Development and Verification of Modeling Practice for CFD Decay Calculations to Obtain Roll Damping of FPSO

2021 ◽  
Author(s):  
Arjen Koop ◽  
Pierre Crepier ◽  
Sebastien Loubeyre ◽  
Corentin Dobral ◽  
Kai Yu ◽  
...  
Keyword(s):  
Model Test ◽  
Test Results ◽  
Cfd Modelling ◽  
Roll Damping ◽  
Natural Period ◽  
Computational Mesh ◽  
Safety Studies ◽  
Offshore Industry ◽  
Decay Tests ◽  
Set Up

Abstract Estimates for roll damping are important input parameters for simulation studies on vessels operating at sea, e.g. FPSO mooring in waves, wind and current, workability and operability investigations, Dynamic Position studies, ship-to-ship operations and safety studies of vessels. To accurately predict the motions of vessels this quantity should be determined with confidence in the values. Traditionally, model experiments in water basins using so-called decay tests are carried out to determine the roll damping. With recent advancements in CFD modelling, the offshore industry has started using CFD as an alternative tool to compute the roll damping of FPSO’s. In order to help adopt CFD as a widely accepted tool, there is a need to develop confidence in CFD predictions. Therefore, a practical CFD modelling practice is developed within the Reproducible CFD JIP for roll decay CFD simulations. The Modelling Practice describes the geometry modelling, computational mesh, model set-up and post-processing for these type of CFD calculations. This modelling practice is verified and validated by three independent verifiers against available model test data. This paper provides an overview of the developed modelling practice and the calculated CFD results from the verifiers. The CFD modelling practice is benchmarked against available model test results for a tanker-shaped FPSO. By following this modelling practice, the CFD predictions for the equivalent linear damping coefficient and natural period of the roll motions are within 10% for all verifiers and within 10% from the model test results. Therefore, we conclude that when following the developed modelling practice for roll decay simulations, reliable, accurate and reproducible results can be obtained for the roll damping of tanker-shaped FPSOs.

Development and Verification of Modeling Practice for CFD Calculations to Obtain Current Loads on FPSO

2020 ◽  
Author(s):  
Arjen Koop ◽  
SeongMo Yeon ◽  
Kai Yu ◽  
Sebastien Loubeyre ◽  
Wei Xu ◽  
...  
Keyword(s):  
Model Test ◽  
Wind Tunnels ◽  
Cfd Modeling ◽  
Test Results ◽  
Geometry Modeling ◽  
Computational Mesh ◽  
Important Input ◽  
Modeling Practice ◽  
Offshore Industry ◽  
Set Up

Abstract Current loads are important input parameters for mooring studies. To accurately predict the motions of moored vessels these quantities should be determined with confidence in the values. Traditionally, these quantities have been determined using model tests in water basins or in wind tunnels. With recent advancements in CFD modeling, the offshore industry has started using CFD as an alternative tool to compute current loads on FPSO’s. In order to help adopt CFD as a widely accepted tool, there is a need to develop confidence in CFD predictions. Therefore, a practical CFD Modeling Practice is developed within the Reproducible Offshore CFD JIP. The Modeling Practice describes the geometry modeling, computational mesh, model set-up and post-processing for these types of CFD calculations. This Modeling Practice is verified and validated by five independent verifiers against model test data, such that reproducible and accurate results can be obtained by following the Modeling Practice. This paper provides an overview of the developed Modeling Practice and the calculated CFD results from the verifiers. The CFD Modeling Practice is benchmarked against available model test results for a barge-type and a tanker-shaped FPSO. By following this Modeling Practice, the CFD predictions for CY and CMZ are within 10% from all verifiers and within 10% from the model test results. Larger differences may be obtained for CX, depending on local grid resolution and turbulence model used, but also due to larger experimental uncertainty for this quantity.

Improved Strake Design for Vortex Induced Motions of Spar Platforms

2005 ◽  
Author(s):  
Mehernosh Irani ◽  
Lyle Finn
Keyword(s):  
Model Test ◽  
Model Tests ◽  
Test Results ◽  
Test Program ◽  
Test Set ◽  
Test Methodology ◽  
Spar Platforms ◽  
Truss Spar ◽  
Set Up

An extensive model test program was conducted to explore the effectiveness of alternate strake designs to reduce Truss Spar VIV response. Different strake configurations were tested to minimize VIV response. The paper presents results of the model tests. The model test set-up is described, important parameters that are modeled (including hull and truss geometry, strake configuration, mass and mooring properties) and considerations of instrumentation and test methodology are discussed. The paper also describes the analysis of the test results and shows the effectiveness of new strake design. The present results are compared with VIV response of existing Truss Spars with conventional strake design.

Model Testing for Vortex Induced Motions of Spar Platforms

2004 ◽  
Author(s):  
Mehernosh Irani ◽  
Lyle Finn
Keyword(s):  
Gulf Of Mexico ◽  
Model Test ◽  
State Of The Art ◽  
Model Testing ◽  
Model Tests ◽  
The State ◽  
Test Results ◽  
Test Set ◽  
Vortex Induced Vibrations ◽  
Set Up

The state-of-the art in model testing for Vortex Induced Vibrations (VIV) of Spars is presented. Important issues related to Spar VIV model testing are highlighted. The parameters that need to be modeled including hull geometry, strake configuration, mass and mooring properties and, considerations of test set-up and instrumentation are discussed. Results are presented from model tests of an as-built Spar deployed in the Gulf of Mexico. It is shown that the model test results compare well with the VIV responses measured in the field.

Stochastic Linearization and its Application in Motion Analysis of Cylindrical Floating Structure With Bilge Boxes

2016 ◽  
Author(s):  
Yan-Lin Shao ◽  
Jikun You ◽  
Einar Bernt Glomnes
Keyword(s):  
Motion Analysis ◽  
Model Test ◽  
Added Mass ◽  
Offshore Structures ◽  
Test Results ◽  
Viscous Effects ◽  
Natural Period ◽  
Stochastic Linearization ◽  
Excitation Force ◽  
Drag Term

To account for the viscous effects of damping devices, for instance, bilge keels or bilge boxes, on the motions of ships and offshore structures, Morison’s equation is often adopted as an empirical but practical approach in the design process. In order to combine the standard engineering panel method with the drag term in Morison’s equation, and remain in the frequency domain, the drag term has to be linearized based on, for instance, stochastic linearization. In this paper, the stochastic linearization scheme is implemented in an in-house code and verified through the comparison with the DNV GL software WADAM. The model test results of a large cylindrical FPSO with bilge box are used to calibrate the drag coefficients in the Morison’s equation. When the linearized drag forces are included, heave motion RAOs correspond better to the model test results. However, the predicted natural periods of heave motions are seen to be smaller than those obtained from model tests. It is suspected that the viscous flow separation around the bilge box increases the added mass of the unit beyond what is predicted by potential flow alone. Discussions are made on the effect of viscous added mass on the heave natural period. It is quite common to only include the damping effects in the motion analysis for large offshore structures and ignore the contribution of the viscous effects on the excitation force. For the considered cylindrical FPSO, this paper demonstrates that the viscous excitation force can be important in survival conditions.

A Comparison Among Alternatives to Assess FPSO Roll Damping via Model Testing

2014 ◽  
Author(s):  
Allan C. de Oliveira ◽  
Antonio Carlos Fernandes ◽  
Anderson R. W. Soares
Keyword(s):  
Model Test ◽  
Model Testing ◽  
Lessons Learned ◽  
Irregular Waves ◽  
Roll Damping ◽  
Test Specifications ◽  
Nonlinear Rolling ◽  
Decay Tests ◽  
Standard Strategy ◽  
Statistic Approach

The prediction of the nonlinear rolling motions of a FPSO with extended bilge keels stills a challenging problem. Despite recent advantages in CFD computations, the use of model testing is considered the standard strategy for roll damping assessments. There are different ways to assess the roll damping via model testing and the three most common are the use of decay tests, tests in regular and irregular waves. The comparison among those different kinds of tests may present incoherent results, sometimes, introducing the question of which methodology is the most appropriated in those scenarios, with impact in model test specifications. Decay tests are the easiest and the most economical way for roll assessments, but they are usually considered inaccurate compared to the other test types. Recent researches, however, have shown that a statistic approach which utilizes several decay data from the same model and loading condition improves the damping predictions. This paper provides comparisons of damping predictions from different test types based in extensive model test campaigns. It also addresses the issues and the lessons learned during the campaigns to obtain the FPSO damping database.

Model Test Data Correlations With Fully Coupled Hull/Mooring Analysis for a Floating Wind Turbine on a Semi-Submersible Platform

2014 ◽  
Author(s):  
Bonjun Koo ◽  
Andrew J. Goupee ◽  
Kostas Lambrakos ◽  
Ho-Joon Lim
Keyword(s):  
Wind Turbine ◽  
Model Test ◽  
Model Tests ◽  
Test Results ◽  
Scaled Model ◽  
Floating Wind Turbine ◽  
Mooring Dynamics ◽  
Set Up ◽  
Fully Coupled ◽  
Turbine Model

The DeepCwind floating wind turbine model tests were performed at MARIN (Maritime Research Institute Netherlands) with a model set-up corresponding to a 1:50 Froude scaling. In the model tests, the wind turbine was a scaled model of the National Renewable Energy Lab (NREL) 5MW, horizontal axis reference wind turbine supported by three different generic floating platforms: a spar, a semi-submersible and a tension-leg platform (TLP) (Ref. [1] and [2]). This paper presents validation of the MLTSIM-FAST [3] code with DeepCwind semi-submersible wind turbine model test results. In this integrated program, the turbine tower and rotor dynamics are simulated by the subroutines of FAST [4], and the hydrodynamic loads and mooring system dynamics are simulated by the subroutines of MLTSIM. In this study, fully coupled hull/mooring dynamics and second-order difference-frequency response are included in MLTSIM-FAST. The analysis results are systematically compared with model test results and show good agreement.

Very Rough Grid Approach for CFD Modelling of Thermoacoustic Oscillations Inside an Annular Premixed Combustor

2006 ◽  
Author(s):  
Stefano Tiribuzi
Keyword(s):  
Computation Time ◽  
Real Data ◽  
Acoustic Oscillations ◽  
Cfd Modelling ◽  
The Real ◽  
Thermoacoustic Instabilities ◽  
Computational Mesh ◽  
Annular Combustor ◽  
Set Up ◽  
Thermoacoustic Oscillations

Large pressure oscillations due to thermoacoustic instabilities may occur in the modern gas turbine equipped with lean premixed burners. The Research Department of ENEL is studying this phenomenon using research methods that include plant supervision, laboratory experiments and modelling. This paper presents a new CFD modelling approach capable of simulating the time evolution of thermofluiddynamic fields during thermoacoustic instabilities in a whole annular combustor. Its peculiarity consists in the adoption of a very rough computational mesh. The use of the Very Rough Grid (VRG) approach allows all the resonant cavities involved in the acoustic oscillations to be considered, as well as to prolonging the computed transient until spontaneous thermoacoustic oscillations onset, with affordable computation time. The rationale of this approach is that thermoacoustic instabilities are more affected by acoustics than by fluiddynamics. KIEN, an in-house low diffusive URANS code capable of simulating 3D reactive flows, has been used. A 3D structured monoblock computational grid of an industrial annular combustor has been set up. It goes from the compressor outlet to the turbine inlet, including both the annular plenum and the annular combustion chamber, and extends over the entire circumferential angle. The results obtained by an exemplifying computed case are illustrated. They appear to be congruent with the real behaviour of thermoacoustic oscillation reported in literature. The type of information that can be extracted directly or by suitable post-processing from these results is shown and their usefulness in interpreting the real data obtained from functioning plants or experimental facilities is demonstrated.

On Roll Hydrodynamics of FPSO’s Fitted With Bilge Keels and Riser Balcony

2011 ◽  
Author(s):  
R. van ’t Veer ◽  
F. Fathi ◽  
J. G. Kherian
Keyword(s):  
Model Test ◽  
Potential Flow ◽  
Model Tests ◽  
Continuous Operation ◽  
Motion Prediction ◽  
Roll Motion ◽  
Test Results ◽  
Site Location ◽  
Cfd Simulations ◽  
Roll Damping

The topic of this paper is the roll motion prediction of ship-shaped FPSO’s, designed for continuous operation at site location. The maximum roll amplitude is a critical operability parameter which is difficult to predict accurately due to the nonlinear roll damping associated with the appendages. This paper contributes to the understanding of roll damping physics through model test results, CFD simulations and potential flow predictions. The model tests discussed concern two different Floating Production, Storage and Offloading (FPSO) units, designed by SBM as spread-moored units for operation offshore Brazil. The relevant roll damping appendages are the bilge keels on both sides and the submerged riser balcony on one side of the vessel. In particular the riser balcony complicates the motion prediction and was a main reason for the model tests and CFD investigation. The results presented focus on roll motion prediction in the frequency domain.

A Novel Passive Riser Tensioning System for a Dry Tree Spread Moored Barge

2004 ◽  
Author(s):  
Amit Katarya
Keyword(s):  
Model Test ◽  
Vertical Motion ◽  
Model Tests ◽  
Test Results ◽  
Test Set ◽  
Payload Capacity ◽  
Set Up ◽  
Floating Systems ◽  
Moon Pool ◽  
Fully Coupled

Dry tree risers on floating systems are presently supported either by TLPs or SPARs, both of which have limited payload capacity and no storage. A spread-moored barge having dry trees, storage and integrated drilling facilities has been developed. Model tests were performed for the riser tensioning system used on such a barge for offshore West Africa conditions. The risers are attached to a rectangular platform in a moon pool of the barge. This platform is supported by means of an articulated Rocker Arm System (RAS) located on the vessel main deck. The RAS has built-in counter weights hinged on pedestals fixed to the barge deck. In this arrangement gravity is used to tension the risers and when the barge heaves, the counterweights in the rocker arm system essentially decouple the barge vertical motion from the riser platform. This system provides a heave-restrained platform for dry trees with minimal dynamic loading of the risers. The model tests confirmed the feasibility of the new design. The paper describes the basic components of the gravity tensioning system. The model test set up and results from the model test are shown. Comparison of model test results with a fully coupled analytic model consisting of the barge and articulated tensioning system is also presented.

Sign in / Sign up

Export Citation Format

Share Document