OBJECTIVE:
Obtain experimental data on the behavior and responses of (1) a moored, passive tanker-based FPSO in storm and high current conditions typical of hurricane and loop currents in the Gulf of Mexico, and (2) an FPSO with a moored shuttle tanker in wind, wave, and current conditions typical of severe operating conditions during offloading operations. Results from these experiments will be used to better understand and characterize the responses of FPSO’s in severe metocean conditions, validate and improve response analysis tools useful in design, and better understand operational limitations of FPSO’s and shuttle tankers during offloading operations.
APPROACH:
Model tests will be conducted in the OTRC wave basin to measure the responses of a moored, passive tanker-based FPSO in Gulf of Mexico hurricanes and loop currents. Parallel and non-parallel wind, wave, and current events will be used to simulate various conditions during the passage of severe storms and loop current events. Directional seas will be simulated as well as unidirectional waves to continue to examine the importance of wave directionality on roll motions and other responses. Measurements will include the 6 DOF vessel motions and mooring loads, and focus on key responses such as roll, sway, and yaw; motions at the turret that impact riser design, and FPSO – shuttle tanker interactions.
These experiments will build upon the initial experiments completed in 2000 and earlier in 2001-2002. Observations and data from the experiments in 2000 showed
1. Roll, yaw, and pitch is significantly (~4X) larger in directional waves
2. Roll responses in directional head-on seas were larger than a non-parallel wave, wind, and current condition typical of hurricanes that was thought to create maximum roll response
3. Large yaw instabilities indicated by large and rapid shifts between “stable” headings in non-parallel wave, wind, and currents
4. Surge, pitch, and heave are similar for unidirectional and directional seas.Experiments completed in 2001-2002 used a soft mooring system to obtain data to better understand responses in the wave frequency range.
DEPLOYMENT OF RESULTS:
These data will be used to calibrate and validate the numerical models being developed in other OTRC projects [Dynamic Analysis Tool for Moored Tanker-based FPSO’s Including Large Yaw Motions (M.H. Kim), FPSO-Shuttle Tanker Interactions and Stability (M.H. Kim), and FPSO Roll Motion Mitigation (S.Y. Kinnas)]. These models will be available for interpreting model tests and predicting FPSO responses. Results from these experiments will also be available to sponsors for their use in validating other design analysis tools.
ANTICIPATED PROJECT DURATION: 3 years
PROJECT PLAN FOR YEAR 2000-2001:
Scope of Work: The 1:60 scale model FPSO built for the initial experiments in 1999 will be utilized for these experiments. The prototype for this model is a 200,000 DWT tanker moored in 6,000 feet of water. A truncated mooring system will be used to simulate this water depth. A new measurement system will increase the accuracy of measured motions.
A number of realistic wave, wind, and current environments will be used to systematically study the FPSO responses in various hurricane and loop current conditions. The turret location and draft will be changed to provide data on the change in responses to these design and operational variables. The experiments will include characterization of the modeled environment and calibration of the model vessel and mooring responses. It is anticipated that about eight different non-parallel environments can be studied within the available budget. The number of different environments would be somewhat reduced as different turret locations and drafts are introduced into the test matrix. Some special experiments will be performed to characterize roll and roll damping. The final test matrix will be reviewed with sponsors and the PI’s involved in the related projects.
Anticipated Results: The experimental data on FPSO responses in non-parallel environments plus that from the previous year is expected to be sufficient to provide a basis for validating dynamic analysis tools in hurricanes and loop currents. The experiments to provide specific data on roll are expected to be sufficient to advance our understanding of roll and to begin validation of theoretical models of roll responses and roll mitigation.
PROJECT PLAN FOR YEAR 2001-2002:
Scope of Work: The experimental program will focus on validating model for roll. Roll suppression device(s) will be added to the FPSO model, and experiments will be conducted to validate the analytical model of the suppression device(s) and the device(s) effectiveness in wave, wind, and current environments that result in significant roll responses (as learned from the previous testing).
The experimental program will also be expanded to initiate tests to characterize the responses and interactions between a moored, weathervaning FPSO and a tandem moored shuttle tanker. These experiments will focus on understanding operational limits for offloading FPSO’s to shuttle tankers in the Gulf of Mexico. The test will include the loop current with various realistic waves and wind conditions plus other environments that could challenge offloading operations.
Anticipated Results: Data on the performance of roll suppression devices will be available to validate the analytical predictive model being developed in a related project [FPSO Roll Motions].
Results from the FPSO-shuttle tanker model tests will be available and useful for evaluating and validating the performance of the modeled system. These results can form the basis for the subsequent study in Year 2002-2003 of other offloading operational plans, equipment and mooring configurations, and developing operational limits and criteria.
PROJECT PLAN FOR YEAR 2002-2003:
Scope of Work: The 1:60 scale model FPSO built for the initial experiments in 1999-2000 will be used for these experiments. The prototype for the FPSO is a 200,000 DWT tanker. Large water depths will be simulated with an equivalent mooring system. An existing tanker model will be used to represent a shuttle tanker. An equivalent mooring will be used to simulate a multi-line mooring system in a water depth of 6000 feet. A soft mooring system will be used to study wave frequency responses.
A number of realistic wave, wind, and current environments will be used to systematically study the FPSO responses in various hurricane and loop current conditions. The draft and bilge keel geometry will be varied to provide data on the change in responses to these design and operational variables. The experiments will include calibration of the basin environment and of the model vessel and mooring responses. Some special experiments will be performed to characterize roll and roll damping.
A series of three experiments are planned.
1. FPSO with a soft mooring in operating wave environments without and with a shuttle tanker,
2. FPSO with a deepwater equivalent mooring system in (1) hurricane environments and (2) operating wave environments without and with a shuttle tanker,
3. FPSO with a deepwater equivalent mooring system (1) in a loop current environment with operating wave environments without and with a shuttle tanker.The wave basin environment will be extensively calibrated before each series of these benchmark experiments.
Completion of the three test series is subject to the availability of basin time. Some planned experiments may have to be deferred due to other basin activities.
Anticipated Results: These experimental data on the responses of the FPSO and the FPSO with shuttle tanker in the variety of storm and loop current environments, plus that from the previous years, is expected to be sufficient to provide a basis for validating numerical models of tanker responses in severe wave and current events such as hurricanes and loop currents, and for FPSO and shuttle tankers in wave and current operating conditions. The experiments to provide specific data on roll are expected to be sufficient to advance our understanding of roll and roll mitigation.
PROJECT PLAN FOR YEAR 2003-2004: The series of experiments described above may extend into this year depending on the availability of wave basin time.
PRINCIPAL INVESTIGATOR (S) & OTHERS INVOLVED IN PROJECT:
PI(s): R.S. Mercier, E.G. Ward
Others: OTRC Wave basin staff
DATE: June, 2007Project Title: FPSO Responses in Gulf of Mexico Environments
MMS Project: 368 TO Number: 18032
Project PI: Richard Mercier
COTR: S. Buffington
Estimated Completion Date: 8/31/2007
Project Description:
Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and Loop Currents in the Gulf of Mexico. Model test data will be used to validate various analytical response models for FPSOs, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (Kim), FPSO-Shuttle Tanker Responses and Interactions (Kim), and FPSO Roll and Roll Mitigation (Kinnas).Progress:
The modeling of the global responses of a ship-shaped FPSO involves a number of special issues:
• the possibility of the vessel undergoing large low frequency yaw motions,
• sensitivity to non-collinear wind, wave and current components,
• complex low frequency forcing due to wave-current interaction,
• use of bilge keels or other devices to suppress resonant roll motions, and
• for offloading situations, multi-body hydrodynamic interactions.The objective of this project is to generate high quality experimental data on the behavior of a turret-moored FPSO exposed to Gulf of Mexico storm and operating environments for use in improving/validating numerical models of global responses. A multi-phase test program sequenced to allow systematic validation of numerical models for individual forcing and response mechanisms is being pursued. The model tests are being performed using a 1:60 scale model of a 200,000 DWT FPSO.
The table below summarizes the test program configured for the stand-alone FPSO, with and without bilge keels. Test Phases I and II are complete. Building on the capabilities and knowledge gained from the prior phases, the Phase III and IV test programs are configured to isolate the differential effect of the current on FPSO responses when combined with collinear and non-collinear waves.
The combined wave + current conditions for the Phase III and IV test programs were calibrated during Jan/Feb, 2007. The conditions include collinear and non-collinear long-crested waves + current, as well short-crested waves + current with collinear primary direction. The conditions were calibrated in pairs (w/ and w/o current) to allow direct evaluation of the current effect. Calibrating the wave + current environments to match target conditions took much longer than expected because of the high degree of nonlinearity associated with non-collinear waves + current. A number of more highly non-collinear conditions were attempted but found to be too non-uniform in the test area. In the end we settled on a maximum 15° spread between long-crested waves and current.Preliminary tests performed in February showed a significant slow drift response associated with wave/current interaction and confirmed the importance of this poorly understood forcing mechanism. The tests had to be interrupted for another project, but were re-initiated at the end of May and are on-going. The Phase III test program will be completed at the end of June, and the Phase IV tests with the turret mooring will be completed in the first two weeks of July.
Reports and Publications:
S. Besnard, “Performance of the MAVS Current Meter for Laboratory Measurements”, MS Thesis, December 2004.Huijs, F., “Current Forces on FPSO’s – Analysis of Towing Tests and Current Tests with a FPSO Model, OTRC Report, January, 2005.
Mercier, R.S. and Huijs, F.A. (2005), “Steady Current Forces on Tanker-Based FPSOs”, Fluid Structure Interaction and Moving Boundary Problems, WIT Transactions of the Built Environment, Vol. 84, pp. 259-268, WIT Press.
DATE: December, 2006Project Title: FPSO Responses in Gulf of Mexico Environments
MMS Project: 368 TO Number: 18032
Project PI: Richard Mercier
COTR: S. Buffington
Estimated Completion Date: 8/31/2007
Project Description:
Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and Loop Currents in the Gulf of Mexico. Model test data will be used to validate various analytical response models for FPSO’s, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (Kim), FPSO-Shuttle Tanker Responses and Interactions (Kim), and FPSO Roll and Roll Mitigation (Kinnas).
Progress:
The modeling of the global responses of a ship-shaped FPSO involves a number of special issues:
• the possibility of the vessel undergoing large low frequency yaw motions,
• sensitivity to non-collinear wind, wave and current components,
• complex low frequency forcing due to wave-current interaction,
• use of bilge keels or other devices to suppress resonant roll motions, and
• for offloading situations, multi-body hydrodynamic interactions.The objective of this project is to generate high quality experimental data on the behavior of a turret-moored FPSO exposed to Gulf of Mexico storm and operating environments for use in improving/validating numerical models of global responses. A multi-phase test program sequenced to allow systematic validation of numerical models for individual forcing and response mechanisms is being pursued.
The model tests are being performed using a 1:60 scale model of a 200,000 DWT FPSO. As with any test program designed to produce high quality data, a number of experimental issues must be addressed. In this case the issues include:
• effect of wall reflections on FPSO responses,
• spatial uniformity of environmental conditions over the large horizontal area occupied by the FPSO (and shuttle tanker),
• viscous scale effects, and
• the generation and calibration of combined, non-collinear wind, current and directional wave environments.The table below summarizes the test program configured for the stand-alone FPSO, with and without bilge keels.
Test Phases I and II are complete. The Phase I tests were analyzed in the context of validating the industry-standard WAMIT software for modeling wave-body interactions in the frequency domain. The results showed that:
• added mass and radiation damping derived from free vibration (decay) tests were in good agreement with WAMIT,
• bilge keels increase damping of free roll oscillations in calm water by 1% to 3% of critical,
• motion RAOs derived from regular and random wave tests were in very good agreement with WAMIT,
• mean drift force transfer functions derived from regular wave tests were in good agreement with WAMIT , and
• damping of resonant roll motions is larger in waves than in calm water (up to 6% of critical).The overall agreement with WAMIT serves as a verification that the effect of wall reflections on the measured FPSO responses was minimal for the conditions tested (although it was noticeable in the free vibration tests, which limited the duration of useful data).
In preparation for the Phase II test program an extensive study was performed to understand the response characteristics of newly-acquired MAVS acoustic current meters and to map the current field in the OTRC basin, with and without superposed waves, for five different pump settings up to the maximum capacity. The purpose of the current tests was to quantify the turbulence levels and to delineate the region of the basin where the current field could be assumed to be reasonably uniform. The tests also showed that the asymmetric placement of the pump intakes in the basin could skew the current field toward the east side of the basin, depending on the pump settings. This information is useful for optimal location of the FPSO model in the basin.
The Phase II tow and current tests were used to quantify the steady flow horizontal force and yaw moment coefficients for the FPSO hull. The initial plan was to perform tow tests only, however inconsistencies in the initial results prompted further investigation using current tests. Though adjustment in test procedures were made to improve the accuracy of the tow test results, it was determined that current tests provided superior results.
Comparison of the tow and current test results with industry-standard OCIMF data showed general agreement in overall trends with some notable differences. The most important finding was that, contrary to OCIMF conclusions, bilge keels have a significant effect on the transverse current forces, as one would expect given the proven effectiveness of bilge keels in mitigating resonant roll motions. Other differences relative to OCIMF data are presumably mostly due to the specific bow and stern configuration of the FPSO tested. The measured current force coefficients will be used in modeling the steady and low frequency drift forces on the FPSO when it is subjected to combined wave and current environments in the Phase III and IV test programs.
Detailed planning is underway for the Phase III and IV test programs, which are scheduled from mid-January through mid-March, 2007. Building on the capabilities and knowledge gained from the prior tests summarized above, the Phase III and IV test programs will be configured to isolate the differential effect of the current on FPSO responses when combined with collinear and non-collinear waves.
The issue of multi-body hydrodynamic interactions during shuttle tanker offloading is being partially addressed through a separately funded research project. The test program for this project was completed in 2006 and the data are currently being analyzed. The tests involved several model configurations:
• a single fixed rectangular barge-like structure,
• two fixed barges in a side-by-side configuration,
• a fixed barge and a fixed ship in a side-by-side configuration, and
• a fixed barge and a floating ship with partially full cargo tanks in a side-by-side configuration.Wave behavior in the gap between the vessels, loads on the fixed barge and ship, motions of the floating ship, and motions of the fluids in the tanks on the ship were measured for a variety of wave conditions and headings. The test results and comparisons with numerical model predictions will be made available to this project and used to optimize future tests of side-by-side operations involving FPSO and shuttle tankers or LNG carriers and fixed receiving terminals.
Reports and Publications:
S. Besnard, “Performance of the MAVS Current Meter for Laboratory Measurements”, MS Thesis, December 2004.Huijs, F., “Current Forces on FPSO’s – Analysis of Towing Tests and Current Tests with a FPSO Model, OTRC Report, January, 2005.
Mercier, R.S. and Huijs, F.A. (2005), “Steady Current Forces on Tanker-Based FPSOs”, Fluid Structure Interaction and Moving Boundary Problems, WIT Transactions of the Built Environment, Vol. 84, pp. 259-268, WIT Press.
Date: June 2006Project Name: FPSO Responses in Gulf of Mexico Environments
MMS Project Number: 368 Task Order: 18032
Principal Investigators: R.S. Mercier, E.G. Ward
Estimated Completion Date: August 31, 2006
Project Description: Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and Loop Currents in the Gulf of Mexico. Model test data will be used to validate various analytical response models for FPSO’s, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (5888G, Kim), FPSO-Shuttle Tanker Responses and Interactions (5888GG, Kim), and FPSO Roll and Roll Mitigation (Kinnas, 5888A).
Progress: A separately funded research project was completed which investigated the fundamental physics of hydrodynamic interactions between multiple fixed and floating bodies in close side-by-side proximity. The tests focused on hydrodynamic effects in the small gap between the bodies and the influence on the forces and motions of the bodies, which is fundamental to understanding FPSO-shuttle tanker and LNG carrier offloading interactions during side-by-side offloading.
The tests involved several model configurations:
• a single fixed rectangular barge-like structure
• two fixed barges in a side-by-side configuration
• a fixed barge and a fixed ship in a side-by-side configuration
• a fixed barge and a floating ship with partially full cargo tanks in a side-by-side configuration
Wave behavior in the gap, loads on the fixed barge and ship, motions of the floating ship, and motions of the fluids in the tanks on the ship were measured for a variety of wave conditions and headings. These data are being used by the test sponsors to improve understanding and capabilities to analytically model the hydrodynamic influences of fixed and floating vessels in close side-by-side proximity.These test results will not only advance the knowledge of the fundamental physics, but have also significantly advanced OTRC’s capabilities and equipment to model floating and fixed bodies in side-by-side configurations. The test results and comparisons with numerical model predictions will be made available to this project and used to optimize future tests of side-by-side operations involving FPSO and shuttle tankers or LNG carriers and fixed receiving terminals.
Reports & Publications:
S. Besnard, “Performance of the MAVS Current Meter for Laboratory Measurements”, MS Thesis, December 2004.
Huijs, F., “Current Forces on FPSO’s – Analysis of Towing Tests and Current Tests with a FPSO Model, OTRC Report, January, 2005.
Mercier, R.S. and Huijs, F.A. (2005), “Steady Current Forces on Tanker-Based FPSOs”, Fluid Structure Interaction and Moving Boundary Problems, WIT Transactions of the Built Environment, Vol. 84, pp. 259-268, WIT Press.
Date: December 2005Project Name: FPSO Responses in Gulf of Mexico Environments
Project Number: 32558-5888G, GG, GA Task Order: 18032
Principal Investigators: R.S. Mercier, E.G. Ward
Estimated Completion Date: August 2006
Project Description: Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and Loop Currents in the Gulf of Mexico. The model test data will be used to validate various analytical response models for FPSO’s, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (5888G, Kim), FPSO-Shuttle Tanker Responses and Interactions (5888GG, Kim), and FPSO Roll and Roll Mitigation (Kinnas, 5888A).
Progress: An opportunity has come up under a separately funded research project to perform model tests of two fixed barges and of a moored ship and barge in a side-by-side configuration. The tests are designed to investigate hydrodynamic effects associated with the small gap between the vessels, which is fundamental to understanding FPSO-shuttle tanker interactions during side-by-side offloading. The barge models and associated load cell mounts were fabricated and preliminary tests were conducted in Sept-Oct, 2005 to validate the test set-up and wave conditions. Final tests of the side-by-side fixed barge configuration will be performed in April 2006, while tests of the moored ship-barge configuration are planned for Jun-Jul, 2006. The test results and comparisons with numerical model predictions will be made available to this project and used to optimize future test phases involving side-by-side FPSO-shuttle tanker configurations.
Reports & Publications:S. Besnard, “Performance of the MAVS Current Meter for Laboratory Measurements”, MS Thesis, December 2004.
Huijs, F., “Current Forces on FPSO’s – Analysis of Towing Tests and Current Tests with a FPSO Model, OTRC Report, January, 2005.
Mercier, R.S. and Huijs, F.A. (2005), “Steady Current Forces on Tanker-Based FPSOs”, Fluid Structure Interaction and Moving Boundary Problems, WIT Transactions of the Built Environment, Vol. 84, pp. 259-268, WIT Press.
Date: June, 2005Project Title: FPSO Responses in Gulf of Mexico Environments
MMS Project: 368 TO Number: 18032
PI: Richard Mercier, E. G. Ward
COTR: A. Konczvald
Estimated Completion Date: August 31, 2006
Project Description: Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and Loop Currents in the Gulf of Mexico. The model test data will be used to validate various analytical response models for FPSO’s, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (5888G, Kim), FPSO-Shuttle Tanker Responses and Interactions (5888GG, Kim), and FPSO Roll and Roll Mitigation (Kinnas, 5888A).
Progress: An opportunity has come up under a separately funded research project to perform model tests of two fixed barges in a side-by-side configuration. The tests are designed to investigate hydrodynamic effects associated with the small gap between the barges, which is fundamental to understanding FPSO-shuttle tanker interactions during side-by-side offloading. Planning for the tests is complete and the tests will be conducted in August, 2005. The test results and comparisons with numerical model predictions will be made available to this project and used to optimize future test phases involving side-by-side FPSO-shuttle tanker configurations.
Reports & Publications:
S. Besnard, “Performance of the MAVS Current Meter for Laboratory Measurements”, MS Thesis, December 2004.
Huijs, F., “Current Forces on FPSO’s – Analysis of Towing Tests and Current Tests with a FPSO Model, OTRC Report, January, 2005.
Mercier, R.S. and Huijs, F.A., “Steady Current Forces on Tanker-Based FPSOs”, to be presented at Fluid Structure Interaction 2005, La Coruña, Spain, September.
Date: December, 2004
Project Title: FPSO Responses in Gulf of Mexico Environments
MMS Project: 368 TO Number: 18032
PI: Richard Mercier, E. G. Ward
COTR: A. Konczvald
Estimated Completion Date: 8/31/05Project Description: Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and Loop Currents in the Gulf of Mexico. The model test data will be used to validate various analytical response models for FPSO’s, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (5888G, Kim), FPSO-Shuttle Tanker Responses and Interactions (5888GG, Kim), and FPSO Roll and Roll Mitigation (Kinnas, 5888A).
Progress: Analysis of the two 2002 test programs of the FPSO (with and without bilge keels) in a soft moor exposed to waves continued. Analysis of the free oscillation tests is complete. Analysis of the regular and unidirectional irregular wave tests to develop vessel motion RAOs and mean drift force transfer functions is complete. A WAMIT hydrodynamic model for the FPSO was set up and used to generate numerical results. As expected, comparison of the measured and WAMIT-predicted RAOs and mean drift force transfer functions is very good. The WAMIT model was used to calibrate values for the additional roll damping resulting from the bilge keels, which appears to be in the 1% to 6% of critical range depending on the seastate and heading. Remaining work on the 2002 test data includes analysis of the directional wave tests and analysis of the wave runup data.
In 3Q and 4Q 2004 an extensive program of FPSO tow tests and current tests was performed, at various headings, drafts and speeds, with and without bilge keels. As part of the test program a survey of the surface current field in the OTRC wave basin was performed for 5 different current speeds. The current mapping tests were used to delineate the region of the basin where the current could be assumed to be reasonably uniform. This information was used to locate the FPSO model in the basin for the current tests. The tow and current tests were used to quantify the steady flow horizontal force and yaw moment coefficients for the FPSO hull. The initial plan was to perform tow tests only, however inconsistencies in the initial results prompted further investigation using current tests. Though adjustment in test procedures were made to improve the accuracy of the tow test results, it was determined that current tests provided superior results.
Comparison of the tow and current test results with OCIMF data showed general agreement in overall trends with some notable differences. The most important finding was that, contrary to OCIMF conclusions, bilge keels have a significant effect on the transverse current forces, as one would expect given the proven effectiveness of bilge keels in mitigating resonant roll motions. Other differences relative to OCIMF data are presumably mostly due to the specific bow and stern configuration of the FPSO tested. The measured current force coefficients will be used in modeling the steady and low frequency drift forces on the FPSO when it is subjected to combined wave and current environments.
The next set of experiments that is being planned for 3Q 2005 involves the FPSO in a soft moor exposed to combined waves and current, with and without bilge keels.
Reports & Publications:
S. Besnard, “Performance of the MAVS Current Meter for Laboratory Measurements”, MS Thesis, December 2004.
Huijs, F., “Current Forces on FPSO’s – Analysis of Towing Tests and Current Tests with a FPSO Model, OTRC Report, January, 2005.
Mercier, R.S. and Huijs, F.A., “Steady Current Forces on Tanker-Based FPSOs”, to be presented at Fluid Structure Interaction 2005, La Coruña, Spain, September.
Date: June 2004Project Name: FPSO Responses in Gulf of Mexico Environments
Project Number: 368 Task Order: 18032
Principal Investigators: R.S. Mercier, E.G. Ward
Estimated Completion Date: August 31, 2005
Project Description:
Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and Loop Currents in the Gulf of Mexico. The model test data will be used to validate various analytical response models for FPSO’s, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (5888G, Kim), FPSO-Shuttle Tanker Responses and Interactions (5888GG, Kim), and FPSO Roll and Roll Mitigation (Kinnas, 5888A).
Progress:
A number of improvements to the wave basin capabilities have been pursued in preparation for further experiments on FPSO responses in hurricane and Loop current environments (at no cost to this project):
1. acquisition and check-out of MAVS current meters,
2. preliminary survey of current field (and associated turbulence) in OTRC wave basin, with and without superposed waves, to quantify the degree of uniformity over horizontal scales comparable to the area occupied by the FPSO and shuttle tanker during tests in hurricane and Loop current environments,
3. acquisition and check-out of upgrade to Qualisys optical tracking system to measure motions of multiple independent rigid bodies (eg. FPSO and shuttle tanker).
Items 1 and 2 are currently being documented as a MS thesis with an expected completion date of August, 2004. Item 3 is in progress, but initial tests of the upgrade look promising.Analysis of the two 2002 test programs of the FPSO (with and without bilge keels) in a soft moor exposed to waves only continued. Analysis of the free oscillation tests is complete. Analysis of the regular and irregular wave tests to develop RAOs for all responses of interest (motions, run-up, mooring line tensions) is in progress. The analysis is being performed as a Master of Engineering project, with the project report expected to be completed in 4Q2004.
The following experiments are planned for 3Q & 4Q 2004:
1. tow tests of FPSO model at various headings and drafts, with and without bilge keels, to quantify steady flow drag coefficients for the hull
2. based on preliminary survey of currents in OTRC basin, adjust current generator to maximize area of uniformity of current field and repeat survey of current, with and without superposed waves.
3. perform tests of FPSO in soft moor exposed to waves and current, with and without bilge keels, to quantify the FPSO wave frequency motions in combined wave and current environments.Reports & Publications:
S. Besnard, “Performance of the MAVS Current Meter for Laboratory Measurements”, MS Thesis, in preparation.
Date: December 2003Project Name: FPSO Responses in Gulf of Mexico Environments
TEES Project Number: 32558-5888G, GG, GA MMS Task Order: 18032 MMS Project Number: 368
Principal Investigators: R.S. Mercier, E.G. Ward
Estimated Completion Date: September 30, 2004
Project Description:
Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and Loop Currents in the Gulf of Mexico. The model test data will be used to validate various analytical response models for FPSO’s, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (5888G, Kim), FPSO-Shuttle Tanker Responses and Interactions (5888GG, Kim), and FPSO Roll and Roll Mitigation (Kinnas, 5888A).
Progress:
As part of a Master of Engineering student project, a comprehensive effort is underway to analyze the data from the two 2002 test programs with the FPSO in a soft moor (with and without bilge keels). The analysis of the free oscillation tests is complete and the documentation of same is nearly complete. The documentation of the free oscillation tests will be delivered to Dr. Kinnas for his work on numerical modeling of the effect of bilge keels. The next focus will be on the analysis of regular and irregular wave tests to develop Response Amplitude Operators (RAO’s) for all responses of interest (motions, run-up, mooring line tensions), which can subsequently be compared with numerical modeling results.
The next planned set of experiments will focus on FPSO responses in waves and currents. The FPSO will again be moored in the horizontal soft moor. In preparation for these experiments, a preliminary study of wave/current interactions in the basin was performed in 4Q 2003. The study was performed with newly purchased MAVS acoustic current meters. While the MAVS current meters are superior to other types of sensors for this application, there were some instrument-related measurement problems that are currently being investigated as a MS thesis. Pending the results of this investigation, we expect to perform a second study of wave/current interactions in the basin in 3Q 2004. These wave/current interaction experiments and studies are being funded under a separate project.
Date: June 2003
Project Name: FPSO Responses in Gulf of Mexico Environments
Project Number: 32558-5888G, GG, GA Task Order: 18032
Principal Investigators: R.S. Mercier, E.G. Ward
Estimated Completion Date:
Project Description:
Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and loop Currents in the Gulf of Mexico. The model test data will be used to validate various analytical response models for FPSOs, including those developed in the OTRC projects Moored Tanker-Based FPSO Responses including Large Yaw Motions (5888G, Kim), FPSO-Shuttle Tanker Responses and Interactions (5888GG, Kim), and FPSO Roll and Roll Mitigation (Kinnas, 5888A).
Progress:
In 2002 two series of model tests were performed with the FPSO in a soft mooring exposed to various regular, random, and multidirectional wave conditions (without wind or current). Tests were performed with and without bilge keels mounted to the hull. The primary objective of the tests was to collect high quality data on first-order (wave frequency) FPSO motion responses and wave runup for use in verifying various numerical models of FPSO responses with and without bilge keels. The soft moor tests not only serve as a benchmark for interpretation of subsequent tests under more realistic mooring and wave/current/wind conditions, but they also provide data for validation of currently available 2D models of ship roll in the presence of bilge keels.
The purpose of the soft mooring was to ensure that the natural periods of the FPSO in surge, sway and yaw were very long, effectively suppressing slow drift motions. Based on experience with modeling TLP, semi-submersible, and spar responses, it is commonly assumed that, given correct (i.e. ideal) input conditions, radiation/diffraction models are quite capable of predicting accurate first-order motion responses. However the wave-induced motions of these column-based structures are not so sensitive to small yaw oscillations or to reflected waves in a wave basin. The purpose of the soft moor FPSO tests was to characterize the extent to which finite amplitude yaw motions and wave reflections from the beach and side walls affect the comparison between measured and predicted first-order responses. Complications also arise in the modeling of roll damping for ship hulls. If the agreement between measured and predicted first-order FPSO responses under carefully controlled test conditions is less than expected, one should not expect to be able to predict second-order slow drift responses of a turret-moored FPSO exposed to waves, wind, and current with any greater accuracy.With the assistance of an undergraduate student intern, in 1Q 2003 a preliminary analysis of the soft moor test data was performed, primarily to verify the general quality of the data, organize and document the database, and develop the data analysis procedures. In addition a numerical (WAMIT) model of the FPSO was set up for use in comparing numerical predictions with measurements. Measured hydrostatic properties and natural periods determined from incline and free decay tests compare quite well with WAMIT results. Vessel Response Amplitude Operators (RAOs) were determined from all regular and unidirectional random wave tests. Extreme value distributions were derived from the random wave tests for all motion responses.
The experimental results clearly show the effect of the bilge keels in reducing the resonant roll response. However the preliminary data analysis indicated a number of inconsistencies in the RAOs that warrant further investigation. Accordingly a second, more comprehensive data analysis effort has just been initiated (with the assistance of a senior undergraduate who will likely continue as a graduate research assistant in the fall semester).
The next planned set of experiments will focus on FPSO responses in waves and currents. The FPSO will again be moored in the horizontal soft moor. In preparation for these experiments, a study of wave/current interactions in the basin will be performed in 3Q 2003 to optimize the configuration of the current generator to achieve the most uniform wave/current field possible in the vicinity of the FPSO model.
Date: December 2002
Project Name: FPSO Responses in Gulf of Mexico Environments
Project Number: 32558-5888G, GG, GA Task Order: 18032
Principal Investigators: E.G. Ward, R.S. Mercier
Estimated Completion Date:
Project Description:
Conduct model tests to measure the responses of a moored tanker-based FPSO in wave, wind, and current conditions typical of hurricanes and loop Currents in the Gulf of Mexico. The model test data will be used to validate various analytical response models for FPSO’s, including Dynamic Analysis Tool for Moored Tanker-Based FPSO Responses Including Large Yaw Motions (5888G, Kim), Dynamic Analysis Tool for FPSO-Shuttle Tanker Responses and Interactions (5888GG, Kim), and FPSO Roll and Roll Mitigation (Kinnas, 5888A).
Progress:
A second series of wave tank tests were successfully completed with the FPSO in a “soft mooring” system. These experiments were conducted for one orientation, quartering waves (45 degrees), and add to the database from the previous experiments conducted for bow-on (0 degrees) and broadside (90 degrees) waves. As for the previous experiments, these tests included,
§ Regular waves
§ Random unidirectional waves
§ Random directional waves
§ Seastates up to 100-year conditions
§ FPSO hull with and without bilge keels
and were conducted with no wind or current so as to focus on the FPSO’s responses to waves.Data from the soft moor experiments emphasize wave frequency responses and minimize lower frequency responses (e.g., slow drift), and will therefore be useful in validating the analytical FPSO response models in the wave frequency range. In the first quarter of 2003, an undergraduate student intern will organize and analyze the database to facilitate its use in validating the various models cited above.
The next set of experiments (anticipated 2Q 2003) will focus on wave and currents responses. The soft moor will again be used so as to focus on the influence of currents on wave diffraction forces and the wave frequency responses of the FPSO.
The validation of the analytical responses at wave frequencies using data from these soft moor experiments will provide a strong foundation for then studying the more complex responses (at low frequencies as well as wave frequencies) of an FPSO in a realistic mooring system. The experimental program will then proceed (anticipated 4Q 2003) with the FPSO in a realistic mooring system.
This experimental program will also provide data on a moored FPSO and shuttle tanker during offloading. As a first step, the most recent experiments included several runs with an FPSO and a shuttle tanker to investigate experimental techniques for tracking the motions of this two-body system. Several measurement problems were identified.
Progress with this experimental program has been somewhat slower than anticipated due to the large number of design validation tests requested by the industry to support their recent high activity level in developing deepwater oil fields.
OTRC PROJECT STATUS REPORT
Project Name: FPSO Responses in GOM Environments
Task Order: 18032 Project Number: 5888G, 5888GG
Principal Investigators: E.G. Ward, R.S. Mercier
Estimated Completion Date: December 2002
Project Description:
Conduct model tests to demonstrate and measure the performance of a moored, passive tanker-based FPSO in hurricanes and loop currents in the Gulf of Mexico. The experiments will focus on transverse behavior (yaw, roll, sway) in non-parallel waves, winds, and currents conditions typical of hurricanes and loop currents. Continued development of the Dynamic Analysis Tool for Moored Tanker-based FPSO’s Including Large Yaw Motions (58887G, Kim) and its expansion to FPSO-Shuttle Tanker responses and interactions is also being supported by this project.
The model test data will be used to calibrate and validate these analytical models as well as the analytical models for FPSO roll and roll mitigation being developed in a companion project FPSO Roll Motions (5888A, Kinnas).
OTRC PROGRESS STATUS REPORTS
Date: June 24, 2002
Project Title: Dynamic Analysis Tool for Moored Tanker-based FPSOs Including Large Yaw Motions and Multi-body Interactions
Task Order: 18032 Project Number: 5888G, 5888GG
Principal Investigator: “Joseph” M. H. Kim
Estimated Completion Date: Oct. 2002 (1st phase); Oct 2003(2nd phase)
Project Description:
During the past several years, PI has developed a very powerful software called WINPOST for hull/mooring/riser nonlinear coupled dynamic analysis in time domain. The program has been extensively tested and verified against experimental results for various kinds of spars and TLPs. During the past two years, the WINPOST was designated by DeepStar Offshore Industry Consortium to produce bench-mark simulation results for spars and TLPs for 3 different water depths. The WINPOST has since been extended to turret-moored FPSO analysis including large yaw motions, and extensively tested and verified against other Deepstar FPSO results and Marin’s experiments. A study is being conducted to compare WINPOST simulations and the OTRC experiments already conducted for a single turret-moored FPSO in various environmental conditions. During the past 10 months, WINPOST has further been extended to handle multi-body interactions (in tandem and side-by-side off-loading position) and the results will be compared with future OTRC experiments.
Progress:
In case of turret-moored FPSO, the yaw response can be large and the wind, wave, and current forces can change significantly depending on the instantaneous yaw angle. The hydrodynamic coefficients may also change as the yaw angle changes. Therefore, for reasonable simulations of turret-moored FPSOs with large yaw motions, the wave, wind, and current forces need to be pre-calculated for each yaw-angle interval and utilized in ensuing simulations. The yaw-angle dependent wind and current forces on FPSO can, for example, be based on existing empirical data, such as OCIMF(Oil Company International Marine Forum) data. This task proposed last year has been successfully completed and the developed program has been verified against DEEP-STAR experiments (for a 3000-ft turret-moored FPSO with 12 chain-wire-chain mooring lines and 13 steel catenary risers) conducted in Marin wave basin. The comparison is excellent and even better than Marin’s DYNFLOAT prediction. The detailed methodology and results are described in Arcandra’s Ph.D. thesis, a SNAME Conference paper (2002), and a ISOPE Conference paper (2002). A journal paper is submitted for publication.
Recently, focus has been shifted to the extension capable of multi-body interactions. For the hydrodynamics of multi-body interactions, WAMIT MLUTI-BODY version has been used. The moored multi-bodies connected by elastic cables and hawser-lines are solved using an iteration method. The cases with and without hydrodynamic interactions can be straightforwardly compared. The published data for multi-body interactions are rare and more verifications are needed. Animation tools have been developed to better illustrate the multi-body coupled analysis results. One of the problems in solving this kind of difficult two-body interactions is lack of empirical data for wind and current forces (such as OCIMF) including shielding effects, especially when they are very close together.
Remaining Tasks (present – Oct.31 2002 and beyond)
· Compare the numerical prediction with OTRC model-test data for a single turret-moored FPSO. Investigate the effects of turret positions and loading condition on the overall performance of the FPSO.
· Compare the present numerical predictions with those of DEEP-STAR contractors.
· Fully develop the multi-body interaction problems for hull/mooring/riser coupled analysis and the corresponding graphics animation tools
· Investigate the effects of hydrodynamic interactions and coupling for various off-loading scenarios (e.g. tandem or side-by-side offloading).
· Investigate possible fish-tailing behavior and relevant instability in tandem off-loading case.
· A major remaining task extending to 2003 is comparison study against future OTRC experiments for FPSO/shuttle-tanker interactions study.Reports and Publications:
Ph.D. Thesis:
Arcandra, “Hull/mooring/riser coupled dynamic analysis of a deepwater floating platform with polyester lines” (August, 2001)Refereed Journal Papers:
Kim, M.H., Ran. Z., and Zheng, W., “Hull/mooring coupled dynamic analysis of a truss spar in time domain”, Journal of Offshore and Polar Engineering, Vol.11, No.1, 42-54, 2001
Arcandra and M.H. Kim, “Hull/mooring/riser coupled dynamic analysis of a turret-moored FPSO” submitted to Journal of Ship Research
Refereed Conference Papers:
Kim, M.H., Arcandra, Y.B. Kim, “Variability of spar motion analysis against design methodologies/parameters” Proc. Offshore Mechanics and Arctic Engineering, OMAE’01, Rio De Janeiro, 2001
Kim, M.H., Arcandra, Y.B. Kim, “Variability of TLP motion analysis against design methodologies/parameters” Proc. 11th International Offshore and Polar Engineering Conference, Stavanger, 2001
M.H. Kim and Y.B. Kim, “Hull/mooring/riser coupled dynamic analysis of a tanker-based turret-moored FPSO in deep water” Proc. 12th International Offshore and Polar Engineering Conference, Kita Kyushu, 2002
Arcandra, Ran, Z. and Kim, M.H., “Hull/mooring/riser coupled spar motion analysis with buoyancy-can effects” Proc. 12th International Offshore and Polar Engineering Conference, Kita Kyushu, 2002
Arcandra, P. Nurtjahyo, and M.H. Kim, “Hull/mooring/riser coupled analysis of a turret-moored FPSO 6000ft: comparison between polyester and buoy-steel mooring lines.” SNAME 2002 Symposium, Texas
OTRC Project Status Report
Project Name: FPSO Responses in GOM Environments
Task Order: 18032 Project Number: 5888G, 5888GG
Principal Investigators: E.G. Ward, R.S. Mercier
Estimated Completion Date: December 2002
Project Description:
Conduct model tests to demonstrate and measure the performance of a moored, passive tanker-based FPSO in hurricanes and loop currents in the Gulf of Mexico. The experiments will focus on transverse behavior (yaw, roll, sway) in non-parallel waves, winds, and currents conditions typical of hurricanes and loop currents. Continued development of the Dynamic Analysis Tool for Moored Tanker-based FPSO’s Including Large Yaw Motions (58887G, Kim) and its expansion to FPSO-Shuttle Tanker responses and interactions is also being supported by this project.
The model test data will be used to calibrate and validate these analytical models as well as the analytical models for FPSO roll and roll mitigation being developed in a companion project FPSO Roll Motions (5888A, Kinnas).
Progress:
A second set of experiments have been planned to build upon and extend the first experiments (5887K). These experiments will focus on (1) the relationships between directional seas and the relative heading between the FPSO and the waves on vessel roll, the influence of current and current direction relative to FPSO heading on FPSO response, (3) the reduction of roll due to bilge keels, and (4) FPSO response in Loop Currents plus non parallel waves and winds. We expect to complete these experiments in Summer-Fall 2002. This initiation of these research experiments has been delayed to the availability of the OTRC wave basin.
A third set of experiments will focus on FPSO roll mitigation and moored FPSO-Shuttle Tanker system responses and interactions. These experiments will be planned for late 2002-early 2003.
