Juan José Ródenas

On the role of enrichment and statical admissibility of recovered fields in a posteriori error estimation for enriched finite element methods

Purpose – This paper aims at assessing the effect of (1) the statical admissibility of the recovered solution; (2) the ability of the recovered solution to represent the singular solution; on the accuracy, local and global effectivity of recovery-based error estimators for enriched finite element methods (e.g. the extended finite element method, XFEM). Design/methodology/approach – We study the performance of two recovery techniques. The first is a recently developed superconvergent patch recovery procedure with equilibration and enrichment (SPR-CX). The second is known as the extended moving least squares recovery (XMLS), which enriches the recovered solutions but does not enforce equilibrium constraints. Both are extended recovery techniques as the polynomial basis used in the recovery process is enriched with singular terms for a better description of the singular nature of the solution. Findings – Numerical results comparing the convergence and the effectivity index of both techniques with those obtained without the enrichment enhancement clearly show the need for the use of extended recovery techniques in Zienkiewicz-Zhu type error estimators for this class of problems. The results also reveal significant improvements in the effectivities yielded by statically admissible recovered solutions. Originality/value – This work shows that both extended recovery procedures and statical admissibility are key to an accurate assessment of the quality of enriched finite element approximations.

3D analysis of the influence of specimen dimensions on fretting stresses

In this paper, the contact conditions and stresses that arise in a fretting test have been analyzed by means of a three-dimensional finite element model of the contact between a sphere and a flat surface. At h-adaptive process, based on element subdivision, has been used in order to obtain a low discretization error at a reasonable computational cost. The influence of finite dimensions of the specimen in the stress fields has been evaluated. The results have been compared with the classical Cattaneo-Mindlin solution.

Element Stiffness Matrix Integration in Image-Based Cartesian Grid Finite Element Method

Patient specific Finite Element (FE) simulations are usually expensive. Time consuming geometry creation procedures are normally necessary to use standard FE meshing software, while direct pixel-based meshing techniques typically lead to a large number of degrees of freedom hence introducing a high computational cost. Image-based Cartesian grid Finite Element Method (image-based cgFEM) allows accurate models to be automatically obtained with a low computational cost without the necessity of defining geometries. In cgFEM the image is directly immersed into a Cartesian mesh which is h-adapted on the basis of the pixel value distribution. A hierarchical structure of nested Cartesian grids guarantees the efficiency of the process. In each element, the material elastic properties are heterogeneous, therefore a critical aspect of image-based cgFEM is the integration of the element stiffness matrices which homogenize the material elastic behavior at the element level. This paper compares accuracy and computational cost of different integration strategies: pixel direct integration schemes (Riemann sum and subdomain Gauss quadrature) and recovery based schemes (Least Squares fitting and Superconvergent Patch Recovery).

Influence of the finite element discretization error over the convergence of structural shape optimization algorithms

This work analyzes the influence of the discretization error contained in the finite element (FE) analyses of each design configuration proposed by structural shape optimization algorithms over the behavior of the algorithm. If the FE analyses are not accurate enough, the final solution will neither be optimal nor satisfy the constraints. The need for the use of adaptive FE analysis techniques in shape optimum design will be shown. The paper also proposes the use of the algorithm described in the previous study conducted in order to reduce the computational cost associated to the adaptive FE analysis of each geometrical configuration when evolutive optimization algorithms are used.

3D Topology Optimization with h-adaptive Refinement Using Cartesian Grids Finite Element Method (cgFEM)

Regarding shape optimization of structural components, topology optimization has become one of the most popular methods to achieve significant reductions in mass and volume, while maintaining stiffness. The basic topology optimization algorithm considered in this paper and a heuristic updating scheme are described in Bendsoe [1].

On the effect of the contact surface definition in the Cartesian grid finite element method

The definition of the surface plays an important role in the solution of contact problems, as the evaluation of the contact force is based on the measure of the gap between the solids. In this work three different methods to define the surface are proposed for the solution of contact problems within the framework of the 3D Cartesian grid finite element method. A stabilized formulation is used to solve the contact problem and details of the kinematic description for each surface definition are provided. The three methods are compared solving some numerical tests involving frictionless contact with finite and small deformations.

Diseño de actividades y uso de la coevaluación para fomentar el desarrollo de competencias transversales en ingeniería mecánica y de materiales

En esta comunicacion se presentan las actividades de evaluacion desarrolladas en el marco de un Proyecto de Innovacion y Mejora Educativa, junto con algunos resultados preliminares. El principal objetivo de este proyecto es el diseno de actividades de evaluacion que fuercen a los estudiantes a desarrollar sus competencias transversales, al mismo tiempo que permitan a los profesores evaluar su desempeno en las competencias cientifico-tecnicas. Se emplea un enfoque de evaluacion formativa, de forma que las actividades de evaluacion sean utiles a los estudiantes para mejorar su aprendizaje. Palabras clave: competencias transversales, actividades de evaluacion, coevaluacion

Desarrollo de estrategias de evaluación de competencias transversales en asignaturas de ingeniería mecánica y de materiales

Por ultimo, los autores quieren agradecer la ayuda economica y el apoyo institucional recibidos de la Universitat Politecnica de Valencia a traves del proyecto PIME/2014/A/012/B.

Propuesta de evaluación de las competencias de comunicación oral y escrita en asignaturas de Ingeniería Mecánica y Ciencia de Materiales

Los autores agradencen la financiacion recibida de la Universitat Politecnica de Valencia a traves del proyecto PIME/2014/A/012/B.

Numerical Simulation from Medical Images: Accurate Integration by Means of the Cartesian Grid Finite Element Method

Nowadays, when it comes to generation of patient-specific Finite Element model, there are two main alternatives. On the one hand, it is possible to generate geometrical models through segmentation, whereupon FE models would be obtained using standard mesh generators. On the other hand, we can create a Cartesian grid of uniform hexahedra in which the elements fit each pixel/voxel perfectly. In both cases, geometries will take part during the analysis either as complete models, in the first case, or as auxiliary entities, to apply boundary conditions properly for instance, in the second case. In any case, once the geometrical entities have been obtained from the medical image, the efficient generation of an accurate Finite Element model for numerical simulation in not trivial. The aim of this paper is to propose an efficient integration strategy, using Cartesian meshes, of 3D geometries defined by parametric surfaces, i.e. NURBS, obtained from medical images.