Development of Corrosion Estimation System With Scanning Vibrating Electrode Technique by usint Boundary Element Inverse Analysis

为了评价扫描振动电极法的精度，提出了一种分析局部腐蚀电场的有效三维边界元方法。随着电极探头离样品表面高度的降低，为了提高SVET的分辨率，电极探头会对电场产生干扰，电流分布的测量误差增大。虽然边界元方法适合用数值方法来估计误差，但仪器的整个容器与测量面积的比例比大于10^5倍，而传统的边界元方法存在单元数大的困难。为了克服这一困难，提出了一种将计算分成几个步骤的新的有效方法，并提出了一种根据远离金属表面的某些点的电位值来估计电偶腐蚀速率的方法。这个反问题是由Employ…提出的进一步介绍了边界元方法。由于所得到的线性方程组是病态的，直接将常规的数值方法应用于该方程组将导致振荡解。为了克服这一困难，首先估计了表示电位和电流密度之间关系的极化特性。为了提高精度，提出了一种利用模糊隶属度函数表示的先验信息的新方法，并对该方法进行了推广。广义方法由以下步骤组成。1.对系数矩阵进行奇异值分解，适当降阶。2.用摩尔·彭罗斯解和零空间表示解的集合。3.利用解的集合和用模糊隶属度函数表示的先验信息，通过模糊推理得到解。为了提高SVET的测量精度，采用三维边界元方法求解了一个反问题，该反问题是根据存在探头扰动误差的数据估计出沿金属表面的真实电流密度分布。然而，这些数据并不是真实的实验数据，而是数值模拟结果。为了利用实验数据进行逆分析，有必要进行进一步的研究，因为在金属表面附近必须存在比模拟更复杂的电化学现象。较少

A new effective three-dimensional boundary element method of analyzing electric field produced by localized corrosions was developed to estimate the accuracy of SVET (Scanning Vibrating Electrode Technique). With decreasing height of the electrode probe from the surface of a sample in order to improve the resolution of SVET,the electrode probe disturbs the electric field and measuring errors of the current distribution increase. Although the boundary element method is suitable for estimating the error by a numerical method, the scale ratio of whole vessel of the instrument to measurement area is larger than a factor of 10^5, and the conventional BEM has a difficulty with huge number of elements. To overcome this difficulty, a new effective method classifing computation into a few steps was proposed.A method for estimating the galvanic corrosion rate from the potential values measured at some points far from the metal surfaces was developed. This inverse problem was formulated by employ … More ing the boundary element method. Since the system of linear equations obtained is ill-conditioned, direct application of conventional numerical procedures to the equation system results in an oscillatory solution. To cope with this difficulty, the polarization characteristics which represent the relationship between potential and current density was estimated first. In order to improve the accuracy, a new method using a priori information which was expressed as fuzzy membership functions was developed.The above method was generalized. The generalized method consists of the following procedures. 1.The singular value decomposition of the coefficient matrix is performed, and then the rank is appropriately reduced. 2.A set of solutions is represented by Moore Penrose's solution and null space. 3.The solution is obtained by fuzzy reasoning using the set of solutions and a priori information which is expressed as fuzzy membership functions. Since the solution is identified by taking into account a priori information, the iteration converges quickly and stably, and oscillatory solutions can be avoided.To improve the measuring accuracy of SVET,an inverse problem, in which the true current density distribution along the metal surface was estimated from the data having errors due to the probe disturbance, was solved by using the 3-D boundary element method. The data were, however, not the real experimental data, but the numerical simulation results. Further study is necessary to perform an inverse analysis using experimental data, because more complicate electro-chemical phenomena than the simulation must prevail near the surface of the metal. Less