Suzhen Liu

Improvement of the element-free Galerkin method for electromagnetic field calculation

The element-free Galerkin method (EFGM) is meshless method, it can solve some problems that the finite element method (FEM) can not solve effectively in electromagnetic field, such as thin plate problems, narrow gap problems, moving conductors, etc. In this paper, an improved formulation of the EFGM is proposed for electromagnetic field computations. Detailed research is conducted on some key problems, such as the selection of the weight function, the treatment of imposing boundary conditions and interface conditions. Finally, numerical examples are cited for demonstration.

Electromagnetic Stimulation of the Acoustic Emission for Fatigue Crack Detection of the Sheet Metal

A new electromagnetically induced acoustic emission technique (EMAE) is presented in this paper. Due to the acoustic emission signal generated by the electromagnetically induced high-density eddy current pulse, EMAE can locate small flaws or cracks in thin-walled structures nondestructively in order to inspect specific areas without loading the whole structure. The acoustic emission (AE) signal captured by conventional or fiber optic AE sensors is modulated at the defect due to the crack closure. The differences can be found by comparing modulated AE signals from the defects and ones from the intact region in the spectrum. In this paper, the finite element model of EMAE has been implemented based on the concrete experiment models. The samples deformation has been analysed when the exciting coil locates at different position. The results of experiments indicate that electromagnetic transient modulation of the acoustic emission could be used to enhance detection of small cracks in thin-walled metallic structures.

Element-free Galerkin modeling of giant magnetostrictive thin films

A meshless method called the element-free Galerkin method (EFGM) is introduced into the calculation of magnetostrictive thin film. With the finite element method (FEM), the distortion of the elements will decrease the precision, so EFGM is used to solve this problem. Two different magnetomechanical coupling models are proposed and a thin film cantilever is simulated with these two modeling methods. At last, the results are compared with the experiment data to illustrate the performance of EFGM and the correctness of the models.

Enhanced acoustic emission detection induced by electromagnetic stimulation with external magnetic field

The application of external magnetic field in the electromagnetically induced acoustic emission technique (EMAE) can enhance the ability of detecting the defects and reduce the stimulation current flow in the coil, due to the even bigger deformations generated by the enhanced Lorentz Force at the defects. In this paper, the finite element model of EMAE including an external magnetic field has been implemented based on the concrete experiment models. The samples deformation has been analyzed when the exciting coil locates at different position. The results of experiments indicate that the defect itself can generate the modulated acoustic emission. That could be used to enhance detection ability of small cracks in the thin-walled metallic structures.

Theoretical and experimental researches on magnetic fluid acceleration sensor

A kind of magnetic fluid acceleration sensor (MFAS) is presented in the paper, which is using the magnetic and fluid characteristic of magnetic fluid. First, the output characteristics of MFAS and its static sensitivity are analyzed based on minimum potential energy principle, the result indicates the linear relationship between output voltage and acceleration. Then, the experimental research is carried out and compared with piezoelectric acceleration sensor simultaneity based on ZJY-601A experiment platform. The output signal of MFAS is sampled and processed by the signal processing system, the output waveform demonstrate that the experimental results are both in agreement with theoretical analysis and output of piezoelectric acceleration sensor. Finally, system errors and influencing factors on measurement sensitivity are analyzed qualitative.

Microscopic Mechanism and Experiment Research of Electromagnetically Induced Acoustic Emission

Based on the electrical activated plastic concept and mobile dislocation model, the mechanism of electromagnetically induced acoustic emission (EMAE) will be studied at a microscopic level. From the perspective of driving effect between electrons and dislocation, a new formulation and numerical calculation for the determination of AE radiation energy in electromagnetic loading will be derived to address the acoustic effect on the crack tip of metals. The EMAE experiments under different exciting conditions are carried out. According to dislocation kinetics theory and plastic AE theory, the mechanism and characteristics of the EMAE have a deeper analysis with experimental AE signals, validating the feasibility of the theoretical prediction of the foundation and demonstrating its superior features and value.

Amplitude Characteristics of Acoustic Emission Signals Induced by Electromagnetic Exciting

The amplitude characteristics of electromagnetically induced acoustic emission (EMAE) are studied through the finite-element method (FEM) and validated by EMAE experiment. The deformation of a crack is calculated and analyzed by using FEM, and the deformation nature of the defect is determined by the fracture mechanics. The EMAE experiments under different exciting currents are carried out and the crack is located by acoustic emission (AE) signals. In addition, the calculated deformation and experimental AE signals are normalized. According to Kaiser effect and AE theory, the partly direct relationship between the acoustic emission signal and the calculated deformation can be obtained. This study provides crucial references for optimization analysis of EMAE. Meanwhile, the application of eddy current greatly reduces the demands of the power supply and improves the detection speed compared using the direct loading, which makes the engineering application of EMAE in possible.

Improved genetic algorithm for optimal design of transverse flux inductor

A procedure is presented for optimal design of transverse flux inductor. To improve the convergence speed and local searching ability for genetic algorithm, subpopulation competition and data exchange method is proposed. One purpose of that is for basic population to decide when to produce a new subpopulation; the other purpose is to introduce quality individuals from subpopulation into basic population. For the electromagnetic-thermal problems, a coupling procedure is presented to reduce the time consuming. The produced heat source in the strip was supposed to move in elements in the opposite direction of the actually continuously moving strip for transverse flux induction heating (TFIH), thus every temperature field computation could take advantage of the heat source distribution resulted from the former eddy current field calculation, which led to the time for numerical simulation of TFIH reduced

Research on Electromagnetically Acoustic Emission Signals Using Sample Entropy

As a new approach of measuring the irregularity of the time series, Sample entropy (SampEn), which is defined as a quantity measuring the rate of information generation, has good anti-jamming capability. In this work, successful researches are performed to analyze the electromagnetically induced acoustic emission (EMAE) signal produced by loading pulse current in the aluminium plates, using SampEn. Besides, it studies the complexity of EMAE signal changing over time, identifies and extracts features of EMAE signal. The SampEns performance on characterizing the signals, demonstrates that SampEn is a promising method in recognition and distinguishment of EMAE signal.

Study of Weight Functions in the Element-Free Galerkin Method

The weight function plays an important role in the performance of the element-free Galerkin Method (EFGM). It can impose a tremendous influence on the accuracy of solutions, the complexity of computation and the rate of convergence. The continuity of the weight function causes the continuity of the shape function in the EFGM. Therefore, it becomes particularly urgent to select an appropriate weight function suited to electromagnetic calculations