A Detailed Description of Flow-Deck Interaction in Consecutive Green Water Events

Abstract

This paper gives a detailed description of the main hydrodynamic characteristics of different types of green water events occurring on a fixed structure in a series of experiments. High-speed video, at 250 fps, was used to capture the flow details from regular waves produced inside a wave flume. The green water events were classified according to their type and the results of the evaluation from the apparent and effective interaction features. The air cavities in the PDB (Plunging Dam Break) type events were almost spherical for longer waves. PDB with large, elliptical cavities, and HF (Hammer Fist) type events occurred with steeper waves. The highest wave front and bow run-up velocities were found in PDB and HF events, respectively. The size of the cavities in PDB events increases and becomes more elliptical for higher bow run-up velocities. The results of these experiments show that not all events can be treated in the same way as the DB (Dam Break) type events when designing structures or implementing models, as not all interactions with the deck happen immediately when the shipping water crosses the bow edge.

On the Evolution of Different Types of Green Water Events

“…Yao and Hu [28] explained that some phenomena could have triplevalued water surface amplitudes, such as the air trapped beneath an overturning plunger. Furthermore, the snapshots presented in [9,12] clearly show that the initial stages of some shipping water events have these features. Recently, Hernández-Fontes et al [29] introduced the concept of multiple-valued water surface (MVWS) elevations to refer to the amplitudes of the several water surfaces that can be measured at a specific location, along a horizontal domain, in some 2D hydrodynamic experiments, as illustrated in Figure 1b.…”

“…In ocean engineering research, experimental observations have suggested various patterns used to characterize different types of green water. Broken flow features are often seen, if they are generated by breaking waves [5][6][7][8], or air cavity formation at the start of the deck, if the incident waves are unbroken or partially broken [9][10][11][12][13][14]. In 2007, a classification of different types of green water was suggested by [9], who described the different events found in regular wave trains: The dam-break (DB), the plunging-dambreak (PDB), and the hammer-fist (HF) types.…”

“…In 2007, a classification of different types of green water was suggested by [9], who described the different events found in regular wave trains: The dam-break (DB), the plunging-dambreak (PDB), and the hammer-fist (HF) types. These events are mainly differentiated by the features formed by the flow at the start of the deck, and have motivated further green water research [11,12,[15][16][17][18].…”

“…In the HF type, no cavities are formed; instead, a block of water remains almost suspended at the beginning of the deck, as a fluid-arm [9]. Then, as the incident wave advances over the deck, this arm falls, and hits the deck (see details in [9,12]). Improving the knowledge of these events' physical behavior, including their formation at the beginning of the deck and their evolution is relevant.…”

“…Recently, Hernández-Fontes et al [12] provided a detailed investigation of some of the features of different types of green water events generated by incoming wave trains in wave flume experiments. With the use of a high-speed camera, the main visual features of the consecutive green water events were discussed, providing, for the first time, a video database with the details of the events, captured at 250 fps.…”