Application developer's tutorial for the CSM testbed architecture

This tutorial serves as an illustration of the use of the programmer interface on the CSM Testbed Architecture (NICE). It presents a complete, but simple, introduction to using both the GAL-DBM (Global Access Library-Database Manager) and CLIP (Command Language Interface Program) to write a NICE processor. Familiarity with the CSM Testbed architecture is required

Variational formulation of high performance finite elements: Parametrized variational principles

High performance elements are simple finite elements constructed to deliver engineering accuracy with coarse arbitrary grids. This is part of a series on the variational basis of high-performance elements, with emphasis on those constructed with the free formulation (FF) and assumed natural strain (ANS) methods. Parametrized variational principles that provide a foundation for the FF and ANS methods, as well as for a combination of both are presented

A variational justification of the assumed natural strain formulation of finite elements

The objective is to study the assumed natural strain (ANS) formulation of finite elements from a variational standpoint. The study is based on two hybrid extensions of the Reissner-type functional that uses strains and displacements as independent fields. One of the forms is a genuine variational principle that contains an independent boundary traction field, whereas the other one represents a restricted variational principle. Two procedures for element level elimination of the strain field are discussed, and one of them is shown to be equivalent to the inclusion of incompatible displacement modes. Also, the 4-node C(exp 0) plate bending quadrilateral element is used to illustrate applications of this theory

Mixed variational formulations of finite element analysis of elastoacoustic/slosh fluid-structure interaction

A general three-field variational principle is obtained for the motion of an acoustic fluid enclosed in a rigid or flexible container by the method of canonical decomposition applied to a modified form of the wave equation in the displacement potential. The general principle is specialized to a mixed two-field principle that contains the fluid displacement potential and pressure as independent fields. This principle contains a free parameter alpha. Semidiscrete finite-element equations of motion based on this principle are displayed and applied to the transient response and free-vibrations of the coupled fluid-structure problem. It is shown that a particular setting of alpha yields a rich set of formulations that can be customized to fit physical and computational requirements. The variational principle is then extended to handle slosh motions in a uniform gravity field, and used to derive semidiscrete equations of motion that account for such effects

Coupled fluid-structure interaction. Part 1: Theory. Part 2: Application

A general three dimensional variational principle is obtained for the motion of an acoustic field enclosed in a rigid or flexible container by the method of canonical decomposition applied to a modified form of the wave equation in the displacement potential. The general principle is specialized to a mixed two-field principle that contains the fluid displacement potential and pressure as independent fields. Semidiscrete finite element equations of motion based on this principle are derived and sample cases are given

The first ANDES elements: 9-DOF plate bending triangles

New elements are derived to validate and assess the assumed natural deviatoric strain (ANDES) formulation. This is a brand new variant of the assumed natural strain (ANS) formulation of finite elements, which has recently attracted attention as an effective method for constructing high-performance elements for linear and nonlinear analysis. The ANDES formulation is based on an extended parametrized variational principle developed in recent publications. The key concept is that only the deviatoric part of the strains is assumed over the element whereas the mean strain part is discarded in favor of a constant stress assumption. Unlike conventional ANS elements, ANDES elements satisfy the individual element test (a stringent form of the patch test) a priori while retaining the favorable distortion-insensitivity properties of ANS elements. The first application of this formulation is the development of several Kirchhoff plate bending triangular elements with the standard nine degrees of freedom. Linear curvature variations are sampled along the three sides with the corners as gage reading points. These sample values are interpolated over the triangle using three schemes. Two schemes merge back to conventional ANS elements, one being identical to the Discrete Kirchhoff Triangle (DKT), whereas the third one produces two new ANDES elements. Numerical experiments indicate that one of the ANDES element is relatively insensitive to distortion compared to previously derived high-performance plate-bending elements, while retaining accuracy for nondistorted elements

Desarrollos recientes en elementos de alto rendimiento basados en la formulación libre

La formulación libre (FF) propuesta por Bergan y Nygard en 1984 ha tenido considerable éxito en la construcción de elementos finitos de alto rendimiento. En su enfoque original la formulación combina campos de desplazamientos internos incompatibles con desplazamientos de frontera compatibles, y una versión especializada de la prueba de la parcela. En este articulo se describen avances recientes que han colocado esta formulación dentro de un esquema variacional, y se discuten extensiones prácticas hechas posibles como consecuencia de estos avances.Peer Reviewe

Principios variacionales parametrizados que abarcan elasticidad compresible e incompresible

Se presenta una familia de principios variacionales parametrizados, con cinco campos independientes, que pueden abarcar hiperelasticidad compresible e incompresible. Los campos independientes son tensiones medias (presiones) y desviadoras, deformaciones medias y desviadoras, y desplazamientos. Con una selección adecuada de los parámetros y de la descomposición de tensiones y desplazamientos, el funcional se reduce a los derivados previamente por Atluri Reissner, Herrmann, y Franca.Peer Reviewe

Principios variacionales parametrizados para elasticidad micropolar

Se presenta un principio variacional parametrizado de seis campos para elasticidad lineal micropolar. Los campos independientes son tensiones simétricas y antisimétricas, deformaciones simétricas y antisimétricas, rotaciones micropolares y desplazamientos. El funcional del principio se carac.teriza por seis parámetros libres. Se examina la conexión entre esta formulación y los funcionales con relajación de simetría de tensiones propuestas por Reissner y Hughes- Brezzi para elasticidad convencional. Se demuestra que los funcionales de Hughes-Brezzi son casos especiales del funcional parametrizado, pero los funcionales de Reissner no lo son. Los funcionales de Hughes-Brezzi pueden interpretarse como una regularización (estabilización consistente) de los funcionales de Reissner que coloca a éstos dentro del marco de elasticidad micropolar.Peer Reviewe

Unificación paramétrica del análsis estructural: formulación clásica y elementos finitos mixtos

En este artículo los conceptos y métodos previamente desarrollados para Principios Variacionales Parametrizados (PVPs) se extienden al Análisis Matricial de Estructuras (AME). Los parámetros libres aparecen como factores de peso de las ecuaciones discretizadas. Combinando esta idea con técnicas de manipulación de matrices se obtiene un espectro continuo de ecuaciones supermatriciales. Dando valores numéricos a los parámetros se generan métodos específicos de solución. Varios de estos métodos son bien conocidos, mientras que otros son oscuros o nuevos. Este procedimiendo se aplica primero al clásico análisis matricial de entramados y pórticos, seguido por el estudio de una clase importante de elementos finitos generados por un PVP mixto con tres parámetros libres, que tienen desplazamientos nodales como grados de libertad conectados. Una ventaja de este desarrollo "descendiente" de esquemas de solución es la unificación y clasificación sistemática de métodos aparentemente desconectados. Adicionalmente, la cuestión de dualidad entre representaciones en el espacio de variación y el espacio nulo se clarifica completamente.In this article concepts and techniques from the field of Parametrized Variatiorial Principles (PVPs) are extended to Matrix Structural Analysis (MSA). Free parameters are used as weighting factors of governing discrete equations. Combining this idea with mati-ix manipulation techniques yields a continuous spectrum of supermatrix equations. Setting parameters to numerical values provides specific solution methods, some of which are well known whereas others are obscure or new. This approach is applied to the classical MSA of truss and framework structures as well as to the important class of displacement-connected finite element models generated by a mixed PVP with three free parameters. The main advantage of this "top down" derivation of solution schemes is the unification of seemingly disjoint methods for classification purposes. In addition, the question of duality between range-space and null-space representations is clqrified once and for all.Peer Reviewe