Andi Merxhani, J. Jensen, João Caetano, Casper Klintø Christiansen
The treatment of early age cyclic loading (EAC) on pile-sleeve grouted connections is one of the challenging problems encountered in the design of offshore jacket structures. ISO 19902 appears to be the only offshore structural design code that quantifies the strength de-rating due to EAC. However, the mechanism of EAC considered in the ISO standard is little understood. Main provision is that the strength reduction due to EAC is considered to be linearly proportional to the compressive strength of the grout. This provision is conservatively applicable for medium strength grouts. However, it is over-conservative when modern high-performance grouts are used, and it can be further argued that it actually loses its physical meaning. Thus, a further investigation into the mechanics of the problem is deemed beneficial in order to understand better its underlying mechanism. Using existing experimental evidence and a simple mechanical model, it is shown that the EAC mechanism considered in ISO 19902 triggers the grout matrix failure mechanism of the grouted connections. This behavior is characteristic of segregating grout materials. The benefit of the approach followed is that it links the interpretation of EAC to the grout material properties. The phenomenon is then understood using methods and experimental results that are well established in concrete mechanics. After a comparison with existing experimental evidence on grouted connections and concrete members, it is suggested that the strength drop for the specific shearing mechanism is independent of the uniaxial compressive strength of the grout material.
{"title":"Critical Review of Early Age Cycling Effects on the Capacity of Pile to Sleeve Grouted Connections As Treated in ISO 19902","authors":"Andi Merxhani, J. Jensen, João Caetano, Casper Klintø Christiansen","doi":"10.1115/omae2019-95626","DOIUrl":"https://doi.org/10.1115/omae2019-95626","url":null,"abstract":"\u0000 The treatment of early age cyclic loading (EAC) on pile-sleeve grouted connections is one of the challenging problems encountered in the design of offshore jacket structures. ISO 19902 appears to be the only offshore structural design code that quantifies the strength de-rating due to EAC. However, the mechanism of EAC considered in the ISO standard is little understood. Main provision is that the strength reduction due to EAC is considered to be linearly proportional to the compressive strength of the grout. This provision is conservatively applicable for medium strength grouts. However, it is over-conservative when modern high-performance grouts are used, and it can be further argued that it actually loses its physical meaning. Thus, a further investigation into the mechanics of the problem is deemed beneficial in order to understand better its underlying mechanism.\u0000 Using existing experimental evidence and a simple mechanical model, it is shown that the EAC mechanism considered in ISO 19902 triggers the grout matrix failure mechanism of the grouted connections. This behavior is characteristic of segregating grout materials. The benefit of the approach followed is that it links the interpretation of EAC to the grout material properties. The phenomenon is then understood using methods and experimental results that are well established in concrete mechanics. After a comparison with existing experimental evidence on grouted connections and concrete members, it is suggested that the strength drop for the specific shearing mechanism is independent of the uniaxial compressive strength of the grout material.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89659535","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}
H. Chan, Evren Armaoğlu, M. Thomson, Alistair Garner
The extended lift operation to deliver the Wellbay module (M5) combined with the Flare Tower (M8) from the Miller Platform in the North Sea to the shore using the Semi-Submersible Crane Vessel S7000 was restricted by the clearances between M5/M8 and the vessel crane booms. A method to calculate the clearances of the M5/M8 normal to the vessel crane booms has been developed and used in a frequency-domain response analysis to define operability limits. Investigations based on a series of scale model tests in regular waves and irregular short-crested waves including motion decay tests in calm water, conducted by the Maritime Research Institute (MARIN) in the Netherlands, were also made to further evaluate the behaviour of the suspended M5/M8 on S7000’s main hooks during transit. The time series of decay motions of the suspended M5/M8 obtained from the decay motion tests and a time domain analysis are compared and used to derive rigging damping. The numerical results of the frequency-domain analysis are validated with the experimental data for response amplitude operators (RAOs) found in regular waves and pink noise waves, significant and 3 hour most probable maximum/minimum (MPM) responses of interest in irregular waves.
{"title":"Behaviour of a Suspended Wellbay Module and Flare Tower in Waves During Transit to Shore","authors":"H. Chan, Evren Armaoğlu, M. Thomson, Alistair Garner","doi":"10.1115/omae2019-95001","DOIUrl":"https://doi.org/10.1115/omae2019-95001","url":null,"abstract":"\u0000 The extended lift operation to deliver the Wellbay module (M5) combined with the Flare Tower (M8) from the Miller Platform in the North Sea to the shore using the Semi-Submersible Crane Vessel S7000 was restricted by the clearances between M5/M8 and the vessel crane booms. A method to calculate the clearances of the M5/M8 normal to the vessel crane booms has been developed and used in a frequency-domain response analysis to define operability limits. Investigations based on a series of scale model tests in regular waves and irregular short-crested waves including motion decay tests in calm water, conducted by the Maritime Research Institute (MARIN) in the Netherlands, were also made to further evaluate the behaviour of the suspended M5/M8 on S7000’s main hooks during transit. The time series of decay motions of the suspended M5/M8 obtained from the decay motion tests and a time domain analysis are compared and used to derive rigging damping. The numerical results of the frequency-domain analysis are validated with the experimental data for response amplitude operators (RAOs) found in regular waves and pink noise waves, significant and 3 hour most probable maximum/minimum (MPM) responses of interest in irregular waves.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84798533","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. B. Araujo, A. C. Fernandes, J. S. Sales, Mario Jorge C. dos Santos, Ana Clara Thurler
Oil offshore Brazil, as well as in other continents, has demanded floating units for oil production. Typical anchored production units are the semi-submersible platforms, FPSO, Spar Buoys and TLPs. All of them use several anchoring lines for station keeping. In the offshore Brazil scenario, the last twelve years the FPSOs adopts the torpedo piles and polyester ropes in the anchoring lines in deep and ultra-deep waters. The FPSO “Cidade de Angra dos Reis” was the first to operate in pre-salt area in October 2010. From then on, it became common the production units with VLCC size, oil production of 150,000 barrels per day and 24 anchoring lines. The reason for such large number of anchors is the 1,200 tonnes torpedo piles holding power restriction. The proposition developed in this paper reduces the number of anchor lines using well know offshore equipment such as: driven piles, mooring chains, polyester ropes and conventional anchoring deck equipment. The main difference is the use of driven piles with holding power above 1,800 tonnes and anchor lines with a breaking strength of more than 2,000 tonnes. It is shown that a decrease of number of anchoring lines from 24 to 12 can be achieved. Consequently, it will decrease also the space occupied by the anchoring lines in the seabed by reducing the subsea layout of risers, flow lines and well head. This allows a technical and economical scenario more feasible when compared with the currently used on the Brazilian oil & gas market.
巴西近海以及其他大陆的石油生产都需要浮式装置。典型的锚固式生产装置有半潜式平台、FPSO、Spar浮标和张力腿平台。它们都使用几条锚线来保持站位。在巴西近海，过去12年fpso在深水和超深水锚索中采用鱼雷桩和聚酯绳。2010年10月，“Cidade de Angra dos Reis”号FPSO首次在盐下区域作业。从那时起，VLCC规模的生产单元、15万桶/日的石油产量和24条锚泊线变得普遍。如此大量锚的原因是1,200吨鱼雷桩持有功率限制。本文提出的建议使用众所周知的海上设备，如:打入桩，系泊链，聚酯绳和常规锚固甲板设备，减少锚索的数量。主要的不同之处在于使用的是支撑力超过1800吨的打桩和断裂强度超过2000吨的锚索。结果表明，锚固线数可由24条减少到12条。因此，通过减少隔水管、流动管线和井口的海底布局，也将减少锚固线在海底占用的空间。与目前在巴西油气市场上使用的方案相比，这使得技术和经济方案更加可行。
{"title":"Efficient Anchoring System for FPSO in Arbitrary Waters","authors":"J. B. Araujo, A. C. Fernandes, J. S. Sales, Mario Jorge C. dos Santos, Ana Clara Thurler","doi":"10.1115/omae2019-96575","DOIUrl":"https://doi.org/10.1115/omae2019-96575","url":null,"abstract":"\u0000 Oil offshore Brazil, as well as in other continents, has demanded floating units for oil production. Typical anchored production units are the semi-submersible platforms, FPSO, Spar Buoys and TLPs. All of them use several anchoring lines for station keeping.\u0000 In the offshore Brazil scenario, the last twelve years the FPSOs adopts the torpedo piles and polyester ropes in the anchoring lines in deep and ultra-deep waters. The FPSO “Cidade de Angra dos Reis” was the first to operate in pre-salt area in October 2010. From then on, it became common the production units with VLCC size, oil production of 150,000 barrels per day and 24 anchoring lines. The reason for such large number of anchors is the 1,200 tonnes torpedo piles holding power restriction.\u0000 The proposition developed in this paper reduces the number of anchor lines using well know offshore equipment such as: driven piles, mooring chains, polyester ropes and conventional anchoring deck equipment. The main difference is the use of driven piles with holding power above 1,800 tonnes and anchor lines with a breaking strength of more than 2,000 tonnes. It is shown that a decrease of number of anchoring lines from 24 to 12 can be achieved. Consequently, it will decrease also the space occupied by the anchoring lines in the seabed by reducing the subsea layout of risers, flow lines and well head. This allows a technical and economical scenario more feasible when compared with the currently used on the Brazilian oil & gas market.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80755886","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 heuristic approach to investigate the characteristics of the numerical waves propagating in various CFD-based NWT set ups is proposed to develop an optimal grid system for a numerical wave tank. Linear dispersion relations of the waves in a Cartesian grid system are derived analytically. The analytic results lead to an optimal grid aspect ratio for the best dispersion approximation. Extensions of the analytic approach to determine an optimal set up of the grid system of CFD-based NWT are discussed. A roadmap to develop CFD modeling practices based on these heuristic approaches and further numerical verification is proposed for the on-going industry efforts to develop the guidelines for numerical wave tanks, such as the Joint Industry Project on “Reproducible CFD Modeling Practices for Offshore Applications”.
{"title":"Wave Propagation in CFD-Based Numerical Wave Tank","authors":"Jang-Whan Kim, Aldric Baquet, Hyunchul Jang","doi":"10.1115/omae2019-96460","DOIUrl":"https://doi.org/10.1115/omae2019-96460","url":null,"abstract":"\u0000 A heuristic approach to investigate the characteristics of the numerical waves propagating in various CFD-based NWT set ups is proposed to develop an optimal grid system for a numerical wave tank. Linear dispersion relations of the waves in a Cartesian grid system are derived analytically. The analytic results lead to an optimal grid aspect ratio for the best dispersion approximation. Extensions of the analytic approach to determine an optimal set up of the grid system of CFD-based NWT are discussed. A roadmap to develop CFD modeling practices based on these heuristic approaches and further numerical verification is proposed for the on-going industry efforts to develop the guidelines for numerical wave tanks, such as the Joint Industry Project on “Reproducible CFD Modeling Practices for Offshore Applications”.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72878513","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}
Charles Fernandez, A. Dev, R. Norman, W. L. Woo, S. Kumar
The Dynamic Positioning (DP) System of a vessel involves complex interactions between a large number of sub-systems. Each sub-system plays a unique role in the continuous overall DP function for safe and reliable operation of the vessel. Rating the significance or assigning weightings to the DP sub-systems in different operating conditions is a complex task that requires input from many stakeholders. The weighting assignment is a critical step in determining the reliability of the DP system during complex marine and offshore operations. Thus, an accurate weighting assignment is crucial as it, in turn, influences the decision-making of the operator concerning the DP system functionality execution. Often DP operators prefer to rely on intuition in assigning the weightings. However, it introduces an inherent uncertainty and level of inconsistency in the decision making. The systematic assignment of weightings requires a clear definition of criteria and objectives and data collection with the DP system operating continuously in different environmental conditions. The sub-systems of the overall DP system are characterized by multi-attributes resulting in a high number of comparisons thereby making weighting distribution complicated. If the weighting distribution was performed by simplifying the attributes, making the decision by excluding part of them or compromising the cognitive efforts, then this could lead to inaccurate decision making. Multi-Criteria Decision Making (MCDM) methods have evolved over several decades and have been used in various applications within the Maritime and Oil and Gas industries. DP, being a complex system, naturally lends itself to the implementation of MCDM techniques to assign weight distribution among its sub-systems. In this paper, the Analytic Hierarchy Process (AHP) methodology is used for weight assignment among the DP sub-systems. An AHP model is effective in obtaining the domain knowledge from numerous experts and representing knowledge-guided indexing. The approach involved examination of several criteria in terms of both quantitative and qualitative variables. A state-of-the-art advisory decision-making tool, Dynamic Positioning Reliability Index (DP-RI), is used to validate the results from AHP. The weighting assignments from AHP are close to the reality and verified using the tool through real-life scenarios.
{"title":"Dynamic Positioning System: Systematic Weight Assignment for DP Sub-Systems Using Multi-Criteria Evaluation Technique Analytic Hierarchy Process and Validation Using DP-RI Tool With Deep Learning Algorithm","authors":"Charles Fernandez, A. Dev, R. Norman, W. L. Woo, S. Kumar","doi":"10.1115/OMAE2019-95485","DOIUrl":"https://doi.org/10.1115/OMAE2019-95485","url":null,"abstract":"\u0000 The Dynamic Positioning (DP) System of a vessel involves complex interactions between a large number of sub-systems. Each sub-system plays a unique role in the continuous overall DP function for safe and reliable operation of the vessel. Rating the significance or assigning weightings to the DP sub-systems in different operating conditions is a complex task that requires input from many stakeholders. The weighting assignment is a critical step in determining the reliability of the DP system during complex marine and offshore operations. Thus, an accurate weighting assignment is crucial as it, in turn, influences the decision-making of the operator concerning the DP system functionality execution. Often DP operators prefer to rely on intuition in assigning the weightings. However, it introduces an inherent uncertainty and level of inconsistency in the decision making. The systematic assignment of weightings requires a clear definition of criteria and objectives and data collection with the DP system operating continuously in different environmental conditions. The sub-systems of the overall DP system are characterized by multi-attributes resulting in a high number of comparisons thereby making weighting distribution complicated. If the weighting distribution was performed by simplifying the attributes, making the decision by excluding part of them or compromising the cognitive efforts, then this could lead to inaccurate decision making.\u0000 Multi-Criteria Decision Making (MCDM) methods have evolved over several decades and have been used in various applications within the Maritime and Oil and Gas industries. DP, being a complex system, naturally lends itself to the implementation of MCDM techniques to assign weight distribution among its sub-systems. In this paper, the Analytic Hierarchy Process (AHP) methodology is used for weight assignment among the DP sub-systems. An AHP model is effective in obtaining the domain knowledge from numerous experts and representing knowledge-guided indexing. The approach involved examination of several criteria in terms of both quantitative and qualitative variables. A state-of-the-art advisory decision-making tool, Dynamic Positioning Reliability Index (DP-RI), is used to validate the results from AHP. The weighting assignments from AHP are close to the reality and verified using the tool through real-life scenarios.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85199491","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}
Yihou Wang, Yuwang Xu, L. Shuai, H. Ren, Shixiao Fu
A fish cage is usually composed of steel columns, buoys, flexible nets and mooring lines. Elastic deformations will occur on these components under waves. The effects of these deformations on the global dynamic responses of the fish cage are still unclear. In this paper, a method considering hydroelastic deformation and a method considering the cage as rigid structure are employed to evaluate the hydrodynamic performance of a fish cage structure. The wave forces acting on these slender components are calculated based on Morison formula. The displacement of the cage and tension forces in the mooring lines obtained from these two methods are compared and the effects of hydroelastic deformation are discussed.
{"title":"Hydrodynamic Analysis of Deep-Water Fish Cage in Waves Based on Two Different Methods","authors":"Yihou Wang, Yuwang Xu, L. Shuai, H. Ren, Shixiao Fu","doi":"10.1115/omae2019-96486","DOIUrl":"https://doi.org/10.1115/omae2019-96486","url":null,"abstract":"\u0000 A fish cage is usually composed of steel columns, buoys, flexible nets and mooring lines. Elastic deformations will occur on these components under waves. The effects of these deformations on the global dynamic responses of the fish cage are still unclear. In this paper, a method considering hydroelastic deformation and a method considering the cage as rigid structure are employed to evaluate the hydrodynamic performance of a fish cage structure. The wave forces acting on these slender components are calculated based on Morison formula. The displacement of the cage and tension forces in the mooring lines obtained from these two methods are compared and the effects of hydroelastic deformation are discussed.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90077199","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}
Minghao Wu, J. Arnout, J. M. Ruiz, C. Chávez, V. Stratigaki, P. Troch
The waves and currents acting near a monopile foundation will potentially lead to scour, which may affect the stability of the wind turbine. The design of scour protection against the seabed lowering around a wind turbine monopile foundation is an important issue for wind energy industries. Many laboratory tests have been carried out to investigate the relationship between the hydrodynamic conditions and the monopile foundation scour protection layer damage, and various design criteria have been proposed. However, the experimental uncertainty of the underlying test results has not been discussed in detail. In the present research, small scale wave flume experiments of a 5m diameter monopile foundation scour protection under waves combined with currents in shallow water are described. Two groups of repetitive experiments are completed under the same wave and current conditions. The erosion development of the scour protection armor layer is measured by using a laser profiler and is evaluated based on three dimensional damage numbers. Together with visualization of the damage pattern, the damage analysis discusses the erosion in different subareas and the variances of the subarea damage number. The analysis of the uncertainty of the erosion results based on two sets of repetitive tests has been carried out. Using the uncertainty analysis methodology stated in ISO GUM standard: JCGM 100-2008, the Type A uncertainty, calibration uncertainty and combined uncertainty of the experiment are evaluated separately. The Type A uncertainty gives an overall uncertainty level and it shows that higher uncertainty occurs in the regions where stronger vortices exist. The combined uncertainty is analyzed based on scour protection dynamic stability design formula. Analysis result shows that the uncertainty due to modelling is a major source of the total uncertainty. The study gives a preliminary result of uncertainty level in wave flume test of monopile scour protection and provides a reference for future experimental research.
{"title":"Evaluation of Uncertainty of Damage Results in Experimental Modelling of Monopile Foundation Scour Protection","authors":"Minghao Wu, J. Arnout, J. M. Ruiz, C. Chávez, V. Stratigaki, P. Troch","doi":"10.1115/omae2019-95793","DOIUrl":"https://doi.org/10.1115/omae2019-95793","url":null,"abstract":"\u0000 The waves and currents acting near a monopile foundation will potentially lead to scour, which may affect the stability of the wind turbine. The design of scour protection against the seabed lowering around a wind turbine monopile foundation is an important issue for wind energy industries. Many laboratory tests have been carried out to investigate the relationship between the hydrodynamic conditions and the monopile foundation scour protection layer damage, and various design criteria have been proposed. However, the experimental uncertainty of the underlying test results has not been discussed in detail.\u0000 In the present research, small scale wave flume experiments of a 5m diameter monopile foundation scour protection under waves combined with currents in shallow water are described. Two groups of repetitive experiments are completed under the same wave and current conditions. The erosion development of the scour protection armor layer is measured by using a laser profiler and is evaluated based on three dimensional damage numbers. Together with visualization of the damage pattern, the damage analysis discusses the erosion in different subareas and the variances of the subarea damage number.\u0000 The analysis of the uncertainty of the erosion results based on two sets of repetitive tests has been carried out. Using the uncertainty analysis methodology stated in ISO GUM standard: JCGM 100-2008, the Type A uncertainty, calibration uncertainty and combined uncertainty of the experiment are evaluated separately. The Type A uncertainty gives an overall uncertainty level and it shows that higher uncertainty occurs in the regions where stronger vortices exist. The combined uncertainty is analyzed based on scour protection dynamic stability design formula. Analysis result shows that the uncertainty due to modelling is a major source of the total uncertainty. The study gives a preliminary result of uncertainty level in wave flume test of monopile scour protection and provides a reference for future experimental research.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"27 ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91463564","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}
Tension Leg Platform (TLP) tendons typically are installed for the life of the platform and incorporate elastomeric flex bearings. The Allegheny TLP, owned and operated by ENI Petroleum, was installed in Gulf of Mexico Green Canyon Block 254A, in 1999. It was designed for a service life of 20 years and currently ENI wants to extend the operating life of the platform. A baseline inspection showed significant degradation of the top tendon connector (TTC) flex bearing and it was concluded that the flex bearings needed to be replaced if the platform was to continue to operate safely. SBM and BHGE came up with a solution for replacing the TTC including the flex bearing, which was accepted by ENI. This involved ballasting the TLP to reduce the tendon pretensions, installing a temporary buoyancy module, and using a hydraulic tool, first of its kind in the world, to take the load off of the old TTC and gradually release the tendon to free stand. The tool was then retrieved with the old TTC, onboard the installation vessel. A second identical tool with the new TTC was then lowered on to the porch and the tendon stretched to the lock-off position by the tool and locked in position with the new TTC. This was done on all six (6) tendons and the platform was de-ballasted to the original tendon pre-tensions. Development of the tendon de-tensioning tool required new designs, extensive shop testing, and planning. The final offshore campaign took place during July 2018 and was completed in three (3) weeks. This represented a successful conclusion to a three (3) year effort. This paper highlights lessons learned in completing a complex first time ever project and makes recommendations for the design of future TLP’s.
{"title":"First in Place Replacement of a TLP Top Tendon Connector Flex Bearing","authors":"J. Otten, Vinu M Kuriakose, Shakib Amini","doi":"10.1115/omae2019-96232","DOIUrl":"https://doi.org/10.1115/omae2019-96232","url":null,"abstract":"\u0000 Tension Leg Platform (TLP) tendons typically are installed for the life of the platform and incorporate elastomeric flex bearings. The Allegheny TLP, owned and operated by ENI Petroleum, was installed in Gulf of Mexico Green Canyon Block 254A, in 1999. It was designed for a service life of 20 years and currently ENI wants to extend the operating life of the platform. A baseline inspection showed significant degradation of the top tendon connector (TTC) flex bearing and it was concluded that the flex bearings needed to be replaced if the platform was to continue to operate safely.\u0000 SBM and BHGE came up with a solution for replacing the TTC including the flex bearing, which was accepted by ENI. This involved ballasting the TLP to reduce the tendon pretensions, installing a temporary buoyancy module, and using a hydraulic tool, first of its kind in the world, to take the load off of the old TTC and gradually release the tendon to free stand. The tool was then retrieved with the old TTC, onboard the installation vessel. A second identical tool with the new TTC was then lowered on to the porch and the tendon stretched to the lock-off position by the tool and locked in position with the new TTC. This was done on all six (6) tendons and the platform was de-ballasted to the original tendon pre-tensions. Development of the tendon de-tensioning tool required new designs, extensive shop testing, and planning.\u0000 The final offshore campaign took place during July 2018 and was completed in three (3) weeks. This represented a successful conclusion to a three (3) year effort. This paper highlights lessons learned in completing a complex first time ever project and makes recommendations for the design of future TLP’s.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"50 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89777837","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}
The use of Very Large Floating Structures, VLFS, may represent a strategic approach in order to cope with some of the future societal challenges arising from the impressive growth of the world population. In this article, the motivations of this perspective are briefly discussed, the main issues for the development of VLFS are summarized and a concept structural design based on building-blocks technology is proposed. A small-scale physical model was manufactured and tested in the wave-current flume of the Laboratory of Maritime Engineering, LABIMA, of the Florence University, Italy. The aim of this study is the assessment of the structural feasibility and the effectiveness of the proposed VLFS concept, in terms of resistance to wave loads and control of floating behavior. The experimental measurements provide a first contribution to the necessary knowledge, about load magnitudes and floating behavior, for sizing some of the key structural components. The results appear to support the feasibility of the system in terms of usage of structural materials, technical components and building technologies, available at present, that can withstand the measured loads. Moreover, the acquired experimental database is fundamental in order to validate numerical models, in the perspective of using also such tools as complementary methodology for further improvement of the knowledge of design issues.
{"title":"Concept Design of Very Large Floating Structures and Laboratory-Scale Physical Modelling","authors":"L. Cappietti, I. Simonetti, Ilaria Crema","doi":"10.1115/omae2019-96259","DOIUrl":"https://doi.org/10.1115/omae2019-96259","url":null,"abstract":"The use of Very Large Floating Structures, VLFS, may represent a strategic approach in order to cope with some of the future societal challenges arising from the impressive growth of the world population. In this article, the motivations of this perspective are briefly discussed, the main issues for the development of VLFS are summarized and a concept structural design based on building-blocks technology is proposed. A small-scale physical model was manufactured and tested in the wave-current flume of the Laboratory of Maritime Engineering, LABIMA, of the Florence University, Italy. The aim of this study is the assessment of the structural feasibility and the effectiveness of the proposed VLFS concept, in terms of resistance to wave loads and control of floating behavior. The experimental measurements provide a first contribution to the necessary knowledge, about load magnitudes and floating behavior, for sizing some of the key structural components. The results appear to support the feasibility of the system in terms of usage of structural materials, technical components and building technologies, available at present, that can withstand the measured loads. Moreover, the acquired experimental database is fundamental in order to validate numerical models, in the perspective of using also such tools as complementary methodology for further improvement of the knowledge of design issues.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88635893","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 describes a numerical study on soil characterization of stiff over soft clays in centrifuge test using cone penetration test (CPT), especially when the top stiff layer is thin relative to the centrifuge cone size. An extensive parametric study was conducted using large deformation finite element (LDFE) analysis, with the cone penetrating continuously from the soil surface. The LDFE model has been validated against existing physical test data with very good agreement. Since the bottom soft clay was normally thick enough to fully mobilise the ultimate cone resistance, its undrained shear strength can be interpreted by the existing approach for cone deep penetration in a uniform clay layer. Thus, the challenge was to interpret the strength of the top stiff layer, where the layer thickness was not thick enough to fully mobilise its ultimate resistance. Both top layer thickness ratios (to the cone diameter) and layer strength ratios were considered in the parametric study. Based on the results from LDFE analyses, the interpretation formula of the undrained shear strength in the top stiff layer was proposed as a set of new bearing factors. The proposed cone bearing factor was a function of the ratio of the measured peak cone resistance in the top layer to the stable/ultimate cone resistance in the bottom layer and the ratio between the top layer thickness to the cone diameter. The formula can be used directly when the top layer thickness was known based on the sample preparation. However, the layer interface can be identified based on the study here, if the top layer thickness was not certain. A design flow chart was provided for interpretations of top clay layer strength and top layer thickness based on the cone resistance profile obtained from CPT test.
{"title":"Cone Penetration Test in Stiff Over Soft Clay in Centrifuge Test","authors":"Q. Xie, Yuxia Hu, M. Cassidy, A. Salehi","doi":"10.1115/omae2019-96698","DOIUrl":"https://doi.org/10.1115/omae2019-96698","url":null,"abstract":"\u0000 This paper describes a numerical study on soil characterization of stiff over soft clays in centrifuge test using cone penetration test (CPT), especially when the top stiff layer is thin relative to the centrifuge cone size. An extensive parametric study was conducted using large deformation finite element (LDFE) analysis, with the cone penetrating continuously from the soil surface. The LDFE model has been validated against existing physical test data with very good agreement. Since the bottom soft clay was normally thick enough to fully mobilise the ultimate cone resistance, its undrained shear strength can be interpreted by the existing approach for cone deep penetration in a uniform clay layer. Thus, the challenge was to interpret the strength of the top stiff layer, where the layer thickness was not thick enough to fully mobilise its ultimate resistance. Both top layer thickness ratios (to the cone diameter) and layer strength ratios were considered in the parametric study. Based on the results from LDFE analyses, the interpretation formula of the undrained shear strength in the top stiff layer was proposed as a set of new bearing factors. The proposed cone bearing factor was a function of the ratio of the measured peak cone resistance in the top layer to the stable/ultimate cone resistance in the bottom layer and the ratio between the top layer thickness to the cone diameter. The formula can be used directly when the top layer thickness was known based on the sample preparation. However, the layer interface can be identified based on the study here, if the top layer thickness was not certain. A design flow chart was provided for interpretations of top clay layer strength and top layer thickness based on the cone resistance profile obtained from CPT test.","PeriodicalId":23567,"journal":{"name":"Volume 1: Offshore Technology; Offshore Geotechnics","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88684551","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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