On the Generation of Isolated Green Water Events Using Wet Dam-Break

Abstract

Green water occurs when an incoming wave exceeds the freeboard and propagates onto the deck of naval/offshore structures, such as floating production storage and offloading units and platforms. This water can affect the integrity of facilities and equipment that are installed on the deck, compromise the safety of the crew, and affect the dynamic stability of the structure. Traditionally, wave trains have been used to study the green water problem, which is a good approach to analyzing consecutive green water events. However, to carry out systematic studies that allow local details to be identified for different types of green water, an alternative method is to study isolated events generated by a single incoming wave. The purpose of this paper was to experimentally investigate the generation of different types of isolated green water events using the wet dam-break (DB) approach as an alternative to generating the incoming wave. Tests were carried out in a rectangular tank with a fixed internal structure. Different freeboard conditions were tested for two aspect ratios of the wet DB (h0/h1=0.40 and 0.6). Conventional wave probes were used to measure the water levels in the tank, and a high-speed camera was set to capture details of the generated green water events. The results demonstrated the ability of this approach to represent different types of green water, similar to those obtained with unbroken regular waves in barge-shaped fixed structures, including DB, plunging-dam-break (PDB) and hammer-fist (HF).

Green Water on A Fixed Structure Due to Incident Bores: Guidelines and Database for Model Validations Regarding Flow Evolution

“…The features observed in the event found for C1 ( Figure 7b) were also found by [15], using the same initial conditions for green water generation (h 0 /h 1 = 0.6, FB = 0.042 m), in a smaller experimental installation (~1 m long,~0.335 m wide). The installation of [15] had the same upstream reservoir length, and the same height for the fixed structure. The main differences are related to the distance available for the bore development and the tank width (~2.49 and~1.49 times greater in the present work, respectively).…”

“…The use of the wet dam-break method to investigate the green water problem on fixed structures can still be extended to explain in more detail the interaction of the incident flow with the structure and to increase the understanding of the physics of different green water patterns. This paper thus extends the experimental wet dam-break application of [14,15], described above, to investigate details of the interaction of bores with a fixed rectangular structure, using image-based analyses to study the flow evolution in time and space. The evolution of the incoming bores and the generated green water events, in terms of water elevations, are included in this research.…”

“…In order to understand details of different types of green water events, Hernández-Fontes et al [14,15] proposed an alternative approach to generate systematic experiments of green water in a controlled environment, investigating the resulting patterns. They used the wet dam-break method in a small rectangular tank (~1 m length) to generate incident bores, which produced isolated green water events on a fixed rectangular structure.…”

“…The wet dam-break method considers the flow generated from the sudden interaction of a water volume located upstream of a vertical gate (initial water depth, h 1 ) with a water volume located downstream of the gate (initial water depth, h 0 ), taking into account that h 1 is always higher than h 0 ( [16]). From a high-speed video, Hernández-Fontes et al [14,15] presented snapshots and descriptions of events that had some resemblance with the dam-break (DB), plunging-dam-break (PDB), and hammer-fist (HF) types reported by [7]. In the DB, the flow flooding the deck resembles a dam-break type flow.…”

“…The use of the wet dam-break approach to study the green water problem in a simplified way is a recent proposal [14,15]. However, the study of the physics and applications of such a method is not new.…”