ABSTRACT A three‐dimensional finite‐element time‐domain forward‐modelling algorithm is developed to simulate transient electromagnetics excited by grounded‐wire sources. The main advantage of this finite‐element time‐domain algorithm is that full transmitting‐current waveforms and complex‐shaped sources resulting from topography can be directly dealt with in this algorithm. The models used to test this algorithm include a homogeneous half‐space model, a stratified‐medium model, the model of a complex conductor at a vertical contact and the Ovoid Zone massive sulfide deposit at Voisey's Bay, Canada. The homogeneous half‐space model is used to determine the truncation boundary for a computational domain, and to compare with the electromagnetic responses excited by step‐off, step‐on and direct current waveforms. For the stratified‐medium model, results demonstrate that full transmitting waveforms have strong effects on the observed electromagnetic responses. The model of a complex conductor at a vertical contact is designed for the grounded electrical source airborne transient electromagnetic method and is also used to examine the effectiveness of the broadside and inline configurations for such a vertical, thin plate embedded in the subsurface. The area of the Ovoid Zone massive sulfide deposit possesses non‐negligible topography, the effects of which on the shapes of the grounded‐wire sources must be taken into account when implementing the finite‐element time‐domain solver. The results show that both the broadside and inline electromagnetic responses are strongly affected by the massive conductive ore body.

中文翻译：

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由接地线源激发的瞬态电磁场的 FETD 正向建模算法

摘要 开发了一种三维有限元时域前向建模算法来模拟接地线源激发的瞬态电磁。这种有限元时域算法的主要优点是可以直接处理由地形引起的完整传输电流波形和复杂形状的源。用于测试该算法的模型包括均质半空间模型、分层介质模型、垂直接触处的复杂导体模型和加拿大 Voisey's Bay 的 Ovoid Zone 块状硫化物矿床。齐次半空间模型用于确定计算域的截断边界，并与步进、步进和直流波形激发的电磁响应进行比较。对于分层介质模型，结果表明，全传输波形对观察到的电磁响应有很强的影响。垂直接触处的复杂导体模型是为接地电源机载瞬态电磁法设计的，还用于检查嵌入地下的这种垂直薄板的宽边和内联配置的有效性。卵形带块状硫化物矿床区域具有不可忽略的地形，在实施有限元时域求解器时必须考虑其对接地线源形状的影响。结果表明，块状导电矿体对宽边和内联电磁响应都有强烈的影响。