- A 2D viscous NWT (Numerical Wave Tank) code based on Navier-Stokes equations by a multi-block FDM/FVM hybrid method has been developed to investigate the interactions of fully nonlinear regular waves with stationary two-dimensional bodies. The CFD code is applied to the case of submerged circular cylinder and extensively tested against published computational and experimental results. The multi-block hybrid method uses rectangular-grid-structured FDM (Finite Difference Method) at far field and body-fitted-coordinate-structured FVM (Finite Volume Method) in the near field. The two solutions are matched in a narrow overlap region assuring the continuity of pressure and velocities. The fully nonlinear free-surface conditions are satisfied through a density-function equation. The NWT is able to reproduce with high accuracy the nonlinear interactions of free-surface viscous flows around arbitrary 2D bodies as long as the turbulence phenomena are not important. The flow simulations for a submerged circular cyl inder are able to reproduce, through advanced computer graphics software, various interesting features observed in the physical experiments for a variety of KC (Keulegan Carpenter) numbers. The developed computer program is proved to be robust and efficient in simulating more complicated flow problems including multiple bodies and bodies in motion.