基于模式分离的兰姆波逆时偏移成像

发布时间：2018-05-23 20:09

本文选题：兰姆波 + 逆时偏移　；参考：《物理学报》2017年21期

【摘要】：应用频率域逆时偏移方法实现各向同性和各向异性板中缺陷的兰姆波成像.由于缺陷引起的多模态散射信号会在重建图像中形成伪像,根据基本导波模式振动对称性的差别进行了模式分离预处理.基于多元阵列超声技术,开展了铝板和复合板内缺陷频率域逆时偏移超声成像方法的数值仿真研究.首先,建立有限元模型,采用环形传感器数值采集由缺陷引起的兰姆波散射信号,然后,将采集到的多模式散射信号进行模式分离处理,再将模式分离后的兰姆波散射信号经时间反转后并在相应的接收器处重新激励,在频域中运用格林函数反向传播兰姆波散射信号,获取监测区域的声场信息,与正向传播声场进行互相关,重建缺陷图像.首先对铝板中单缺陷以及复合材料板中相邻的两个相同缺陷进行数值仿真,对比有无模式分离处理的缺陷逆时偏移成像效果,体现出模式分离的重要性.在此基础上,采用逆时偏移方法对复合板材内位置邻近、深度不同的双缺陷进行识别.数值结果表明,模式分离预处理后的缺陷重建图像能够有效去除多模式干扰产生的伪像.文中提出的成像方法对各向同性板和各向异性板内缺陷的检测和成像具有很好的发展潜力,可以准确地探测多个缺陷的形状、尺寸和深度.
[Abstract]:Lamb wave imaging of defects in isotropic and anisotropic plates is realized by inverse time migration in frequency domain. Because the multi-mode scattering signal caused by the defect will form a false image in the reconstructed image, the mode separation preprocessing is carried out according to the difference of the vibration symmetry of the basic guided wave mode. Based on the multi-element array ultrasonic technique, the numerical simulation of the inverse time offset ultrasonic imaging method in frequency domain for defects in aluminum plate and composite plate is carried out. Firstly, the finite element model is established, and the Lamb wave scattering signal caused by the defect is collected numerically by ring sensor, and then the multi-mode scattering signal is processed by mode separation. Then, the Lamb wave scattering signal after the mode separation is reversed and re-excited at the corresponding receiver, and then the Green function is used to reverse propagate the Lamb wave scattering signal in the frequency domain to obtain the sound field information of the monitoring area. The defect image is reconstructed by cross-correlation with the forward propagating sound field. First, the single defect in aluminum plate and two adjacent same defects in composite plate are numerically simulated, and the effect of inverse time migration of defect with or without pattern separation is compared, which shows the importance of pattern separation. On this basis, the inverse time migration method is used to identify the double defects with different depths and adjacent positions in the composite plate. The numerical results show that the defect reconstruction image after mode separation preprocessing can effectively remove the artifacts generated by multi-mode interference. The imaging method proposed in this paper has great potential for detecting and imaging defects in isotropic and anisotropic plates, and can accurately detect the shape, size and depth of multiple defects.
【作者单位】：上海大学通信与信息工程学院;上海工程技术大学城市轨道交通学院;
【基金】：国家自然科学基金(批准号:11674214,11474195,51478258) 上海市科委重点支撑项目(批准号:16030501400)资助的课题~~
【分类号】：TP212;TP391.41

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