Mingda Yang, Yanli Tang, F. Zhao, Shiji Xu, Guangjie Fang
Artificial reefs (ARs) are one of the key man-made constructs to restore the offshore fishery resources and recover the ecological environment. However, it is found that many ARs lost their stability and function due to scour. In order to ensure the functional effect of ARs, it is of great significance to study the instability of ARs, like burying caused by scour in different flow conditions. The three-dimensional numerical model established by FLOW-3D is used to study the local scour characteristics around the AR in steady currents. The RANS equations, closed with the RNG k-ε turbulence model, are established for simulating a stable flow field around one AR. The simulation results are compared with previous experimental results and shows good agreement. Then, the effect of the opening number and the incident angles of ARs on the scour characteristics, the equilibrium scour depth and maximum scour volume are investigated. The results indicate that the scour depth and scour volume decrease with the increasing opening number. Moreover, the empirical equations of the effect of the opening number of the AR on the equilibrium scour depth and maximum scour volume are proposed based on the numerical results. The change of the incident angles will affect the change of bed shear stress at the most upstream corner of the AR. The greater bed shear stress results in a more intense scour. This study will provide theoretical support, and practical guidance for the optimized engineering design and construction of ARs.
{"title":"Numerical Simulation of Local Scour Around Square Artificial Reef","authors":"Mingda Yang, Yanli Tang, F. Zhao, Shiji Xu, Guangjie Fang","doi":"10.1115/omae2022-78941","DOIUrl":"https://doi.org/10.1115/omae2022-78941","url":null,"abstract":"\u0000 Artificial reefs (ARs) are one of the key man-made constructs to restore the offshore fishery resources and recover the ecological environment. However, it is found that many ARs lost their stability and function due to scour. In order to ensure the functional effect of ARs, it is of great significance to study the instability of ARs, like burying caused by scour in different flow conditions. The three-dimensional numerical model established by FLOW-3D is used to study the local scour characteristics around the AR in steady currents. The RANS equations, closed with the RNG k-ε turbulence model, are established for simulating a stable flow field around one AR. The simulation results are compared with previous experimental results and shows good agreement. Then, the effect of the opening number and the incident angles of ARs on the scour characteristics, the equilibrium scour depth and maximum scour volume are investigated. The results indicate that the scour depth and scour volume decrease with the increasing opening number. Moreover, the empirical equations of the effect of the opening number of the AR on the equilibrium scour depth and maximum scour volume are proposed based on the numerical results. The change of the incident angles will affect the change of bed shear stress at the most upstream corner of the AR. The greater bed shear stress results in a more intense scour. This study will provide theoretical support, and practical guidance for the optimized engineering design and construction of ARs.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"7 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82116044","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}
Designing a subsea production system is a task that takes several months to complete by an experienced and multidisciplinary team of engineers. In this work, a computerized hybrid method to find optimal designs and support subsea production system design using a genetic algorithm combined with a gradient search method is proposed. The genetic algorithm is formulated to optimize the structure of the production system, while the gradient method solves the continuous non-linear variables related to flow rates, reservoir deliverability, equipment capacities, and others. The study case is based on the Goliat field. This hybrid approach is compared with an exact method. The hybrid method successfully finds subsea configurations that maximize the net present value in shorter running times when compared to an exact method. The methodology presented provides an advancement toward modelling and automated decision-making in subsea production system design.
{"title":"Designing Subsea Processing Systems Using a Hybrid Genetic Algorithm","authors":"Leonardo Sales, J. Jäschke, M. Stanko","doi":"10.1115/omae2022-78647","DOIUrl":"https://doi.org/10.1115/omae2022-78647","url":null,"abstract":"\u0000 Designing a subsea production system is a task that takes several months to complete by an experienced and multidisciplinary team of engineers. In this work, a computerized hybrid method to find optimal designs and support subsea production system design using a genetic algorithm combined with a gradient search method is proposed.\u0000 The genetic algorithm is formulated to optimize the structure of the production system, while the gradient method solves the continuous non-linear variables related to flow rates, reservoir deliverability, equipment capacities, and others. The study case is based on the Goliat field. This hybrid approach is compared with an exact method.\u0000 The hybrid method successfully finds subsea configurations that maximize the net present value in shorter running times when compared to an exact method. The methodology presented provides an advancement toward modelling and automated decision-making in subsea production system design.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90268029","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}
Self-elevating units (SEUs), with a water-tight hull fitted with long support legs and spudcans, are widely used in offshore drilling and operations, as well as offshore wind turbine installations. SEUs are also known as jack-up rigs. A jack-up rig undergoes several stages of operations involving different leg configurations, such as legs retracted, legs suspended in the water, spudcans pre-loaded into the soil, and legs deployed in the seabed with the hull lifted clear above water. The hull and the legs will therefore be subjected to various external environmental actions. Transit operation (when the hull is in water) is only carried out in mild environmental conditions, due to safety concerns. The dynamic response of the SEU in the transit operation is less investigated in contrast to normal operation when the hull is in elevated condition supported by the legs. In this paper, we investigate the dynamic behavior of a generic (in-house designed) three-legged SEU. The configuration is such that the hull is in the water while the spudcans are secured in the seabed. A nonlinear time-domain model is established for the coupled hull and legs through Cummins’s equation. The hull is assumed as a rigid body with motions in six degrees of freedom, and the hydrodynamic coefficients are calculated from radiation and diffraction analysis. The legs are simplified as lumped mass models with equivalent stiffness value as the prototype, and Morison-type hydrodynamic loads are applied. Various scenarios of boundary conditions are considered, i.e., constant spudcan constraint stiffness, pin, fixed boundary conditions, and incidental cases when up to two spudcans are released while the other is still secured in the seabed. The dynamic responses of the SEU under operating sea conditions are examined. The results are compared to those from the conventional quasi-static analysis where the legs are simplified as linear springs. It is found that the dynamic response of the SEU with the hull-in-water condition can be as large as that in the elevated condition, despite the much milder sea conditions. The operational limit can be significantly reduced if the resonant motion occurs. These results show the importance of a full coupled dynamic analysis for a rational design of an SEU and may serve to guide operations for mobile offshore drilling units. It is even more crucial for certain SEUs where the hulls are intended to be in the water for a longer period, such as offshore wind turbine installation vessels. It may also allow the transit operations to be performed under slightly more severe conditions by better defining safe operational limits and reducing uncertainty.
{"title":"Dynamic Response of a Generic Self-Elevating Unit in Operation With Hull in Water","authors":"Chi Zhang, H. Santo, M. Cai, A. Magee","doi":"10.1115/omae2022-78850","DOIUrl":"https://doi.org/10.1115/omae2022-78850","url":null,"abstract":"\u0000 Self-elevating units (SEUs), with a water-tight hull fitted with long support legs and spudcans, are widely used in offshore drilling and operations, as well as offshore wind turbine installations. SEUs are also known as jack-up rigs. A jack-up rig undergoes several stages of operations involving different leg configurations, such as legs retracted, legs suspended in the water, spudcans pre-loaded into the soil, and legs deployed in the seabed with the hull lifted clear above water. The hull and the legs will therefore be subjected to various external environmental actions. Transit operation (when the hull is in water) is only carried out in mild environmental conditions, due to safety concerns. The dynamic response of the SEU in the transit operation is less investigated in contrast to normal operation when the hull is in elevated condition supported by the legs.\u0000 In this paper, we investigate the dynamic behavior of a generic (in-house designed) three-legged SEU. The configuration is such that the hull is in the water while the spudcans are secured in the seabed. A nonlinear time-domain model is established for the coupled hull and legs through Cummins’s equation. The hull is assumed as a rigid body with motions in six degrees of freedom, and the hydrodynamic coefficients are calculated from radiation and diffraction analysis. The legs are simplified as lumped mass models with equivalent stiffness value as the prototype, and Morison-type hydrodynamic loads are applied. Various scenarios of boundary conditions are considered, i.e., constant spudcan constraint stiffness, pin, fixed boundary conditions, and incidental cases when up to two spudcans are released while the other is still secured in the seabed. The dynamic responses of the SEU under operating sea conditions are examined. The results are compared to those from the conventional quasi-static analysis where the legs are simplified as linear springs.\u0000 It is found that the dynamic response of the SEU with the hull-in-water condition can be as large as that in the elevated condition, despite the much milder sea conditions. The operational limit can be significantly reduced if the resonant motion occurs. These results show the importance of a full coupled dynamic analysis for a rational design of an SEU and may serve to guide operations for mobile offshore drilling units. It is even more crucial for certain SEUs where the hulls are intended to be in the water for a longer period, such as offshore wind turbine installation vessels. It may also allow the transit operations to be performed under slightly more severe conditions by better defining safe operational limits and reducing uncertainty.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74410405","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}
Yutao Wang, H. Wolgamot, Wenhua Zhao, S. Draper, I. Milne
One of the key challenges associated with an FLNG facility is to optimise its offloading operability. LNG offloading operations typically use a side-by-side (SBS) configuration, where a carrier is moored parallel to the FLNG, leaving only a relatively small gap between the two vessels. In this paper, a numerical model for predicting the relative motion between an FLNG vessel and LNG carrier during offloading is developed using potential flow theory, and compared to wave basin experiments on simplified box geometries. In particular, this study addresses the prediction of roll motion, which is critical to SBS operation but difficult to model within the potential theory framework due to its dependence on viscous damping. The Ikeda method, which is an industry standard method for calculating ship roll damping, is applied in the model. However, since the Ikeda method was developed for a single hull, a modification is proposed to deliver improved performance in the context of the SBS offloading operation. More specifically, the small clearance between the vessels will influence the flow field and subsequently modify the fluid velocity around the bilge. This study suggests that the relative velocity between the fluid and hull roll motion is a better input for the original Ikeda method.
{"title":"Validation of a Simplified Numerical FLNG-Carrier Side-by-Side Offloading Model With Experiment","authors":"Yutao Wang, H. Wolgamot, Wenhua Zhao, S. Draper, I. Milne","doi":"10.1115/omae2022-79449","DOIUrl":"https://doi.org/10.1115/omae2022-79449","url":null,"abstract":"\u0000 One of the key challenges associated with an FLNG facility is to optimise its offloading operability. LNG offloading operations typically use a side-by-side (SBS) configuration, where a carrier is moored parallel to the FLNG, leaving only a relatively small gap between the two vessels. In this paper, a numerical model for predicting the relative motion between an FLNG vessel and LNG carrier during offloading is developed using potential flow theory, and compared to wave basin experiments on simplified box geometries.\u0000 In particular, this study addresses the prediction of roll motion, which is critical to SBS operation but difficult to model within the potential theory framework due to its dependence on viscous damping. The Ikeda method, which is an industry standard method for calculating ship roll damping, is applied in the model. However, since the Ikeda method was developed for a single hull, a modification is proposed to deliver improved performance in the context of the SBS offloading operation. More specifically, the small clearance between the vessels will influence the flow field and subsequently modify the fluid velocity around the bilge. This study suggests that the relative velocity between the fluid and hull roll motion is a better input for the original Ikeda method.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"16 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81168935","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}
Helena Karatvuo, M. Linde, A. Dolatshah, S. Mortensen
Due to their low-lying coastal location, ports are vulnerable to climate change induced increases to flooding, waves, extreme winds, and the associated costly damages to port infrastructure and operational disruptions. For these reasons, there is an increasing need for ports to undertake regular risk assessments of the vulnerability of their infrastructure and operations due to the impacts of climate change. A digital twin, cloud-based climate change modelling solution has been developed to enable in-house risk assessments of climate change vulnerability to be undertaken for any port. Once set-up, the system supports the continued sustainable operation of ports and enhancing stakeholder confidence in corporate sustainability strategies by allowing in-house re-evaluation of the ports climate risk as new predictions are released. The basis of the digital twin model of the port are numerical wave and hydrodynamic models, configured with the actual port geography and bathymetry enabling highly detailed simulations of the ports physical environment. The numerical model simulations are supplemented with observations of wind, rainfall, and sea level to identify trends and extreme event probabilities under the historic climate conditions. Scenarios describing the predicted impacts of climate change can be superimposed on the historical climate via a web-based interface where the user (port) selects a planning horizon (e.g., 2050), storm event frequency (e.g., 100-year storm), and climate change predictions (e.g. RCP8.5). The resulting climate change simulations shows great potential to enable port-specific predictions of future impacts of extreme occurrences of wind, waves, water levels, and currents. The ports asset portfolio is incorporated in the risk assessment through dynamic GIS layouts and damage curves identifying the damage cause and cost for each vulnerable port asset. As new climate science becomes available, this cloud-based digital twin model enables ports to rapidly complete updated risk assessments and respond to stakeholder queries and concerns. The capability of the tool was validated by comparing the model results against a large conventional study of the region, and a historical flood event of 2011. Both validation exercises displayed a reasonable agreement increasing confidence in the model’s capacity as a predictive tool. Additionally, six climate change scenarios were modelled for one of Australia’s fastest growing container ports, Port of Brisbane and the results were successfully incorporated in the ports overall sustainability strategy.
{"title":"Improved Climate Change Adaptation in Port of Brisbane Using a Digital Twin Cloud-Based Modelling Approach","authors":"Helena Karatvuo, M. Linde, A. Dolatshah, S. Mortensen","doi":"10.1115/omae2022-79613","DOIUrl":"https://doi.org/10.1115/omae2022-79613","url":null,"abstract":"\u0000 Due to their low-lying coastal location, ports are vulnerable to climate change induced increases to flooding, waves, extreme winds, and the associated costly damages to port infrastructure and operational disruptions. For these reasons, there is an increasing need for ports to undertake regular risk assessments of the vulnerability of their infrastructure and operations due to the impacts of climate change.\u0000 A digital twin, cloud-based climate change modelling solution has been developed to enable in-house risk assessments of climate change vulnerability to be undertaken for any port. Once set-up, the system supports the continued sustainable operation of ports and enhancing stakeholder confidence in corporate sustainability strategies by allowing in-house re-evaluation of the ports climate risk as new predictions are released.\u0000 The basis of the digital twin model of the port are numerical wave and hydrodynamic models, configured with the actual port geography and bathymetry enabling highly detailed simulations of the ports physical environment. The numerical model simulations are supplemented with observations of wind, rainfall, and sea level to identify trends and extreme event probabilities under the historic climate conditions. Scenarios describing the predicted impacts of climate change can be superimposed on the historical climate via a web-based interface where the user (port) selects a planning horizon (e.g., 2050), storm event frequency (e.g., 100-year storm), and climate change predictions (e.g. RCP8.5). The resulting climate change simulations shows great potential to enable port-specific predictions of future impacts of extreme occurrences of wind, waves, water levels, and currents. The ports asset portfolio is incorporated in the risk assessment through dynamic GIS layouts and damage curves identifying the damage cause and cost for each vulnerable port asset.\u0000 As new climate science becomes available, this cloud-based digital twin model enables ports to rapidly complete updated risk assessments and respond to stakeholder queries and concerns.\u0000 The capability of the tool was validated by comparing the model results against a large conventional study of the region, and a historical flood event of 2011. Both validation exercises displayed a reasonable agreement increasing confidence in the model’s capacity as a predictive tool. Additionally, six climate change scenarios were modelled for one of Australia’s fastest growing container ports, Port of Brisbane and the results were successfully incorporated in the ports overall sustainability strategy.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78814377","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}
K. E. Kaasen, H. Ludvigsen, N. Fonseca, H. Lie, L. Bjørheim
A number of incidents of wave-induced loss of position for dynamically positioned semi-submersible under normal operating conditions have occurred in the Norwegian offshore sector in recent years. A study has been carried out to seek their cause. One hypothesis for the cause has been slamming load from an extremely tall and steep wave that is not effectively counteracted by the DP system due to delays in signal filters and thruster response. Another cause could the loads from a train of tall and steep waves. A linear single-degree-of-freedom numerical model is made for a vessel with DP. The model is essential in that it represents the basic characteristics of the DP system: State observer/filter and feedback control. The model is used to calculate the frequency response and the impulse response of the dynamically positioned semi-submersible. By calculating extreme impulsive load based on published theory it is established that slamming will not cause great vessel excursion. Still, due to delays, the DP system gives more than twice as large excursion as a mass-spring-damper system with identical restoring stiffness and damping. Using an advanced model for vessel with DP, three-hour simulations of stochastic vessel response are carried out for five steep wave states of moderate significant height, The likely cause of large vessel excursion is found to be wave-drift. Due to additional viscous loads on the semi’s columns the wave-drift loads will be significantly larger than predicted with potential theory.
{"title":"The Likely Cause of Loss of Position for Dynamically Positioned Semi-Submersibles Under Moderate Wave Conditions","authors":"K. E. Kaasen, H. Ludvigsen, N. Fonseca, H. Lie, L. Bjørheim","doi":"10.1115/omae2022-79149","DOIUrl":"https://doi.org/10.1115/omae2022-79149","url":null,"abstract":"\u0000 A number of incidents of wave-induced loss of position for dynamically positioned semi-submersible under normal operating conditions have occurred in the Norwegian offshore sector in recent years. A study has been carried out to seek their cause. One hypothesis for the cause has been slamming load from an extremely tall and steep wave that is not effectively counteracted by the DP system due to delays in signal filters and thruster response. Another cause could the loads from a train of tall and steep waves.\u0000 A linear single-degree-of-freedom numerical model is made for a vessel with DP. The model is essential in that it represents the basic characteristics of the DP system: State observer/filter and feedback control. The model is used to calculate the frequency response and the impulse response of the dynamically positioned semi-submersible. By calculating extreme impulsive load based on published theory it is established that slamming will not cause great vessel excursion. Still, due to delays, the DP system gives more than twice as large excursion as a mass-spring-damper system with identical restoring stiffness and damping.\u0000 Using an advanced model for vessel with DP, three-hour simulations of stochastic vessel response are carried out for five steep wave states of moderate significant height, The likely cause of large vessel excursion is found to be wave-drift. Due to additional viscous loads on the semi’s columns the wave-drift loads will be significantly larger than predicted with potential theory.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"41 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79898020","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 increase in costs in the exploration and production of oil and gas in deep waters has led companies in the sector to invest in innovative technologies to detect, locate and correct faults in their production systems. This research aims to develop a methodology for monitoring and detecting leaks in subsea structures based on deep neural networks, allowing automated, efficient, and less costly monitoring than conventional monitoring methodologies. A set of monitoring data will be pre-processed for noise elimination, resolution improvement and resizing, to obtain a better performance of the algorithm. The next step consists of extracting relevant characteristics from the dataset to clearly identify the leak. The results show the metrics used to evaluate the performance of the neural network as the accuracy and efficiency of the algorithm to detect leaks in the underwater structures and equipment. Images of the Gulf of Mexico oil spill were used to test the methodology and the successful detection of the leak demonstrates the potential of the methodology for underwater leak detection.
{"title":"A Deep Learning Approach for Underwater Leak Detection","authors":"Viviane F. da Silva, T. Netto, Bessie A. Ribeiro","doi":"10.1115/omae2022-79757","DOIUrl":"https://doi.org/10.1115/omae2022-79757","url":null,"abstract":"\u0000 The increase in costs in the exploration and production of oil and gas in deep waters has led companies in the sector to invest in innovative technologies to detect, locate and correct faults in their production systems.\u0000 This research aims to develop a methodology for monitoring and detecting leaks in subsea structures based on deep neural networks, allowing automated, efficient, and less costly monitoring than conventional monitoring methodologies.\u0000 A set of monitoring data will be pre-processed for noise elimination, resolution improvement and resizing, to obtain a better performance of the algorithm. The next step consists of extracting relevant characteristics from the dataset to clearly identify the leak.\u0000 The results show the metrics used to evaluate the performance of the neural network as the accuracy and efficiency of the algorithm to detect leaks in the underwater structures and equipment.\u0000 Images of the Gulf of Mexico oil spill were used to test the methodology and the successful detection of the leak demonstrates the potential of the methodology for underwater leak detection.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"39 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81715574","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}
Ø. Gabrielsen, Svein-Arne Reinholdtsen, B. Skallerud, P. Haagensen, Marius Andersen, P. Kane
Fatigue capacity of mooring chains is one of the important parameters in design of mooring systems for floating offshore structures. Fatigue life is often a limiting factor. With life extension of existing offshore installations, the fatigue capacity and effects of corrosion become even more important, as there will be large costs for mooring line replacements if safe life extension can not be granted, and the effect of fatigue failure can be fatal. Estimation of the fatigue capacity of mooring chains is thus of high importance both for safe and cost-effective design of new mooring systems, and for the safe life extension of older mooring systems. The standards used for design of mooring systems outline a somewhat simplified approach for fatigue analysis, where load cycle range is the only parameter included in the analysis. The fatigue capacity curves used are based on full scale fatigue tests of new chains, where effects of heavily corroded surfaces are not considered. Further it is indirectly assumed that mean load does not have any effect on fatigue capacity. Work presented the last years has indicated a strong effect of both mean load and surface condition, where also formulas for fatigue capacity including these parameters have been developed and presented. The conclusions are based on a large set of full-scale fatigue tests of both new chains and used chains, where the used chains are tested at different mean loads and different levels of corrosion. Equinor has run a large number of used chain fatigue tests. For these tests, each set of tests is typically made from one chain length, with similar condition on all links, and usually run at one mean load only. There are test sets with some variation in either mean load or surface condition, which have added valuable data for the understanding and verification of the effect of these parameters. The effects are well documented, but due to small variation within each set there are uncertainties regarding the quantification of the effects. The latest full-scale fatigue test results, from a chain with significant corrosion pits, include a systematic approach to quantify the effect of mean load. For the chain tested, five tests have been run at low mean load, and five tests at high mean load. This paper presents the results from these fatigue tests. The results are discussed and compared with other fatigue test results on both new and used chain, and with the formulas for fatigue capacity accounting for mean load and surface corrosion.
{"title":"Fatigue Capacity of Used Mooring Chain - Results From Full Scale Fatigue Testing at Different Mean Loads","authors":"Ø. Gabrielsen, Svein-Arne Reinholdtsen, B. Skallerud, P. Haagensen, Marius Andersen, P. Kane","doi":"10.1115/omae2022-79649","DOIUrl":"https://doi.org/10.1115/omae2022-79649","url":null,"abstract":"\u0000 Fatigue capacity of mooring chains is one of the important parameters in design of mooring systems for floating offshore structures. Fatigue life is often a limiting factor. With life extension of existing offshore installations, the fatigue capacity and effects of corrosion become even more important, as there will be large costs for mooring line replacements if safe life extension can not be granted, and the effect of fatigue failure can be fatal. Estimation of the fatigue capacity of mooring chains is thus of high importance both for safe and cost-effective design of new mooring systems, and for the safe life extension of older mooring systems.\u0000 The standards used for design of mooring systems outline a somewhat simplified approach for fatigue analysis, where load cycle range is the only parameter included in the analysis. The fatigue capacity curves used are based on full scale fatigue tests of new chains, where effects of heavily corroded surfaces are not considered. Further it is indirectly assumed that mean load does not have any effect on fatigue capacity. Work presented the last years has indicated a strong effect of both mean load and surface condition, where also formulas for fatigue capacity including these parameters have been developed and presented. The conclusions are based on a large set of full-scale fatigue tests of both new chains and used chains, where the used chains are tested at different mean loads and different levels of corrosion.\u0000 Equinor has run a large number of used chain fatigue tests. For these tests, each set of tests is typically made from one chain length, with similar condition on all links, and usually run at one mean load only. There are test sets with some variation in either mean load or surface condition, which have added valuable data for the understanding and verification of the effect of these parameters. The effects are well documented, but due to small variation within each set there are uncertainties regarding the quantification of the effects. The latest full-scale fatigue test results, from a chain with significant corrosion pits, include a systematic approach to quantify the effect of mean load. For the chain tested, five tests have been run at low mean load, and five tests at high mean load. This paper presents the results from these fatigue tests. The results are discussed and compared with other fatigue test results on both new and used chain, and with the formulas for fatigue capacity accounting for mean load and surface corrosion.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81738722","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 is a growing interest in applying the technology to small and medium-sized Liquefied Natural Gas (LNG) carriers to meet the recent increase in demand for LNG as an ecofriendly fuel and for expanding LNG bunkering infrastructure. The purpose of this study is to apply the IMO Type B tank to small and medium-sized LNG carriers and verify the safety and suitability of the design. One of the key technical issues of Type B LNG tank is heat transfer analysis and selection of hull steel grade. In this study, a heat transfer analysis was performed for hull temperature calculation and steel grade selection. Also, the stress levels and the thermal movements of the tank were checked through thermal stress analysis applying thermal and mechanical loads. Another key technical issue of a Type B tank is to determine the size of a partial secondary barrier based on fracture mechanics. For the accurate analysis, a procedure was developed and verified based on direct analysis and international regulations. Finally, the related safety and suitability of the IMO Type B for LNG cargo tanks required by International Gas Carrier (IGC) code were verified. Two key technical issues with applied examples are thoroughly analyzed in this study, could be applied in the design of independent Type B LNG carrier.
{"title":"Development of Design Procedure for LNG Carriers With IMO Type-B Independent Tank","authors":"Beomil Kim, M. Islam","doi":"10.1115/omae2022-79445","DOIUrl":"https://doi.org/10.1115/omae2022-79445","url":null,"abstract":"\u0000 There is a growing interest in applying the technology to small and medium-sized Liquefied Natural Gas (LNG) carriers to meet the recent increase in demand for LNG as an ecofriendly fuel and for expanding LNG bunkering infrastructure. The purpose of this study is to apply the IMO Type B tank to small and medium-sized LNG carriers and verify the safety and suitability of the design. One of the key technical issues of Type B LNG tank is heat transfer analysis and selection of hull steel grade. In this study, a heat transfer analysis was performed for hull temperature calculation and steel grade selection. Also, the stress levels and the thermal movements of the tank were checked through thermal stress analysis applying thermal and mechanical loads. Another key technical issue of a Type B tank is to determine the size of a partial secondary barrier based on fracture mechanics. For the accurate analysis, a procedure was developed and verified based on direct analysis and international regulations. Finally, the related safety and suitability of the IMO Type B for LNG cargo tanks required by International Gas Carrier (IGC) code were verified. Two key technical issues with applied examples are thoroughly analyzed in this study, could be applied in the design of independent Type B LNG carrier.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80683467","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}
Model test campaigns conducted recent years indicate large wave impact loads on vertical surfaces above the waterline for various types of moored floating structures. These impacts are caused by breaking or near breaking waves in extreme sea states. Due to the large variability of the load, it is challenging to estimate the characteristic slamming loads, defined as the q-annual extreme 3-hour slamming load level of 10-2 for the Ultimate Limit State (ULS) and 10-4 for the Accidental Limit State (ALS). Hence, many tests realizations are necessary to assess extreme loads. It is common practice to assume long crested waves in design against slamming loads. This assumption is regarded as conservative, and there have been indications that the effect of short crested waves on impact loads could be significant. In the present work an experimental investigation was set up to study effect of short crested waves for slamming against a rigid vertical column. Influence of current and other modeling parameters like type of wavemaker (single vs double flap), were also studied. A test model in scale 1:55 of a 31m diameter column at water depth 121m was used. The area of the column facing the incoming wave was instrumented by slamming panels. The setup covers 80 degrees of the cylinder circumference over a height of 24 meters from the still water surface and upwards. In addition to the slamming loads measured on the column, shear force and bending moment at the base of the column and global accelerations for the column were measured. High-speed video recordings were made for slamming events above a given threshold.
{"title":"Experimental Investigation of Slamming Loads on Vertical Column Exposed to Short and Long Crested Waves","authors":"O. Økland, G. Lian, Tone M. Vestbøstad","doi":"10.1115/omae2022-79076","DOIUrl":"https://doi.org/10.1115/omae2022-79076","url":null,"abstract":"\u0000 Model test campaigns conducted recent years indicate large wave impact loads on vertical surfaces above the waterline for various types of moored floating structures. These impacts are caused by breaking or near breaking waves in extreme sea states. Due to the large variability of the load, it is challenging to estimate the characteristic slamming loads, defined as the q-annual extreme 3-hour slamming load level of 10-2 for the Ultimate Limit State (ULS) and 10-4 for the Accidental Limit State (ALS). Hence, many tests realizations are necessary to assess extreme loads.\u0000 It is common practice to assume long crested waves in design against slamming loads. This assumption is regarded as conservative, and there have been indications that the effect of short crested waves on impact loads could be significant. In the present work an experimental investigation was set up to study effect of short crested waves for slamming against a rigid vertical column. Influence of current and other modeling parameters like type of wavemaker (single vs double flap), were also studied. A test model in scale 1:55 of a 31m diameter column at water depth 121m was used. The area of the column facing the incoming wave was instrumented by slamming panels. The setup covers 80 degrees of the cylinder circumference over a height of 24 meters from the still water surface and upwards. In addition to the slamming loads measured on the column, shear force and bending moment at the base of the column and global accelerations for the column were measured. High-speed video recordings were made for slamming events above a given threshold.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85307329","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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