Coupling Freak Wave Events with Green Water Simulations

In this paper a VoF method will be presented together with a coupling to a non-linear potential flow solver. The non-linear flow input is generated using a FEM/FD method described by Westhuis [8]. The generation of a freak wave event is based on the description of the freak wave as a realization of a soliton on a finite background (see Andonowati [1]) The VoF method has shown to represent most of the non-linear characteristics of waves as will be demonstrated by a soliton splitting example. The use of the non-linear inflow conditions has shown to be relevant when computing green water incidents. The pressure calculations on a fixed object in waves do show a high frequency noise behaviour due to the simulation of the body boundary conditions. Introduction The term green water describes the situation when the relative water height exceeds the freeboard and considerable amount of water comes onto the deck. The compact mass of water flush- ing onto the deck may cause serious damage to superstructures, deck plating, hatches and equipment on the deck. Therefore, the effect of green water loading should be taken into account at the design stage of ships. Hereto, at the Maritime Research Insti- tute Netherlands (MARIN) a research program was started to simulate green water loading using a Navier-Stokes solver based on the Volume of Fluid (VoF) method [3]. Earlier investigations involving model tests, [2], have shown that the flow of the water on deck appears to resemble the theoretical dam break problem. Therefore, a wall of water with zero speed is placed around the bow as an initial condition in [3]. The height of the wall was derived from model tests. At the design stage of the ship, no model tests are available.

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