Generation of 3hr Long-Crested Waves of Extreme Sea States With Hos-Nwt Solver

Abstract

The accurate control of wave fields generated in experiments and numerical simulations is of great interest for the ocean engineering community. In the context of wave-structure interactions, the recommended practices of classification societies are indeed based on the definition of a wave spectrum, that needs to be reproduced. The present work intends to address this problem from the numerical point of view, using a Numerical Wave Tank equipped with a wavemaker and an absorbing beach, based on the High-Order Spectral method (HOS-NWT). The challenging case of the generation of 3-hours long-crested extreme sea states is studied in details. An iterative procedure to reproduce a target wave spectrum at a given distance from the wavemaker is proposed. The quality of the sea state obtained is evaluated using several criteria defined from spectral quantities. A validation is first performed with a highly nonlinear but non-breaking sea-state. Statistical crest distributions obtained are compared with the Forristall and Huang distributions [1,2]. Then, the Gulf of Mexico 1,000 Year Return Period wave condition is generated. This corresponds to an extreme sea state with significant wave breaking occurrence. The numerical solver needs to be able to account for this phenomenon [3]. The Tian breaking model [4,5] is calibrated to realistically reproduce the dissipation due to breaking, with particular attention paid to the spatial discretization, enlightening its significant effect on breaking model actions. Consequences on the iterative correction process * Address all correspondence to this author. are studied. The computed statistical quantities appear to be significantly different changing the spatial discretization, while the wave energy spectrum stands the same. It questions the relevance of the characterization of a sea state with the sole wave energy spectrum.

Qualification Criteria for the Verification of Numerical Waves – Part 1: Potential-Based Numerical Wave Tank (PNWT)

“…Table 3 summarizes part of the numerical set up that was used for the verification cases of the PNWT models. Other details on the numerical scheme and wave breaking model are not covered in this paper and can be found at [8] and [29] for TPNWT and HOS-NWT, respectively.…”

“…All PNWT models apply linear wave kinematics, freesurface elevation and fluid velocity, at around inlet boundary to generate irregular wave inside the numerical domain. With the nonlinear physics modeled by the PNWT models the wave spectrum varies in space and successive corrections of input signal, either wave maker motion at inlet boundary for HOS-NWT [29] or forcing wave kinematics in overlay or relaxation zone for IGN, REEF3D and TPNWT [8], must be made to meet the criteria at the target location as done usually with experiments. In case of HAWASSI simulation, however, linear input wave kinematics derived from the target wave spectrum is forced at around the inlet boundary without further iterative corrections [8,36].…”