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.

Green Water on FPSO Predicted by a Practical Engineering Method and Validated Against Model Test Data for Irregular Waves

2014 ◽  
Author(s):  
Rafael Vergara Schiller ◽  
Csaba Pâkozdi ◽  
Carl Trygve Stansberg ◽  
Douglas Gustavo Takashi Yuba ◽  
Daniel Fonseca de Carvalho e Silva
Keyword(s):  
Model Test ◽  
Model Tests ◽  
Irregular Waves ◽  
Green Water ◽  
Wave Impact ◽  
Irregular Wave ◽  
Beam Seas ◽  
Practical Engineering ◽  
The University ◽  
Wave Induced

This paper presents a series of numerical analyses performed with the potential theory-based Green Water engineer tool KINEMA3. KINEMA3 was designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in design load analysis. The purpose of the study presented herein is to validate KINEMA3 green water (deck overtopping) predictions in nonlinear irregular waves with results from model tests performed at the TPN (Tanque de Provas Numérico) laboratory at the University of São Paulo, Brazil. Comparisons are made for a selection of irregular wave cases, for two choices of anchoring conditions (free floating vessel and fixed vessel) and for three wave headings (180°, 225° and 270°: head, quartering and beam seas, respectively). KINEMA3 statistical green water predictions present a general good agreement with observations from the TPN model tests for all wave cases, headings and mooring conditions. Overall, observed trends for occurrence of green water and standard deviation/maximum of relative wave height are successfully reproduced by KINEMA3. In agreement with model test results, it is predicted that green water occurs more frequently for a free floating vessel and for beam seas. Additional comparisons between KINEMA3 predictions using different FPSO panel models (low-order and high-order models) present negligible differences with respect to green water estimates. The results presented herein demonstrate the robustness of the tool towards the prediction of green water for variable wave headings and sea states, and highlight the capability of KINEMA3 to be employed as an engineering-like tool for fast and multiple estimates of green water in early design studies. This work is a part of the research project “Green Water and Wave Impact on FPSO” carried out for and in cooperation with PETROBRAS.

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.

scholarly journals Experimental Investigation of Wave-Induced Hydroelastic Vibrations of Trimaran in Oblique Irregular Waves

2016 ◽  
Vol 2016 ◽  
pp. 1-17 ◽  
Author(s):  
Haoyun Tang ◽  
Huilong Ren ◽  
Hui Li ◽  
Qi Zhong
Keyword(s):  
Longitudinal Vibration ◽  
Model Tests ◽  
Irregular Waves ◽  
Wave Impact ◽  
Wave Condition ◽  
Strength Assessment ◽  
Irregular Wave ◽  
Hydroelastic Vibrations ◽  
Structural Parts ◽  
Wave Induced

The irregular wave condition, especially the oblique irregular wave condition, is the actual circumstances when trimaran is sailing in sea. In order to identify the characteristic of the wave-induced hydroelastic vibration in irregular waves, as well as investigate the change of vibration in different oblique irregular wave conditions, trimaran model tests were conducted to measure vibrations, wave impact, and motion under different azimuth and wave height. The vibration on main hull, side hull, and cross-desk is measured and analyzed separately to observe the influence of irregular wave in different structural parts. The longitudinal vibration, transverse vibration, and torsion are also included in the model tests measurement to investigate the relationship between these vibration deformation components and parameters of the irregular waves. The wave-induced hydroelastic vibrations and whipping effect is extracted and analyzed to find influence of whipping and springing on the total vibration. Based on the analysis, the dangerous positions and the critical waves condition is introduced to ensure that the subsequent structural strength assessment is more reliable.

Simple Tool for Prediction of Green Water and Bow Flare Slamming on FPSO

2009 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Kjetil Berget
Keyword(s):  
Water Reservoir ◽  
Software Tool ◽  
Practical Method ◽  
Irregular Waves ◽  
Green Water ◽  
Ship Motions ◽  
Wave Impact ◽  
Bow Flare ◽  
Dam Breaking ◽  
Flare Slamming

A practical method for prediction of green water and wave impact on FPSO’s in steep irregular waves is described. The relative wave elevation and kinematics are found from combining ship motions, wave diffraction and nonlinear irregular waves. Water heights on deck and related velocities are estimated by simple analytical formulas originally derived from dam-breaking theory but modified in this work to take into account a non-zero water velocity input and the effects from a dynamic and finite wave-determined water reservoir. A bulwark is also included. Deckhouse slamming and bow flare slamming loads are computed by simple formulas from the local velocities and, in the latter case, also the relative angle between the water surface and the flare. Verification against more advanced models and to model test data show promising results. The method is being implemented into a simple research-type software tool.

Investigation of Bottom Slamming on Ships in Irregular Waves

2018 ◽  
Author(s):  
Shan Wang ◽  
Suresh Rajendran ◽  
C. Guedes Soares
Keyword(s):  
Vertical Motion ◽  
Time Instant ◽  
Irregular Waves ◽  
Green Water ◽  
Ship Motions ◽  
Threshold Velocity ◽  
Added Masses ◽  
Entry Velocity ◽  
Longitudinal Position ◽  
Wave Induced

The bottom slamming of a chemical tanker and a LNG carrier advancing in irregular waves is investigated numerically and compared with experiments. The probability of slamming occurrence on longitudinal locations and the slamming induced pressures on the bottom of two ships are discussed. It is considered that slamming occurrence at a point is dependent upon two conditions: the relative vertical motion at the same longitudinal position of the ship being larger than the vertical distance from the still water to the concerned position, and the entry velocity exceeding some threshold velocity. Ship motions in irregular waves predicted by a time domain seakeeping code and measured from the model tests are used to calculate the slamming occurrence statistically based on the two conditions mentioned above. Only heave and pitch motions are considered in the calculations. The seakeeping code combines body linear radiation and diffraction forces with body nonlinear Froude-Krylov forces, hydrostatic forces and shipping of green water on the bow. The effects of body nonlinearity are considered by a simplified method: the memory functions, infinite frequency added masses and the radiation restoring coefficients are assessed at each time instant as function of the instantaneous wetted surface. A similar procedure is used to calculate the diffraction forces. The experimental data of the wave-induced loads on these two vessels in different sea states are analyzed statistically. Probability of exceedance of entry velocities and pressure peaks for the sections at the bow and stern are computed for various irregular sea states. The results of the slamming occurrence on longitudinal locations and wave induced loads on these two types of ships are discussed.

scholarly journals Assessment of Extreme Wave Impact on Coastal Decks with Different Geometries via the Arbitrary Lagrangian-Eulerian Method

2021 ◽  
Author(s):  
Tao Xiang ◽  
Denis Istrati
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Wave Structure ◽  
Arbitrary Lagrangian Eulerian ◽  
Wave Impact ◽  
Arbitrary Lagrangian Eulerian Method ◽  
Wave Heights ◽  
Multi Phase ◽  
Wave Induced ◽  
Uplift Forces

Given the documented wave-induced damage of elevated coastal decks during extreme natural hazards (e.g. hurricanes) in the last two decades, it is of utmost significance to decipher the wave-structure-interaction of complex deck geometries and quantify the associated loads. Therefore, this study focuses on the assessment of solitary wave impact on open-girder decks that allow the air to escape from the sides. To this end, an arbitrary Lagrangian-Eulerian (ALE) numerical method with a multi-phase compressible formulation is used for the development of three-dimensional hydrodynamic models, which are validated against a large-scale experimental dataset of a coastal deck. Using the validated model as a baseline, a parametric investigation of different deck geometries with a varying number of girders Ng and three different widths, was conducted. The results reveal that the Ng of a superstructure has a complex role and that for small wave heights the horizontal and uplift forces increase with the Ng, while for large waves the opposite happens. If the Ng is small the wave particles accelerate after the initial impact on the offshore girder leading to a more violent slamming on the onshore part of the deck and larger pressures and forces, however, if Ng is large then unsynchronized eddies are formed in each chamber, which dissipate energy and apply out-of-phase pressures that result in multiple but weaker impacts on the deck. The decomposition of the total loads into slamming and quasi-static components, reveals surprisingly consistent trends for all the simulated waves, which facilitates the development of predictive load equations. These new equations, which are a function of Ng and are limited by the ratio of the wavelength to the deck width, provide more accurate predictions than existing empirical methods, and are expected to be useful to both engineers and researchers working towards the development of resilient coastal infrastructure.

Prediction of Wave Impact Pressures on Horizontal Plate

2010 ◽  
Author(s):  
Yanqiu Meng ◽  
Guoping Chen ◽  
Shichang Yan
Keyword(s):  
Wave Length ◽  
Wave Structure ◽  
Impact Pressure ◽  
Detailed Knowledge ◽  
Wave Impact ◽  
Wave Condition ◽  
Model Studies ◽  
Wave Induced ◽  
The Impact ◽  
Wave Structure Interaction

An optimal design of deck of jetty, platform and similar ocean structures requires detailed knowledge on wave impact pressure which affects its function. Investigations on wave induced impact pressures on deck were carried out by using physical model studies. The influences of wave and structure parameters on wave impact pressures were investigated. It is found that the wave impact pressure increases with increased deck clearance. The increasing trend continues up to the relative deck clearance Δh/η = 0.3–0.8, and then the impact pressure starts to decrease after that deck clearance. The wave steepness has some effect on the wave impact pressure, but the trend of variation is not consistent for different wave condition. The maximum impact pressure occurs when the ratio of wave length to deck width equals 3.97. Increase of wave period results in increase of the distance between the location of the maximum impact pressure and the seaward end of deck. Based on analysis of the physics of the wave structure interaction, empirical formula was proposed to estimate wave impact pressure on deck.

scholarly journals Assessment of Extreme Wave Impact on Coastal Decks with Different Geometries via the Arbitrary Lagrangian-Eulerian Method

2021 ◽  
Vol 9 (12) ◽  
pp. 1342
Author(s):  
Tao Xiang ◽  
Denis Istrati
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Wave Structure ◽  
Arbitrary Lagrangian Eulerian ◽  
Wave Impact ◽  
Arbitrary Lagrangian Eulerian Method ◽  
Wave Heights ◽  
Multi Phase ◽  
Wave Induced ◽  
Uplift Forces

Given the documented wave-induced damage of elevated coastal decks during extreme natural hazards (e.g., hurricanes) in the last two decades, it is of utmost significance to decipher the wave-structure-interaction of complex deck geometries and quantify the associated loads. Therefore, this study focuses on the assessment of solitary wave impact on open-girder decks that allow the air to escape from the sides. To this end, an arbitrary Lagrangian-Eulerian (ALE) numerical method with a multi-phase compressible formulation is used for the development of three-dimensional hydrodynamic models, which are validated against a large-scale experimental dataset of a coastal deck. Using the validated model as a baseline, a parametric investigation of different deck geometries with a varying number of girders Ng and three different widths, was conducted. The results reveal that the Ng of a superstructure has a complex role and that for small wave heights the horizontal and uplift forces increase with the Ng, while for large waves the opposite happens. If the Ng is small the wave particles accelerate after the initial impact on the offshore girder leading to a more violent slamming on the onshore part of the deck and larger pressures and forces, however, if Ng is large then unsynchronized eddies are formed in each chamber, which dissipate energy and apply out-of-phase pressures that result in multiple but weaker impacts on the deck. The decomposition of the total loads into slamming and quasi-static components, reveals surprisingly consistent trends for all the simulated waves, which facilitates the development of predictive load equations. These new equations, which are a function of Ng and are limited by the ratio of the wavelength to the deck width, provide more accurate predictions than existing empirical methods, and are expected to be useful to both engineers and researchers working towards the development of resilient coastal infrastructure.

Experimental study of the effect of wind above irregular waves on the wave-induced load statistics

2021 ◽  
pp. 103940
Author(s):  
Julie Caroee Kristoffersen ◽  
Henrik Bredmose ◽  
Christos Thomas Georgakis ◽  
Hubert Branger ◽  
Christopher Luneau
Keyword(s):  
Experimental Study ◽  
Irregular Waves ◽  
Wave Induced

A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures

2014 ◽  
Author(s):  
Xin Lu ◽  
Pankaj Kumar ◽  
Anand Bahuguni ◽  
Yanling Wu
Keyword(s):  
Real World ◽  
Offshore Structures ◽  
Air Gap ◽  
Irregular Waves ◽  
Linear Wave ◽  
Extreme Wave ◽  
Wave Impact ◽  
Loading Test ◽  
Wide Range ◽  
Wave Maker

The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms. The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications. We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.

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