Inthis study, we use CFD simulations to model a fullynonlinear water wave tank. Firstly, for validation purpose, regular waveswith different wave steepness are simulated and the results arecompared with the second-order potential flow solution for the freesurface displacement time history at fixed locations, the instantaneous freesurface spatial profiles, and the velocity and pressure fields underthe free surface. It is shown that for small wavesteepness, the CFD solutions agree very well with the second-orderpotential flow solutions while for large wave steepness, apparent differencesbetween these two solutions are observed. The validation and fullynonlinear feature of the CFD solutions are therefore demonstrated. Secondly,plunging breaking waves are simulated using the CFD wave tankby focusing a large number of linear wave components ata prescribed time and location. The time histories and normalizedvariance of free surface displacement at various locations along thetank are obtained from the CFD simulation and compared tothe lab experiments. In particular, the CFD results predict reasonablywell the wave breaking location and the loss of energyflux due to wave breaking. Finally, a vertical circular cylinderis placed in the CFD wave tank to simulate thebreaking wave impact on a fixed structure. The pressure timehistories at various points on the cylinder surface are obtainedfor several cylinder locations with respect to the prescribed wavebreaking point. The CFD results are compared with previous experimentsand discussed.