Accuracy of numerical surface integrals in the indirect boundary integral method

This paper describes the accuracy of surface integrals in the indirect boundary integral method containing singular integrals. Here, the surface integral is carried out directly and numerically by the use of Simpson's and Legendre-Gauss's quadrature formulae. Also, the line integral, obtained by applying Gauss-Ostrogradskii's transformation to the surface integral, is examined. The accuracy is evaluated by the convergence behaviors of surface and line integrals and by the comparison with the analytically obtained integral values.