Nonlinear Modal Analysis Of A Helicopter Tail Drive Shaft System Based On Frequency Response Function

Traditionally,the study of helicopter tail drive shafting is mainly based on linear theory.However,due to the influence of the connection mode of the intermediate diaphragm coupling and the stiffness of the viscous damper,the tail drive shaft system will gradually exhibit nonlinear dynamic characteristics when the excitation amplitude is large.There is a need to study the nonlinearity existing in the tail drive shafting.In this paper,linear modal test and non-linear modal test of tail drive shafting are carried out.Based on the standard modal test data,the nonlinear modal parameters of tail drive shafting is identified.The accuracy of the nonlinear modal theory is verified qualitatively and quantitatively by simulation analysis.Combined with finite element simulation and model updating technology,the non-linearity of the tail drive shafting can be accurately identified,which lays a foundation for further accurate study of the dynamic characteristics of the helicopter tail drive shafting.The research of this paper has important theoretical significance and practical engineering value for helicopter dynamic design.The main research contents of the paper are as follows:(1)A method based on the frequency response function to identify the nonlinear mode of the helicopter tail drive shafting is proposed.The accuracy of the nonlinear modal test method is verified qualitatively and quantitatively by simulation test.Finally,the nonlinear modal test method is applied to the nonlinear process of identifying the tail transmission shafting.(2)According to the idea from the component to the whole,the linear modal test at the low excitation level is carried out on the tail drive single shaft,the connected tail drive shaft system,and the tail drive shaft system under the damper support state.The finite element solid model and the finite element simplified model of the tail drive shafting are established respectively.Based on the modal test data,the relevant parameters are corrected,and finally a simplified model of the tail drive shafting system is obtained.(3)In the free-free state,the nonlinear modal test under different excitation amplitudes is carried out on the tail drive shaft system,and the shaft system is excited in the horizontal and vertical directions respectively,to identify the nonlinear modal parameters at the connection of the tail drive shaft system.Combined with the established simplified model of the tail drive shaft system in the free-free state,the nonlinear stiffness parameters along the tail drive shaft connection are identified.(4)The nonlinear modal test under different excitation amplitudes is carried out on the tail drive shaft system under the damper support state,and the shaft system is excited in the horizontal and vertical directions respectively to identify the nonlinear modal parameters of the tail drive shaft support.Combined with the established simplified model of the tail drive shafting under the support state,the nonlinear stiffness parameters of the tail drive shaft support are identified.