등가정하중을 이용한 자동차 천정 구조물의 구조최적설계

Abstract

In a vehicle rollover accident, the passenger is injured by penetration of the roof structure. The National Highway Traffic Safety Administration (NHTSA) proposes strength requirements of the roof structure on roof crush resistance in the regulation of FMVSS 216. Recently, there have been a lot of structural optimization studies that design the structure of a vehicle to satisfy this safety regulation. Most of the previous studies used approximation methods such as the response surface method (RSM) since a crash problem has high non-linearity and difficulty in sensitivity calculation. However, the solution from RSM may not be accurate and has a limit on the number of design variables. In this research, nonlinear dynamic (transient) response optimization using equivalent static loads (ESL) is proposed to design the structure of a vehicle to satisfy the safety regulation. Equivalent static loads for linear response analysis 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 for linear response optimization, which are not costly in the linear response optimization process. Size optimization using ESL is performed to reduce the structural mass while the FMVSS 216 regulation is satisfied. The optimum results using ESL are compared with those from RSM. As a result, the proposed method is very efficient and derives good solutions. Nonlinear analysis is performed using the commercial code LS-DYNA. NASTRAN is used in calculating the ESL and linear response optimization. LS-OPT is utilized for structural optimization using RSM.