Abstract

In laboratories such as ocean basins, surface waves are generated mechanically by imposing an oscillatory motion on one or several vertical boundaries. The shape and characteristics of the wavemaker have a direct impact on the wave heights and periods that can be generated, but also on the quality of the waves obtained in the basin. Here, quality is defined in terms of spurious waves generation, meaning it is directly related to the predictability of the wave field in the basin. Additional factors affecting wave quality can be either mechanical, like the precision of the imposed flap motion, or hydrodynamic, like the amplitude of the flap angle.

In this paper, we investigate the quality of waves generated mechanically by several types of flap-wavemakers, including double-hinged and single-hinged ones, with various hinge depths. The amplitude of second-order spurious waves is evaluated analytically and compared to laboratory experiments carried out in SINTEF’s ocean basin. Third-order effects that results from using a second-order correction of the flap motion are also addressed. Then, the ability of deep-hinged wavemakers to generate short waves, either steep or with small amplitudes, is assessed based on measurements performed at NRC’s towing tank facility. Finally, recommendations on choosing a wavemaker design are proposed.

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