Papers by Author: Xue Feng Chen

Abstract: Instantaneous speed (IS) is of great significance of fault diagnosis and condition monitoring of the high speed spindle. In this paper, we propose a novel zoom synchrosqueezing transform (ZST) for IS estimation of the high speed spindle. Due to the limitation of the Heisenberg uncertainty principle, the conventional time-frequency analysis (TFA) methods cannot provide both good time and frequency resolution at the whole frequency region. Moreover, in most cases, the interested frequency component of a signal only locates in a narrow frequency region, so there is no need to analyze the signal in the whole frequency region. Different from conventional TFA methods, the proposed method arms to analyze the signal in a specific frequency region with both excellent time and frequency resolution so as to obtain accurate instantaneous frequency (IF) estimation results. The proposed ZST is an improvement of the synchrosqueezing wavelet transform (SWT) and consists of two steps, i.e., the frequency-shift operation and the partial zoom synchrosqueezing operation. The frequency-shift operation is to shift the interested frequency component from the lower frequency region to the higher frequency to obtain better time resolution. The partial zoom synchrosqueezing operation is conducted to analyze the shifted signal with excellent frequency resolution in a considered frequency region. Compared with SWT, the proposed method can provide satisfactory energy concentrated time-frequency representation (TFR) and accurate IF estimation results. Additionally, an application of the proposed ZST to the IS fluctuation estimation of a motorized spindle was conducted, and the result showed that the IS estimated by the proposed ZST can be used to detect the quality of the finished workpiece surface.

Abstract: The micromechanical investigation of fiber cross-section shape effect on the rate sensitive nonlinear behavior of a glass/epoxy was performed at 10^-5/s and 1/s, which considering four shapes, square, cross, circle and ellipse. With the strain of different rate loadings measured by Fibre Bragg gratings (FBGs) sensors, the rate-dependent inelastic constitutive relationship of epoxy is built by using an internal state variables viscoplasticity model. Then, through homogenizing the properties of unit cells, the responses of resin and its composites at 30° and 60° off-axis loadings are predicted by a micromechanical model compared with the experiments data. The effect of fiber cross-section fiber on the 30° and 90° off-axis responses are discussed with respect to the viscoplastic parameters of the resin determined. The results indicate that the micromechanical model accurately calculates the behavior of the PMCs employed. The square fiber causes the largest flow stress and plastic strain in the four cases. And the influences on overall responses for the four fiber shapes are enhanced with raising off-axis angles but weaken with the rate increase. However, the elliptical fiber yields the highest modulus in linear elastic stage. The square fiber is the most effective and the elliptical fiber is the least effective in the nonlinear deformation stage. Besides, the elastic properties are unaffected by loading rates when it is less than 1/s.

Abstract: The conventional modal methods become inefficient when expanded to the high frequency region. This leads to a large number of degrees of freedom (DOF) even for one-dimension structures. Meanwhile, a short computational time is also the requirement of on-line structural health monitoring. This paper presented an application of B-spline wavelet on interval (BSWI) finite element for one-dimension elastic wave propagation problems. By using central difference method in time domain, numerical results involving wave propagations in crack free rod and beam were obtained and compared with results calculated by classical finite element method. Numerical examples validated the good performance of BSWI. BSWI could provide a accurate and efficient solution for wave propagation problems. The proposed method provides a good reference for structural health monitoring.

Abstract: As the requirements for industrial operation and military work, the frequency characteristics should be changed artificially sometimes. Active control is a good choice, but the current active control mainly focuses on time domain for vibration control. In this paper, the structural active control on frequency domain is studied through theory and experiment. Firstly, multivariable wavelet finite element method with two kinds of variables (TWFEM) which is suitable for modeling of great and complex structures with high efficiency and precision is used to construct the mathematical model for the controlled structure and do static and dynamic analysis. Then the control algorithm based on neural network including two parts, identification implement and controller is constructed. The present study takes frequency response as control objective, and can not only do vibration control but also change the vibration frequency characteristics, providing a new perspective for active control.

Abstract: Due to the fact that near a crack singularity, gradients of the solution are large and are also subject to abrupt changes, so that the solution cannot locally be accurately approximated by a piecewise polynomial function on a quasi-uniform mesh. Lifting wavelet finite element has good ability in modal analysis for singularity problems like a cracked pipe. The first three natural frequencies of the cracked pipe were solved with lifting wavelet finite element, and the database for crack diagnosis was obtained. The first three measured natural frequencies were employed as inputs and the intersection of the three frequencies contour lines predicted the normalized crack location and size. The experimental examples denote the method is of higher identification precision.

Abstract: Ceramic discs are prepared with PZT powder doped with Sr and Mn, which is prepared through a modified Pechini process. A micro-actuator consists of two concentric rings with thickness of 0.15 mm made of PZT doped with Sr and Mn, a copper disc, on which the PZT rings are firmly mounted with organic glue, and a ceramic rod of φ2.5x100 mm stuck at the center of the disc. The top of the ceramic rod serves as pointer of the actuator. The outer PZT ring is equally divided into four quadrants separated each other, of which two vicinal parts are poled with the same direction as that of the inner PZT ring. The other two quadrants in the outer ring are poled with the opposite direction. The inner ring and the four quadrants of the outer ring are excited by three DC powers, respectively. Bending deformation of the copper disc is caused by properly regulating the excitation voltages exerted on the PZT ceramics. The position of the top of the ceramic rod varies with the bending deformation of the copper disc.

Abstract: Empirical mode decomposition (EMD) method is introduced, and a new EMD based approach for damage detection of rolling bearings is presented. In this approach, the characteristic high-frequency signal with amplitude modulation of rolling bearings with local damage is separated from the mechanical vibration signal as an intrinsic mode function (IMF) by using EMD, and an envelope signal can be obtained by using Hilbert transform. Then, the characteristic frequency of damage of rolling bearings is extracted by applying Fourier transform to the envelope signal. The presented approach is used to analyse experimental signals collected from rolling bearings with outer race damage or inner race damage, and the results indicate that the EMD based approach can detect damage of rolling bearings more effectively comparing with traditional envelope analysis method.

Abstract: Wavelet transform is a powerful technique well suited to non-stationary signal processing. The properties of wavelet are determined by its basis function. In the fields of modal analysis, mechanical condition monitoring and fault diagnosis, impulse responses or transient responses are very common signals to be analyzed. The Laplace wavelet is a single-sided damped exponential wavelet and is a desirable wavelet basis to analyze signals of impulse response. A correlation filtering approach is introduced using the Laplace wavelet to identify the impulse response from vibration signals. Successful results are obtained in identifying the natural frequency of a hydro-generator shaft, and diagnosing the wear fault of intake valve of an internal combustion engine.

Abstract: Vibration signals acquired from a gearbox usually are complex, and it is difficult to detect the symptoms of an inherent fault in a gearbox. In this paper, an adaptive redundant second generation wavelet (ARSGW) based on second generation wavelet (SGW) is developed. It adopts data-based optimization algorithm to design the initial prediction operator and update operator at each scale. The initial operators are interpolated with zero, and then the redundant prediction operator and update operator are obtained. The splitting step in ARSGW is removed, the approximation signal at each scale is predicted and updated with redundant prediction operator and update operator directly, and the length of approximation signal and detail signal at every scale remains the same, ARSGW eliminates translation variance of SGW. Since the redundant prediction operator and update operator lock on to the dominant structure of the signal, ARSGW can well reveal the characteristics of the signal in time domain. ARSGW is found to be very effective in detection of symptoms from the vibration signal of a large air compressor gearbox with impact rub fault. SGW is also used to analyze the same signal for comparison, no modulation signals and periodic impulses appear at any scale.

Abstract: An improved method to identify the crack location and size is presented which takes advantages of wavelet finite element (WFE). The important property of wavelet analysis is the capability to represent functions in a dynamic multiscale manner, so solution with WFE enables a hierarchical approximation to the exact solution. WFE has good ability in modal analysis for singularity problems like a cracked beam. The crack in a beam is modeled with WFE and represented as a rotational spring. The additional flexibility caused by crack in its vicinity is evaluated according to linear and elastic fracture mechanics theory. The WFE stiffness matrix of the crack is constructed and the algorithm for crack identification through the use of vibration-based inspection (VBI) is developed. With the accurate natural frequencies obtained from the transient signal measured, graphs of crack equivalent stiffness versus crack location are plotted, by providing the first three natural frequencies as an input. The intersection of the three curves gives the crack location and size. Experimental studies of cracked shafts are presented to demonstrate the accuracy of the method. The error in identification of crack location and size are both less than 2%. This study provides the new method for the diagnosis of incipient small crack.