Análisis del estado de tensiones en uniones carpinteras de empalme de llave por el método de los elementos finitos

El objeto del presente trabajo es la determinación de la distribución de tensiones en la unión carpintera de empalme de llave mediante el método de los elementos finitos y su comparación con los valores obtenidos mediante la teoría de Resistencia de Materiales. Se analizan las zonas donde se produce concentración de tensiones y se estudia la influencia del refino de la malla sobre los resultados con el fin de determinar el tamaño que proporciona los valores de tensión más ajustados a la teoría. En las zonas donde la concentración de tensiones es menor, distintos tamaños de la malla muestran valores de tensión similares. Los resultados muestran una simetría central de la distribución de isotensiones donde el centro de simetría se corresponde con el centro geométrico de la unión. En las zonas donde se produce concentración de tensiones, los valores de las mismas aumentan considerablemente con el refino de la malla. La comparación de los niveles de tensiones normales obtenidos por el MEF y la teoría clásica muestran diferencias reducidas, excepto en los puntos de concentración de tensiones. The purpose of this study is to determine the stress distribution in the joint carpenter of halved and tabled joint with the finite element method and its comparison with the values obtained using the theory of Strength of Materials. The stress concentration areas where analyzed and the influence of mesh refinement was studied on the results in order to determine the mesh size that provides the stress values more consistent with the theory. In areas where stress concentration is lower, different mesh sizes show similar stress values. The results show a central symmetry of the isobar lines distribution where the centre of symmetry corresponds to the geometric centre of the joint. In areas where stress concentration occurs, the same values increase considerably with the refinement of the mesh. Comparison of normal stress levels obtained by the FEM and the classical theory shows small differences, except at points of stress concentration.

Estudios de confort de vehículos ferroviarios mediante técnicas combinadas de simulación FEM y MBS

La elasticidad de la caja de viajeros de los vehículos ferroviarios tiene una gran influencia sobre el confort. Por esta razón, cuando se desea simular el comportamiento dinámico del vehículo para estudios de confort, resulta conveniente construir un modelo elástico de caja, a fin de obtener resultados más precisos. La construcción de este tipo de modelos pasa por el desarrollo de dos etapas fundamentales, que comprenden la generación de un modelo de caja mediante la técnica de los elementos finitos (FEM) para su caracterización dinámica como cuerpo elástico y la definición de un modelo de sistema multicuerpo (MBS) que englobe los restantes componentes del vehículo. En este artículo se presentan los resultados obtenidos en un estudio comparativo llevado a cabo con modelos de caja rígida y elástica, en los que se ha valorado el nivel de confort obtenido con ambas configuraciones. Para ello, se ha simulado el comportamiento del vehículo a dos velocidades distintas, de 70 y 110km/h, y con dos niveles de irregularidades. Se han analizado las aceleraciones de la caja, que se han procesado de acuerdo a las especificaciones de la norma EN12299, a fin de obtener el índice de comodidad. Este parámetro se ha utilizado para comparar el nivel de confort obtenido con ambos modelos, habiéndose encontrado una gran diferencia en los índices calculados con caja rígida y con caja elástica, lo que confirma la gran influencia de la elasticidad de la caja en los estudios de confort llevados a cabo mediante técnicas de simulación dinámica.

Comparison of Mesh Adaptation Using the Adjoint Methodology and Truncation Error Estimates

Mesh adaptation based on error estimation has become a key technique to improve th eaccuracy o fcomputational-fluid-dynamics computations. The adjoint-based approach for error estimation is one of the most promising techniques for computational-fluid-dynamics applications. Nevertheless, the level of implementation of this technique in the aeronautical industrial environment is still low because it is a computationally expensive method. In the present investigation, a new mesh refinement method based on estimation of truncation error is presented in the context of finite-volume discretization. The estimation method uses auxiliary coarser meshes to estimate the local truncation error, which can be used for driving an adaptation algorithm. The method is demonstrated in the context of two-dimensional NACA0012 and three-dimensional ONERA M6 wing inviscid flows, and the results are compared against the adjoint-based approach and physical sensors based on features of the flow field.

Coupled model of initiation and propagation of corrosion in reinforced concrete

Corrosion of reinforcing steel in concrete due to chloride ingress is one of the main causes of the deterioration of reinforced concrete structures. Structures most affected by such a corrosion are marine zone buildings and structures exposed to de-icing salts like highways and bridges. Such process is accompanied by an increase in volume of the corrosión products on the rebarsconcrete interface. Depending on the level of oxidation, iron can expand as much as six times its original volume. This increase in volume exerts tensile stresses in the surrounding concrete which result in cracking and spalling of the concrete cover if the concrete tensile strength is exceeded. The mechanism by which steel embedded in concrete corrodes in presence of chloride is the local breakdown of the passive layer formed in the highly alkaline condition of the concrete. It is assumed that corrosion initiates when a critical chloride content reaches the rebar surface. The mathematical formulation idealized the corrosion sequence as a two-stage process: an initiation stage, during which chloride ions penetrate to the reinforcing steel surface and depassivate it, and a propagation stage, in which active corrosion takes place until cracking of the concrete cover has occurred. The aim of this research is to develop computer tools to evaluate the duration of the service life of reinforced concrete structures, considering both the initiation and propagation periods. Such tools must offer a friendly interface to facilitate its use by the researchers even though their background is not in numerical simulation. For the evaluation of the initiation period different tools have been developed: Program TavProbabilidade: provides means to carry out a probability analysis of a chloride ingress model. Such a tool is necessary due to the lack of data and general uncertainties associated with the phenomenon of the chloride diffusion. It differs from the deterministic approach because it computes not just a chloride profile at a certain age, but a range of chloride profiles for each probability or occurrence. Program TavProbabilidade_Fiabilidade: carries out reliability analyses of the initiation period. It takes into account the critical value of the chloride concentration on the steel that causes breakdown of the passive layer and the beginning of the propagation stage. It differs from the deterministic analysis in that it does not predict if the corrosion is going to begin or not, but to quantifies the probability of corrosion initiation. Program TavDif_1D: was created to do a one dimension deterministic analysis of the chloride diffusion process by the finite element method (FEM) which numerically solves Fick’second Law. Despite of the different FEM solver already developed in one dimension, the decision to create a new code (TavDif_1D) was taken because of the need to have a solver with friendly interface for pre- and post-process according to the need of IETCC. An innovative tool was also developed with a systematic method devised to compare the ability of the different 1D models to predict the actual evolution of chloride ingress based on experimental measurements, and also to quantify the degree of agreement of the models with each others. For the evaluation of the entire service life of the structure: a computer program has been developed using finite elements method to do the coupling of both service life periods: initiation and propagation. The program for 2D (TavDif_2D) allows the complementary use of two external programs in a unique friendly interface: • GMSH - an finite element mesh generator and post-processing viewer • OOFEM – a finite element solver. This program (TavDif_2D) is responsible to decide in each time step when and where to start applying the boundary conditions of fracture mechanics module in function of the amount of chloride concentration and corrosion parameters (Icorr, etc). This program is also responsible to verify the presence and the degree of fracture in each element to send the Information of diffusion coefficient variation with the crack width. • GMSH - an finite element mesh generator and post-processing viewer • OOFEM – a finite element solver. The advantages of the FEM with the interface provided by the tool are: • the flexibility to input the data such as material property and boundary conditions as time dependent function. • the flexibility to predict the chloride concentration profile for different geometries. • the possibility to couple chloride diffusion (initiation stage) with chemical and mechanical behavior (propagation stage). The OOFEM code had to be modified to accept temperature, humidity and the time dependent values for the material properties, which is necessary to adequately describe the environmental variations. A 3-D simulation has been performed to simulate the behavior of the beam on both, action of the external load and the internal load caused by the corrosion products, using elements of imbedded fracture in order to plot the curve of the deflection of the central region of the beam versus the external load to compare with the experimental data.

Automatic mesh generation processor for 3-D parabolic boundary discretization

An automatic Mesh Generation Preprocessor for BE Programs with a considerable of capabilities has been developed. This program allows almost any kind of geometry and tipology to be defined with a small amount of external data, and with an important approximation of the boundary geometry. Also the error checking possibility is very important for a fast comprobation of the results.

An interpolation tool for aerodynamic mesh deformation problems based on octree decomposition

Desarrollo de algoritmo de interpolación basado en descomposición octree y funciones radiales de soporte compacto para movimiento de mallas en problemas aerolásticos

A comparison between PML, infinite elements and an iterative BEM as mesh truncation methods for HP self-adaptive procedures in electromagnetics

Finite element hp-adaptivity is a technology that allows for very accurate numerical solutions. When applied to open region problems such as radar cross section prediction or antenna analysis, a mesh truncation method needs to be used. This paper compares the following mesh truncation methods in the context of hp-adaptive methods: Infinite Elements, Perfectly Matched Layers and an iterative boundary element based methodology. These methods have been selected because they are exact at the continuous level (a desirable feature required by the extreme accuracy delivered by the hp-adaptive strategy) and they are easy to integrate with the logic of hp-adaptivity. The comparison is mainly based on the number of degrees of freedom needed for each method to achieve a given level of accuracy. Computational times are also included. Two-dimensional examples are used, but the conclusions directly extrapolated to the three dimensional case.