Abstract:Based on Maxwell curl equations,the three-dimensional finite difference time domain formula about UPML absorbing boundary of conductive medium is derived;without considering permeability,the link between simulation area and UPML absorbing boundary field is established;UPML absorbing boundary formula is used for forward simulation with different coefficients;but the area and temporary storage space are reduced and the speed is improved. Using Matlab programming to forward simulate the tunnel lining cavity and obtain the corresponding forward synthesis of three-dimensional profiles and slice maps,the three-dimension forward data visualization is achieved;and the three-dimensional map features of cavity are discussed. Through the physical model test of tunnel lining cavity,the results of numerical simulation and physical model test are similar so as to verify that the three-dimensional numerical simulation is feasibility and effectiveness. The results show that three-dimensional detection can not only determine the size,shape and location of cavity,but also understand accurate information of cavity comprehensively;it can improve the reliability and the accuracy of radar map interpretation,and the harmful level of cavity in lining can be assessed according to the distribution of defecting location and size. The study provides a reliable theoretical basis and method for automatic recognition technology of radar cavity map;and it has a great significance in tunnel detection project and tunnel quality of judicial expertise.
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