Statistics of wave orbital velocities in random directional sea states

The inclusion of at least the second order nonlinear contribution is necessary to achieve an accurate representation of ocean waves. While this is well known for the surface elevation, the importance of second order nonlinearity on the velocity potential, and hence on the wave kinematics and associated wave loads, is still unclear. To explicitly address the effect of nonlinear contribution on wave velocities Monte-Carlo simulations with a second order wave model are carried out with different initial random conditions. Results show that the statistical distribution of the horizontal components of wave orbital velocity departs substantially from Normality due to second order contributions for both unidirectional and directional wave fields.