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.
Highlights
Wave tanks are centerpieces when it comes to studying hydrodynamics and wave structure interaction in offshore and marine engineering
The numerical model reproduced the motion of a solid body piston-type wavemaker by moving a solid boundary driven by an external arbitrary signal waveform
We considered a fully viscous model solving the unsteady Navier–Stokes equations on the basis of a two-phase flow strategy and the volume of fluid method to capture the free surface dynamics
Summary
Wave tanks are centerpieces when it comes to studying hydrodynamics and wave structure interaction in offshore and marine engineering. Local solutions near the piston wall are provided by Joo et al. using the Laplace equation and expansion series for small Froude numbers and basing their work on Ref. 12 They investigated the contact line motion at initial times of the piston wavemaker for ramp, step, exponential, and harmonic velocities. While experimental wave tanks provide a physical platform to implement such systems, testing may be expensive or not suitable to comply with similarity restrictions, whereas numerical studies once performed exclusively with potential codes (irrotational, incompressible, and nonviscous flows) are commonly carried out taking into account viscous effects that, require more computational resources. We present a numerical study of a piston wavemaker at a laboratory scale to investigate the wave generation process and characterize the piston wavemaker dynamics, extending Froude number regimes far beyond the ones that were studied before.
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