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为了应用时间域电磁法进行深部勘探,需要计算大尺度模型的晚时时域响应.本文将待求解的电磁响应分解为一次场和二次场之和,实现了波形为拟高斯脉冲的大功率脉冲源激励的一次场的计算.对于三维异常体产生的二次场,采用基于非均匀步长交错网格的时域有限差分(FDTD)和非等时步长的迭代算法求解,在层状介质模型的上阶跃响应计算结果对比以及与积分方程计算的瞬断响应结果对比验证基础上,实现了大功率脉冲源激励下晚时时域电磁响应的计算.通过设计一个简单异常体的三维模型,采用电偶极源脉冲电流激发,计算的时间域响应很好的揭示了大功率脉冲源激励的场在地中随时间扩散,以及三维异常体产生的异常场并二次扩散的过程.
In order to apply the time domain electromagnetic method for deep exploration, it is necessary to calculate the late-time time-domain response of the large-scale model.In this paper, the electromagnetic response to be solved is decomposed into the sum of the primary field and the secondary field and the high power pulse whose waveform is quasi-Gaussian pulse Calculation of the primary field of source excitation For the second field generated by the three-dimensional anomaly, an iterative algorithm based on finite difference time-domain (FDTD) and non-isochronous steps based on staggered grid with non-uniform steps is adopted. Based on the contrast between the upper-step response of the model and the comparison with the instantaneous response calculated by the integral equation, the electromagnetic response of the late-time electromagnetic field under high-power pulse excitation is calculated.By designing a three-dimensional model of the simple abnormal body, Using the electric dipole pulse current excitation, the calculated time-domain response shows the diffusion process of the high-power pulsed-source excited field over time in the ground and the secondary diffusion caused by abnormal three-dimensional anomalies.