Study On Method Of Online Modal Parameters Identification Of Variable Mass Slender Beam

In this paper,we focus on the linear time-varying system and a variable mass cantilever beam finite element model is established.The recursive stochastic subspace method is used to identify the modal parameters of online tracking and the numerical simulation and experiments show that this method is effective and practical.Main work content is as follows:Firstly,the finite element model of the cantilever beam is established.By constructing the time-varying mass matrix,the theoretical model of variable mass cantilever beam is built,and the mutative curve of natural frequency is calculated.Based on the dynamic equation of the structure under basement excitation,the random vibration response of the time varying system is obtained by the numerical method.The state space model of continuous time and discrete time is derived,and two kinds of stochastic subspace methods based on state space model are derived.The relationship between the autocorrelation function of output data and the matrix of structure system is analyzed when the input is white noise.Finally,the modal parameters are identified through the obtained system matrix,and the validity of the method is verified by simulation.The simulation results are used to identify the low order frequency of the cantilever beam system with the stability diagram.A fast subspace tracking technique is introduced,which is applied to the stochastic subspace algorithm,and the recursive stochastic subspace algorithm is obtained.We mainly analyze the influence of parameters selection on the recognition results and the effects of parameters obtained by simulation.The simulation results show that this method can not only guarantee the recognition accuracy,but also can reduce the amount of calculation and is suitable for online identification.In the experiment,the vibration test of a cantilever beam with mass reduction over time is made,and the frequency in two conditions is estimated at first as a reference.The vibration response data is measured in the whole process,and the response data obtained by the proposed method is used to track the frequency.The results show that the method is effective.