In a recent paper, Raman et al (RJV) [1] 2 presented a second- order solution for the wave interaction with a large-diameter, bottom-mounted, surface-piercing, fixed vertical cylinder. Earlier, Chakrabarti [2,3] obtained an approximate solution for the vertical cylinder due to Stokes's fifth-order wave. Later, Yamaguchi and Tsuchiya (YT) [4] proposed a second-order solution in a closed form for the wave interaction problem with the vertical cylinder which was examined by Chakrabarti [5]. All these solutions are different due to the assumptions regarding the frequency of the scattered wave and the kinematic free-surface boundary condition. RJV [1] claim that their solution is superior to the earlier solutions because, according to them, it satisfies the nonlinear free-surface boundary conditions completely.

A nonlinear diffraction theory for interaction of waves with a vertical cylinder of large diameter is presented. The nonlinear second-order solution is examined in comparison with a linear solution and other existing second-order solutions. The computed nonlinear wave forces are found to compare very well with the experimental results. The effect of nonlinearity on the crest height distribution around the cylinder is also studied. It is found that as the ratio of wave height to water depth decreases the nonlinear solution approaches the linear solution.