The Discrete Optimization Design Method For Auto-Body Beam Section Based On Complex Engineering Constraints

In load supporting vehicle body, beam structure bears most of the load, its carrying capacity is determined by the section properties, therefore, the performance of the beam cross-section largely determines the mechanical properties of the vehicle, and directly affects the safety of the car. In the body design stage, designers consider not only ensuring good performance of the structure, but also achieving body lightweight in the permitted range of cost, which puts forward higher requirements on the design of the beam section. At present, the design of beam cross section in the concept design stage is mostly according to the past design experience or directly apply the existing similar models section, section from this method is difficult to well match with the new car in performance, and the defects in the pre design is very difficult to modify in the subsequent work. This has become a bottleneck of new models development and further performance improvement.The section not only needs to have the property section shape which can meet the requirements of body performance, but also can be manufactured by the existing industrial equipment. Fully consider of engineering constraints in the body section design,such as manufacturability and assembly performance, the paper uses a special coding method control the section shape and establishes a material parameters and thickness database, taking continuous beam cross section shapes, discrete material thickness, material type, and plate number of the beam section as optimal design variables, and taking body beam section performance and the minimum weight, lowest cost as the optimal design goals, establishes a multi-objective optimization model. This method based on the NSGA-II genetic algorithm, via VC programming realizes the computation of the model, and integrates the application module in UG using UG secondary development functions. Instances show that the multi-objective optimization module can be used in concept design phase to solve the beam cross section shape parameter under the premise of meeting the engineering constraints and the structure performance; and it also can be applied to the detailed design stage to optimize the existing section parameter to improve the section performance of the section and achieve the goal of lightweight.This paper consists of five chapters, the first chapter introduces the background and the significance of beam section optimization, and briefly introduces the work; the second chapter describes the basic theoretical knowledge used in this section optimization method, including optimization model and optimization algorithm; the third chapter briefly introduces the VCD_ICAE system developed by the research group, this study is an expansion functions of the system; The fourth chapter explains the realization process of sectional optimization, which includes the function framework, interface design and process parameter setting; The fifth chapter through to the three optimization analysis examples, effective proof of this section optimization function can according to different design goals optimization for single section beam with variable cross section beam body structure to achieve the better, the fifth chapter through optimization analysis of three examples, which effective prove that the section optimization function module can realize the optimization of single beam section as well as continuous variable beam section in the vehicle body according to different design goals.