Investigation On The Fault Feature Analysis Method Of Rotating Machinery Based On HOS

The typical faults of rotor systems,such as unbalance,misalignment,rub and crack would lead the system to generate the sum and difference of the fault character frequency.The vibration signal of a rotating machinery often have a non-Gaussian distribution.In the frequency domain,the non-Gaussian distribution can be explained as the non-linear phase coupling between different harmonics,such as the frequency multiplication in rotor misalignment or rotor rub,or the amplitude modulation between fault characteristic frequency and the rotational frequency in bearing failure.The traditional power spectrum analysis method,which is commonly used in vibration signal anaslysis,considers harmonics with different frequency separately and ignores the phase information of the signal.Therefore,the power spectrum analysis cannot detect the nonlinear phase coupling,which make it weaker in detecting the modulation behavior in bearing defect.The Higher Order Spectrum(HOS)overcomes the shortcoming of the power spectrum mentioned above.The HOS correlated different harmonics to detect the phase coupling,which is useful in detecting the modulation behavior in bearing defect.This thesis finished the following work:(1)Studied and summaried the non-linear phase coupling phenomenon in rotor system faults and the detection of non-linear phase coupling via HOS.(2)Researched the problem of parameter selection in Higher Order Spectrum analysis,including the frequency resolution and averaging times.Proposed a method to judge the non-linear phase coupling via the bicoherence threshold and a method to reconstruct the orbit of rotor system based on the bispecum phase.(2)Developed a rotor system vibration analysis software.The software contain several modules,such as time domain analysis,spectrum analysis,higher order spectrum analysis,etc.It also contains some auxiliary functions,such as FIR filter,trend analysis,peak marking,etc.The module of Higher Order Spectrum contains all of the methods researched in this thesis.The software has a friendly user interface and high calculating efficiency.(4)Conducted the fault simulation experiement of the rotor system.Simulated several common fault of rotor system,including unbalance,mislignement,rotor rub,cracked rotor and bearing wear on the a rotor sig.Analysed the vibration signal for different faults,and summarized its higher order spectrum feature.Validated the amplitude modulation detection by Higher Order Spectrum for rolling element bearing faults.