Lightweight Study Of Bus Body Based On Local Topology Optimization

Lightweight design has been a constant concern since the dawn of the automotiveengineering. Since the body of a typical car makes up20%to30%of its total weight, thereduction of the car body under the constraint of maintaining its functions is of greatsignificance in terms of automotive lightweight design. Being as the most common andeffective methodology, topology optimization has been considered to be of vital importanceto structure and lightweight related problems. In view of the importance of reducing carbody mass and the effectiveness of topology optimization in dealing with lightweight,topology optimization was employed for the lightweight design of a bus body in this thesis.The motivation of automotive lightweight design was analyzed, and backgroundinformation about lightweight design was explained, as the start of the thesis. After that, thestat-of-the-art of the application of lightweight materials, and typical optimization methodsfor vehicle designs were investigated. Following the summarization of basic concepts andterminologies of structural optimization, three typical problem of structural optimizationwere discussed. The topology optimization and variable density method were analyzed ingreat detail. Base on the above investigation and current research problems of topologyoptimization of bus bodies, a local optimization method based on beam-shell mixed modelwas proposed.The local optimization method can be interpreted as follows:1) choose those local bodystructures that have great performance contribution or optimizing potential as targets ofoptimization;2) determine relevant parameters of the optimizing scheme to carry outoptimization by the consideration of potential risks and physical characteristics of localstructures; and3) each time after completing optimization of a local area, interpret theobtained results according the rule of optimization interpretation, and thus turn the optimizedstructures into machinable ones by combining the specific characteristics of local structures.To elevate the accuracy and efficiency of the proposed method, iterative method wasemployed for the optimization. In other words, the obtained results or structures of theformer round were set to be the input or boundary of the next round instead of using originalstructures. The above mentioned process was applied to all local areas, and the results wereinterpreted. A finite element model of optimized bus was created accordingly, and the performanceof which was compared to that of original bus. It was found in the optimized bus:1) theweights of the middle area of the sider panel and the middle area of the under frame weredecreased by11%and24.6%respectively,2) the overall stress levels of optimized bus weresignificant smaller in all three typical working conditions, and3) the local stress levels oftarget areas were also considerably smaller.It can be conclude that the proposed method (local topology optimization) is ofpractical application in terms of the lightweight of bus body. It can reduce vehicle weightwhile maintaining good performance, and also elevate the efficiency of structuraloptimization by weakening the conflict between computational cost and accuracy.