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为了提高时域逆时偏移成像的计算精度,基于辛几何算法能获得半解析解精度结果的特点,结合逆时偏移成像条件构建了时域辛几何逆时偏移成像算法.首先,用有限元软件建立含缺陷结构和未知缺陷结构的有限元离散模型,然后用勒让德变换将二阶微分方程组变换成保辛的一阶微分方程组,用精细积分方法求解该一阶微分方程组;最后,基于逆时偏移成像条件,通过偏移叠加算法获得含缺陷结构的成像结果.结果表明,成像结果与预设缺陷吻合良好,该方法可以精确地检测出结构内部的缺陷.
In order to improve the accuracy of inverse time migration imaging in time domain, the symplectic geometry algorithm is used to obtain the resolution of semi-analytical solution. Combined with the inverse time migration imaging conditions, a symplectic geometric inverse time migration imaging algorithm is constructed. Firstly, Finite element software is used to establish the finite element discrete model with defect structure and unknown defect structure. Secondly, the second-order differential equations are transformed into first-order differential equations by Paul Legend transformation, and the first-order differential equations Finally, based on the reverse migration imaging conditions, the imaging results of the defect-containing structures are obtained by the offset-stacking algorithm.The results show that the imaging results are in good agreement with the prefabricated ones, which can accurately detect the defects in the structures.