Development of an expert system for analyzing galvanic corrosion problems by using the Boundary Element Method

为了减少电偶腐蚀造成的经济损失，需要开发一种基于腐蚀行为定量分析的专家系统。在本研究中，发展了一种定量分析方法。介绍了一种用于预测阳极/阴极相互作用产生的电场响应的三维边界元方法。虽然控制方程是线性的(拉普拉斯)，但基于实验确定的极化曲线实施的边界条件通常是非线性的。为此，采用了牛顿-拉夫森迭代法。为了验证边界元方法在实际复杂电场中预测电偶腐蚀和阴极保护的计算精度，分别用单…和多…对屏蔽板电磁场进行了分析更多的三重区域方法。结果表明，随着屏幕高度的增加，两种方法的计算结果相差较大。然而，通过减小网格尺寸，两种方法得到的结果吻合较好。应用边界元方法确定了阴极保护系统的最佳外加电流密度。在该系统中，必须施加足够的电流才能将金属表面的电位分布降低到临界值。确定了使保护电源最小的最佳外加电流密度。采用共轭梯度法求解，其中控制方程和保护条件由罚函数法考虑，所考虑的材料的电化学极化曲线并不总是有效的。在这种情况下，根据电解液中的电位值估计材料上的电流密度的逆方法是必要的。这个反问题通常会产生一个病态的线性方程组。利用系数矩阵的奇异值分解，提出了一种正则化方法，并给出了确定矩阵有效秩值的判据。最后给出了涂层损伤检测的数值算例，说明了该方法的有效性。较少

In order to reduce the economic loss due to galvanic corrosion, it is desired to develop an expert system based on a quantitative analysis of the corrosion behaviors. In this research, a method of the quantitative analysis was developed. A three-dimensional boundary element method was introduced for predicting electrogalvanic field responses resulting from anodic/cathodic interaction. Although the governing equation is linear (Laplace), the boundary condition, which is enforced based on experimentally determined polarization curves, is generally non-linear. Therefore, Newton-Raphson iterative procedure was employed. The validity and usefulness of the present prediction method were demonstrated by comparing the calculated results and the experimental data.To examine the computational accuracy of the boundary element method for predicting galvanic corrosion and cathodic protection in the actual complicated field, the galvanic field with a screen plate was analyzed by using single and mul … More tiple region methods. It was found that the difference between the computational results by the two methods increased with increasing screen height. However, the results by the two methods agreed well with each other by reducing the mesh size.A boundary element method was applied to determine the optimal impressed current densities in a cathodic protection system. In this system, enough current must be impressed to lower the potential distribution on the metal surface to the critical values. The optimal impressed current densities were determined in order to minimize the power supply for protection. The solution was obtained by using the conjugate gradient method in which the governing equations and the protecting conditions were taken into account by the penalty function method.The electrochemical polarization curves of the materials considered are not always available. In this case, the inverse approach, in which the current density across the materials is estimated from the potential values in the electrolyte, is necessary. This inverse problem generally yields an ill-conditioned system of linear equations. A regularization method was introduced using the singular value decomposition of the coefficient matrix, and a criterion for determining an effective rank of matrix was presented. A numerical example of coating damage detection was presented to illustrate the usefulness of the method. Less