The internal solitary waves, have properties of two-way shear profile, significant velocity and acceleration, etc., which threaten the safety of deepwater floating systems in South China Sea (SCS), for the frequent occurrence and the high intensity of internal solitary waves in SCS. In recent years, offshore oil companies of China encountered many strong internal waves during its deepwater oil and gas exploration and development activities in South China Sea. However, the action mechanism of ISWs to floating structures is not understood clearly, and the internal solitary waves are classified as ocean current in API RP 2SK (3rd edition), therefore engineers ignore the velocity variance and long period “wave” characteristics in the design of floating structures. Furthermore, the offshore floating structures is oscillating under the action of environmental forces, due to the horizontal velocity of the platform is comparative to that of ISWs, thus fluid-body coupling is significant that one cannot analyse it by simply adding a specified ISW force time history to the floater. This paper proposes a new iterative updating method for ISW loading calculation considering the fluid-body coupling, and applied this method to a semi MODU, numerical study shows the iteration is efficient and the result is more reasonable compared to conventional method, and it is found that the maximal offset decreases significantly.
南海内孤立波具有双向剪切剖面、显著的速度和加速度等特性，由于南海内孤立波的频繁发生和强度大，威胁着南海深水浮式系统的安全。近年来，中国海上石油公司在南海深水油气勘探开发活动中，多次遭遇强烈内浪。然而，isw对浮式结构的作用机理尚不清楚，且API RP 2SK(第3版)将内孤立波归类为海流，因此工程师在浮式结构的设计中忽略了速度变化和长周期“波”特性。此外，由于平台的水平速度与ISW的水平速度相当，因此海上浮式结构在环境力的作用下会发生振荡，因此流体-体耦合非常重要，不能简单地通过在浮子上添加指定的ISW力时程来分析。本文提出了一种考虑流-体耦合的ISW载荷计算迭代更新新方法，并将该方法应用于半MODU，数值研究表明，该方法迭代效率高，计算结果比传统方法更合理，最大偏移量明显减小。
{"title":"An Iterative Updating Method for Dynamic Responses of a Floating Platform Under Action of Internal Solitary Waves","authors":"Wang Junrong, Du Junfeng, Zhang Min, Chang Anteng","doi":"10.1115/omae2019-96553","DOIUrl":"https://doi.org/10.1115/omae2019-96553","url":null,"abstract":"\u0000 The internal solitary waves, have properties of two-way shear profile, significant velocity and acceleration, etc., which threaten the safety of deepwater floating systems in South China Sea (SCS), for the frequent occurrence and the high intensity of internal solitary waves in SCS. In recent years, offshore oil companies of China encountered many strong internal waves during its deepwater oil and gas exploration and development activities in South China Sea. However, the action mechanism of ISWs to floating structures is not understood clearly, and the internal solitary waves are classified as ocean current in API RP 2SK (3rd edition), therefore engineers ignore the velocity variance and long period “wave” characteristics in the design of floating structures. Furthermore, the offshore floating structures is oscillating under the action of environmental forces, due to the horizontal velocity of the platform is comparative to that of ISWs, thus fluid-body coupling is significant that one cannot analyse it by simply adding a specified ISW force time history to the floater. This paper proposes a new iterative updating method for ISW loading calculation considering the fluid-body coupling, and applied this method to a semi MODU, numerical study shows the iteration is efficient and the result is more reasonable compared to conventional method, and it is found that the maximal offset decreases significantly.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81816889","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}
This paper presents our verification work on CFD modeling practice for the prediction of FPSO wind loads. The modeling practice was developed from the TESK CFD JDP [1]. In the verification, the measured data from a benchmark model test were used to check CFD simulation results. The exact physical model of the model test was used in the numerical modeling (model-of-the-model). To establish high confidence in the CFD modeling and simulations, the modeling practice was thoroughly verified, which covered the following critical elements: mesh resolution, domain size, outlet boundary condition, turbulence model, Reynolds effect, wind profile, prism layer effect on total wind forces, effects of the gap between wind tunnel floor and model bottom, blockage effect due to tunnel side walls and ceiling, and effects of geometry details (small size pipes). The verification results show that CFD can be used as an alternative tool for predicting wind loads and moments on a FPSO for engineering purposes following the modeling practice, and careful QA and QC.
{"title":"Thorough Verification and Validation of CFD Prediction of FPSO Wind Load for Confident Applications","authors":"Wei Xu, Z. Huang, Hyunjoe Kim","doi":"10.1115/omae2019-95018","DOIUrl":"https://doi.org/10.1115/omae2019-95018","url":null,"abstract":"\u0000 This paper presents our verification work on CFD modeling practice for the prediction of FPSO wind loads. The modeling practice was developed from the TESK CFD JDP [1]. In the verification, the measured data from a benchmark model test were used to check CFD simulation results. The exact physical model of the model test was used in the numerical modeling (model-of-the-model). To establish high confidence in the CFD modeling and simulations, the modeling practice was thoroughly verified, which covered the following critical elements: mesh resolution, domain size, outlet boundary condition, turbulence model, Reynolds effect, wind profile, prism layer effect on total wind forces, effects of the gap between wind tunnel floor and model bottom, blockage effect due to tunnel side walls and ceiling, and effects of geometry details (small size pipes). The verification results show that CFD can be used as an alternative tool for predicting wind loads and moments on a FPSO for engineering purposes following the modeling practice, and careful QA and QC.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85081093","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}
Plunging breakers, unlike non-breaking waves, impose additional slamming load on the offshore structures. This additional slamming load is considered an extreme event and is one of the most devastating forces that an offshore structure could encounter during its operational lifecycle. Whilst there are design guidelines for offshore structures pertaining to breaking waves, however it is limited to only cylindrical shape. The amount of slamming load contribution by the plunging jet is also dependent on the cross section geometries of the offshore structures. Different geometries would give rise to different air entrainment phenomenon during wave breaking and therefore affecting the slamming load contributions. In this research, JONSWAP spectrum was used to create plunging breakers via the focusing method at Newcastle University’s Wind Wave and Current tank. The crux of this research is to investigate the wave-breaking impact load on cylindrical structures with different cross section geometries commonly used in the offshore industry.
{"title":"Slamming Force Contribution due to Plunging Breakers on Circular, Square and Diamond Cylinders","authors":"Xin Wang, A. Dev, L. Tao, D. Chia, Yali Zhang","doi":"10.1115/omae2019-95126","DOIUrl":"https://doi.org/10.1115/omae2019-95126","url":null,"abstract":"\u0000 Plunging breakers, unlike non-breaking waves, impose additional slamming load on the offshore structures. This additional slamming load is considered an extreme event and is one of the most devastating forces that an offshore structure could encounter during its operational lifecycle.\u0000 Whilst there are design guidelines for offshore structures pertaining to breaking waves, however it is limited to only cylindrical shape. The amount of slamming load contribution by the plunging jet is also dependent on the cross section geometries of the offshore structures. Different geometries would give rise to different air entrainment phenomenon during wave breaking and therefore affecting the slamming load contributions.\u0000 In this research, JONSWAP spectrum was used to create plunging breakers via the focusing method at Newcastle University’s Wind Wave and Current tank. The crux of this research is to investigate the wave-breaking impact load on cylindrical structures with different cross section geometries commonly used in the offshore industry.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88828524","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}
D. Qiao, Wei Tang, Yunfei Suo, Jun Yan, Li Yugang, Zhou Daocheng
The large amplitude motion of floating structures could cause slack-taut transformation in the taut mooring system, which may result in snap load. The dynamic finite element analysis model is established to simulate the slack-taut process through adding a series of sinusoidal excitation with different amplitudes and frequencies to the upper end of a taut mooring line. During the slack-taut process, the minimum dynamic tension could be close to zero, and the maximum dynamic tension could come up to several times of pretension. The change laws of dynamic tension during the slack-taut process are compared and summarized. The calculation results show that the phenomenon of slack-taut could occur when the amplitude and frequency of excitation reach some certain value. The mooring line tension spectra show that the doubling and higher frequency components appear in addition to the frequency of excitation. The results could provide a reference for further investigating on the mechanism of snap load and the design of mooring system.
{"title":"Snap Load Induced by Slack-Taut Process in a Taut Mooring Line","authors":"D. Qiao, Wei Tang, Yunfei Suo, Jun Yan, Li Yugang, Zhou Daocheng","doi":"10.1115/omae2019-95016","DOIUrl":"https://doi.org/10.1115/omae2019-95016","url":null,"abstract":"\u0000 The large amplitude motion of floating structures could cause slack-taut transformation in the taut mooring system, which may result in snap load. The dynamic finite element analysis model is established to simulate the slack-taut process through adding a series of sinusoidal excitation with different amplitudes and frequencies to the upper end of a taut mooring line. During the slack-taut process, the minimum dynamic tension could be close to zero, and the maximum dynamic tension could come up to several times of pretension. The change laws of dynamic tension during the slack-taut process are compared and summarized. The calculation results show that the phenomenon of slack-taut could occur when the amplitude and frequency of excitation reach some certain value. The mooring line tension spectra show that the doubling and higher frequency components appear in addition to the frequency of excitation. The results could provide a reference for further investigating on the mechanism of snap load and the design of mooring system.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75176181","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 jack-up rig has to be designed for extreme storm conditions in its elevated mode during operations. Guidelines of ISO 19905-1 and SNAME TR-5-5A for site specific assessment of jack-up rigs explain in detail such analysis and assessment requirements. The stability of the foundation is extremely important for a jack-up rig during its operations when it may have to withstand harsh environments. The legs of the jack-up are preloaded to achieve the maximum expected vertical loading and penetration in the soil during the entire duration of operation at that location. This preloading is done to prevent any unusual settlements to a spudcan in the event that it exceeds the bearing capacity of the soil during operations, particularly in extreme environments. During installation of a jack-up rig, the hull is normally raised few feet above the waterline and the preload is applied by pumping in water to the preload tanks and the legs are allowed to penetrate. The reason this is normally done with the hull only a few feet above the waterline is that, if required, the hull buoyancy may be able to counter excessive uneven penetration of the different legs and tilting of the hull. The preloading process may be repeated until the required penetration is achieved. As the leg penetrates, possibility exists that differential penetration occurs among the legs and the rig settles in with some inclination. This differential penetration can cause additional penetration and inclination of the hull due to shift in the center of gravity and may lead to rapid penetration of a leg, until the hull reaches the water. This rapid penetration is called “punch-through”. This can happen due to various causes of the soil strata such as a weak layer of soil, most likely clay, underlying a strong layer, possibly sand. There may be other scenarios of soil strata that can cause punch-through. These geotechnical considerations are not discussed in the present paper. Punch-through may lead to overstressing of legs (chords and diagonals) or the overloading of the jacking units. The present paper describes the structural analysis that can predict the maximum allowable hull inclination angle or the depth of penetration of a leg during a punch-through event. The unit considered is a cantilever type Self-Elevating jack-up drilling rig. The rig unit is modeled with the hull, jack house and three independent truss legs. The nonlinear analysis is performed by incrementing the gravity load and assuming only one leg penetrates further, while the other two legs do not penetrate. Several cases are studied as described below. Preload Condition with a small air gap for three water depths for the following cases: • Preload condition without any buoyancy effect on the hull and with no Rack Contact (R.C) reversal • Preload condition with buoyancy springs for a selected water depth but without Rack Contact (R.C) reversal • Preload condition with buoyancy springs and considering Rack Contact (R.C)
{"title":"Punch-Through Structural Analysis of Jack-Up Rigs During Preloading of the Foundations","authors":"P. Chakrabarti, Abhijeet Chawan","doi":"10.1115/omae2019-95537","DOIUrl":"https://doi.org/10.1115/omae2019-95537","url":null,"abstract":"\u0000 A jack-up rig has to be designed for extreme storm conditions in its elevated mode during operations. Guidelines of ISO 19905-1 and SNAME TR-5-5A for site specific assessment of jack-up rigs explain in detail such analysis and assessment requirements. The stability of the foundation is extremely important for a jack-up rig during its operations when it may have to withstand harsh environments. The legs of the jack-up are preloaded to achieve the maximum expected vertical loading and penetration in the soil during the entire duration of operation at that location. This preloading is done to prevent any unusual settlements to a spudcan in the event that it exceeds the bearing capacity of the soil during operations, particularly in extreme environments. During installation of a jack-up rig, the hull is normally raised few feet above the waterline and the preload is applied by pumping in water to the preload tanks and the legs are allowed to penetrate. The reason this is normally done with the hull only a few feet above the waterline is that, if required, the hull buoyancy may be able to counter excessive uneven penetration of the different legs and tilting of the hull. The preloading process may be repeated until the required penetration is achieved.\u0000 As the leg penetrates, possibility exists that differential penetration occurs among the legs and the rig settles in with some inclination. This differential penetration can cause additional penetration and inclination of the hull due to shift in the center of gravity and may lead to rapid penetration of a leg, until the hull reaches the water. This rapid penetration is called “punch-through”. This can happen due to various causes of the soil strata such as a weak layer of soil, most likely clay, underlying a strong layer, possibly sand. There may be other scenarios of soil strata that can cause punch-through. These geotechnical considerations are not discussed in the present paper.\u0000 Punch-through may lead to overstressing of legs (chords and diagonals) or the overloading of the jacking units.\u0000 The present paper describes the structural analysis that can predict the maximum allowable hull inclination angle or the depth of penetration of a leg during a punch-through event. The unit considered is a cantilever type Self-Elevating jack-up drilling rig. The rig unit is modeled with the hull, jack house and three independent truss legs. The nonlinear analysis is performed by incrementing the gravity load and assuming only one leg penetrates further, while the other two legs do not penetrate. Several cases are studied as described below.\u0000 Preload Condition with a small air gap for three water depths for the following cases:\u0000 • Preload condition without any buoyancy effect on the hull and with no Rack Contact (R.C) reversal\u0000 • Preload condition with buoyancy springs for a selected water depth but without Rack Contact (R.C) reversal\u0000 • Preload condition with buoyancy springs and considering Rack Contact (R.C)","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87858236","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}
Yi-zhi Guo, Longfei Xiao, Handi Wei, Li Lei, Yanfei Deng
Offshore platforms operating in harsh ocean environments often suffer from severe wave impacts which threaten the structural integrity and staffs safety. An experimental study was carried out to investigate the wave impact load and its effect on the global response of a semi-submersible. First, two typical wave impact events occurring successively in the wave test run are analyzed, including the characteristics of incident waves, relative wave elevations and the spatial distribution of the wave impact load. Subsequently, the corresponding global response of the semi-submersible under these two wave impacts are investigated in time domain. It reveals that compared with the incident wave, the relative wave elevation has a more straightforward relationship with the wave impact load. The relative wave crest height is associated with the spatial distribution of the wave impact load, while the local wave steepness matters more in the magnitude of the wave impact load. The impulsive effect of the wave impact load on the motion behaviors is not obvious. But severe wave impacts can introduce excessive horizontal accelerations and nonlinear behaviors like ringing in the acceleration response.
{"title":"Wave Impact Load and Corresponding Nonlinear Response of a Semi-Submersible","authors":"Yi-zhi Guo, Longfei Xiao, Handi Wei, Li Lei, Yanfei Deng","doi":"10.1115/omae2019-95693","DOIUrl":"https://doi.org/10.1115/omae2019-95693","url":null,"abstract":"\u0000 Offshore platforms operating in harsh ocean environments often suffer from severe wave impacts which threaten the structural integrity and staffs safety. An experimental study was carried out to investigate the wave impact load and its effect on the global response of a semi-submersible. First, two typical wave impact events occurring successively in the wave test run are analyzed, including the characteristics of incident waves, relative wave elevations and the spatial distribution of the wave impact load. Subsequently, the corresponding global response of the semi-submersible under these two wave impacts are investigated in time domain. It reveals that compared with the incident wave, the relative wave elevation has a more straightforward relationship with the wave impact load. The relative wave crest height is associated with the spatial distribution of the wave impact load, while the local wave steepness matters more in the magnitude of the wave impact load. The impulsive effect of the wave impact load on the motion behaviors is not obvious. But severe wave impacts can introduce excessive horizontal accelerations and nonlinear behaviors like ringing in the acceleration response.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82188574","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}
Shallow skirted foundations have been applied widely in ocean engineering. Under the action of external excitation, the shallow skirted foundations on soft soil undergo cyclic displacements during service state. Under the action of cyclic displacements, the foundations drive the surrounding soft soil to produce a continuous accumulation of absolute plastic shear strain, which weakens the shear strength of the soft soil around the foundations. Therefore, the bearing capacities of shallow skirted foundations reduce after the action of cyclic displacements considering soil degradation. In order to study the evolutions of bearing capacities of shallow skirted foundations after the action of multi-directional cyclic displacements considering soil degradation, the elastoplastic finite element models of shallow skirted foundations with different embedment ratio are established. Cyclic displacements are applied along different displacement loading paths, and the evolutions of soil shear strength and bearing capacities of shallow skirted foundations after the action of cyclic displacements are analyzed. The results show that the soil softening zone gradually expands from the stress concentration zone of the soft soil to the surrounds with increasing number of loading cycles. Due to the enlargement and weakening of the soil softening zone, the failure envelopes of shallow skirted foundations gradually shrink, but the shrinkage trend gradually converges with increasing number of loading cycles. The shapes of the failure envelopes are relatively less affected by the cyclic number of displacements. The size of the failure envelopes is greatly affected by the loading paths while the shape of the failure envelopes is relatively less affected.
{"title":"Bearing Capacities of Shallow Skirted Foundations After the Action of Multi-Directional Cyclic Displacements Considering Soil Degradation","authors":"Zhong Xiao, Donghai Zhang, Haixiao Liu, Ying Liu","doi":"10.1115/omae2019-96036","DOIUrl":"https://doi.org/10.1115/omae2019-96036","url":null,"abstract":"\u0000 Shallow skirted foundations have been applied widely in ocean engineering. Under the action of external excitation, the shallow skirted foundations on soft soil undergo cyclic displacements during service state. Under the action of cyclic displacements, the foundations drive the surrounding soft soil to produce a continuous accumulation of absolute plastic shear strain, which weakens the shear strength of the soft soil around the foundations. Therefore, the bearing capacities of shallow skirted foundations reduce after the action of cyclic displacements considering soil degradation. In order to study the evolutions of bearing capacities of shallow skirted foundations after the action of multi-directional cyclic displacements considering soil degradation, the elastoplastic finite element models of shallow skirted foundations with different embedment ratio are established. Cyclic displacements are applied along different displacement loading paths, and the evolutions of soil shear strength and bearing capacities of shallow skirted foundations after the action of cyclic displacements are analyzed.\u0000 The results show that the soil softening zone gradually expands from the stress concentration zone of the soft soil to the surrounds with increasing number of loading cycles. Due to the enlargement and weakening of the soil softening zone, the failure envelopes of shallow skirted foundations gradually shrink, but the shrinkage trend gradually converges with increasing number of loading cycles. The shapes of the failure envelopes are relatively less affected by the cyclic number of displacements. The size of the failure envelopes is greatly affected by the loading paths while the shape of the failure envelopes is relatively less affected.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86413246","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 floating platform in deep water East Canada is required to withstand iceberg loads and/or be disconnected and towed away in the event of very large approaching icebergs, leaving the mooring lines and risers in-place, support large topsides and in most cases, provide large quantities of oil storage in the hull. Concepts considered for deep water application in the area include ship shaped self-propelled disconnectable FPSO and disconnectable and permanently connected deep draft floaters. This paper presents the details of Concrete Spar platforms that have been configured to satisfy all the above requirements. Several variations in the functionality and configurations of the platforms were studied to understand the impact on the overall cost and risks. The case variations primarily included: • Disconnectable options for hull, mooring and risers • Non-disconnectable option able to handle the full iceberg load • With and without crude oil storage in hull • Sacrificial or non-sacrificial mooring or risers • Steel riser configurations (freely hanging catenary, SCR vs. lazy wave, SLWR) • Hull with and without riser support Buoy • Location of mooring fairleads (on Upper hull or Buoy) • Riser support configuration (Pull Tubes or Flex Joints) The iceberg loads experienced by the hull depended on the disconnection philosophy. The Concrete Spar hull is a 6-cell structure with the risers located inside the open centerwell. The paper describes several key features of the hull, mooring and riser systems for each case that are specifically designed to withstand iceberg loads and other environment loads while maintaining the characteristic low motion response for all the options considered. Additionally, the system has been designed to minimize the disconnection and reconnection time for the disconnectable cases. The platform dimensions and weights have been compared for the various options considered. The cases without oil storage in the hull have significantly smaller and lighter hull relative to similar cases with oil storage. The cases without hull disconnection option had similar hull dimensions but marginally higher concrete weight relative to the hull disconnection option. However, the cost of Buoy, required for the disconnection option, compensates for the concrete cost difference. The SCRs work for the inplace extreme environment and iceberg load cases. Depending on the hull offset required to avoid icebergs for the non-disconnection cases or the risers lowering depth for disconnection cases, SLWR may be needed. Recommendations are made for the preferred option for field development.
{"title":"Development of Harsh Environment Field With Ice Loadings Using Concrete Spar: Variability of Options","authors":"A. Sablok, E. Hovland, S. Stromme, Andrew Blundon","doi":"10.1115/omae2019-96322","DOIUrl":"https://doi.org/10.1115/omae2019-96322","url":null,"abstract":"\u0000 A floating platform in deep water East Canada is required to withstand iceberg loads and/or be disconnected and towed away in the event of very large approaching icebergs, leaving the mooring lines and risers in-place, support large topsides and in most cases, provide large quantities of oil storage in the hull. Concepts considered for deep water application in the area include ship shaped self-propelled disconnectable FPSO and disconnectable and permanently connected deep draft floaters. This paper presents the details of Concrete Spar platforms that have been configured to satisfy all the above requirements. Several variations in the functionality and configurations of the platforms were studied to understand the impact on the overall cost and risks. The case variations primarily included:\u0000 • Disconnectable options for hull, mooring and risers\u0000 • Non-disconnectable option able to handle the full iceberg load\u0000 • With and without crude oil storage in hull\u0000 • Sacrificial or non-sacrificial mooring or risers\u0000 • Steel riser configurations (freely hanging catenary, SCR vs. lazy wave, SLWR)\u0000 • Hull with and without riser support Buoy\u0000 • Location of mooring fairleads (on Upper hull or Buoy)\u0000 • Riser support configuration (Pull Tubes or Flex Joints)\u0000 The iceberg loads experienced by the hull depended on the disconnection philosophy. The Concrete Spar hull is a 6-cell structure with the risers located inside the open centerwell. The paper describes several key features of the hull, mooring and riser systems for each case that are specifically designed to withstand iceberg loads and other environment loads while maintaining the characteristic low motion response for all the options considered. Additionally, the system has been designed to minimize the disconnection and reconnection time for the disconnectable cases.\u0000 The platform dimensions and weights have been compared for the various options considered. The cases without oil storage in the hull have significantly smaller and lighter hull relative to similar cases with oil storage. The cases without hull disconnection option had similar hull dimensions but marginally higher concrete weight relative to the hull disconnection option. However, the cost of Buoy, required for the disconnection option, compensates for the concrete cost difference. The SCRs work for the inplace extreme environment and iceberg load cases. Depending on the hull offset required to avoid icebergs for the non-disconnection cases or the risers lowering depth for disconnection cases, SLWR may be needed.\u0000 Recommendations are made for the preferred option for field development.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88288696","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 this paper, we focus on the effect of the non-Gaussian distribution in the fully-nonlinear wave on offshore platform response. The motion responses of two kinds of floating platforms are investigated numerically using a conventional time domain program. The input wave is generated using two methods. In the first method, linear wave components with randomly distributed wave phases are used as input in the time domain software as it is usually done in the global performance analysis during offshore projects. In the second method, the wave components come from a nonlinear irregular wave simulation using a potential numerical wave tank (PNWT). For both cases, twenty realizations of 3-hour duration are performed and the ocean wave is described by a JONSWAP spectrum. Then the response spectra, the probability distributions and the extreme responses of the platform motions and air gaps are compared.
{"title":"Effect of Non-Gaussian Distribution of Fully-Nonlinear Waves on Offshore Platform Motion Responses","authors":"Aldric Baquet, H. Lim, Jang-Whan Kim","doi":"10.1115/omae2019-96465","DOIUrl":"https://doi.org/10.1115/omae2019-96465","url":null,"abstract":"\u0000 In this paper, we focus on the effect of the non-Gaussian distribution in the fully-nonlinear wave on offshore platform response. The motion responses of two kinds of floating platforms are investigated numerically using a conventional time domain program. The input wave is generated using two methods. In the first method, linear wave components with randomly distributed wave phases are used as input in the time domain software as it is usually done in the global performance analysis during offshore projects. In the second method, the wave components come from a nonlinear irregular wave simulation using a potential numerical wave tank (PNWT). For both cases, twenty realizations of 3-hour duration are performed and the ocean wave is described by a JONSWAP spectrum. Then the response spectra, the probability distributions and the extreme responses of the platform motions and air gaps are compared.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89498108","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}
M. Leimeister, A. Kolios, M. Collu, Philipp Thomas
The trend towards larger offshore wind turbines (WTs) implies the need for bigger support structures. These are commonly derived from existing structures through upscaling and subsequent optimization. To reduce the number of design steps, this work proposes a direct optimization approach, by which means a support structure for a larger WT is obtained through an automated optimization procedure based on a smaller existing system. Due to the suitability of floating platforms for large MW-class WTs, this study is based on the OC3 spar-buoy designed for the NREL 5 MW WT. Using a Python-Modelica framework, developed at Fraunhofer IWES, the spar-buoy geometry is adjusted through iterative optimization steps to finally support a 7.5 MW WT. The optimization procedure focuses on the global system performance in a design-relevant load case. This study shows that larger support structures, appropriate to meet the objective of the hydrodynamic system behavior, can be obtained through automated optimization of existing designs without the intermediate step of upscaling.
{"title":"Larger MW-Class Floater Designs Without Upscaling?: A Direct Optimization Approach","authors":"M. Leimeister, A. Kolios, M. Collu, Philipp Thomas","doi":"10.1115/OMAE2019-95210","DOIUrl":"https://doi.org/10.1115/OMAE2019-95210","url":null,"abstract":"\u0000 The trend towards larger offshore wind turbines (WTs) implies the need for bigger support structures. These are commonly derived from existing structures through upscaling and subsequent optimization. To reduce the number of design steps, this work proposes a direct optimization approach, by which means a support structure for a larger WT is obtained through an automated optimization procedure based on a smaller existing system. Due to the suitability of floating platforms for large MW-class WTs, this study is based on the OC3 spar-buoy designed for the NREL 5 MW WT. Using a Python-Modelica framework, developed at Fraunhofer IWES, the spar-buoy geometry is adjusted through iterative optimization steps to finally support a 7.5 MW WT. The optimization procedure focuses on the global system performance in a design-relevant load case. This study shows that larger support structures, appropriate to meet the objective of the hydrodynamic system behavior, can be obtained through automated optimization of existing designs without the intermediate step of upscaling.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76159602","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：