Use of Wet Dam-Break to Study Green Water Problem

2017 ◽  
Author(s):  
Jassiel V. Hernández-Fontes ◽  
Marcelo A. Vitola ◽  
Monica C. Silva ◽  
Paulo de Tarso T. Esperança ◽  
Sergio H. Sphaier
Keyword(s):  
High Speed ◽  
Good Practice ◽  
Offshore Structures ◽  
Dam Break ◽  
Irregular Waves ◽  
Green Water ◽  
Incoming Wave ◽  
Water Problem ◽  
Different Types ◽  
Fixed Structure

Green water occurs when an incoming wave exceeds the freeboard and propagates on the deck of naval/offshore structures, such as FPSO’s and platforms. The water on deck can affect the integrity of facilities and equipments installed on it, compromise the safety of the crew and affect the dynamic stability of the structure. Traditionally, regular or irregular waves generated by different types of wave-makers have been used to reproduce green water events. This is a good practice to study consecutive events. However, to study isolated events, an alternative could be the use of the wet dam-break approach to generate the incoming flow. The purpose of this paper is to investigate experimentally the use of the wet dam-break approach to generate isolated green water events. Tests were carried out in a rectangular tank with a fixed structure. Different freeboard conditions were tested for one aspect ratio of the wet dam-break (h0/h1 = 0.6). High speed cameras were used to investigate the initial phases of green water. Results demonstrated the ability of this approach to represent different types of green water events.

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

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Jassiel V. Hernández-Fontes ◽  
Marcelo A. Vitola ◽  
Monica C. Silva ◽  
Paulo de Tarso T. Esperança ◽  
Sergio H. Sphaier
Keyword(s):  
High Speed ◽  
Offshore Structures ◽  
Dam Break ◽  
Water Levels ◽  
Green Water ◽  
Incoming Wave ◽  
Aspect Ratios ◽  
Water Problem ◽  
Different Types ◽  
Wave Trains

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).

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

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2584 ◽  
Author(s):  
Jassiel V. Hernández-Fontes ◽  
Paulo de Tarso T. Esperança ◽  
Juan F. Bárcenas Graniel ◽  
Sergio H. Sphaier ◽  
Rodolfo Silva
Keyword(s):  
High Speed ◽  
Temporal Distribution ◽  
Dam Break ◽  
Green Water ◽  
Two Dimensional ◽  
High Resolution Data ◽  
Water Elevations ◽  
Fixed Structure ◽  
Flow Propagation ◽  
Air Cavities

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.

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

2020 ◽  
Vol 143 (4) ◽  
Author(s):  
Jassiel V. Hernández-Fontes ◽  
Edgar Mendoza ◽  
Irving D. Hernández ◽  
Rodolfo Silva
Keyword(s):  
High Speed ◽  
Effective Interaction ◽  
Dam Break ◽  
Green Water ◽  
Hydrodynamic Characteristics ◽  
Wave Flume ◽  
Series Of Experiments ◽  
Run Up ◽  
Fixed Structure ◽  
Air Cavities

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 plunging-dam-break (PDB)-type events were almost spherical for longer waves. PDB with large, elliptical cavities, and hammer-fist (HF)-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 dam-break (DB)-type events when designing structures or implementing models, as not all interactions with the deck happen when the shipping water crosses the bow edge.

Design Aspects of Green Water Loading on FPSOs

2003 ◽  
Author(s):  
Bas Buchner ◽  
Joaqui´n Lopez-Cortijo Garcia
Keyword(s):  
Evaluation Method ◽  
Offshore Structures ◽  
Green Water ◽  
Evaluation Procedure ◽  
Design Evaluation ◽  
Water Impact ◽  
Advantages And Disadvantages ◽  
Water Problem ◽  
Semi Empirical ◽  
Empirical Design

Green water is a significant problem for floating ship-type offshore structures, which needs to be assessed in the early design of the structure. First the present paper summarises a new semi-empirical design evaluation procedure that can assist in this design process. Then the practical design considerations related to the green water problem are discussed. There are different ways to solve the green water problem for a particular structure at a specific location: • Design the vessel and structures on the deck against the predicted green water impact load levels. • Optimise the bow shape (underwater shape and above water bow flare). • Increase the freeboard height such that green water is prevented completely. • Increase the freeboard height such that the green water loads are reduced to acceptable levels and design for these load levels. • Optimise the structures on the deck to minimise the green water impact loads. • Use protecting breakwaters in front of critical structures on the deck. All these options have their advantages and disadvantages. The semi-empirical design evaluation method and the different design options are discussed in a case study, focussing on a new DP FPSO concept.

scholarly journals Theoretical and Experimental Study on Nonlinear Hydroelastic Responses and Slamming Loads of Ship Advancing in Regular Waves

2018 ◽  
Vol 2018 ◽  
pp. 1-26 ◽  
Author(s):  
Jialong Jiao ◽  
Yulin Zhao ◽  
Yufei Ai ◽  
Chaohe Chen ◽  
Tianhui Fan
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Irregular Waves ◽  
Green Water ◽  
Design Stage ◽  
Regular Waves ◽  
Restoring Force ◽  
Wave Basin ◽  
Hull Structure ◽  
Hydrodynamic Wave

Wave loads estimation and structural strength evaluation are the fundamental work at the ship design stage. The hydroelastic responses and slamming strength issues are also concerned especially for large-scale high-speed ships sailing in harsh waves. To accurately predict the wave-induced motions and loads acting on the ship sailing in regular waves, a fully coupled 3D time-domain nonlinear hydroelasticity theory is developed in this paper. The vibration modal characteristics of the flexible hull structure derived by the 3D finite element method (FEM) and simplified 1D nonuniform Timoshenko beam theory are firstly described. The hydrostatic restoring force and hydrodynamic wave force are calculated on the real-time wetted surface of hull to address geometric nonlinearity due to the steep wave and large amplitude motions. The bow slamming and green water loads acting on the ship in severe regular waves are estimated by the momentum impact method and dam-breaking method, respectively. Moreover, a small-scaled segmented ship model is designed, constructed, and tested in a laboratory wave basin to validate the hydroelasticity algorithm. The results predicted by theoretical and experimental approaches are systemically compared and analyzed. Finally, future work for predictions of ship hydroelasticity and slamming loads in irregular waves is prospected.

Green Water and Wave Impact on FPSOs in Santos Basin: Challenges and Prediction Tools

2014 ◽  
Author(s):  
Rafael Vergara Schiller ◽  
Csaba Pâkozdi ◽  
Carl Trygve Stansberg ◽  
Daniel Fonseca de Carvalho e Silva
Keyword(s):  
Wave Structure ◽  
Sensitivity Study ◽  
Irregular Waves ◽  
Green Water ◽  
Wave Impact ◽  
Wave Amplification ◽  
Campos Basin ◽  
Water Problem ◽  
In Transit ◽  
Wave Induced

Green water (water-on-deck) and subsequent wave impact is a strongly non-linear, random and complex phenomenon that represents an important factor to be considered in the design of moored vessels and vessels in transit. The Santos Basin, in southeast Brazil, is a new frontier for deep water oil production, where FPSO green water issues are expected to be more important. In this paper, we investigate new green water challenges associated with the Santos Basin. We employ an engineering prediction tool, KINEMA, designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in early design load analysis. We perform a sensitivity study to arbitrary wave directions and present preliminary results from a case study that would be illustrating for the Santos Basin. Firstly, a comparison between numerical green water predictions and a set of earlier model test data for a Campos Basin case shows satisfactory agreement. A sensitivity study suggests that an empirical tuning factor, which is related to wave amplification and wave-structure interaction, should decrease with increasing wave heading. Then, a preliminary numerical investigation of the green water problem in Santos Basin wave conditions demonstrates that although the wave impact from the largest waves (S-SW) may be avoided by heading the vessel towards S-SW, other wave directions have to be taken into consideration. The results presented herein confirm that multi-directional wave heading is a green water challenge in the Santos Basin. Further studies that address this problem in detail, in special variations in the wave-structure interactions due to wave heading, and for actual particular Santos Basin FPSO’s, are recommended.

scholarly journals On the Evolution of Different Types of Green Water Events

Water ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1148
Author(s):  
Jassiel V. H. Fontes ◽  
Irving D. Hernández ◽  
Edgar Mendoza ◽  
Rodolfo Silva ◽  
Eliana Brandão da Silva ◽  
...  
Keyword(s):  
Water Surface ◽  
Early Stage ◽  
Dam Break ◽  
Green Water ◽  
Wave Steepness ◽  
Wave Flume ◽  
Initial Stage ◽  
Different Types ◽  
Wave Trains ◽  
First Time

Green water events may present different features in the initial stage of interaction with the deck of a structure. It is therefore important to investigate the evolution of different types of green water, since not all the events interact with the deck at the same time. In this paper, the evolution of three types of green water events (dam-break, plunging-dam-break, and hammer-fist) are studied. The water surface elevations and volumes over the deck in consecutive green water events, generated by incident [wave trains in a wave flume, were analyzed using image-based methods. The results show multiple-valued water surface elevations in the early stage of plunging-dam-break and hammer-fist type events. Detailed experimental measurements of this stage are shown for the first time. The effect of wave steepness on the duration of the events, maximum freeboard exceedance, and volumes were also investigated. Although the hammer-fist type showed high freeboard exceedances, the plunging-dam-break type presented the largest volumes over the deck. Some challenges for further assessments of green water propagation are reported.

State-of-the-Art of Green Water on FPSO in Harsh Environment

2011 ◽  
Vol 464 ◽  
pp. 465-468
Author(s):  
Tao Ni ◽  
Yun Wang ◽  
Bing Nan Li ◽  
Shen Tao Tang ◽  
Yong Kang Zhang
Keyword(s):  
State Of The Art ◽  
Single Point ◽  
Offshore Structures ◽  
Green Water ◽  
Harsh Environment ◽  
Mooring System ◽  
Wave Runup ◽  
Auxiliary Equipment ◽  
Forming Mechanism ◽  
Water Problem

The phenomena of green water are the maximum vertical extent of wave uprush over freeboard on the deck with the result of damage to the deck, bow and auxiliary equipment. The FPSO with Single-point mooring system or disconnectable mooring system always operates in the severe deepwater or ultra-deepwater environment such as Gulf of Mexico or Southeast Asia, which should be allowed to weathervane. Therefore, FPSO is always exposed to wave runup and overtopping. Nowadays green water problem has become one of the most important factors to endanger offshore structures, such as FPSO, TLPs and SPARS. This paper gives a comprehensive review of the state-of-the-art in green water, including the forming mechanism, numerical simulation and model test of wave runup. Finally the prospect of simulating green water is discussed.

Green water evolution on a fixed structure induced by incoming wave trains

2020 ◽  
pp. 1-29 ◽  
Author(s):  
Jassiel V. Hernández-Fontes ◽  
Irving D. Hernández ◽  
Edgar Mendoza ◽  
Rodolfo Silva
Keyword(s):  
Green Water ◽  
Incoming Wave ◽  
Wave Trains ◽  
Fixed Structure

scholarly journals Stochastic Uncertainty in a Dam-Break Experiment with Varying Gate Speeds

2021 ◽  
Vol 9 (1) ◽  
pp. 67
Author(s):  
Hiroshi Takagi ◽  
Fumitaka Furukawa
Keyword(s):  
High Speed ◽  
Pressure Sensors ◽  
Dam Break ◽  
Maximum Pressure ◽  
Vertical Acceleration ◽  
Ship Wakes ◽  
Dam Break Flow ◽  
Statistical Relationships ◽  
Flow Propagation ◽  
Impulsive Pressure

Uncertainties inherent in gate-opening speeds are rarely studied in dam-break flow experiments due to the laborious experimental procedures required. For the stochastic analysis of these mechanisms, this study involved 290 flow tests performed in a dam-break flume via varying gate speeds between 0.20 and 2.50 m/s; four pressure sensors embedded in the flume bed recorded high-frequency bottom pressures. The obtained data were processed to determine the statistical relationships between gate speed and maximum pressure. The correlations between them were found to be particularly significant at the sensors nearest to the gate (Ch1) and farthest from the gate (Ch4), with a Pearson’s coefficient r of 0.671 and −0.524, respectively. The interquartile range (IQR) suggests that the statistical variability of maximum pressure is the largest at Ch1 and smallest at Ch4. When the gate is opened faster, a higher pressure with greater uncertainty occurs near the gate. However, both the pressure magnitude and the uncertainty decrease as the dam-break flow propagates downstream. The maximum pressure appears within long-period surge-pressure phases; however, instances considered as statistical outliers appear within short and impulsive pressure phases. A few unique phenomena, which could cause significant bottom pressure variability, were also identified through visual analyses using high-speed camera images. For example, an explosive water jet increases the vertical acceleration immediately after the gate is lifted, thereby retarding dam-break flow propagation. Owing to the existence of sidewalls, two edge waves were generated, which behaved similarly to ship wakes, causing a strong horizontal mixture of the water flow.

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