Papers by Author: Jin Chen

Abstract: A passively suspended road vehicle rolls outwards under the influence of lateral acceleration when cornering, which is very dangerous under large lateral acceleration. In this paper, time lag between steering input and vehicle lateral acceleration response is systematically studied to implement the active roll control algorithm from the viewpoint of vehicle system dynamics. A 3 DOF yaw-roll vehicle model is established based on vehicle lateral, roll and yaw dynamics. Vehicle parameters of a 1997 Jeep Cherokee is used for parametric study, where the influences of vehicle velocity, steering frequency, mass, length, roll, yaw moment of inertia, position of vehicle centre of gravity, and tyre cornering stiffness are studied via numerical simulation. The analysis results will help improve the real time rollover warning/control algorithm design for vehicle safety.

Abstract: In this paper, a simplified finite element model of the cracked crankshaft is proposed, and a new method for simulating the nonlinear vibration of operating crankshaft with several cracks is presented. For crankshaft, cracks occur frequently in the parts of crankpin-web fillet region and the edge of oil aperture because of fatigue or damage. According to the characteristic of those cracks, the cracked parts are modeled by the corresponding cracked spatial finite elements respectively, and two cracked elements are discussed in this study. The other, un-cracked, crankshaft parts are modeled by spatial Timoshenko beam elements. Flywheel and front pulley are simplified as lumped mass elements, and main bearings are simulated by equivalent linear springs and dashpots. In order to find the dynamic response of crankshaft-bearing system, a right-handed rotating coordinate system attached to crankshaft is applied. Based on the proposed finite element model, the breathing behavior of cracks in operating crankshaft is studied, and the nonlinear motion equation with variational stiffness is formed. Finally, a four-in-line crankshaft is taken as an example, and its vibration response corresponding to different kinds of crack are calculated and analyzed. Some conclusions are drawn, and a foundation is laid for diagnosing crack fault of crankshaft.

Abstract: Minor and random slip between rolling elements and races in rolling element bearings makes vibration signals have periodically time-varying ensemble statistics, which is known as cyclostationarity. Two second-order cyclostationary methods, the spectral correlation density (SCD) and the degree of cyclostationarity (DCS), are talked about in this paper based on a statistical model of rolling element bearings. The SCD provides redundant information in bi-frequency plane and cyclic frequency domain embodies the majority of it, which is a series of non-zero discrete cyclic frequencies completely reflecting the fault characters of rolling element bearings. The DCS has virtues of less computation and clearer representation, at the same time keeps the same characters with SCD in cyclic frequency domain. And the DCS is also proved to be resistant to the additive and multiplicative stationary noise. Simulation and experiential results from three rolling element bearing faults: outer race defect, inner race defect and rolling element defect, indicate practicability of the DCS analysis in rolling element bearing condition monitoring and fault diagnosis.

Abstract: Bispectrum is a powerful tool for non-Gaussian signal processing and nonlinearity detection. However, it is difficult to use in practical applications due to that it is a 2-dimensional function. Bispectral slices are widely used reduction methods, and they can only represent a small part of the whole bispectral information. Integrated bispectrum contains more signal features than that of the bispectral slices, whereas the integration will lose the focus of some signal features. To overcome these problems, a new approach called maximal bispectrum is proposed to extract signal features. Maximal bispectrum is obtained by selecting the maximal values of every row of the magnitude bispectrum in the whole bispectral plane and it is a 1-dimensional function. Feature extraction based on maximal bispectrum is investigated and the maximal bispectrum is used to extract features of gear fault. Experimental results indicate that the maximal bispectrum is effective for diagnosing gear crack fault.

Abstract: Noise is the biggest obstacle that makes the incipient fault prognosis results uncorrected. According to the theories of correlation analysis and threshold de-noising by wavelets, wavelet transform domain filter (WTDF) is constructed. WTDF is an iterative process. By selecting the process parameters adaptively, WTDF can de-noise signal efficiently. More important, the faint component in the signal will become stronger. WTDF method is used to analyze the signals collected from a bearing that has incipient unbalance and misalignment faults. Results show that WTDF is effective for bearing incipient fault prognosis.

Abstract: The demodulation analysis has been extensively used for gear diagnosis. However these techniques mainly deal with the amplitude-modulated signal instead of the frequency-modulated signal. Due to the symmetrical phase relationship of the sidebands, the amplitude-demodulated methods are not suitable for the frequency-modulated signal. This paper introduces the theory of cyclostationary processes as a powerful frequency-demodulation tool for the diagnosis of gears. The Cyclic Autocorrelation Function (CAF) is an important second-order cyclic statistics and acts as an efficient parameter to the frequency-demodulated analysis. In this paper, the CAF of frequency-modulated signal is deduced carefully. Through the discussion of frequency feature of the CAF slice at different cyclic frequency, two useful conclusions have been arrived about the frequency-demodulation. Firstly, the CAF slice at even multiples of the modulator-frequency can demodulate the frequency-modulated signal directly. Secondly, the amplitude-demodulated methods are suitable for the CAF slice of frequency-modulated signal at some special cyclic frequencies, which are equal to odd multiples of the modulator-frequency or close to the double carrier-frequency. These features of the CAF slice mentioned above overcome the invalidation of amplitude-demodulated methods for the frequency-modulated signal and increase it’s application range in engineering. Application in simulated and experimental data from a gear rig verifies the effectiveness of the frequency-demodulated method based on cyclostationarity.