A. Ghasemi, Y. Drobyshevski, M. Kimiaei, M. Efthymiou
Response based analysis (RBA) is a comprehensive approach for the prediction of extreme responses and design metocean conditions of offshore facilities. For RBA, the structural system needs to be modelled, and its behavior analyzed when subjected to large metocean datasets, usually comprising thousands of different sea states. Due to the dynamic and nonlinear behavior of mooring systems in floating structures, application of conventional time domain analysis for RBA of these systems is a computationally demanding process. Hence, investigation of faster solvers and more efficient methods for the RBA is inevitable. Peak distribution method (PDM), which has recently been introduced and used for response analysis of mooring systems under extreme design conditions, is a possible solution to reduce the computational efforts in RBA by reducing the number of simulations. This study explores the utilization of the PDM for RBA of the mooring system of a turret-moored large FPSO subjected to tropical storms. Large variability of metocean parameters within such storms limits the applicability of intuitive judgement for the selection of governing sea states. The results are compared through both time-domain and frequency-domain simulations and a computationally efficient methodology is proposed. It provides a general robust framework of computing the extreme value distribution of the system response. The proposed methodology can be used for RBA of mooring lines tension under storm conditions comprising large number of sea states.
{"title":"Application of Peak Distribution Method for Response Based Analysis of Mooring Lines Under Tropical Storms","authors":"A. Ghasemi, Y. Drobyshevski, M. Kimiaei, M. Efthymiou","doi":"10.1115/omae2020-18534","DOIUrl":"https://doi.org/10.1115/omae2020-18534","url":null,"abstract":"\u0000 Response based analysis (RBA) is a comprehensive approach for the prediction of extreme responses and design metocean conditions of offshore facilities. For RBA, the structural system needs to be modelled, and its behavior analyzed when subjected to large metocean datasets, usually comprising thousands of different sea states. Due to the dynamic and nonlinear behavior of mooring systems in floating structures, application of conventional time domain analysis for RBA of these systems is a computationally demanding process. Hence, investigation of faster solvers and more efficient methods for the RBA is inevitable. Peak distribution method (PDM), which has recently been introduced and used for response analysis of mooring systems under extreme design conditions, is a possible solution to reduce the computational efforts in RBA by reducing the number of simulations.\u0000 This study explores the utilization of the PDM for RBA of the mooring system of a turret-moored large FPSO subjected to tropical storms. Large variability of metocean parameters within such storms limits the applicability of intuitive judgement for the selection of governing sea states. The results are compared through both time-domain and frequency-domain simulations and a computationally efficient methodology is proposed. It provides a general robust framework of computing the extreme value distribution of the system response. The proposed methodology can be used for RBA of mooring lines tension under storm conditions comprising large number of sea states.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"54 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78372387","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}
Fully coupled time domain turret/FPSO simulations are conducted using TechnipFMC proprietary software MLTSIM. To analyze hydrodynamic interactions and mechanical coupling effects between an FPSO and its turret, a multi-body interaction model is developed and analyzed. In the multi-body interaction model, full coupled hydrodynamic interactions are considered, and the bearing connections are modeled with nonlinear springs and frictional damping. The global performance analysis results are systematically compared with model test results (Kim et al. [1]), and hydrodynamic loads and mechanical coupling loads on the turret are presented in this paper.
利用TechnipFMC专有软件MLTSIM进行了炮塔/FPSO全耦合时域仿真。为了分析FPSO与其转塔之间的水动力相互作用和力学耦合效应，建立并分析了多体相互作用模型。在多体相互作用模型中，考虑了全耦合流体动力相互作用，并采用非线性弹簧和摩擦阻尼对轴承连接进行建模。将整体性能分析结果与模型试验结果(Kim et al.[1])进行了系统比较，并给出了转塔的水动力载荷和机械耦合载荷。
{"title":"Time Domain Turret Load and Motion Analyses for a FPSO","authors":"Hyoungchul Kim, Bonjun Koo, J. Kyoung","doi":"10.1115/omae2020-18847","DOIUrl":"https://doi.org/10.1115/omae2020-18847","url":null,"abstract":"\u0000 Fully coupled time domain turret/FPSO simulations are conducted using TechnipFMC proprietary software MLTSIM. To analyze hydrodynamic interactions and mechanical coupling effects between an FPSO and its turret, a multi-body interaction model is developed and analyzed. In the multi-body interaction model, full coupled hydrodynamic interactions are considered, and the bearing connections are modeled with nonlinear springs and frictional damping. The global performance analysis results are systematically compared with model test results (Kim et al. [1]), and hydrodynamic loads and mechanical coupling loads on the turret are presented in this paper.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"132 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76666234","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}
As the worldwide oil and gas market continues to grow and environmental concerns with respect to in-port offloading of gas have increased, there has been a boom of interest in new liquefied natural gas LNG terminals in the past years. Loading - offloading operations at LNG and bulk terminals are generally protected by a breakwater to ensure high operability. For these terminals, caisson breakwaters are generally a preferred solution in water depth larger than 15 m due to its advantages compared to rubble mound breakwaters. The caisson installation is generally planned to be carried out in the period where sea conditions are relatively calm. However, many of these terminal locations are exposed to swell conditions, making the installation particularly challenging and subject to large downtime. There is no clear guidance on the caisson installation process rather than contractors’ experiences from different projects/sites. Therefore, studies are required in order to provide general guidance on the range of acceptable wave conditions for the installation operations and to have a better understanding of the influence of the caisson geometry. This paper presents a numerical study to determine the limiting wave conditions for caisson installing operations at larger water depth of 30–35 m for a confidential project along the African coast. Three caisson sizes/geometries are considered in order to assess and compare the wave-structure hydrodynamic interaction. The linear frequency-domain hydrodynamic analysis is performed for various seastates to determine the limiting wave conditions. Viscous effects due to flow separation at the sharp edges of the caisson are considered by using a stochastic linearization approach, where empirical drag coefficients are used as inputs. Parametric studies on caisson size and mooring stiffness are also presented, which can be used as a basis for future optimization. The uncertainty in the applied empirical viscous drag coefficients taken from the literature is examined by using a range of different drag coefficients. Further, the use of clearance-independent hydrodynamic coefficients (e.g. added mass and damping) may be questionable when the caisson is very close to the seabed, due to a possible strong interaction between caisson bottom and seabed. This effect is also checked quantitatively by a simplified approach. The findings of the study are presented in the form of curves and generalized to be used by designers and contractors for general guidance in future projects.
{"title":"Caisson Breakwater for LNG and Bulk Terminals: A Study on Limiting Wave Conditions for Caisson Installation","authors":"Yu Lin, Ghassan El Chahal, Yanlin Shao","doi":"10.1115/omae2020-19081","DOIUrl":"https://doi.org/10.1115/omae2020-19081","url":null,"abstract":"\u0000 As the worldwide oil and gas market continues to grow and environmental concerns with respect to in-port offloading of gas have increased, there has been a boom of interest in new liquefied natural gas LNG terminals in the past years. Loading - offloading operations at LNG and bulk terminals are generally protected by a breakwater to ensure high operability. For these terminals, caisson breakwaters are generally a preferred solution in water depth larger than 15 m due to its advantages compared to rubble mound breakwaters. The caisson installation is generally planned to be carried out in the period where sea conditions are relatively calm. However, many of these terminal locations are exposed to swell conditions, making the installation particularly challenging and subject to large downtime. There is no clear guidance on the caisson installation process rather than contractors’ experiences from different projects/sites. Therefore, studies are required in order to provide general guidance on the range of acceptable wave conditions for the installation operations and to have a better understanding of the influence of the caisson geometry.\u0000 This paper presents a numerical study to determine the limiting wave conditions for caisson installing operations at larger water depth of 30–35 m for a confidential project along the African coast. Three caisson sizes/geometries are considered in order to assess and compare the wave-structure hydrodynamic interaction. The linear frequency-domain hydrodynamic analysis is performed for various seastates to determine the limiting wave conditions. Viscous effects due to flow separation at the sharp edges of the caisson are considered by using a stochastic linearization approach, where empirical drag coefficients are used as inputs. Parametric studies on caisson size and mooring stiffness are also presented, which can be used as a basis for future optimization. The uncertainty in the applied empirical viscous drag coefficients taken from the literature is examined by using a range of different drag coefficients. Further, the use of clearance-independent hydrodynamic coefficients (e.g. added mass and damping) may be questionable when the caisson is very close to the seabed, due to a possible strong interaction between caisson bottom and seabed. This effect is also checked quantitatively by a simplified approach.\u0000 The findings of the study are presented in the form of curves and generalized to be used by designers and contractors for general guidance in future projects.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"7 10","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91452510","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Zhang, Junrong Wang, Junfeng Du, N. Fonseca, Galin Tahchiev, E. Engebretsen
The paper presents calibration and validation of a time domain numerical model for mooring analysis of a spread moored FPSO in moderate seastates with and without current. The equations of motion are solved in the time domain with a fully coupled method, accounting for linear wave frequency (WF) radiation and diffraction, second order wave drift forces and nonlinear low frequency (LF) damping. The mooring system dynamics is solved by a FEM. Uncalibrated numerical models are based on input from the mooring system, vessel mass, radiation/diffraction analysis, decay tests and current coefficients. WF responses are very well predicted by standard radiation/diffraction linear analysis, therefore the focus is on the LF responses. LF motions are underpredicted by the uncalibrated numerical model. Calibration is performed by comparing simulations with model test data and adjusting hydrodynamic coefficients known to be affected by uncertainty. These include wave drift force coefficients and LF damping. Correction of the drift coefficients is based on empirical quadratic transfer functions (QTFs) identified from the test data by a nonlinear data analysis technique known as “cross-bi-spectral analysis”. The LF damping coefficients are then adjusted by matching low frequency surge and sway spectra from the model tests and from the simulations.
{"title":"Time-Domain Hydrodynamic Model for Mooring Analysis of a Spread Moored FPSO With Calibration of Wave Drift Forces","authors":"M. Zhang, Junrong Wang, Junfeng Du, N. Fonseca, Galin Tahchiev, E. Engebretsen","doi":"10.1115/omae2020-18717","DOIUrl":"https://doi.org/10.1115/omae2020-18717","url":null,"abstract":"\u0000 The paper presents calibration and validation of a time domain numerical model for mooring analysis of a spread moored FPSO in moderate seastates with and without current. The equations of motion are solved in the time domain with a fully coupled method, accounting for linear wave frequency (WF) radiation and diffraction, second order wave drift forces and nonlinear low frequency (LF) damping. The mooring system dynamics is solved by a FEM. Uncalibrated numerical models are based on input from the mooring system, vessel mass, radiation/diffraction analysis, decay tests and current coefficients. WF responses are very well predicted by standard radiation/diffraction linear analysis, therefore the focus is on the LF responses. LF motions are underpredicted by the uncalibrated numerical model.\u0000 Calibration is performed by comparing simulations with model test data and adjusting hydrodynamic coefficients known to be affected by uncertainty. These include wave drift force coefficients and LF damping. Correction of the drift coefficients is based on empirical quadratic transfer functions (QTFs) identified from the test data by a nonlinear data analysis technique known as “cross-bi-spectral analysis”. The LF damping coefficients are then adjusted by matching low frequency surge and sway spectra from the model tests and from the simulations.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"22 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85168379","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}
Exploitation of the Arctic’s resources requires the mastery of the risks caused by extreme ice conditions. The design of offshore structures subjected to extreme ice conditions is a challenge for engineers since there are very few advanced numerical design tools available in the market. Especially those able to cope with any kind of structure geometry and a large variety of ice interaction & failure mechanisms. For developments in arctic shallow water between 50m to 200m water depth it is not possible to use conventional drilling rigs as it is either too deep for fixed or too shallow for floating operations. The other possibility is to have drilling equipment on the platform such as on Prirazlomnaya but then, with a drilling campaign of 5 to 7 years this represents a significant CAPEX compared to the remaining operations time and could imperil the economics of the project. A smart solution would be to use a MODU for full year operations in Arctic regions. Such a solution would not only place the rig into OPEX but also reduce the living quarters on the platform to the minimum strictly necessary for the operations of the platform, the drilling staff being housed on the MODU. Such a solution could reduce the weight of the platform by nearly 50%. This paper presents how it is possible to use an Arctic class MODU such as Arcticheskaya for full year operations in ice infested water.
{"title":"Full Year Drilling Season for MODU in Arctic Area","authors":"M. Cahay","doi":"10.1115/omae2020-18136","DOIUrl":"https://doi.org/10.1115/omae2020-18136","url":null,"abstract":"\u0000 Exploitation of the Arctic’s resources requires the mastery of the risks caused by extreme ice conditions. The design of offshore structures subjected to extreme ice conditions is a challenge for engineers since there are very few advanced numerical design tools available in the market. Especially those able to cope with any kind of structure geometry and a large variety of ice interaction & failure mechanisms.\u0000 For developments in arctic shallow water between 50m to 200m water depth it is not possible to use conventional drilling rigs as it is either too deep for fixed or too shallow for floating operations. The other possibility is to have drilling equipment on the platform such as on Prirazlomnaya but then, with a drilling campaign of 5 to 7 years this represents a significant CAPEX compared to the remaining operations time and could imperil the economics of the project.\u0000 A smart solution would be to use a MODU for full year operations in Arctic regions. Such a solution would not only place the rig into OPEX but also reduce the living quarters on the platform to the minimum strictly necessary for the operations of the platform, the drilling staff being housed on the MODU. Such a solution could reduce the weight of the platform by nearly 50%.\u0000 This paper presents how it is possible to use an Arctic class MODU such as Arcticheskaya for full year operations in ice infested water.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"9 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83090376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the downturn of the shipping industry, optimizing the speed of ships sailing on fixed routes has important practical significance for reducing operating costs. Based on the ship-engine-propeller matching relationship, this paper uses BP neural network to build main engine power model, and correction factors are introduced into the main engine power model to reflect the influence of wind and wave. The Kalman filter algorithm is used to filter the data collected by a river-sea direct ship during the voyage from Zhoushan to Zhangjiagang. The filtered data and the meteorological data obtained from the European Medium-Range Weather Forecast Center are used as the data set of the BP neural network to predict the main engine power. Based on the main engine power model, a multi-objective optimization model of ship speed under the influence of actual wind and waves was established to solve the conflicting goals of reducing sailing time and reducing main engine fuel consumption. This multi-objective model is solved by a non-dominated fast sorting multi-objective genetic algorithm to obtain the Pareto optimal solution set, thereby obtaining the optimal speed optimization scheme. Compared with the original navigation scheme, the navigation time is reduced by 8.83%, and the fuel consumption of the main engine is reduced by 12.95%. The results show that the optimization model can effectively reduce the fuel consumption and control the sailing time, which verifies the effectiveness of the algorithm.
{"title":"Research on Fixed Route Speed Optimization Based on Deep Neural Network and Genetic Algorithm","authors":"Ziming Wang, Shunhuai Chen, Liang Luo","doi":"10.1115/omae2020-18442","DOIUrl":"https://doi.org/10.1115/omae2020-18442","url":null,"abstract":"\u0000 In the downturn of the shipping industry, optimizing the speed of ships sailing on fixed routes has important practical significance for reducing operating costs. Based on the ship-engine-propeller matching relationship, this paper uses BP neural network to build main engine power model, and correction factors are introduced into the main engine power model to reflect the influence of wind and wave. The Kalman filter algorithm is used to filter the data collected by a river-sea direct ship during the voyage from Zhoushan to Zhangjiagang. The filtered data and the meteorological data obtained from the European Medium-Range Weather Forecast Center are used as the data set of the BP neural network to predict the main engine power. Based on the main engine power model, a multi-objective optimization model of ship speed under the influence of actual wind and waves was established to solve the conflicting goals of reducing sailing time and reducing main engine fuel consumption. This multi-objective model is solved by a non-dominated fast sorting multi-objective genetic algorithm to obtain the Pareto optimal solution set, thereby obtaining the optimal speed optimization scheme. Compared with the original navigation scheme, the navigation time is reduced by 8.83%, and the fuel consumption of the main engine is reduced by 12.95%. The results show that the optimization model can effectively reduce the fuel consumption and control the sailing time, which verifies the effectiveness of the algorithm.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78926908","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}
David Vågnes, Thiago Gabriel Monteiro, K. Halse, H. P. Hildre
With the increasing demand for renewable energy sources in the past years, the interest in expanding the use of wind energy has grown. The next frontier in this expansion process is the use of floating wind turbines offshore. One of the main factors dictating the economic feasibility of such wind turbines is the complexity of their installation process. The dimensions of modern offshore wind turbines, the distance from the installation sites to the coast and demanding environmental factors all contribute to the difficult of developing an efficient installation concept for this kind of structures. In this work, we present a new concept for a catamaran vessel capable of handling the deployment of offshore wind turbines on floating spar platforms using a low-height lifting system that connects to the lower end of the wind turbine. The low-height lifting system is controlled by an active heave compensation system and constant tension tugger wires attached to the turbine mid-section are used to ensure the balance of the tower during the installation process. We conducted a series of hydrodynamic analysis using the software suit SIMA to study the dynamic response of the proposed system under different weather conditions and different operational layouts. This preliminary concept was proven feasible from a hydrodynamic point of view and can now be pushed forward for further studies regarding other aspects of the operation, such as impact and structural loads and mechanical design of components.
{"title":"Low-Height Lifting System for Offshore Wind Turbine Installation: Modelling and Hydrodynamic Response Analysis Using the Commercial Simulation Tool SIMA","authors":"David Vågnes, Thiago Gabriel Monteiro, K. Halse, H. P. Hildre","doi":"10.1115/omae2020-19183","DOIUrl":"https://doi.org/10.1115/omae2020-19183","url":null,"abstract":"\u0000 With the increasing demand for renewable energy sources in the past years, the interest in expanding the use of wind energy has grown. The next frontier in this expansion process is the use of floating wind turbines offshore. One of the main factors dictating the economic feasibility of such wind turbines is the complexity of their installation process. The dimensions of modern offshore wind turbines, the distance from the installation sites to the coast and demanding environmental factors all contribute to the difficult of developing an efficient installation concept for this kind of structures. In this work, we present a new concept for a catamaran vessel capable of handling the deployment of offshore wind turbines on floating spar platforms using a low-height lifting system that connects to the lower end of the wind turbine. The low-height lifting system is controlled by an active heave compensation system and constant tension tugger wires attached to the turbine mid-section are used to ensure the balance of the tower during the installation process. We conducted a series of hydrodynamic analysis using the software suit SIMA to study the dynamic response of the proposed system under different weather conditions and different operational layouts. This preliminary concept was proven feasible from a hydrodynamic point of view and can now be pushed forward for further studies regarding other aspects of the operation, such as impact and structural loads and mechanical design of components.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90067140","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, S. Kumar, W. L. Woo, R. Norman, A. Dev
In this study, a framework using Long Short Term Memory (LSTM) for prediction of reliability of Dynamic Positioning (DP) sub-systems for computation of Dynamic Positioning Reliability Index (DP-RI) has been proposed. The DP System is complex with significant levels of integration between many sub-systems such as the Reference System, DP Control System, Thruster / Propulsion System, Power System, Electrical System and the Environment System to perform diverse control functions. The proposed framework includes a mathematical computation approach to compute reliability of DP sub-systems and a data driven approach to predict the reliability at a sub-system level for evaluation of model performance and accuracy. The framework results demonstrate excellent performance under a wide range of data availability and guaranteed lower computational burden for real-time non-linear optimization. There are three main components of the proposed architecture for the mathematical formulation of the DP sub-systems based on individual sensor arrangements within the sub-system, computation of reliability of sub-systems and optimized LSTM deep learning algorithm for prediction of its reliability. Firstly, the mathematical formulation for the reliability of sub-systems is determined based on the series/parallel arrangement of the sensors of each individual equipment item within the sub-systems. Secondly, the computation of the reliability of sub-systems is achieved through an integrated approach during complex operation of the vessel. Thirdly, the novel optimized LSTM network is constructed to predict the reliability of the subsystems while minimizing integral errors in the algorithm. In this paper, numerical simulations are set-up using a state-of-the-art advisory decision-making tool with mock-up and real-world data to give insights into the model performance and validate it against the existing risk assessment methodologies. Furthermore, we have analyzed the efficiency and stability of the proposed model against various levels of data availability. In conclusion the prediction accuracy of the proposed model is scalable and higher when compared with other model results.
{"title":"Real-Time Prediction of Reliability of Dynamic Positioning Sub-Systems for Computation of Dynamic Positioning Reliability Index (DP-RI) Using Long Short Term Memory (LSTM)","authors":"Charles Fernandez, S. Kumar, W. L. Woo, R. Norman, A. Dev","doi":"10.1115/omae2020-18844","DOIUrl":"https://doi.org/10.1115/omae2020-18844","url":null,"abstract":"\u0000 In this study, a framework using Long Short Term Memory (LSTM) for prediction of reliability of Dynamic Positioning (DP) sub-systems for computation of Dynamic Positioning Reliability Index (DP-RI) has been proposed. The DP System is complex with significant levels of integration between many sub-systems such as the Reference System, DP Control System, Thruster / Propulsion System, Power System, Electrical System and the Environment System to perform diverse control functions. The proposed framework includes a mathematical computation approach to compute reliability of DP sub-systems and a data driven approach to predict the reliability at a sub-system level for evaluation of model performance and accuracy. The framework results demonstrate excellent performance under a wide range of data availability and guaranteed lower computational burden for real-time non-linear optimization.\u0000 There are three main components of the proposed architecture for the mathematical formulation of the DP sub-systems based on individual sensor arrangements within the sub-system, computation of reliability of sub-systems and optimized LSTM deep learning algorithm for prediction of its reliability. Firstly, the mathematical formulation for the reliability of sub-systems is determined based on the series/parallel arrangement of the sensors of each individual equipment item within the sub-systems. Secondly, the computation of the reliability of sub-systems is achieved through an integrated approach during complex operation of the vessel. Thirdly, the novel optimized LSTM network is constructed to predict the reliability of the subsystems while minimizing integral errors in the algorithm.\u0000 In this paper, numerical simulations are set-up using a state-of-the-art advisory decision-making tool with mock-up and real-world data to give insights into the model performance and validate it against the existing risk assessment methodologies. Furthermore, we have analyzed the efficiency and stability of the proposed model against various levels of data availability. In conclusion the prediction accuracy of the proposed model is scalable and higher when compared with other model results.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"134 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77868447","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}
Coupled aero-hydro-servo-elastic time-domain analysis is required for robust design and engineering of Floating Offshore Wind Turbines (FOWTs). For spar-type FOWTs, it is convenient to adopt a nonlinear beam finite element formulation in order to capture the coupled structural response of substructure, tower, blades and mooring lines accurately. The Distributed Potential Theory (DPT) approach applies first-order frequency-dependent added mass, radiation damping and excitation loads distributed over all submerged beam elements in the coupled time-domain simulation, as obtained from diffraction/radiation analysis. This approach therefore includes frequency-dependent diffraction effects for all wavelengths, while keeping the substructure flexible, thus enabling hydro-elastic coupling and extraction of internal sectional loads along the substructure. This paper demonstrates the use of DPT in coupled aero-hydro-servo-elastic time-domain analysis of a spar-type FOWT and illustrates the effect on tower and substructure fatigue life compared to using the classical Morison approach.
{"title":"Distributed Potential Theory and its Application for Spar-Type Floating Offshore Wind Turbines","authors":"E. Engebretsen, H. Haslum, O. Aagaard","doi":"10.1115/omae2020-18284","DOIUrl":"https://doi.org/10.1115/omae2020-18284","url":null,"abstract":"\u0000 Coupled aero-hydro-servo-elastic time-domain analysis is required for robust design and engineering of Floating Offshore Wind Turbines (FOWTs). For spar-type FOWTs, it is convenient to adopt a nonlinear beam finite element formulation in order to capture the coupled structural response of substructure, tower, blades and mooring lines accurately.\u0000 The Distributed Potential Theory (DPT) approach applies first-order frequency-dependent added mass, radiation damping and excitation loads distributed over all submerged beam elements in the coupled time-domain simulation, as obtained from diffraction/radiation analysis. This approach therefore includes frequency-dependent diffraction effects for all wavelengths, while keeping the substructure flexible, thus enabling hydro-elastic coupling and extraction of internal sectional loads along the substructure.\u0000 This paper demonstrates the use of DPT in coupled aero-hydro-servo-elastic time-domain analysis of a spar-type FOWT and illustrates the effect on tower and substructure fatigue life compared to using the classical Morison approach.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"6 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83908732","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}
Csaba Pákozdi, Sébastien Fouques, M. Thys, A. Kamath, Weizhi Wang, F. Dadmarzi, E. Bachynski, H. Bihs
As offshore wind turbines increase in size and output, the support structures are also growing. More sophisticated assessment of the hydrodynamic loads is needed, particularly for the ultimate limit state design. For higher-order phenomena related to rare steep wave events such as ringing, a better understanding of the stochastic loads is needed. As an innovative step forward to reduce the cost of extensive model tests with irregular waves, a larger number of investigations can be carried out using high-performance high-fidelity numerical simulations after an initial stochastic validation with model test data. In this paper, the open-source hydrodynamic model REEF3D::FNPF (Fully Nonlinear Potential Flow) is used to carry out three-hour long simulations with the JONSWAP spectrum in intermediate water depth conditions. Statistical properties of the free surface elevation in the numerical wave tank are validated using the available data from model tests carried out at SINTEF Ocean/NTNU. The spectral shape, significant wave height, peak period, skewness, kurtosis, and wave crest height statistics are compared. The results are analyzed and it is found that the numerical model provides reasonably good agreement with the model test data.
{"title":"Validation of Numerical Wave Tank Simulations Using REEF3D With JONSWAP Spectra in Intermediate Water Depth","authors":"Csaba Pákozdi, Sébastien Fouques, M. Thys, A. Kamath, Weizhi Wang, F. Dadmarzi, E. Bachynski, H. Bihs","doi":"10.1115/omae2020-18298","DOIUrl":"https://doi.org/10.1115/omae2020-18298","url":null,"abstract":"\u0000 As offshore wind turbines increase in size and output, the support structures are also growing. More sophisticated assessment of the hydrodynamic loads is needed, particularly for the ultimate limit state design. For higher-order phenomena related to rare steep wave events such as ringing, a better understanding of the stochastic loads is needed. As an innovative step forward to reduce the cost of extensive model tests with irregular waves, a larger number of investigations can be carried out using high-performance high-fidelity numerical simulations after an initial stochastic validation with model test data.\u0000 In this paper, the open-source hydrodynamic model REEF3D::FNPF (Fully Nonlinear Potential Flow) is used to carry out three-hour long simulations with the JONSWAP spectrum in intermediate water depth conditions. Statistical properties of the free surface elevation in the numerical wave tank are validated using the available data from model tests carried out at SINTEF Ocean/NTNU. The spectral shape, significant wave height, peak period, skewness, kurtosis, and wave crest height statistics are compared. The results are analyzed and it is found that the numerical model provides reasonably good agreement with the model test data.","PeriodicalId":23502,"journal":{"name":"Volume 1: Offshore Technology","volume":"102 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80493193","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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