This paper presents a review of experimental investigations of green water problems conducted in small scale laboratory flumes or large scale model basins. A brief description of the green water problems and related laboratory based studies is provided in the paper, addressing formation of green water incidents, simplification using dam break models, green water freeboard exceedance, green water impacts on structures, and measurement techniques for green water flows. Knowledge gaps and challenges are identified based on a summary discussion of major findings.
In severe sea states, the waves can become so large that water overtops and flows onto the deck of a ship. This overtopping water is known as shipping of water or green water (referred hereafter). Green water is generally referred as direct seawater flows travelling on the deck that are distinguished from merely white spray or from splashing.
Green water is similar to wave overtopping on coastal defense structures, such as dikes or breakwaters. The difference from the traditional definition is that the occurrence of green water is mostly associated with floating and moving structures, either restrained (e.g., moored) or freely floating. Most green water events have occurred on ships or ship-shaped floating, production, storage and offloading units (FPSOs). Fixed or floating offshore structures, such as compliant tower platforms, tensionleg platforms, or semi-submersibles, may be threatened by green water, particularly for lower deck elements or as a result of insufficient freeboard.
The presence of green water raises concerns of potential damage to sensitive equipment and on the safety of personnel. Green water may also affect the dynamic stability of a floater by exerting heavy loading, or even deteriorate the deck structure integrity by localized impacts with large momentum. Even though green water may incur disastrous consequences, the associated hydromechanics are not yet fully understood due to the nonlinear, violent, multiphase, and turbulent nature of the discontinuous free surface flow.
