Publications

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Researchers review the challenges and opportunities that we are facing in the modeling and simulation of additive manufacturing processes for metals and the predictive representation of their mechanical performance at the different scales. They highlight the current modeling efforts taking place at the US Department of Energy National Nuclear Security Administration (NNSA) Laboratories, such as process modeling, microstructure modeling, properties modeling, performance and topology and process optimization. All these various modeling developments at different scales and regimes are necessary to move toward an integrated computational approach of process-structure-properties-performance that will ultimately enable the engineering and optimization of materials to specific performance requirements. Truchas, a continuum thermo-mechanical modeling tool originally designed for the simulation of casting processes, is being extended to simulate directed energy deposition additive manufacturing processes.

Welcome to CUBIT, the Sandia National Laboratory automated mesh generation toolkit. CUBIT is a full-featured software toolkit for robust generation of two- and three-dimensional finite element meshes (grids) and geometry preparation. Its main goal is to reduce the time to generate meshes, particularly large hex meshes of complicated, interlocking assemblies. It is a solidmodeler based preprocessor that meshes volumes and surfaces for finite element analysis.

CUBIT is a full-featured software toolkit for robust generation of two- and three-dimensional finite element meshes (grids) and geometry preparation. Its main goal is to reduce the time to generate meshes, particularly large hex meshes of complicated, interlocking assemblies. It is a solid-modeler based preprocessor that meshes volumes and surfaces for finite element analysis. Mesh generation algorithms include quadrilateral and triangular paving, 2D and 3D mapping, hex sweeping and multi-sweeping, tetrahedral meshing, and various special purpose primitives. CUBIT contains many algorithms for controlling and automating much of the meshing process, such as automatic scheme selection, interval matching, sweep grouping, and also includes state-of-the-art smoothing algorithms.

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The challenges of simulation streamlining and automation continue. The need for analysis verification, reviews, quality assurance, pedigree, and archiving are strong. These automation and archival needs can alternate between competing and complementing when determining how to improve the analysis environment and process. The needs compete for priority, resource allocation, and business practice importance. Likewise, implementation strategies of both automation and archival can swing between rather local work groups to more global corporate initiatives. Questions abound about needed connectivity (and the extent of this connectivity) to various CAD systems, product data management (PDM) systems, test data repositories and various information management implementations. This is a complex set of constraints. This presentation will bring focus to this complex environment through sharing experiences. The experiences are those gleaned over years of effort at Sandia to make reasonable sense out of the decisions to be made. It will include a discussion of integration and development of home grown tools for both automation and archival. It will also include an overview of efforts to understand local requirements, compare in-house tools to commercial offerings against those requirements, and options for future progress. Hopefully, sharing this rich set of experiences may prove useful to others struggling to make progress in their own environments.

The generation of all-hexahedral finite element meshes has been an area of ongoing research for the past two decades and remains an open problem. Unconstrained plastering is a new method for generating all-hexahedral finite element meshes on arbitrary volumetric geometries. Starting from an unmeshed volume boundary, unconstrained plastering generates the interior mesh topology without the constraints of a pre-defined boundary mesh. Using advancing fronts, unconstrained plastering forms partially defined hexahedral dual sheets by decomposing the geometry into simple shapes, each of which can be meshed with simple meshing primitives. By breaking from the tradition of previous advancing-front algorithms, which start from pre-meshed boundary surfaces, unconstrained plastering demonstrates that for the tested geometries, high quality, boundary aligned, orientation insensitive, all-hexahedral meshes can be generated automatically without pre-meshing the boundary. Examples are given for meshes from both solid mechanics and geotechnical applications.

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Unconstrained Plastering is a new algorithm with the goal of generating a conformal all-hexahedral mesh on any solid geometry assembly. Paving[1] has proven reliable for quadrilateral meshing on arbitrary surfaces. However, the 3D corollary, Plastering [2][3][4][5], is unable to resolve the unmeshed center voids due to being over-constrained by a pre-existing boundary mesh. Unconstrained Plastering attempts to leverage the benefits of Paving and Plastering, without the over-constrained nature of Plastering. Unconstrained Plastering uses advancing fronts to inwardly project unconstrained hexahedral layers from an unmeshed boundary. Only when three layers cross, is a hex element formed. Resolving the final voids is easier since closely spaced, randomly oriented quadrilaterals do not over-constrain the problem. Implementation has begun on Unconstrained Plastering, however, proof of its reliability is still forthcoming. © 2005 Springer-Verlag Berlin Heidelberg.

This report describes the progress of the three-dimensional mesh generation research, using plastering, during the 1990 fiscal year. Plastering is a 3-D extension of the two-dimensional paving technique. The objective is to fill an arbitrary volume with hexahedral elements. The plastering algorithm`s approach to the problem is to remove rows of elements from the exterior of the volume. Elements are removed, one level at a time, until the volume vanishes. Special closure algorithms may be necessary at the center. The report also discusses the common development environment and software management issues. 13 refs.

This paper describes the impact of paving, a new automatic mesh generation algorithm, on the analysis portion of the design process. Paving generates an all-quadrilateral mesh in arbitrary 2D geometries. The paving technique significantly impacts the analysis process by drastically reducing the time and expertise requirements of traditional mesh generation. Paving produces a high quality mesh based on geometric boundary definitions and user specified element sizing constraints. In this paper we describe the paving algorithm, discuss varying aspects of the impact of the technique on design automation, and elaborate on current research into 3D all-hexahedral mesh generation. © 1991.