The Numberical Simulation Of Acoustic Emission Signals Based On The Finite Volume Method

With the rapid development of high-speed railway in our country, the safety of trains operating is getting more and more attentions. Rail damage detection is one of the important measure to ensure the safety of train operation. Compared with the traditional nondestructive testing methods, such as ultrasonic flaw detection, acoustic emission technology(AET) is applied in rail damage detection for its unique advantages, which is that AET can detect dynamic defects and achieve real-time monitoring without damage to the track. For acoustic emission technology, the numerical simulation of elastic waves is one of the important research contents, is effective means for further research and analysis of acoustic emission signals. The topic of this thesis is numerical simulation of elastic waves which are generated by acoustic emission source of rails.The numerical algorithm of elastic waves in the rails based on finite volume method is studied in detail. It can not only solve the problems of complex geometrical shape with high precision, but also improve the computational efficiency by controlling storage variables artificially. Main research contents of the thesis are as follows:Effectiveness of the numerical algorithm in plane problems is researched. Two kinds of plane discrete element, called constant strain triangle element and bilinear quadrilateral element, are discussed. For the stability of the numerical algorithm, discrete time step and grid size in plane issues are discussed. Three models are built to ensure the validity of the numerical algorithm.The numerical algorithm to deal with three dimensional space problems is researched. Two kinds of space discrete grids, called constant strain tetrahedral grid and bilinear parallel hexahedron grid, are discussed. For the stability of the numerical algorithm, discrete time step and grid size in space issues are discussed. Two models are built to ensure the validity of the numerical algorithm.A rail three-dimensional discrete model is established, and the acoustic emission signals in it are modeled by the numerical algorithm presented in this thesis. Because of the length of rail line is much larger than the size of its cross section, and acoustic emission signal energy decay gradually through its propagation, we only need to focus on a certain period of rail. Then, in order to simulate elastic waves propagation to infinity, we discuss the irregular grid absorbing boundary to absorb the incident waves within objects.