Development of Optimization System of Cathodic Protection for a Long Buried Structure by Boundory Element Method

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An optimization system of the cathodic protection for a long buried structure was constructed by developing a new direct analysis method, optimization method and inverse method based on the boundary element method.At first, a new boundary element direct analysis method for the galvanic corrosion of a long underground structure was developed. To cope with the case where a long structure was buried in soil with non-uniform electric conductivity, the fundamental solution for a field with linear change of conductivity was introduced. On the other hand, an application of the fast multipole boundary element method to corrosion problems was studied. It was found that this method can be usefully used for large scale corrosion problems.Then, the research to determine the optimum locations of electrodes and the optimum impressed current to each electrode in a cathodic protection system was reviewed, It was found that the problem was reduced to minimizing the power supply under the protecting con … More dition which was taken into account by the penalty function method. Following this method, an optimization of the locations and impressed currents of electrodes for a long pipeline buried in soil with non-uniform electric conductivity was performed. In the optimization, the multi-region method was applied, and the fundamental solution suitable to the linear change of the electric conductivity was used. The protection condition was taken into account by introducing the penalty function.Finally, a method for improving the accuracy of measuring polarization curves was proposed. In this method, a boundary element inverse analysis method was employed to eliminate the error due to the nonuniform current distribution, The method is applicable to an arbitrarily shaped specimen without any restriction of the location of a reference electrode. Furthermore, a boundary element analysis of an inverse problem in which the density of current across the surface of the metal surfaces is estimated from the measured potential values at some points far from the metal surfaces was discussed. The system of boundary element equations obtained was so ill-conditioned that a reasonable solution could not be obtained by the conventional regularization methods. A method using fuzzy a priori informations was proposed for solving this kind of ill-posed inverse problem. Less