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[en] The success of a computational method depends on the solution algorithm and mesh generation techniques. cell distributions are needed, which allow the solution to be calculated over the entire body surface with sufficient accuracy. to handle the mesh generation for multi-connected region such as multi-element bodies, the unstructured finite volume method will be applied. the advantages of the unstructured meshes are it provides a great deal more flexibility for generating meshes about complex geometries and provides a natural setting for the use of adaptive meshing. the governing equations to be discretized are inviscid and rotational euler equations. Applications of the method will be evaluated on flow around single and multi-component bodies
[en] The boundary layer of a finite domain [ a, b ] covers mesoscopic lateral neighborhoods, inside [ a, b ], of the endpoints a and b. The correct diagnostic of the integrand behavior at a and b, based on its sampling inside the boundary layer, is the first from a set of hierarchically ordered criteria allowing a priori Bayesian inference on efficient mesh generation in automatic adaptive quadrature.
[en] Fast, effective monitoring following airborne releases of toxic substances is critical to mitigate risks to threatened population areas. Wireless sensor nodes at fixed predetermined locations may monitor such airborne releases and provide early warnings to the public. A challenging algorithmic problem is determining the locations to place these sensor nodes while meeting several criteria: 1) provide complete coverage of the domain, and 2) create a topology with problem dependent node densities, while 3) minimizing the number of sensor nodes. This manuscript presents a novel approach to determining optimal sensor placement, Advancing Front mEsh generation with Constrained dElaunay Triangulation and Smoothing (AFECETS) that addresses these criteria. A unique aspect of AFECETS is the ability to determine wireless sensor node locations for areas of high interest (hospitals, schools, high population density areas) that require higher density of nodes for monitoring environmental conditions, a feature that is difficult to find in other research work. The AFECETS algorithm was tested on several arbitrary shaped domains. AFECETS simulation results show that the algorithm 1) provides significant reduction in the number of nodes, in some cases over 40%, compared to an advancing front mesh generation algorithm, 2) maintains and improves optimal spacing between nodes, and 3) produces simulation run times suitable for real-time applications
[en] Recently developed porous body approach codes such as SPACE and CUPID require a CAD system to estimate the porosity. Since they use the unstructured mesh and they also require reliable mesh generation system. The combination of CAD system and mesh generation system is necessary to cope with a large number of cells and the complex fluid system with structural materials inside. In the past, a CAD system Pro/Engineer and mesh generator Pointwise were evaluated for this application. But, the cost of those commercial CAD and mesh generator is sometimes a great burden. Therefore, efforts have been made to set up a mesh generation system with open source programs. The evaluation of the TetGen has been made in focusing the application for the polyhedral mesh generation. In this paper, SALOME will be described for the efforts to combine TetGen with it. In section 2, brief introduction will be made on the CAD and mesh generation capability of SALOME and Tetgen. SALOME and TetGen codes are being integrated to construct robust polyhedral mesh generator. Procedures to merge boundary faces and to cut concave cells are developed to remove concave cells to get final convex polyhedral mesh. Treating the internal boundary face, i.e. non-manifold face will be the next task in the future investigation
[en] Currently, incremental algorithms may be seen as the lowest-cost computational methods to generate Delaunay tessellations in several point distributions. In this work, eight point-insertion sequences in incremental algorithms for generating Delaunay tessellations are evaluated. More specifically, four point-insertion sequences in incremental algorithms for generating Delaunay tessellations are proposed: with orders given by the red–black tree with in-order and level-order traversals, spiral ordering, and H-indexing. These four incremental algorithms with such sequences are compared with four incremental algorithms with point-insertion orders given by the following sequences: the Hilbert and Lebesgue curves, cut-longest-edge kd-tree, and random order. Six 2-D and seven 3-D point distributions are tested, with sets ranging from 25,000 to 8,000,000 points. The results of computational and storage costs of these eight algorithms are analyzed. It follows that the incremental algorithm with a point-insertion sequence in the order given by the cut-longest-edge kd-tree shows the lowest computational and storage costs of the sequences tested.
[en] A general introduction of TetGen will be made in section 2. The important properties of it will be presented. A detailed procedure to apply TetGen to produce the polyhedral mesh will be described in section 3. Several examples are shown in section 4. Conclusions are made in section 5. A procedure to generate polyhedral mesh is devised for the TetGen code using the internal boundaries. The Gabiel property of TetGen code that Voronoi regions generated with this procedure can be used as polyhedral cells. ParaFoam will be a candidate for the post-processing tool. An interfacing program between TetGen and ParaFoam is being developed. A major advantage of polyhedral cells is that they have many neighbors (typically of order 10), so gradients can be much better approximated (using linear shape functions and the information from nearest neighbors only) than is the case with tetrahedral cells. Even along wall edges and at corners, a polyhedral cell is likely to have a couple of neighbors, thus allowing for a reasonable prediction of both gradients and local flow distribution. The fact that more neighbors means more storage and computing operations per cell is more than compensated by a higher accuracy. Polyhedral cells are also less sensitive to stretching than tetrahedral cells. Smart grid generation and optimization techniques offer limitless possibilities: cells can automatically be joined, split, or modified by introducing additional points, edges and faces. Indeed, substantial improvements in grid quality are expected in the future, benefiting both solver efficiency and accuracy of solutions. Most of the commercial computational fluid dynamics (CFD) codes have the capability to accept the polyhedral mesh. Even the recently developed safety analysis code such as CUPID and SPACE have the same capability. But they can't be fully utilized because there not many robust polyhedral mesh generator available in the world. Only STAR-CD mesh generator provides the capability of generating polyhedral mesh. In principle, any Delaunay tetrahedral mesh generator can be used to generate polyhedral mesh using the duality of the Delaunay cell and the Voronoi region. But there are two practical problems to be resolved before using the duality principle. The genuine Delaunay cells can produce the Voronoi regions but these region may cross the boundary faces. Crossing boundary faces make it difficult to control the shape of the Voronoi regions. Another problem is arisen from the concave boundary faces. Any concave vertex point will produce the concave surface that cover the Voronoi cells. In this paper, open source program TetGen, will be investigated to see whether it can be used to generate polyhedral mesh circumventing the above mentioned problems
[en] This paper is concerned with the discretization error in the finite element method. The reliability of any finite element mesh is checked from a simple criteria for the linear isotropic case. This criteria is easy to implement on a computer; its evolution is analyzed with a usual subdivision of the F.E. mesh
[fr]On propose un critere de jugement simple, ''a posteriori'' des resultats obtenus par la methode des elements finis dans le cas statique lineaire et pour un materiau isotrope. La methode s'applique a tout type d'element fini. Elle peut etre facilement implantee dans n'importe quel code. L'evolution de ce critere en fonction de la densite du maillage est analysee a partir d'une methode classique de subdivision des elements
[en] A new method for lessening skew in mapped meshes is presented. This new method involves progressive subdivision of a surface into loops consisting of four sides. Using these loops, constraints can then be set on the curves of the surface, which will propagate interval assignments across the surface, allowing a mesh with a better skew metric to be generated