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吸收边界条件对于全空间瞬变电磁计算的稳定性和精确性是至关重要的.将Laplace方程应用于巷道中,避免了对巷道内空气电阻率的设置;将廖氏边界条件进行必要的修正,导出了适用于扩散方程的新的吸收边界条件;计算了新边界条件的应用效果和巷道底板内低阻薄板的响应特征.结果表明:巷道边界两侧瞬变场的扩散速度明显改变;应用Dirichlet边界条件使边界处的磁场约在0.05 ms后发生畸变,并对计算区域内部磁场产生影响,而新吸收边界条件采用N=4阶精度并取控制系数为β=0.9时,计算的磁场值与理论值具有相同的衰减规律,该方法能较好的反映出薄板的位置及倾斜角度.新的吸收边界条件适用于全空间瞬变电磁场的有限差分计算.
Absorption boundary conditions are crucial for the stability and accuracy of the full-space transient electromagnetic calculation.The Laplace equation is applied to the roadway to avoid the setting of the air resistivity in the roadway and the necessary modification of the Liao boundary condition , The new absorption boundary conditions for the diffusion equation are deduced and the application effects of the new boundary conditions and the response characteristics of the low-resistivity sheet in the roadway floor are calculated. The results show that the diffusion speed of the transient field on both sides of the roadway boundary changes obviously. The Dirichlet boundary condition distorts the magnetic field at the boundary after about 0.05 ms and affects the magnetic field inside the calculation area. The new absorption boundary condition uses N = 4 order precision and the control coefficient is β = 0.9. The calculated magnetic field value Which has the same attenuation law as the theoretical value, which can well reflect the position and inclination angle of the thin plate.The new absorption boundary conditions are suitable for the finite difference calculation of the full space transient electromagnetic field.