3D viscous-spring artificial boundary in time domain

After a brief review of studies on artificial boundaries in dynamic soil-structure interaction, a three-dimensional viscous-spring artificial boundary （VSAB） in the time domain is developed in this paper. First, the 3D VSAB equations in the normal and tangential directions are derived based on the elastic wave motion theory. Secondly, a numerical simulation technique of wave motion equations along with the VSAB condition in the time domain is studied. Finally, numerical examples of some classical elastic wave motion problems are presented and the results are compared with the associated theoretical solutions, demonstrating that high precision and adequate stability can be achieved by using the proposed 3D VSAB. The proposed 3D VSAB can be conveniently incorporated in the general finite element program, which is commonly used to study dynamic soil-structure interaction problems.     

低温SQUID瞬变电磁法中去除地磁场影响的方法研究

采用低温SQUID(Superconducting Quantum Interference Device)进行瞬变电磁测量,具有高灵敏度的优势,但易受到地磁场的影响.由于地磁场变化为nT量级,而低温SQUID灵敏度可达■.使用传统的双极性脉冲激励叠加对地磁场的抑制作用有限.当晚期道二次场信号叠加了地磁场信号后,导致晚期道信号发生整体抬升或降低,甚至出现负值,使得晚期道信号无法直接利用,从而直接影响勘探深度.本文研究不同噪声环境下信号叠加对噪声压制的机理,并结合地磁场的特点,对off-time晚期道噪声段进行一次线性拟合,获得近似地磁场变化规律,并通过外推得到整个off-time地磁场干扰,最终去除off-time信号中的地磁场.去除地磁场后晚期道瞬变电磁信号信噪比明显改善,勘探深度得到较大提高.