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

Abstract

This paper presents a two-dimensional experimental study of the interaction of wet dam-break bores with a fixed structure, regarding the evolution of the incident flows and the resultant green water events on the deck. The study employs image-based techniques to analyse flow propagation from videos taken by high-speed cameras, considering five different shipping water cases. The features of small air-cavities formed in some green water events of the plunging-dam-break type were analysed. Then, the spatial and temporal distribution of water elevations of the incident bores and green water were investigated, providing a database to be used for model validations. Some guidelines for the selection of the freeboard exceedance, which is of relevance for green water simulations, were provided. Finally, the relationship between the incident bore and water-on-deck kinematics was discussed. The proposed study can be used as a reference for performing simplified and systematic analyses of green water in a different two-dimensional setup, giving high-resolution data that visually capture the flow patterns and allow model validations to be performed.

On the Evolution of Different Types of Green Water Events

“…In green water research, the time series of water elevation measured at the start of the deck are known as freeboard exceedance [1,20,42] and are important in the application of analytical and numerical models used in ocean engineering to analyze the water-on-deck behavior, such as [16,19,43]. In this research, the measurements given by sensor d2 defined in Figure 4 (positive measurements from the deck level), are considered as the freeboard exceedance of the green water events.…”

“…Operation condition: Green water events can occur in structures operating in various conditions, which can have significant effects on the propagation of the water on deck. Research performed on fixed structures, for example [2,6,9,11,19,30,50,54,55], has been valuable in understanding important physical phenomena related to the patterns, elevations, and kinematics of such events. However, green water behavior can be different if the structures are moving, such as when they are floating freely (e.g., free heave-pitch oscillation [56]), when they are moored (e.g., [1,21,22,57]), or when they move with forward speed (e.g., [58][59][60][61][62][63][64]).…”

“…The main difference between the DB and the PDB types of green water is that an air cavity is often formed at the deck's edge in the latter. As water propagates over the deck, this cavity is entrapped and fragments inside the flow, producing bubbles that tend to escape when the water travels along the deck [19]. 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].…”

“…Regarding the research of green water evolution, in terms of water elevations, recent investigations have been performed using image-based measurements in simplified experiments, providing useful information [17,19,30,31]. From these works, Hernández-Fontes et al [31] employed the concept of Virtual Wave Probes (VWP, [32]) in green water research to investigate the distribution of water-on-deck through binary image processing and analysis.…”

A simplified and open-source approach for multiple-valued water surface measurements in 2D hydrodynamic experiments

“…Measuring the water surface elevations in two-dimensional (2D) hydrodynamic experiments is of importance in several types of studies regarding coastal [1][2][3][4][5] and ocean [6][7][8][9][10] engineering applications. The main reason is that they are very useful in the development of analytical and numerical approaches, particularly for validation purposes.…”