Dynamic Load Identification Based On The Cuckoo Search Algorithm

Engineering structures are often subjected to dynamic loads,which has an important influence on structures.The dynamic load applied on the structure is difficult to obtain by direct measurement method.Therefore,it is necessary to seek an accurate and effective method to obtain the load state of the structure.Combined with the finite element method(FEM)and the Newmark-? method,a dynamic load identification method based on the cuckoo search(CS)algorithm is developed to reverse the dynamic loads.Dynamic load identification belongs to the second inverse problem of structural dynamics,and the identification process for dynamic load includes two steps.Firstly,the dynamic model of the system is established based on the FEM.The time is discretized into several time steps,and the discretization equation of motion is obtained.The motion equation of the discrete motion system is solved and the response of the structure under dynamic load is calculated by the Newmark-? method.Secondly,the dynamic response is selected as the optimization variable.The objective function of the dynamic load identification problem is defined as the difference between the calculated response and the measured response of the dynamic load.The dynamic load is determined through minimization of the objective function with the CS algorithm.This paper mainly identifies the periodic dynamic load with fixed position and the moving load.The accuracy and effectiveness of the inversion results are based on direct problems solving results.For simply supported beams subjected to dynamic load with fixed or moving position,the dynamic models established by FEM are solved by Newmark-? method.The results are compared with the analytical solution.According to the comparison results,the dynamic response obtained by Newmark-? method is in good agreement with the analytical solution.The identification of periodic position disturbance load is extended to truss structure.In the process of dynamic load identification,the inverse calculation of the system matrix is avoided.The proposed method has the advantage of concise inversion process.Numerical examples are taken to verify the accuracy and effectiveness of the algorithm.Through numerical examples,the effects of the number of nests,the measurement point position,the number of measurement points and the measurement noise on the inversion results are investigated.The results show that the number of cuckoo nests have negligible influence on the accuracy of the inversion results.And the inversion results are better.Contrarily,the position of the measurement point greatly affects the inversion results.As the number of measurement points increases,the error of inversion results decreases and the accuracy of inversion results improves.Moreover,with the increase of measurement error,the accuracy of inversion results decreases.Compared with conjugate gradient method,the inversion results of CS algorithm are more accurate and effective.Numerical examples show that the CS algorithm based on FEM and Newmark-? method can accurately and effectively reverse the dynamic load.