Jiao Jingpin

A new acoustic emission source location technique based on wavelet transform and mode analysis

For wave propagation in dispersive media, the arrival time of the acoustic emission signal to the sensor is dependent on the setting of the threshold voltage, which results in the inaccuracy of the acoustic emission location. Based on the wavelet transform and the theory of modal acoustic emission, a new method is proposed to improve the accuracy of acoustic emission source location. It is believed that the acoustic emission signal propagation in the structure has the characteristics of multi-mode and dispersion, and the acoustic emission source location should use the arrival time to sensors obtained from the output signals not only at the same mode but also at the same frequency. The wavelet transform is used to resolve the problem. By utilizing the time-frequency data of the wavelet, the frequency-dependent arrival time traveling is easily obtained; by numerical computation of the wave’s propagation in structure, the group velocity of the guided mode is also obtained, therefore the accuracy source location is realized. The acoustic emission source location experiments were conducted in a thin steel plate and results show that the technique is an effective tool for acoustic emission source location.

Numerical Simulation of Multi-path Ultrasonic Flowmeter: Ultrasonic Path Error Analysis

The precision of ultrasonic flowmeter is mainly depending on ultrasonic path adaptability for velocity profile of pipe, especially for the special cases, such as ultrasonic flowmeter located near the elbow of pipe. In this paper, the flow fields of some typical pipes were numerically calculated with commercial CFD software, and the velocity profiles in different section of pipe were investigated. Based on the simulated velocity profile, flow rate in special section of the double bend pipe was measured using different ultrasonic path configuration methods, such as Gaussian-path, Jacobianpath and diametral-path. According to the error of the measured flow rate, it is easy to get the optimal layout of ultrasonic path for the particular velocity profile. It is proved that the numerical simulation of flow field is useful for the optimization of the ultrasonic paths of flowmeter.

Research on mixed-frequency nonlinear Lamb waves for micro-cracks detection in plate

As linear ultrasonic technique is usually limited in detection of micro-cracks in plate, a nonlinear ultrasonic technique using mixed-frequency Lamb waves was proposed. Interaction of pure S0 mode Lamb waves and micro-cracks was simulated by finite element method. Spectrum analysis was utilized to extract the amplitude of sum frequency and difference frequency in receiving signal. The impact of crack length and crack thickness on the amplitude of sum and difference frequency was also taken into account. The results showed that there is a positive relationship between the crack length and the amplitude of sum and difference frequency, and this two amplitudes would decrease while the crack thickness kept increasing. Then an experiment was conducted to prove the feasibility of micro-cracks detection using the mixed-frequency nonlinear Lamb waves technique.