| Finite element mesh technology is one of the key technologies in finite element analysis for sheet metal forming. Feature extraction, local modification and data segmentation on shell meshes are investigated deeply in this paper. The main research contents are as follows:(1) Algorithms of feature extraction on shell meshes are studied. A new algorithm is presented for feature line extraction through controlling the angle deviation of element normal. A method is presented to extract rounding feature on shell meshes, According to curvature characteristic of rounding surface. By means of curvature estimation of vertices, arc identification and arc grouping, a set of profile curves are computed to describe a rounding feature. Meanwhile, a rounding mesh is extracted from the mesh model.(2) Approaches of feature-based local modification on shell meshes are studied. Profile curves of a rounding surface are calculated along a feature line with a given radius. Then inner elements of a rounding mesh is created with these profile curves, and sewn with the original mesh which is pre-trimmed. A feature-based mesh modification method is proposed for existing rounding feature. After direct manipulation of radius, constant or variable radius area in mesh model can be modified quickly and exactly. Using this method, rounding shape of a part or die can be directly modified on shell meshes for finite element analysis.(3) Data segmentation on shell meshes is studied. A data segmentation algorithm is developed through partition growing based on rounding feature extracted. Then the partitions can be optimized by several methods such as combining small partitions into adjacent one, decomposing cane partitions into neighbors and smoothing the borders. The final partitions coincide with the feature of objects. It is the foundation for surface reconstruction and mesh re-meshing.All the algorithms proposed can apply to hybrid meshes, and lots of experimental results demonstrate them. |
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