Development Of Multi-objective Optimization Module In Vehicle Body Structure Concept Design System

Modern vehicle body design method includes concept design stage and detail design stage, and estimation and optimization about vehicle body structure performance in vehicle body concept design stage can avoid modifying vehicle body repeatedly in the later design stage. In vehicle body design stage, static structure stiffness of vehicle body (bending stiffness and torsion stiffness) and dynamic low order modal (bending vibration frequency and torsion vibration frequency of the whole vehicle body) are important evaluating indicators about the structure performance. Vehicle body performance needs to be optimized in order to realize optimization design, lightweight and cost reduction of vehicle body. However, the common optimization design is the single-objective optimization about a single indicator, and the optimum structure parameter which meets the demands of vehicle body design is hard to obtain. So, multi-objective optimization whose objectives are multiple evaluating indicators about structure performance needs to be made.This paper studies multi-objective optimization mathematical models based on vehicle body concept structure and develops multi-objective optimization module in VCD-ICAE system (Vehicle Concept Design Intelligent CAE) through program writing and interface designing by secondary development about UG NX5.0 CAD software. It can create parameterized geometry model and finite element model of BIW, and multi-objective optimization whose objectives are structure stiffness and low order modal can be realized on condition of mass requirement with the design variables of thicknesses, then the whole body concept structure performance can be improved and this can help designer to obtain optimum design parameter and model design project.Chapter one of this paper introduces the important function of vehicle body structure concept design stage and the significance of multi-objective optimization design about vehicle body structure concept model in this stage. Chapter two introduces the theory about evaluating indicators of vehicle body structure and the establishment of mathematical models about objective functions in multi-objective optimization module. Chapter three introduces the key technology and major functions of VCD-ICAE system. Chapter four develops multi-objective optimization module in VCD-ICAE system through secondary development about UG NX5.0 CAD software by UG/OPEN secondary development tools. Chapter five creates panel structure concept model and beam structure concept model of vehicle body based on the detail model of a specific BIW style. Multi-objective optimization design of stiffness about the panel structure concept model and comparison test about the detail model are made, then validity and practicability of the multi-objective optimization module in VCD-ICAE system are proved. Multi-objective optimizations of three styles about the beam structure concept model are made, then multiple evaluating indicators are improved on condition of mass requirement, and optimization result can guide to improve the vehicle body detail model. Besides, chapter six of this paper studies the optimization about windshield deformation of the vehicle body detail model, and this makes windshield deformation satisfied with limiting value of design requirement, then the stiffness performance of vehicle body structure is improved.