Free-form Grid Generation Methods From Point Cloud

Free-form spatial grid structure is the grid structure that has no analytic expression and its forms can change in any way. The grid generation of this kind of structure is difficult because of the characterics of its various and free forms. This paper proposed a new method to generate grids from point cloud which developed the existing methods of grid generation and grid optimization.Based on the existing research, this paper summarized the applications of reverse modeling on free-form grid structures. An overview of the method of grid generation of point cloud, feature detection of point cloud and grid optimization is given.The quadrilateral grid-generation is developed based on3D point cloud. The Paving Method widely used in FEM is applied. An effective way to search for the K nearest neighboring points of the cloud point is stated and the way to detect point cloud boundary and calculate normals of points is introduced. The strategy of creating new nodes when advancing fronts and closure detection is perfected and finally develop the program which can be applied to generate grids from point cloud.The detection and extraction of point cloud is the important funmental of grid generation. This paper employed the curvature as the standard to detect sharp points and elaborated the fundamentals and necessary steps.After extracting the sharp points from point cloud, the grid optimization method reserving features considering internal boundaries and point constraints is researched.The grid quality criteria is summarized. Two steps to optimize the grids are put forward including topological optimization and geometry optimization. The topological optimization can improve local grid quality while the Laplacian optimization can improve overall grid quality. In the end, examples are proposed to show the quality improvement of grids after grid optimization while reserving features.A program to generate quadrilateral meshes from point cloud and optimize grids reserving features is developed based on the above theory and methods. This program can generate girds effectively.This paper summarized the existing research and concluded three different approaches to generate grids of free-form structures. A discussion and categorization of the fundamental methods currently in use to generate grids of free-form structures is also proposed. The program developed by our team is mainly composed of four modules including surface reconstruction mudule, grid generation from surface module, grid generation from point cloud and grid evalution module. Optimization is also conducted to make the proram more user-friendly and operating manual is composed to help the users to use th program.By theoretical derivation and the algorithms mentioned above, a grid generation program for free-form grid structures is developed. The program is proved by examples to be feasible and effective and can provide technical support for engineering applications. In the end, conclusions and problems to be solved are put forward and discussed.