Breaking wave impacts on the front deck of a ship

An experimental and numerical study about green water on ships in focused breaking waves

Master thesis (2021)

Authors

F.L. Beöthy Mechanical Engineering

Contributors

P.R. Wellens Ship Hydromechanics and Structures - Mechanical, Maritime and Materials Engineering (supervisor 1)
A.D. Boon Ship Hydromechanics and Structures - Mechanical, Maritime and Materials Engineering (coach)
G.H. Keetels Offshore and Dredging Engineering - Mechanical, Maritime and Materials Engineering (coach)
M. Brühl Team Sander Wahls - Mechanical, Maritime and Materials Engineering (coach)
Faculty
Mechanical Engineering
Copyright: © 2021 Farkas Beöthy
Ship Green water Focused wave Breaking wave Wave impact Fluid-structure intera
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Published Date

21-12-2021

Language

English

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Faculty

Mechanical Engineering

Abstract

Green water events on ships in extreme waves pose a considerable risk to personal, operational, and structural safety. Considering these issues, novel experiments were done to investigate the interaction between focused breaking waves and a ship at forward speed. The investigated interactions are global motion, global loads, and forces on a deck structure.

For the experiments focused, breaking waves were created, which served as loads of the green water events. First, wave focusing with prescribed characteristics was investigated in numerical settings. It was shown that focusing the waves with iterative methods does not lead to a converging solution. Three breaking waves were created in a wave basin. The characteristics of the waves were retrieved from 2D numerical simulations. The parameters of the spectrum of each wave were calculated from the simulation results.

The experiments were conducted systematically, where the position of the longitudinal center of gravity (LCG) of the ship was varied with respect to the focus point of the breaking wave at the focusing time. Using the same wave input resulted in green water events and loads on deck structure with different characteristics caused by different breaking stages of the focused wave. The effects of different ship velocities and different focused breaking waves were also explored throughout the experiments. It was shown that using the same focused wave, i.e., the same energy input, the breaking stage of the wave during the impact has a large influence on both the magnitude and time development of the loads on the deck structure. Force and pressure peaks were the largest and had an initial spike-like development when the wave during impact was in an unbroken stage. Impacts with the wave in its broken stage resulted in significantly lower loads and longer-duration load development. Such changes in the loads show that the ship's position with respect to the breaking wave is essential to consider even for the same input energy, posing additional challenges for establishing the maximum load in a sea state.