Un elemento de sólido con una mejora en el comportamiento del corte transversal para el tratamiento de láminas

In this work a solid finite element based on a Total Lagrangian Formulation using logarithmic strains is combined with a classical assumed strain approach of the transverse strains for thick shells. The target is to use the element for shell simulations without shear locking. The selective mass scaling technique used to avoid that the discretization across the thickness reduce the critical time in codes with explicit integration of the momentum equations is summarized. Several examples are presented showing that the element is shear-locking free, the consequences of the selective mass scaling and the possibilities of the element for the analysis of composites laminates in non-linear material regime.     

Un modelo predictivo de la evolución en costas rocosas

The recession of coastal cliffs is a widespread phenomenon on the rocky shores that are exposed to the combined incidence of marine and meteorological processes that occur in the shoreline. This phenomenon is revealed violently and occasionally as gravitational movements of the ground and can cause material or human losses. Their prediction is difficult; however it is basic for the proper coastal management and the clear understanding of erosion risks. There are several models of the coastal cliff recession processes. From the stochastic type models based on historical erosion events, to the theoretical models as described by Eikonal or Boussinesq equations. In this work an intermediate solution is adopted (process-response model), such as models based on simplified balance of forces as trigger mechanisms involved in the erosion of the rocks. This model fits the marine dynamics: sea level changes, tidal range and wave transformation; along with the evolution of the land: the slope of the surf zone, erosion and rock falls. So far these models have been limited to small slope cliffs, since its numerical stability and the propagation of errors are unknowns. For these reasons, the development of a generic model that reproduces the spatial and temporal evolution of a cliff-2D profile (platform, beach and slope) consisting on semi-consolidated heterogeneous materials, is presented. In addition, the computational implementation, the study of different numerical resolution techniques and the produced errors, are also exposed and analysed.     

Un modelo numérico para la simulación de disolución de precipitados en aleaciones de aluminio con endurecimiento utilizando redes neuronales

The motivation of this work is the modeling of the hardening precipitate and hardness evolutions of fully hardened heat treatable aluminium alloys during friction stir welding (FSW) and/or heat treatment processes. The model used is based on the kinetics of dissolution of precipitates model for hardened aluminium alloys given by Myhr and Grong (1991). This model contains a single independent variable, the time, and a single state variable, the volume fraction of hardening precipitates. A key point of this model is the identification of the effective activation energy for precipitates dissolution and the master curve defining the model, which was given by a look-up table. The goal of this work is to find an estimation of the effective activation energy and to model the dissolution rate of hardening precipitate in aluminium alloys using neural networks, avoiding the use of look-up tables. For this purpose a new and more convenient parametrization of the master curve is defined, a neural networks class is proposed, an objective functional is defined and a variational problem including independent parameters is solved. The novel methodology has been applied to different aluminium alloys, including the AA 6005A T6, AA 7449 T79 and AA 2198 T8. Experimental tests have been carried out for those aluminium alloys in order to get the HV1 hardness after isothermal heat treatments at different temperatures and for different treatment time durations. The effective activation energy for hardening precipitates dissolution and the master curve of the model have been obtained, using different network architectures, for the aluminium alloys considered in this work.     

Aplicación de un algoritmo evolutivo para la optimización del modelado computacional de la pirólisis de materiales

The pyrolysis models undergoes a fast development due to the enhancement of both the computational power and the new test used to characterize the behaviour of materials under thermal stresses, which were widely used in the field of the chemical engineering to obtain the reaction rates. Thus, these models allow us to characterize either the transient heat of material (thermal inertia) or the complete chemical scheme of mass loss processes (kinetic triplet). The pyrolysis model needs a several number of parameters what does the optimization of a suitable set of parameters a difficult task. Two kinds of materials have been investigated; the first one was a real material which mass loss process was characterized as “one-step” reaction and the second one as a “two-steps” process. Further, it has been analyzed the influence of some algorithm features (initial population number, parameter range, crossover influence) in the optimization time and also in the accuracy of results.     

Aplicación del método level set para modelar el proceso de combustión premezclada en un motor Otto de dos tiempos

In this paper, the numerical method level set has been used to model the combustion process in an Otto two-stroke engine. The level set has been implemented in a CFD (Computational Fluid Dynamics) software based in finite volumes. The pressure and temperature fields have been obtained, such as the propagation of the flame front. In order to validate this model, the numerically obtained results have been compared with experimental data, verifying a satisfactory concordance between both of them. Besides, the level set method has been compared with other numerical procedure, showing the difference between both results.     

Fórmulas para el cálculo del factor de impacto de estructuras semienterradas en líneas de ferrocarril de alta velocidad

Underpasses are common in modern railway lines. Wildlife corridors and drainage conduits often fall into this category of partially buried structures. Their dynamic behavior has received far less attention than that of other structures such as bridges, but their large number makes their study an interesting challenge from the viewpoint of safety and cost savings. The bridge design rules in accordance with the Eurocode involve checks on stresses according to dynamic loading. In the case of underpasses, those checks may be as much as those for bridges. Therefore, simplified design rules may align the design effort with their cost. Such a set of rules may provide estimations of response parameters based on the key parameters influencing the result. This paper contains a proposal based on a parametric study.     

Función de Green para el problema elastodinámico armónico en un semiespacio con amortiguamiento histerético

This paper presents an analytical solution for the steady-state response of a homogeneous three-dimensional half-space subject to a time-harmonic point load. This expresion is of great importance in the formulation of three-dimensional elastodynamic problems in a half-space by means of boundary element methods which can be employed as a Fundamental Solution. The expressions are validated comparing the results with those obtained with the boundary element method solution, where the free surface is discretized. The solution is further compared to that of a 2.5D half-space, and with experimental results available in the literature.The asymptotic behaviour of the solution is explored for different limits of the distance, frequency and wave number, and the ensuing limits are compared to existing fundamental solutions.     

Cálculo de la función distancia para el método Level Set usando la formulación estabilizada USFEM/Rothe

In this work we use the Unusual Stabilized Finite Element Method (USFEM) associated to Rothe's method for solving the redistancing problem in the Level Set Method. Rothe's method is used first for advancing the solution in (pseudo)time and USFEM for solving the resulting steady advective–reaction problem in each time step. Several 2D problems are solved and results compared with SUPG scheme supplemented with a nonlinear discontinuity–capturing operator.     

Implementación eficiente de una formulación semirrecursiva para la dinámica de sistemas multicuerpo de gran tamaño

This article shows an efficient implementation of a dynamic semi-recursive formulation for large and complex multibody system simulations, with interesting applications in the automotive field and especially with industrial vehicles. These systems tend to have a huge amount of kinematic constraints, becoming usual the presence of redundant but compatible systems of equations. The maths involved in the solution of these problems have a high computational cost, making very challenging to achieve real-time simulations.In this article, two implementations to increase the efficiency of these computations will be shown. The difference between them is the way they consider the Jacobian matrix of the constraint equations. The first one treats this matrix as a dense one, using the BLAS functions to solve the system of equations. The second one takes into account the sparse pattern of the Jacobian matrix, introducing the sparse function MA48 from Harwell.Both methodologies have been applied on two multibody system models with different sizes. The first model is a vehicle IVECO DAILY 35C15 with 17 degrees of freedom. The second one is a semi-trailer truck with 40 degrees of freedom. Taking as a reference the standard C/C + + implementation, the efficiency improvements that have been achieved using dense matrices (BLAS) have been of 15% and 50% respectively. The results in the first model have not improved significantly by using sparse matrices, but in the second one, the times with sparse matrices have been reduced 8% with respect to the BLAS ones.     

Modelación del funcionamiento hidráulico de los dispositivos de aireación de desagües de fondo de presas mediante el método de partículas y elementos finitos

Dam bottom are key elements to control the water surface elevation below the spillway crest level. As a consequence, they are essential in reservoir management, and play a vital role in dam safety.The convenience of installing an aeration system in dam bottom outlets is well known nowadays. Otherwise, damages due to cavitation and vibration are frequently serious, as could be observed in several dams built in the beginning of the 20th century.The intrinsic features of the phenomenon make it hard to analyze either in situ or in full scaled experimental facilities. As a consequence, most of the previous studies have been carried out in small-scale physical models. The results of these works have been used to develop empirical formulas which provide an estimation of the maximum air demand of the aeration system.The progress in the development of numerical methods allows addressing this problem using numerical modeling. The Particle Finite Element Method (PFEM) had been previously applied and validated for the analysis of the performance of other hydraulic structures. In this work, it has been used to simulate air-water interaction in free-flowing gated conduits. The objective is to avoid the scale effects of physical modeling and to study in detail the key parameters. The results clarify the behaviour of the involved fluids (air and water) and provide information about the influence of the main variables that affect their circulation.     

Propuesta y validación de un algoritmo Simulated annealing modificado para la solución de problemas de optimización

Over the last decades, heuristic optimization methods based on imitating natural, biological, social or cultural processes on a computational level have aroused the interest of the scientific community due to their ability to effectively explore multimodal and multidimensional solution spaces. Despite all the papers published in the international literature, most heuristic algorithms still have low precision and accuracy. In this context, a modified Simulated annealing algorithm (MSAA) is proposed and validated for solving optimization problems. Performance evaluation was performed on test functions (benchmark functions) with and without restrictions reported in the international literature and practical design problems in civil engineering. In all cases analyzed MSAA obtained equal or better results than those reported by other authors, illustrating the applicability of the proposed algorithm.     

Relación entre el parámetro flecha-luz y la carga crítica de pandeo lateral para arcos parabólicos biempotrados bajo diferentes hipótesis de cálculo

Curved graphs that relate the f/L ratio and the λ = qL³/EI_y parameter for clamped arches with the different calculation hypothesis are going to be proposed in this article.It has been necessary to determine the real critical lateral strength of a series of clamped arches considering different calculation hypothesis respect to geometrical linearity and a steel material characteristic.The elastic-plastic material hypothesis with non geometrical linearity considers the existence of residual stresses and initial lateral deflection.     

Esquema adaptativo para problemas tridimensionales de convección-difusión

We present an adaptive scheme for three-dimensional convection-diffusion problems discretized by the Finite Element Method. The adaptive scheme is based on a remeshing strategy that applies a maximum volume constraint to the elements of a reference mesh. The remeshing can increase or decrease drastically the size of the elements in a single step automatically. With this strategy, the mesh quality does not deteriorate; as a consequence, the number of iterations required to solve the system of linear equations using iterative algorithms is kept constant. Two examples of very different characteristics are presented in order to analyze the proposal for a wide range of situations. The first is a three-dimensional extension of the Smolarkiewicz problem and the second is a simplified version of a point source pollutant transport problem. The results show the flexibility of the proposal. An optimal remeshing frequency, from a computational cost and accuracy of the results point of view, can be defined for both kinds of problems.     

Desarrollo de un algoritmo de optimización global en colonias de hormigas con selección de región factible para espacios continuos

This study introduces a new algorithm for the ant colony optimization (ACO) method, which has been proposed to solve global optimization problems with continuous decision variables. This algorithm, namely ACO-FRS, involves a strategy for the selection of feasible regions during optimization search and it performs the exploration of the search space using a similar approach to that used by the ants during the search of food. Four variants of this algorithm have been tested in several benchmark problems and the results of this study have been compared with those reported in literature for other ACO-type methods for continuous spaces. Overall, the results show that the incorporation of the selection of feasible regions allows the performing of a global search to explore those regions with low level of pheromone, thus increasing the feasibility of ACO for finding the global optimal solution.     

Descomposición en pistones circulares para la obtención de la radiación acústica de un pistón rectangular

Obtaining pressure radiated by flat surfaces is not a new problem. This problem has studied by the complexity of the topic and its application to design flat speakers. These kind of speakers are the speakers that we use in televisions, ceilings, cinema screens, panels, etc. in this cases usually we have rectangular speakers.The single source model is the simplest model to convert the surface vibration to radiated pressure in a point. This is an easy model but it is very slow, especially when we want calculate at high frequencies. For rectangular surfaces there are models that use relatively complex auxiliary functions. In this case the calculation is accelerated but its implementation is more complicated and is necessary to particularize each situation.This paper presents the decomposition of a rectangular surface in several circular surfaces, by means of area associations, seeking a rapid method based on circular pistons whose behavior is known with an acceptable error in the allocation.     

Integración temporal explícita con grandes pasos de tiempo de la ecuación de transmisión del calor

We present a novel fully explicit time integration method that remains stable for large time steps, requires neither matrix inversions nor solving a system of equations and therefore allows for nearly effort-less parallelization. In this first paper the proposed approach is applied to solve conduction heat transfer problems, showing that it is stable for any time step as is the case with implicit methods but with a much lower computation time.     

Evaluación numérica del efecto del espesor de la placa de contacto en la acción de palanca en conexión de acero tipo «T»

This paper presents a numerical study of «T-Stub» steel connections using FEM analyses. In such connections prying action phenomenon may take place. Prying action effect on the bolts has been studied before but the location of the prying action forces has always been simplified. The effect of the thickness of «T-Stub» flanges on contact areas between flanges and support base is investigated in this paper. A 3D finite element model is used and interface elements are employed for the investigation. Nonlinear FE analyses are undertaken on connection with different flange thickness and bolt preload with two bolts. Nonlinear gap elements are used as interfaces. Discussion and conclusions on contact areas and stresses, prying action distributions and resultant of loads on bolts in the «T-Stub» connections are presented.