Study On The Time-frequency Analysis By Emd And Cohen's Kernel And Application In Track Irregularities

Track irregularities will be generated in vertical, level and gauge, due to the initial bend, run deformation and wear. Track irregularities are the main source of vehicle vibration. They will cause the coupling vibration of the vehicle in ups and downs, roll placed horizontally, swinging left and right. This vibration intensifies the wheel and rail vibration wear, increasing the track irregularities. With increasing the train speed, researching the track irregularities is more significant.First, the track irregularities research current situation was summarized, then the non-stationary signals features of EMU running gear was analyzed. To analyze the track irregularities based on the axle-box acceleration, a method based on Empirical Mode Decomposition (EMD) and Cohen's class distribution was advanced. Compared with the result by track inspection car, the consistent results were getting. It indicated that this approach was a good method to compensate some shortage for track inspection vehicle, and it play an important role in the high-speed high-density test track irregularities by means of contact methods.This dissertation included the following research contents:(1) The algorithm in exponential kernel was improved. In traditional way, time-frequency representation method using exponential kernel is only suitable in the condition that self-variable is along theξandτaxis. An improved time-frequency representation method was proposed to solve this problem. Using coordinates rotations, Self-terms in fuzzy function can as far as possible all pass the exponential kernels function, and the cross-terms in fuzzy function can far away from the exponential kernels function. This approach was testified affected through a chirp signal and the simulation result proved that this method cans repression the interference satisfactorily, and an ideal time-frequency analysis result can be acquired.(2) Several key issues in EMD were studies. In EMD, to suppress the ending effect, extending the data near the two end points was used by mathematics fitting usually. In practice, extending the sampling-time can also extend the end points and suppress the ending effect. Comparison has been made among the data extending method between the Mathematics fitting and terminal intercept near the two end points. To test the effect of EMD, the correlation coefficient between the practical results and ideal results were calculated. As a result of simulation and numerical experiment, it is shown that:if the signal intercept around half the length of data signals, better results can be obtained than endpoint extending. More the interception of points approximates more ending effect can be effectively restrained.(3) To minimize the cross-term interference in quadratic time-frequency distribution, a method based on EMD and Cohen class distribution was advanced. For the method, at first, the time-domain signal was separated into multiple intrinsic mode functions (IMFs) using EMD, then the Cohen class distributions of the IMFs were calculated. At last a sum of all Cohen class distributions was acquired. By this way, the cross terms between IMFs can be restrained. So the general cross-term interference was restrained in theory. This approach was testified effected through three typical simulation signals and the result was consistent with the theory. Compared with Wigner-Ville distribution, and Cohen class distributions; it indicates that this approach can repression the interference satisfactorily, and the time-frequency analysis result is a better reflection of signal.(4) The theory aforementioned was applied in track irregularity monitoring. To minimize the cross-term interference, a method based on EMD and Cohen's class distribution was advanced. For the method, at first, the time-domain signal was separated into multiple IMFs using EMD, then the Cohen's class distributions of the IMFs were calculated. And a sum of all Cohen's class distributions was acquired. This approach was testified effected through three typical simulation signals and the result was consistent with the theory. At last this approach was applied to analyze the track irregularities based on the axle-box acceleration. Compared with the result by track inspection car, the Consistent results were getting. It indicated that this approach was a good can compensate some shortage for track inspection vehicle, and it plays an important role in the high-speed high-density test track irregularities.