In recent years, there has been an increasing issue of seabed trenches developing around mooring lines attached to suction anchors in West Africa, likely related to relatively large motions of the mooring lines. These trenches are recognised by means of numerical modelling and of centrifuge testing program as significant concern to the in-place holding capacity, the integrity of the anchor and the safety of the floating facility. Conservative trench geometries and complete absence of soil and of soil resistance in front of the anchor above the padeye depth (in the loading direction) were essential assumptions due to lack of observation. Results suggested that a reduction in holding capacity of 20% to 40% for typical mooring line load angles of 30° to 45° can be expected and that the presence of the trench does not affect the portion of holding capacity developed by passive suction at the pile tip. Nevertheless, recent survey data has evidenced a wedge of soil remaining within trenches in front of suction anchors leading to a new problem-solving approach. Consequently, this paper describes a Plaxis 3D Finite Element modelling in a parametric study as a reliable tool for the assessment of the holding capacity of the suction anchors in presence of seabed trench taking into account the presence of residual soil within the trench in front of the anchor pile. Analyses were performed under 30° inclined loading (actual case of taut deep water mooring systems) with various scenarios of trench shapes, padeye depths and anchor geometries in very soft highly plastic Gulf of Guinea clays. Thus, the consideration of the residual wedge of soil in front of the anchor leads to a much less reduction in holding capacity compared to initial studies done with too pessimistic assumptions on the final trench shape. In addition, this study aims at looking at changes in the pile geometry, including the position of the attachment point, to compensate the unavoidable formation of a trench for taut moorings.
{"title":"Effect of Seabed Trenching on Holding Capacity of Suction Anchors in Deepwater Gulf of Guinea Clays: A Numerical Study","authors":"Pablo Castillo Garcia, R. Wallerand, D. H. Doan","doi":"10.1115/omae2019-96096","DOIUrl":"https://doi.org/10.1115/omae2019-96096","url":null,"abstract":"\u0000 In recent years, there has been an increasing issue of seabed trenches developing around mooring lines attached to suction anchors in West Africa, likely related to relatively large motions of the mooring lines. These trenches are recognised by means of numerical modelling and of centrifuge testing program as significant concern to the in-place holding capacity, the integrity of the anchor and the safety of the floating facility. Conservative trench geometries and complete absence of soil and of soil resistance in front of the anchor above the padeye depth (in the loading direction) were essential assumptions due to lack of observation. Results suggested that a reduction in holding capacity of 20% to 40% for typical mooring line load angles of 30° to 45° can be expected and that the presence of the trench does not affect the portion of holding capacity developed by passive suction at the pile tip. Nevertheless, recent survey data has evidenced a wedge of soil remaining within trenches in front of suction anchors leading to a new problem-solving approach. Consequently, this paper describes a Plaxis 3D Finite Element modelling in a parametric study as a reliable tool for the assessment of the holding capacity of the suction anchors in presence of seabed trench taking into account the presence of residual soil within the trench in front of the anchor pile. Analyses were performed under 30° inclined loading (actual case of taut deep water mooring systems) with various scenarios of trench shapes, padeye depths and anchor geometries in very soft highly plastic Gulf of Guinea clays. Thus, the consideration of the residual wedge of soil in front of the anchor leads to a much less reduction in holding capacity compared to initial studies done with too pessimistic assumptions on the final trench shape. In addition, this study aims at looking at changes in the pile geometry, including the position of the attachment point, to compensate the unavoidable formation of a trench for taut moorings.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88359307","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 reports on a series of centrifuge tests to investigate the feasibility and performance of a novel spudcan foundation design featuring a peripheral skirt with side openings. The ‘skirted spudcan’, designed and patented by Keppel, is particularly beneficial in layered seabeds with a clay layer overlaying sand. The purpose of the side openings is to enable the clay trapped within the spudcan skirt to flow outside the skirt, so the skirt can penetrate into the sand and develop the required fixities against combined vertical, horizontal and moment loading. The centrifuge tests considered different skirted spudcan designs, each 10 m in diameter, but with a skirt length of either 1.38 m or 2.76 m, two spudcan invert shapes and various configurations of side and top openings. The model skirted spudcans were penetrated into a soil sample featuring a clay layer 6 m thick (in prototype scale) with an average undrained shear strength of about 15 kPa, overlaying a silica sand layer with a relative density of about 40%. The skirted spudcan embedded the sand layer by more than the skirt height at the maximum penetration resistance of about 4 MPa. However, examination of the model after retrieval demonstrated that a clay layer remained inside the skirt, despite the openings on the side of the skirt. The comparison between the eight tests demonstrated that the thickness of the clay plug reduces with the strength of the soil and with the size of the openings. Large horizontal openings located at the top of the skirt were shown to generate the lowest plug thickness and the largest skirt embedment into the sand. Somehow surprisingly, the addition of top openings (in addition of side openings) does not have beneficial effects. In general, the results demonstrated the efficiency of the skirted spudcan with side openings concept. Although the clay plug inside the skirt compartment was only partially expelled, significant skirt embedment into the sand layer (and hence high fixities) could be achieved. The high compressive stresses within the residual clay plug should limit concerns about potential rocking of the spudcan when clay remains trapped within the skirt compartment.
{"title":"Centrifuge Modelling of a Novel Skirted Spudcan for Penetration in Layered Soil","authors":"C. O’Loughlin, C. Gaudin, M. Quah, M. Perry","doi":"10.1115/omae2019-96541","DOIUrl":"https://doi.org/10.1115/omae2019-96541","url":null,"abstract":"\u0000 This paper reports on a series of centrifuge tests to investigate the feasibility and performance of a novel spudcan foundation design featuring a peripheral skirt with side openings. The ‘skirted spudcan’, designed and patented by Keppel, is particularly beneficial in layered seabeds with a clay layer overlaying sand. The purpose of the side openings is to enable the clay trapped within the spudcan skirt to flow outside the skirt, so the skirt can penetrate into the sand and develop the required fixities against combined vertical, horizontal and moment loading. The centrifuge tests considered different skirted spudcan designs, each 10 m in diameter, but with a skirt length of either 1.38 m or 2.76 m, two spudcan invert shapes and various configurations of side and top openings. The model skirted spudcans were penetrated into a soil sample featuring a clay layer 6 m thick (in prototype scale) with an average undrained shear strength of about 15 kPa, overlaying a silica sand layer with a relative density of about 40%. The skirted spudcan embedded the sand layer by more than the skirt height at the maximum penetration resistance of about 4 MPa. However, examination of the model after retrieval demonstrated that a clay layer remained inside the skirt, despite the openings on the side of the skirt. The comparison between the eight tests demonstrated that the thickness of the clay plug reduces with the strength of the soil and with the size of the openings. Large horizontal openings located at the top of the skirt were shown to generate the lowest plug thickness and the largest skirt embedment into the sand. Somehow surprisingly, the addition of top openings (in addition of side openings) does not have beneficial effects. In general, the results demonstrated the efficiency of the skirted spudcan with side openings concept. Although the clay plug inside the skirt compartment was only partially expelled, significant skirt embedment into the sand layer (and hence high fixities) could be achieved. The high compressive stresses within the residual clay plug should limit concerns about potential rocking of the spudcan when clay remains trapped within the skirt compartment.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85492433","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}
Large soil deformation can be induced during spudcan penetration into stratum near an existing piled foundation of a fixed offshore platform, and some research has been done on the effects of spudcan penetration on the lateral response of an adjacent pile. However, available centrifuge model tests found that the maximum vertical soil displacements are manifested in the same magnitude compared with those in the lateral direction, leading to large negative friction along the pile shaft. Also, the combined loading effects of transmitted loads from the upper structure should be taken into account in axial analysis during spudcan penetration, which has been proved important in prediction of axial pile response due to soil movement. This paper investigates a method to quantitatively evaluate the effect of spudcan penetration on vertical response of an adjacent pile. The vertical soil displacement is found by first simulating a free field spudcan penetration by Coupled Eulerian-Lagrange (CEL) method. The flow field is then analyzed to calculate the displacement components at specific pile location. Then the predicted vertical soil displacement profile is input into the nonlinear foundation pile model to determine the axial response of an adjacent pile subjected to spudcan penetration-induced axial and pile head loads. The proposed method is adopted to analyze centrifuge model tests in sand and clay, and predicted results prove to be basically in agreement with measured ones.
{"title":"Method Evaluating Axial Response of Vertically-Loaded Piles During Spudcan Penetration","authors":"Yifei Fan, Jianhua Wang","doi":"10.1115/omae2019-95422","DOIUrl":"https://doi.org/10.1115/omae2019-95422","url":null,"abstract":"\u0000 Large soil deformation can be induced during spudcan penetration into stratum near an existing piled foundation of a fixed offshore platform, and some research has been done on the effects of spudcan penetration on the lateral response of an adjacent pile. However, available centrifuge model tests found that the maximum vertical soil displacements are manifested in the same magnitude compared with those in the lateral direction, leading to large negative friction along the pile shaft. Also, the combined loading effects of transmitted loads from the upper structure should be taken into account in axial analysis during spudcan penetration, which has been proved important in prediction of axial pile response due to soil movement. This paper investigates a method to quantitatively evaluate the effect of spudcan penetration on vertical response of an adjacent pile. The vertical soil displacement is found by first simulating a free field spudcan penetration by Coupled Eulerian-Lagrange (CEL) method. The flow field is then analyzed to calculate the displacement components at specific pile location. Then the predicted vertical soil displacement profile is input into the nonlinear foundation pile model to determine the axial response of an adjacent pile subjected to spudcan penetration-induced axial and pile head loads. The proposed method is adopted to analyze centrifuge model tests in sand and clay, and predicted results prove to be basically in agreement with measured ones.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85616085","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}
There are currently 365 FPSOs in service around the world. These vessels all use mooring lines to maintain position and provide stability, keeping the vessel and cargo safe. However, more than 21 failures have occurred between 2001 and 2011 and approximately 50% of the reported failures occurred in the first 3 years of 20-year design life. Each mooring line failure represents the potential for serious environmental and economic consequences. Based on industry surveys, the most common failure mode is fatigue failure. In the current offshore standards, the surface degradation due to wear and corrosion is modelled as a diameter loss at a standards rate. To assess whether the uniform reduction in chain diameter suggested in the offshore standards is able to explain the early chain failures seen in service, this paper incorporates two wear rates into a fatigue life calculation; one wear rate is taken from DNV-OS-E301 and is compared against one taken from NORSOK M-001. Three fatigue life estimation approaches: tension, nominal stress and hotspot, are used to compare the differences in fatigue method. The stress in the chain is calculated using an analytical model, which is verified against an FE model. The effect of wear degradation on the ultimate strength of the chain is calculated based on the minimum breaking load. The results show that the diameter loss rates suggested in the offshore standards are not able to explain the early mooring chain failures seen in the past and that the reduction of diameter cannot solely explain the early failures seen in service. The hotspot approach, not often used in mooring line predictions, is best able to predict these shorter lives, as it offers more accurate fatigue predictions by considering high peak stresses compared to standard methods such as tension and nominal stress approaches.
{"title":"Fatigue Approaches for Mooring Chains Subjected to Wear Degradation","authors":"G. Gemilang, P. Reed, A. Sobey","doi":"10.1115/omae2019-96386","DOIUrl":"https://doi.org/10.1115/omae2019-96386","url":null,"abstract":"\u0000 There are currently 365 FPSOs in service around the world. These vessels all use mooring lines to maintain position and provide stability, keeping the vessel and cargo safe. However, more than 21 failures have occurred between 2001 and 2011 and approximately 50% of the reported failures occurred in the first 3 years of 20-year design life. Each mooring line failure represents the potential for serious environmental and economic consequences. Based on industry surveys, the most common failure mode is fatigue failure. In the current offshore standards, the surface degradation due to wear and corrosion is modelled as a diameter loss at a standards rate. To assess whether the uniform reduction in chain diameter suggested in the offshore standards is able to explain the early chain failures seen in service, this paper incorporates two wear rates into a fatigue life calculation; one wear rate is taken from DNV-OS-E301 and is compared against one taken from NORSOK M-001. Three fatigue life estimation approaches: tension, nominal stress and hotspot, are used to compare the differences in fatigue method. The stress in the chain is calculated using an analytical model, which is verified against an FE model. The effect of wear degradation on the ultimate strength of the chain is calculated based on the minimum breaking load. The results show that the diameter loss rates suggested in the offshore standards are not able to explain the early mooring chain failures seen in the past and that the reduction of diameter cannot solely explain the early failures seen in service. The hotspot approach, not often used in mooring line predictions, is best able to predict these shorter lives, as it offers more accurate fatigue predictions by considering high peak stresses compared to standard methods such as tension and nominal stress approaches.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89822269","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}
Srikanth V Srigiriraju, A. Chakraborty, B. Ozturk, Devvrat Rathore
The objective of this study is to explore the opportunity to improve the design and sizing of mudmat for subsea structures, such as Pipeline End Termination (PLET). This is done by comparing the traditional approach following the limit equilibrium methods in API RP 2GEO with a more rigorous simplified integrated analysis approach that involves a single finite element analysis (FEA) model that includes both the pipeline and jumpers together along with the soil-mudmat interaction modeled as non-linear springs, and to quantify any conservatism inherent in the traditional approach. A mudmat design with aspect ratio of 1:2 was considered for detailed analysis. Initially, jumper and pipeline loads were determined by imposing artificial boundary conditions at the hubs and end terminals. Using analytical methods and considering a total dead (submerged) weight of the mudmat and superstructure, a mudmat size was determined per the American Petroleum Institute (API) approach. Factor of Safety (FOS) for bearing and sliding loads were also determined. Thereon, using this mudmat size, the FOS for bearing and sliding were determined using the simplified integrated approach with nonlinear springs representing soil-mudmat interactions. The FOS values using the simplified approach were observed to be higher than those obtained using the traditional approach. This provides an opportunity for a “leaner” design, especially as new high pressure, high temperature (HPHT) fields are made feasible where the mudmat size, if designed with conservatism in API RP 2GEO, may be impractically large for installation.
本研究的目的是探索改进水下结构泥板的设计和尺寸的机会，例如管道末端终端(PLET)。这是通过比较API RP 2GEO中遵循极限平衡方法的传统方法与更严格的简化集成分析方法来完成的，该方法涉及单个有限元分析(FEA)模型，该模型包括管道和跳线以及将土壤-泥层相互作用建模为非线性弹簧，并量化传统方法中固有的保守性。考虑长径比为1:2的泥板设计进行详细分析。最初，跳线和管道载荷是通过在枢纽和终端施加人工边界条件来确定的。根据美国石油协会(API)的方法，采用分析方法并考虑泥层和上部结构的总沉水(水下)重量，确定泥层尺寸。同时确定了承载和滑动载荷的安全系数。在此基础上，利用该泥层尺寸，采用非线性弹簧表示土-泥层相互作用的简化集成方法确定了承载和滑动FOS。采用简化方法得到的FOS值高于传统方法得到的FOS值。这为“精简”设计提供了机会，特别是当新的高压高温(HPHT)油田变得可行时，如果按照API RP 2GEO的保守设计，泥层尺寸可能不太适合安装。
{"title":"FEA Based Simplified Integrated Analysis for Mudmat Design","authors":"Srikanth V Srigiriraju, A. Chakraborty, B. Ozturk, Devvrat Rathore","doi":"10.1115/omae2019-96754","DOIUrl":"https://doi.org/10.1115/omae2019-96754","url":null,"abstract":"\u0000 The objective of this study is to explore the opportunity to improve the design and sizing of mudmat for subsea structures, such as Pipeline End Termination (PLET). This is done by comparing the traditional approach following the limit equilibrium methods in API RP 2GEO with a more rigorous simplified integrated analysis approach that involves a single finite element analysis (FEA) model that includes both the pipeline and jumpers together along with the soil-mudmat interaction modeled as non-linear springs, and to quantify any conservatism inherent in the traditional approach.\u0000 A mudmat design with aspect ratio of 1:2 was considered for detailed analysis. Initially, jumper and pipeline loads were determined by imposing artificial boundary conditions at the hubs and end terminals. Using analytical methods and considering a total dead (submerged) weight of the mudmat and superstructure, a mudmat size was determined per the American Petroleum Institute (API) approach. Factor of Safety (FOS) for bearing and sliding loads were also determined. Thereon, using this mudmat size, the FOS for bearing and sliding were determined using the simplified integrated approach with nonlinear springs representing soil-mudmat interactions.\u0000 The FOS values using the simplified approach were observed to be higher than those obtained using the traditional approach. This provides an opportunity for a “leaner” design, especially as new high pressure, high temperature (HPHT) fields are made feasible where the mudmat size, if designed with conservatism in API RP 2GEO, may be impractically large for installation.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80744740","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}
Sixteen loss of position incidents on fourteen units are reported to us from the petroleum activity on the Norwegian continental shelf, from 2014 to 2018. The incidents had a mixture of severity, with pollution of 360m3 mud, damage to drilling and production equipment, falling objects and three autolifts of bridges as the most severe consequences. The incidents are described briefly and the most common causes of the events are found. The cases are discussed in view of several approaches. The barrier concept, and modifications of previous established barrier functions and barrier elements are discussed. I discuss the man-technology-organisation examinations in the investigations. Further the application of the single failure analysis philosophy is reviewed, and I discuss limitations to the method based on our cases. Our cases are compared with previous learning from incidents on shuttle tankers. A discussion is done on the slow reactions to changes in the weather conditions. In the last section I discuss needs for improvement.
{"title":"Learning From Dynamic Positioning Events","authors":"A. Kvitrud","doi":"10.1115/omae2019-96710","DOIUrl":"https://doi.org/10.1115/omae2019-96710","url":null,"abstract":"\u0000 Sixteen loss of position incidents on fourteen units are reported to us from the petroleum activity on the Norwegian continental shelf, from 2014 to 2018. The incidents had a mixture of severity, with pollution of 360m3 mud, damage to drilling and production equipment, falling objects and three autolifts of bridges as the most severe consequences. The incidents are described briefly and the most common causes of the events are found. The cases are discussed in view of several approaches. The barrier concept, and modifications of previous established barrier functions and barrier elements are discussed. I discuss the man-technology-organisation examinations in the investigations. Further the application of the single failure analysis philosophy is reviewed, and I discuss limitations to the method based on our cases. Our cases are compared with previous learning from incidents on shuttle tankers. A discussion is done on the slow reactions to changes in the weather conditions. In the last section I discuss needs for improvement.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85488331","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}
Accurate prediction for the liquefaction depth of a porous seabed is crucial to the design of shallow foundations; nevertheless most previous studies are predominantly limited to wave-only conditions. In this study, the combined wave-current induced instantaneous liquefaction of a sandy seabed is investigated analytically. The explicit expression of liquefaction depth under combined wave-current loading condition is derived, which can converge to that under the linear wave condition when the current velocity approaches zero. Parametric study indicates that the effects of imposing a current onto progressive waves on the distribution of excess pore pressures and the corresponding liquefaction depth are unneglectable, especially for the opposite current conditions.
{"title":"Combined Wave-Current Induced Instantaneous Liquefaction of a Sandy Seabed","authors":"Li-Jing Yang, Chang-Fei Li, Jun-qin Wang, F. Gao","doi":"10.1115/omae2019-96655","DOIUrl":"https://doi.org/10.1115/omae2019-96655","url":null,"abstract":"\u0000 Accurate prediction for the liquefaction depth of a porous seabed is crucial to the design of shallow foundations; nevertheless most previous studies are predominantly limited to wave-only conditions. In this study, the combined wave-current induced instantaneous liquefaction of a sandy seabed is investigated analytically. The explicit expression of liquefaction depth under combined wave-current loading condition is derived, which can converge to that under the linear wave condition when the current velocity approaches zero. Parametric study indicates that the effects of imposing a current onto progressive waves on the distribution of excess pore pressures and the corresponding liquefaction depth are unneglectable, especially for the opposite current conditions.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83159050","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, Thiago Miliante, E. V. Haaften, Finlay McPhail
Prelude floating liquefied natural gas (FLNG) facility reached a significant milestone in June 2018 when gas was introduced onboard for the first time as part of the facility startup process, loaded from an LNG Carrier (LNGC) moored in side-by-side (SBS) configuration. This first offshore LNG SBS operation allowed Prelude’s utilities to switch from running on diesel to running on gas. SBS mooring is the base case configuration for offloading both LNG and Liquefied Petroleum Gas (LPG) into product carriers using Marine Loading Arms (MLA) once the Prelude FLNG facility is fully operational. These complex and weather sensitive operations are expected to take place on a weekly basis. This means critical decisions about weather-window and timing should be supported as much as possible by predictive analysis and modelling of forecast environment to reduce the risks. There are multiple criteria for evaluating the operability of LNGC or LPGC SBS offloading. These criteria cover the various phases of an operation, such as personnel transfer to the visiting carrier, Terminal Team Leader (TTL) transfer, spool fitting and fender lowering, approach and mooring, connection and testing of the loading arms, ramp-up of product transfer, full rate cargo transfer, loading arm purging and recovery, de-berthing, and people and hardware recovery. The criteria have been tailored to be appropriate to the phase of the operation. They comprise both environment-based criteria (maximum acceptable wind and waves conditions), and criteria related to motion or mooring (carrier roll, MLA envelope, mooring line tension, fender deflection). Motion and mooring criteria are evaluated through dynamic time-domain simulations. This allows an accurate modelling of non-linear effects, including mooring characteristics and partially filled cargo tanks. Thrusters can be used to control Prelude FLNG facility position if needed. The required thruster force to maintain the selected heading is calculated with frequency-domain calculation for all possible headings. This paper presents a visual reporting tool, developed by TechnipFMC in partnership with Shell. This tool has been used to support operational decisions during commissioning and startup, for SBS LNG and LPG import to Prelude FLNG facility. The daily reports used weather forecasts, in combination with numerical simulations, to predict the maximum motion and mooring criteria which contribute to determine both the timing and the decision to proceed with the operation. The format of the report has been designed to be user friendly for offshore operational staff, summarizing efficiently and in a visual manner the usage factors for each criterion separately. An overall operability is also presented for a quick overview. This paper also presents the details of numerical simulations, summarizes the different studies carried out to ensure the reliability of these simulations and discusses the possibilities for future development.
{"title":"Support of Operational Decisions for Prelude’s Side-by-Side LNG Offloading","authors":"E. Auburtin, Thiago Miliante, E. V. Haaften, Finlay McPhail","doi":"10.1115/omae2019-96090","DOIUrl":"https://doi.org/10.1115/omae2019-96090","url":null,"abstract":"\u0000 Prelude floating liquefied natural gas (FLNG) facility reached a significant milestone in June 2018 when gas was introduced onboard for the first time as part of the facility startup process, loaded from an LNG Carrier (LNGC) moored in side-by-side (SBS) configuration. This first offshore LNG SBS operation allowed Prelude’s utilities to switch from running on diesel to running on gas.\u0000 SBS mooring is the base case configuration for offloading both LNG and Liquefied Petroleum Gas (LPG) into product carriers using Marine Loading Arms (MLA) once the Prelude FLNG facility is fully operational. These complex and weather sensitive operations are expected to take place on a weekly basis. This means critical decisions about weather-window and timing should be supported as much as possible by predictive analysis and modelling of forecast environment to reduce the risks.\u0000 There are multiple criteria for evaluating the operability of LNGC or LPGC SBS offloading. These criteria cover the various phases of an operation, such as personnel transfer to the visiting carrier, Terminal Team Leader (TTL) transfer, spool fitting and fender lowering, approach and mooring, connection and testing of the loading arms, ramp-up of product transfer, full rate cargo transfer, loading arm purging and recovery, de-berthing, and people and hardware recovery. The criteria have been tailored to be appropriate to the phase of the operation. They comprise both environment-based criteria (maximum acceptable wind and waves conditions), and criteria related to motion or mooring (carrier roll, MLA envelope, mooring line tension, fender deflection). Motion and mooring criteria are evaluated through dynamic time-domain simulations. This allows an accurate modelling of non-linear effects, including mooring characteristics and partially filled cargo tanks. Thrusters can be used to control Prelude FLNG facility position if needed. The required thruster force to maintain the selected heading is calculated with frequency-domain calculation for all possible headings.\u0000 This paper presents a visual reporting tool, developed by TechnipFMC in partnership with Shell. This tool has been used to support operational decisions during commissioning and startup, for SBS LNG and LPG import to Prelude FLNG facility. The daily reports used weather forecasts, in combination with numerical simulations, to predict the maximum motion and mooring criteria which contribute to determine both the timing and the decision to proceed with the operation. The format of the report has been designed to be user friendly for offshore operational staff, summarizing efficiently and in a visual manner the usage factors for each criterion separately. An overall operability is also presented for a quick overview. This paper also presents the details of numerical simulations, summarizes the different studies carried out to ensure the reliability of these simulations and discusses the possibilities for future development.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81684950","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}
Nanhai Shengli (NHSL) FPSO, which is serviced in the South China Sea, was dry-docking to upgrade its internal turret mooring system in the first half of 2018, and the mooring system was re-hooked up to the FPSO subsequently in July. The whole installation of the mooring system will last for more than a month. Based on the metocean data of the South China Sea and operation experience, the mooring system installation may encounter typhoon conditions. The NHSL mooring system consists a 10-legs catenary system. The installation sequence of anchor legs may affect the performance of the mooring system under different intensity typhoon conditions. Steps in the design process of anchor leg installation sequence are described in this paper. Based on the tension and offset derived from the time domain mooring analysis, an optimized installation sequence is obtained in order that the mooring system has a better ability to withstand typhoon conditions.
{"title":"Study on Anchor Leg Installation Sequence of Nanhai Shengli FPSO Under Typhoon Season","authors":"Hui Shen, Huoping Wang, Weiquan Zhu, Deyang Wang","doi":"10.1115/omae2019-96650","DOIUrl":"https://doi.org/10.1115/omae2019-96650","url":null,"abstract":"\u0000 Nanhai Shengli (NHSL) FPSO, which is serviced in the South China Sea, was dry-docking to upgrade its internal turret mooring system in the first half of 2018, and the mooring system was re-hooked up to the FPSO subsequently in July. The whole installation of the mooring system will last for more than a month. Based on the metocean data of the South China Sea and operation experience, the mooring system installation may encounter typhoon conditions. The NHSL mooring system consists a 10-legs catenary system. The installation sequence of anchor legs may affect the performance of the mooring system under different intensity typhoon conditions. Steps in the design process of anchor leg installation sequence are described in this paper. Based on the tension and offset derived from the time domain mooring analysis, an optimized installation sequence is obtained in order that the mooring system has a better ability to withstand typhoon conditions.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88257263","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}
J. Sterenborg, N. Grasso, Rogier Schouten, A. Tjallema
One of the aims of The Ocean Cleanup is to develop technologies to extract plastic pollution from the world’s oceans. Several concepts of passive floating systems were considered that are supposed to confine plastics to ease their collection. Such concepts consist of a floating member and a submerged flexible skirt and have in common that their span is generally more than 500 meters. Consequently, fluid-structure interaction plays an important role in the response of such a floating system. To support numerical simulations, MARIN carried out extensive model tests on a 120 meter system section of the final concept, with focus on the fluid-structure interaction (FSI) of the submerged skirt in operating conditions and in towing configuration. The ability to capture plastics was not investigated in these model tests. Novel for wave-basin tests were non-intrusive measurements using underwater Digital Image Correlation (DIC) to obtain the displacements and deformations of the flexible skirt. DIC proved to be a capable measurement technique for this type of structure in combination with a wave basin. Detailed quantitative data on skirt motions and deformations were delivered and the last concept of the cleanup system was tested in the towing configuration and operational configuration.
{"title":"The Ocean Cleanup System 001 Performance During Towing and Seakeeping Tests","authors":"J. Sterenborg, N. Grasso, Rogier Schouten, A. Tjallema","doi":"10.1115/omae2019-96207","DOIUrl":"https://doi.org/10.1115/omae2019-96207","url":null,"abstract":"\u0000 One of the aims of The Ocean Cleanup is to develop technologies to extract plastic pollution from the world’s oceans. Several concepts of passive floating systems were considered that are supposed to confine plastics to ease their collection. Such concepts consist of a floating member and a submerged flexible skirt and have in common that their span is generally more than 500 meters. Consequently, fluid-structure interaction plays an important role in the response of such a floating system. To support numerical simulations, MARIN carried out extensive model tests on a 120 meter system section of the final concept, with focus on the fluid-structure interaction (FSI) of the submerged skirt in operating conditions and in towing configuration. The ability to capture plastics was not investigated in these model tests. Novel for wave-basin tests were non-intrusive measurements using underwater Digital Image Correlation (DIC) to obtain the displacements and deformations of the flexible skirt. DIC proved to be a capable measurement technique for this type of structure in combination with a wave basin. Detailed quantitative data on skirt motions and deformations were delivered and the last concept of the cleanup system was tested in the towing configuration and operational configuration.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78880030","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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