Abstract
NewWave-type focused wave groups are commonly used to simulate the design wave for a given sea state. These extreme wave events are challenging to reproduce numerically by the various Numerical Wave Tanks (NWTs), due to the high steepness of the wave group and the occurring wave-wave interactions. For such complex problems, the validation of NWTs against experimental results is vital for confirming the applicability of the models. Intercomparisons among different solvers are also important for selecting the most appropriate model in terms of balancing between accuracy and computational cost. The present study compares three open-source NWTs in OpenFOAM, SWASH and HOS-NWT, with experimental results for limiting breaking focused wave groups. The comparison is performed by analysing the propagation of steep wave groups and their extracted harmonics after employing an accurate focusing methodology. The scope is to investigate the capabilities of the solvers for simulating extreme NewWave-type groups, which can be used as the “design wave” for ocean and coastal engineering applications. The results demonstrate the very good performance of the numerical models and provide valuable insights to the design of the NWTs, while highlighting potential limitations in the reproduction of specific harmonics of the wave group.
Highlights
The existence of abnormally large waves was mainly based on anecdotes from mariners, who referred to them as “walls of water”, “holes in the sea”, “three sisters”and “mad dogs” [1]
The wave group dispersion is studied in the spectral domain and later the evolution of the individual harmonics at consecutive locations is examined in the time domain
To the best of the authors’ knowledge, the models have not been compared in the past under the exact same conditions, neither all of them have been validated against experiments for steep focused waves and for the reproduction of high order harmonics
Summary
The existence of abnormally large waves was mainly based on anecdotes from mariners, who referred to them as “walls of water”, “holes in the sea”, “three sisters”and “mad dogs” [1]. There are threshold criteria used to characterize extreme waves, but they are set to an extent empirically and say little about the underlying physics that distinguish extremes from normal large waves. From an engineering design perspective, the distinction between very large and extreme waves may be less relevant, and what is required to model these waves is the spectral characteristics of the design storm and its return period. The former can be found from historic data and the use of spectral models for hindcasting and forecasting. A series of random-phase simulations can be performed for finding the largest wave events that the design storm can give at the location of interest
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