Analysis Method Of Nonlinear Response Based On Reduce-order Method

Hypersonic vehicles use quantities thin-walled structures in order to reduce the weight of structures and improve flight efficiency.During service,the structures of hypersonic vehicles experience complicated loadings such as acoustic loading,mechanical loading and thermal loading.Under this coupling environment,structures will generate a complicated stress-strain relationship and will produce a nonlinear response caused by large geometric deformation.The fatigue life of structures will be largely reduced when the responses are nonlinear.When we are designing the structures of hypersonic vehicles,the nonlinear responses must be obtained firstly.As there are so many limitations and high computing cost of the classic calculation methods,this paper studies the feasibility of reduced-order method in calculating the nonlinear responses.Firstly,the paper introduces the theoretical derivation process of reduced-order method systematically.As the nonlinear stiffness force components cannot be obtained directly from the commercial finite element software,the paper puts forward the indirect method to build the reduced-order model by calculating the nonlinear stiffness coefficients.Secondly,the paper studies how to choose the modal vector as the reduced-order base in the modal reduction technique flow.Taking the stiffened plate structure as the research object,the nonlinear response of the different reduced-order modal are calculated and compared with the nonlinear response of the full-order model.At the same time,the paper puts forwards a method for selecting the reduced-order base based on eigen-orthogonal decomposition.Thirdly,the paper use the lab structure as the research object,get the optimal reduced-order base of this object by the eigen-orthogonal decomposition method.Then the nonlinear stiffness coefficient of the reduced-order model is obtained indirectly by the hypothesis displacement method.In the end,the paper calculate the nonlinear response of reduce-order modal under coupling loading of thermal and acoustic.At the same time,the paper design and test the thermal noise test and obtained the experimental data.Finally,the paper proposed an acoustic-structure coupling model considering the coupling relationship between sound field and structure and acoustic.The nonlinear response of the coupling model is calculated and compared with the nonlinear response of the experimental results.It is verified the acoustic-structure coupling model can improve the accuracy of nonlinear response calculation.