| Structure must fit the basic requirements, such as safety, durability and sustainability for a long-term operation. In the long time service, its performance may go through being weake--ned slowly, it also may suffer damage or even destroyed when suffering from serious nature disasters. Damage detection has caught attention in Aerospace, Civil Engineering and Mecha--nical Structures. Due to the good performance of long propagation distance, fast velocity and sensitive to minute damage in plate-like structures, Ultrasonic Lamb wave has been used in nondestructive testing and attracted great interests of scholars at home and abroad.However, Due to its high requirements in simulating the propagation of Lamb wave in plate, such as the great density of grids and tiny step of time. The detection range is always very wide, so the computation time is usually very long. Thus, it is necessary to find a valid method to advance the computation efficiency. This paper mainly did the jobs as follows:The ultrasonic wave propagation theory in plate is firstly introduced, and then implement-ed the finite element software ABAQUS to simulate the ultrasonic wave propagation in plate. Ultrasonic Lamb wave has been widely used in nondestructive testing and damage detection and localization. This paper implemented Four-point localization method, implemented ABAQUS to establish an effective finite element model of plate with damage and to simulate wave propagation in plate with damage, achieved the goal of identification and localization of damage in plate with ultrasonic wave.Secondly, as very useful tools of signal processing methods, Fourier Transform could translate time domain analysis of the structure dynamic response to frequency domain analysis. This paper firstly used Fourier Transform to translate the Finite Element Dynamics Equations into frequency domain and simulated the dynamic response in frequency domain. At the same time, this paper deduced the formulation of Finite element in frequency domain with Laplace Transform, and realized the numerical simulation of its transverse transform based on FFT in MATLAB. This paper also verified its validity.Finally, wavelet transform has been widely used in signal processing as the magnifying glass in math, it is very necessary to do some research on wave propagation formulation with wavelet transform. This paper deduced two different methods of wave propagation based on wavelet transform, one of which is the method of simulating the ultrasonic wave propagation in plate with Daubechies wavelet transform, and the other one is based on B-spline wavelet finite element method. This paper used an example with B-WFEM to verify its validity. |
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