Equivalent Static Loads Method Based On Gradient And Structure Crashworthiness Optimization Of Key Parts In Vehicle

Many structural optimization problems such as vehicle structure crashworthiness optimization have dynamic effect and nonlinear characteristics, However, the traditional structure optimization design is under static linear load, so the results of static optimization design can't meet the requirements of structural nonlinear dynamic performance. It often leads to huge computing scale and is difficult to achieve convergence when numerical optimization algorithm based on gradient or global optimization algorithm are directly applied to dynamic optimization design, because it is difficult to deal with time-dependent dynamic constraint, so this method is not acceptable in engineering application. As a result, a feasible approach to solve structural nonlinear dynamic optimization is to convert the dynamic loads into equivalent static loads.Equivalent static loads method (ESLM) using linear static structure optimization technology to solve structure nonlinear dynamic optimization problem, compared with the direct dynamic optimization design method. This method can greatly improve the efficiency of optimization. However, when the structure nonlinear characteristics are significant or the design variable scale are large, the differences of nonlinear optimization and linear optimization will increase, thus lead to reduce the optimization efficiency of equivalent static load method and poor convergence.Combined with structure static linear optimization and the Steepest Descent Method (SDM), an Equivalent Static Loads Method based on Gradient (ESLMG) is proposed to overcome the disadvantages of difficulty to achieve convergence and low efficiency of Equivalent Static Loads Method (ESLM) when solving large deformation and multi-variable structure nonlinear dynamic optimization under displacement constraint. The proposed method is based on node displacement equivalent, and can improve the convergence speed under the premise of algorithm convergence. Numerical examples show that the method is effective for dealing with large deformation and structure dynamic nonlinear multivariable optimization problem, and it has great advantage compared with ESLM and numerical optimization algorithms in terms of convergence rate.Many structural optimization problems have stress constraint besides displacement constraint. The equivalent static loads method based on element stress is proposed on the basis of ESLMG, combined with structure initial stress analysis and corrected equivalent stress. A 10 bar truss structure optimization examples under stress constraints verify the effectiveness of the proposed method.ESLM has not yet to do some research on structure nonlinear dynamic continuum topology optimization, therefore the ESLMG for topology optimization is proposed combined with the Variable Density Method. Numerical example verify the effectiveness of ESLMG for nonlinear structure topology optimization.In order to apply the proposed method into structure crashworthiness optimization of key parts in vehicle, The nonlinear response such as equivalent velocity, equivalent acceleration and strain energy in automotive structural crashworthiness optimization are solved first, then a car B pillar thickness distribution optimization design, a crash box structure optimization design and a knee bumper topology optimization design are respectively realized.