Validation of the initialization of a numerical wave flume using a time ramp

This study investigates the initialization of nonlinear free-surface simulations in a numerical wave flume. The numerical wave flume has been detailed in a previous paper (Zhao et al2009Fluid Dyn. Res.41 035510). Due to mismatch between linear input wavemaker motion and the kinematics of fully nonlinear waves, direct numerical simulations of progressive waves, generated by a sinusoidally moving wavemaker, are prone to high-frequency wave instability unless the flow is given sufficient time to adjust. A time ramp is superimposed on wavemaker motion at the start, which allows nonlinear free-surface simulations to be initialized with linear input. Three time ramp functions are introduced to check the difference of the time ramp. The time-frequency information of waves is also investigated by means of wavelet analysis. Numerical results show that the difference of the time ramp function is minor and the time ramp scheme is effective in stabilizing wave instability at the start of the simulation in a wave flume.