A Study About The Propagation Characteristics Of The Elastic Wave In A Shaft Under Axial Force

This dissertation is supported by the National Natural Fund project ‘Research on method of crack detection for shafts of large rotating machinery based on propagation characteristics of elastic wave'(No.51505430).Based on the method of transfer matrix,the axial forces,axial crosssectional area and the rotational speed have been investigated.The propagation characteristics of the elastic wave influenced by those factors have been confirmed.The propagation characteristics of the elastic wave in the rotating shaft is influenced by axial forces,geometric size,shape,etc.The rotational speed may also affect the propagation characteristics of the elastic wave in the rotating shaft.According to the numerical experiments,the finite element method is implemented.The experimental system is designed and constructed,and the theoretical analysis is verified by experiments and finite element simulation analysis.The research results are helpful to solve the problem of elastic wave propagation mechanism when the variable cross-section rotating shaft and other mechanical components are under axial load,,which can provide reference for identifying the load condition on the component by the propagation characteristics of elastic wave and analyzing the dynamic characteristics of the rotating shaft.The main research work and chapters of thesis are as follows:Chapter ? expounds the research background and significance of elastic wave propagation.This paper summarizes the research methods and application prospects of elastic wave propagation in media such as rotating shafts at home and abroad,and summarizes some problems such as the characteristics of the elastic wave propagation in the rotating shaft that are still unresolved at present,and then puts forward the research objectives and contents of this paper.Firstly,the concept of elastic wave,the propagation characteristics and transfer matrix of elastic wave in the rotating shaft are introduced in Chapter ?.The relation between axial force and elastic wave transfer matrix is deduced.Then based on the obtained transfer matrix without axial force,the transfer matrix of the variable cross-section rotating shaft is deduced by using the superposition principle.In chapter ?,the eigenvalues of the elastic wave transfer matrix are first analyzed by using numerical analysis method.Then the influence of the axial force,the area ratio between both the ends of the shaft and the rotational speed on the propagation characteristics of the elastic wave are studied.For the result of numerical analysis,the finite element simulation analysis is carried out.The simulation results are consistent with the theoretical analysis results,which proves the correctness of the theoretical analysis.That is,when the variable cross-section rotating shaft is subjected to axial force,a new stop band will appear when the elastic wave propagates in the rotating shaft.As the axial force increases,the center frequency of the cut-off frequency decreases.When the variable cross-section rotating shaft receives a constant axial force,as the ratio of the cross-sectional area of the rotating shaft increases,the center frequency of the stop band becomes higher.In order to further verify the theoretical and simulation results,the fourth chapter builds the experimental system and conducts the related experiments.The whole experimental system and experimental scheme are introduced.The experimental data of axial force and the area ratio between both the ends of the shaft are analyzed.The experimental results are close to the theoretical analysis and finite element simulation results.Conclusions of this study is summarized in Chapter ?,in which some advanced topics of future work could be found also.