Dynamic and kinematic characterization of the impulsive wavemaker system in a numerical wave tank

Abstract

We study the dynamical response of a piston-type wavemaker in a numerical wave tank. The two-dimensional, fully viscous unsteady Navier-Stokes equations are solved on a two-phase flow configuration using the volume of fluid method to capture the free surface dynamics. The wavemaker is a moving wall driven by an arbitrary signal waveform. The step response of the wavemaker may generate pulse-like waves similar to an undular bore propagating along the tank. Wave elevation at the piston wall has close similarity to the time response of second order systems found in feedback theory. The scaling found for water elevation at the piston wall for different step velocities and mean still water levels is in agreement with that in the available theory at low Froude numbers. The results along the tank for continuous waves agree with those of potential theory. The power input during the step response was determined during the whole wave generation process showing that net piston forces are predominantly hydrostatic. A power scaling for different mean still water levels and step velocities as a function of the Froude number was obtained. An active absorption strategy based upon a feedback controller driving a secondary piston was implemented. Wave absorption was successfully achieved on regular and irregular waves.