| The thesis focuses on spectrum correction, time-frequency analysis methods and the development of virtual instrument software.The following three aspects are mainly studied:Firstly, the amplitude correction under the condition of unstable rotary speed is studied. ft is known that severe energy leakage occurs under such condition. After a detailed study on the existing discrete spectrum correction theories, the author puts forwards a convenient and effective method to reduce the appreciable amplitude error.The simulation results show that this method is easily implemented with high precision and high anti-noise ability.Secondly, the characteristics and their computer algorithms of time-frequency analysis methods including waterfall spectrum, Wigner-Ville Distribution(WVD) as well as Hilbert-Huang Transform(HHT) are studied. Waterfall spectrum is an effective tool for analyzing the vibration modulation, especially amplitude modulation. But it's not so applicable for analyzing the windowed signal with big frequency fluctuation for the fact that waterfall spectrum is based on the traditional FFT. Compared with waterfall spectrum. WVD is more effective in analyzing non-stationary signal, which can locate the time-frequency distribution precisely. The algorithm which improves the analysis speed of WVD is presented in the thesis. Also, several methods to reduce cross-terms of WVD are studied. Simulation results show that they can greatly reduce the cross-terms, which makes them very useful in engineering application. The author makes use of these methods in analyzing the signal of oil whipping, which shows that it's effective in time-frequency distribution analysis. Also, the end effect, threshold selection, sampling frequency and the algorithm of HHT are studied in details. Simulation result shows that it is very effective in analyzing non -stationary signal.Lastly, the mixed programming by Visual C++ & Matlab is studied. By adopting the latest research results on discrete spectrum analysis and the idea of virtual instrument, a software system for dynamic signal analysis is developed, which is based on windows operating system and has good performance. |
