Octree-based hexahedral mesh generation for viscous flow simulations (original) (raw)
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Octree-based generation of hexahedral element meshes
1996
We present a new algorithm for the generation of hexahedral element meshes. The algorithm starts with an octree discretization of the interior of the input object which is converted to a conforming hexahedral element mesh. Then the isomorphism technique 9] is used to adapt the mesh to the object boundary. keywords. hexahedra, mesh generation, octree 1 Introduction The last decades have seen immense progress in the development of numerical algorithms for the simulation of technical and physical processes. Finite element, nite di erence and nite volume methods are now routinely used in engineering. Therefore interest has grown in reducing simulation turnaround time, and the development of powerful, easy-to-use mesh generation programs has become an important issue. Much work has been done on algorithms for the generation of triangular, quadrilateral and tetrahedral element meshes. The state of the art is reviewed in 1], online information can be found in 2] and 3]. Mesh generators of this type have been integrated in many commercial programs. Unfortunately, the situation is worse in the eld of hex meshing. Most existing programs use mapped-meshing and multiblock techniques which require much user interaction and are therefore very time-consuming. Algorithms for the automatic generation of hexahedral element meshes have come up only recently, in essence the following techniques are used:
Parallel octree-based hexahedral mesh generation for eulerian to lagrangian conversion
2010
Computational simulation must often be performed on domains where materials are represented as scalar quantities or volume fractions at cell centers of an octree-based grid. Common examples include bio-medical, geotechnical or shock physics calculations where interface boundaries are represented only as discrete statistical approximations. In this work, we introduce new methods for generating Lagrangian computational meshes from Eulerian-based data. We focus specifically on shock physics problems that are relevant to ASC codes such as CTH and Alegra. New procedures for generating all-hexahedral finite element meshes from volume fraction data are introduced. A new primal-contouring approach is introduced for defining a geometric domain. New methods for refinement, node smoothing, resolving non-manifold conditions and defining geometry are also introduced as well as an extension of the algorithm to handle tetrahedral meshes. We also describe new scalable MPI-based implementations of these procedures. We describe a new software module, Sculptor, which has been developed for use as an embedded component of CTH. We also describe its interface and its use within the mesh generation code, CUBIT. Several examples are shown to illustrate the capabilities of Sculptor. Presto Sandias in-house explicit, transient, dynamic finite-element software package. Sculptor New CAMAL software component developed as part of this work to generate hexahedral and tetrahedral meshes from volume fraction data. Spyplot Data manipulation and visualization module used by CTH. Volume fraction data can be dumped from Spyplot module for use in Sculptor.
Concurrency and Computation: Practice and Experience, 2012
We show a parallel implementation and performance analysis of a linear octree-based mesh generation scheme designed to create reasonable-quality, geometry-adapted unstructured hexahedral meshes automatically from triangulated surface models. We present algorithms for the construction, 2:1 balancing and meshing large linear octrees on supercomputers. Our scheme uses efficient computer graphics algorithms for surface detection, allowing us to represent complex geometries. An isogranular analysis demonstrates good scalability. Our implementation is able to execute the 2:1 balancing operations over 3.4 billion octants in less than 10 s per 1.6 million octants per CPU core. .
Unstructured mesh generation for 3D viscous flow
29th AIAA, Fluid Dynamics Conference, 1998
In this paper we review the procedures which are currently available for the generation of unstructured meshes suitable for use in the simulation of high Reynolds number viscous ows. For such simulations, computational e ciency generally dictates the requirement for the use of highly stretched cells in viscous dominated regions. Meshes of this type cannot be directly generated by the classical unstructured mesh generation procedures and, therefore, special techniques need to be devised to deal with these highly anisotropic grids. In this context, this paper will consider hybrid structured/unstructured meshing procedures and also truly unstructured approaches, including a directional mesh re nement algorithm.
Octree-based reasonable-quality hexahedral mesh generation using a new set of refinement templates
International Journal for Numerical Methods in Engineering, 2009
An octree-based mesh generation method is proposed to create reasonable-quality, geometry-adapted unstructured hexahedral meshes automatically from triangulated surface models without any sharp geometrical features. A new, easy-to-implement, easy-to-understand set of refinement templates is developed to perform local mesh refinement efficiently even for concave refinement domains without creating hanging nodes. A buffer layer is inserted on an octree core mesh to improve the mesh quality significantly. Laplacian-like smoothing, angle-based smoothing and local optimization-based untangling methods are used with certain restrictions to further improve the mesh quality. Several examples are shown to demonstrate the capability of our hexahedral mesh generation method for complex geometries.
An octree structured finite volume based solver
Applied Mathematics and Computation, 2020
The present work describes the development of a parallel distributed-memory implementation, of an octree data structure, linked to an adaptive cartesian mesh to solve the Navier-Stokes equations. The finite volume method was used in the spatial discretization where the advective and diffusive terms were approximated by the central differences method. The temporal discretization was accomplished using the Adams-Bashforth method. The velocity-pressure coupling is done using the fractional-step method of two steps. Moreover, all simulated results were obtained using a external solver for the Poisson equation, from the pressure correction, in the fractional step method. Results are presented both for adaptive octree mesh and for a mesh without refinement. These were determined in the verification and validation processes for the present computational code. Finally, we consider the simulations for the problems of a laminar jet and the lid-driven cavity flow. Numerical results are compared with numerical and experimental data.
Free surface flow modelling on dynamically refined hexahedral meshes
Russian Journal of Numerical Analysis and Mathematical Modelling, 2008
An efficient method for modelling incompressible free surface flows is presented. The method unites the projection method for solving the Navier-Stokes equations and the particle level set method for free surface evolution. The method uses adaptively refined hexahedral meshes built on an enhanced octree data structure.
Hybrid Grid Generation for Viscous Flow Simulations in Complex Geometries
In this paper, we present a hybrid grid generation approach for viscous flow simulations by marching a surface triangulation on viscous walls along certain directions. Focuses are on the computing strategies used to determine the marching directions and distances since these strategies determine the quality of the resulting elements and the reliability of the meshing procedure to a large extent. With respect to marching direction, three strategies featured with different levels of efficiencies and robustness performance are combined to compute the initial normals at front nodes to balance the trade-off between efficiency and robustness. A novel weighted strategy is used in the normal smoothing scheme, which evidently reduce the possibility of early stop of front generation at complex corners. With respect to marching distances, the distance settings at concave and/or convex corners are locally adjusted to smooth the front shape at first; a further adjustment is then conducted for fr...
Unstructured mesh generation including directional refinement for aerodynamic flow simulation
Finite Elements in Analysis and Design, 1997
A method for generating directionally refined unstructured tetrahedral meshes is presented. The motivation is the need to efficiently mesh the complex computational domains which are frequently encountered in aerospace applications. In this context, the method is applicable to the construction of meshes suitable for the simulation of inviscid and viscous aerodynamic flows. Minimum user intervention is required and the user specified stretching distribution is achieved by locally modifying an existing mesh. The interfacing of the mesh generation procedure with available geometry modellers is discussed and certain implementation issues are also addressed. Examples which illustrate the performance of the proposed methodology are presented.
Development of Octree-Based High-Quality Mesh Generation Method for Biomedical Simulation
Lecture Notes in Computer Science, 2018
This paper proposes a robust high-quality finite element mesh generation method which is capable of modeling problems with complex geometries and multiple materials and suitable for the use in biomedical simulation. The previous octree-based method can generate a high-quality mesh with complex geometries and multiple materials robustly allowing geometric approximation. In this study, a robust mesh optimization method is developed combining smoothing and topology optimization in order to correct geometries guaranteeing element quality. Through performance measurement using sphere mesh and application to HTO tibia mesh, the validity of the developed mesh optimization method is checked.