. In ANSYS CFX a threedimensional classical CFD approach is employed for the mold filling which is of course very accurate but extremely time consuming. Cadmould 3D-F pursues a generalized Hele­Shaw approximation (also known as so-called 2,5-D approach) which is due to some simplifying assumptions less accurate but also much less costly in terms of computing time [2, 5].

]]> Scipedia content https://www.scipedia.com/public/Amani_et_al_2021b Thu, 11 Mar 2021 17:45:55 +0100 https://www.scipedia.com/public/Amani_et_al_2021b In this work, a numerical framework aimed at simulating high-viscous and viscoelastic liquid injection processes is presented. The study of fluid injection with viscoelastic properties, such as synthetic polymers, is of great importance in several industrial sectors, such as metallurgy, automotive, food and pharmaceutical products, ink jets and 3D printers. In this work, a Geometrical Volume-of-Fluid (VOF) method is used to represent the interface, while finite-volume discretizations of Navier-Stokes equations on collocated unstructured meshes are solved through a fractional step method. Viscoelastic constitutive models are used to resolve the non-Newtonian behaviours. The employed implementations allow integrating different types of constitutive equations and stabilization approaches. The test case proposed in the current work consist of the simulation of the discharge of a polymeric jet from an upper nozzle into an air-containing cavity with solid bottom. The behavior of the fluids under analysis is validated by observing the onset of fluid-buckling s tructures. This phenomenon consists in the appearance of toroidal oscillation (as coiling and folding patterns) after the jet hits the solid surface and begins to accumulate. First, low-Reynolds number (Re<1.0) Newtonian Jets are analyzed, with the objective of validating the appearance of buckling as a function of Re number, and comparing the results with reference works. Finally, the potentialities of the proposed numerical methods are shown by simulating buckling phenomena in viscoelastic Jets described with the Oldroyd-B constitutive model.

]]> Scipedia content https://www.scipedia.com/public/Amani_et_al_2021a Thu, 11 Mar 2021 17:45:47 +0100 https://www.scipedia.com/public/Amani_et_al_2021a Three-dimensional numerical simulation of Taylor gas bubbles as primary unites of slug flow patterns rising in non-Newtonian environments is performed in the context of Direct Numerical Simulation (DNS) of the governing equations, where the whole physics of fluid motions will be taken into account. State-of-the-art numerical tools are proposed to tackle the numerical challenges in the DNS study of this problem. E.g. a coupled level-set volume-of-fluid (CLSVOF) interface capturing method is used to solve the topological changes of the interface. Physical formulations are integrated with moving-mesh (MM) technique to decrease the computational cost of 3D simulations and adaptivemesh-refinement (AMR) technique to increase the local accuracy around the interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. To the best of the authors' knowledge, this is the first work dealing with three-dimensional direct numerical simulation of Taylor bubbles rising in non-Newtonian environments.

]]> Scipedia content https://www.scipedia.com/public/Marin-Montin_et_al_2021a Thu, 11 Mar 2021 17:45:39 +0100 https://www.scipedia.com/public/Marin-Montin_et_al_2021a In this work, we propose a lattice-particle approach to study ionic diffusion across graphite electrodes. In our approach, we generate virtual representative volume elements (RVE) of the electrode material based on its composition, i.e., active particles, carbon additives, and binder. Porosity is also accounted for as an input parameter. To account for the evolution of the ionic concentration, Fickean diffusion is considered. This problem is solved within a network of one-dimensional elements, which is constructed upon the particles of the RVE, yielding a three-dimensional lattice. We use the centraldifference time-integration scheme to solve the transient problem within the framework of the finite element method for the spatial discretization. One of the main advantages of our approach is that we are able to reduce the number of degrees of freedom and thus the computational cost in comparison to the conventional continuum-based finite element simulations. For the transport simulations, we consider Li ions, although our approach can be also applied to other type of species, such as PF-

]]> Scipedia content https://www.scipedia.com/public/Folch_et_al_2021a Thu, 11 Mar 2021 17:45:31 +0100 https://www.scipedia.com/public/Folch_et_al_2021a The incompressible Navier-Stokes equations stand as the best mathematical model for turbulent flows. However, direct numerical simulations at high Reynolds numbers are not yet feasible because the convective term produces far too many relevant scales of motion, thus remaining limited to relatively low-Reynolds numbers. Dynamically less complex mathematical formulations have been developed for coarse-grain simulations, like the well known eddy-viscosity models. Most of these models are based on the combination of invariants of a symmetric tensor that depends on the gradient of the resolved velocity field, G=∇u, and should properly detect different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime, etc.). Brand-new models have been constructed considering the first three invariants of the symmetric tensor GG^T with excellent results;¹ hence, it is formally based on the lowest-order approximation of the subgrid stress tensor, τ(u) = (∆²/12) GG^T +O(∆⁴), i.e. the gradient model proposed by Clark.² Furthermore, these models have been implemented on a pseudo-spectral algorithm with a fully-explicit second-order time-integration method.³ The performance of this special configuration has been successfully tested for decaying isotropic turbulence and a turbulent channel flow. It is currently being developed for a semi-infinite boundary layer with periodic conditions as a previous step to carry out wind farm simulations. Details of the implementation and numerical results will be presented.

]]> Scipedia content https://www.scipedia.com/public/Miller_et_al_2021a Thu, 11 Mar 2021 17:45:23 +0100 https://www.scipedia.com/public/Miller_et_al_2021a The efficiency of time-domain acoustic simulations is improved immensely if the degrees of freedom imparted by the spatial discretization are reduced. Time-stable model order reduction strategies achieve this by ensuring that frequency-domain system realizations transform in a physical manner after reduction. Frequency dependent damping matrices add to the challenge and require additional consideration. Handling the associated boundary condition imposition in the time domain is one way to approach the problem. Convolution complicates this strategy but the obstacle can be surmounted using a recursive formulation. This work proposes such a method, combining Krylov subspace projection based model order reduction with an efficient time domain-impedance boundary condition implementation. The mass and stiffness matrices are frequency independent and reduced using a second-order Arnoldi algorithm. As Arnoldi iterations implicitly match the moments of the system transfer function, the complex damping matrix must still be contended with. Discussion is included on when reduced order, time-domain, simulations bear fruit. Comparison with full-order time and frequency-domain calculations demonstrate the effectiveness of the proposed algorithms with system degrees of freedom decreased from NDOF= 13125 to RDOF= 63, and simulation time reductions of 91­97%.

]]> Scipedia content https://www.scipedia.com/public/Kazakis_et_al_2021a Thu, 11 Mar 2021 17:45:13 +0100 https://www.scipedia.com/public/Kazakis_et_al_2021a The most computationally demanding part of structural design optimization is the solution of the FE equations and design of the structural model. Therefore, there is a need for the implementation of strategies that can reduce the computational cost of each iteration and thus manage to achieve the same optimized result with considerable reduction in the optimization time. High Performance Optimization Computing Platform (HP-OCP) is an optimization software developed in C# programming language by ISAAR-NTUA and OptiStructre Ltd. [1] which provides a holistic optimization approach for civil engineering structures. It combines powerful derivative-based and derivative-free optimization algorithms like the Projected Quasi-Newton (PQN), Constrained Optimization by Linear Approximation (COBYLA), Latin Hypercube (LH), Differential Evolution etc. [2] integrated with different structural analysis software's like SAP2000, ETABS & SCIA Engineer utilizing their abilities in finite element analysis and most importantly different design codes into the optimization procedure. To deal with the computational demand deriving from this coupling of optimization algorithms and commercial structural analysis software's parallel computational procedures have been implemented to HP-OCP. These procedures were tested in real world civil engineering problems and produced very good results. Parallel strategies are implemented both at the level of the optimization algorithm, by exploiting the natural parallelization features of the evolutionary algorithms, as well as at the level of the repeated structural analysis problems that are required by the optimization algorithm. The numerical tests presented demonstrate the computational advantages of the proposed parallel strategies, which become more pronounced in large-scale optimization problems. 1

]]> Scipedia content https://www.scipedia.com/public/Filonets_et_al_2021a Thu, 11 Mar 2021 17:45:05 +0100 https://www.scipedia.com/public/Filonets_et_al_2021a High Intensity Focused Ultrasound (HIFU) is a non-invasive technology that can be applied for treatment of different diseases and ablation of tumours in different parts of the body. When high intensity ultrasound propagates through the medium bubbles can be formed, a phenomenon known as acoustic cavitation. There are two different regimes of acoustic cavitation: stable cavitation when a bubble just oscillates around an equilibrium state, and inertial cavitation which is accompanied by bubble collapse. These two different regimes can be used for different biomedical applications. However, in some cases it can also make the treatment less predictable. Therefore, fundamental understanding of these effects is very important. In the current study theoretical investigation of the bubble dynamics in viscoelastic medium is performed and inertial cavitation thresholds have been calculated. To describe the bubble dynamics, Gilmore-Akulichev-Zener model has been used, which is suitable for a large bubble oscillations and high ultrasound powers. The results showed that using the dual-frequency driving signal the threshold value of inertial cavitation can be significantly reduced compared to single-frequency signal mode. Large difference between frequencies in the dual-frequency signal leads to lower threshold values. Numerical simulations also showed the dependencies of the cavitation threshold on the bubble radius.

]]> Scipedia content https://www.scipedia.com/public/Alzaben_et_al_2021a Thu, 11 Mar 2021 17:44:57 +0100 https://www.scipedia.com/public/Alzaben_et_al_2021a In this paper we discuss some aspects related to the practical implementation
of a method that has been introduced recently for the approximation of the eigenvalues of the
linear elasticity problem. The scheme, based on a least-squares finite element formulation, gives
rise to a non-symmetric discrete formulation that may have complex eigenvalues. Moreover the
algebraic eigenvalue problem to be solved is singular, so that the theoretical estimates about the
convergence of the scheme should be carefully interpreted.

]]> Scipedia content https://www.scipedia.com/public/Alsalti-Baldellou_et_al_2021a Thu, 11 Mar 2021 17:44:49 +0100 https://www.scipedia.com/public/Alsalti-Baldellou_et_al_2021a It is well known that the solution by means of iterative methods of very ill-conditioned systems leads to very poor convergence rates. In this context, preconditioning becomes crucial in order to modify the spectrum of the system being solved and improve the performance of the solvers. A proper balance between the reduction in the number of iterations and the overhead of the construction and application of the preconditioner needs to be sought to actually decrease the total execution time of the solvers. This is particularly important when considering variable coefficients matrices as, in general, its preconditioners will also be variable and need to be updated regularly at an affordable cost. In this work we present a family of variable preconditioners designed for the effective solution of variable Poisson equation with extreme contrasts in the coefficients, which represents a particularly challenging case as it translates into a variable and extremely ill-conditioned system arising in many situations such as with multiphase flows presenting high density ratios or in the presence of highly-stretched adaptive mesh refinements. Finally, the results of the numerical experiments performed are presented and discussed, confirming our preconditioners as extremely affordable, highly-parallelizable and easy-to-implement alternatives to the more standard (and usually unfeasible) preconditioners, still showing great improvements in the rate of convergence of the solvers without requiring the variable coefficients matrix to be explicitly rebuilt at each iteration.

]]> Scipedia content https://www.scipedia.com/public/Guidio_Jeong_2021a Thu, 11 Mar 2021 17:44:42 +0100 https://www.scipedia.com/public/Guidio_Jeong_2021a There is a need to estimate complex seismic input motions in a near-surface domain, without resorting to the hypocenter, from restricted seismic measurement data. Thus, engineers can replicate responses within structures and soils after an earthquake occurrence by using the estimated seismic inputs and evaluate the impact of an earthquake on the built environment. To date, there has been no robust numerical method that can identify complex seismic input motions in a solid, truncated by a wave-absorbing boundary condition. Existing methods are limited to large-scale seismic-source inversion approaches and deconvolution. To fill this gap, a new inversion modeling method is presented for reconstructing complex, incoherent SH wave input motions in a two-dimensional (2D) domain that is truncated by a wave-absorbing boundary condition (WABC), using a partial differential equation (PDE)constrained optimization method. In a set of numerical examples, targeted, dynamic traction at the WABC mimics seismic incident wavefield. The discretize-then-optimize (DTO) approach is used in the mathematical modeling and numerical implementation, and the finite element method (FEM) is applied to solve state and adjoint problems. The numerical results indicate that the presented inversion algorithm can reconstruct incident, inclined plane waves. Second, the accuracy of our inversion solver is not compromised by the material complexity of a background domain. Lastly, the minimizer suffers less from solution multiplicity when it identifies lower frequency traction (e.g., a realistic seismic signal).

]]> Scipedia content https://www.scipedia.com/public/Hurtado-de-Mendoza_et_al_2021a Thu, 11 Mar 2021 17:44:33 +0100 https://www.scipedia.com/public/Hurtado-de-Mendoza_et_al_2021a The present study introduces an application of the non-modal analysis to multigrid operators with explicit Runge-Kutta smoothers in the context of Flux Reconstruction discretizations of the linear convection-diffusion equation. A dissipation curve is obtained that reflects upon the convergence properties of the multigrid operator. The number of smoothing steps, the type of cycle (V/W) and the combination of pand h-multigrid are taken into account in order to find those configurations which yield faster convergence rates. The analysis is carried out for polynomial orders up to P = 6, in 1D and 2D for varying degrees of convection (Péclet number), as well as for high aspect ratio cells. The non-modal analysis can support existing evidence on the behaviour of multigrid schemes. W-cycles, a higher number of coarse-level sweeps or the combined use of hp-multigrid are shown to increase the error dissipation, while higher degrees of convection and/or high aspect-ratio cells both decrease the error dissipation rate.

]]> Scipedia content https://www.scipedia.com/public/Vanna_et_al_2021a Thu, 11 Mar 2021 17:44:25 +0100 https://www.scipedia.com/public/Vanna_et_al_2021a This present paper reports a novel methodology to simulate wall-bounded flows in the LargeEddy Simulation framework using an automatic transition between a wall-modelled and a wall-resolved approach. The proposed technique aims at prescribing the right (modelled or resolved) wall shear stress and wall heat flux, preserving at the same time the no-slip/no-penetration conditions for the velocity and the isothermal/adiabatic conditions for the temperature fields. The approach is successfully implemented in a high-order finite-difference framework, and it is found able to adapt smoothly to the available nearwall grid spacing. Thus, the method falls into the wall-resolved case, when the near-wall dynamic is directly computed, whereas it employs the wall stress model when a full resolution of the near-wall region is not achievable. The method is tested on a nearly-incompressible turbulent channel flow and a supersonic spatially-devolving boundary layer flow. The obtained results highlight an excellent accuracy in representing the wall turbulence dynamics in terms of mean velocity profiles and fluctuations, almost independently of the near-wall spatial resolution. Thus, the proposed method results in a promising technique for analysis of high-Reynolds wall-bounded flows.

]]> Scipedia content https://www.scipedia.com/public/Morozova_et_al_2021a Thu, 11 Mar 2021 17:44:17 +0100 https://www.scipedia.com/public/Morozova_et_al_2021a In this work, we study the accuracy of CFD-based data-driven models, which predict comfortrelated flow parameters in a ventilated cavity with a heated floor. We compare the computational cost and accuracy of three different models, namely artificial neural network, support vector regression, and gradient boosting regression. The tested scenarios include short and long cavities with different inlet velocities. Among the studied frameworks, the artificial neural network provides the most accurate predictions for most of the tested flow configurations. However, test configurations with jet separation and a secondary vortex are more difficult to predict correctly; thus more high-fidelity data is required in order to construct a more robust and reliable model.

]]> Scipedia content https://www.scipedia.com/public/Salinas_et_al_2021a Thu, 11 Mar 2021 17:44:08 +0100 https://www.scipedia.com/public/Salinas_et_al_2021a This work presents a numerical and experimental study in a laboratorial rig to measure local flame temperature during the biomass combustion. Most of practical situations of biomass combustion is a transient and non-stable phenomenon. A spectral analysis method in the visible spectrum range was used for measurement of local temperatures in a sugarcane bagasse flame. The two-color method considering spectral flame emissivity variation joint with an inverse numerical procedure is used to simultaneous estimation of flame temperature and spectral emissivity. Also, a sequential iterative numerical procedure is tested. It includes the application of two-color method considering grey emissivity between two near spectral intensity data in a first step. In a second step and iterative procedure considering spectral emissivity variation along whole spectral range is applied. To apply the numerical methods was used several spectral intervals in the visible range. In inverse estimation, the LevenbergMarquardt method is used and a polynomial and a cosine models for estimation of coefficients were tested. Six test of biomass combustion were made focusing the sensor to the reaction zone, and spectral data collected. The flame temperature estimated for the six spectral data were closed to 1530 to 1540 K. Also, the spectral emissivity is closed in all sixcombustion test. Instantaneous bagasse flame temperature in the range of 1400 K to 1500 K in the reactive combustion zone were found. An image processing method was used to measure the temperature in the same reactive combustion zone and the comparison show

]]> Scipedia content https://www.scipedia.com/public/Castrillo_et_al_2021a Thu, 11 Mar 2021 17:44:01 +0100 https://www.scipedia.com/public/Castrillo_et_al_2021a The cyclic impact force between a reed valve and the seat plate is the main reason of the valve failure in many thermo-technical devices as compressors, engines, etc. According to experimental observations the latter is due to fatigue and usually occurs in the leading part of the valve `neck'. In this work, a complex numerical analysis is presented aimed to studying the external forces and internal stresses suffered by the valve. In particular, the impact force between the valve and the seat is studied. The numerical analysis relies on the coupled synergy of two different simulation concepts. In order to do so, two codes are used: (1) first, the in-house Computational Fluid Dynamics (CFD) code presented in [1] is employed to simulate the Fluid-Structure Interaction (FSI) between gas and valve, extracting reference data for valve displacement and external gas pressures; (2) second, the analysis of the internal structure stresses, together with the impact forces with the plate is implemented in a Computational Solid Dynamics (CSD) code developed in FreeFEM++ [2]. The impact force representation is based on the formulation presented in [3] where a conserving algorithm for frictionless dynamic contact/impact is developed. Due to the importance of obtaining an adequate impact force, an exhaustive study is carried out on its characterization in terms of numerical parameters, such as the penalty stiffness. Under this framework, the valve displacement and impact velocities are verified. Hence, impact forces are analysed in different scenarios, obtaining interesting observations about stresses distribution, with a particular focus on the points where failure is experienced.

]]> Scipedia content https://www.scipedia.com/public/Syrimi_et_al_2021a Thu, 11 Mar 2021 17:43:52 +0100 https://www.scipedia.com/public/Syrimi_et_al_2021a Aiming to enhance the stiffness and damping properties of cellular materials, the idea of inserting viscoelastic fillers into the gaps of cells is developed. A representative volume element of typical hexagonal honeycomb cells with and without inclusions is examined under dynamic shear loading, in order to define the mechanical properties of the proposed composite material. Within each cell the viscoelastic material is either through viscoelastic shell elements or through viscoelastic bars attached to the hexagonal cell apexes. The calibrated viscoelastic bar RVE model is, by extent, implemented to a shear wall, tested under dynamic shear loading, to verify the efficiency of the viscoelastic inclusions. Finally, different viscoelastic filler patterns are explored to study the proposed system's performance.

]]> Scipedia content https://www.scipedia.com/public/Glushkov_et_al_2021a Thu, 11 Mar 2021 17:43:45 +0100 https://www.scipedia.com/public/Glushkov_et_al_2021a Numerical simulation of guided wave excitation, propagation, and diffraction in laminate structures with local inhomogeneities (obstacles) is associated with high computational cost due to the need for a mesh-based approximation of extended domains with a rigorous account for the radiation conditions at infinity. To obtain computationally efficient solutions, hybrid numerical-analytical approaches are currently being developed, based on linking a numerical solution in a local vicinity of the source and/or obstacles with an explicit analytical representation in the external semi-infinite domain. However, the developed methods are generally not widely spread because the possibility of such coupling with an external multimode wave field is generally not provided in standard finite-element (FE) software. We propose a scheme that allows the use of the FE software as a black box for the required correct matching of local numerical and global analytical solutions (FEM-An). The FEM is used to obtain a set of local numerical solutions that serve as a basis in the inner domain. These solutions satisfy the boundary conditions induced by guided wave modes so that they fit correctly with the modal expansion in the outer region. The expansion coefficients of both FE and modal decompositions are determined then from the condition of stress and displacement continuity at the interface between the inner and outer domains. This scheme was numerically validated against analytical solutions to test problems and FE solutions for long waveguide sections with perfect match layer absorbing conditions at the ends (FEM PML). Along the way, it turned out that the FEM-PML approach gives an incorrect result in the backward-wave bands and at high frequencies. The application of the FEM-An hybrid scheme is illustrated by examples of Lamb wave diffraction by elastic inclusions and delaminations.

]]> Scipedia content https://www.scipedia.com/public/Lichtenheldt_et_al_2021a Thu, 11 Mar 2021 17:43:37 +0100 https://www.scipedia.com/public/Lichtenheldt_et_al_2021a In planetary exploration, testing under the actual mission conditions is inherently not possible. Hence, simulation campaigns complement ground test campaigns. This specially applies to surface missions that include the complex behaviour of soils under non-terrestrial gravitation. Increasingly ambitious mission goals made large simulation campaigns with very precise particle models necessary for the simulation of soil interaction. Thus, to limit the amount of time and the computation hardware needed, DLR developed the particle simulation tool 'Sir partsival'. This tool does not only speed up simulations by usage of GPU computing, but also integrates the institute's experience in modelling of soil on Earth and beyond. Using partsival it was possible to speed up simulations by more than a factor of ten and thus conduct large simulation campaigns. Two examples are shown: a large, on-going validation campaign of DEM for wheel simulations, and the completed traction optimization for the MMX rover wheel.

]]> Scipedia content https://www.scipedia.com/public/Diaz_et_al_2021a Thu, 11 Mar 2021 17:43:29 +0100 https://www.scipedia.com/public/Diaz_et_al_2021a In this work, the application of an artificial neural network (ANN) is proposed to develop a predicting model for the holdup of a two-phase flow composed of water and mineral oil in a horizontal pipe. For this, the surface velocities of each fluid and the differential pressure in the pipeline are used as input parameters of the multilayer artificial neural network with backpropagation, while the holdup of the fluids is used as the output parameter for the training. A set of 56 experimental data was obtained in the LabPetroCEPETRO-UNICAMP laboratory. The best performing results for the predictive model show a mean absolute error (AAPE) of 3.01% and a coefficient of determination 2 of 0.9964 using 15 neurons in the hidden layer of the network and the TanSig transfer function.

]]> Scipedia content https://www.scipedia.com/public/Watanabe_Furukawa_2021a Thu, 11 Mar 2021 17:43:22 +0100 https://www.scipedia.com/public/Watanabe_Furukawa_2021a Vertical Taylor-Couette flow with a free surface at its top has been examined by numerical and experimental approaches. Being compared with the ideal case with infinite length cylinders, this system has effects of the finite lengths, the gravitational acceleration and the surface tension. The inner cylinder rotates and the outer cylinder and the bottom wall are stationary. The numerical approach uses the VOF method to model the free surface. In the experiment, the flow patterns are observed from the top and the meridional views, and the displacement of the free surface is measured. The flow modes are classified by the number of vortices appearing in the meridional plane and the radial flow directions at the top and the bottom. The power spectra of the displacement of the free surface and the bulk energy are numerically evaluated and the bulk energy tends to give favorable agreement with the spectra of the displacement obtained experimentally. The transition from the secondary mode flow appearing at higher Reynolds number to the primary mode flow at lower Reynolds number is examined and comparison between the numerical and experimental results are made.

]]> Scipedia content https://www.scipedia.com/public/deSousa_et_al_2021 Thu, 11 Mar 2021 17:43:13 +0100 https://www.scipedia.com/public/deSousa_et_al_2021 This paper applies the peridynamic continuum mechanics theory on a new type of material known as harmonic-structured materials. Using the Peridigm software, rapid uniaxial elongation is simulated on a peridynamic model of a thin bimodal harmonic-structured metal sheet. Mechanical wave initiation, propagation, and reflection, as well as fracture initiation and propagation are successfully simulated.

]]> Scipedia content https://www.scipedia.com/public/Kishida_Kurahashi_2021a Thu, 11 Mar 2021 17:43:05 +0100 https://www.scipedia.com/public/Kishida_Kurahashi_2021a In this study, we carried out the topology optimization based on the density method in the unsteady oscillation problems. This paper considers two items, the proposal of new performance function and the relationship between each sensitivity term and results of topology optimization. In other studies, the adjoint analysis must be performed for the propose of minimizing strain energy. Optimization problems are classified into the problem of maximizing work in the negative and the problem of minimizing work in the positive, and self-adjoint relationships are derived. When using this method for cantilever beam model, there is a problem that numerous high-density elements is distributed at the load point, i.e., the tip. By classifying the sensitivity, it is found that the mass term has a great influence on the problem. In our study, some results are shown by changing the penalization parameter in the SIMP method that determines the mass coefficient, damping coefficient and elastic coefficient.

]]> Scipedia content https://www.scipedia.com/public/Pagano_et_al_2021 Thu, 11 Mar 2021 17:42:55 +0100 https://www.scipedia.com/public/Pagano_et_al_2021 The purpose of this work is to introduce time delays in an Oregonator-based model [11] to describe molecular communication in a system of coupled chemical oscillators [5]. With this approach we assume that the molecules responsible for communication (signal molecules) take a non-zero time to cross the barrier (phospholipid membrane) which physically separate the oscillators. In particular, here we present numerical results and we discuss and highlight the differences between delayed and non-delayed models.

]]> Scipedia content https://www.scipedia.com/public/Pacheco_Steinbach_2021a Thu, 11 Mar 2021 17:42:48 +0100 https://www.scipedia.com/public/Pacheco_Steinbach_2021a Various materials of engineering and biomedical interest can be modelled as generalised Newtonian fluids, i.e., via an apparent viscosity depending locally on the flow field. In spite of the particular features of those models, they are often handled in practice by classical numerical techniques originally conceived for Newtonian fluids. Methods designed specifically for the generalised case are rather scarce in the literature, as well as their use in practical applications. As it turns out, tackling nonNewtonian problems with standard finite element formulations can have undesired consequences such as the induction of spurious pressure boundary layers and the emergence of natural boundary conditions not suitable for realistic flow scenarios. In this context, we introduce a novel framework that deals with those issues while maintaining simplicity and low computational cost. The new stabilised formulation is based on a modified system combining the continuity equation with a Poisson equation for the pressure and consistent pressure boundary conditions. A weak enforcement of the rheological law is employed to enable full consistency even for first-order finite element pairs. Simple numerical examples are provided to demonstrate the potential of our method in yielding accurate solutions for relevant problems.

]]> Scipedia content https://www.scipedia.com/public/Kampitsis_2021a Thu, 11 Mar 2021 17:42:41 +0100 https://www.scipedia.com/public/Kampitsis_2021a In this study, the dynamic response of a Offshore Wind Turbine (OWT) tower under wind loading is investigated adopting the vibration absorption concepts. Application of vibration control systems (VCS) to OWT towers has the potential to significantly improve the dynamics of the tower and the nacelle, increasing its reliability. The first vibration mitigation approach is the classical tuned mass damped (TMD) and it is used as benchmark. In the TMD approach an additional mass is installed inside the nacelle at the top of the OWT tower. Usually, a large additional mass is required to achieve significant effective damping, which may lead to undesirable second order effects and ultimately increase the tower displacement. In the second approach, a passive vibration absorption concept is implemented, namely the Extended KDamper (EKD). The KDamper device is a special mechanical configuration consisting of an additional mass, an artificial damper and both positive and negative stiffness elements. The OWT is subjected to extreme environmental loading such as the wind and sea waves. These OWT loadings, are usually calculated based on stochastic interpolation of meteorological data or by artificial time-histories. In this study, the Blade Element Momentum (BEM) theory is taken into consideration in order to produce the wind load time histories. The improvement on the dynamic response of the OWT tower using vibration control systems is illustrated. Moreover, this research shown that the EKD presents a significant increase of the damping ratio with a minimal value of added mass at the top of the tower.

]]> Scipedia content https://www.scipedia.com/public/Pia_et_al_2021a Thu, 11 Mar 2021 17:42:33 +0100 https://www.scipedia.com/public/Pia_et_al_2021a Numerical simulations of gravitational planar liquid sheet flows, interacting with unconfined gaseous environments located on both sides of the liquid phase, are performed through Volume-of-Fluid (VOF) technique. The global unsteady dynamics of the non-parallel flow is analyzed by perturbing the initial steady configuration by means of a Gaussian bump in the transverse velocity component of relatively very small amplitude, thereby exciting sinuous modes. Thanks to the development of a theoretical linear one-dimensional model, more physical insights are gained on the flow system. It is found that surface tension plays a stabilizing role for the gravitational sheet, and for relatively high values of density ratio r_ρ of gaseous-to-liquid phases it becomes unstable. An analogy is shown between the global unstable behavior exhibited by the liquid sheet as r_ρ increases, and the shear-induced global instability found by Tammisola et al. [“Surface tension-induced global instability of planar jets and wakes”, J. Fluid Mech. 713, 632–658 (2012)] for planar jet and wake flows of two immiscible fluids in the presence of surface tension.

]]> Scipedia content https://www.scipedia.com/public/Bagheri_et_al_2021a Thu, 11 Mar 2021 17:42:25 +0100 https://www.scipedia.com/public/Bagheri_et_al_2021a The application of finite element techniques for the analysis and optimization of complex thermo-mechanical structures typically involves highly nonlinear models for material characterization, tribological contact, large deformation, damage, etc. These nonlinearities usually call for a higher-order Spatio-temporal discretization, including a large number of elements and time-steps in order to provide good convergence and sufficiently accurate simulation results. This inevitably leads to many expensive simulations in terms of cost and time if an optimization or adaption of model parameters has to be done. In this work, a FEM simulation modeling approach is proposed, which uses radial basis function interpolations (RBF) as efficient surrogate models to save FEM simulations. Also, a surrogate-assisted optimization algorithm [3] is utilized to find the parameter setting, which would lead to maximum damage in a simple tensile testing scenario involving a notched specimen with as few FEM simulations as possible. The relatively high accuracy of the utilized surrogate models showcases promising results and indicates the potential of surrogate models in saving time-expensive simulations.

]]> Scipedia content https://www.scipedia.com/public/Brandl_Battipede_2021a Thu, 11 Mar 2021 17:42:18 +0100 https://www.scipedia.com/public/Brandl_Battipede_2021a The estimation of the Angle of Attack (AOA) and Angle of Sideslip (AOS) is crucial for flight monitoring and control. However, a gap has been identified on the data selection technique for the class of estimators based on data-driven methods, such as the synthetic sensor based on Neural Network (NN). This paper proposes a Cross Validation (CV) technique applied on a manoeuver-based partitioning method to provide evidence that a given selection of data can lead to better estimation performance, with the final aim of providing a list of manoeuvers suitable for the training phase of the estimator. Results are shown using simulated data related to the CleanSky 2 project MIDAS.

]]> Scipedia content https://www.scipedia.com/public/Kurahashi_et_al_2021a Thu, 11 Mar 2021 17:42:09 +0100 https://www.scipedia.com/public/Kurahashi_et_al_2021a In this study, we present application of the level-set type topology optimization analysis for the cavity shape estimation problem in structures based on the non-destructive hammering test. The cavity shape is identified so as to minimize a performance function. The performance function is defined as the square sum of the residual between computed and the observed displacements on structure surface. In this study, accuracy of identified cavity shape is investigated by changing numerical parameters in the topology optimization.

]]> Scipedia content https://www.scipedia.com/public/Fahmy_2021a Thu, 11 Mar 2021 17:42:02 +0100 https://www.scipedia.com/public/Fahmy_2021a The main objective of this paper is to develop a novel boundary element technique for describing the three-dimensional (3D) biothermomechanical behavior of anisotropic biological tissues. The governing equations are studied on the basis of the dual phase lag bioheat transfer and Biot's theory for oneand two-temperature models. Because of the benefits of CQBEM, such as not being restricted by the complex shape of biological tissues and not requiring discretization of the interior of the treated region, it can cope with complex bioheat models and has low use of RAM and CPU. CQBEM is therefore a flexible and efficient tool for modeling the distribution of bioheat in anisotropic biological tissues and associated deformation. The resulting linear equations arising from CQBEM are solved by the generalized modified shift-splitting (GMSS) iterative method which reduces the number of iterations and the total time of the CPU. Numerical findings show the validity, efficacy and consistency of the proposed technique.

]]> Scipedia content https://www.scipedia.com/public/Hamdane_et_al_2021a Thu, 11 Mar 2021 17:41:53 +0100 https://www.scipedia.com/public/Hamdane_et_al_2021a soil in shallow depths could be used as heat sink / heat source for cooling / heating devices. To predict its thermal behaviour during year, some authors use data from soil temperature records some else use data from average yearly air temperature measurements of meteorologic stations to avoid measure soil temperature in shallow depths for long time. In this research paper, we present a comparison study about the use of soil data and the use of air data for soil temperature prediction, where transient heat conduction in semi-infinite solids is utilised in the study. We measured the soil temperature of three sites for three years in Covilha -Portugal to support the current study. Later, we create reference years of soil temperature in the three sites.

]]> Scipedia content https://www.scipedia.com/public/Nosko_Mrzyglod_2021a Thu, 11 Mar 2021 17:41:45 +0100 https://www.scipedia.com/public/Nosko_Mrzyglod_2021a Manufacturers of light motorcycles have always sought the use of more and more advanced materials. The application of carbon fiber in motorcycle parts design can bring high strength, stiffness, and low weight in a manner previously unavailable. This article contains selected problems regarding the construction of a swingarm made of carbon fiber reinforced plastics (CFRP). The swingarm was made specifically for Honda NSF 100. For the analysis, series of tests such as geometry, FEM, and structural analysis was chosen. The analysis concludes that the swingarm shape that was adopted from the original steel made part is not suitable for CFRP use. The analysis showed manufacturing errors, like the inconsistent thickness of laminate and poor quality of assembling. The full potential of the CFRP material was not used.

]]> Scipedia content https://www.scipedia.com/public/Marin-Montin_Montero-Chacon_2021a Thu, 11 Mar 2021 17:41:38 +0100 https://www.scipedia.com/public/Marin-Montin_Montero-Chacon_2021a The performance,durability of lithium-ion batteries (LIBs) are constrained by the degradation mechanisms that take place during charge,discharge cycles. Degradation of active particles (APs) of LIBs is a complex problem involving several physical phenomena (e.g.,diffusion,mechanical deformation,heat transfer,to cite a few). During lithium insertion,extraction cycles,volume changes in the AP result in high mechanical stresses and,consequently,mechanical damage that promotes capacity fade. In this work,we present a microscale 3D finite element model that takes into account the coupled effects between lithium diffusion,mechanical stress within the AP. Using the surface of an ellipsoid as the base for the geometrical construction,we are able to generate different shapes of APs,with both concave,convex surfaces. Porosity,other types of defects that may be present inside the AP are explicitly modeled,different volume fractions,shapes,orientations are also accounted for. In our approach,the material is discretized into a lattice of one-dimensional elements: we consider beam elements for the mechanical problem,while in the diffusive approach,the material is treated as an assembly of 'nanopipes' through which the flow of Li-ions takes place. The same lattice network is used for both simulations. We follow a classical lattice model approach to characterize the fracture behavior of a single AP of a LIB anode when subjected to charge/discharge cycles. The material of the APs analyzed in this work is graphite,which presents a brittle,disordered material structure,making it suitable for lattice modeling. The mechanical problem is solved,obtaining the crack patterns associated with specific charge,discharge strategies,potential initial defects. The simulation results correctly reproduce the experimental observations on mechanical stresses,the evolution of damage. This lattice model framework analyzing the degradation in the APs of LIBs (durability) can be used to provide more information regarding the microstructural evolution,morphological changes,mechanical degradation in APs,identify improvement strategies.

]]> Scipedia content https://www.scipedia.com/public/Huang_Leyendecker_2021a Thu, 11 Mar 2021 17:41:31 +0100 https://www.scipedia.com/public/Huang_Leyendecker_2021a Dielectric elastomers show promising performance as actuators for soft robotics. Thus, accurate and efficient numerical algorithms for the simulation of Dielectric Elastomer Actuators (DEAs) are required for the design and control of the soft robotic system. In this work, the Cosserat formulation of geometrically exact beam dynamics is extended by adding the electric potential as an additional degree of freedom to account for the electrical effects. A formulation of electric potential and electric field for the geometrically exact beam model is proposed such that complex beam deformations can be generated by the electrical forces. The kinematic variables in continuum electromechanics are formulated in terms of beam strains. The electromechanically coupled constitutive model for the beam formulation is obtained by integrating the strain energy in continuum electromechanics over the beam cross section, which leads to a direct transfer of the dielectric constitutive models in continuum mechanics to the beam model. The electromechanically coupled beam dynamics is solved with a variational time integrator scheme. By applying different electrical boundary conditions to the beam nodes, different deformation modes of the beam are obtained in the numerical example.

]]> Scipedia content https://www.scipedia.com/public/Houssein_et_al_2021a Thu, 11 Mar 2021 17:41:23 +0100 https://www.scipedia.com/public/Houssein_et_al_2021a This paper presents an algorithm and a method to solve mechanical contact problems between two bodies or more, for linear elastic and finite deformation problems. The contact problem is considered as an optimization one, more specifically as a minimization problem. The interior point method is used to solve the minimization problem. This algorithm is symmetric and the user does not need to specify anymore a slave and a master body. The algorithm was developed using FreeFEM and IPOPT software.

]]> Scipedia content https://www.scipedia.com/public/Boychev_et_al_2021a Thu, 11 Mar 2021 17:41:15 +0100 https://www.scipedia.com/public/Boychev_et_al_2021a A parametric study of Multiple Shock Wave Boundary Layer Interactions is presented in this paper. All results were obtained using the Computational Fluid Dynamics Solver of Glasgow University. Such interactions often occur in high-speed intakes, depending on the state of the upstream boundary layer, and can adversely affect the performance of the intake. First simulations of multiple shock wave boundary layer interaction in a rectangular duct were performed and compared to the experiments followed by simulations at different Mach and Reynolds numbers and flow confinement levels. The results showed that Reynolds-stress based turbulence models are better suited than linear turbulence models in predicting the interaction. The employed Explicit Algebraic Reynolds Stress Model showed good agreement for the corner and centreline separations and resulted only in a small underprediction of the wall pressure. Flow distortion and total pressure recovery efficiency metrics were defined and evaluated for each interaction. Lower upstream Mach number and/or lower levels of flow confinement were required to achieve higher total pressure recoveries and lower flow distortion levels.

]]> Scipedia content https://www.scipedia.com/public/Liu_Karube_2021a Thu, 11 Mar 2021 17:41:08 +0100 https://www.scipedia.com/public/Liu_Karube_2021a In this paper, we utilized a simulation approach based on the dynamic explicit FEM (Finite Element Method) to evaluate the stress distributions and the bulk density of catalyst pellets filled in a pipe reactor. We clarified that the shape of catalyst pellets affects their bulk density and stress distribution and found an optimal catalyst pellet shape that can increase the bulk density and reduce the average stress in the pipe reactor. The optimally shaped catalyst pellets are expected to improve their filled state in the pipe reactor, extend the durability of the catalyst pellets and increase the efficiency of production of environmentally friendly refrigerants. At the same time, the proposed simulation method can contribute to speeding up the development of production equipment and improving its completeness.

]]> Scipedia content https://www.scipedia.com/public/Hazmi_et_al_2021a Thu, 11 Mar 2021 17:40:59 +0100 https://www.scipedia.com/public/Hazmi_et_al_2021a A novel approach is presented for efficiently training a neural network (NN)-based surrogate model when the training data set is to be generated using a computationally intensive high-fidelity computational model. The approach consists in using a Gaussian Process (GP), and more specifically, its acquisition function, to adaptively sample the parameter space of interest and generate the minimum amount of training data needed to achieve the desired level of approximation accuracy. The overall approach is explained and illustrated with numerical experiments associated with the prediction of the lift-over-drag ratio for a NACA airfoil in a large, two-dimensional parameter space of free-stream Mach number and free-stream angle of attack. The obtained numerical results demonstrate the superior accuracy delivered by the proposed training over standard trainings using uniform and random samplings.

]]> Scipedia content https://www.scipedia.com/public/MA_et_al_2021a Thu, 11 Mar 2021 17:40:52 +0100 https://www.scipedia.com/public/MA_et_al_2021a Suffusion is a typical phenomenon of seepage-induced internal erosion, corresponding to fine particles erosion from the coarse matrix under the action of a fluid. A three-dimensional and spatially resolved fluid-solid coupling method based on lattice Boltzmann method (LBM) and discrete element method (DEM) is proposed to simulate suffusion in binary mixtures under anisotropic stress states. Based on such numerical simulations, eroded grains are identified and the mean squared displacement as well as the ratio between drag force and contact force of these eroded particles are computed to describe the detachment mechanism. The results show that the fluid force acting on eroded particles increases in the simulation which corresponding to the steep slope in squared displacements. Regardless of the initial state, the ratio between the fluid force and the contact force of the eroded particles displays a downward trend over time, reflecting the gradual dominance of the fluid force, which eventually leads to particle detachment and erosion. Based on the judgment between the direction of the fluid force and the direction of the contact force, a contact index P is then proposed to determine whether the contact is going to slide or strengthen under the action of the fluid. The distribution of indexes P for the contacts of eroded particles just prior to their detachment reflects that fluid induced sliding dominates. A particle detachment index is thus proposed and the overall detachment sensitivity of the binary samples is eventually investigated with respect to the fluid flow direction.

]]> Scipedia content https://www.scipedia.com/public/Schmidt_et_al_2021a Thu, 11 Mar 2021 17:40:44 +0100 https://www.scipedia.com/public/Schmidt_et_al_2021a Electricly enhanced flows can be found in various technical applications as, for example, in air cleaning devices and liquid metal or redox flow batteries. For both examples mentioned it is crucial to develop a general understanding of the relevant physical processes and model them economically. Additionally, a correct upscaling procedure is specifically relevant for the transition into the industrial scale. All of these aspects are challenging because of the multiscale and multiphysics nature of these flows. In this paper we present a lower-order modeling strategy that aims to bridge the gap between fundamental research and applications by utilizing stochastic one-dimensional turbulence (ODT). Two case studies are performed. One is for two-way coupled turbulent Couette flow of electrolytes and another for one-way coupled planar Poiseuille flow in a wire-plate electrostatic precipitator. By comparison with reference data, we show that the modeling approach is robust and has predictive capabilities. Nevertheless, we also discuss some limitations of the purely one-dimensional and stochastic dynamical representation.

]]> Scipedia content https://www.scipedia.com/public/Moosavi_et_al_2021a Thu, 11 Mar 2021 17:40:35 +0100 https://www.scipedia.com/public/Moosavi_et_al_2021a Manufacturing-oriented Topology Optimization (TO) is an active field of research both in academic and in industrial world. On one hand, the potential offered by topology optimization as a powerful design method is undeniable in improving the structural performance in different areas of engineering. On the other hand, Additive Manufacturing (AM) technology provides numerous industrial mechanisms of manufacturing and producing complex structure where classical methods fail to deliver an outcome. Merging both branches of TO and AM together introduces encouraging results in terms of designing optimized structures showing an acceptable mechanical response. In our contribution, we present a topology optimization model developed for additive manufacturing design. Using an innovative meshing algorithm, we particularly showed how the topology optimization could be implemented in order to consider the constraints of additive manufacturing specifically the printability of the parts with overhang angle. The design of the self-supporting structures is a challenging part of the additive manufacturing process, without which the process becomes tedious in terms of time, efficiency and financial resources. Therefore, a continuous effort for a better understanding of such issue is justified. In this paper, we suggest an improvement on the work carried out by Langelaar in this context. The model used in this study is a more complicated geometry compared to

]]> Scipedia content https://www.scipedia.com/public/Pinto_et_al_2021 Thu, 11 Mar 2021 17:40:27 +0100 https://www.scipedia.com/public/Pinto_et_al_2021 The tonal noise generated by the flow over elongated cylinders is measured using microphones in the anechoic wind tunnel BETI of Institut Pprime. The effect of the length to diameter ratio of the cylinder is assessed by varying the diameter from 6 mm to 20 mm within the constant width (750mm), open jet, test section. The velocity is varied from 10 to 40 m/s, leading to a Reynolds number range of about 4,000 ­ 53,000. A proper normalization is needed to obtain a good collapse of experimental data from nearly 10 studies on the same evolution in 3 steps: for very short cylinders, the tone level does not depend on the length; for semi-long cylinders, it follows the fourth power of the length to diameter ratio; for very long cylinder, the length's influence vanishes in the form of a sound level asymptote. This sigmoidal evolution is noticed for both the circular section and the square section cylinders, and questions the classical modelling of the aeroacoustic process using compact, coherent segments of cylinder associated with a coherence length to account for spanwise phase loss. Literature data from numerical simulation or experiment using end-plates are included in the analysis too.

]]> Scipedia content https://www.scipedia.com/public/Guo_et_al_2021a Thu, 11 Mar 2021 17:40:20 +0100 https://www.scipedia.com/public/Guo_et_al_2021a Structure-preserving algorithms exhibit superior long-run numerical stability in nonlinear solid and elasto-multibody dynamics. This paper provides time integrators for large flexible dynamic systems combining the carrier-sliding contact pair between two beams. The time integrators maintain some of the structural characteristics, which include the momentum, energy, symplecity et al. In research of the beam modeling, the director-based geometrically exact beam formulation has been compared with the three-dimensional absolute nodal coordinate beam formulation, which is also widely used in dynamic modeling of slender structures. The sliding contact transition between adjacent elements on the sliding line has been finely considered to keep the continuity of the sliding contact. The structurepreserving method has been embedded into the numerical solvers for dynamic analysis. The advantage of the structure-preserving methods over the time-decaying methods on energy and momentum preserving properties has been demonstrated in the dynamic analysis for the flexible beams that undergo sliding contact.

]]> Scipedia content https://www.scipedia.com/public/Suja_et_al_2021a Thu, 11 Mar 2021 17:40:12 +0100 https://www.scipedia.com/public/Suja_et_al_2021a All engineering problems consider uncertainties. These range from small production uncertainties to
large-scale uncertainties coming from outside, such as variable wind speed or sunlight. Currently, modern methods for uncertainty propagation have large difficulties with estimation of statistics for large-scale
problems which considers hundreds of these uncertain parameters. Due to the complexity of the problem
and limitations of the modern methods, a common approach for modelling large scale problems is to
select a few important parameters and model statistics for these parameters.
However, this can lead to an important problem. In this paper, an application of the UptimAI’s UQ propagation algorithm is used to discuss a new problem arising from very high dimensional spaces where a
large number of parameters have negligible impact on the final solution. In other words, when a problem consists of a great number of uncertain design parameters, common practice is to focus on the most
important ones and neglect the non-influential ones. However, a combination of a great number of noninfluential parameters can lead to completely different results. This is especially a problem for modelling
large dimensional statistical models where a common approach is to perform sensitivity analysis and neglect the non-influential variables, i.e. set the non-influential variables to nominal value. Therefore,
using a common approach of neglecting the non-influential variables could lead to a dramatic error and
hence, we call this problem ”many times nothing killed a horse”. This problem cannot be observed for
cases with a small number of design parameters, which are commonly solved in statistical modelling.
The reason for this issue is that the combined influence of neglected variables is extremely small and
such that has no influence on the final output.
Application of the UptimAl’s UQ propagation algorithm to modern engineering problems and the possibilities of mitigation of the cumulative influence of non-influential parameters is discussed in detail.
The problem is shown on a case of economic load dispatch (ELD) problem which consist of 140 dimensions [1]. To this problem was applied UptimAI’s UQ propagation algorithm to obtain accurate
statistics for the problem and to get deeper insight into the statistics. Using the accurate model obtained
by UptimAI’s algorithm, we compare statistics of using only important variables and using all variables.
This lead to a significant difference between results and such that put a large question mark on standard
approach. The obtained results are validated with the Monte Carlo simulation applied directly to ELD
problem.
Application of UptimAl’s UQ propagation algorithm to modern engineering problems and the possibilities of mitigation of the cumulative influence of non-influential parameters is discussed in detail.

]]> Scipedia content https://www.scipedia.com/public/Kireenkov_2021a Thu, 11 Mar 2021 17:40:05 +0100 https://www.scipedia.com/public/Kireenkov_2021a It is proposed applications of the theory of combined dry friction [1-14] in the problem of the ball rolling on boundaries of two identical frames. Father development of this model can be used in investigation of the dynamic of the a so-called 'Butterfly' robot, consisting of two identical shaped plates rigidly placed parallel to each other on a small distance aimed at manipulating a ball that can freely roll on the plates' boundaries as on rails [15]. The difficult control system, considered in [16-18] are another engineering application of the combined dry theory. Following developed in previous investigation approach, the friction force and torque are computed by the integration over the contact area so that the exact dynamically coupled integral model accounting the relationship of all the components of friction is obtained. This exact model is replaced by approximated analytical model [6] which is completely satisfy to all analytical properties of integral model as function kinematics parameters without increasing the number of coefficients.

]]> Scipedia content https://www.scipedia.com/public/Sladek_et_al_2021a Thu, 11 Mar 2021 17:39:57 +0100 https://www.scipedia.com/public/Sladek_et_al_2021a The size effect observed in nano-sized structures is considered in the proposed advanced continuum model for heat transfer. It is important for structures, where characteristic microstructural length is comparable with the phonon mean free-path. This feature can be captured by higher-grade continuum models and/or nonlocal modelling of constitutive laws in continuum theories. Both these approaches can be shown equivalent under certain assumptions. The governing equations are given by the PDE with higher-order derivatives than in classical continuum models, with the response of physically conjugated field being proportional to the gradients of primary fields. The variational principle is applied to derive the finite-element formulation for the solution of a thermoelectric 2-d boundary-value problem. Due to higherorder derivatives in gradient theory, it is necessary to use C1-continuous elements to guarantee the continuity of the derivatives at the element interfaces. Since it is not an easy task, a mixed FEM formulation is developed here.

]]> Scipedia content https://www.scipedia.com/public/Lau_Huang_2021a Thu, 11 Mar 2021 17:39:50 +0100 https://www.scipedia.com/public/Lau_Huang_2021a The falling of a plate is a simply posed problem that offers complex fluid-structure interactions. It also gives rise to different flow structures in relation to specific flight patterns of a plate such as autorotating tumble, side-to-side flutter, or constant abrupt turning in a chaotic manner depending on the Reynolds number and the non-dimensional moment of inertia In actual falling flights such as tree leaves and organisms, the bodies possess flexibility. Here, direct numerical simulation is used to portray the free fall of a flexible plate. The Navier-Stokes equations are solved via the upper-lower decomposition method. The effect of the flow on the solid plate is transferred through the immersed boundary method. A strictly spatially dependent stencil of the IB is adapted to provide a solution to the fourth-order beam equation via the pent-diagonal matrix algorithm. Comparing to the conventional method that couples with the temporal domain, this enables stability of solution through a range of bending rigidity k from k= 50 to k = 0.01. A plate with high stiffness resembles to a plate of non-flexible solution. The tumbling flight trajectory is found to change as a plate is more flexible, or as k is decreased. Further decrease in k result in changes flight states.

]]> Scipedia content https://www.scipedia.com/public/Alvarez-Farre_et_al_2021a Thu, 11 Mar 2021 17:39:42 +0100 https://www.scipedia.com/public/Alvarez-Farre_et_al_2021a The sparse matrix-vector product is a widespread operation amongst the scientific computing community. It represents the dominant computational cost in many large-scale simulations relying on iterative methods, and its performance is sensitive to the sparse pattern, the storage format and kernel implementation, and the target computing architecture. In this work, we are devoted to the efficient execution of the sparse matrix-vector product on (potentially hybrid) modern supercomputers with non-uniform memory access configurations. A hierarchical parallel implementation is proposed to minimise the number of processes participating in distributed-memory parallelisation. As a result, a single process per computing node is enough to engage all its hardware and ensure efficient memory access on manycore platforms. The benefits of this approach have been demonstrated on up to 9,600 cores of MareNostrum 4 supercomputer, at Barcelona Supercomputing Center.

]]> Scipedia content https://www.scipedia.com/public/Benvenuti_Orlando_2021a Thu, 11 Mar 2021 17:39:34 +0100 https://www.scipedia.com/public/Benvenuti_Orlando_2021a We have devised a crack-tracking methodology for general crack paths in elasto-damaging materials based on the regularized extended finite element method. The resulting procedure is in-between nonlocal models, where the discontinuity surface is replaced by a finite width zone, and cohesive zone models, where the discontinuous regime is governed by a traction-separation law.

]]> Scipedia content https://www.scipedia.com/public/MADUGULA_et_al_2021a Thu, 11 Mar 2021 17:39:26 +0100 https://www.scipedia.com/public/MADUGULA_et_al_2021a The objective of this paper is to optimise the internal structure of 3D printed parts produced by Fused Deposition Modelling (FDM) process. In 3D printing, the term infill refers to the internal structure of the part. The infill design is generally uniform throughout the part. In this paper, we propose a methodology based on an iterative process using remeshing techniques coupled to Finite Element simulation (FE simulation) to control the internal structure of the part without changing the contour. The aim of this methodology is to reinforce the part in the area where the mechanical strength must be improved in order to strengthen the structure, but also to minimize the amount of material in order to minimize the printing time. The proposed method is integrated in a computational environment using the ABAQUS (6.14) and the BL2D adaptive mesher. To validate this methodology, it has been applied on a structure subjected to four point bending. The material used for this structure is PLA (Poly lactic acid).

]]> Scipedia content https://www.scipedia.com/public/Liu_et_al_2021a Thu, 11 Mar 2021 17:39:18 +0100 https://www.scipedia.com/public/Liu_et_al_2021a Fluid-Structure Interaction (FSI) is a phenomenon that appears in a wide range of scientific research and engineering applications at different spatial and temporal scales. There are many in-house/commercial solvers capable of modelling FSI, but high numerical robustness and high scalability codes are still in demand. In this study, a numerical framework for FSI simulations has been developed using a partitioned approach aimed at both high numerical robustness and good computational scalability. Open-source software is used for each component of the coupled solution, with OpenFOAM and FEniCS adopted to simulate the computational fluid dynamics and computational structural mechanics, respectively. A coupling interface between the fluid and structural computational domains is realised using the open-source Multiscale Universal Interface (MUI) scientific code coupling library. To achieve a tight and stable coupling, various FSI coupling algorithms have been implemented in the MUI. The behaviour of this framework has been assessed for simulations of a blunt trailing edge hydrofoil at different working conditions with vortex-shedding induced vibration.

]]> Scipedia content https://www.scipedia.com/public/REN_et_al_2021a Thu, 11 Mar 2021 17:39:10 +0100 https://www.scipedia.com/public/REN_et_al_2021a In this paper, an approach is proposed to conduct reliability analysis on an offshore jacket considering corrosion degradation under extreme load cases. Corrosion degradation is considered as thickness wastage of the jacket element, which is seen as time-dependent variables. One probabilistic corrosion in literature is adopted by using different distribution models. Also, three different inspection cases (environmental conditions) of the corrosion are studied. The reliability assessment is evaluated by Crude Monte Carlo simulation based on the trained surrogate model. Deep neural networks are used to train the surrogate model, because they are not limited by the distribution and dimension of variables. The results show that using different corrosion distribution model, the probabilities of failure of the jacket are different, even though they have the same mean and standard deviation values. In addition, with same assumption of the distribution model in corrosion, the reliability of the jacket changes a lot concerning different inspection cases. Furthermore, it is noted that the inspection cases have more influences on the reliability analysis of jacket than different corrosion distribution assumptions. At the end, two recommendations are derived from this work.

]]> Scipedia content https://www.scipedia.com/public/Batoz_et_al_2021a Thu, 11 Mar 2021 17:39:01 +0100 https://www.scipedia.com/public/Batoz_et_al_2021a In this paper we present the formulation of a solid-shell element with 24 dof (the three cartesian components of displacement at the eight nodes of a solid hexahedron element), taking into account previous contributions to avoid shear, trapezoidal and thickness locking. But we also enhance the 3D displacement field by incomplete quadratic terms to improve the bending and transverse shear energies as was done for the performing DKMQ plate bending element proposed by Katili. After the formulation aspects, we present the results for some classical benchmark problems and for the linear analysis of a particular shallow foundation system called 'spider net system footing' used in Indonesia.

]]> Scipedia content https://www.scipedia.com/public/Ameres_et_al_2021a Thu, 11 Mar 2021 17:38:53 +0100 https://www.scipedia.com/public/Ameres_et_al_2021a The gridless Particle-In-Fourier method where particles are directly deposited onto a Fourier basis features excellent energy and momentum conservation properties, but is computationally expensive due to the global nature of its basis functions. In this paper, we investigate analytically and numerically how well a back-filtered spectral Particle-In-Cell method can approximate the Particle-In-Fourier method. The study is extended to a recent variational spectral PIC method which has a discrete Hamiltonian structure.

]]> Scipedia content https://www.scipedia.com/public/Xiao_et_al_2021b Thu, 11 Mar 2021 17:38:45 +0100 https://www.scipedia.com/public/Xiao_et_al_2021b Fiber reinforced polymers (FRPs) are increasingly used in thick primary load-bearing structures, while manufacturing and in-service defects occur with a higher chance as the composite thickness increases, which entails the nondestructive detection and evaluation of potential structure defects. This study focuses on the imaging qualities of defects at different depth in thick FRPs via total focusing method (TFM), aiming at determining the optimum imaging strategy for thick FRPs (25 mm for discussion). Dynamic homogenization based on Floquet theory and numerical finite element analysis are performed to interrogate the wave propagation characteristics. The Frequency-dependent time correction method for TFM imaging (F-TFM) is proposed for accurate defect imaging in periodically layered crossply FRP. Finally, the results show that the proposed F-TFM method is able to detect and locate the defects of 2 mm size at all possible depth.

]]> Scipedia content https://www.scipedia.com/public/Sau_et_al_2021a Thu, 11 Mar 2021 17:38:38 +0100 https://www.scipedia.com/public/Sau_et_al_2021a In a number of applications, large size structures subjected to loads that cause highly non-linear behavior need to be analyzed. With the peridynamic theory, proposed by Stewart Silling in 2000 and 2007, elasticity and damage in quasibrittle structures such as plain and reinforced concrete structures can be modeled with the peridynamic theory. To model these structures, lattice models with brittle beam elements are used to model concrete. A shortcoming of lattice and particle models is that they are highly demanding of computational power. Molecular dynamics may be, in some cases an appropriate tool for analyzing microcracks in quasibrittle materials in compression, but molecular dynamics becomes infeasible at scales larger than a few million atoms. For example, in masonry structures, cracks form in the brick mortar joints, and concrete blocks can be assumed to have a uniform displacement field. This allows us to use the peridynamic finite element model, which is an improvement over discrete lattice models. This model assumes a continuous displacement field within each finite element, with displacement discontinuities allowed to develop between finite elements. The objective of this work is to model cracks in quasibrittle structures, with the peridynamic model. The peridynamic finite element model is shown to be much more computer timeand memoryefficient than the similar discrete particle-based models. Results show that this implementation appears to be more computationally efficient than particle or lattice models.

]]> Scipedia content https://www.scipedia.com/public/Singh_Melnik_2021a Thu, 11 Mar 2021 17:38:31 +0100 https://www.scipedia.com/public/Singh_Melnik_2021a Radiofrequency ablation is a medical procedure that is becoming increasingly used for disease treatments. During this procedure, part of dysfunctional tissues is ablated by using the heat, typically generated from medium frequency electric current. It is a field of medicine where mathematical and computational models play a substantial role in assisting clinical practitioners with quantifications of some of the most critical characteristics, including temperature distributions and ablated volumes. In this contribution, we describe a framework for the development of coupled thermo-electro-mechanical models in this field. While our framework and the described validation procedures can be applicable to a variety of ablation modalities and treatments, a major focus has been given to some of the pecularities related to cardiac ablation at tissue-cellular scales and a role played by cell organelles such as microtubules, as well as by the cell nucleus. We have discussed the effects their inclusion makes on the calculation of the main characteristics of the radiofrequency ablation procedures. The importance of domain heterogeneity, as well as the integration of fluid-structure interaction in the developed framework along with other effects, have been highlighted and the details on ablation modalities in the context of clinical experimental research have been given. Finally, future generalizations of the proposed framework with hybrid stochastic-deterministic models have been put forward.

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