Three-dimensional Finite Element Data Field And Implementation Of Visualization Technology

The visualization techniques play a very important role in finite element analysis. Not only does it reveal to engineers and technicians the significant characteristics of the complicated computing results by visual tools, but also improves and develops efficient computing methods and new strategy based on steering computing. Although two dimensional visualization algorithms have been widely used in the engineering software, most of the advanced 3D methods are now still under research because it hardly meet the real-time requirement of FEM application software due to the complexity and irregularity of 3D solid FEM models and meshes.The thesis is mainly focused on two points: slicing and volume rendering. Some improvement and new algorithms are proposed to improve the image accuracy and interactivity.The main work and the originality of the thesis is listed as follows:1. Volume rendering is a principal method to reveal the distributing characteristic of 3D data set. A direct volume rendering algorithm MS based on Incremental Slicing is proposed in chapter 2. It can deal with multiple types of finite elements. In accordance with the complexity of 3D finite element irregular data field, the concept of element important function and small element compensation algorithm are introduced to give improvement both on the efficiency and image quality. According to the particularity of out-faces in FEM, the geometrical facets and volumes are rendered together in a new hybrid algorithm to improve the clarity and realistic of the image. Linear interpolation introduces more errors due to the nonlinear distribution of FEM data set. A new interpolation method based on the shape function is given to improve the image accuracy. The algorithm also gives consideration to the abnormal elements.2. The clipping of volume is an important problem in the volume rendering application. A Clipping algorithm based on the Stencil test in OpenGL pipeline is proposed to clip the volume with arbitrary convex polyhedra. The rendering time is decreased to the minimum due to the stencil reference combination by using the binary tree. The 3D clipping box and integration of stencil operation between front and back face greatly decreased the unnecessary stencil test and pixel filling.3. Iso-surface is an important method for the visualization of 3D data set. The hybrid rendering method of volume data and iso-surfaces are implemented on the basis of Alpha test of OpenGL. The shelter problem between iso-surfaces and wrong rendering when the iso-surface crossed a hole are analyzed in detail and solved.4. The contour plotting on arbitrary slicing plane is an important method in 3D data-field visualization of FEM analysis. Based on the element-information table, a general slicing algorithm suitable to various types of 3D finite elements is proposed in chapter 5.On the base of the algorithms mentioned above, a visualization software GRAFE-VR for finite element computing was developed to be a subsystem of the Structural FEM Analysis and Optimization Design software - JIFEX. The advantages of the algorithms have been fully proven by several large-scale complicate FEM data sets. They have greatly improved the functions of visualization in the commercial engineering software.