Fully nonlinear diffractions due to the bottom-mounted circular cylinders were simulated in a 3-dimensional numerical wave tank under the time marching scheme. Rankine source-based integral equation was discretized by employing a quadratic order boundary element method. The free surface conditions were integrated using a predictor-corrector method with Eulerian approach. The exact body boundary condition was imposed under the updated free surface. Open boundary condition was treated by combining two schemes of absorbing beach and potential stretching. The beach was placed in the longitudinal as well as transverse directions of the wave tank. The proposed modeling of the open boundary is validated and found to be effective. The present diffraction forces were compared with the experimental data and found to be generally bigger than the experimental values.
Perturbation scheme has been widely utilized in the diffraction due to surface piercing cylinders. For the linear problem, the time domain and frequency domain solutions are complementary since they are related by Fourier transforms. Most computations are done in frequency domain due to its simplicity. MacCamy&Fuchs(1954) generalized the theory for the cylinder at the water finite depth. The second order theories were also introduced in frequency domain, for instance, Chakrabarti (1975), Molin(1979), Eatock Taylor&Hung (1987), Kim&Yue (1989) and in the time domain by Isaacson&Cheung (1992). For the nonlinear load computation, the different schemes from the conventional approach were made by Lin&Yue (1991) and Boo&Kim (1995). They solved the so called body-exact problem in the time domain. The body boundary condition was imposed on the instant wetted surfaces while the free surface condition was satisfied on the mean surface. In this case Boo&Kim (1995) represented the forces acting on the surface-piercing cylinder are of higher harmonics, say up to 3rd order.
