등가정하중을 이용한 자동차 천정 구조물의 구조최적설계

Abstract

Due to the crush of the roof in a vehicle rollover accident, the passenger is damaged by penetration of the roof structure. National Highway Traffic Safety Administration (NHTSA) proposes strength requirements of the roof structure on roof crush resistance FMVSS 216. When the roof structure of a vehicle is designed, not only safety regulation but also light weight of a vehicle should be considered. Recently, there have been a lot of structural optimization studies that consider simultaneously both safety for a crash accident and light weight. However, the crashworthiness problem has difficulties in sensitivity analysis and high nonlinearity. Some practical problems have been solved by an approximation method such as the response surface method (RSM). The results of RSM have large accidental errors, because it generates an approximated optimum. Moreover, RSM has a limit on the number of design variables. Therefore, a large-scale problem is replaced by a simplified model or changed to reduce the number of design variables. The equivalent static loads (ESL) method has been proposed to solve such problems. The ESL are made to generate the same displacement field as the one from nonlinear dynamic loads at each time step of nonlinear dynamic analysis. A dynamic load is transformed to a set of ESL. The static loads are used as the multiple loading conditions, which are not costly in linear optimization process. Therefore, the ESL reduces the number of nonlinear dynamic analysis and derives good solutions. In this research, a light design is derived to satisfy the FMVSS 216 regulation using the ESL method and RSM. The optimum results using ESL are compared with there from RSM. As a result, the ESL is very efficient. Nonlinear analysis is performed using the commercial code LS-DYNA. LS-OPT is used for structural optimization using RSM. NASTRAN is used for calculating ESL and linear structural optimization.