Papers by Author: Kazuhiro Suga

Abstract: This study evaluates effects of the diffusion layer thickness and the share stress on metal surface for the polarization curve under flow field on metal corrosion. We measure the polarization curves under the different diffusion boundary layer thickness and the wall share stress. Metal surface conditions are observed from microscopic and macroscopic view points to evaluate tendencty of corrosion and shape of corrosion product.

Abstract: This study presents a mesh generation technique considering the measurement accuracy of the potential on an inverse analysis using the boundary element analysis. We evaluate the effects of the distance between layered rebar and corrosion size on measured potential distribution on the concrete surface, and then propose a technique to select reasonable and efficient size of boundary element. A numerical simulation demonstrates the validity and efficiency of the proposed technique.

Abstract: This study presents an optimization technique with hierarchical mesh generation technique and genetic algorithm. The present technique is applied to optimize layout of electrodes on cathodic protection.

Abstract: A numerical simulation of corrosion in a tube is performed with the solution velocity effect taken into account. A two dimensional tube, the cross-section of which is widening or narrowing with increase in distance, is considered. The velocity distribution in the tube is calculated with the Finite Volume Method (Open FOAM), and the derivatives of velocity with respect to the distance from the tube wall is determined at any location of the tube. The corrosion rate of the tube wall is estimated under the assumption that the corrosion rate depends on the velocity gradient, i.e. , it is estimated by solving the Laplace equation under the boundary conditions given with the polarization curves measured under various velocity gradients. The Boundary Element Method (3D-CAFE) is used to solve the Laplace equation. It is shown that the distribution of corrosion rate, including the maximum corrosion rate and its location, is different between the widening and narrowing tubes, even if the average velocities in the two tubes are equal.

Abstract: This study proposes a monitoring method for corrosion on reinforced concrete structure using inverse analysis approach. At first, we define an inverse problem to identify the real and imaginary parts of the concrete conductivity and the impedance between concrete and steel. The observation of the inverse problem is the electric potential on the concrete structure surface when the AC impedance measurement is performed. The observation condition, such as layout of observation point and type of observation, of the inverse is optimized. The optimization is achieved by minimizing the average of eigen values of a posteriori estimate error covariance matrix based on the Kalman Filter estimation algorithm. We show a numerical simulation to solve the inverse problem on the optimized observation condition to evaluate the effectiveness of the condition. The simulation shows the real parts of the concrete conductivity and the impedance are well identified but imaginary parts of them are not. To overcome this difficulty, we evaluate the sensitivity of the imaginary part of the impedance to the real part and the imaginary part of the electric potential. We find the possibility that the observation of the imaginary part of the electric potential improves the estimation. Finally, a numerical simulation is performed under the optimized observation condition considering the above discussion. In the numerical simulation shows that considering the sensitivity of the parameters to the potential improves the solution on the inverse problem.