Wrinkling and folding analysis of elastic membranes using an enhanced rotation-free thin shell triangular element

This paper presents a formulation for analysis of thin elastic membranes using a rotation-free shell element within an explicit time integration strategy. The applications presented are isotropic/anisotropic rectangular membranes under shear forces and fabric drapes falling over a pedestal. Results are compared with other numerical results existing in the literature

A basic thin shell triangle with only translational DOFs for large strain plasticity

A simple finite element triangle for thin shell analysis is presented. It has only nine translational degrees of freedom and is based on a total Lagrangian formulation. Large strain plasticity is considered using a logarithmic strain–stress pair. A plane stress isotropic behaviour with an additive decomposition of elastic and plastic strains is assumed. A hyperelastic law is considered for the elastic part while for the plastic part a von Mises yield function with non‐linear isotropic hardening is adopted. The element is an extension of a previous similar rotation‐free triangle element based upon an updated Lagrangian formulation with hypoelastic constitutive law. The element termed BST (for basic shell triangle) has been implemented in an explicit (hydro‐) code adequate to simulate sheet‐stamping processes and in an implicit static/dynamic code. Several examples are shown to assess the performance of the present formulation

A rotation‐free shell triangle for the analysis of kinked and branching shells

This paper extends the capabilities of previous BST and EBST rotation‐free thin shell elements to the analysis of kinked and branching surfaces. The computation of the curvature tensor is first redefined in terms of the angle change between the normals at the adjacent elements. This allows to deal with arbitrary large angles between adjacent elements and to treat kinked surfaces. A relative stiffness between elements is introduced to consider non‐homogeneous surfaces. This idea is latter generalized to deal with branching shells. Several linear and non‐linear examples are presented showing that the formulation leads to the correct results. Copyright © 2006 John Wiley & Sons, Ltd

Advanced solid elements for sheet metal forming simulation

The solid-shells are an attractive kind of element for the simulation of forming processes, due to the fact that any kind of generic 3D constitutive law can be employed without any additional hypothesis. The present work consists in the improvement of a triangular prism solid-shell originally developed by Flores [2, 3]. The solid-shell can be used in the analysis of thin/thick shell, undergoing large deformations. The element is formulated in total Lagrangian formulation, and employs the neighbour (adjacent) elements to perform a local patch to enrich the displacement field. In the original formulation a modified right Cauchy-Green deformation tensor (C¯) is obtained; in the present work a modified deformation gradient (F¯) is obtained, which allows to generalise the methodology and allows to employ the Pull-Back and Push-Forwards operations. The element is based in three modifications: (a) a classical assumed strain approach for transverse shear strains (b) an assumed strain approach for the in-plane components using information from neighbour elements and (c) an averaging of the volumetric strain over the element. The objective is to use this type of elements for the simulation of shells avoiding transverse shear locking, improving the membrane behaviour of the in-plane triangle and to handle quasi-incompressible materials or materials with isochoric plastic flow.Postprint (published version

Simple and efficient numerical tools for the analysis of parachutes

This work describes a set of simple yet effective, numerical method for the design and evaluation of parachute-payload system. The developments include a coupled fluidstructural solver for unsteady simulations of ram-air type parachutes. For an efficient solution of the aerodynamic problem, an unsteady panel method has been chosen exploiting the fact that large areas of separated flow are not expected under nominal flight conditions of ram-air parachutes. A dynamic explicit finite element solver is used for the structure. This approach yields a robust solution even when highly non-linear effects due to large displacements and material response are present. The numerical results show considerable accuracy and robustness. An added benefit of the proposed aerodynamic and structural techniques is that they can be easily vectored and thus suitable for use in parallel architectures. The main features of the computational tools are described and several numerical examples are provided to illustrate the performance and capabilities of the technique

A 3D low-order panel method for unsteady aerodynamic problems

An unsteady low-order panel method for three-dimensional subsonic analyses is presented. The method, which is based on well-established techniques in computational aerodynamics, is intended to achieve a cost-effective solution of unsteady flows around arbitrary aerodynamic configurations. This work has two main objectives. First, to relax geometry discretization requirements and, second, to simplify the treatment of problems in which the analysis configuration moves along specified flight paths and/or changes its geometry during the simulation. Following this aim, a time-marching solution procedure is adopted in conjunction with a free-wake model which avoids iterative solutions for wake shape and position. The suitability of the present approach for solving typical aerodynamic problems is illustrated by means of several numerical examples

A-posteriori error estimation for the finite point method with applications to compressible flow (preprint)

An a-posteriori error estimate with application to inviscid compressible flow problems is presented. The estimate is a surrogate measure of the discretization error, obtained from an approximation to the truncation terms of the governing equations. This approximation is calculated from the discrete nodal differential residuals using a reconstructed solution field on a modified stencil of points. Both the error estimation methodology and the flow solution scheme are implemented using the Finite Point Method, a meshless technique enabling higher-order approximations and reconstruction procedures on general unstructured discretizations. The performance of the proposed error indicator is studied and applications to adaptive grid refinement are presented

A rotation free shell triangle with embedded stiffeners

In this paper a rotation free shell element with embedded stiffeners is presented. The element is based on a previous one where the membrane and bending strains are obtained using a patch of four triangular elements centered on the analyzed one. The stiffener is located between two adjacent elements, thus its position is defined by the two end nodes of the corresponding triangle side. The curvature of the stiffener in the tangent plane to the surface is disregarded as it is assumed that the surface is quite rigid in its plane. The torsion and surface normal curvature of the stiffener are computed from the curvatures of its two adjacent elements. A classical beam theory is used for the stiffener disregarding shear strains while the axial strain is standard. An example is presented for a preliminary assessment of the developed element

El cumplimiento de la contabilidad gubernamental y su efecto en la fiscalización de recursos federales

The General Law on Government Accounting (LGCG), came into force in Mexico as of 2009 as a mandatory law for all public entities, 2014 was the year in wich the federal entities had to conclude with the accounting harmonization process, however, to date, according to the latest figure published by the CONAC, there is an average compliance of 71.98%. The LGCG establishes that the ASF will verify that the federal resources are exercised in accordance with the applicable provisions. This investigation tries to analyze the observations made by the ASF of the control of programable federalized spending and the exercise of federal participations, of the 2018 public accounts, to identify those that are related to infringement of the LGCG.La Ley General de Contabilidad Gubernamental (en adelante: LGCG), entró en vigor en México a partir de 2009 como una ley obligatoria para todos los entes públicos, el 2014 fue el año en que las entidades federativas y sus entes públicos debieron de concluir con el proceso de armonización contable, sin embargo, a la fecha, de acuerdo a la última cifra publicada por el Consejo Nacional de Armonización Contable, a nivel nacional se tiene un cumplimiento promedio del 71.98%. La LGCG establece que la Auditoría Superior de la Federación (ASF) verificará que los recursos federales sean ejercidos de acuerdo a las disposiciones aplicables. La presente investigación pretende analizar las observaciones efectuadas por la ASF de la fiscalización del gasto federalizado programable y del ejercicio de participaciones federales, de las cuentas públicas de 2018, para identificar aquellas que estén relacionadas con incumplimientos a la LGCG