Browsing by Subject "Numerical grid generation (Numerical analysis)"
Now showing 1 - 4 of 4
- Results Per Page
- Sort Options
Item Hybrid prismatic/tetrahedral grid generation for complex 3-D geometries(1992) Ward, Steven Bryan; Not availableAn algorithm for the generation of hybrid prismatic/tetrahedral grids for complex 3-D geometries is presented. The method marches a triangulated surface grid away from the body to form a semi-unstructured prismatic grid. The outermost layer of this grid is then used in an octree refinement scheme to produce a tetrahedral grid. The tetrahedra are linked directly to the nodes of the outermost prismatic layer. The resulting hybrid grid is suitable for performing Navier-Stokes calculations in the viscous region (prismatic grid) near the body and Euler calculations in the inviscid region (tetrahedral grid) away from the body. The hybrid grid approach provides considerable flexibility in generating meshes around complex 3-D geometries. Other advantages of the developed grid generator are its speed, simplicity, direct control of grid orthogonality and spacing, as well as its generality for treatment of 3-D geometries. An F-16A aircraft was considered in the applications in order to investigate efficiency and to demonstrate robustness of the method in handling relatively complex topologies. Grid generation time for the entire aircraft domain was less than 10 minutes on a Sun workstation running at 2 mflops.Item A new incompressible Navier-Stokes method with general hybrid meshes and its application to flow/structure interactions(2005) Ahn, Hyung Taek; Dawson, Clinton N.; Kallinderis, Y.A new incompressible Navier-Stokes method is developed for unstructured general hybrid meshes which contain all four types of elements in a single computational domain, namely tetrahedra, pyramids, prisms, and hexahedra. Various types of general hybrid meshes are utilized and appropriate numerical flux computation schemes are presented. The artificial compressibility method with a dual time-stepping scheme is used for the time-accurate solution of the incompressible Navier-Stokes equations. The Spalart-Allmaras turbulence model is also presented in the dual time-stepping form and is solved in a strongly coupled manner with the incompressible Navier-Stokes equations. The developed scheme is applied to the study of the inflow turbulence effect on the hydrodynamic forces exerted on a circular cylinder. In order to accommodate possible structural and mesh motion, the method is extended to the arbitrary Lagrangian-Eulerian (ALE) frame of reference. The geometric conservation law is satisfied with the proposed ALE scheme in moving mesh simulations. The developed ALE scheme is applied to the vortex induced vibration of a cylinder. A strong coupling of fluid and structure interaction based on the predictor-corrector method is presented. The superior stability property of the strong coupling is demonstrated by a comparison with the weak coupling. Finally, the developed methods are parallelized for distributed memory machines using partitioned general hybrid meshes and an efficient parallel communication scheme to minimize CPU time.Item Serial and parallel dynamic adaptation of general hybrid meshes(2008-08) Kavouklis, Christos; Becker, E. B.; Kallinderis, J.Item A variational grid optimization method based on a local cell quality metric(2005) Branets, Larisa Vladimirovna; Carey, Graham F.Computational grid optimization, correction, improvement and remeshing techniques have become increasingly important as the application problem and domain complexity in creases. It is well recognized that distorted elements may degrade accuracy of finite element and finite volume simulations or cause them to fail. Hence, automatically generated grids containing millions of cells, created to fit a domain with complex geometry and adapt to features of different scales, often require correction before they can be effectively used for a numerical simulation. In this work a new variational grid smoothing formulation is devel oped and an extensive study of its mathematical properties, applicability and limitations is performed. The approach is based on a local cell quality metric, which is introduced as a function of the Jacobian matrix of the fundamental map from the reference cell. The math ematical properties of the local quality measure are analyzed and new theoretical results are proved. The grid improvement strategy is formulated as an optimization problem and a modified Newton scheme is used in the optimization algorithm which is implemented in a new software package. The effectiveness of the algorithm is tested on several representative v grids and for different transport application problems. The resulting methodology is applicable to general unstructured hybrid meshes in 2 and 3 dimensions. It overcomes several difficulties encountered by other smoothing algo rithms, such as effects of changing valence (number of cells sharing the same node). The formulation includes extensions to unfolding, adaptive redistribution, treatment of tangen tially “sliding” boundary nodes and hanging nodes, as well as elements with curved edges or surfaces, commonly used to provide better fit of domain boundaries or interfaces. The above techniques are applied to a set of mathematically representative prob lems including problems of geometric design as well as transport processes with the aim of studying the effect of the smoothing approach on the solvability and accuracy. Both 2D and 3D test problems are considered, including a moving mesh Lagrangian formulation for a fluid interface problem, non-Newtonian blood flow in curved branched pipes and a brain mapping/deformation problem. The associated numerical simulations are made on both serial and parallel PC cluster systems.