Scipedia: Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería

Operational influence of the nature of the damping considered in the adjustment of the structural response model on the results of the scale factors for operational modal analysis

LUIS MANUEL VILLA GARCIA — Thu, 11 Apr 2019 19:52:20 +0200

The consideration of the assumption of viscous damping as a starting hypothesis in the dynamic analysis of structures can introduce a substantial error in the calculations. This is due to the energy dissipated by the structure in its oscillation being frequency dependent under that premise, while experimentally the opposite becomes apparent, when structural or hysteretic damping is taken into account. The modes of vibration obtained in the operational modal analysis are not scaled, since the magnitude of the excitation on the structure is unknown. For this reason it is necessary to resort to additional calculation procedures, such as the mass change method, to determine the scale factors of each mode. However, all variants of this method, in the current state of the art, have been deduced in the undamped situation. In this paper we analyze the influence of the deviation of the results for the scale factors, obtained by means of a viscous damping analysis, compared to that same deviation determined under the consideration of hysteretic or structural damping, independent of the frequency, whose results align much better with the experimental behavior of the structure.

A modified Taylor Galerkin scheme for turbulent compressible flow simulation.

Horacio Pedro Burbridge — Sun, 26 May 2019 17:16:39 +0200

As already demonstrated by different authors, the Taylor-Galerkin (TG) scheme, in the context of the Finite Element Method (FEM), is particularly suitable for the solution of supersonic flows. The TG scheme, using hexahedral finite elements with analytical evaluation of element matrices, is applied in this work. Tools to avoid locking and a shock capturing technique for the solution of supersonic viscous and non-viscous compressible flows are also employed. However, TG scheme usually presents instabilities in subsonic flows. Even in cases in which the free stream Mach number corresponds to supersonic flows, there are always flow regions, specifically near the walls of the immersed obstacles, where the speed is lower and the local Mach number corresponds to a subsonic flow. The Characteristic Based Split (CBS) scheme was developed in order to obtain a single method to improve the behavior with respect to TG method in subsonic and supersonic regimes. In the last two decades some works have shown advantages in convergence rates of the CBS method when compared to the TG algorithm. However, simulation time increases in the CBS method since split operations, typical of this algorithm, imply in additional element loops. In this paper a hybrid algorithm called Modified-Taylor-Galerkin scheme (MTG) is proposed. This algorithm presents advantages with respect to TG and CBS schemes in terms of convergence properties and computational processing time. In order to get an efficient algorithm, the element matrices are analytically integrated. This is performed with two different approaches. In the first approach the inverse matrix and the determinant of the Jacobian matrix at element level are evaluated with a reduced integration form, using the point located in the center of the element for mass, convective, diffusive and stabilization element matrices; all these matrices are integrated analytically. In the second approach, mass and convective matrices are calculated by a complete integration scheme (including the inverse matrix and the determinant of the Jacobian matrix at element level in the analytical expression to be integrated) and the diffusive and stabilization matrices are calculated with a reduced integration form, using the point located at the center of the element to calculate the inverse matrix and the determinant of the Jacobian matrix at element level. Finally, this work incorporates the Spalart-Allmaras (S-A) turbulence model using a conservative version of the transport equation, as proposed by the authors of the original S-A model in a later paper. Algorithms are tested to determine convergence rate improvements in both laminar and turbulent cases and for different Mach numbers (supersonic, transonic and subsonic flows).

Integration methodology of different softwares for constrained tubular truss size optimization problems

Carmem Miranda Lage — Thu, 10 Jan 2019 20:35:07 +0100

Practical size structural optimization problems can involve a large number of variables and constraints that meet regulatory requirements for safety and structural performance. Most optimization problems tend to find the minimum value of the objective function within a feasible set that satisfies the constraints. Among evolutionary computation techniques, genetic algorithms (GAs) have been successfully used for the optimization of structures, including lattice systems. This article proposes an automated interactive methodology for the optimization of structures based on the integration of two commercial programs: Ansys and Matlab. The developed script uses the Finite Element Method for the analysis of the structure, together with the Genetic Algorithms for the optimization. The objective of the article is to evaluate the applicability, precision and efficiency of the proposed methodology. Two numerical examples of trusses were solved with the proposed methodology, classic truss of the literature and truss with normative restrictions. The results show that the methodology is adequate for the solution of size structural optimization problems with a good precision of the results.

Optimum design of composite twin-girder road bridges

José Manuel Baraibar — Sun, 25 Mar 2018 23:29:30 +0200

Composite structures have not been able to compete in Spain with more conventional prestressed concrete bridges in the lower range of medium spans (30 - 90 m.). In this context, twin-girder sections are revealed as a more competent typology because of its sobriety, ease of construction and good structural performance.

At present the optimal character of the designs in structural projects is rarely challenged. The present study undertakes an in-depth analysis of the twin-girder section, involving a complete optimisation for the deck. To this end a specific 2D grillage model has been developed, integrating the composite and evolutive character of twin-girder decks, as well as the instability phenomena inherent to thin-walled structures.

Several conclusions are drawn after a parametric calculation using this model, regarding the optimum dimensions of all the variables that define the twin-girder section. These conclusions crystallise in a series of formulas that can be used as a design guide.

Optimization of the heating system by electrical resistances in a rapid thermal response mold based on MSR-PSO-FEM

Francisco Javier Cervantes Vallejo — Wed, 05 Jun 2019 23:42:04 +0200

The aim of this work to optimization of the heating system by electrical resistances for a rapid thermal response mold (MRTR), using the response surface methodology (MSR). Applying the design technique of the Box-Behnken experiments, a matrix of experiments with four factors and three levels was designed. The design variables that are used to describe the design and shape of the heating system are the heat flux per unit area of the electrical resistance, the distances from the center of the heaters to the surface of the cavity, the distance between the adjacent electrical resistors and the thickness of the heating plate. The heating time, the variation of the temperature in the cavity and the Von-Mises stress were considered as the variables of the model. Thermal and thermal-structural resistance analyzes of the model based on finite element method (FEM) are performed to acquire the objective variables. Mathematical response surface models are developed using the mixed regression model and the response surface model and the variance analysis method (ANOVA) is used to verify the accuracy of these mathematical models. With the obtained models, the position of the electric resistances is optimized and the ratio between mass and volume of the cavity insert is reduced to minimize the heating time within a reasonable temperature distribution and structural strength, coupling the surface models of response developed with the method of particle swarm optimization (PSO). The results obtained indicate that the required heating time on the surface of the cavity can be significantly reduced in the molding cycle, demonstrating with these the effectiveness of the heating system.

Variability in uncertainty cost for micro-Wind Energy Generation (WEG)

Sergio Rivera — Sat, 19 Jan 2019 05:56:02 +0100

Faced with the problem of wind speed in generation and the difficulty that this entails in the economic future of electric power, mathematical formulations (functions), called uncertainty costs, have been developed. The term is used in a model composed of two parts, an implication of penalization costs for overestimation and the other due to the underestimation of a programmed power. Through analytical mathematics and Monte Carlo simulations, we have found the expected value of the costs of uncertainty, the stability of primary resources through the distribution of probability. However, the results can not be evaluated accurately from an analytical point of view, without taking into account the variability around the average value. In this article we calculate the analytical function of the variance, we understand as a measure of dispersion of the expected values of uncertainty costs for the specific case of wind operators; Likewise, this formulation has been validated through Monte Carlo simulations. The function found is used to observe the dispersion of the data around its expected average value, by applying the standard deviation.

Numerical study of mixed-phase ice crystal icing based on Eulerian method

Yan TAN — Sat, 03 Aug 2019 10:10:08 +0200

Ice crystals mainly cause compressor blades icing, and it is difficult to reveal the icing mechanism by experimental methods. Therefore, an Eulerian method was used to study ice crystal icing on a wedge airfoil in this paper. The calculation process was divided into three parts. First, the air flow field was calculated by Spalart-Allmaras turbulence model. Then the Eulerian method was used to obtain the trajectory of ice crystal and droplet. At last, the Messinger model was used to calculate the ice shape. The feasibility of the numerical method was verified by the NRC’s experiments. Then the effect of pressure on icing was analyzed. It could be found that the lower the pressure, the stronger the sublimation (evaporation) of ice crystals (droplets), and the more obvious the icing was. In addition, the ratio of LWC/TWC (Liquid Water Content/ Total Water Content) had a great effect on icing. It also could be found that too little or too much liquid water was not conductive for icing. The conclusions obtained by calculation were basically consistent with the NRC’s. The method in this paper could provide some reference for the subsequent study of engine icing mechanism or the design of anti-icing system.

Chaos control via Mathieu-Van der Pol system and Linear Optimal Control design with a non-ideal excitation and parametric uncertainties

Fábio Roberto Chavarette — Thu, 18 Apr 2019 01:00:03 +0200

In this work, a non-ideal system based on the Mathieu-Van der Pol System is modeled considering its parameters as uncertain, which makes it closer to reality. Numerical simulations are presented demonstrating that the system has a chaotic behavior with three positive Lyapunov exponents. Given such unstable and unpredictable behavior, the linear optimal control design is proposed to reduce the chaotic movement of this system to a fixed point. The simulation results show that the identification by Linear Optimal Control is very effective.

Study of the influence of protuberances in the trailing edge of airfoils and determination of their aerodynamic efficiency through CFD using Ansys Fluent

Jorge Hinojosa — Fri, 18 Jan 2019 20:46:03 +0100

In the present research, the effect of incorporating protuberances in the leading edge to the aerofoil NACA-0012 was studied. For the simulations, two profiles were designed: parametric profile (NACA 0012) and modified profile (0012-MOD), with help of CAD Program Inventor Professional 2016. The 0012-MOD profile incorporates modifications in the leading edge, whose inspiration comes from malformations present on the flippers of the humpback whale (Megaptera novaeangliae). The computational simulations were performed in Ansys Fluent, using the turbulent viscosity model k-ε realizable, with SIMPLE calculation algorithm. The study fluid is air in the incompressible range with Ma: 0.11. To obtain the lift and drag curves for both profiles, they were simulated for angles of attack α: between 0° and 40°, this way it will be possible to compare the profiles and determine their aerodynamic behaviour.

Optimization Study For The Cross-Section Of A Concrete Gravity Dam: Genetic Algorithm Model And Application.

LEILSON JOAQUIM ARAUJO — Sat, 20 Oct 2018 17:51:23 +0200

Concrete gravity dams have trapezoidal shape in their cross section and shall guarantee the global stability against acting loads like hydrostatic and uplift pressures through his gravitational actions (self-weight and others). This study focuses on the shape optimization of concrete gravity dams using genetic algorithms. In this case, the dam cross section area is considered as the objective function and the design variables are the geometric parameters of the gravity dam. The optimum cross-section of a concrete gravity dam is achieved by the Genetic Algorithm (GA) through a Matlab routine developed by the author. Sliding, overturning and floating verifications are implemented in the program. In order to assess the efficiency of the proposed methodology for gravity dams optimization, one application is presented adopting the concrete gravity dam of Belo Monte Hydropower Plant (HPP), considering normal loading condition and others assumptions presented.

Mono-objective minimization of operation cost for a microgrid with renewable power generation, energy storage and electric vehicles

Sergio Rivera — Sun, 21 Oct 2018 01:28:02 +0200

The term Microgrid refers to a power system in a small scale, made of active elements operating between them, namely renewable and traditional generation, energy storage and controllable charges. Previous studies have evaluated and modelled the operation cost of many elements that make up the Microgrid, in order to identify the correct point of operation. In this study, the researchers evaluated a model of Microgrid with diesel as traditional generator, a park of photovoltaic generation, two wind generators, one battery bank and two aggregators that manage electric vehicles. The objective of this research is to propose an equation capable of describing the operation cost of a Microgrid as a set, taking into account the modelling of the operation cost of photovoltaic energy, wind energy, and energy storage in battery banks and electric vehicles. This equation also seeks to obtain the best possible cost efficiency, i.e., decreasing the operation cost of the Microgrid. For this purpose, the Metauristic method DEEPSO (Differential Evolutionary Particle Swarm Optimization) was used, recognized for its performance for applications in power systems. Through this method, and determinate the conditions of operation of the different elements in the Microgrid. Taking into account all the parameters, the behavior of each one of the elements of the Microgrid in a 24-hour lapse was found and visualized.

Interval-based Recording of Generated Pseudorandom Numbers

Slobodan Bojanic — Tue, 20 Feb 2018 15:24:45 +0100

For some applications that use pseudorandom numbers it is essential to keep the record of numbers generated so far. Such a representative example is cryptanalytic TMTO approach. In order to save the space, instead of straightforward recording of individual numbers generated, an ordered tree-like data structure which tracks the intervals of generated numbers is proposed. For estimating the memory requirements of this structure as a function of pseudorandom numbers range size, an analytical probabilistic model is established and used. This model determines the maximum number of intervals during recording which corresponds to the tree size. The result obtained from analytical model is fully validated experimentally by means of simulation for a wide spectrum of range sizes.

Numerical analysis of side hull configuration in Trimaran

Milad Heidari — Tue, 23 Apr 2019 07:42:05 +0200

A trimaran is a multihull vessel designed to reduce wave-making resistances at high speeds. Optimization of the hull shape increases hull efficiency and speed of a vessel. The behavior of a ship is generally analyzed through numerical methods to save time and reduce high expenditures as compared to experimental methods. Although wide ranges of studies have investigated the hydrodynamic behavior of a vessel, the effect of trim angle, yaw angle, and heel angle of side hulls on hydrodynamic behavior of a trimaran has not been addressed properly. In the present study, a trimaran was modeled using computer-aided design software. Dimensions of the computational domain and boundary conditions were applied. Furthermore, mesh convergence was carried out. The accuracy of the method was validated. Analyses are based on the finite volume method. The analysis is carried out to obtain the resistance of side hulls and its effect on total trimaran resistance, effect of speed on hulls vessel resistance, wave patterns generated by the vessel at different trim and yaw angles, effect of trim, heel and yaw angles on side hull and total resistance of trimaran, the wetted surface at different trim, yaw, and heel angles, shape of free surface between the hulls, and the optimal position and trim angle of side hulls relative to the main hull. This computational analysis represents a step in quantifying the role of the trim, heel and yaw angles of side hulls on hydrodynamic characteristics of trimaran in calm water. The worth of information from present study may express the importance of the factors that could reduce the total resistance of a trimaran.

Análisis del comportamiento del contrato de distribución de ingresos en una cadena de abastecimiento frutícola

Diego León Peña Orozco — Tue, 11 Sep 2018 08:58:03 +0200

Supply chains are systems characterized by inter-organizational and inter-functional relationships where the markets dynamics and lack of will towards collaborative relationships, lead to each member attempting to maximize their individual performance, generating inefficient global results. To address this problem, it is necessary to adopt appropriate coordination mechanisms to improve the global performance of the decentralized supply chain [10]. Among the coordination mechanisms are information technologies, information exchange and data, joint decision-making and supply contracts [2]. Among the types of contracts, the shared revenue is highlighted, which in addition to promoting coordination in the chain, is concerned with better distribution of income between its echelons [6] by modifying two values to be defined, the wholesale price and income distribution coefficient. In this paper, a mathematical model that represents the revenue sharing contract that attempt to maximize the performance of the supply chain is developed. Finally, a case study in a fruit supply chain composed by three echelons is formulated and the comparative economic results between the current scenario and the scenario using the revenue sharing contract as a coordination mechanism are shown.

Analysis and design of concrete structures using strut and tie model by FEM: Application in foundation blocks, short consoles, wall beams and rigid shoes

MIGUEL LIMA — Thu, 03 Aug 2017 15:31:55 +0200

The present work has as main objective to perform elastic-linear analyzes through a computational program with numerical approach of the strut-and-tie model using a formulation based on the Finite Element Method (FEM). In this model, it is possible to analyze the behavior of structural elements such as foundation blocks, wall beams, short consoles, also represent the values of tensions, deformations and displacements in the region of a beam represented as the Model of cranks developed by MONTOYA et al. [1], besides numerically modeling via FEM a wall beam with a large aperture, developed by SCHLAICH et al. [2]. In order to validate the numerical implementations, the results were compared with numerical modeling performed with the aid of ANSYS software 17 and with normative expressions.

Comparison of Wind Loads on Flat and Gabled Roofs calculated with the Colombian Building Code and Numerical Results using CFD

Martha Elena Delgado Osorio — Mon, 03 Dec 2018 23:33:03 +0100

The Colombian building code, NSR-10, specifies three methods for estimating wind loads on structures: a) a Simplified Method, b) an Analytical Method and c) Wind Tunnel Testing. The first two of these methods are widely used by structural engineers in Colombia, as wind tunnel testing is comparatively expensive and time consuming, and only mandatory in special cases. Although the Simplified Method is only valid for buildings with regular shaped roofs and overall heights less than 18 m, the Analytical Method can be used for any regular building, regardless of the height. However, when these two methods are used to estimate wind loads for buildings with heights less than 18 m, they often produce very different results and, at times, contradictory values. In this study, Computational Fluids Dynamic (CFD) analyses were performed on flat and gabled roofed building models in order to compare the pressures on the roofs with those calculated using the standard design methods specified by the Colombian building code. The results illustrate the significant differences produced from the Simplified and Analytical methods of the NSR-10 and highlight the need of conducting wind tunnel tests in order to propose a more consistent method for estimating design wind loads in Colombia

Determining the micro film of hexyl alcohol in laminar condition on a rotating drum

Christ Trang — Tue, 18 Dec 2018 04:17:03 +0100

In this research, the free surface of micro film of hexyl alcohol on a partially submerged rotating drum has been predicted using CFD (computational fluid dynamics) and compared with experimental data and analytical solution. The trend of has been found very comparable with experimental and analytical solution. A Matlab code was used to model the flow and film dynamics. Computationally it was an unsteady state problem and semi-steady state was achieved. No surfactant was present on the surface. The speed of the moving rotating drum was set a ''rpm''. With the increase of rotating drum, the minimum film thickness increases with ''rpm'' (for \alpha _o = 47^{0} and for \alpha _o = 58^{0}).

Efficient combined SSIM- and landmark-driven image registration in a variational framework

Jorge Larrey-Ruiz — Thu, 13 Sep 2018 13:28:10 +0200

Image registration methods are used to establish geometrical correspondences between different datasets. Various characteristics of image data can be exploited to drive image registration algorithms. Thus, the currently available schemes can be roughly divided into two classes: intensity-based and feature-based registration schemes. In this paper, we present a mathematical framework, based on the calculus of variations, for combining these two classes in order to benefit from the advantages of both strategies. The goal is to obtain a registration algorithm which achieves a good matching of datasets near landmark locations but also away from them (by matching the corresponding intensities). The proposed approach includes the novel formulation of a disparity term which simultaneously takes into account the structural similarity index (a similarity measure which considers spatial dependencies in the images) and the location of outstanding points. Since the iteration which results of the variational formulation is translated into the frequency domain, the implementation of the proposed algorithm offers a good speed-performance trade-off when compared to other state-of-the-art image registration implementations. Experimental results show the advantages, in the medical setting, of the combined SSIM- and landmark-based approach over well-established registration techniques which use either landmark or intensity information alone. In particular, the registration of triple-phase 3D computed tomographies of the liver under injection of a contrast agent has been chosen for such a comparison. The datasets are acquired at different times depending on the arrival time of the contrast agent in arteries, portal and hepatic veins, so they have to be registered in order to show the liver structures acquired at each phase in a common framework. These multi-phase studies provide tumor enhancement on the arterial and portal venous phases that support differential diagnosis of lesions in the liver.

Modified simulated annealing algorithm for optimal design of steel structures

Carlos Millan-Paramo — Sun, 01 Apr 2018 22:25:04 +0200

Structural optimization aims to design structures under certain constraints to achieve better behavior and have a proper manufacturing cost. This type of optimization corresponds to highly non-linear and non-convex problems including several local optima. Therefore, to solve such problems effectively, designers need to use adequate optimization methods which can make a good balance between the computational cost and the quality of solutions. In this paper the modified simulated annealing algorithm (MSAA) is employed to solve optimal design of steel structures. MSSA is a newly improved version of the simulated annealing (SA) algorithm with three modiﬁcations: preliminary exploration, search step and a new probability of acceptance. The performance, robustness and applicability of the MSAA are demonstrated through six structural optimization problems. Obtained results in all considered examples indicate that the MSAA is superior to several other methods in existing literature in terms of the quality of solution and convergence speed.

Estimation of the transverse sway motion of a biped robot during the march

Rogelio de Jesús Portillo-Vélez — Wed, 01 Aug 2018 19:48:16 +0200

Due to the balancing generated by the natural dynamics and disturbances during the march of a biped robot, it is difficult to predict its position at a certain moment along the same, thus complicating the development of tasks like manipulation, cooperation, obstacles, avoidance, servo-visual feedback, among others. In this document, we describe a methodology to predict the sway motion in the transverse plane of a biped robot, given the trajectory of a fixed point in its mechanical structure. It is considered the study of two mathematical models to approximate the rolling movement of the robot: approximation by means of a sinusoidal function and approximation by Fourier series. In both cases, it is necessary to know the parameters involved in each mathematical model, so three parametric approximation techniques are implemented: least squares indentification and algebraic identification for the case of the sinusoidal approach, and the calculation of coefficients for the case of the Fourier series. To validate the methodology, real-time monitoring of a biped robot is carried out since the trajectory of the point of interest is affected by various factors such as friction, inclination and imperfections of the surface, the state of conservation of the robot, among others. From different experiments, a quantitative comparison between the different approaches is developed to verify the one that best reproduces the dynamis of the robot's sway.

The effect of the mesh refinement on a multiscale domain decomposition method for the non-linear simulation of composite structures

Karin Saavedra — Mon, 04 Jun 2018 14:22:46 +0200

This article is focused on the study of a micro-macro LaTIn based Domain Decomposition Method (LaTIn-DDM) for the prediction of the nonlinear behavior of slender composite structures subjected to bending, buckling and delamination. Previous studies have shown that an adequate selection of the iterative parameters (search directions and macroscopic space) allow to improve the convergence rate and ensure scalability (i.e. number of iterations is independent of the number of subdomains) of the iterative schema. To obtain precise solutions, only the size reduction of the subdomains' discretization has been addressed (h-refinement), disregarding the option of increasing the polynomial degree of the finite elements (p-refinement) and ignoring their underlying effects on the information's transmission through the interfaces between subdomains. In this work and using linear and quadratic finite elements, h and p refinements on the subdomains and local h-refinement only along the edges of the subdomains were investigated. It is conclude that the p-refinement in the whole subdomain not only enables to reach more exact solutions than using global or local h-refinement, but also the convergence rate is improved. These enhancements allow more complex simulations but using less degrees of freedom and less calculation time, even up to 97% faster.

On the robustness of the multigrid method combining ILU and Partial Weight applied in an orthotropic diffusion problem

Grazielli Vassoler Rutz — Mon, 09 Apr 2018 21:16:51 +0200

This paper proposes an efficient and robust algorithm for solving a physical orthotropy problem. The algorithm is based on choosing the most efficient restriction operator and on an incomplete LU decomposition suited for each orthotropy direction. Local Fourier Analysis (LFA) is carried out in order to increase the efficiency of the multigrid method. Pure diffusion with orthotropy aligned to the coordinate axis x is the model considered. Equations are discretized by Finite Difference Method with uniform grid and second-order numerical scheme. Problems are solved with geometric multigrid method, correction scheme, V-cycle and standard coarsening ratio. The asymptotic convergence factor is calculated for different multigrid components, such as restriction operators, prolongation operators and solvers. Based on the optimum components obtained by LFA, we carried out experiments to analyze the complexity and computational cost of the algorithm proposed. The main conclusion is that the methodology proposed is efficient for the resolution of problems with strong orthotropy.

Design and manufacture of a customised temporomandibular prosthesis

JJ Hernández-Gómez — Sat, 03 Feb 2018 03:10:02 +0100

In this work, design, manufacture and surgical success of a personalised temporomandibular prosthesis is featured. A fused deposition modelling technique and Die forging process constitute the methodology used in a patient who had an amputation in the upper third branch of the mandible, without considering the joint capsule. The implant was designed using a processed resection image of a computational tomography and using the methodology of Özkaya and Nordin. The jaw operating conditions were simulated by the finite element method (FEM). The main considered factors were the morphological geometry of the patient, implant fixation in the first third of the branch, implant fixation on the chin, dental post for placement of the teeth, and the form of the sub-lingual fossa weight optimisation. Special consideration was to preserve the patients facial aesthetics.

Thermal model of a solar concentration cooker: a parameter variation study to estimate thermal properties

Mauricio Gonzalez-Aviles — Mon, 28 Aug 2017 16:55:47 +0200

This document describes the development of a thermal model to explain the behavior of a solar concentration cooker. The model is presented in terms of a coupled system consisting of three ordinary, differential non-lineal equations used to calculate average temperatures of the surface of the reflectors, the surface of the container, and the liquid placed inside the container. Numerical results compared to measurements from experimental tests show that good concordance was obtained. A study of variation was conducted using some of the design parameters of the solar cooker to estimate standard cooking power and thermal efficiency. We conclude that the parameter ‘emittance of selective absorbent film’ on the surface of the cooking pot exerts the greatest influence on the thermal properties assessed.

Structural health monitoring by combining machine learning and dimensionality reduction techniques

Francisco Chinesta — Sat, 10 Feb 2018 15:44:26 +0100

Structural Health Monitoring is of major interest in many areas of structural mechanics. This paper presents a new approach based on the combination of dimensionality reduction and data-mining techniques able to differentiate damaged and undamaged regions in a given structure. Indeed, existence, severity (size) and location of damage can be efficiently estimated from collected data at some locations from which the fields of interest are completed before the analysis based on machine learning and dimensionality reduction techniques proceed.

Structural assessment of gravity dams by means of a semi-discrete approach

Fernando Peña — Tue, 05 Dec 2017 17:44:03 +0100

A new numerical model for the structural assessment of gravity dams by means of a semi-discrete approach is proposed. Gravity dams are massive structures, which their stability depends on the gravity loads applied into the structure. Mainly, its structural assessment is performed by means of a gravity approach. However, this approach is too conservative and mostly does not reflect the real structural behaviour of the dam. In this context, there is the need of models that are simplified enough to allow a simple and fast parametric analyses. The proposed model idealizes the dam as a set of rigid elements, where the damage and the deformation are concentrated in the contact sides between adjacent elements. Thus, the elements are rigid, but the material is considered as deformable. As the proposed model is semi-discrete, it can detect separation or sliding between elements. However, initial contacts do not change during the analyisis and a relative continuity among elements exists, in order to simplify the computational effort. The effective performance of the proposed model is demonstrated by numerical validation and by comparisons with some numerical models presented in the literature.

Simulation of resistance and deformability of rocks via discrete elements with cemented particles

Leandro Rasmussen — Tue, 27 Nov 2018 21:55:04 +0100

The Discrete Element Method (DEM) appears as one of the most attractive methods for understanding general geotechnical problems and specifically the behavior of rocks due to their unique advantages in dealing with fracturing processes. In this work, unconfined compression and indirect tensile tests were performed for a magmatic rock, known as Lac du Bonnet granite, based on a discrete approach using DEM and a specific contact and cementation model between the particles. Concluding, a parametric analysis of the influence of Young's modulus on some macroscopic properties of the rock’s numerical model was carried out, with the objective of generating contributions as to the understanding of the deformability and strength behavior of hard rocks.

Positioning system for 3D scans inside objects

Jose-Joel Gonzalez-Barbosa — Mon, 11 Sep 2017 21:53:09 +0200

In this work we present an active positioning system for 3D scan of interior parts. The design of the proposed system consists of two modules: an active 2D dimensional system and positional system based on active vision. The active 2D dimensional system is able to determine the depth of the 2D dimensional system inside the object to be scanned using several sensors.
The main contributions of this work are the characterization of the 2D dimensional system and the development of active light positioning algorithms with emphasis on the modeling and fusion of the sensors. The system can be used as a dimensional system in industrial applications such as the metal mechanical industry, aeronautics industry, medicine, quality control and computer vision.

Mathematical Formulation and Numerical Validation of Uncertainty Costs for Controllable Loads

Sergio Rivera — Fri, 19 Oct 2018 06:37:13 +0200

This document presents an analysis in the development of a new mathematical formulation with which it will be possible to determine, through probabilistic approaches, the cost that can be generated if a diversified electricity market existed, in which the demand is able to actively participate. For this, it is considered that the electrical demand in a moment of time has associated a probability distribution and a system that makes it controllable. The cost of uncertainty of demand is mathematically developed by calculating the expected cost of supplying the most convenient demand value for the power system. The validation of the analytical formula is done through the Monte Carlo method, which allows us to compare the penalty costs in the case of underestimating or overestimating the demand for electrical energy.

Experimental evaluation of correlations used to calculate friction factor for turbulent flow in cylindrical pipes

Alan Olivares — Fri, 13 Jul 2018 04:46:23 +0200

The hydraulic systems that distribute water to users have an important role in their quality of life. For this reason, the precise determination of the friction factor in pipes is of great importance in the design of water distribution networks because it directly influences the calculation of pressure drop (head losses) in hydraulic systems. The objective of the present work was to evaluate in an experimental manner different correlations that describe, in an explicit form, the friction factor in a pipe under turbulent flow and the implicit Colebrook-White correlation. This was done by comparing the numerical values predicted by the correlations in regard to the experimental value, finding that the Colebrook-White correlation predicts the friction factor with the lowest error percentage among the 27 correlations studied. For the solution of the Colebrook-White equation the Newton-Raphson method was used, given that it presents a recurrent structure that can be taken to algorithms and quickly solved by computer programs. In this work, a tool was developed in the C ++ programming language to solve the Colebrook-White equation.

Experimental and numerical fracture tests in concrete. Towards the Virtual Laboratory

Francisco Zarate — Mon, 03 Dec 2018 10:32:06 +0100

This paper describes a computation methodology to evaluate the ultimate strength and fracture of concrete samples and structures and its application to four typical tests of experimental laboratories of strength of materials. The tests results are compared and analysed from the experimental and numerical points of view in order to highlight the need for experimental trials to use the information derived from numerical results and, in turn, to validate that numerical models follow the behaviour and physics that occur in laboratory tests This comparison allows to explain the different mechanisms that occur throughout the experiments.

Elasto-plastic finite element analysis of reinforced concrete T-shaped column frame joint

Yang Liu — Mon, 11 Dec 2017 11:19:15 +0100

By the integral finite element analysis of elasto-plastic constitutive relationship, the process of crack formation and development of the T-shaped frame joint in reinforced concrete and its stress distribution under monotonic and low-cycle repeated loading were studied . The nonlinear constitutive relation of concrete and the failure mechanism of T-shaped column joint were further discussed. The work of this paper provides a reference to the design and construction of T-shaped column joints.

Efficiency Maximization of a Jet Pump for an Hydraulic Artificial Lift System

Rogelio de Jesús Portillo-Vélez — Wed, 13 Jun 2018 21:37:05 +0200

This work presents a simpler numerical design method for efficiency maximization of an Hydraulic Jet Pump (HJP) for oil-well extraction process, considering its hydraulic and geometric parameters. The design process consists in setting and solving a constrained non-linear optimization problem by taking into account the hydraulic model of the HJP in terms four design variables: throat area, nozzle area, injection flow, and injection pressure to the oil-well. The objective function of this case aims to maximize the HJP's efficiency avoiding to approach cavitation condition as well fulfilling technical constraints. A numerical technique, Differential Evolution Algorithm (DEA), has been implemented to solve the optimization problem. The proposed methodology leads to a solution set by considering only commercial geometries and feasible operating conditions for the HJP, which facilitates its practical implementation. A set of ten oil-wells with land production data, operating in the southeaster of Mexico, is used to compare and validate several Jet pump designs, i. e., through comparison with actual oil-well's operation condition.

Dynamic Analysis of Hypar Membrane Structures Subjected to Seismic Excitations

Jesús Gerardo Valdés-Vázquez — Thu, 24 May 2018 20:16:22 +0200

The seismic response of tensile membrane structures (TMS) is investigated. To the authors knowledge, this is the first study on TMSs subjected to a seismic record reported in the literature. A type of membrane structures usually considered as a reference in other works are employed in the present study. The selected hyperbolic-paraboloid fabric structures, also referred as hypar TMSs, are subjected to an earthquake accelerogram from a relatively large earthquake recorded at Norcia, Italy. To obtain the TMSs seismic re-
sponse, a finite element formulation reported in a previous study, and which accounts for wrinkling phenomena, orthotropic material modeling, and geometrical nonlinearity, is employed. The analyses are performed in two stages; first for the prestressed case and then the seismic loading is added. It is found that the seismic response of TMSs should not be disregarded by designers beforehand, since important increments in the dynamic response of the displacements produce an incremet of around 9% for stresses. However, a very important increment of around 80% for support reaction forces is computed, when compared with the static case. It is also found that the orientation of the frame-supporting structure has a significant impact on the computed seismic reactions.

Dynamic analysis in the domain of frequency by the method of the harmonic balance

Rafael Zaltron — Tue, 20 Mar 2018 20:55:21 +0100

The analysis of structures in the frequency domain has been gaining ground in the last decades, first, because of the computational development and strategies to evaluate the Discrete Fourier Transform more efficiently. The advantages of evaluating the frequency response are that there is no need to know the initial conditions, and the response to systems with frequency-dependent properties can be evaluated more accurately, eg, soil-structure interaction. This work aims to evaluate the dynamic response of a discrete structural system in the frequency domain through the resonance curves using the Harmonic Balance Method HBM. The response is evaluated in the permanent phase for actions and / or harmonic loads for systems with proportional and non-proportional viscous damping. The properties of the system, such as mass and rigidity, are taken as constants. For the models developed and analyzed in this study are presented the respective spectra of frequency response and history of displacement in time through the HBM. The system responses obtained through the HBM are compared with two other methods also based on the frequency domain (ImFT and PseudoForces), allowing to evaluate the amplitudes and critical frequencies of the system.

Damping performance of viscoelastic material applied to blades

Fusheng Wang — Mon, 22 Jan 2018 03:54:09 +0100

'''High-frequency vibration can result in failure of the working blades. So suppressing vibration failure of blades becomes more and more important. Damping performance of viscoelastic block on blades is researched based on principle of finite element method, contact theory of elastic body and the solving equations of natural frequency. Modal and harmonic response is analyzed to obtain natural frequency, vibration displacement and stress, in which different finite element models of blade are established. Effects of different adding position and thickness of viscoelastic block on damping performance are analyzed. Elastic modulus and loss factor of viscoelastic material is also changed to study their influence on damping performance. The results show that viscoelastic block applied to blades has excellent performance in reducing blade vibration. When viscoelastic block is added to mortise side, the damping performance of blade is the best. In addition, thickness of viscoelastic block and parameters of viscoelastic material have a significant effect on vibration reduction of blade. '''Key words''': Viscoelastic damping material, blades, vibration reduction, modal analysis, harmonic response Corresponding author. E-mail: [mailto:fswang@nwpu.edu.cn fswang@nwpu.edu.cn] (Fusheng Wang)

Change of effective properties of concrete by alkali-silica reaction

Guilherme Augusto Pianezzer — Tue, 18 Jul 2017 16:38:02 +0200

The present work develops a model of computer simulation of the actual properties of concrete under the action of alkali-silica reaction. Obtains a computational representation from the analysis of the chemical reaction and homogenenization techniques. Alkali-Silica reaction forms a gel that changes the effective properties of concrete and can lead to damage to structures, especially of hydroelectric dams. The model consists of three phases, generation of representative element of concrete, gel formation and dissemination by alkali-silica reaction and homogeneization of the final material. The first stage is the development of representative concrete element that is simulated from the granulometric curve and uses a computacional collision detection algorithm to ellipses. To model the behavior of chemical evolution, it uses a system based on equations of chemical kinetics, known as Guldberg - Waage Law and uses a gel diffusion model developed to mesh of representative element of concrete. To model the variation of the effective properties, it uses homogenization schemes (Reuss method, Voigt Method, Self-Consistent method and Mori-Tanaka method) to provide, thus, elasticity coefficientes of the composite material. The combination of the models allowed to predict the evolution and damage to the material over time and analyze the influence of the volume fraction of agregates in the lifetime of concrete.

Assessment of methods of identification of dynamic properties based on measured seismic response of a building

Pablo Alcaíno — Thu, 28 Dec 2017 14:47:11 +0100

The structural monitoring, which is becoming increasingly common, makes it necessary to choose one or more methods of processing and analyzing the obtained data. This choice is key to meeting the objectives of this monitoring. Considering that there are many methods with different capacities and requirements, this choice is a complex problem. This paper presents a methodology for the assessment and selection of methods for the identification of dynamic response properties of buildings using vibration monitoring. In this work, well-known methods based on time domain analysis (subspace-state) and non-parametric methods based on the frequency domain are studied when applied to seismic vibration records for a reinforced concrete building instrumented with a network of tri-axial force-balance accelerometers. For two and a half years, the sensor network has recorded close to 500 sensitive earthquakes. Nonetheless, it only includes those with a magnitude higher than 4.8 (M_L or M_W) and that occurred between September, 2015 and September, 2016. Using six versions of identification methods, modal response parameters are determined for each of the two main directions of the building, considering different levels of information acquired by the sensor network (floor information). An assessment of the performance of each method is conducted based on the number of identified modal frequencies and damping ratios; their variability (coefficient of variation); and the processing time of each method. As a result and conclusion regarding the use of this methodology, it is not only possible to choose the most convenient method for processing vibration records applied to structural health monitoring (SHM) according to its own objective, but also to progressively improve the design of the sensor network.

Approximation of the scalar convection-diffusion-reaction equation with stabilized finite element formulations of high order

Ramon Codina — Wed, 20 Jun 2018 07:44:05 +0200

In this paper we present stabilized finite element formulations to solve the scalar convection-diffusion-reaction equation in the case of small diffusion. On the one hand, we summarize the application of the ASGS and OSS formulations based on the concept of variational multiscale methods. On the other hand, we discuss aspects of the use of high order elements, focusing our numerical experiments on quadratic, cubic and fourth order elements. Likewise, the application of the OSS method requires the introduction of a projection, for which we introduce a modification of the fourth order simplicial element with an associated numerical integration rule.

Annual distribution of the Sun’s angular positions, study at 21 degrees of latitude

Cesar Acosta — Wed, 06 Sep 2017 17:24:28 +0200

It is well know that the Sun position, measured over the heart surface is a function of the latitude and the hour of a particular day. Usually, the Sun follows a different path from one day to the next, and this is determined by the azimuth and zenith angles. The analytical calculations for determining the angular position at any time (solar hour) are an overwhelming task. We use the Mathematica® software to write a home code for determining at any time (in intervals of one minute) and latitude, the azimuth and zenith angles of the Sun for every day of the year. In order to show general results of interest, in this work we present the annual distribution of the angular positions and the length of the day (hours of light) for the 21 degrees of latitude. This information could be used for optimizing the orientation of solar panels and collectors and for the design of cheap houses where the walls can be exposed to the minimal solar incidence.

A rapid aeroelasticity optimization method based on the stiffness characteristics

Zhe Yuan — Thu, 15 Mar 2018 08:53:58 +0100

A rapid aeroelasticity optimization method based on the stiffness characteristics was proposed in the present study. Large time expense in static aeroelasticity analysis based on traditional time domain aeroelasticity method is solved. Elastic axis location and torsional stiffness are discussed firstly. Both torsional stiffness and the distance between stiffness center and aerodynamic center have a direct impact on divergent velocity. The divergent velocity can be adjusted by changing the correlative structural parameters. The relation between structural parameters and divergent velocity is introduced to aeroelasticity optimization design as a constraint condition. After optimization, the structural and aerodynamic characteristics have a large improvement while satisfying the constraint conditions. The optimization method can be well used in high aspect ratio wing and has great computational efficiency.

A methodology for the design of dam spillways with wedge shaped blocks based on numerical modeling

Javier San Mauro — Mon, 04 Jun 2018 17:41:06 +0200

Wedge shaped blocks spillways are an innovative solution that allows spilling over the downstream shoulder of earth and rock-fill dams in a safe way. However, they have been barely used as main spillway due to the lack of practical design criteria. An innovative procedure for computer-aided design of wedge shaped blocks spillways is presented in this paper. It includes the design of the drainage and supporting layer considering its seepage capacity and stability. The leakage flow through the joints between blocks is estimated by means of a numerical model calibrated and validated from experimental results. Stability against sliding of the downstream shoulder or the drainage layer is ensured, considering the properties of the granular material selected by the designer and non-linear resistance laws. The procedure will also suggest the shape of a toe protection.

A geometric description of Discrete Exterior Calculus for general triangulations

Rafael Herrera — Thu, 07 Jun 2018 03:36:02 +0200

We revisit the theory of Discrete Exterior Calculus (DEC) in 2D for general triangulations, relying only on Vector Calculus and Matrix Algebra. We present DEC numerical solutions of the Poisson equation and compare them against those found using the Finite Element Method with linear elements (FEML).

3D printed scaled setup for smoke transport analysis in a subterranean passenger platform

L. A. Flores-Herrera — Tue, 15 Aug 2017 19:30:02 +0200

In this work, the study of smoke fire transportation inside of a subway passenger platform is presented. The study includes a set of numerical simulations to observe the behavior of the air inside the platform. Two smoke transport simulations using the FDS program are also included. Subsequently, the development of a 3D - 1:100 scale model is described and it was used to perform an experimental observation of the phenomenon. The model was built by using a 3D printer which allowed to include more architectural details of the real scenario. The inclusion of these details allowed to observe qualitative similarity between the results of the simulation and the experimental work. Although there are clear differences between what could happen in a real scenario and what was observed in the scale model, it was identified that the model is an important complement to the simulations. In addition to the simulations, the use of this type of 3D models allows the observation of the phenomenon by different specialists such as firefighters, policeman, medical personnel, etc., in the same place and its intention is to provide a more interactive tool to the observation group, increasing the time devoted to the development of contingency actions and reducing the costs associated with the logistics of a real simulacrum. The model allows to better identify the strengths, opportunities, weaknesses and threats of the contingency procedures developed by the safety and hygiene groups and to make their corresponding adjustments if necessary.

Elastoplastic analysis of steel frames with interaction surfaces in stress resultants obtained for multiple linear regression

Pedro Vieira — Tue, 02 Apr 2019 12:33:06 +0200

The interaction surfaces in stress resultants can be of great use in the structural analysis processes, but their obtaining for plane or space frames, generally, is in combined efforts of bending moments and normal. The literature presents the surfaces in plane, quadric, complex or mixed forms for nonlinear analysis of structures that have the problems of local and global instability in the executing. The multiple linear regression model is a method that permit obtain interaction surfaces in the stress resultants from 3D solid element analysis. The plane and space frames elastoplastic analysis using these surfaces facilitate the structural analysis processes for the execution of projects with better structural safety. In this work, the approach will be for metallic structures with stress resultants surfaces obtained by Timoshenko 3D beams damage model non-linear analysis.

Application of optimization techniques to the determination of modal parameters in civil structures by the identification method

LUIS MANUEL VILLA GARCIA — Tue, 04 Dec 2018 20:36:08 +0100

In the present paper, the application of optimization techniques –via FRF– is developed for determining modal parameters by means of the identification method that are exclusively limited to: systems with viscous damping, low levels of damping, and methods that work within the frequency domain. Decomposition techniques are proposed for working with complex magnitudes that allow the real and imaginary parts to be treated separately (which can, in this way, be implemented in commercial optimization programs), even in matrix product operations. The influence of high and low modes is rigorously taken into consideration via the selfsame optimization algorithm. To illustrate this work we have analyzed a structure unique in its slenderness, La Cartuja Bridge (Seville, Spain), which also constitutes a very light structure with very little damping. Its design contributed in its day a new structural framework of complicated geometries through the use of a new material: high yield strength steel.

Partially saturation effect on fine sands and earth pressure in a sheetpile wall

Juan Carlos Ruge C. — Thu, 22 Nov 2018 06:45:29 +0100

Generally, the effects of suction in fine sands can be evidenced by a stiffening of the material, as the capillary front advances in the granular skeleton. In geotechnical retention structures this effect can be translated in an increasing of earth pressure, which is not normally considered in geotechnical designs. This study analyzes the capillary effects by implementing a physical modelling in centrifuge and a numerical simulation, using different constitutive models that involve suction within the analysis. The modelling is based on a structure of retention in sheetpiles built on a real scale. Some factors that affect both physical and numerical modelling were taken into account and should be considered in the analysis of the results obtained and, in the comparisons, carried out by both methodologies. As a point of interest, numerical modelling showed less dispersion in the results obtained than physical modelling, these and other aspects are analyzed in the document