电磁检测中的开域电磁场数值计算

STUDY OF NUMERICAL COMPUTATION OF OPEN BOUNDARY FIELD IN ELECTROMAGNETIC DETECTION

该文以涡流电缆偏心检测为例,针对电磁检测中开域涡流磁场难于求解这一问题,根据有限元和边界元的特点,对开域电磁场,采用设定虚拟边界的方法将无界场域分割成闭合的内部区域和开放的外部区域,在两个区域分别采用有限元法(FEM)和边界元法(BEM),在虚拟边界上采用直接耦合方法,使有限元方程和边界元方程得以成功组合,从而获得全域解。该方法避免了利用自然边界划分有限元区和边界元区,使开放的边界元区含有多种媒质及源,造成边界元方程组非对称满阵阶数过高,难于计算的缺点。得出了磁场的分布及其检测对象的涡流损耗。计算结果与偏心量变化的线性关系和实验结果与偏心量变化的线性关系在视在阻抗的物理意义上具有良好的一致性。

This paper gives an example of the eddy current detection of the Biased Cable, aiming at boundary eddy field difficult to be calculated in electromagnetic detection, according to the characteristics of FEM and BEM, for open boundary electromagnetic field, the infinite regions were divided into finite inner region and infinite outer regions by the method of setting a virtual boundary. FEM and BEM were used respectively to derived the A?φ, A formulation with Coulomb’s gauge. On the suppositional border field, FEM and BEM equations were combined successfully to get the all solutions in the directly coupled method. This method avoids containing several kinds of medias and sources in opened sub-region and making equations unsymmetrical ranks too high by subdividing the entire region according to natural boundary. Furthermore, the distribution of magnetic field and cables eddy current losses was achieved. The results of computation and experiment were in good agreement in the sense of apparent impedance, and the trend of distribution of magnetic field was reasonable.