Papers by Author: Fu Lei Chu

Abstract: Acoustic Emission (AE) signal has been used pervasively in the extraction of fault feature and the location of damage. The precision of the extraction and location is determined by the propagation characteristics of AE signal in different structures. In this paper, the propagation characteristics of AE wave in the point contact sphere under continuous and transient AE signal is analyzed; a series of experiments under different condition are conducted; based on wave propagation theory, a simulation model is built using the software of ANSYS LS-DYNA. The results of experiments and simulation models reveal that the propagation characteristics-attenuation, frequency features-of AE signal can be manifested clearly in the experiments and are simulated correctly by the simulation model.

Abstract: Spalling of the races or rolling elements is one of the most common faults in rolling element bearings. Exact estimation of the spall size is helpful to the life prediction for rolling element bearings. In this paper, the dual-impulsive phenomenon in the response of a spalled rolling element bearing is investigated experimentally, where the acoustic emission signals are utilized. A new method is proposed to estimate the spall size by extracting the envelope of harmonics of the ball passing frequency on the outer race from the squared envelope spectrum. Compared with the cepstrum analysis, the proposed procedure shows more powerful anti-noise ability in the fault size evaluation.

Abstract: Tooth breakage is a typical failure form of wind-turbine planetary gear transmission system, it is important to study the influence of tooth breakage on vibration characteristics of planetary gear transmission system. In this paper, considering the tooth breakage defect, a lumped parameter vibration model of a planetary gear system with time-periodic mesh stiffness is established. Effects of the length and width of tooth breakage on meshing stiffness and dynamic response are discussed in detail. The relation between characteristic frequency of the tooth breakage fault and rotating speeds is pointed out. Several statistical indicators are utilized to show the influence of two parameters (length of planet tooth breakage and input speed) on the dynamic response of the system. Experiments are carried out to verify the simulation results. These results would be useful for fault diagnosis of wind turbine transmission system at different operation conditions.

Abstract: In this paper, the vibration characteristics of the rotating thin circular cylindrical shell subjected to the radial excitation are presented. Based on the Love’s shell theory, the governing equation of the rotating thin circular cylindrical shell is derived by using the Hamilton’s principle. Then, the amplitude-frequency responses for traveling wave vibration of the circular cylindrical shell are investigated. The results indicate that there exists the traveling wave vibration for the rotating thin circular cylindrical shell, namely: the forward wave and the backward wave. The effects of the damping and excitation on the amplitude-frequency response are analyzed.

Abstract: The disc-drum type rotors are commonly used in large gas turbine engines. In this paper, the dynamic characteristics of single stage disc-drum structure are studied based on the finite element model, where the connecting bolts are modeled using solid elements and the frictional contact at the joint interface is accommodated. In order to evaluate the nonlinearity resulting from the bolted joints, a finite element (FE) model fixing the disc and drum together is also established, and the simulation results based on the two models are compared. The effects of the bolt preload and the rotating speed on the dynamic characteristics of the disc-drum structure are also discussed. The works proposed in this paper help to enhance the understanding of the dynamics of the disc-drum type rotor.

Abstract: Periodic impulses in vibration signals and its repeating frequency are the key indicators for diagnosing the localized damage of rolling element bearings. A new method, so called time-wavelet energy spectrum, is proposed to extract the characteristic frequency of faulty elements. It is applied to analyzing the vibration signals of bearings under normal and faulty (with damage on outer race, inner race and ball respectively) statuses. The analysis results show that the time-wavelet energy spectrum is effective in extracting the repeating frequency of periodic impulses. It can not only extract the relatively significant fault feature of outer race damage, but also can extract the weaker fault features of inner race and ball damage.

Abstract: Fractal dimension reflects the complexity of dynamic systems, and contains the health status information of machinery. The experimental vibration signals of a gearbox with different gear crack size are analyzed using correlation dimension, and it is found that the correlation dimension increases monotonically with the increasing crack level. This is consistent with the nature of a nonlinear dynamic system: the more severe the fault, the more complicated the dynamic system, and accordingly the larger the fractal dimension. Correlation dimension has potential to assess gear localized damage.

Abstract: The acoustic emission signals of rolling bearing with different type of defects are de-noised and illustrated by the continuous wavelet transform and scalogram. Morlet wavelet function is selected and the wavelet parameters are optimized based on the principle of minimal wavelet entropy. The soft-threshold de-noising is used to filter the wavelet transform coefficients. The de-noised signals obtained by reconstructing the wavelet coefficients show the obvious impulsive features. Based on the optimized waveform parameters, the wavelet scalogram is used to analyze the real AE signal from the defective rolling bearing in experimental test rig. The results indicate that the proposed method is useful and efficient for signal purification and features extraction.

Abstract: The cyclic autocorrelation function is used with regard to the cyclostationarity of gear vibrations in order to extract the modulation features of gearbox vibration signals, and to detect localized gear damage. The properties of the amplitude and frequency modulated signals in the cyclic frequency domain are summarized in order to investigate the differences between the modulation features of normal and faulty gearbox vibration signals. Gear tooth spalling is detected by the presence of many sidebands in a zero-lag time-slice of the cyclic autocorrelation function, thereby indicating an increase in the degree of modulation effect. The damage source is located by the spacing of the sidebands.

Abstract: Based on pattern spectrum entropy and proximal support vector machine (PSVM), a motor rolling bearing fault diagnosis method is proposed in this paper. It is very difficult to filter the fault vibration signals from the strong noise background because the roller bearing fault diagnosis is a problem of multi-class classification of inner ring fault, outer ring fault and ball fault. Firstly, vibration signals are processed by the pattern spectrum. Secondly, the morphological pattern spectrum entropy, and pattern spectrum values are utilized to identify the fault features of input parameters of PSVM classifiers. The experiment results demonstrate that the pattern spectrum quantifies various aspects of the shape-size content of a signal, and PSVM costs a little time and has better efficiency than the standard SVM.