Green water and slamming wave impacts can lead to severe damage or operability issues for marine structures. It is therefore essential to consider their probability and loads in design. This is difficult, as impacts are both hydrodynamically complex and relatively rare. The complexity requires high-fidelity modelling (experiments or CFD), whereas a statistically sound analysis of rare events requires long durations. High-fidelity tools are too demanding to run a Monte-Carlo simulation; low-fidelity tools do not include sufficient physical details. The use of extreme value theory and / or multi-fidelity modelling is therefore required. The present paper reviews the state-of-the-art methods to find wave impact design loads, which include response-conditioning methods, screening methods and adaptive sampling methods. Their benefits and shortcomings are discussed, as well as challenges for the wave impact problem. One challenge is the role of wave non-linearity. Another is the validation of the different methods; it is hard to obtain long-duration high-fidelity wave impact data. A planned case study is introduced, where different techniques will be put to the test and these challenges will be addressed.
{"title":"Finding Dangerous Waves – Towards an Efficient Method to Obtain Wave Impact Design Loads for Marine Structures","authors":"S. V. van Essen, H. Seyffert","doi":"10.1115/omae2022-79479","DOIUrl":"https://doi.org/10.1115/omae2022-79479","url":null,"abstract":"\u0000 Green water and slamming wave impacts can lead to severe damage or operability issues for marine structures. It is therefore essential to consider their probability and loads in design. This is difficult, as impacts are both hydrodynamically complex and relatively rare. The complexity requires high-fidelity modelling (experiments or CFD), whereas a statistically sound analysis of rare events requires long durations. High-fidelity tools are too demanding to run a Monte-Carlo simulation; low-fidelity tools do not include sufficient physical details. The use of extreme value theory and / or multi-fidelity modelling is therefore required. The present paper reviews the state-of-the-art methods to find wave impact design loads, which include response-conditioning methods, screening methods and adaptive sampling methods. Their benefits and shortcomings are discussed, as well as challenges for the wave impact problem. One challenge is the role of wave non-linearity. Another is the validation of the different methods; it is hard to obtain long-duration high-fidelity wave impact data. A planned case study is introduced, where different techniques will be put to the test and these challenges will be addressed.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87953232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hyunchul Jang, M. Agrawal, Z. Huang, F. Jiang, Jie Wu, H. Lie, Eloise Croonenborghs
Hydrodynamic force coefficients are important parameters in the design and assessment of marine risers. The hydrodynamic coefficients are widely used for assessing marine riser responses due to floater motion excitation and vortex-induced vibrations (VIV). Traditionally, the hydrodynamic coefficients have been obtained from physical model tests on short rigid riser sections. Recently, the offshore industry has started to use Computational Fluid Dynamics (CFD) analysis for predicting the hydrodynamic coefficients, due to the recent advancement of CFD software and high-performance computing capabilities. However, a reliable CFD modeling practice is required for CFD analysis to be a more widely accepted prediction tool in the industry. A joint industry effort has been initiated for developing and verifying a reliable CFD modeling practice through a working group of the Reproducible Offshore CFD JIP. Within the working group, a CFD modeling practice document was written based on existing practices already validated with model test data and verified by blind validations with three CFD practitioners. The first year work focused on a bare riser with circular cross-section and has been published in OMAE 2021. This paper presents the working group’s second-year verification activities for a staggered buoyancy module and a straked riser. The verification work covers three numerical test problems: 1) stationary riser in steady current, 2) riser under forced-oscillation in calm water, 3) riser under forced-oscillation in steady current. In the stationary riser simulation, drag coefficient and lift coefficient from verifiers are compared. In the forced-oscillation simulation in calm water, the fully-submerged riser section oscillates with a sinusoidal motion, and damping and added-mass coefficients are compared. In the forced-oscillation simulation in steady current, where the riser oscillates in either inline or perpendicular direction to the steady current, lift coefficient and added mass coefficient are compared. By following the modeling practice, the CFD predictions are consistent with each other and close to the model test data for the majority of the test cases.
{"title":"A Joint-Industry Effort to Develop and Verify CFD Modeling Practice for Predicting Hydrodynamic Coefficients of Risers: Part II – Staggered Buoyancy Module and Straked Riser","authors":"Hyunchul Jang, M. Agrawal, Z. Huang, F. Jiang, Jie Wu, H. Lie, Eloise Croonenborghs","doi":"10.1115/omae2022-79147","DOIUrl":"https://doi.org/10.1115/omae2022-79147","url":null,"abstract":"\u0000 Hydrodynamic force coefficients are important parameters in the design and assessment of marine risers. The hydrodynamic coefficients are widely used for assessing marine riser responses due to floater motion excitation and vortex-induced vibrations (VIV). Traditionally, the hydrodynamic coefficients have been obtained from physical model tests on short rigid riser sections. Recently, the offshore industry has started to use Computational Fluid Dynamics (CFD) analysis for predicting the hydrodynamic coefficients, due to the recent advancement of CFD software and high-performance computing capabilities. However, a reliable CFD modeling practice is required for CFD analysis to be a more widely accepted prediction tool in the industry. A joint industry effort has been initiated for developing and verifying a reliable CFD modeling practice through a working group of the Reproducible Offshore CFD JIP. Within the working group, a CFD modeling practice document was written based on existing practices already validated with model test data and verified by blind validations with three CFD practitioners. The first year work focused on a bare riser with circular cross-section and has been published in OMAE 2021.\u0000 This paper presents the working group’s second-year verification activities for a staggered buoyancy module and a straked riser. The verification work covers three numerical test problems: 1) stationary riser in steady current, 2) riser under forced-oscillation in calm water, 3) riser under forced-oscillation in steady current. In the stationary riser simulation, drag coefficient and lift coefficient from verifiers are compared. In the forced-oscillation simulation in calm water, the fully-submerged riser section oscillates with a sinusoidal motion, and damping and added-mass coefficients are compared. In the forced-oscillation simulation in steady current, where the riser oscillates in either inline or perpendicular direction to the steady current, lift coefficient and added mass coefficient are compared. By following the modeling practice, the CFD predictions are consistent with each other and close to the model test data for the majority of the test cases.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86987539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A systematic study of the hydrodynamic coefficients for simplified subsea modules has been performed, to support the estimation of the coefficients needed for planning of subsea installation operations. The coefficients are assessed for a nearly two-dimensional test setup. The tests are performed as forced oscillations at various amplitudes and periods, representing the forces on the module lowered through the water column. The importance of each of the main components of the subsea modules — mudmat, protection roof and process equipment of different shapes inside the modules are studied at fully submerged condition. Results for the module elements, generic contents and different combinations of these elements are presented. For the tested modules, damping is generally the dominating hydrodynamic force. However, the presence of the content inside the modules will generally increase the importance of added mass. Estimation of the hydrodynamic coefficients by summation of the coefficients for the individual structure elements generally overestimates the damping, compared to the coefficients measured for the complete modules. For added mass, estimation based on summation gives generally good results.
{"title":"Hydrodynamic Coefficients of Generic Subsea Modules in Forced Oscillation Tests – Importance of Structure Parts","authors":"Mia Abrahamsen-Prsic, F. Solaas, T. Kristiansen","doi":"10.1115/omae2022-79718","DOIUrl":"https://doi.org/10.1115/omae2022-79718","url":null,"abstract":"\u0000 A systematic study of the hydrodynamic coefficients for simplified subsea modules has been performed, to support the estimation of the coefficients needed for planning of subsea installation operations. The coefficients are assessed for a nearly two-dimensional test setup. The tests are performed as forced oscillations at various amplitudes and periods, representing the forces on the module lowered through the water column.\u0000 The importance of each of the main components of the subsea modules — mudmat, protection roof and process equipment of different shapes inside the modules are studied at fully submerged condition. Results for the module elements, generic contents and different combinations of these elements are presented.\u0000 For the tested modules, damping is generally the dominating hydrodynamic force. However, the presence of the content inside the modules will generally increase the importance of added mass.\u0000 Estimation of the hydrodynamic coefficients by summation of the coefficients for the individual structure elements generally overestimates the damping, compared to the coefficients measured for the complete modules. For added mass, estimation based on summation gives generally good results.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83551884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In late 2020, International Maritime Organization (IMO) released interim guidelines on the second generation intact stability criteria. In this paper direct stability assessment in design situations using deterministic approach for parametric rolling failure mode is presented. A 3D nonlinear direct time domain method based on mixed-Eulerian-Lagrangian (MEL) scheme as opposed to impulse response function (IRF) method is used to simulate parametric rolling in both regular and irregular waves. Computed numerical results of roll amplitude in regular head waves is validated with other available literature results. This study further examines the influence of incident wave height and roll damping coefficient on computed heave, roll, and pitch motions in regular head wave conditions. Mean 3-hour maximum roll amplitude is obtained for design situations as recommended by the IMO guidelines.
{"title":"IMO Level 3: Parametric Roll Stability Failure Simulation Using 3D Numerical Wave Tank","authors":"Shivaji Ganesan T., A. Negi, D. Sen","doi":"10.1115/omae2022-79654","DOIUrl":"https://doi.org/10.1115/omae2022-79654","url":null,"abstract":"\u0000 In late 2020, International Maritime Organization (IMO) released interim guidelines on the second generation intact stability criteria. In this paper direct stability assessment in design situations using deterministic approach for parametric rolling failure mode is presented. A 3D nonlinear direct time domain method based on mixed-Eulerian-Lagrangian (MEL) scheme as opposed to impulse response function (IRF) method is used to simulate parametric rolling in both regular and irregular waves. Computed numerical results of roll amplitude in regular head waves is validated with other available literature results. This study further examines the influence of incident wave height and roll damping coefficient on computed heave, roll, and pitch motions in regular head wave conditions. Mean 3-hour maximum roll amplitude is obtained for design situations as recommended by the IMO guidelines.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75570836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hyunchul Jang, M. Agrawal, Dongwhan Lee, Wei Xu, Jerry Huang, F. Jiang, Wu Jie, Eloise Croonenborghs
Hydrodynamic force coefficients are important parameters in design and assessment of marine risers. The hydrodynamic coefficients are widely used for assessing marine riser responses due to floater motion excitation and vortex-induced vibrations (VIV). Traditionally, the hydrodynamic coefficients have been obtained from physical model tests on short rigid riser sections. Recently, the offshore industry has started to use computational fluid dynamics (CFD) analysis for predicting the hydrodynamic coefficients due to the recent advancement of CFD software and high-performance computing capabilities, but a reliable CFD modeling practice is requested for CFD analysis to be a more widely accepted prediction tool in the industry. A joint industry effort has been made for developing and verifying the reliable CFD modeling practice through a working group of the Reproducible Offshore CFD JIP. In the working group, a CFD modeling practice document was written based on existing practices already validated for model test data, and verified by blind validations with three CFD practitioners. The first year works are focused on the bare riser with circular cross-section, and the second year work will be extended to the other riser sections such as staggered buoyancy module and straked riser. This paper presents the working group’s first-year verification activities for a bare riser with circular cross-section. The verification works covers three test problems: 1) stationary simulation in steady current, 2) forced-oscillation in calm water, 3) forced-oscillation in steady current. In the stationary simulation, mean drag coefficient, standard deviation of lift coefficient, and Strouhal numbers are compared. In the forced-oscillation simulation in calm water, the fully-submerged riser section oscillates with a sinusoidal motion, and damping and added mass coefficients are compared. In the forced-oscillation simulation in current, the riser section oscillates in cross-flow direction to the steady current, and lift coefficient and added mass coefficient are compared. By following the modeling practice, the CFD predictions are consistent with each other and close to the model test data for a majority of test cases.
{"title":"A Joint-Industry Effort to Develop and Verify CFD Modeling Practice for Predicting Hydrodynamic Coefficients on Bare Riser Surfaces","authors":"Hyunchul Jang, M. Agrawal, Dongwhan Lee, Wei Xu, Jerry Huang, F. Jiang, Wu Jie, Eloise Croonenborghs","doi":"10.1115/omae2021-63800","DOIUrl":"https://doi.org/10.1115/omae2021-63800","url":null,"abstract":"\u0000 Hydrodynamic force coefficients are important parameters in design and assessment of marine risers. The hydrodynamic coefficients are widely used for assessing marine riser responses due to floater motion excitation and vortex-induced vibrations (VIV). Traditionally, the hydrodynamic coefficients have been obtained from physical model tests on short rigid riser sections. Recently, the offshore industry has started to use computational fluid dynamics (CFD) analysis for predicting the hydrodynamic coefficients due to the recent advancement of CFD software and high-performance computing capabilities, but a reliable CFD modeling practice is requested for CFD analysis to be a more widely accepted prediction tool in the industry. A joint industry effort has been made for developing and verifying the reliable CFD modeling practice through a working group of the Reproducible Offshore CFD JIP. In the working group, a CFD modeling practice document was written based on existing practices already validated for model test data, and verified by blind validations with three CFD practitioners. The first year works are focused on the bare riser with circular cross-section, and the second year work will be extended to the other riser sections such as staggered buoyancy module and straked riser.\u0000 This paper presents the working group’s first-year verification activities for a bare riser with circular cross-section. The verification works covers three test problems: 1) stationary simulation in steady current, 2) forced-oscillation in calm water, 3) forced-oscillation in steady current. In the stationary simulation, mean drag coefficient, standard deviation of lift coefficient, and Strouhal numbers are compared. In the forced-oscillation simulation in calm water, the fully-submerged riser section oscillates with a sinusoidal motion, and damping and added mass coefficients are compared. In the forced-oscillation simulation in current, the riser section oscillates in cross-flow direction to the steady current, and lift coefficient and added mass coefficient are compared. By following the modeling practice, the CFD predictions are consistent with each other and close to the model test data for a majority of test cases.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72700202","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vortex Induced Motion (VIM) of multi-column floating platforms, such as Tension Leg Platform (TLP) and semi-submersible (SEMI), in current is well-acknowledged. Substantial VIM response of the multi-column floating platform may cause fatigue failure of mooring and riser systems, which can affect the normal operation of the platform. The present paper focuses on the numerical investigation on VIM of a TLP with circular columns using Computational Fluid Dynamics (CFD). Sensitivity analyses (e.g., mesh size, the number of prism layers and time-step size) for the VIM responses of the TLP are conducted. The effects of the current heading and mooring stiffness on the VIM are investigated. The three degrees of freedom VIM responses (in-line, transverse and yaw responses) and corresponding amplitude spectra are computed and analyzed. Motion trajectories are plotted to understand the VIM behaviors. Regarding the effect of the current heading, the largest transverse response is examined at 15° current heading and the corresponding maximum nominal amplitude is around 0.43. The difference of the maximum nominal amplitudes between the cases at 0° and 15° current headings is less than 5%. For 15°, 30° and 45° current headings, the nominal transverse amplitudes decrease as the current heading increases in the lock-in range. For the four studied current headings, the maximum width of the lock-in range is found at 0° current heading and narrows as the current incidence increases. The largest yaw response is observed at 0° current heading and the maximum nominal amplitude is around 9.1°. Regarding the effect of the mooring stiffness, the lock-in ranges and the maximum nominal amplitudes of the transverse motions have little difference for the four mooring stiffnesses. The maximum nominal transverse and yaw responses are around 0.25 and 5.1°, respectively, which occur when the mooring stiffness reaches the maximum. The flow pattern analyses indicate that the flow interference between the upstream and downstream columns may have significant effects on the VIM responses and a stronger interference at the present spacing ratio may lead to a larger VIM response. The contours of the vertical vorticity in the horizontal plane show that the mean positions of the flow separation points are always on highest or lowest (in the transverse direction perpendicular to the current heading) points of the columns, which is the reason that the VIM trajectories for the TLP with circular columns are always along the direction perpendicular to the current heading.
{"title":"Numerical Investigation on Vortex Induced Motions of a Tension Leg Platform With Circular Columns","authors":"Pen Zhi, Xinshu Zhang","doi":"10.1115/omae2021-66612","DOIUrl":"https://doi.org/10.1115/omae2021-66612","url":null,"abstract":"\u0000 Vortex Induced Motion (VIM) of multi-column floating platforms, such as Tension Leg Platform (TLP) and semi-submersible (SEMI), in current is well-acknowledged. Substantial VIM response of the multi-column floating platform may cause fatigue failure of mooring and riser systems, which can affect the normal operation of the platform.\u0000 The present paper focuses on the numerical investigation on VIM of a TLP with circular columns using Computational Fluid Dynamics (CFD). Sensitivity analyses (e.g., mesh size, the number of prism layers and time-step size) for the VIM responses of the TLP are conducted. The effects of the current heading and mooring stiffness on the VIM are investigated. The three degrees of freedom VIM responses (in-line, transverse and yaw responses) and corresponding amplitude spectra are computed and analyzed. Motion trajectories are plotted to understand the VIM behaviors. Regarding the effect of the current heading, the largest transverse response is examined at 15° current heading and the corresponding maximum nominal amplitude is around 0.43. The difference of the maximum nominal amplitudes between the cases at 0° and 15° current headings is less than 5%. For 15°, 30° and 45° current headings, the nominal transverse amplitudes decrease as the current heading increases in the lock-in range. For the four studied current headings, the maximum width of the lock-in range is found at 0° current heading and narrows as the current incidence increases. The largest yaw response is observed at 0° current heading and the maximum nominal amplitude is around 9.1°. Regarding the effect of the mooring stiffness, the lock-in ranges and the maximum nominal amplitudes of the transverse motions have little difference for the four mooring stiffnesses. The maximum nominal transverse and yaw responses are around 0.25 and 5.1°, respectively, which occur when the mooring stiffness reaches the maximum. The flow pattern analyses indicate that the flow interference between the upstream and downstream columns may have significant effects on the VIM responses and a stronger interference at the present spacing ratio may lead to a larger VIM response. The contours of the vertical vorticity in the horizontal plane show that the mean positions of the flow separation points are always on highest or lowest (in the transverse direction perpendicular to the current heading) points of the columns, which is the reason that the VIM trajectories for the TLP with circular columns are always along the direction perpendicular to the current heading.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80165896","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
E. Auburtin, Jang-Whan Kim, Hyunchul Jang, L. Lai, J. McConochie, Y. Drobyshevski, E. Van Haaften
The Prelude Floating Liquefied Natural Gas (FLNG) facility is moored with an internal turret allowing it to perform offloading operations of liquefied natural and petroleum gas products. It does so in either a Free Weathervaning (FW) mode, i.e. by allowing the unit to rotate according to environmental loads, or in a Thruster-Assisted (TA) mode, i.e. by using the stern thrusters to maintain a fixed heading deemed preferable for the entire operation, or a particular phase. An accurate estimation of the various environment effects, in terms of forces on the FLNG and LNG carrier, is critical to ensure a correct prediction of its heading or the required thruster forces, depending on the selected operating mode. The predominant loads driving the weathervaning behavior are wind and current loads. These loads have been estimated from wind tunnel tests during the engineering phase. Since the Prelude FLNG has been installed on-site, field measurements have provided an opportunity for comparison and shown some differences with the numerical predictions based on the estimated loads, prompting a need for verification of current loads by an independent method. For the Prelude FLNG application, current loads play an important role due to facility size and significant tidal currents. It has been shown in some previous studies that wind tunnel tests for a model of under-water geometry may underestimate current loads compared to those on a full-scale vessel. There is a boundary layer along the wind tunnel floor in wind tunnel tests, while the current profile is relatively uniform over the hull draft in the real ocean condition. Moreover experimental tests present some additional drawbacks: they are performed at a reduced scale (1:225), the Reynolds number is lower than full-scale even with a large wind tunnel speed, and it is difficult to model the long (150m full-scale) Water Intake Risers (WIR) extending below the hull bottom. In order to investigate these effects, state-of-the-art full-scale CFD simulations were performed for the Prelude hull and WIR. The test program included different current speeds and directions, and several sensitivity studies: Reynolds number effect between model- and full-scales, effect of current speed profile (comparing uniform and boundary layer profiles at model scale), effect of FLNG rotation in yaw, impact of unsteady current, and presence of marine growth. Extreme dimensions of Prelude FLNG and requirements for accuracy of this study called for the CFD calculations to be performed on the High Performance Computing (HPC) clusters - Stampede2 and Frontera - at the Texas Advanced Computing Center (TACC), which are both amongst the world’s largest supercomputers. This paper describes the assumptions and challenges of the CFD study and discusses the results of the main program and various sensitivities. The main conclusions and lessons learnt are also discussed.
{"title":"Current Forces on Prelude Hull and Water Intake Riser by CFD: Full Scale Model Using Two of the World’s Largest Supercomputers","authors":"E. Auburtin, Jang-Whan Kim, Hyunchul Jang, L. Lai, J. McConochie, Y. Drobyshevski, E. Van Haaften","doi":"10.1115/omae2021-62276","DOIUrl":"https://doi.org/10.1115/omae2021-62276","url":null,"abstract":"\u0000 The Prelude Floating Liquefied Natural Gas (FLNG) facility is moored with an internal turret allowing it to perform offloading operations of liquefied natural and petroleum gas products. It does so in either a Free Weathervaning (FW) mode, i.e. by allowing the unit to rotate according to environmental loads, or in a Thruster-Assisted (TA) mode, i.e. by using the stern thrusters to maintain a fixed heading deemed preferable for the entire operation, or a particular phase.\u0000 An accurate estimation of the various environment effects, in terms of forces on the FLNG and LNG carrier, is critical to ensure a correct prediction of its heading or the required thruster forces, depending on the selected operating mode. The predominant loads driving the weathervaning behavior are wind and current loads.\u0000 These loads have been estimated from wind tunnel tests during the engineering phase. Since the Prelude FLNG has been installed on-site, field measurements have provided an opportunity for comparison and shown some differences with the numerical predictions based on the estimated loads, prompting a need for verification of current loads by an independent method. For the Prelude FLNG application, current loads play an important role due to facility size and significant tidal currents.\u0000 It has been shown in some previous studies that wind tunnel tests for a model of under-water geometry may underestimate current loads compared to those on a full-scale vessel. There is a boundary layer along the wind tunnel floor in wind tunnel tests, while the current profile is relatively uniform over the hull draft in the real ocean condition.\u0000 Moreover experimental tests present some additional drawbacks: they are performed at a reduced scale (1:225), the Reynolds number is lower than full-scale even with a large wind tunnel speed, and it is difficult to model the long (150m full-scale) Water Intake Risers (WIR) extending below the hull bottom.\u0000 In order to investigate these effects, state-of-the-art full-scale CFD simulations were performed for the Prelude hull and WIR. The test program included different current speeds and directions, and several sensitivity studies: Reynolds number effect between model- and full-scales, effect of current speed profile (comparing uniform and boundary layer profiles at model scale), effect of FLNG rotation in yaw, impact of unsteady current, and presence of marine growth.\u0000 Extreme dimensions of Prelude FLNG and requirements for accuracy of this study called for the CFD calculations to be performed on the High Performance Computing (HPC) clusters - Stampede2 and Frontera - at the Texas Advanced Computing Center (TACC), which are both amongst the world’s largest supercomputers.\u0000 This paper describes the assumptions and challenges of the CFD study and discusses the results of the main program and various sensitivities. The main conclusions and lessons learnt are also discussed.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86757950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kai-tung Ma, Yongyan Wu, Simen Fodstad Stolen, Leopoldo Bello, Menno ver der Horst, Yong Luo
As renewable energy developers start venturing into deeper waters, the floating offshore wind turbines (FOWTs) are becoming the preferred solutions over fixed supporting structures. Many similarities can be identified between a FOWT and a floating oil & gas facility, such as floater concepts (spar, semi-submersible, tension leg platform, etc) and their mooring system designs. This paper focuses on the mooring designs for FOWTs by leveraging the extensive experience gained from the offshore oil & gas industry. Similarities and differences are highlighted in design criteria, mooring analysis, long-term integrity management, installation method and project execution. The established practices regarding mooring design and analysis are reviewed. Anchor radius is recommended based on water depth by referencing sample mooring designs from the oil & gas industry. Long-term mooring integrity and failure rates are summarized. Meanwhile, a few well-known issues are discussed, such as line break due to fatigue, corrosion on chain, and known issues with components such as clump weights. Regarding mooring installation, the established method for prelay and hook-up is reviewed. Finally, opportunities for cost reduction of mooring systems of FOWTs are presented related to project execution of large scale wind farms as well as potential areas of innovation, such as installation methods, use of synthetic fiber rope, and digitalization. In summary, the state-of-the-art practices from the oil & gas industry are reviewed and documented to benefit the developments of upcoming FOWT projects.
{"title":"Mooring Designs for Floating Offshore Wind Turbines Leveraging Experience From the Oil & Gas Industry","authors":"Kai-tung Ma, Yongyan Wu, Simen Fodstad Stolen, Leopoldo Bello, Menno ver der Horst, Yong Luo","doi":"10.1115/omae2021-60739","DOIUrl":"https://doi.org/10.1115/omae2021-60739","url":null,"abstract":"\u0000 As renewable energy developers start venturing into deeper waters, the floating offshore wind turbines (FOWTs) are becoming the preferred solutions over fixed supporting structures. Many similarities can be identified between a FOWT and a floating oil & gas facility, such as floater concepts (spar, semi-submersible, tension leg platform, etc) and their mooring system designs. This paper focuses on the mooring designs for FOWTs by leveraging the extensive experience gained from the offshore oil & gas industry. Similarities and differences are highlighted in design criteria, mooring analysis, long-term integrity management, installation method and project execution. The established practices regarding mooring design and analysis are reviewed. Anchor radius is recommended based on water depth by referencing sample mooring designs from the oil & gas industry. Long-term mooring integrity and failure rates are summarized. Meanwhile, a few well-known issues are discussed, such as line break due to fatigue, corrosion on chain, and known issues with components such as clump weights. Regarding mooring installation, the established method for prelay and hook-up is reviewed. Finally, opportunities for cost reduction of mooring systems of FOWTs are presented related to project execution of large scale wind farms as well as potential areas of innovation, such as installation methods, use of synthetic fiber rope, and digitalization. In summary, the state-of-the-art practices from the oil & gas industry are reviewed and documented to benefit the developments of upcoming FOWT projects.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83366811","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Flavio Jaime Pol Gonçalves, Vinicius Cleves de Oliveira Carmo, Vinicius Toquetti de Melo, R. D. S. Cunha, I. Santos, Rodrigo A. Barreira, C. Cugnasca, Fabio Gagliardi Cozman, E. Gomi
This paper presents a computing pipeline architecture for semantic search in the domain of Offshore Engineering. The proposed system combines modules such as document retriever, passage retriever, and answer extractor to produce textual responses to queries in natural language such as: “What FPSO motion is mostly affected by viscous damping?” Such responses are often needed in Offshore Engineering activities, and linguistic techniques such as those based on inverted indexes with a syntactic focus tend to perform poorly. Instead, this research explores semantic techniques that take into account the meaning of words in the domain of Offshore Engineering. This paper describes a Linguistic QA pipeline architecture built that provides a way to retrieve answers instantly from a collection of 13,000 unstructured technical documents about Offshore Engineering, reports the achieved results and future work. This paper also presents additional modules under construction that exploit Neural Networks and ontologies approaches for semantic search in the domain of Offshore Engineering.
{"title":"Semantic Search in Offshore Engineering With Linguistics And Neural Processing Pipelines","authors":"Flavio Jaime Pol Gonçalves, Vinicius Cleves de Oliveira Carmo, Vinicius Toquetti de Melo, R. D. S. Cunha, I. Santos, Rodrigo A. Barreira, C. Cugnasca, Fabio Gagliardi Cozman, E. Gomi","doi":"10.1115/omae2021-62979","DOIUrl":"https://doi.org/10.1115/omae2021-62979","url":null,"abstract":"\u0000 This paper presents a computing pipeline architecture for semantic search in the domain of Offshore Engineering. The proposed system combines modules such as document retriever, passage retriever, and answer extractor to produce textual responses to queries in natural language such as: “What FPSO motion is mostly affected by viscous damping?” Such responses are often needed in Offshore Engineering activities, and linguistic techniques such as those based on inverted indexes with a syntactic focus tend to perform poorly. Instead, this research explores semantic techniques that take into account the meaning of words in the domain of Offshore Engineering. This paper describes a Linguistic QA pipeline architecture built that provides a way to retrieve answers instantly from a collection of 13,000 unstructured technical documents about Offshore Engineering, reports the achieved results and future work. This paper also presents additional modules under construction that exploit Neural Networks and ontologies approaches for semantic search in the domain of Offshore Engineering.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90856177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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