Multi-objective Robust Optimization Design Of A New W-beam Guardrail

As the widely used roadside safety protection devices on highways,W-beam guardrail can contain,buffer and redirect the errant vehicles,which can protect the life safety of occupants in errant vehicles and avoid getting involved in a second crash with normal driving vehicles.Thus,it is of great research significance to optimize the W-beam guardrail.However,when a car impacts a traditional W-beam guardrail(TWG),the wheel is easily snagged by the guardrail post and produces the snagging.The snagging decreases the performance of the guardrail greatly and makes a serious traffic accident.The present methods of solving the snagging are mainly to reduce the likelihood of snagging though improve the rigidity of the guardrail,which will reduce the buffering performance of the guardrail and this is not a good solution to the problem of snagging.Besides,the current optimization studies of guardrail didn't consider the uncertainties existed in the actual machining of design parameters,which will lead to poor robustness of the optimization design results of the guardrail.To solve the problems discussed above,this paper carried out the research works as follow:(1)The finite element(FE)model of vehicle and guardrail with high accuracy and good stability was established.Actually,the collision process between vehicle and guardrail is a very complex dynamic process,which includes many nonlinear mechanical problems,such as material nonlinearity,geometric nonlinearity and contact nonlinearity.Therefore,the simplification of the FE model,the treatment of contact and connection,and the application of the load and boundary condition were the difficulties.Finally,though the adjustment and validation of the model,the FE model of vehicle and guardrail was established in this paper,which had high accuracy and good stability.(2)A new W-beam guardrail system was proposed to solve the snagging problem of wheel.The new W-beam guardrail system which has a new type of post with the geometry shape like the Greek letter ? and thus was named as ?-shaped W-beam guardrail(?-WG).Using the nonlinear FE methods through LS-DYNA,the safety performance of the TWG and ?-WG were both investigated in this paper.The comparison of simulation results demonstrated that the ?-WG could avoid the snagging effectively and the safety performance of the ?-WG was better than that of the TWG.(3)The efficient multi-objective robust optimization(MRO)method was developed to realize the high efficient and robust optimization design of guardrail structure.This paper combined the design demands of guardrail structure,FE simulations,radial basis functions(RBF),Monte Carlo simulation,"3-sigma" robust design and non-dominated sorting genetic algorithm to develop the efficient MRO method of guardrail structure.In this method,the RBF metamodels were employed to replace the expensive FE simulations to improve the efficiency of optimization calculation.And,the uncertainties existed in the actual machining of design parameters was considered to improve the robustness of the optimum design.The result of research in this paper showed that the robust optimal ?-WG not only had excellent crashworthiness,but also had high reliability,and had good potential application in the future' highway.In addition,the robust optimization method employed in this work could also be employed in other structural optimization design involving complex computation.