Rolling stock condition monitoring using emitted noise signal under car body

초록

This paper concerns parametric studies and algorithms for online condition monitoring of rolling stocks using noise signals measured under the car body. This study is primarily aimed at detecting abnormal objects and their locations under driving circumstances. The whole detecting system comprises microphone arrays, signal processing tools, which has the function to detect the different signal compared to that from Rolling stocks under normal operating condition. For the application of the developing system in the railway rolling stock maintenance fields and for the users who are not familiar with noise signal processing, the system produces a noise map of the under car section including information of the locations and characteristics of components under unusual conditions. It will enable not only fast and detailed examination of the rolling stock defects but also systematical data base system for the maintenance works. To do this the acoustical holography technology and beam forming technology are investigated. These technologies have been using in various fields not only for machinery noise mapping, but also for moving aircrafts and automobiles etc. For it is the main purpose to differentiate certain patterns from a standard vehicle condition (and not just mapping the emitted noise), additional parametrical studies and principles for noise mapping the under part of the moving railway rolling stocks are required. First the noise characteristics of defected components under driving circumstances have to be clarified. To apply this technology to the defect monitoring and maintenance in rolling stocks the type and range of the defects has to be considered. To select the appropriate algorithm technology the radiation and propagation has to be investigated under various conditions such as speed, background noise and environment at the measuring locations. Related topics are doppler effects, reflecting effects under the car body. For optimization of the detecting and visualization technology, related parameters, their relation and limits, boundary conditions are studied. The acoustical holography technology has been studied based on frequency domain. The limits for usable frequency range which are dependent on periods of the noise signal and train speed are found and studied. At the end it was possible to draw crucial factors and optimal conditions. Under these conditions it was also possible to find out the location of the unusual motion from the components. To verify the applicability to the railway system model tests are performed and the results are discussed.