Sparse Reconstruction Of Lamb Wavefield And Damage Imaging Based On Compressive Sensing

In the damage detection and evaluation of thin-plate structures,the Lamb wave field analysis method can not only accurately image the damage,but also evaluate the damage quantitatively.However,in the process of acquiring full-wave field signals,limited by Nyquist sampling law,it is necessary to set at least one measuring point in the minimum half-wavelength distance in space,which results in a huge number of measuring points and time-consuming measurement process.Moreover,the massive data collected also brings great challenges to data storage,transmission and analysis.The sparse reconstruction method of Lamb wave field based on compressed sensing can accurately reconstruct the original wave field by a small amount of spatial signal.However,all these methods depend on the Jitter Sparse Sampling(JSS)strategy in space,and the jitter sampling is random,which requires additional control components to be added to the Scanning Laser Doppler Vibrometer(SLDV),which increases system complexity and cost.Aiming at solving the above problems,this paper presents a scheme of Lamb wave field reconstruction based on Uniform Sparse Sampling(USS).Based on the above process of wave field reconstruction,a method of damage scattering wave field separation is developed.Meanwhile,RMS imaging technique is introduced to process the reconstructed wave field data to obtain energy distribution of the damage scattering wave field,based on which the structural damage is further analyzed.The specific contents of this paper are as follows:1.The research background and application significance of this topic are expounded,and the research status and development trend of guided wave NDT based on Lamb wave are discussed.By investigating the existing research cases of sparse reconstruction method of guided wave field,the research direction and specific content of this topic are finally determined.2.Through theoretical analysis of ultrasonic Lamb wave,the multi-mode and dispersion characteristics of Lamb wave are clarified,and the theoretical dispersion curve of isotropic plate is obtained by numerical calculation method.Then the Lamb wave signals of linear array is collected from the isotropic plate,and the dispersion curve is extracted by two-dimensional Fourier transform method,and compared with the theoretical dispersion curve.3.A sparse reconstruction model of Lamb wave field based on compressed sensing is established by using the propagation characteristics of Lamb wave and the assumption of sparsity of structural features in wave field.In order to make spatial sparse sampling more convenient for SLDV measurement system,this paper proposes a USS strategy,which uses sparse points with uniform spatial distribution instead of those generated by jittered sampling,and sets the potential source points as jittered distribution,which not only ensures the accuracy of wave field reconstruction,but also breaks through the limitation of classical Nyquist sampling rate,which greatly improves the efficiency of wave field acquisition and the convenience of data acquisition.In order to eliminate the interference of the incident wave field of the excitation source on the damage analysis,a method of separating the scattered wave field of damage is developed based on the mentioned wave field reconstruction process.The method zeroes the potential source excitation functions at the known excitation source and reconstructs the wave field with new potential source excitation functions to obtain the scattered wave field of damage.In the post-processing of reconstructed wave field data,RMS imaging technique is introduced to obtain the energy distribution of Lamb wave field,and then the damage size is estimated,which further improves the technical framework of sparse reconstruction of Lamb wave field.4.An isotropic plate model with single damage is established by numerical simulation.The Lamb wave data are collected on the model by USS strategy,and the wave field reconstruction and damage imaging are carried out.The feasibility of the proposed wave field reconstruction scheme is verified.It is also compared with JSS reconstructed wave field in the aspects of damage location accuracy,wave field reconstruction accuracy and computation time.The reconstructed results are compared and analyzed.The results show that the proposed scheme can achieve the same effect as the existing methods in the case of low sampling rate.The reconstruction data of Lamb wave field corresponding to USS are processed by separating damage scattering wave field and RMS imaging.The results show that damage scattering wave field can be extracted from the original wave field.The damage size can be estimated by using RMS imaging results of damage scattering wave field.The relative error of the estimated results is 16%,which is about the calculated frequency band.A quarter of the smallest wavelength within.5.In the isotropic plate model with single damage,the sparse sampling point M,the assumed source point S and the noise water constant are studied,and the optimal parameters of wave field reconstruction are obtained.On the basis of the above model,more complex damage is set up,and the accurate results of damage imaging and wave field reconstruction are obtained by sampling and calculating with USS strategy and optimization parameters,which verifies the detection effect of the proposed wave field reconstruction scheme and damage analysis method in complex damage cases.6.The experimental platform of PZT excitation/SLDV sensing is built.The Lamb wave field data are collected on the aluminum plate specimens by USS strategy to reconstruct the wave field.The reconstructed results are compared with the JSS reconstructed wave field.The damage scattering wave field is separated by the damage scattering wave field separation method,and RMS imaging is carried out.The experimental results show that the proposed reconstruction scheme can achieve the same reconstruction accuracy as JSS.Compared with JSS,the USS strategy is easier to implement in experiments,and can reduce the acquisition time of full-wave field by more than 90%,which greatly improve the efficiency of full-wave field pickup process.At the same time,the damage size can be estimated from the RMS imaging results of the damage scattering wave field with a relative error of 20%.7.Summarize the research work of this paper,and point out the direction of the next research.