| This research used multidisciplinary design optimization to optimize the ladder frame chassis of a Zero Emission Vehicle by simultaneously considering chassis mass, deceleration during collision and manufacturability. Additionally, design constraints were placed on torsional and bending stiffness, maximum von-Mises stress, and the natural frequency in torsion and bending.; To calculate the mass objective function and extract values of the design constraints, the Finite Element Analysis tool ANSYS was used. LS-DYNA was used to determine the deceleration of the chassis during a full-frontal collision into a rigid barrier. Microsoft Excel was used to parametrically and graphically represent the measure of hydroformability: the ability of a part to be manufactured using the hydroforming process. MATLAB was used to conduct the optimization, and to provide seamless integration between all other software applications.; For computational efficiency, optimization was conducted in three separate, but equally important phases: phase one used a simplified chassis model to conduct topology optimization with Genetic Algorithms; phase two was conducted to determine an optimum cross sectional shape; and phase three incorporated results from phase one and two, into a high-fidelity, 3-dimensional chassis model, for gradient based bi-objective and tri-objective optimization.; Results from all phases of the design optimization indicated that improvements could be made over the baseline configuration. Through examination of Pareto frontiers in phase three, distinct trade-offs were identified between all objective functions: a 1.2% reduction in hydroformability was required to minimize the chassis mass; minimization of the mass also required a 90% increase in deceleration; and minimization of deceleration required an 18% decrease in hydroformability. Tri-objective optimization was further used to generate a 3-dimensional Pareto frontier 'surface' to show the impact of one objective function on all others simultaneously.; This research has shown that chassis design for a Zero Emission Vehicle can be significantly improved by employing multidisciplinary design optimization. The Pareto frontiers and surfaces generated accurately describe the trade-off between all objective functions, and can be used to assist engineers in identifying regions of maximum gain, with minimal trade-offs. |
