Arne S. Gullerud

Presto User's Guide Version 1.05

Presto is a Lagrangian, three-dimensional explicit, transient dynamics code for the analysis of solids subjected to large, suddenly applied loads. Presto is designed for problems with large deformations, nonlinear material behavior, and contact. There is a versatile element library incorporating both continuum and structural elements. The code is designed for a parallel computing environment. This document describes the input for the code that gives users access to all of the current functionality in the code. Presto is built in an environment that allows it to be coupled with other engineering analysis codes. The input structure for the code, which uses a concept called scope, reflects the fact that Presto can be used in a coupled environment. This guide describes the scope concept and the input from the outermost to the innermost input scopes. Within a given scope, the descriptions of input commands are grouped based on code functionality. For example, all material input command lines are described in a section of the users guide for all of the material models in the code.

MPI-based implementation of a PCG solver using an EBE architecture and preconditioner for implicit, 3-D finite element analysis

Abstract This work describes a coarse-grain parallel implementation of a linear preconditioned conjugate gradient solver using an element-by-element architecture and preconditioner for computation. The solver, implemented within a nonlinear, implicit finite element code, uses an MPI-based message-passing approach to provide portable parallel execution on shared, distributed, and distributed-shared memory computers. The flexibility of the element-by-element approach permits a dual-level mesh decomposition; a coarse, domain-level decomposition creates a load-balanced domain for each processor for parallel computation, while a second level decomposition breaks each domain into blocks of similar elements (same constitutive model, order of integration, element type) for fine-grained parallel computation on each processor. The key contribution here is a new parallel implementation of the Hughes–Winget (HW) element-by-element preconditioner suitable for arbitrary, unstructured meshes. The implementation couples an unstructured dependency graph with a new balanced graph-coloring algorithm to schedule parallel computations within and across domains. The code also includes the diagonal preconditioner and a modern parallel (threaded) sparse direct solver for comparison. Three example problems with up to 158,000 elements and 180,000 nodes analyzed on an SGI/Cray Origin 2000 illustrate the parallel performance of the algorithms and preconditioners. Analyses with varying block sizes illustrate that the two-level decomposition improves overall execution speed with the block size tuned for the cache memory architecture of the executing platform. This implementation of the HW preconditioner shows reasonable parallel efficiency – typically 80% on 48 processors. Efficiency for the diagonal preconditioner is also high, with total speedups reaching 86% on 48 CPUs. Calculation of the tangent element stiffnesses shows superlinear speedups for each of the test problems, while the computation of strains/stresses/residual forces shows 80% parallel efficiency on 48 processors.

ACME: Algorithms for Contact in a Multiphysics Environment API Version 1.3

An effort is underway at Sandia National Laboratories to develop a library of algorithms to search for potential interactions between surfaces represented by analytic and discretized topological entities. This effort is also developing algorithms to determine forces due to these interactions for transient dynamics applications. This document describes the Application Programming Interface (API) for the ACME (Algorithms for Contact in a Multiphysics Environment) library.

Virtual Simulation of the Effects of Intracranial Fluid Cavitation in Blast-Induced Traumatic Brain Injury

A microscale model of the brain was developed in order to understand the details of intracranial fluid cavitation and the damage mechanisms associated with cavitation bubble collapse due to blast-induced traumatic brain injury (TBI). Our macroscale model predicted cavitation in regions of high concentration of cerebrospinal fluid (CSF) and blood. The results from this macroscale simulation directed the development of the microscale model of the superior sagittal sinus (SSS) region. The microscale model includes layers of scalp, skull, dura, superior sagittal sinus, falx, arachnoid, subarachnoid spacing, pia, and gray matter. We conducted numerical simulations to understand the effects of a blast load applied to the scalp with the pressure wave propagating through the layers and eventually causing the cavitation bubbles to collapse. Collapse of these bubbles creates spikes in pressure and von Mises stress downstream from the bubble locations. We investigate the influence of cavitation bubble size, compressive wave amplitude, and internal bubble pressure. The results indicate that these factors may contribute to a greater downstream pressure and von Mises stress which could lead to significant tissue damage.Copyright

Presto User's Guide Version 2.6

Presto is a Lagrangian, three-dimensional explicit, transient dynamics code for the analysis of solids subjected to large, suddenly applied loads. Presto is designed for problems with large deformations, nonlinear material behavior, and contact. There is a versatile element library incorporating both continuum and structural elements. The code is designed for a parallel computing environment. This document describes the input for the code that gives users access to all of the current functionality in the code. Presto is built in an environment that allows it to be coupled with other engineering analysis codes. The input structure for the code, which uses a concept called scope, reflects the fact that Presto can be used in a coupled environment. This guide describes the scope concept and the input from the outermost to the innermost input scopes. Within a given scope, the descriptions of input commands are grouped based on code functionality. For example, all material input command lines are described in a section of the users guide for all of the material models in the code.

Computational Assessment of Brittle Fracture in Glass-to-Metal Seals

Glass-to-metal seals are widely used in engineering applications, but are often plagued by cracking and loss of hermeticity despite design efforts to avoid these problems. Standard computational approaches typically rely on under-refined meshes and rule-of-thumb approaches that are not always effective. This paper investigates improvements to current practice in glass-to-metal seal design. First, material models with more extensive temperature dependence are used to enhance the accuracy of residual stress prediction. Second, a Weibull-statistics approach is adopted for the prediction of the likelihood of failure. These approaches are then applied to a simplified seal geometry. The paper demonstrates that the application of these methods, especially the Weibull-statistics approach, have difficulties that need to be addressed before this proposed set of approaches can be effectively used for seal design. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.© 2010 ASME

Presto User's Guide 2.7 (Version 1)

Presto is a Lagrangian, three-dimensional explicit, transient dynamics code for the analysis of solids subjected to large, suddenly applied loads. Presto is designed for problems with large deformations, nonlinear material behavior, and contact. There is a versatile element library incorporating both continuum and structural elements. The code is designed for a parallel computing environment. This document describes the input for the code that gives users access to all of the current functionality in the code. Presto is built in an environment that allows it to be coupled with other engineering analysis codes. The input structure for the code, which uses a concept called scope, reflects the fact that Presto can be used in a coupled environment. This guide describes the scope concept and the input from the outermost to the innermost input scopes. Within a given scope, the descriptions of input commands are grouped based on code functionality. For example, all material input command lines are described in a section of the user’s guide for all of the material models in the code.

Solution Verification of Frictional Contact Problems in Explicit Transient Dynamics

Contact is a commonly used capability i n explicit transient dynamics codes. Yet the quality of the solution to these problems is often unknown. Typically, users are left to determine if they “look acceptable.” In this talk we present the solution verification efforts underway for frictional con tact problems in PRESTO, a massively parallel large deformation transient dynamics code developed at Sandia National Laboratories. It is common practice in explicit transient dynamics to seek a balance between computational efficiency and accuracy (especia lly on massively parallel computers). In this presentation, the constrained set of fully discretized equations of motion is examined and various approaches for verifying solution accuracy of them are discussed. A set of frictional contact verification prob lems will be presented that give results of our investigations, including solution and mesh converge studies. I. Introduction HIS paper describes ongoing efforts in the verification and validation of frictional contact in large deformation solid mechanics problems with dynamic effects. Such explicit codes are now commonly used for a variety of applications, especially those involving contact/impact, contact with sliding, and contact with frictional sliding using some interface response (typically Coulomb f riction). Central difference time integration is the time integrator of choice for most of thee problems because of its simplicity and efficiency. Over the many years that explicit transient dynamics codes have been used, their efficiency has been the domi nant focus. It is common practice to seek a balance between computational efficiency and accuracy, especially on massively parallel computers. Here, we wish to explore the quality of explicit solutions, particularly those involving frictional contact. Spe cifically, in this paper we present the solution verification efforts underway (and challenges) for frictional contact problems in Presto, a massively parallel large deformation transient dynamics code developed at Sandia National Laboratories. We begin with an examination of the fully discretized equations of motion and then look at various approaches for verifying solution accuracy of them. Finally, we conclude with a set of frictional contact verification problems used to present the results of our ong oing investigation, including solution and mesh convergence studies.

ACME Algorithms for Contact in a Multiphysics Environment API Version 0.3a

An effort is underway at Sandia National Laboratories to develop a library of algorithms to search for potential interactions between surfaces represented by analytic and discretized topological entities. This effort is also developing algorithms to determine forces due to these interactions for transient dynamics applications. This document describes the Application Programming Interface (API) for the ACME (Algorithms for Contact in a Multiphysics Environment) library.