Scipedia: Documents published in 2020

In-situ co-design of Mobile Games using Design Thinking’s resources approach

Scipedia content — Fri, 24 Apr 2020 15:32:59 +0200

The contribution of this paper is to explore how in-situ co-design of indoor spaces (e.g. building) of Location-based Mobile Games could be handle, by describing the learned lessons on this topic. This paper presents a conceptual framework for in-situ co-design of indoor spaces on Location-based Mobile Games to assist to carry out this kind of experience using useful resources (as Design Thinking's resources). An experience of in-situ co-design for an indoor space on a Location-based Mobile Game is presented using this framework; for some phases an authoring tool was used which allows in-situ co-design of relevant locations for an application. Based on this experience, the authoring tool was extended to create a specific kind of Location-based Mobile Game. This paper presents this extension along with a proof of concept that shows how an in-situ co-designed game created by this extension was used by end-users.

Review of the state of art of DX-SAHP systems to obtain domestic hot water

Scipedia content — Fri, 24 Apr 2020 15:32:49 +0200

The investigation purpose is to elaborate a detailed review about previous published investigations with direct-expansion solar-assisted heat pumps (DX-SAHP) used for water heating, in the last years. The growing energy consumption, the using of refrigerants that weaken the ozone layer, the greenhouse gases emission to the atmosphere and the global warming effect are the main problems that the conventional water heating systems present. Using hydrocarbons as refrigerants represents a pollution reduction and it is also the best option to replace hydrochlorofluorocarbons and chlorofluorocarbons, due to their low values of global warming potential and ozone depletion potential, close to 0. A DX-SAHP system takes advantage of the thermal solar energy directly by using a bare flat-plate solar collector. These systems provide domestic hot water over 50 °C and heating water volumes until 200 liters reaching COP values higher than 4. Solar energy and the using of alternative refrigerants with a low environmental impact are proposed to reach this purpose.

Design, evaluation and validation of an effluent treatment system for the leather tanning process: case Pieles del Sur E.I.R.L.

Scipedia content — Fri, 24 Apr 2020 15:32:23 +0200

In this project a treatment system for the effluents of a leather tanning process was designed. This system was evaluated based on laboratory tests to ensure its viability, and the treatment was validated by analyzing effluents from the plant already installed. The system has three units: the first one is a Pretreatment that allows the oxidation of sulphides for the liming and draught baths, as well as the precipitation of chromium for the leather tanning baths; the second one is a Physical-Chemical Treatment for the general effluents of the process that allows to obtain treated effluents and decanted solids; the third is a sludge treatment that allows to obtain conditioned and low volume sludge to be collected for final disposal. The analysis of treated effluents showed a considerable reduction in the concentration of polluting chemicals that allows reusing the water and brings the company closer to compliance with the maximum levels allowed.

Evaluation of the efficiency of three oil extraction equipments with different oil palm genotypes (Elaeis sp.)

Scipedia content — Fri, 24 Apr 2020 15:32:14 +0200

This work was performed in the oil extraction laboratory of the African Palm Program, of the Experimental Station “Santo Domingo” of the INIAP. The main objective was to determine the efficiency of three oil extraction equipments, in three oil palm genotypes. The equipments used were Velp solvent extractor, Soxhlet extractor and a 1500 psi hydraulic press. The genotypes evaluated are part of the germplasm bank of the Palm Program at INIAP: Elaeis guineensis (african palm), Elaeis oleifera (american palm) and E. oleifera x E. guineensis (interspecific hybrid). The experimental design was a complete random design (DCA), with 20 observations, followed by student’s test and Tukey test at a 5 significance, to determine differences between treatment means. The results showed highly significant differences between the different factors evaluated. The higher percentage of oil per bunch was obtained with the genotype E. guineensis in the Soxhlet extractor (18.43 %) and the lowest percentage for E. oleifera with the hydraulic press (0.34 %). The analysis of costs determined that the lowest cost was obtained with the hydraulic press with USD 8,20 per sample.

In situ morphological characterization of soursop (Annona muricata L.) plants in Manabí, Ecuador

Scipedia content — Fri, 24 Apr 2020 15:32:05 +0200

Soursop (Annona muricata L.) germplasm, from the central region of the Ecuadorian littoral, has diverse phenotypic characteristics, which have been little studied. The main objective of this research was to characterize in situ the morphological variability of 60 accessions of soursop. The morphological traits were evaluated using 20 quantitative and 10 qualitative variables of the plant and the fruit. Multivariate statistical methods were used as principal components, hierarchical conglomerate aggregation, discriminant and correlation analysis (Pearson) were performed. Descriptive analysis such as central tendency and dispersion (coefficient of variation, range, mean and standard deviation) were determined for the quantitative data; while frequencies were calculated for qualitative data. In terms of morphological traits, 74 % of the total variability was explained by the fourth component. Three conglomerates of similarity were formed, in which the height, diameter of canopy and fruit number per tree, were the characters of greater contribution for its conformation.

Passion fruit oil (Passiflora edulis): Use of the seeds in cosmetic products

Scipedia content — Fri, 24 Apr 2020 15:31:56 +0200

The work documented in this essay is focused on harnessing the properties of Passion fruit seeds Passiflora edulis f.flavicarpa Deg to achieve the design of a cosmetic product: an exfoliating cream containing passion fruit seed oil and solid residue generated from oil extraction. The applied methodology for the formulation of the cream was initially based on a combination of a mechanical process through pressing, and oil extraction from the seeds by the use of organic solvents, ethyl ether. The physicochemical analysis variables evaluated in the exfoliating cream were pH, extensibility and emulsion capacity. The physical properties were considered as listed, colour, odour, brightness and grittiness. Furthermore, the absence of lumps was evaluated as macroscopic indicators of adequate particle size distribution and uniform texture. It was concluded that the oil from passionfruit seeds due to its composition in protein and liquid elements, optimally conserves the inherent properties of a product designed for skincare and conditioning. The use of solid residue that for primary industries is considered as unstable waste, represents an innovative alternative in the range of available semi-finished raw materials with properties capable of enhancing the products for human consumption.

Morphological, phenological and pomological differentiation of commercial cultivars of blackberry (Rubus glaucus Benth)

Scipedia content — Fri, 24 Apr 2020 15:31:48 +0200

The genus Rubus is one of the most diverse in terms of morphology and genetics, presenting a wide spectrum of wild and cultivated species that are desired by their edible fruits. In Ecuador, the cultivation of blackberry (R. glaucus and Rubus sp.) is present along the Inter-Andean region, grown between 2000 and 3100 masl. This fruit crop is economically important for its high demand for fresh and processed consumption. This research was carried out in the Tumbaco Experimental Farm of INIAP (Ecuador) with the objective of finding characters that allow the morphological, phenological and pomological differentiation of four blackberry cultivars (Castilla, Andimora, Colombiana and Brazos). The multivariate analysis showed three conglomerates (C). Cultivars Andimora and Colombiana (C3) do not have spines unlike Castilla (C2) and Brazos (C1). Colombian was the earliest cultivar (161 days of sprouting to harvest) and Castilla the latest (186 days). Brazos cultivar showed the highest fruit weight (5.85 g). Andimora reached the highest content of soluble solids (11.86 ºBrix) and had firm fruits. The differentiating characters observed in this study make possible to establish parameters of distinction between the cultivars that are currently cultivated in Ecuador.

Technological alternatives for the control of Botrytis sp. In Andean blackberry (Rubus glaucus)

Scipedia content — Fri, 24 Apr 2020 15:31:31 +0200

The Andean blackberry crop (Rubus glaucus) is very important for the farmers, since they must implement cultural practices that allow reducing the use of synthetic pesticides. The objective of the study was to evaluate the effect of different technological alternatives for the control of Botrytis sp. in the blackberry crop. The treatments were: 1: Absolute control (silwet+water), 2: Traditional chemical treatment (Carbendazim), 3: Mirtaceae extract (Iridium®), 4: Bacterial metabolite (Balus®) and 5: Trichoderma spp. (Tricomix®). The applications were carried out every 15 days for the synthetic product and every 8 days for the biologicals, organic and the control. A randomized complete block design (RCBD) was used with 3 repetitions and Tukey test at 5 % were made. The studied variables were botrytis incidence (%), yield (g/plot), weight (g), polar and equatorial diameter (mm), firmness (N), total soluble solids (Brix), titratable acidity (% citric acid) and pH (log H+). Throughout a weekly incidence analysis, it was possibly to identify that the Carbendazim, Trichoderma spp. and mirtaceae extract had a better control in the incidence of Botrytis sp. in the blackberry fruit.

Effect of neem on Phyllocnistis citrella Stainton and its parasitoid Ageniaspis citricola Logvinovskaya in Ecuador

Scipedia content — Fri, 24 Apr 2020 15:31:22 +0200

Efficacy of neem on Citrus Leafminer (CLM) and effect on its parasitoid Ageniaspis citricola was evaluated, using field, cage and olfactometer tests. Treatments were: aqueous extract of neem (50 gL-1), formulated oil of neem (10 mL L-1) and control. Field study was done in a Citrus aurantifolia orchard, three applications were carried out, which were evaluated every 48 hours until ten days after the treatment. Cage and olfactometer tests were performed in a greenhouse and repeated twice each time. In the cage, it were used 50 infested Citrus reticulata plants per experimental unit, while for the olfactometer test, as experimental arena, transparent plastic jars with 20 adults of CLM inside were used. Variables evaluated were: CLM infestation, dead, live and predated larvae, pupae, emerged adults and parasitized pupal chambers. The highest mortality of the CLM was caused by the aqueous extract of neem with 77.17%, which began 48 hours after application, suggesting inhibition of feeding. The aqueous extract of neem showed in average 88.80 % of repellency of adults of CLM and neem oil 85.64%. The high mortality of CLM and the repellent effect of neem, seem to influence negatively in parasitism which fluctuated between 9.45 % and 20.16 % in treated trees.

Impact of Ecodriving on fuel emissions and consumption on road of Quito

Scipedia content — Fri, 24 Apr 2020 15:30:55 +0200

This article presents the results of the impact of ecodriving on fuel consumption and the emission factors of polluting gases from a gasoline vehicle when performing road testing in the city of Quito, located at 2 810 meters above sea level. A route with traffic validated by the Technology Transfer Center has been selected for the training and investigation of vehicle emission control. A Chevrolet Aveo Family was used as a test vehicle, , considering is the bestselling vehicle in the city at the moment. And the equipment used to measure fuel consumption and the concentration of emissions was an onboard gas analyzer and a canister. The success and the measuring of the data in this experimentation were determined using the STATGRAPHICS Centurion XVI software. The results showed significant differences in fuel consumption and pollutant emissions of CO and NOx when applying an efficient driving, except for the HC in which there is no significant difference, but the emission is lower when is used on standard driving.

Analysis of the safety compartment material of a light vehicle by multi-criteria method

Scipedia content — Fri, 24 Apr 2020 15:30:38 +0200

There is a wide variety of materials with various properties available for designers to meet different design requirements. The objective of this study was to evaluate the properties of the relevant materials available in Ecuador through the multicriteria meth-od such as: Proportional complex evaluation (COP-RAS), Technique for the order of preference for similarity to real solution (TOPSIS), Optimization multi-disciplinary and compromise solution (VIKOR), in order to indicate which material would be a potential substitute for the original. It was concluded that 1045 steel is the best choice as a substitute for a safety compartment compared the base line the Aluminum-Magnesium alloy, considering that, despite being a light material, has low resistance to impact forces.

Precompression design for secondary settlement reduction

María Jesús Samper — Fri, 24 Apr 2020 14:57:42 +0200

A large water treatment plant is to be built on soft deltaic deposits. Precompression has been selected as the method for achieving the required ground improvement. An instrumented preload test has been carried out to obtain reliable information on precompression performance. Distributions of displacements throughout the foundation depth, obtained using sliding micrometer extensometers, have proved extremely useful for identifying the mechanisms of behaviour controlling ground deformation. The magnitudes of displacements are largely dependent on the overconsolidation state of the soil. As primary consolidation settlements take place rather quickly, they can be largely controlled by applying a preload over a limited period. The main design criterion therefore concerns secondary settlements. Laboratory and field data indicate clearly that overconsolidating the soil, even in moderate amounts, significantly reduces the secondary compression rate. The performance of an unloading stage in the preload test provides crucial information in this regard. Therefore applying a preload surcharge larger than the final structure load is quite effective in controlling the magnitude of subsequent secondary settlements. The information collected during the site investigation and in the preload test provides the basis for the development of a ground deformation model that can be used for computing settlement histories. The model is used as a design tool for the final proposal of the precompression treatment required for the various structures of the plant

A stress point algorithm for an elastoplastic model in unsaturated soils

María Jesús Samper — Fri, 24 Apr 2020 14:47:17 +0200

Two stress fields, combination of total stresses, liquid pressure and gas pressure have to be considered to explain the deformational behaviour of unsaturated media. Elastoplastic models developed for these materials consider generally two yield surfaces, each one associated to a stress field, and whose intersection produces a corner in the space of generalised stress components. In this paper, a stress point algorithm is proposed to cope with the integration of such constitutive laws, which can be seen as non smooth multisurface plastic models in the space of the two stress fields. The basic model developed by Alonso et al. (Alonso, E.E., Gens, A., 1990. A constitutive model for partially saturated soils. Géotechnique 40 (3), 405–430), which will be used to test the algorithm, is first described. Generalised stress and strain variables are then defined. Implementation of the return mapping algorithm, based on an implicit integration scheme, is presented with special attention devoted to the problem of mixed control imposed by the F.E. formulation generally used to analyse the hydromechanical behaviour of unsaturated media. Validation results on distinct generalised stress paths are given at the end.

Vapour transport in low permeability unsaturated soils with capillary effects

María Jesús Samper — Fri, 24 Apr 2020 14:39:03 +0200

A discussion of water phase change in unsaturated soils that develop capillary effects is first carried out in the paper. A distinction between the GR (geothermal reservoir) and the NUS (nonisothermal unsaturated soil) approaches is performed. Several aspects concerning advective and nonadvective fluxes of vapour are described secondly and some relationships concerning the case of mass motion in a closed system subjected to temperature gradients derived. Since the structure of unsaturated clays changes with moisture content, in order to correctly simulate the coupled phenomena induced by temperature gradients a model for intrinsic permeability as a function of humidity is required. A preliminary version of the model is presented and applied to interpret a laboratory test by means of a numerical simulation using CODE BRIGHT

Water permeability, water retention and microstructure of unsaturated compacted Boom clay

María Jesús Samper — Fri, 24 Apr 2020 14:17:50 +0200

Three classes of experiments are considered in this paper to provide information for two artificially prepared Boom clay fabrics: mercury intrusion/extrusion tests; main wetting/drying paths; and water inflow/outflow transient (permeability) tests. These tests, which are usually treated separately, are joined in a common reference frame to provide information about the morphology of the porous medium and factors influencing Boom clay unsaturated hydraulic states with reference to water retention curves and relative water permeability values. The main objective is to interpret mercury intrusion porosimetry results in order to define an entrance pore size region at ca 130 to 180 nm separating intra-aggregate and inter-aggregate zones. This pore size region is further associated to a delimiting zone in the retention curve separating regions of ‘intra-aggregate governing suction’ at gravimetric water contents lower than 13–15% (gravimetric water content is not affected by mechanical effects) and ‘inter-aggregate governing suction’ (gravimetric water content is sensible to mechanical actions). This water content is further used to define a threshold zone around a relative water permeability of kw/kws=0.01 delimiting a zone of greater water relative permeability from others that present a restricted flow in a generalised Darcian sense. All these results are consistent with the existence of two main pore size regions: an intra-aggregate porosity with quasi-immobile water that is little affected by loading processes and an inter-aggregate porosity for which the loading mechanism results in a reduction of interconnected macropores affecting free water. Testing results show that intra-aggregate water represents between 54 and 59% of the total volume of water in soil in a low-porosity packing compacted at a dry unit weight of 16.7 kN m-3, whereas it corresponds to ca 28 and 38% in the case of a high-porosity packing compacted at a dry unit weight of 13.7 kN m-3.

Modelling the mechanical behaviour of expansive clays

María Jesús Samper — Fri, 24 Apr 2020 14:06:06 +0200

A simple formalism is presented to model the behaviour of expansive clays. Two levels of structure are considered. The behaviour of the macrostructure follows the model developed for unsaturated materials by Alonso et al. [Géotechnique 40 (3) (1990) 405–430]. The behaviour of the microstructure is adapted from the work of Gens and Alonso [Can. Geotech. J. 29 (1992) 1013–1032] in order to include the possibility of the micropores being partially saturated. Mechanical coupling between both levels of structure are defined through two functions, one for wetting and the other for drying. They express the change in macrostructural void ratio due to a change in microstructural void ratio, and their value depends on the state of compaction of the macrostructure. The general shape of these curves is discussed on the basis of experimental evidence. Phenomena such as the dependency of strain on stress–suction path, accumulation of expansion strain during suction cycles at low confining stress, accumulation of compression strain during suction cycles at high confining stress, strain fatigue during drying–wetting cycles, macropore invasion by expanded microstructure and development of macroporosity during strong drying can be represented. A mathematical formulation of the model is described and its performance finally assessed by comparison with laboratory tests.

Analysis of a full scale "in situ" test simulating repository conditions

María Jesús Samper — Fri, 24 Apr 2020 13:44:36 +0200

Coupled thermo‐hydro‐mechanical (THM) analyses have been used to examine the interacting phenomena associated with the simultaneous heating and hydration of an engineered bentonite barrier placed in a drift excavated in granite. The specific problem studied is an in situ test being carried out in the underground laboratory at Grimsel (Switzerland). After describing the test and the theoretical formulation, the results of a coupled THM analysis using the best parameter estimation currently available are presented and discussed. The effect of various features of analysis are explored by means of additional analyses in which each of those features are varied, one at the time. Finally, sensitivity analyses have been carried out to examine some critical aspects of the in situ test design. Performance of coupled THM analyses has led to a better understanding of the various inter‐related phenomena occurring during heating and hydration of the engineered clay barrier.

Porosity variations in saline media caused by temperature gradients coupled to multiphase flow and dissolution/precipitation

María Jesús Samper — Fri, 24 Apr 2020 13:35:17 +0200

We present a theoretical-numerical investigation of porosity variations induced by temperature gradients in unsaturated saline media. It is known that temperature variations cause humidity variations which lead to liquid flow towards and vapour flow away from the hot source. When this phenomenon occurs in saline media, the liquid is salt saturated brine, so that evaporation causes salt precipitation and an ensuing porosity reduction. Condensation of water causes salt dissolution and porosity increase. This process may be important in the case of heat generating waste because it suggests that selfsealing may take place near the waste. On the other hand, salt mass balance will lead to porosity increases in other zones.

Coupled analysis of a backfill hydration test

María Jesús Samper — Fri, 24 Apr 2020 13:30:56 +0200

BACCHUS2 in situ isothermal wetting experiment has been analysed by means of a coupled flow-deformation approach. Backfill material, a mixture of Boom clay powder and high density pellets, has been extensively tested in the laboratory in order to determine its hydraulic and mechanical properties. Parameters of constitutive equations were derived from this experimental data base. Two mechanical constitutive models have been used in the simulation of the 'in situ' experiment: a state surface approach and an elastoplastic model. Calculations have shown several features of the hydration process which help to understand the behaviour of expansive clay barriers. Predictions using both models have been compared with each other and with actual measurement records. This has allowed a discussion of the comparative mertis of both approaches and the identiÞcation of some critical parameters of backfill behaviour. Overall agreement between calculations and field measurements is encouraging and shows the potential of the methods developed to model the behaviour of engineered clay barriers in the context of nuclear waste disposal.

Evaluation of safety factors in discontinuous rock

María Jesús Samper — Fri, 24 Apr 2020 13:13:59 +0200

Safety factors for kinematically admissible failure mechanisms in jointed rock masses have been defined with linear and nonlinear failure criteria for rock discontinuities. Data required to compute these safety factors are obtained by means of two finite element anlayses of the effects of selfweight and external (structural) loading, respectively. Both types of analysis are closely linked since they share a common geometry. Joint elements are used to simulate the behaviour of rock discontinuities. If kinematically admissible mechanisms are possible under field conditions, the finite element mesh should also allow them to develop. Different aspects of the methodology have been illustrated through the safety evaluation of a 150 m high arch dam and its foundation in fractured cretaceous limestone. Special attention has been paid to the modelling of a realistic geometry including three-dimensional rock blocks and discontinuities. The paper discusses the effect of initial state of stress, the evolution of safety as the external load increases and the relation between the defined safety factors. It also provides practical guidelines for conducting this type of analysis in complex situations.

Estimation of parameters in geotechnical backanalysis. I- Maximum likehood approach

María Jesús Samper — Fri, 24 Apr 2020 12:56:51 +0200

The estimation of soil and rock parameters based on field instrumentation data is a common procedure in geomechanics. The use of system identification and optimization techniques allows the performance of this type of analyses in a more rational and objective manner. In this paper a probabilistic formulation for the backanalysis problem is presented. The procedure described involves the evaluation of the measurement covariance matrices, which are derived for some geotechnical instruments used in field instrumentation. The algorithm used to solve the mathematical problem of optimization is also presented, as well as its coupling to a finite element code. The algorithm requires the computation of the sensitivity matrix, which can be evaluated “exactly” in terms of the finite element method. Finally, a synthetic example, based on the excavation of a tunnel, is presented in which the elastic modulus E and the K0 parameter of the material are identified from measured displacements. The effect of the number of measurements and their error structure is also discussed.

Estimation of parameters in geotechnical backanalysis. II- Application to a tunnel excavation problem

María Jesús Samper — Fri, 24 Apr 2020 12:48:58 +0200

A general statistical framework to perform backanalysis in geotechnical problems from field instrumentation has been presented in a companion paper. Here, an application to a real case involving the excavation of a tunnel in stiff overconsolidated clay is described. Both, extensometer and inclinometer measurements are used as input data and elastic moduli of the ground and the value of the K0 coefficient are estimated. The finite element method is used as the computational procedure to solve the direct problem, and has been coupled to the identification algorithm as described in the companion paper. In addition, a discussion on the reliability of the parameters identified is presented.

Hidratación de un relleno compactado que contiene agregados de alta intensidad

María Jesús Samper — Fri, 24 Apr 2020 12:27:54 +0200

Se han investigado, mediante ensayos de laboratorio, las características de hidratación de mezclas expansivas constituídas por una matriz de polvo arcilloso y agregados (pastillas de pequeño tamaño) de arcilla de alta densidad. Estas mezclas se han propuesto como material de relleno para aislar residuos potencialmente contaminantes del medio geológico que los rodea. Se ha simulado el comportamiento de este material de relleno bajo las condiciones existentes "in situ" mediante un analisis hidro-mecánico acoplado. En el análisis, el relleno se caracterizó de acuerdo con los resultados del programa de ensayos de laboratorio. Hydration characteristics of an expansive mixture of compacted clay matrix and high density pellets ha ve been investigated by means of laboratory tests. These mixtures are proposed as a suitable barrier material to isolate hazardous wastes from the surrounding geological environment. The behaviour of this material under conditions prevailing "in situ" has been simulated by means of a coupled flow-deformation analysis. The backfill was characterized according to the results of the laboratory tests program.

Parameter and variance estimation in geotechnical backanalysis using prior information

María Jesús Samper — Fri, 24 Apr 2020 11:27:45 +0200

A probabilistic framework to perform inverse analysis of geotechnical problems is presented. The formulation allows the incorporation of existing prior information on the parameters in a consistent way. The method is based on the maximum likelihood approach that allows a straightforward introduction of the error structure of field measurements and prior information. The difficulty of ascribing definite values to the uncertainties associated with the various types of observations is overcome by including the corresponding variances in the set of parameters to be identified. The inverse analysis results in a minimization problem that is solved by coupling the optimization technique to the finite element method. Two examples are presented to illustrate the performance of the method. The first one corresponds to a synthetic case simulating the excavation of a tunnel. Young's modulus, K0 value and measurements variances are identified. The second case concerns the excavation of a large underground cavern in which again Young's modulus and K0 are identified. It is shown that introduction of prior information permits the estimation of parameters more consistent with all available informations that include not only monitored displacements but also results from in situ tests carried out during the site investigation stage.

A paste slurry mass prediction numerical model for backfilling coal mining

Wenyu Lv — Fri, 24 Apr 2020 11:00:26 +0200

With the increasing importance of environmental protection, more and more attention has been paid to backfilling coal mining. The prediction and design of the proportioning of backfill materials are significantly important for paste backfilling coal mining. In this study, the key factors affecting paste slurry mass optimization are identified, including mass concentration, solid-cement ratio, and fly ash-cement ratio. According to the identified factors, a paste slurry mass prediction numerical model is established to effectively predict the paste slurry mass of backfilling mining, based on a hybrid algorithm of the back propagation neural network (BPNN) with chaos optimization (CO). With the adopted model indicators, the orthogonal test data of backfill materials are used as samples for learning, training and testing. The performance of the COBPNN and traditional BPNN models are assessed using experimental results. Finally, a mechanical model of gob-side entry retaining is development, and the surface convergence of surrounding rock of roadway and the internal load of filling body are detected in the tested working face. The results indicate that the proposed model has improved the performance of the traditional BPNN model, in terms of tardy convergence, low convergence precision, proneness to local minimum, enables high fitting accuracy and strong generalization, and more accurate and reliable prediction for the paste slurry mass, thus providing a more effective approach for optimizing the proportioning of paste slurry for backfilling coal mining.

Numerical formulation for a simulator (CODE_BRIGHT) for the coupled analysis of saline media

María Jesús Samper — Fri, 24 Apr 2020 10:50:12 +0200

Presents numerical aspects of the program CODE_BRIGHT, which is a simulator for COupled DEformation, BRIne, Gas and Heat transport problems. It solves the equations of mass and energy balance and stress equilibrium and, originally, it was developed for saline media. The governing equations also include a set of constitutive laws and equilibrium conditions. The main peculiarities of saline media are in the dissolution/precipitation phenomena, presence of brine inclusions in the solid salt and creep deformation of the solid matrix.

Nonisothermal multiphase flow of brine and gas through saline media

María Jesús Samper — Fri, 24 Apr 2020 10:34:17 +0200

We propose a general formulation for nonisothermal multiphase flow of brine and gas through saline media. The balance equations include mass balance (three species), equilibrium of stresses and energy balance (total internal energy). Salt, water and air mass balance equations are established. The balance of salt allows the establishment of the equation for porosity evolution due to solid skeleton deformation, dissolution/precipitation of salt and migration of brine inclusions. Water and air mass balance equations are also obtained. Two equations are required for water: total water in the medium and water present in solid phase brine inclusions. The mechanical problem is formulated through the equation of stress equilibrium. Finally, the balance of internal energy is established assuming thermal equilibrium between phases. Some general aspects of the constitutive theory are also presented.

The landslide of Cortes de Pallas, Spain

María Jesús Samper — Fri, 24 Apr 2020 10:21:32 +0200

A large landslide in Cretaceous limestone and marl formations, reactivated by quarry excavations, has been stabilized by weight-transfer procedures designed by using a conventional limit-equilibrium analysis. The analysis was based on strength parameters derived from a back-analysis of the conditions leading to instability. Slide reactivation, excavation and Ailing have also been modelled by a finite element analysis in which the sliding surface has been represented by elastoplastic joint elements. This has provided important information regarding the sliding mechanisms and the effects of the remedial measures. Shear strength parameters determined in the laboratory are compared with those obtained from back-analysis. A significant discrepancy was reconciled when it was found that the sliding surface was located in a very thin and continuous clay layer of uncertain origin; possible mechanisms explaining the presence of the clay layer are suggested. The case demonstrated the importance of knowing in detail the geometry of the sliding surface, proves the value of field instrumentation and shows the fundamental role that geological details play in landslide problems.

Desarrollo de un modelo elastoplástico para suelos no saturados

María Jesús Samper — Fri, 24 Apr 2020 10:00:15 +0200

En este artículo se presenta un modelo elastoplástico para describir el comportamiento tenso-deformacional de los suelos no saturados. La formulación se ha realizado en el marco de la teoría de la plasticidad con rigidización isótropa, empleando dos variables tensionales independientes, la presión media neta y la succión. El modelo es capaz de reproducir, de forma consistente y unificada, gran parte de las características fundamentales del comportamiento de los suelos no saturados que anteriormente habían sido tratadas de forma inconexa. Debido a que la información experimental es relativamente escasa, el planteamiento se ha realizado de forma simple con objeto de que sirva de base para posibles extensiones futuras. El modelo se ha desarrollado para suelos no saturados poco o moderadamente expansivos y se transforma en un modelo convencional de estado crítico al alcanzarse la saturación. En el artículo se presentan las formulaciones para estados isótropos y triaxiales, se describen las predicciones típicas para dichos estados y se las compara, de manera cualitativa, con las tendencias características del comportamiento de los suelos no saturados. Posteriormente se emplean los resultados de un conjunto de ensayos de laboratorio con succión controlada, realizados con un caolín y con una arena arcillosa, con objeto de evaluar la capacidad del modelo para reproducir cuantitativamente los comportamientos observados. El ajuste obtenido entre los resultados experimentales y los calculados es considerado satifactorio y confirma la posibilidad de reproducir las características más importantes del comportamiento de los suelos no saturados utilizando un marco de referencia general y sencillo.

A framework for the behaviour of unsaturated expansive clays

María Jesús Samper — Thu, 23 Apr 2020 17:41:30 +0200

The paper presents a framework for describing the mechanical behaviour of unsaturated expansive clays. It is an extension of an existing formulation developed for unsaturated soils of low activity. The extended framework is based on the distinction within the material of a microstructural level where the basic swelling of the active minerals takes place and a macrostructural level responsible for major structural rearrangements. By adopting simple assumptions concerning the coupling between the two levels, it is possible to reproduce major features of the behaviour of unsaturated expansive clays. Some selected qualitative comparisons between model predictions and experimental results reported in the literature are presented. Despite the simplified hypotheses made, a very encouraging agreement is obtained.

Pruebas de carga horizontal de columnas de suelo tratado mediante «Jet-Grouting»

María Jesús Samper — Thu, 23 Apr 2020 17:25:22 +0200

La realización de dos pruebas de carga a escala real sobre dos pares de columnas de «jet-grouting», ha proporcionado una interesante oportunidad para constatar la capacidad de los métodos de análisis convencionales para predecir el comportamiento de las columnas. Se ha comprobado que para poder reproducir el comportamiento observado en las columnas mediante las teorías existentes para predecir movimientos horizontales en pilotes, es necesario considerar la disminución exponencial de los módulos de deformación del suelo con el desplazamiento de la cabeza de la columna. Este efecto se mantiene para desplazamientos laterales muy pequeños y es consistente con resultados publicados previamente para grandes desplazamientos. Los ensayos de laboratorio e «insitu» (triaxial, columna resonante y sísmicos de «Crosshole»), son difíciles de usar para la predicción del comportamiento y además proporcionan una información limitada. Las teorías existentes para estudiar el comportamiento lateral de pilotes, son razonablemente capaces de predecir la deformada de la columna y sus momentos flectores cuando se incorpora en el análisis una variación correcta del módulo con la deformación.

A constitutive model for partially saturated soils

María Jesús Samper — Thu, 23 Apr 2020 17:01:04 +0200

The Paper presents a constitutive model for describing the stress-strain behaviour of partially saturated soils. The model is formulated within the framework of hardening plasticity using two independent sets of stress variables: the excess of total stress over air pressure and the suction. The model is able to represent, in a consistent and unified manner, many of the fundamental features of the behaviour of partially saturated soils which had been treated separately by previously proposed models. On reaching saturation, the model becomes a conventional critical state model. Because experimental evidence is still limited, the model has been kept as simple as possible in order to provide a basic framework from which extensions are possible. The model is intended for partially saturated soils which are slightly or moderately expansive. After formulating the model for isotropic and triaxial stress states, typical predictions are described and compared, in a qualitative way, with characteristic trends of the behaviour of partially saturated soils. Afterwards, the results of a number of suction-controlled laboratory tests on compacted kaolin and a sandy clay are used to evaluate the ability of the model to reproduce, quantitatively, observed behaviour. The agreement between observed and computed results is considered satisfactory and confirms the possibilities of reproducing the most important features of partially saturated soil behaviour using a simple general framework.

Análisis retrospectivo usando un criterio de máxima verosimilitud

María Jesús Samper — Thu, 23 Apr 2020 16:41:59 +0200

El artículo presenta una formulación probabilística del problema del análisis retrospectivo, basado en un criterio de máxima verosimilitud. La formulación está organizada de forma jerárquica, de manera que se pueden considerar análisis de diferente grado de complejidad dentro de un mismo marco teórico. Se presentan dos ejemplos de aplicación. El primero (el depósito de ensayo de Mundford) sólo requiere la adopción de un criterio de optimización de mínimos cuadrados, mientras que para el segundo (excavación de la caverna de la central reversible de Estanygento), es necesario introducir información previa sobre los parámetros y adoptar una expresión para la función objetivo basada en un criterio de optimización de máxima verosimilitud más general. Los ejemplos presentados ilustran las posibilidades de este procedimiento para llevar a cabo análisis retrospectivos.

A constitutive model for rock joints formulation and numerical implementation

María Jesús Samper — Thu, 23 Apr 2020 16:26:32 +0200

An elastoplastic constitutive law for describing the three-dimensional mechanical behaviour of rock joints is presented. The model is intended for use in numerical analysis and is formulated with sufficient flexibility so that it can reproduce a wide range of observed joint stress-strain behaviour. An hyperbolic failure criterion is shown to fit well reported joint strength data and the same type of function is adopted to define the family of yield surfaces. The evolution of hardening/softening is controlled by the total length of the plastic tangential strain path. Locking behaviour under normal loading and dilatancy varying with stress and strain level are also accounted for. Examples of application of the model to the reproduction of test results are presented. The model can be generalized to include anisotropy effects. Finally, some aspects of the procedures used in the numerical implementation of the constituive law are described.

La predicción del hinchamiento de suelos expansivos

María Jesús Samper — Thu, 23 Apr 2020 16:06:52 +0200

El examen de ensayos de hinchamiento en laboratorio sugiere la existencia de dos etapas en las curvas expansión-tiempo. El primer mecanismo, de tipo «primario», se asocia con fenómenos de flujo no estacionario en la red de poros interconectados del suelo. Se piensa que el segundo mecanismo responsable del comporta miento a largo plazo, es el resultado de la hidratación de minerales arcillosos activos. Se ha desarrollado un modelo que incorpora estos dos mecanismos básicos. Las nociones actuales de microestructura de suelos han proporcionado un marco de referencia conveniente para la formulación teórica. El modelo se ha utilizado para reproducir ensayos edométricos de hinchamiento de margas expansivas. Los parámetros derivados en el proceso de ajuste ensayo modelo se han utilizado para reproducir los hinchamientos medidos, a lo largo de diez años, en una central nuclear cimentada sobre margas expansivas

An interface element formulation for the analysis of soil-reinforcement interaction

María Jesús Samper — Thu, 23 Apr 2020 15:46:19 +0200

The formulation of a family interface elements belonging to the zero-thickness class is briefly described. The formulation is isoparametric and can be applied to 2-D and 3-D analysis. A flexible constitutive law, based on elastoplasticity, describing the mechanical behaviour of the interface is presented. In order to assess the suitability of the elements for the analysis of soil-reinforcement interaction, they are employed in the simulation of a pull-out test in two and three dimensions. It is shown that the performance of the elements can depend strongly on the type of integration rule adopted. The use of integration schemes, such as that of Newton-Cotes, which result in the uncoupling of the degrees of freedom of the element is shown to be very advantegeous. An application to the analysis of a problem involving softening behaviour of the interface is also included.

Anisotropy in 2D Discrete Exterior Calculus

Humberto Esqueda — Wed, 22 Apr 2020 23:26:09 +0200

We present a local formulation for 2D Discrete Exterior Calculus (DEC) similar to that of the Finite Element Method (FEM), which allows a natural treatment of material heterogeneity (assigning material properties element by element). It also allows us to deduce, in a principled manner, anisotropic fluxes and the DEC discretization of the pullback of 1-forms by the anisotropy tensor, i.e. we deduce the the discrete action of the anisotropy tensor on primal 1-forms. Due to the local formulation, the computational cost of DEC is similar to that of the Finite Element Method with Linear interpolating functions (FEML). The numerical DEC solutions to the anisotropic Poisson equation show numerical convergence, are very close to those of FEML on fine meshes and are slightly better than those of FEML on coarse meshes.

CFD analysis of flow pattern in labyrinth weirs

María Jesús Samper — Wed, 22 Apr 2020 14:04:30 +0200

The hydraulic performance of a labyrinth weir was analysed using numerical simulation. The head-discharge relation was compared to the results of an empirical formula, and the flow 3D pattern was studied. The results showed the reliability of the numerical model results, especially for intermediate to high heads. Moreover, they were used to unveil complex phenomena that are difficult to observe in laboratory tests.

Highly-converging chutes as an overtopping protection for concrete dams: physical and numerical modelling

María Jesús Samper — Wed, 22 Apr 2020 10:58:22 +0200

Spillways with highly-converging chutes are a non-conventional kind of spillway in which the length of the crest is greater than the width of the stilling basin. A pair of converging chutes leads the water into the stilling basin. This typology has two possible advantages: increase of the discharge capacity or reduction of the hydraulic head for a given discharge flow. The first improves dam safety, whereas the second results in higher storage capacity and power generation. In this proceeding, the authors present the investigation performed in order to study and characterize this kind of spillways. The utilization of this typology as an overtopping protection has emerged as a third possibility, presenting some particularities that are introduced here.

Physical and numerical modeling for understanding the hydraulic behaviour of Wedge-Shaped-Blocks spillways

María Jesús Samper — Wed, 22 Apr 2020 10:53:00 +0200

The technology of Wedge Shaped Blocks (WSB) for spillways had a slow development through decades but has proven its practical reliability. Ongoing additional research aims to complete the theoretical knowledge, improve current design criteria and make this technology available to practitioners as one more solution to consider when designing an embankment dam spillway. Here a summary is provided about recent physical and numerical modelling of WSB spillways performed by UPM and CIMNE.

Physical and numerical modeling of labyrinth weirs with polyhedral bottom

María Jesús Samper — Wed, 22 Apr 2020 10:12:10 +0200

In order to comply with the new safety regulations a significant number of Spanish dam spillways must be upgraded. In this scenario and with the aim of increasing the discharge capacity with a reduced investment innovative designs become interesting solutions. One of these innovative designs are the labyrinth weirs. Project POLILAB is carrying out with the objective of optimize the design of labyrinth weirs, physical and numerical tests exposed in this article were developed within this framework. The most relevant results are related with the discharge capacity, the flow pattern and the structural reinforcement achieved by the implementation of a polyhedral bottom.

Solving anisotropic Poisson problems via discrete exterior calculus

Rafael Herrera — Wed, 22 Apr 2020 01:48:07 +0200

An Interactive Tool for Automatic Predimensioning and Numerical Modeling of Arch Dams

María Jesús Samper — Tue, 21 Apr 2020 17:59:31 +0200

The construction of double-curvature arch dams is an attractive solution from an economic viewpoint due to the reduced volume of concrete necessary for their construction as compared to conventional gravity dams. Due to their complex geometry, many criteria have arisen for their design. However, the most widespread methods are based on recommendations of traditional technical documents without taking into account the possibilities of computer-aided design. In this paper, an innovative software tool to design FEM models of double-curvature arch dams is presented. Several capabilities are allowed: simplified geometry creation (interesting for academic purposes), preliminary geometrical design, high-detailed model construction, and stochastic calculation performance (introducing uncertainty associated with material properties and other parameters). This paper specially focuses on geometrical issues describing the functionalities of the tool and the fundamentals of the design procedure with regard to the following aspects: topography, reference cylinder, excavation depth, crown cantilever thickness and curvature, horizontal arch curvature, excavation and concrete mass volume, and additional elements such as joints or spillways. Examples of application on two Spanish dams are presented and the results obtained analyzed.

Development and validation of a multivariate predictive model for rheumatoid arthritis mortality using a machine learning approach

María Jesús Samper — Tue, 21 Apr 2020 17:40:26 +0200

We developed and independently validated a rheumatoid arthritis (RA) mortality prediction model using the machine learning method Random Survival Forests (RSF). Two independent cohorts from Madrid (Spain) were used: the Hospital Clínico San Carlos RA Cohort (HCSC-RAC; training; 1,461 patients), and the Hospital Universitario de La Princesa Early Arthritis Register Longitudinal study (PEARL; validation; 280 patients). Demographic and clinical-related variables collected during the first two years after disease diagnosis were used. 148 and 21 patients from HCSC-RAC and PEARL died during a median follow-up time of 4.3 and 5.0 years, respectively. Age at diagnosis, median erythrocyte sedimentation rate, and number of hospital admissions showed the higher predictive capacity. Prediction errors in the training and validation cohorts were 0.187 and 0.233, respectively. A survival tree identified five mortality risk groups using the predicted ensemble mortality. After 1 and 7 years of follow-up, time-dependent specificity and sensitivity in the validation cohort were 0.79–0.80 and 0.43–0.48, respectively, using the cut-off value dividing the two lower risk categories. Calibration curves showed overestimation of the mortality risk in the validation cohort. In conclusion, we were able to develop a clinical prediction model for RA mortality using RSF, providing evidence for further work on external validation.

Analysis of temporal and spatial variability of water balance components in a Mediterranean river basin: the Spanish part of the Duero basin.

María Jesús Samper — Tue, 21 Apr 2020 17:12:39 +0200

Water balances have been identified as an effective tool for assessing the amount of water and its availability in a region. In particular, the System of Environmental-Economic Accounting for Water (SEEA-W) has emerged as one of the most complete methodologies to undertake this action. Despite the great effort made to offer a common methodology for elaborating the SEEA-W tables, there are multiple aspects that prevent its standardization in a generalized way. This leads both to multiple approaches in the realization of water balances and to the introduction of high uncertainty in the accounts obtained.The data series variability, both temporal and spatial, is one of the factors that can introduce large uncertainty into the water balances if they are not correctly evaluated. This aspect has not yet been specifically studied, and most of the case studies in the literature only provide the water balance values for a short period (usually a natural or hydrological year) and for a specific basin. In the case of having data corresponding to several years, average values are typically used to elaborate the calculations. In the present study, the SEEA-W methodology was applied to the Spanish part of Duero river basin. Each component of the water asset accounts was calculated using simulated data from three models: SIMPA (rainfall-runoff model), ASTER (snow-related processes model) and SIMGES (water allocation and management model). These models were developed and calibrated by different Spanish entities. Then, the uncertainty associated with the temporal and spatial irregularity of the data series was also estimated.The Duero basin is located in a semi-arid Mediterranean region, where hydrological processes are affected by high intra- and inter-annual variability. To analyse this issue both monthly and annual resolutions were used. The first allowed identifying a significant intra-annual variability. The second was analysed using a period of 26 years, from 1980 to 2006. The results show a high variability for certain hydrological components which can lead to a great degree of uncertainty. In addition, each hydrological year was classified as dry, average or wet and water balances were calculated under the same classification. This approach would improve the estimation of water resources including the prediction of future climate changes scenarios.Regarding the spatial variability, the water resources of the basin, like many of the large Mediterranean rivers, are not evenly distributed and showed large differences in hydrological processes. These differences are caused by climatic and geomorphological differences (the area comprises an extensive central plateau with a peripheral mountain arch). In addition, the analysis considers the different human activities coexisting within the basin and the heterogeneity of their spatial distribution. The water balances split into a more disaggregated territorial units could help to detect the areas with both positive and negative balances and improve the water resources management in the whole basin.

Engaging soft computing in material and modeling uncertainty quantification of dam engineering problems

María Jesús Samper — Tue, 21 Apr 2020 17:04:35 +0200

Due to complex nature of nearly all infrastructures (and more specifically concrete dams), the uncertainty quantification is an inseparable part of risk assessment. Uncertainties might be propagated in different aspects depending on their relative importance such as epistemic and aleatory, or spatial and temporal. The objective of this paper is to focus on the material and modeling uncertainties, and to couple them with soft computing techniques aiming to reduce the computational burden of the conventional Monte Carlo-based finite element simulations. Several scenarios are considered in which the concrete and foundation material properties, the water level, and the dam geometry are assumed as random variables. Five soft computing techniques (i.e., random forest, boosted regression trees, multi-adaptive regression splines, artificial neural networks, and support vector machines) are employed to predict various quantities of interest based on different training sizes. It is argued that the artificial neural network is the most accurate algorithm in majority of cases, with enough accuracy as to be useful in reliability analysis as a complement to numerical models. The results with 200 samples in the training set are enough for reaching useful accuracy in most cases. For the simple prediction tasks, the results were predicted with less than 1% error. It is observed that increasing the number of input parameters increases the prediction error. The partial dependence plots provided most sensitive variables in dam design, which were consistent with the physics of the problem. Finally, several practical recommendations are provided for future applications.

A performance comparison of machine learning algorithms for arced labyrinth spillways

María Jesús Samper — Tue, 21 Apr 2020 16:53:54 +0200

Labyrinth weirs provide an economic option for flow control structures in a variety of applications, including as spillways at dams. The cycles of labyrinth weirs are typically placed in a linear configuration. However, numerous projects place labyrinth cycles along an arc to take advantage of reservoir conditions and dam alignment, and to reduce construction costs such as narrowing the spillway chute. Practitioners must optimize more than 10 geometric variables when developing a head–discharge relationship. This is typically done using the following tools: empirical relationships, numerical modeling, and physical modeling. This study applied a new tool, machine learning, to the analysis of the geometrically complex arced labyrinth weirs. In this work, both neural networks (NN) and random forests (RF) were employed to estimate the discharge coefficient for this specific type of weir with the results of physical modeling experiments used for training. Machine learning results are critiqued in terms of accuracy, robustness, interpolation, applicability, and new insights into the hydraulic performance of arced labyrinth weirs. Results demonstrate that NN and RF algorithms can be used as a unique expression for curve fitting, although neural networks outperformed random forest when interpolating among the tested geometries.

Statistical analysis for rupture risk prediction of abdominal aortic aneurysms (AAA) based on its morphometry

María Jesús Samper — Tue, 21 Apr 2020 15:49:40 +0200

The morphometry of the abdominal aortic aneurysms (AAA) it has been recognized as one of the main factors that may predispose its rupture. The variation of the AAA morphometry, over time, induces modifications in hemodynamic behavior which, in turn, alters the spatial and temporal distribution of hemodynamic stress on the aneurismatic wall, establishing a bidirectional process that can influence the rupture phenomenon. In order to evaluate potential correlations between the main geometric parameters characterizing the AAA and hemodynamic stresses, 13 unrupture AAA patient-specific models were created. To AAA geometric characterization, twelve indices based on lumen center line were defined and determined. The computing of temporal and spatial distributions of hemodynamic stresses was conducted through Computational Fluid Dynamics. Statistical techniques were used to assess the relationships between the hemodynamic parameters and the different geometrical indices of the AAA. Regression analyses were conducted to obtain linear predictor models for hemodynamic stresses using the different indices defined in this paper as predictor variables. The statistical analysis confirmed that the length L, the asymmetry and the saccular index significantly influenced the hemodynamic stresses. The results obtained show the potential of the use of statistical techniques in predicting the rupture risk of patient-specific AAA.

Valoración de los ángulos del cuello del aneurisma de aorta abdominal. Estudio en 507 pacientes

María Jesús Samper — Tue, 21 Apr 2020 15:40:46 +0200

Angulation in different planes of the neck of abdominal aortic aneurysms may be considered a limiting factor in the implantation of different prostheses in the treatment of this pathology. It is necessary to make an assessment of the angles in different planes in routine studies prior to the planning of the procedures and especially by AngioTAC. The study evaluated the measurement of 507 patients with abdominal aortic aneurysms and treated endovascular procedures and of whom the complete information was available at the level of neck angulations. In a prospective and descriptive study the situation of this aortic sector was evaluated, contributing information about the tendency in the morphological presentation of the aorta in patients with this aetiology

Study of angulations of visceral abdominals arteries in their abdominal aorta emergency

María Jesús Samper — Tue, 21 Apr 2020 15:31:33 +0200

Recently, fenestrated, branched and stent grafts have been developed in order to treat endovascular aneurysmal pathology at the level of the aorta in the emergence of the visceral arteries. For the implantation of stents, it is necessary to have a precise planimetry of the origin and orientation of the visceral branches in order firstly to perform the correct manufacture of the endoprosthesis and secondly the placement with precision of the same. The knowledge of the emergency of the vessels of the aortic wall and its orientation knowing the angle of emergency. The data obtained for the planning of the endovascular treatment of 37 patients in order to obtain data from the descriptive point of view of this sector.

Estimation of wall shear stress using 4D flow cardiovascular MRI and computational fluid dynamics

María Jesús Samper — Tue, 21 Apr 2020 15:20:48 +0200

Company In the last few years, wall shear stress (WSS) has arisen as a new diagnostic indicator in patients with arterial disease. There is a substantial evidence that the WSS plays a significant role, together with hemodynamic indicators, in initiation and progression of the vascular diseases. Estimation of WSS values, therefore, may be of clinical significance and the methods employed for its measurement are crucial for clinical community. Recently, four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has been widely used in a number of applications for visualization and quantification of blood flow, and although the sensitivity to blood flow measurement has increased, it is not yet able to provide an accurate three-dimensional (3D) WSS distribution. The aim of this work is to evaluate the aortic blood flow features and the associated WSS by the combination of 4D flow cardiovascular magnetic resonance (4D CMR) and computational fluid dynamics technique. In particular, in this work, we used the 4D CMR to obtain the spatial domain and the boundary conditions needed to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. Similar WSS distributions were found for cases simulated. A sensitivity analysis was done to check the accuracy of the method. 4D CMR begins to be a reliable tool to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. The combination of both techniques may provide the ideal tool to help tackle these and other problems related to wall shear estimation

Mechanical stress in abdominal aortic aneurysms using artificial neural networks

María Jesús Samper — Tue, 21 Apr 2020 15:05:31 +0200

Combination of numerical modeling and artificial intelligence (AI) in bioengineering processes are a promising pathway for the further development of bioengineering sciences. The objective of this work is to use Artificial Neural Networks (ANN) to reduce the long computational times needed in the analysis of shear stress in the Abdominal Aortic Aneurysm (AAA) by finite element methods (FEM). For that purpose two different neural networks are created. The first neural network (Mesh Neural Network, MNN) creates the aneurysm geometry in terms of four geometrical factors (asymmetry factor, aneurism diameter, aneurism thickness, aneurism length). The second neural network (Tension Neural Network, TNN) combines the results of the first neural network with the arterial pressure (new factor) to obtain the maximum stress distribution (output variable) in the aneurysm wall. The use of FEM for the analysis and design of bioengineering processes often requires high computational costs, but if this technique is combined with artificial intelligence, such as neural networks, the simulation time is significantly reduced. The shear stress obtained by the artificial neural models developed in this work achieved 95% of accuracy respect to the wall stress obtained by the FEM. On the other hand, the computational time is significantly reduced compared to the FEM.

Modeling human tissues : an efficient integrated methodology

María Jesús Samper — Tue, 21 Apr 2020 14:34:37 +0200

Geometric models of human body organs are obtained from imaging techniques like computed tomography (CT) and magnetic resonance image (MRI) that oallow an accurate visualization of the inner body, thus providing relevant information about their its structure and pathologies. Next, these models are used to generate surface and volumetric meshes, which can be used further for visualization, measurement, biomechanical simulation, rapid prototyping and prosthesis design. However, going from geometric models to numerical models is not an easy task, being necessary to apply image-processing techniques to solve the complexity of human tissues and to get more simplified geometric models, thus reducing the complexity of the subsequent numerical analysis. In this work, an integrated and efficient methodology to obtain models of soft tissues like gray and white matter of brain and hard tissues like jaw and spine bones is proposed. The methodology is based on image-processing algorithms chosen according to some characteristics of the tissue: type, intensity profiles and boundaries quality. First, low-quality images are improved by using enhancement algorithms to reduce image noise and to increase structures contrast. Then, hybrid segmentation for tissue identification is applied through a multi-stage approach. Finally, the obtained models are resampled and exported in formats readable by computer aided design (CAD) tools. In CAD environments, this data is used to generate discrete models using finite element methed (FEM) or other numerical methods like the boundary element method (BEM). Results have shown that the proposed methodology is useful and versatile to obtain accurate geometric models that can be used in several clinical cases to obtain relevant quantitative and qualitative information.

CFD modelling of abdominal aortic aneurysm on hemodynamic loads using a realistic geometry with CT

María Jesús Samper — Tue, 21 Apr 2020 14:25:58 +0200

The objective of this study is to find a correlation between the abdominal aortic aneurysm (AAA) geometric parameters, wall stress shear (WSS), abdominal flow patterns, intraluminal thrombus (ILT), and AAA arterial wall rupture using computational fluid dynamics (CFD). Real AAA 3D models were created by three-dimensional (3D) reconstruction of in vivo acquired computed tomography (CT) images from 5 patients. Based on 3D AAA models, high quality volume meshes were created using an optimal tetrahedral aspect ratio for the whole domain. In order to quantify the WSS and the recirculation inside the AAA, a 3D CFD using finite elements analysis was used. The CFD computation was performed assuming that the arterial wall is rigid and the blood is considered a homogeneous Newtonian fluid with a density of 1050¿kg/m3 and a kinematic viscosity of Pa·s. Parallelization procedures were used in order to increase the performance of the CFD calculations. A relation between AAA geometric parameters (asymmetry index (ß), saccular index (¿), deformation diameter ratio (¿), and tortuosity index (e)) and hemodynamic loads was observed, and it could be used as a potential predictor of AAA arterial wall rupture and potential ILT formation.

Hemodynamic features associated with abdominal aortic aneurysm (AAA) geometry

María Jesús Samper — Tue, 21 Apr 2020 14:11:52 +0200

Recent findings have shown that maximum diameter of abdominal aortic aneurysm (AAA) and its growth rate are not entirely reliable indicators of rupture potential. The AAA geometrical shape and size may be related to the rupture risk which is a clinical manifestation of the balance between the forces generated by blood flow within the AAA and its strength. This study aims at assessing the hemodynamic features associated with the geometry of AAAs.

An explicit/implicit Runge–Kutta-based PFEM model for the simulation of thermally coupled incompressible flows

María Jesús Samper — Tue, 21 Apr 2020 13:39:50 +0200

A semi-explicit Lagrangian scheme for the simulation of thermally coupled incompressible flow problems is presented. The model relies on combining an explicit multi-step solver for the momentum equation with an implicit heat equation solver. Computational cost of the model is reduced via application of an efficient strategy adopted for the solution of momentum/continuity system by the authors in their previous work. The applicability of the method to solving thermo-mechanical problems is studied via various numerical examples.

Computational modeling of the fluid flow and the flexible intimal flap in type B aortic dissection via a monolithic arbitrary Lagrangian/Eulerian fluid-structure interaction model

María Jesús Samper — Tue, 21 Apr 2020 13:32:42 +0200

In the present work, we perform numerical simulations of the fluid flow in type B aortic dissection (AD), accounting for the flexibility of the intimal flap. The interaction of the flow with the intimal flap is modeled using a monolithic arbitrary Lagrangian/Eulerian fluid-structure interaction model. The model relies on choosing velocity as the kinematic variable in both domains (fluid and solid) facilitating the coupling. The fluid flow velocity and pressure evolution at different locations is studied and compared against the experimental evidence and the formerly published numerical simulation results. Several tear configurations are analyzed. Details of the fluid flow in the vicinity of the tears are highlighted. Influence of the tear size upon the fluid flow and the flap deformation is discussed.

An explicit–implicit finite element model for the numerical solution of incompressible Navier–Stokes equations on moving grids

María Jesús Samper — Tue, 21 Apr 2020 13:22:35 +0200

In this paper an efficient mesh-moving Finite Element model for the simulation of the incompressible flow problems is proposed. The model is based on a combination of the explicit multi-step scheme (Runge–Kutta) with an implicit treatment of the pressure. The pressure is decoupled from the velocity and is solved for only once per time step minimizing the computational cost of the implicit step. Novel solution algorithm alleviating time step restrictions faced by the majority of the former Lagrangian approaches is presented. The method is examined with respect to its space and time accuracy as well as the computational cost. Two numerical examples are solved: one involving a problem on a domain with fixed boundaries and the other one dealing with a free surface flow. It is shown that the method can be easily parallelized.

A semi-explicit multi-step method for solving incompressible navier-stokes equations

María Jesús Samper — Tue, 21 Apr 2020 13:17:14 +0200

The fractional step method is a technique that results in a computationally-efficient implementation of Navier–Stokes solvers. In the finite element-based models, it is often applied in conjunction with implicit time integration schemes. On the other hand, in the framework of finite difference and finite volume methods, the fractional step method had been successfully applied to obtain predictor-corrector semi-explicit methods. In the present work, we derive a scheme based on using the fractional step technique in conjunction with explicit multi-step time integration within the framework of Galerkin-type stabilized finite element methods. We show that under certain assumptions, a Runge–Kutta scheme equipped with the fractional step leads to an efficient semi-explicit method, where the pressure Poisson equation is solved only once per time step. Thus, the computational cost of the implicit step of the scheme is minimized. The numerical example solved validates the resulting scheme and provides the insights regarding its accuracy and computational efficiency

An embedded approach for immiscible multi-fluid problems

María Jesús Samper — Tue, 21 Apr 2020 11:59:08 +0200

An embedded formulation for the simulation of immiscible multi-fluid problems is proposed. The method is particularly designed for handling gas-liquid systems. Gas and liquid are modeled using the Eulerian and the Lagrangian formulation, respectively. The Lagrangian domain (liquid) moves on top of the fixed Eulerian mesh. The location of the material interface is exactly defined by the position of the boundary mesh of the Lagrangian domain. The individual fluid problems are solved in a partitioned fashion and are coupled using a Dirichlet-Neumann algorithm. Representation of the pressure discontinuity across the interface does not require any additional techniques being an intrinsic feature of the method. The proposed formulation is validated, and its potential applications are shown.

Método de puntos finitos. Un análisis sobre el efecto de los parámetros que definen las nubes en aproximaciones de segundo y cuarto orden

María Jesús Samper — Mon, 20 Apr 2020 10:21:23 +0200

Se investiga en el presente trabajo la influencia de los distintos parámetros que definen la aproximación local en el Método de Puntos Finitos y su relación con la calidad de la misma. Este análisis se realiza sobre la solución de un problema de Poisson tridimensional el cual se emplea como caso testigo. Haciendo uso de este último se propone un método para ajustar los parámetros de la aproximación local mediante la definición individual de la función de ponderación en cada nube de puntos. Ello posibilita flexibilizar la definición de parámetros y lograr la mejor aproximación para el problema planteado. El análisis se extiende a funciones de aproximación de segundo y cuarto orden y distribuciones estructuradas y no estructuradas de puntos.

Solución de las ecuaciones de flujo compresible mediante el método de puntos finitos

María Jesús Samper — Mon, 20 Apr 2020 09:44:07 +0200

El trabajo desarrollado consiste en la resolución numérica de las ecuaciones de flujo bidimensional, compresible y no viscoso; mediante el Método de Puntos Finitos (FPM). Este último se ubica dentro del conjunto de métodos “meshless” cuya característica principal es prescindir de una malla o grilla a efectos de realizar la discretización numérica. En FPM, la función incógnita y derivadas de la misma se obtienen exclusivamente a partir de las coordenadas de un conjunto de puntos pertenecientes al dominio de análisis. Esto último, sumado a un procedimiento de colocación puntual para la derivación del sistema de ecuaciones discreto, convierten a FPM en un verdadero método sin malla. La discretización temporal de las ecuaciones se lleva a cabo mediante un esquema explícito de segundo orden del tipo Lax-Wendroff en dos pasos. Difusión artificial de Jameson, de segundo y cuarto orden, se introduce en las ecuaciones. Se implementa además un esquema corrector de los flujos difusivos o ‘Flux-Corrected Transport’, con la finalidad de regular la cantidad de difusión agregada al esquema y lograr una mayor precisión y calidad de la solución numérica. La performance del algoritmo desarrollado se ilustra mediante la resolución de distintos ejemplos numéricos.

Impact of short-sales in stock market efficiency

María Jesús Samper — Fri, 17 Apr 2020 15:19:17 +0200

In the last two decades, the hedge fund sector has experienced a spectacular growth, up to the point that it is currently estimated to move more than 50% of the daily volume of stock markets. In contrast to other financial institutions, hedge funds are subject to less restrictive regulations which, in particular, allow them to sell short. As they exploit the asset mispricings, their action is thought to contribute to market efficiency. In this paper we aim at studying the impact that short sales have on the informational efficiency of a financial market. This can be used not only to assess the effect that hedge fund actions have in financial markets, but also the consequences of regulatory measures such as short-selling restrictions or bans. Building on an agent-based market, the simulation results indicate that short sales are beneficial to market efficiency, although the market does not become completely efficient even when all the population can sell short.

Impact of Basel III Countercyclical Measures on Financial Stability: An Agent-Based Model

María Jesús Samper — Fri, 17 Apr 2020 15:15:14 +0200

The financial system is inherently procyclical, as it amplifies the course of economic cycles, and precisely one of the factors that has been suggested to exacerbate this procyclicality is the Basel regulation on capital requirements. After the recent credit crisis, international regulators have turned their eyes to countercyclical regulation as a solution to avoid similar episodes in the future. Countercyclical regulation aims at preventing excessive risk taking during booms to reduce the impact of losses suffered during recessions, for example increasing the capital requirements during the good times to improve the resilience of financial institutions at the downturn. The Basel Committee has already moved forward towards the adoption of countercyclical measures on a global scale: the Basel III Accord, published in December 2010, revises considerably the capital requirement rules to reduce their procyclicality. These new countercyclical measures will not be completely implemented until 2019, so their impact cannot be evaluated yet, and it is a crucial question whether they will be effective in reducing procyclicality and the appearance of crisis episodes such as the one experienced in 2007-08. For this reason,we present in this article an agent-based model aimed at analysing the effect of two countercyclical mechanisms introduced in Basel III: the countercyclical buffer and the stressed VaR. In particular, we focus on the impact of these mechanisms on the procyclicality induced by market risk requirements and, more specifically, by value-at-risk models, as it is a issue of crucial importance that has received scant attention in the modeling literature. The simulation results suggest that the adoption of both of these countercyclical measures improves market stability and reduces the emergence of crisis episodes

Using realistic trading strategies in an agent-based stock market model

María Jesús Samper — Fri, 17 Apr 2020 14:45:01 +0200

The use of agent-based models (ABMs) has increased in the last years to simulate social systems and, in particular, financial markets. ABMs of financial markets are usually validated by checking the ability of the model to reproduce a set of empirical stylised facts. However, other common-sense evidence is available which is often not taken into account, ending with models which are valid but not sensible. In this paper we present an ABM of a stock market which incorporates this type of common-sense evidence and implements realistic trading strategies based on practitioners literature. We next validate the model using a comprehensive approach consisting of four steps: assessment of face validity, sensitivity analysis, calibration and validation of model outputs.

Impact of value-at-risk models on market stability

María Jesús Samper — Fri, 17 Apr 2020 14:36:39 +0200

Financial institutions around the world use value-at-risk (VaR) models to manage their market risk and calculate their capital requirements under Basel Accords. VaR models, as any other risk management system, are meant to keep financial institutions out of trouble by, among other things, guiding investment decisions within established risk limits so that the viability of a business is not put unduly at risk in a sharp market downturn. However, some researchers have warned that the widespread use of VaR models creates negative externalities in financial markets, as it can feed market instability and result in what has been called endogenous risk, that is, risk caused and amplified by the system itself, rather than being the result of an exogenous shock. This paper aims at analyzing the potential of VaR systems to amplify market disturbances with an agent-based model of fundamentalist and technical traders which manage their risk with a simple VaR model and must reduce their positions when the risk of their portfolio goes above a given threshold. We analyse the impact of the widespread use of VaR systems on different financial instability indicators and confirm that VaR models may induce a particular price dynamics that rises market volatility. These dynamics, which we have called `VaR cycles’, take place when a sufficient number of traders reach their VaR limit and are forced to simultaneously reduce their portfolio; the reductions cause a sudden price movement, raise volatility and force even more traders to liquidate part of their positions. The model shows that market is more prone to suffer VaR cycles when investors use a short-term horizon to calculate asset volatility or a not-too-extreme value for their risk threshold.

Higher-order simulations: Strategic investment under model-induced price patterns

María Jesús Samper — Fri, 17 Apr 2020 14:24:50 +0200

The trading and investment decision processes in financial markets become ever more dependent on the use of valuation and risk models. In the case of risk management for instance, modelling practice has become quite homogeneous and the question arises as to the effect this has on the price formation process. Furthermore, sophisticated investors who have private information about the use and characteristics of these models might be able to make superior gains in such an environment. The aim of this article is to test this hypothesis in a stylised market, where a strategic investor trades on information about the valuation and risk management models used by other market participants. Simulation results show that under certain market conditions, such a'higher-order'strategy generates higher profits than standard fundamental and momentum strategies that do not draw on information about model use.

Simulación basada en agentes del efecto inestabilizador de las técnicas VaR

María Jesús Samper — Fri, 17 Apr 2020 14:12:07 +0200

En los últimos años ha habido un gran número de crisis financieras con graves efectos en la economía de los países afectados. Para evitar o minimizar estos efectos negativos es necesario entender qué factores pueden desencadenar una crisis financiera. Sin embargo, la literatura sólo ofrece explicaciones de tipo cualitativo o modelos analíticos muy estilizados que resultan poco operativos. Proponemos en este artículo un modelo basado en agentes que permite estudiar, mediante simulación, los efectos agregados que emergen de la interacción de los inversores de un mercado financiero. Nuestro objetivo es analizar con este modelo la influencia en la dinámica de un mercado del uso generalizado de modelos basados en técnicas VaR de gestión de riesgo. Los resultados de la simulación corroboran la tesis que señala el uso homogéneo de estos modelos como uno de los factores que pueden inducir episodios de inestabilidad financiera.

A new formulation for air-blast fluid–structure interaction using an immersed approach: part II—coupling of IGA and meshfree discretizations

María Jesús Samper — Fri, 17 Apr 2020 13:10:59 +0200

In this two-part paper we begin the development of a new class of methods for modeling fluid–structure interaction (FSI) phenomena for air blast. We aim to develop accurate, robust, and practical computational methodology, which is capable of modeling the dynamics of air blast coupled with the structure response, where the latter involves large, inelastic deformations and disintegration into fragments. An immersed approach is adopted, which leads to an a-priori monolithic FSI formulation with intrinsic contact detection between solid objects, and without formal restrictions on the solid motions. In Part I of this paper, the core air-blast FSI methodology suitable for a variety of discretizations is presented and tested using standard finite elements. Part II of this paper focuses on a particular instantiation of the proposed framework, which couples isogeometric analysis (IGA) based on non-uniform rational B-splines and a reproducing-kernel particle method (RKPM), which is a meshfree technique. The combination of IGA and RKPM is felt to be particularly attractive for the problem class of interest due to the higher-order accuracy and smoothness of both discretizations, and relative simplicity of RKPM in handling fragmentation scenarios. A collection of mostly 2D numerical examples is presented in each of the parts to illustrate the good performance of the proposed air-blast FSI framework.

A cut finite element method for the solution of the full-potential equation with an embedded wake

María Jesús Samper — Thu, 16 Apr 2020 13:25:32 +0200

Potential flow solvers represent an appealing alternative for the simulation of non-viscous subsonic flows. In order to deliver accurate results, such techniques require prescribing explicitly the so called Kutta condition, as well as adding a special treatment on the “wake” of the body. The wake is traditionally modelled by introducing a gap in the CFD mesh, which requires an often laborious meshing work. The novelty of the proposed work is to embed the wake within the CFD domain. The approach has obvious advantages in the context of aeroelastic optimization, where the position of the wake may change due to evolutionary steps of the geometry. This work presents a simple, yet effective, method for the imposition of the embedded wake boundary condition. The presented method preserves the possibility of employing iterative techniques in the solution of the linear problems which stem out of the discretization. Validation and verification of the solver are performed for a NACA 0012 airfoil.

A robust algorithm for implicit description of immersed geometries within a background mesh

María Jesús Samper — Thu, 16 Apr 2020 13:19:17 +0200

The paper presents a robust algorithm, which allows to implicitly describe and track immersed geometries within a background mesh. The background mesh is assumed to be unstructured and discretized by tetrahedrons. The contained geometry is assumed to be given as triangulated surface. Within the background mesh, the immersed geometry is described implicitly using a discontinuous distance function based on a level-set approach. This distance function allows to consider both, “double-sided” geometries like membrane or shell structures, and “single-sided” objects for which an enclosed volume is univocally defined. For the second case, the discontinuous distance function is complemented by a continuous signed distance function, whereas ray casting is applied to identify the closed volume regions. Furthermore, adaptive mesh refinement is employed to provide the necessary resolution of the background mesh. The proposed algorithm can handle arbitrarily complicated geometries, possibly containing modeling errors (i.e., gaps, overlaps or a non-unique orientation of surface normals). Another important advantage of the algorithm is the embarrassingly parallel nature of its operations. This characteristic allows for a straightforward parallelization using MPI. All developments were implemented within the open source framework “KratosMultiphysics” and are available under the BSD license. The capabilities of the implementation are demonstrated with various application examples involving practice-oriented geometries. The results finally show, that the algorithm is able to describe most complicated geometries within a background mesh, whereas the approximation quality may be directly controlled by mesh refinement.

Three embedded techniques for finite element heat flow problem with embedded discontinuities

María Jesús Samper — Thu, 16 Apr 2020 13:09:24 +0200

The present paper explores the solution of a heat conduction problem considering discontinuities embedded within the mesh and aligned at arbitrary angles with respect to the mesh edges. Three alternative approaches are proposed as solutions to the problem. The difference between these approaches compared to alternatives, such as the eXtended Finite Element Method (X-FEM), is that the current proposal attempts to preserve the global matrix graph in order to improve performance. The first two alternatives comprise an enrichment of the Finite Element (FE) space obtained through the addition of some new local degrees of freedom to allow capturing discontinuities within the element. The new degrees of freedom are statically condensed prior to assembly, so that the graph of the final system is not changed. The third approach is based on the use of modified FE-shape functions that substitute the standard ones on the cut elements. The imposition of both Neumann and Dirichlet boundary conditions is considered at the embedded interface. The results of all the proposed methods are then compared with a reference solution obtained using the standard FE on a mesh containing the actual discontinuity.

Open tools for electromagnetic simulation programs

María Jesús Samper — Thu, 16 Apr 2020 11:43:57 +0200

Purpose

The aim of the paper is to propose three computer tools to create electromagnetic simulation programs: GiD, Kratos and EMANT.

Design/methodology/approach

The paper presents a review of numerical methods for solving electromagnetic problems and presentation of the main features of GiD, Kratos and EMANT.

Findings

The paper provides information about three computer tools to create electromagnetic simulation packages: GiD (geometrical modeling, data input, visualisation of results), Kratos (C++ library) and EMANT (finite element software for solving Maxwell equations).

Research limitations/implications

The proposed platforms are in development and future work should be done to validate the codes for expecific problems and to provide extensive manual and tutorial information.

Practical implications

The tools could be easily learnt by different user profiles: from end‐users interested in simulation programs to developers of simulation packages.

Originality/value

This paper offers an integrated vision of open and easily customisable tools for the demands of different users profiles.

Disaster risk reduction: a decision-making support tool based on the morphological analysis

María Jesús Samper — Thu, 16 Apr 2020 10:16:33 +0200

Risk management due to natural hazards is a multidimensional and complex problem since it requires the knowledge and experience of several disciplines. The effectiveness of risk management can be analyzed, inviting to the action through weakness identification of the urban area. This article proposes a methodology based on the morphological analysis to support the decision-making on disaster risk management, taking as a starting point the results of a holistic evaluation of the seismic risk. The results of the holistic evaluation of risk are achieved aggravating the physical risk using the contextual conditions, such as the socio-economic fragility and the lack of resilience. In consequence, the risk mitigation can be performed through the reduction of the potential damage and consequences involved; and the improvement of social conditions. The proposed methodology allows prioritizing the risk reduction strategies according to i) performance level of component indicators involved into the Disaster Risk Management index, DRMi; ii) physical risk factors dependent from the potential damages, and iii) aggravating factors involved in the aggravating coefficient. Moreover, it involves 35 strategies to reduce the physical risk and the aggravating social conditions of the urban area. The proposed methodology has been applied to the city of Mérida (Venezuela), located within an area of high seismic activity. The performance level of the indicators involved in the DRMi was evaluated by a survey to local experts. As a result, eleven strategies have been identified to reduce the potential damage and to improve the social conditions of this city

Methodologies and tools of risk management: Hurricane Risk index (HRi)

María Jesús Samper — Thu, 16 Apr 2020 09:49:17 +0200

Mexico is recognized worldwide for the extension of its coastlines and its tourist exploitation. Quintana Roo is one of the Mexican states, which has a shoreline of approximately 800 km, known as the Mexican Caribbean. The hurricanes that form in the Atlantic Ocean are the main natural hazard to which this region is exposed. In this article, hurricane risk is evaluated for coastal cities through the definition of a system of indicators. Based on this indicators system, the Hurricane Risk Index (HRi) is calculated. This system allows the construction of vulnerability indices for different dimensions: physical, environmental, social, economic, cultural and institutional. The obtained results can contribute to the definition of public prevention policies and actions to reduce the levels of vulnerability and increase the resilience of these communities. This indicators model is applied to two coastal cities of the Mexican Caribbean; Mahahual, obtaining an HRi of 82.13%, and Chetumal obtaining an HRi of 69.31%, corresponding to the impact of Hurricane Dean in 2007. The proposed indicators system can be replicated for different hazards

Latin American and Caribbean earthquakes in the GEM’s Earthquake Consequences Database (GEMECD)

María Jesús Samper — Wed, 15 Apr 2020 17:51:13 +0200

Among the activities developed under the framework of the Global Earthquake Model, the development of a global consequences database was included. This was defined with the objective of serving as public repository of damages and losses, occurred on different types of elements because of a selected list of earthquakes with epicentres at varying locations around the globe, but also to be used as a benchmark for the development of vulnerability models that capture specific characteristics of the building typologies in each country. The online earthquakes consequences’ database has information on 71 events where 16 of them occurred in the Latin America and the Caribbean Region. A complete and comprehensive review and data gathering process were developed for these selected earthquakes accounting for different aspects and dimensions that were considered of interest, besides the physical damage, such as casualties, socio-economic implications, damages and disruptions in critical facilities and infrastructures, together with the occurrence of secondary events triggered by the ground shaking such as landslides and tsunamis. When possible, the damage and casualties were geo-located using a standardized approach and included in the database. The contributions of the Latin America and Caribbean Region to the database were at the same time a challenge and an opportunity to collect, review, put together and standardize, up to a certain point, damage data of previous earthquakes additionally of being a step forward in the field of open data.

Evaluation of social context integrated into the study of seismic risk for urban areas

María Jesús Samper — Wed, 15 Apr 2020 17:05:56 +0200

Usually the seismic risk evaluation involves only the estimation of the expected physical damage, casualties or economic losses. This article corresponds to a holistic approach for seismic risk assessment which involves the evaluation of the social fragility and the lack of resilience. The complementary evaluation of social context aspects such as the distribution of the population, the absence of economic and social development, deficiencies in institutional management, and lack of capacity for response and recovery; is useful in order to have seismic risk evaluation suitable to support a decision making processes for risk reduction. The proposed methodology allows a standardized assessment of the social fragility and lack of resilience, by means of an aggravating coefficient of which summarizes the characteristics of the social context using fuzzy sets and Analytic Hierarchy Process (AHP). The selection of 20 social indicators is based on the indicators used by urban observatories of United Nations and other social researchers. These indicators are classified according to social item they describe, in six categories. Applying the determination level analysis, thirteen prevailing social indicators are selected. The proposed methodology has been applied in the cities of Merida (Venezuela) and Barcelona (Spain)

Probabilistic assessment of seismic risk of Barcelona, Spain, using the CAPRA platform

María Jesús Samper — Wed, 15 Apr 2020 16:21:49 +0200

The Comprehensive Approach for Probabilistic Risk Assessment (CAPRA), is a robust methodology for modeling risk which allows identifying the most important aspects of catastrophes. CAPRA performs the evaluation of losses of the exposed elements using probabilistic metrics, such as the loss exceedance curve, the expected annual loss and the probable maximum loss, which are useful for multi-hazard risk analysis. The outcomes obtained with such a technical-scientific methodology are oriented to facilitate decision-making. They allow designing risk transfer instruments, evaluating the cost–benefit ratio, developing risk mitigation strategies and loss scenarios for emergency response, etc. The CAPRA platform is described in this paper by using as a testbed the city of Barcelona, Spain. Nevertheless, the results included for this urban area have not only a high scientific interest but also a practical one, because they are useful in taking risk reduction decision by the Municipality

Comportamiento sismico de los edificios de Lorca

María Jesús Samper — Wed, 15 Apr 2020 15:51:21 +0200

Después de ocurrido el terremoto de Lorca, el 11 de mayo de 2011, el Institut Geològic de Catalunya (IGC), la Universidad Politécnica de Cataluña (UPC) y la Asociación Española de Ingeniería Sísmica (AEIS) organizaron, junto con las asociaciones de ingeniería sísmica francesa (AFPS) y portuguesa (SPES), una visita técnica con el objeto de realizar observaciones que permitieran calibrar, verificar y validar los métodos utilizados en las evaluaciones de riesgo sísmico en zonas urbanas. Este artículo resume los aspectos más destacados en cuanto a la observación de la vulnerabilidad de edificios de vivienda, así como de edificios de especial importancia como son hospitales y escuelas. After the earthquake of Lorca, May 11, 2011, the Geological Institute of Catalonia (IGC), the Technical University of Catalonia (UPC) and the Spanish Association for Earthquake Engineering (AEIS) organized a technical visit in order to compile information that allow to calibrate, to verify and to validate the methods used in seismic risk assessments in urban areas. This article summarizes the highlights regarding the vulnerability of residential buildings and buildings of special importance such as hospitals and schools

A fractional step method for computational aeroacoustics using weak imposition of Dirichlet boundary conditions

María Jesús Samper — Wed, 15 Apr 2020 13:38:59 +0200

In this work we consider the approximation of the isentropic Navier–Stokes equations. The model we present is capable of taking into account acoustic and flow scales at once. After space and time discretizations have been chosen, it is very convenient from the computational point of view to design fractional step schemes in time so as to permit a segregated calculation of the problem unknowns. While these segregation schemes are well established for incompressible flows, much less is known in the case of isentropic flows. We discuss this issue in this article and, furthermore, we study the way to weakly impose Dirichlet boundary conditions via Nitsche’s method. In order to avoid spurious reflections of the acoustic waves, Nitsche’s method is combined with a non-reflecting boundary condition. Employing a purely algebraic approach to discuss the problem, some of the boundary contributions are treated explicitly and we explain how these are included in the different steps of the final algorithm. Numerical evidence shows that this explicit treatment does not have a significant impact on the convergence rate of the resulting time integration scheme. The equations of the formulation are solved using a subgrid scale technique based on a term-by-term stabilization.

Pseudoplastic fluid flows for different Prandtl numbers: steady and time-dependent solutions

María Jesús Samper — Wed, 15 Apr 2020 13:34:07 +0200

In this work, a variational multiscale (VMS) finite element formulation is used to approximate numerically the natural convection in square cavity with differentially heated from sidewalls problem for Newtonian and power-law fluids. The problem is characterized for going through a Hopf bifurcation when reaching high enough Rayleigh numbers, which initiates the transition between steady and time dependent behavior, however, results found in the literature are only for air Prandtl number. The presented VMS formulation is validated using existing results, and is used to study highly convective cases, to determine the flow conditions at which it becomes time dependent, and to establish new benchmark solutions for non-Newtonian fluid flows for different Pr and power-law indexes n. The range of solutions were found in the range 0.6

An oil sloshing study: adaptive fixed-mesh ALE analysis and comparison with experiments

María Jesús Samper — Wed, 15 Apr 2020 13:21:00 +0200

We report in this work a numerical analysis of the sloshing of a squared tank partially filled with a domestic vegetable oil. The tank is subject to controlled motions with a shake table. The free-surface evolution is captured using ultrasonic sensors and an image capturing method. Only confirmed data within the error range is reported. Filling depth, imposed amplitude and frequency effects on the sloshing wave pattern are specifically evaluated. The experiments also reveal the nonlinear wave behavior. The numerical model is based on a stabilized finite element method of the variational multi-scale type. The free-surface is captured using a level set technique developed to be used with adaptive meshes in Arbitrary Lagrangian–Eulerian framework. The numerical results are compared with the experiments for different sloshing conditions near the first sloshing mode. The simulations satisfactorily match the experiments, providing a reliable tool for the analysis of this kind of problems.

A dynamic spring element model for the prediction of longitudinal failure of polymer composites

María Jesús Samper — Wed, 15 Apr 2020 13:07:15 +0200

A spring element model that takes into account the dynamic effects associated with fibre failure in composite materials is presented. The model is implemented in a parallel environment to allow a better performance in the prediction of the complex mechanisms associated with longitudinal tensile failure. The model is used to identify the changes in the stress fields around a broken fibre representing fibre failure as a dynamic phenomenon. In light of these changes in the stress fields, the cluster formation and failure development is analysed and the results are compared with the static spring element model. It is observed that the stress redistribution around a broken fibre is strongly dependent on the dynamic effects and it varies with the material in study, specially if the matrix is considered linear elastic. The changes in local stress redistribution are seen to affect the materials tensile behaviour and cluster formation, being this changes higher for a material with an elastic matrix

Large-scale stochastic topology optimization using adaptive mesh refinement and coarsening through a two-level parallelization scheme

María Jesús Samper — Wed, 15 Apr 2020 11:48:38 +0200

Topology optimization under uncertainty of large-scale continuum structures is a computational challenge due to the combination of large finite element models and uncertainty propagation methods. The former aims to address the ever-increasing complexity of more and more realistic models, whereas the latter is required to estimate the statistical metrics of the formulation. In this work, the computational burden of the problem is addressed using a sparse grid stochastic collocation method, to calculate the statistical metrics of the topology optimization under uncertainty formulation, and a parallel adaptive mesh refinement method, to efficiently solve each of the stochastic collocation nodes. A two-level parallel processing scheme (TOUU-PS2) is proposed to profit from parallel computation on distributed memory systems: the stochastic nodes are distributed through the distributed memory system, and the efficient computation of each stochastic node is performed partitioning the problem using a domain decomposition strategy and solving each subdomain using an adaptive mesh refinement method. A dynamic load-balancing strategy is used to balance the workload between subdomains, and thus increasing the parallel performance by reducing processor idle time. The topology optimization problem is addressed using the topological derivative concept in combination with a level-set method. The performance and scalability of the proposed methodology are evaluated using several numerical benchmarks and real-world applications, showing good performance and scalability up to thousands of processors

Refficientlib: an efficient load-rebalanced adaptive mesh refinement algorithm for high-performance computational physics meshes

María Jesús Samper — Tue, 14 Apr 2020 14:33:20 +0200

In this paper we present a novel algorithm for adaptive mesh refinement in computational physics meshes in a distributed memory parallel setting. The proposed method is developed for nodally based parallel domain partitions where the nodes of the mesh belong to a single processor, whereas the elements can belong to multiple processors. Some of the main features of the algorithm presented in this paper are its capability of handling multiple types of elements in two and three dimensions (triangular, quadrilateral, tetrahedral, and hexahedral), the small amount of memory required per processor, and the parallel scalability up to thousands of processors. The presented algorithm is also capable of dealing with nonbalanced hierarchical refinement, where multirefinement level jumps are possible between neighbor elements. An algorithm for dealing with load rebalancing is also presented, which allows us to move the hierarchical data structure between processors so that load unbalancing is kept below an acceptable level at all times during the simulation. A particular feature of the proposed algorithm is that arbitrary renumbering algorithms can be used in the load rebalancing step, including both graph partitioning and space-filling renumbering algorithms. The presented algorithm is packed in the Fortran 2003 object oriented library \textttRefficientLib, whose interface calls which allow it to be used from any computational physics code are summarized. Finally, numerical experiments illustrating the performance and scalability of the algorithm are presented. No separate or additional fees are collected for access to or distribution of the work

Parameter-free, weak imposition of Dirichlet boundary conditions and coupling of trimmed and non-conforming patches

María Jesús Samper — Tue, 14 Apr 2020 13:39:04 +0200

We present a parameter-free domain sewing approach for low-order as well as high-order finite elements. Its final form contains only primal unknowns; that is, the approach does not introduce additional unknowns at the interface. Additionally, it does not involve problem-dependent parameters, which require an estimation. The presented approach is symmetry preserving; that is, the resulting discrete form of an elliptic equation will remain symmetric and positive definite. It preserves the order of the underlying discretization, and we demonstrate high-order accuracy for problems of non-matching discretizations concerning the mesh size h as well as the polynomial degree of the order of discretization p. We also demonstrate how the method may be used to model material interfaces, which may be curved and for which the interface does not coincide with the underlying mesh. This novel approach is presented in the context of the p-version and B-spline version of the finite cell method, an embedded domain method of high order, and compared with more classical methods such as the penalty method or Nitsche's method.

A scalable parallel finite element framework for growing geometries: application to metal additive manufacturing

María Jesús Samper — Tue, 14 Apr 2020 11:30:43 +0200

This work introduces an innovative parallel, fully-distributed finite element framework for growing geometries and its application to metal additive manufacturing. It is well-known that virtual part design and qualification in additive manufacturing requires highly-accurate multiscale and multiphysics analyses. Only high performance computing tools are able to handle such complexity in time frames compatible with time-to-market. However, efficiency, without loss of accuracy, has rarely held the centre stage in the numerical community. Here, in contrast, the framework is designed to adequately exploit the resources of high-end distributed-memory machines. It is grounded on three building blocks: (1) Hierarchical adaptive mesh refinement with octree-based meshes; (2) a parallel strategy to model the growth of the geometry; (3) state-of-the-art parallel iterative linear solvers. Computational experiments consider the heat transfer analysis at the part scale of the printing process by powder-bed technologies. After verification against a 3D benchmark, a strong-scaling analysis assesses performance and identifies major sources of parallel overhead. A third numerical example examines the efficiency and robustness of (2) in a curved 3D shape. Unprecedented parallelism and scalability were achieved in this work. Hence, this framework contributes to take on higher complexity and/or accuracy, not only of part-scale simulations of metal or polymer additive manufacturing, but also in welding, sedimentation, atherosclerosis, or any other physical problem where the physical domain of interest grows in time.

Scalable solvers for complex electromagnetics problems

María Jesús Samper — Tue, 14 Apr 2020 11:25:32 +0200

In this work, we present scalable balancing domain decomposition by constraints methods for linear systems arising from arbitrary order edge finite element discretizations of multi-material and heterogeneous 3D problems. In order to enforce the continuity across subdomains of the method, we use a partition of the interface objects (edges and faces) into sub-objects determined by the variation of the physical coefficients of the problem. For multi-material problems, a constant coefficient condition is enough to define this sub-partition of the objects. For arbitrarily heterogeneous problems, a relaxed version of the method is defined, where we only require that the maximal contrast of the physical coefficient in each object is smaller than a predefined threshold. Besides, the addition of perturbation terms to the preconditioner is empirically shown to be effective in order to deal with the case where the two coefficients of the model problem jump simultaneously across the interface. The new method, in contrast to existing approaches for problems in curl-conforming spaces does not require spectral information whilst providing robustness with regard to coefficient jumps and heterogeneous materials. A detailed set of numerical experiments, which includes the application of the preconditioner to 3D realistic cases, shows excellent weak scalability properties of the implementation of the proposed algorithms.

Maximum-principle preserving space–time isogeometric analysis

María Jesús Samper — Tue, 14 Apr 2020 11:09:03 +0200

In this work we propose a nonlinear stabilization technique for convection–diffusion–reaction and pure transport problems discretized with space–time isogeometric analysis. The stabilization is based on a graph-theoretic artificial diffusion operator and a novel shock detector for isogeometric analysis. Stabilization in time and space directions are performed similarly, which allow us to use high-order discretizations in time without any CFL-like condition. The method is proven to yield solutions that satisfy the discrete maximum principle (DMP) unconditionally for arbitrary order. In addition, the stabilization is linearity preserving in a space–time sense. Moreover, the scheme is proven to be Lipschitz continuous ensuring that the nonlinear problem is well-posed. Solving large problems using a space–time discretization can become highly costly. Therefore, we also propose a partitioned space–time scheme that allows us to select the length of every time slab, and solve sequentially for every subdomain. As a result, the computational cost is reduced while the stability and convergence properties of the scheme remain unaltered. In addition, we propose a twice differentiable version of the stabilization scheme, which enjoys the same stability properties while the nonlinear convergence is significantly improved. Finally, the proposed schemes are assessed with numerical experiments. In particular, we considered steady and transient pure convection and convection–diffusion problems in one and two dimensions.

On a general implementation of h- and p-adaptive curl-conforming finite elements

María Jesús Samper — Tue, 14 Apr 2020 10:57:56 +0200

Edge (or Nédélec) finite elements are theoretically sound and widely used by the computational electromagnetics community. However, its implementation, especially for high order methods, is not trivial, since it involves many technicalities that are not properly described in the literature. To fill this gap, we provide a comprehensive description of a general implementation of edge elements of first kind within the scientific software project FEMPAR . We cover into detail how to implement arbitrary order (i.e., p-adaptive) elements on hexahedral and tetrahedral meshes. First, we set the three classical ingredients of the finite element definition by Ciarlet, both in the reference and the physical space: cell topologies, polynomial spaces and moments. With these ingredients, shape functions are automatically implemented by defining a judiciously chosen polynomial pre-basis that spans the local finite element space combined with a change of basis to automatically obtain a canonical basis with respect to the moments at hand. Next, we discuss global finite element spaces putting emphasis on the construction of global shape functions through oriented meshes, appropriate geometrical mappings, and equivalence classes of moments, in order to preserve the inter-element continuity of tangential components of the magnetic field. Finally, we extend the proposed methodology to generate global curl-conforming spaces on non-conforming hierarchically refined (i.e., h-adaptive) meshes with arbitrary order finite elements. Numerical results include experimental convergence rates to test the proposed implementation.

Physics-based balancing domain decomposition by constraints for multi-material problems

María Jesús Samper — Tue, 14 Apr 2020 10:16:59 +0200

In this work, we present a new variant of the balancing domain decomposition by constraints preconditioner that is robust for multi-material problems. We start with a well-balanced subdomain partition, and based on an aggregation of elements according to their physical coefficients, we end up with a finer physics-based (PB) subdomain partition. Next, we define corners, edges, and faces for this PB partition, and select some of them to enforce subdomain continuity (primal faces/edges/corners). When the physical coefficient in each PB subdomain is constant and the set of selected primal faces/edges/corners satisfy a mild condition on the existence of acceptable paths, we can show both theoretically and numerically that the condition number does not depend on the contrast of the coefficient across subdomains. An extensive set of numerical experiments for 2D and 3D for the Poisson and linear elasticity problems is provided to support our findings. In particular, we show robustness and weak scalability of the new preconditioner variant up to 8232 cores when applied to 3D multi-material problems with the contrast of the physical coefficient up to 108 and more than half a billion degrees of freedom. For the scalability analysis, we have exploited a highly scalable advanced inter-level overlapped implementation of the preconditioner that deals very efficiently with the coarse problem computation. The proposed preconditioner is compared against a state-of-the-art implementation of an adaptive BDDC method in PETSc for thermal and mechanical multi-material problems.

Simulation of high temperature superconductors and experimental validation

María Jesús Samper — Tue, 14 Apr 2020 10:09:06 +0200

In this work, we present a parallel, fully-distributed finite element numerical framework to simulate the low-frequency electromagnetic behaviour of superconducting devices, which efficiently exploits high performance computing platforms. We select the so-called H-formulation, which uses the magnetic field as a state variable. Nédélec elements (of arbitrary order) are required for an accurate approximation of the H-formulation for modelling electromagnetic fields along interfaces between regions with high contrast medium properties. An h-adaptive mesh refinement technique customized for Nédélec elements leads to a structured fine mesh in areas of interest whereas a smart coarsening is obtained in other regions. The composition of a tailored, robust, parallel nonlinear solver completes the exposition of the developed tools to tackle the problem. First, a comparison against experimental data is performed to show the availability of the finite element approximation to model the physical phenomena. Then, a selected state-of-the-art 3D benchmark is reproduced, focusing on the parallel performance of the algorithms.

Mixed aggregated finite element methods for the unfitted discretization of the Stokes problem

María Jesús Samper — Tue, 14 Apr 2020 09:40:11 +0200

In this work, we consider unfitted finite element methods for the numerical approximation of the Stokes problem. It is well-known that these kinds of methods lead to arbitrarily ill-conditioned systems and poorly approximated fluxes on unfitted interfaces/boundaries. In order to solve these issues, we consider the recently proposed aggregated finite element method, originally motivated for coercive problems. However, the well-posedness of the Stokes problem is far more subtle and relies on a discrete inf-sup condition. We consider mixed finite element methods that satisfy the discrete version of the inf-sup condition for body-fitted meshes and analyze how the discrete inf-sup is affected when considering the unfitted case. We propose different aggregated mixed finite element spaces combined with simple stabilization terms, which can include pressure jumps and/or cell residuals, to fix the potential deficiencies of the aggregated inf-sup. We carry out a complete numerical analysis, which includes stability, optimal a priori error estimates, and condition number bounds that are not affected by the small cut cell problem. For the sake of conciseness, we have restricted the analysis to hexahedral meshes and discontinuous pressure spaces. A thorough numerical experimentation bears out the numerical analysis. The aggregated mixed finite element method is ultimately applied to two problems with nontrivial geometries. No separate or additional fees are collected for access to or distribution of the work.

PHARMACOLOGICAL LEARNING PROCESS IN MEDICAL STUDENTS: EDUCATIONAL PERSPECTIVES AND DILEMMAS

Juan Manuel Pérez-Agudelo — Sun, 12 Apr 2020 16:18:29 +0200

Pharmacology is taught in medical schools in the years of basic science and in the transition to the clinical field, this science is in charge of studying the interactions between drugs and living matter; at the time of medical practice it teaches how a chemical substance (active principle) has benefits and helps to improve certain pathologies, as well as which substances should not be used. The teaching of this subject is a process of great importance in the introduction of students to clinical practice and their subsequent professional development. Although the importance of this subject in the medical field is taken into account, the learning gaps and the lack of theoretical-practical correlation on the part of students become evident, since when it comes to focusing knowledge on problem solving, very few students have an adequate picture of what is the most appropriate management in a specific scenario. It has been observed for several years that the educational process of pharmacology and therapeutics is not enough, and this is evidenced by the fact that the conceptual gaps of medical students and medical graduates are found. This global review of the education-learning process focuses on the most used pedagogical elements and which are most appropriate to impact on learning, solid understanding and depth of both pharmacological terminology and concepts and their applicability to achieve academic and professional competence.

Diseño de túneles usando Elementos Finitos 2D y 3D y la influencia de los parámetros mecánicos y geométricos para el diseño

Luisa Equihua-Anguiano — Wed, 08 Apr 2020 19:32:03 +0200

In practice, tunnels design uses analytical methods and numerical models. The last methods are because tunnels need solutions that provide a high level of security given their complexity and civil use. In this paper the study of the influence of the geometric and the mechanical soil properties on the tunnel displacements is presented, when it is used the finite element method (FEM) in two (2D) and three (3D) dimensions. Validation of results was through of the displacements comparison with an elastic analytical method. The constitutive model used was the Mohr-Coulomb and the soil parameters are of a soil in Mexico. Results shows a convergence towards a similar behavior for the elastic case and a difference when a perfect elasto-plastic behavior is considered in design. As fundamental conclusions, it is observed that it is possible to speed up the time using the 2D-FEM method, as well as the feasibility of quickly reviewing a 3D tunnel using a 2D program. '''Key words: '''Finite elements; two-dimensions; three-dimensions; tunnels.

Robust and scalable domain decomposition solvers for unfitted finite element methods

María Jesús Samper — Tue, 07 Apr 2020 17:46:36 +0200

Unfitted finite element methods, e.g., extended finite element techniques or the so-called finite cell method, have a great potential for large scale simulations, since they avoid the generation of body-fitted meshes and the use of graph partitioning techniques, two main bottlenecks for problems with non-trivial geometries. However, the linear systems that arise from these discretizations can be much more ill-conditioned, due to the so-called small cut cell problem. The state-of-the-art approach is to rely on sparse direct methods, which have quadratic complexity and are thus not well suited for large scale simulations. In order to solve this situation, in this work we investigate the use of domain decomposition preconditioners (balancing domain decomposition by constraints) for unfitted methods. We observe that a straightforward application of these preconditioners to the unfitted case has a very poor behavior. As a result, we propose a customization of the classical BDDC methods based on the stiffness weighting operator and an improved definition of the coarse degrees of freedom in the definition of the preconditioner. These changes lead to a robust and algorithmically scalable solver able to deal with unfitted grids. A complete set of complex 3D numerical experiments shows the good performance of the proposed preconditioners.

Nonlinear parallel-in-time Schur complement solvers for ordinary differential equations

María Jesús Samper — Tue, 07 Apr 2020 17:40:59 +0200

In this work, we propose a parallel-in-time solver for linear and nonlinear ordinary differential equations. The approach is based on an efficient multilevel solver of the Schur complement related to a multilevel time partition. For linear problems, the scheme leads to a fast direct method. Next, two different strategies for solving nonlinear ODEs are proposed. First, we consider a Newton method over the global nonlinear ODE, using the multilevel Schur complement solver at every nonlinear iteration. Second, we state the global nonlinear problem in terms of the nonlinear Schur complement (at an arbitrary level), and perform nonlinear iterations over it. Numerical experiments show that the proposed schemes are weakly scalable, i.e., we can efficiently exploit increasing computational resources to solve for more time steps the same problem.

The aggregated unfitted finite element method for elliptic problems

María Jesús Samper — Tue, 07 Apr 2020 17:22:09 +0200

Unfitted finite element techniques are valuable tools in different applications where the generation of body-fitted meshes is difficult. However, these techniques are prone to severe ill conditioning problems that obstruct the efficient use of iterative Krylov methods and, in consequence, hindersthe practical usage of unfitted methods for realistic large scale applications. In this work, we present a technique that addresses such conditioning problems by constructing enhanced finite element spaces based on a cell aggregation technique. The presented method, called aggregated unfitted finite element method, is easy to implement, and can be used, in contrast to previous works, in Galerkin approximations of coercive problems with conforming Lagrangian finite element spaces. The mathematical analysis of the method states that the condition number of the resulting linear system matrix scales as in standard finite elements for body-fitted meshes, without being affected by small cut cells, and that the method leads to the optimal finite element convergence order. These theoretical results are confirmed with 2D and 3D numerical experiments.

Differentiable monotonicity-preserving schemes for discontinuous Galerkin methods on arbitrary meshes

María Jesús Samper — Tue, 07 Apr 2020 17:11:22 +0200

This work is devoted to the design of interior penalty discontinuous Galerkin (dG) schemes that preserve maximum principles at the discrete level for the steady transport and convection–diffusion problems and the respective transient problems with implicit time integration. Monotonic schemes that combine explicit time stepping with dG space discretization are very common, but the design of such schemes for implicit time stepping is rare, and it had only been attained so far for 1D problems. The proposed scheme is based on a piecewise linear dG discretization supplemented with an artificial diffusion that linearly depends on a shock detector that identifies the troublesome areas. In order to define the new shock detector, we have introduced the concept of discrete local extrema. The diffusion operator is a graph-Laplacian, instead of the more common finite element discretization of the Laplacian operator, which is essential to keep monotonicity on general meshes and in multi-dimension. The resulting nonlinear stabilization is non-smooth and nonlinear solvers can fail to converge. As a result, we propose a smoothed (twice differentiable) version of the nonlinear stabilization, which allows us to use Newton with line search nonlinear solvers and dramatically improve nonlinear convergence. A theoretical numerical analysis of the proposed schemes shows that they satisfy the desired monotonicity properties. Further, the resulting operator is Lipschitz continuous and there exists at least one solution of the discrete problem, even in the non-smooth version. We provide a set of numerical results to support our findings.

Convergence to suitable weak solutions for a finite element approximation of the Navier–Stokes equations with numerical subgrid scale modeling

María Jesús Samper — Tue, 07 Apr 2020 17:04:16 +0200

In this work we prove that weak solutions constructed by a variational multiscale method are suitable in the sense of Scheffer. In order to prove this result, we consider a subgrid model that enforces orthogonality between subgrid and finite element components. Further, the subgrid component must be tracked in time. Since this type of schemes introduce pressure stabilization, we have proved the result for equal-order velocity and pressure finite element spaces that do not satisfy a discrete inf-sup condition