Numerical Investigation of Green Water for A Two Dimensional Fixed Rectangular Structure

This paper presents results from a numerical study of wave overtopping leading to the occurrence of green water on a two-dimensional fixed rectangular structure, representative of a large ship. The problem is investigated using Computational Fluid Dynamics (CFD) with a Volume of Fluid (VOF) surface capturing scheme. Validation of the CFD model has been made with linear potential flow theory for small wave steepness and existing experimental measurements for larger wave steepness. The model has then been used to investigate overtopping events resulting from incident focused wave groups (representative of a NewWave type focused wave group) for a range of wave parameters. In agreement with Greco et al. [4] a range of overtopping events have been identified across this parameter space, including dam-break (DB) type, plunging plus dam-break (PDB) type, hammer-fist (HF) type and plunging wave (PW) type overtopping. The flow of green water on deck resulting from overtopping is divided into a transition zone and a “dam-break” zone (in which the water front velocity is almost constant). The water front velocity in the dambreak zone is investigated and summarized for the different types of overtopping events. Results show that the traditional design procedure may overestimate the green water loads, especially for PDB and DB events, by assuming the dam height to be freeboard exceedance in classic dam-break solution.