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.

Green Water Loading on a FPSO

2002 ◽  
Vol 124 (2) ◽  
pp. 97-103 ◽  
Author(s):  
O. M. Faltinsen ◽  
M. Greco ◽  
M. Landrini
Keyword(s):  
Nonlinear Effects ◽  
Rigid Wall ◽  
Green Water ◽  
Ship Motions ◽  
Sea Waves ◽  
Coupled Flow ◽  
Local Flow ◽  
Water Loading ◽  
Dam Breaking ◽  
The Impact

Green Water Loading in the bow region of a Floating Production Storage and Offloading unit (FPSO) in head sea waves is studied by numerical means. A 2-D method satisfying the exact nonlinear free-surface conditions within potential-flow theory has been developed as a step towards a fully 3-D method. The flow is assumed 2-D in a plane containing the ship’s centerplane. The method is partly validated by model tests. The importance of environmental conditions, 3-D flow effects, ship motions, and hull parameters are summarized. The wave steepness of the incident waves causes important nonlinear effects. The local flow at the bow is, in general, important to account for. It has become popular to use a dam-breaking model to study the propagation of water on the deck. However, the numerical studies show the importance of accounting for the coupled flow between the deck and outside the ship. When the water is propagating on the deck, a suitable distance from the bow can be found from where shallow-water equations can be used. Impact between green water on deck and a vertical deck-house side in the bow area is studied in details. A similarity solution for impact between a wedge-formed water front and a vertical rigid wall is used. Simplified solutions for an impacting fluid wedge with small and large interior angles are developed, both to support the numerical computations and to provide simpler formulas of practical use. It is demonstrated how the local design of the deck house can reduce the slamming loads. The importance of hydroelasticity during the impact is discussed by using realistic structural dimensions of a deck house. This indicates that hydroelasticity is insignificant. On the contrary, first results from an ongoing experimental investigation document blunt impacts against the deck during the initial stage of water shipping, which deserve a dedicated hydroelastic analysis.

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.

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.

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.

The Usefulness of Response Monitoring for Estimation of Bow

1986 ◽  
Vol 23 (03) ◽  
pp. 201-216
Author(s):  
George L. Petrie ◽  
Walter M. Maclean ◽  
H. Paul Cojeen ◽  
Gregg Schudel
Keyword(s):  
Structure Design ◽  
Green Water ◽  
Response Monitoring ◽  
Ship Motions ◽  
Exploratory Research ◽  
Prediction Of Response ◽  
Structural Responses ◽  
Bow Flare ◽  
In Trans ◽  
Scale Data

During the 1970's, the Maritime Administration, as part of its Exploratory Research Program, supported the development of shipboard instrumentation systems for the sensing of ship motions and structural responses and the prediction of response changes to be expected when a ship's course or speed is altered. Two systems were installed, one on the SS LASH Italia operating in the Atlantic/Mediterranean service and the other on the USNS Furman operating in trans-Pacific service. These systems were operated for several years during which time significant data were obtained on midship bending, bow accelerations, bow side frame stresses and rolling. Filtering allowed identification of slamming and green water events. SNAME Panel HS-2 (Impact Loads and Responses), long in need of full-scale data on heavy-weather transient loadings of the hull, wished to determine whether these data, collected for other purposes, could be useful for predicting the frequency and magnitude of loads on the bow flare structure due to slamming and green water events. This paper presents the results of the investigation that was carried out and suggests some implications regarding the establishment of criteria for bow structure design in regard to loadings of this type.

Efficient and Simplified Time Domain Simulation of Nonlinear Responses of Ships in Waves

2003 ◽  
Vol 47 (03) ◽  
pp. 262-273
Author(s):  
XueKang Gu ◽  
JinWei Shen ◽  
Torgeir Moan
Keyword(s):  
Model Test ◽  
Time Domain ◽  
High Efficiency ◽  
Coupling Effect ◽  
Irregular Waves ◽  
Green Water ◽  
Bending Moments ◽  
Strip Theory ◽  
Bow Flare ◽  
Theoretical Results

In this paper, a nonlinear time-domain strip theory is developed to predict nonlinear vertical ship motions and structural responses in severe waves. The effects of bottom impact, bow flare slamming, and green water on bending moments have been simulated. The flexible modes of the ship hull girder are accounted for by a Timoshenko beam theory. To validate the predicted responses, a model test was conducted for a ship with large bow flare and low bending rigidity, in both regular and irregular waves. The agreements between the calculated results and the model test are fairly good. The coupling effect between higher-order harmonic and the whipping components of vertical bending moments are verified by numerical calculations. Comparative studies with test and other theoretical results are also carried out for an S-175 containership with two kinds of bow flare forms. The causes of whipping and the variance in theoretical results are discussed. The good performance and high efficiency will make it possible to use the theory and its code for direct calculation of nonlinear bending moments in a long-term period and to develop a rule formula of design wave loads in the future.

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.

A Quasi-three-dimensional Finite-volume Shallow Water Model for Green Water on Deck

2013 ◽  
Vol 57 (03) ◽  
pp. 125-140
Author(s):  
Daniel A. Liut ◽  
Kenneth M. Weems ◽  
Tin-Guen Yen
Keyword(s):  
Shallow Water ◽  
Finite Volume ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Green Water ◽  
Water Model ◽  
Ship Motions ◽  
Shallow Water Model

A quasi-three-dimensional hydrodynamic model is presented to simulate shallow water phenomena. The method is based on a finite-volume approach designed to solve shallow water equations in the time domain. The nonlinearities of the governing equations are considered. The methodology can be used to compute green water effects on a variety of platforms with six-degrees-of-freedom motions. Different boundary and initial conditions can be applied for multiple types of moving platforms, like a ship's deck, tanks, etc. Comparisons with experimental data are discussed. The shallow water model has been integrated with the Large Amplitude Motions Program to compute the effects of green water flow over decks within a time-domain simulation of ship motions in waves. Results associated to this implementation are presented.

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