本文選題：蘭姆波 + 逆時偏移　； 參考：《物理學(xué)報》2017年21期

【摘要】：應(yīng)用頻率域逆時偏移方法實現(xiàn)各向同性和各向異性板中缺陷的蘭姆波成像.由于缺陷引起的多模態(tài)散射信號會在重建圖像中形成偽像,根據(jù)基本導(dǎo)波模式振動對稱性的差別進行了模式分離預(yù)處理.基于多元陣列超聲技術(shù),開展了鋁板和復(fù)合板內(nèi)缺陷頻率域逆時偏移超聲成像方法的數(shù)值仿真研究.首先,建立有限元模型,采用環(huán)形傳感器數(shù)值采集由缺陷引起的蘭姆波散射信號,然后,將采集到的多模式散射信號進行模式分離處理,再將模式分離后的蘭姆波散射信號經(jīng)時間反轉(zhuǎn)后并在相應(yīng)的接收器處重新激勵,在頻域中運用格林函數(shù)反向傳播蘭姆波散射信號,獲取監(jiān)測區(qū)域的聲場信息,與正向傳播聲場進行互相關(guān),重建缺陷圖像.首先對鋁板中單缺陷以及復(fù)合材料板中相鄰的兩個相同缺陷進行數(shù)值仿真,對比有無模式分離處理的缺陷逆時偏移成像效果,體現(xiàn)出模式分離的重要性.在此基礎(chǔ)上,采用逆時偏移方法對復(fù)合板材內(nèi)位置鄰近、深度不同的雙缺陷進行識別.數(shù)值結(jié)果表明,模式分離預(yù)處理后的缺陷重建圖像能夠有效去除多模式干擾產(chǎn)生的偽像.文中提出的成像方法對各向同性板和各向異性板內(nèi)缺陷的檢測和成像具有很好的發(fā)展?jié)摿?可以準確地探測多個缺陷的形狀、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.
【作者單位】： 上海大學(xué)通信與信息工程學(xué)院;上海工程技術(shù)大學(xué)城市軌道交通學(xué)院;
【基金】：國家自然科學(xué)基金(批準號:11674214,11474195,51478258) 上海市科委重點支撐項目(批準號:16030501400)資助的課題~~
【分類號】：TP212;TP391.41

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