Catálogo de publicaciones - libros

Today, finite element technologies allow engineers to analyze complex assemblies and subsystems. With CPU power constantly increasing, it is not unreasonable to state that the engineer will hope to analyze the whole complex system, such as an entire automobile, in a single study. This study may include parameteric design, result animation, crash analysis, and so on. The traditional mesh data structure, which mainly serves a particular type of mesh algorithm, is far from enough to meet the challenges of tomorrow. This paper mainly focuses on storing, accessing, and manipulating mesh data within the vast scope of the analysis system for multiple purposes, such as meshing generators, solvers, pre- and post-processors, and so on. It details the decision-making put into the design of the ANSYS Corporate Mesh Object, the programming methods used to implement those designs, and future enhancements planned to meet ever-changing requirements.

An advanced Volume-of-Fluid or VOF procedure for locally conservative reconstruction of multi-material interfaces based on volume fraction information in cells of an unstructured mesh is presented in this paper. The procedure employs improved neighbor definitions and topological consistency checks of the interface for computing a more accurate interface approximation. Comparison with previously published results for test problems involving severe deformation of the materials (such as vortex-in-a-box problem) show that this procedure produces more accurate results and reduces the “numerical surface tension” typically seen in VOF methods.

Realization of the full benefits of variable p-version finite elements requires the careful construction of prismatic elements in thin sections. This paper presents a procedure to automatically isolate the thin sections using the points on an approximate medial surface computed by an octree-based algorithm. Using the pairs of triangles associated with medial surface (MS) points, in conjunction with adjacency, classification and distance information, sets of surface triangles that are on opposite face patches in thin sections are identified. Mesh modifications are then executed to match the surface triangulations on the opposite face patches such that prismatic elements can be generated without diagonal edges through the thickness directions.

This paper proposes a framework for generating sizing function in meshing assemblies. Size control is crucial in obtaining a high-quality mesh with a reduced number of elements, which decreases computational time and memory use during mesh generation and analysis. This proposed framework is capable of generating a sizing function based on geometric and non-geometric factors that influence mesh size. The framework consists of a background octree grid for storing the sizing function, a set of source entities for providing sizing information based on geometric and non-geometric factors, and an interpolation module for calculating the sizing on the background octree grid using the source entities. Source entities are generated by performing a detailed systematic study to identify all the geometric factors of an assembly. Disconnected skeletons are extracted and used as tools to measure 3D-proximity and 2D-proximity, which are two of the geometric factors. Non-geometric factors such as user-defined size and pre-meshed entities that influence size are also addressed. The framework is effective in generating a variety of meshes of industry models with less computational cost.

This paper presents a generic approach to generation of surface and volume unstructured meshes for complex free-form objects, obtained by laser scanning. A four-stage automated procedure is proposed for discrete data sets: surface mesh extraction from Delaunay tetrahedrization of scanned points, surface mesh simplification, definition of triangular interpolating subdivision faces, Delaunay volumetric meshing of obtained geometry. The mesh simplification approach is based on the medial Hausdorff distance envelope between scanned and simplified geometric surface meshes. The simplified mesh is directly used as an unstructured control mesh for subdivision surface representation that precisely captures arbitrary shapes of faces, composing the boundary of scanned objects. CAD model in Boundary Representation retains sharp and smooth features of the geometry for further meshing. Volumetric meshes with the MezGen code are used in the combined Finite-Discrete element methods for simulation of complex phenomena within the integrated Virtual Geoscience Workbench environment (VGW).

Elliptic differential equations are derived for the generation of structured meshes and difference equations for the generation of smooth hybrid meshes from metric identity. A parabolic procedure is used to march the solution of the difference equations simultaneously for both types of meshes away from surface patches meshed by quads or triangles. An aerodynamic application for the ONERA M6 wing demonstrates how the blocking at the wing tip is simplified by using both types of meshes instead of a purely structured mesh. On the other hand it is shown that a large number of points can be saved compared to a purely hybrid grid.

Hydrodynamic engineering makes profitably use of numerical simulations which rely on discrete element meshes of the topography. To cope with specific circumstances in river hydraulics, the presented hybrid meshing scheme comprises following proposals: river beds and areas of significant terrain slopes are meshed with regular elements to support user specified edge ratio and element orientation representing flow gradients appropriately; floodplains are represented as irregular triangle meshes, concatenating disconnected regular meshes while warranting high approximation quality. Automatic breakline detection approximates flow relevant changes in topographic gradients and defines borders of different mesh types. This paper presents an enhanced strategy for a terrain feature analysis based on b-spline analysis grids and on an interpolation scheme for breakline points in order to reduce the zigzag property of detected breaklines. This scheme for terrain analysis and meshing functionality is implemented in the open source software tool HybridMesh.

We present a method to decompose an arbitrary 3D piecewise linear complex (PLC) into a constrained Delaunay tetrahedralization (CDT). It successfully resolves the problem of non-existence of a CDT by updating the input PLC into another PLC which is topologically and geometrically equivalent to the original one and does have a CDT. Based on a strong CDT existence condition, the redefinition is done by a segment splitting and vertex perturbation. Once the CDT exists, a practically fast cavity retetrahedralization algorithm recovers the missing facets. This method has been implemented and tested through various examples. In practice, it behaves rather robust and efficient for relatively complicated 3D domains.

An algorithm for quality Delaunay meshing of 2D domains with curved boundaries is presented. The algorithm uses Ruppert’s “corner lopping” heuristic [MR96b:65137]. In addition to admitting a simple termination proof, the algorithm can accept curved input without any bound on the tangent angle between adjoining curves. In the limit case, where all curves are straight line segments, the algorithm returns a mesh with a minimum angle of arcsin ( $${1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}\sqrt 2 $$ ), except “near” input corners. Some loss of output quality is experienced with the use of curved input, but this loss is diminished for smaller input curvature.