Xingwu Zhang

Nonlinear squeezing time-frequency transform for weak signal detection

Conventional time-frequency analysis methods can characterize the time-frequency pattern of multi-component nonstationary signals. However, it is difficult to detect weak components hidden in complex signals because the time-frequency representation is influenced by the signal amplitude. In this paper, a novel algorithm called nonlinear squeezing time-frequency transform (NSTFT) is proposed to characterize the time-frequency pattern of multi-component nonstationary signals. Most importantly, theoretical analysis shows that the NSTFT method is independent of the signal amplitude and is only relevant to the signal phase, thus it can be used for weak signal detection. Moreover, an improved ridge detection algorithm is proposed in this paper for instantaneous frequency estimation. The experiments on simulated and real-world signals show that the NSTFT method can effectively detect weak components in complex signals, and the comparison study with some other time-frequency analysis methods also shows the advantages of the NSTFT method in weak signal detection. Nonlinear squeezing time-frequency transform (NSTFT) is proposed for weak signal detection.Theoretical analysis shows that the NSTFT is independent of the signal amplitude and is only relevant to the signal phase.An improved ridge detection algorithm is proposed for IF estimation.Experiments and comparison demonstrate the effectiveness of the NSTFT in weak signal detection.

A Frequency-Shift Synchrosqueezing Method for Instantaneous Speed Estimation of Rotating Machinery

Instantaneous speed (IS) measurement is crucial in condition monitoring and real-time control of rotating machinery. Since the direct measurement of instantaneous rotating speed is not always available, the vibration measurement has been used for indirect estimation methods. In this paper, a novel indirect method is proposed to estimate the IS of rotating machinery. First, a frequency-shift synchrosqueezing transform is proposed to process the vibration signal to obtain the time–frequency (TF) representation. Second, the Viterbi algorithm is employed to extract the shifted instantaneous frequency (IF) from the TF representation. Finally, the extracted IF is used to recover the IF of the measured vibration signal. The IS of rotating machinery can be calculated from the estimated IF. The proposed method is validated with both numerical simulations and experiments. The results show that the proposed method could provide much higher frequency resolution, better TF concentration results, and more accurate IF estimation of the considered signal compared with the synchrosqueezing method. Furthermore, the proposed method was confirmed to be less sensitive to noise, especially for high-frequency components. [DOI: 10.1115/1.4029824]

THE ANALYSIS OF SHALLOW SHELLS BASED ON MULTIVARIABLE WAVELET FINITE ELEMENT METHOD

Based on the generalized variational principle and B-spline wavelet on the interval (BSWI), the multivariable BSWI elements with two kinds of variables (TBSWI) for hyperboloidal shell and open cylindrical shell are constructed in this paper. Different from the traditional method, the present one treats the generalized displacement and stress as independent variables. So differentiation and integration are avoided in calculating generalized stress and thus the precision is improved. Furthermore, compared with commonly used Daubechies wavelet, BSWI has explicit expression and excellent approximation property and thus further guarantee satisfactory results. Finally, the efficiency of the constructed multivariable shell elements is validated through several numerical examples.

A Novel Hybrid Error Criterion-Based Active Control Method for on-Line Milling Vibration Suppression with Piezoelectric Actuators and Sensors

Milling vibration is one of the most serious factors affecting machining quality and precision. In this paper a novel hybrid error criterion-based frequency-domain LMS active control method is constructed and used for vibration suppression of milling processes by piezoelectric actuators and sensors, in which only one Fast Fourier Transform (FFT) is used and no Inverse Fast Fourier Transform (IFFT) is involved. The correction formulas are derived by a steepest descent procedure and the control parameters are analyzed and optimized. Then, a novel hybrid error criterion is constructed to improve the adaptability, reliability and anti-interference ability of the constructed control algorithm. Finally, based on piezoelectric actuators and acceleration sensors, a simulation of a spindle and a milling process experiment are presented to verify the proposed method. Besides, a protection program is added in the control flow to enhance the reliability of the control method in applications. The simulation and experiment results indicate that the proposed method is an effective and reliable way for on-line vibration suppression, and the machining quality can be obviously improved.

Modeling and active vibration control of a coupling system of structure and actuators

A model is extremely important to the controller designing and system analysis of an active vibration control system. However, the influence of actuators is always ignored by considering them as proportion links when modeling the control system. In this work, a joint model of a clamped-free shell structure and electrodynamic actuators was constructed. The shell was modeled using the finite element method while the actuators were simplified as lumped parameter models. It was found that the connections of actuators diminish the natural frequencies and smooth the resonance peaks of the structure. The optimal configuration of actuators and sensors was studied by harmonic response analysis and modal analysis. It was suggested to avoid the central line and give priority to the free end or the edges of the clamped-free shell when mounting actuators and sensors. The active control was carried out using the FXLMS algorithm, which effectively suppressed the disturbance of the vibration source. The control was conducted point by point on the transient response model of the structure and can easily be extended to a real life system.

Hermitian plane wavelet finite element method: Wave propagation and load identification

Abstract The two-dimensional Hermitian interpolation wavelet is constructed by using the tensor product of the modified Hermitian wavelets expanded at each coordinate. Then the two-dimensional Hermitian interpolation wavelet is substituted into finite element formulations to address the wave propagation and load identification problems. Hermitian wavelet finite element can be used to describe the wave propagation and to reveal the rule of the wave propagation in plane. The wave propagation response is used to solve the load identification inverse problem. Results show that the identified load value is similar to the applied load when the location of the response node is close to the applied load position. The proposed method can accurately identify the location, waveform and amplitude of the applied load.

Analysis of Laminated Plates and Shells Using B-Spline Wavelet on Interval Finite Element

Composite materials, with characteristics of light weight and high strength, are useful in manufacturing. Therefore, precise design and analysis is the first key procedure in composite applications, improper analysis or use of composite materials may cause serious failures. In this paper, wavelet finite element method (WFEM) based on B-spline wavelet on the interval (BSWI) is constructed for precise analysis of laminated plates and shells, which gives a guidance in design and application of composite structures. First, FEM formulations are derived from the generalized potential energy function based on the generalized variational principle and virtual work principle. Then, BSWI scaling functions are used as interpolation function to discretize the solving displacement field variables. At the same time, transformation matrix is constructed and used to translate the meaningless wavelet coefficients into physical space. At last, the static analysis results can be obtained by solving the FEM formulations. Due to the excellent features of BSWI, such as multiresolution, multiscale, localization and excellent numerical approximation characteristics etc., BSWI-based FEM can achieve accurate and efficient analysis by comparing with traditional methods. In the end, the effectiveness of the constructed BSWI WFEM is verified through several numerical examples.

Simulation and Experimental Investigation of Structural Dynamic Frequency Characteristics Control

In general, mechanical equipment such as cars, airplanes, and machine tools all operate with constant frequency characteristics. These constant working characteristics should be controlled if the dynamic performance of the equipment demands improvement or the dynamic characteristics is intended to change with different working conditions. Active control is a stable and beneficial method for this, but current active control methods mainly focus on vibration control for reducing the vibration amplitudes in the time domain or frequency domain. In this paper, a new method of dynamic frequency characteristics active control (DFCAC) is presented for a flat plate, which can not only accomplish vibration control but also arbitrarily change the dynamic characteristics of the equipment. The proposed DFCAC algorithm is based on a neural network including two parts of the identification implement and the controller. The effectiveness of the DFCAC method is verified by several simulation and experiments, which provide desirable results.

A Stochastic Wavelet Finite Element Method for 1D and 2D Structures Analysis

A stochastic finite element method based on B-spline wavelet on the interval (BSWI-SFEM) is presented for static analysis of 1D and 2D structures in this paper. Instead of conventional polynomial interpolation, the scaling functions of BSWI are employed to construct the displacement field. By means of virtual work principle and BSWI, the wavelet finite elements of beam, plate, and plane rigid frame are obtained. Combining the Monte Carlo method and the constructed BSWI elements together, the BSWI-SFEM is formulated. The constructed BSWI-SFEM can deal with the problems of structural response uncertainty caused by the variability of the material properties, static load amplitudes, and so on. Taking the widely used Timoshenko beam, the Mindlin plate, and the plane rigid frame as examples, numerical results have demonstrated that the proposed method can give a higher accuracy and a better constringency than the conventional stochastic finite element methods.

Multiple-harmonic amplitude and phase control method for active noise and vibration reshaping:

With the development of active noise and vibration control technology, there are increasing demands for active noise and vibration reshaping (ANVR) other than cancellation in the fields of active sound quality control, psychoacoustics, medical devices, military equipment, etc. The active noise equalizer (ANE) is one of the most popular ANVR methods. However, the ANE only controls (scales) the amplitude of the residual noise without considering the control of phase, and is unable to control frequency components that are excluded in primary noise. In this paper, we propose a more general and effective algorithm, called amplitude and phase control (APC), for ANVR, which can control amplitude and phase, simultaneously, of any interesting frequency component of the residual noise. Firstly, a modified active noise equalizer (MANE) algorithm with improved convergence is proposed based on the reference amplitude normalization and structure modification. Then, the APC algorithm is derived based on the MANE algorithm. Furthermore, numerical simulations and analytical investigations of the APC algorithm are conducted. Finally, case studies using experimental data are carried out. The multiple-harmonic primary noise was measured from a rotor test-platform and the secondary path model was identified according to a random vibration test on a shell structure. The results further verify the validity and robustness of the proposed APC algorithm.