Research On Dynamic Load Identification Method Of Mechanical Structures Based On Step-by-step Integration

In the research on mechanical system optimization design,structural strength calculation,dynamics analysis and reliability analysis,dynamic load is the basis of calculation and analysis as the important original data.In many cases,the dynamic loads applied on mechanical structures can not be directly measured by sensors.Therefore,theoretical research of dynamic load identification method is of great significance.In this paper,the structural dynamic load identification methods in time domain are studied for the linear elastic system and the nonlinear system with stiffness variation.The main research works are stressed as follows:(1)The basic principles of three step-by-step integration methods,including the central difference method,the Houbolt method and the Newmark-β method,for solving the dynamic response of mechanical systems are analyzed.The stability conditions of the three methods are clarified.Numerical examples are given to analyse and compare the errors between caculation results obtained by the three methods for solving system dynamic differential equations and theoretical solutions of the mode superposition method.The validity and accuracy of the three numerical methods are determined accordingly.(2)Based on the basic principle of Houbolt method solving the equations of dynamic systems for the responses,the iteration algorithm preenting the relationships between the input excitation,the system characteristic parameters and the output response is derived,and a novel dynamic load identification method being unconditionally stable for the linear multi-degree-of-freedom system(MDOFS)is proposed.Numerical examples are given to verify the validity and noise immunity of the proposed method for identifying the dynamic loads of one-dimensional and two-dimensional structures with single and multiple input excitations.Compared with the state space method,the proposed method has higher identification accuracy and better noise immunity.(3)Based on the basic principle of Newmark-β method solving the system dynamic response,an iterative algorithm indentifying the dynamic load of the linear MDOFS is derived,the effectiveness of which is verified by numerical examples.Based on the Newmark-β and modified Newton-Raphson iteration algorithms,an iterative algorithm is derived to identify the dynamic load of the nonlinear single-degree-of-freedom system with variable stiffness.Numerical examples demonstrate that the algorithm can effectively eliminate the cumulative error of calculation and improve the calculation accuracy.