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An innovative design process is proposed to be applicable in the early conceptual design phase as a means of front loading design. The objective of the study is to minimize trial and errors in the detailed design phase and to shorten the overall design period. The process includes design optimization which is based on efficient modeling techniques. An integrated CAD/CAE modeling method and a simplified quality FE model are key factors in the course of effectuation. The conceptual modeling takes into account the adaptability of computer-generated models with the use of CAD/CAE integrated design environment. To achieve maximum efficiency in the repeated computations in optimization, an FE modeling approach is introduced in terms of simplicity and quality. The proposed FE modeling employs beam and spring elements to construct vehicle body models, which is targeted to produce an instant analysis result with a robust conceptual design at the incipient phase of development.

An engineering strategy to develop a new 27-ton dump truck is introduced in the process of design and analysis. Main engineering concerns in development of the new dump truck are focused on reducing weight as much as 180kg without deteriorating structural strength and fatigue life of its upper body - deck and subframe. To achieve this goal, a stress analysis and a fatigue life prediction based on CAE technique are employed at the early stage of design process. A finite element model of the full vehicle was constructed for the strength analysis. Then the fatigue life was predicted through the strength analysis and an S-N curve of high strength steel. The S-N curve for welded structures made of high strength steel was used along with a prototype vehicle's endurance test in order to set strength targets. As a result, the upper body was successfully developed without any fatigue issues.

A new body structure of low-floor city bus is proposed in terms of optimization in the multiple levels of the structural system. In the framework of multi-level optimization, a bus body system is viewed as an integration of sub-systems like roof, side structure and front/rear body modules, and each of the sub-systems is seen as an assembly of components. Once the system is decomposed into the lower level sub-systems, the design target is cascaded for the lower level. That is, the design target of the bus body system is cascaded into the design targets of the sub-systems, and the target cascading procedure eventually gives the design targets in the component level. Analytical evaluation and prediction of the target values of each level is provided by computations based on computer aided engineering (CAE) so that an optimized design can be obtained through a number of iterations.