Some Researches On Feature-preserving Morphing Design For Autobody Finite Element Model

Analysis-driven-design method with CAD/CAE integration as its core plays an increasingly important role in the design of industrial products. As one of the most representative complex industrial products, design of automobile products incorporates the digital design technology with CAD/CAE integration as its core more deeply and in turn promotes the development of its technology significantly. Along with increasingly intensified competition of global automo-bile industry, it has become a common issue for automobile industry that how to design rapidly new products meeting customer’s demand and promote the research and development ability of autobody on behalf of the automobile industrial core technology level. To shorten the develop-ment cycle and reduce the development cost of industrial products, it is urgent to carry out the independent research and development work of data reuse technology supporting rapid product design with CAD/CAE integration as its core. For this reason, in order to build a CAE-oriented product rapid design system for autobody finite element model with complex geometrical and structural constraints, this dissertation carries on research deeply on some of the key techniques of CAD/CAE integration involved in rapid design and data reuse of autobody finite element model. The main contents of the dissertation are as follows:(1) A design method based on isoparametric free-form morphing is proposed for the rapid design and data reuse of autobody finite element model. Combined with the composite control parametric volume, which consists of a collection of polyhedron elements, such as hexahedron, pentahedron and tetrahedron, the basic function derived from isoparametric transformation is introduced to modify the traditional free-form morphing and then achieve fast computation of morphing design. Taking advantage of the isoparametric transformation and its inverse one, the algorithm avoids the problem of high computational cost of the parametrization of local coordinates. Combined with the free-form morphing framework of image-based driven, it is able to achieve the conceptual design of autobody products and verify the ideas of styling designers. The software module based on the above algorithm, called DCiP-MeshMorpher, is developed on the platform KMAS COMX. It is ease to achieve the data reuse of existing models. Some numerical experiments demonstrate its industrial application value. (2) For the problem of decrease of mesh quality and hindering the downstream applications caused by various operations on models, an approach to mesh optimization based on quad-dominant remeshing is presented. By means of local/global parametrization with the property of best approximate isometric, the original problem is transformed into a2D remeshing one. In the process of mesh conversion, the geometrical or/and structural line features on the original model should be preserved to meet the desired fidelity. Simultaneously, to improve the accuracy of simulation, an offsetting technique was employed to construct the well-shape elements in the vicinity of boundaries and features, the configuration of which most simulation is much more sensitive to. The analysis of experimental results illustrates the effectiveness of the proposed approach.(3) To promote the simulation efficiency of one-step inverse forming, an optimization method based on adaptive mesh strategy is proposed. Considering the geometrical characteristic (e.g. curvature) of model and/or the distribution of these physical variables (such as, thickness, stress, strain and so on) derived from one-step inverse forming integrally, the field of element size reflecting the previous various distributions is constructed with the aid of Riemannian met-ric. Then the adaptive resultant model is obtained. Simultaneously, the geometrical and/or structural line features of the original mesh, such as welding point, a stiffener for reinforcement, forming lines or holes in the interior of model, is preserved in the process of mesh optimization to guarantee the fidelity of optimized model. Numerical examples demonstrate that the pro-posed method reduces the number of degrees of freedom while preserving the desired level of simulation accuracy and improves the simulation efficiency.(4) With respect to the expression and description of continuous curve on surfaces, an ap-proach to adaptive feature-preserving B-spline curve fitting on the surface in the sense of feature sensitive metric is present. In this algorithm, a set of dominant points is selected from the origi-nal point set with the aid of its evaluation of geometrical characteristic (normal curvature). Then the knot placement corresponding to B-spline curve and least square curve fitting are carried out. Furthermore, the dominant points can be progressively increased depending on approximation error to iteratively optimize the original fitting curve, and the reconstruction of curve fitting is done. Numerical experiments show that the proposed method exhibits good performance.