In this study, numerical prediction of a ship maneuvering in calm water area with varying water depth are carried out to investigate the shallow water effect on ship’s maneuverability. The system based prediction approach is adopted by establishing a 3 degrees of freedom (DOF) mathematical model based on the modular concept. The lateral added mass and added moment of inertia are obtained by a strip theory method. Other coefficients including the longitudinal added mass, the maneuvering derivatives and the coefficients for estimating the resistance on the hull in straight moving, the propulsive force by the propeller, steering force by the rudder, and the interaction between hull-propeller-rudder are obtained by commonly used empirical and semi-empirical formulae, or directly from published data. The MOERI KVLCC2 tanker vessel is selected as the sample ship. The free running manoeuvers in deep and shallow water at different water depths are simulated and compared with available experimental results for validation. A special simulation case of stepped bottom varying from deep water to shallow water which resembles the real situation in harbor area is also carried out. The shallow water effects on ship’s maneuverability are discussed and recommendations on steering operations in shallow water are given.
{"title":"System Based Prediction of Ship’s Manoeuverability in Varying Water Depth Area","authors":"Shi He, A. Incecik, Zhiming Yuan, Paula Kellett","doi":"10.1115/omae2019-95868","DOIUrl":"https://doi.org/10.1115/omae2019-95868","url":null,"abstract":"\u0000 In this study, numerical prediction of a ship maneuvering in calm water area with varying water depth are carried out to investigate the shallow water effect on ship’s maneuverability. The system based prediction approach is adopted by establishing a 3 degrees of freedom (DOF) mathematical model based on the modular concept. The lateral added mass and added moment of inertia are obtained by a strip theory method. Other coefficients including the longitudinal added mass, the maneuvering derivatives and the coefficients for estimating the resistance on the hull in straight moving, the propulsive force by the propeller, steering force by the rudder, and the interaction between hull-propeller-rudder are obtained by commonly used empirical and semi-empirical formulae, or directly from published data. The MOERI KVLCC2 tanker vessel is selected as the sample ship. The free running manoeuvers in deep and shallow water at different water depths are simulated and compared with available experimental results for validation. A special simulation case of stepped bottom varying from deep water to shallow water which resembles the real situation in harbor area is also carried out. The shallow water effects on ship’s maneuverability are discussed and recommendations on steering operations in shallow water are given.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131456623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents a proportional-integral-derivative (PID) control strategy for navigation of a compact autonomous underwater vehicle (AUV) developed in-house. The AUV has a closed frame, neutrally buoyant, three-part modular structure made up of glass fibre composite material. Three fix position bi-directional thrusters are used for propulsion. A detailed CAD model of the AUV is developed using the modelling software SOLIDWORKS to estimate different system parameters. Hydrodynamic parameters are estimated from the ANSYS Fluent simulations of the AUV structure. Using the system parameters, a six degrees of freedom (DOF) dynamic model is developed, which is further simplified to a 4 DOF model. A 3D guidance system is developed for path planning using Line-of-Sight (LOS) strategy with way-point navigation. A closed loop PID controller is developed to follow the trajectory developed by the guidance system. The controller is simulated using MATLAB Simulink and the results are discussed.
{"title":"Development of a PID Control Strategy for a Compact Autonomous Underwater Vehicle","authors":"A. Sahoo, S. K. Dwivedy, P. Robi","doi":"10.1115/omae2019-95345","DOIUrl":"https://doi.org/10.1115/omae2019-95345","url":null,"abstract":"\u0000 This paper presents a proportional-integral-derivative (PID) control strategy for navigation of a compact autonomous underwater vehicle (AUV) developed in-house. The AUV has a closed frame, neutrally buoyant, three-part modular structure made up of glass fibre composite material. Three fix position bi-directional thrusters are used for propulsion. A detailed CAD model of the AUV is developed using the modelling software SOLIDWORKS to estimate different system parameters. Hydrodynamic parameters are estimated from the ANSYS Fluent simulations of the AUV structure. Using the system parameters, a six degrees of freedom (DOF) dynamic model is developed, which is further simplified to a 4 DOF model. A 3D guidance system is developed for path planning using Line-of-Sight (LOS) strategy with way-point navigation. A closed loop PID controller is developed to follow the trajectory developed by the guidance system. The controller is simulated using MATLAB Simulink and the results are discussed.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114840627","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}
Shanshan Tao, Jialing Song, Zhifeng Wang, Yong Liu, S. Dong
Hong Kong is impacted by tropical cyclones from April to December each year. The duration of tropical cyclones is one key factor to impact the normal operation of port or coastal engineering, and longer time interval between two tropical cyclones can provide longer operation or construction time. Therefore, it is quite important to study on the long-term laws of the duration and time intervals of tropical cyclones which attacked Hong Kong. The Hong Kong Observatory issues the warning signals to warn the public of the threat of winds associated with a tropical cyclone. Choose the tropical cyclones with warning signal No. 3 or above as the research object. A statistical study was conducted on the duration of each tropical cyclone, the time interval between every two continuous tropical cyclones during the year, and the time interval between the last cyclone of each year and the first cyclone of the following year. Poisson compound extreme value distributions are constructed to calculate the return values, which can make people know how long a tropical cyclone with a fixed duration or time interval occurs once in statistical average sense. Based on bivariate copulas, the joint probability distribution of duration and time intervals of tropical cyclones are presented. Then when the duration of a tropical cyclone is known, the conditional probability that the time interval before the next tropical cyclone occurs is greater than a certain value can be calculated. The results provide corresponding conditional probability distributions. Similarly, for the sum of the duration of tropical cyclones each year, and the time interval between the last cyclone of each year and the first cyclone of the following year, their joint probability distribution and conditional probability distributions are also presented. The conditional probability can provide the probabilistic prediction of the length of the stationary period (with no impact of tropical cyclones).
{"title":"Statistical Analysis for the Duration and Time Intervals of Tropical Cyclones, Hong Kong","authors":"Shanshan Tao, Jialing Song, Zhifeng Wang, Yong Liu, S. Dong","doi":"10.1115/omae2019-95791","DOIUrl":"https://doi.org/10.1115/omae2019-95791","url":null,"abstract":"\u0000 Hong Kong is impacted by tropical cyclones from April to December each year. The duration of tropical cyclones is one key factor to impact the normal operation of port or coastal engineering, and longer time interval between two tropical cyclones can provide longer operation or construction time. Therefore, it is quite important to study on the long-term laws of the duration and time intervals of tropical cyclones which attacked Hong Kong. The Hong Kong Observatory issues the warning signals to warn the public of the threat of winds associated with a tropical cyclone. Choose the tropical cyclones with warning signal No. 3 or above as the research object. A statistical study was conducted on the duration of each tropical cyclone, the time interval between every two continuous tropical cyclones during the year, and the time interval between the last cyclone of each year and the first cyclone of the following year. Poisson compound extreme value distributions are constructed to calculate the return values, which can make people know how long a tropical cyclone with a fixed duration or time interval occurs once in statistical average sense. Based on bivariate copulas, the joint probability distribution of duration and time intervals of tropical cyclones are presented. Then when the duration of a tropical cyclone is known, the conditional probability that the time interval before the next tropical cyclone occurs is greater than a certain value can be calculated. The results provide corresponding conditional probability distributions. Similarly, for the sum of the duration of tropical cyclones each year, and the time interval between the last cyclone of each year and the first cyclone of the following year, their joint probability distribution and conditional probability distributions are also presented. The conditional probability can provide the probabilistic prediction of the length of the stationary period (with no impact of tropical cyclones).","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126730786","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 higher-order boundary element method (HOBEM) using three dimensional translating-pulsating (3DTP) Green’s function is developed and applied to calculate the hydrodynamic forces on vessels advancing in waves in the present study. In this HOBEM, geometrical and physical variables are expressed by the shape functions defined by four nodal values; and Green’s function in Havelock form is adopted in the numerical implementation. The Gauss-Legendre quadrature is first adopted for the integral of 3DTP Green’s function over panel. However, due to the highly oscillating characteristic of Green’s function near the free surface, numerical instability is observed in the final results. To avoid this unstable problem, an improved algorithm for the integral of Green’s function is proposed. We discretize the panel into a series of horizontal line segments and derive an integral expression of 3DTP Green’s function distributing on the line segment. By accumulating a series of 3DTP Green’s function distributing on various horizontal line segments, the panel integral of Green’s function is obtained. To validate the performance of the improved algorithm, hydrodynamic forces on a mathematical ship model Wigley III are first calculated. The results are compared with those of the former algorithm and experimental data, which shows that improved algorithm is more stable and accurate. The present HOBEM is then applied to analyse the radiation and diffraction problems for a Series 60 hull and a catamaran hull. The computed hydrodynamic coefficients and wave forces are found to be in good agreement with experimental data.
{"title":"Computations of Hydrodynamic Forces on Vessels Advancing in Waves by Four-Node Higher-Order Boundary Element Method","authors":"Yuntao Yang, R. Zhu, Shan Huang","doi":"10.1115/omae2019-96792","DOIUrl":"https://doi.org/10.1115/omae2019-96792","url":null,"abstract":"\u0000 A higher-order boundary element method (HOBEM) using three dimensional translating-pulsating (3DTP) Green’s function is developed and applied to calculate the hydrodynamic forces on vessels advancing in waves in the present study. In this HOBEM, geometrical and physical variables are expressed by the shape functions defined by four nodal values; and Green’s function in Havelock form is adopted in the numerical implementation. The Gauss-Legendre quadrature is first adopted for the integral of 3DTP Green’s function over panel. However, due to the highly oscillating characteristic of Green’s function near the free surface, numerical instability is observed in the final results. To avoid this unstable problem, an improved algorithm for the integral of Green’s function is proposed. We discretize the panel into a series of horizontal line segments and derive an integral expression of 3DTP Green’s function distributing on the line segment. By accumulating a series of 3DTP Green’s function distributing on various horizontal line segments, the panel integral of Green’s function is obtained. To validate the performance of the improved algorithm, hydrodynamic forces on a mathematical ship model Wigley III are first calculated. The results are compared with those of the former algorithm and experimental data, which shows that improved algorithm is more stable and accurate. The present HOBEM is then applied to analyse the radiation and diffraction problems for a Series 60 hull and a catamaran hull. The computed hydrodynamic coefficients and wave forces are found to be in good agreement with experimental data.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"158 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132793111","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 experimental measurements presented here describe the major features of the loads exerted by internal solitary waves (ISWs) on columns and caissons of a semi-submersible platform in a two-layer fluid system. Particular attention is paid on the forces acted on the platform under different layer thickness ratio. By use of the dynamometer for forces of three degree of freedom (DOF), the wave forces exerted by the ISWs on the columns and caissons of the model are measured quantificationally, so the variations of forces with ISW’s amplitude and upper layer depth are derived. Comparisons are made between the experimental results and calculations based on the modified Morison equation and pressure integral method. The calculated results are well consistent with the measurements, so the method is capable of providing satisfactory predictions on the forces. Besides, the results show that the wave height has a considerable influence on the wave loads produced by the ISWs, and the forces varies with the different locations of the interface between the upper and lower layer.
{"title":"Experimental Study of Wave Loading by Internal Solitary Waves on a Semi-Submersible Platform","authors":"Jingjing Zhang, Ke Chen, Y. You, Xinshu Zhang","doi":"10.1115/omae2019-95891","DOIUrl":"https://doi.org/10.1115/omae2019-95891","url":null,"abstract":"\u0000 The experimental measurements presented here describe the major features of the loads exerted by internal solitary waves (ISWs) on columns and caissons of a semi-submersible platform in a two-layer fluid system. Particular attention is paid on the forces acted on the platform under different layer thickness ratio. By use of the dynamometer for forces of three degree of freedom (DOF), the wave forces exerted by the ISWs on the columns and caissons of the model are measured quantificationally, so the variations of forces with ISW’s amplitude and upper layer depth are derived. Comparisons are made between the experimental results and calculations based on the modified Morison equation and pressure integral method. The calculated results are well consistent with the measurements, so the method is capable of providing satisfactory predictions on the forces. Besides, the results show that the wave height has a considerable influence on the wave loads produced by the ISWs, and the forces varies with the different locations of the interface between the upper and lower layer.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133160626","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. Immas, Mohsen Saadat, J. Navarro, Matthew C. Drake, Julie Shen, Mohammad-Reza Alam
We present a new method for underwater wireless communication with high bandwidth and over long distance. A swarm of Autonomous Underwater Vehicles (AUVs) is used to relay an optical signal between two points at any distance. Each vehicle is equipped with multiple attitude stabilization systems to reach the required pointing and tracking accuracy for optical communication. This technology would enable fast and efficient underwater exploration which is highly needed as only 5% of the world’s oceans have been explored so far. We carried out an experimental proof of concept to show that it is possible to relay an optical signal underwater between two points using a swarm of AUVs. The experiment took place in a 2m deep water tank. We modified and controlled two submarine models to reflect the laser beam stemming from a laser pointer at the bottom of the tank to the desired location. To know their positions, we developed an image processing technique which required the setup of a RF communication link at 315Mhz between the computers processing the camera’s videos and the units.
{"title":"High-Bandwidth Underwater Wireless Communication Using a Swarm of Autonomous Underwater Vehicles","authors":"A. Immas, Mohsen Saadat, J. Navarro, Matthew C. Drake, Julie Shen, Mohammad-Reza Alam","doi":"10.1115/omae2019-96270","DOIUrl":"https://doi.org/10.1115/omae2019-96270","url":null,"abstract":"\u0000 We present a new method for underwater wireless communication with high bandwidth and over long distance. A swarm of Autonomous Underwater Vehicles (AUVs) is used to relay an optical signal between two points at any distance. Each vehicle is equipped with multiple attitude stabilization systems to reach the required pointing and tracking accuracy for optical communication. This technology would enable fast and efficient underwater exploration which is highly needed as only 5% of the world’s oceans have been explored so far. We carried out an experimental proof of concept to show that it is possible to relay an optical signal underwater between two points using a swarm of AUVs. The experiment took place in a 2m deep water tank. We modified and controlled two submarine models to reflect the laser beam stemming from a laser pointer at the bottom of the tank to the desired location. To know their positions, we developed an image processing technique which required the setup of a RF communication link at 315Mhz between the computers processing the camera’s videos and the units.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"36 5","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133426059","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}
Wenhua Wu, Lyu Baicheng, Yao Ji, Q. Yue, Zhang Yantao, Xinglin Guo
The soft yoke single-point mooring (SYMS) system is the main mooring approach for the floating production storage and offloading (FPSO) unit. As a typical multi-rigid-body system, a SYMS consists of the single-point turret, yoke, mooring legs, and mooring support. It releases the rotational degrees of freedom of an FPSO through the combined effects of multiple joint structures, so as to deliver the weather-vane effect of the FPSO. In this paper, a multi-body dynamics model of the soft yoke mooring system was established. To deal with the difficult integration in the process of solving differential-algebraic equations, a symplectic numerical integration method was proposed on the basis of the Zu Chongzhi method. The proposed solution format had simple symplectic property automatically satisfying the Hamilton system, as well as a high accuracy in solving nonlinear systems. The measured data of the FPSO’s six degrees of freedom (6DoF) under two different sea conditions were selected, and the mooring restoring force of the SYMS was calculated. The calculated results showed that the symplectic solution method could the actual stress state of the structures with more obvious dynamic characteristics. Furthermore, the displacement and stress state of the single-body structures, such as the mooring legs and yoke, and the analysis result could comprehensively evaluate the overall working state of the SYMS.
{"title":"Study on the Multi-Body Dynamic Characteristics of FPSO Soft Yoke Mooring System Based on Symplectic Algorithm","authors":"Wenhua Wu, Lyu Baicheng, Yao Ji, Q. Yue, Zhang Yantao, Xinglin Guo","doi":"10.1115/omae2019-96464","DOIUrl":"https://doi.org/10.1115/omae2019-96464","url":null,"abstract":"\u0000 The soft yoke single-point mooring (SYMS) system is the main mooring approach for the floating production storage and offloading (FPSO) unit. As a typical multi-rigid-body system, a SYMS consists of the single-point turret, yoke, mooring legs, and mooring support. It releases the rotational degrees of freedom of an FPSO through the combined effects of multiple joint structures, so as to deliver the weather-vane effect of the FPSO. In this paper, a multi-body dynamics model of the soft yoke mooring system was established. To deal with the difficult integration in the process of solving differential-algebraic equations, a symplectic numerical integration method was proposed on the basis of the Zu Chongzhi method. The proposed solution format had simple symplectic property automatically satisfying the Hamilton system, as well as a high accuracy in solving nonlinear systems. The measured data of the FPSO’s six degrees of freedom (6DoF) under two different sea conditions were selected, and the mooring restoring force of the SYMS was calculated. The calculated results showed that the symplectic solution method could the actual stress state of the structures with more obvious dynamic characteristics. Furthermore, the displacement and stress state of the single-body structures, such as the mooring legs and yoke, and the analysis result could comprehensively evaluate the overall working state of the SYMS.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"208 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127034155","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 development of component models to populate a proposed OpenModelica standard library for the ocean engineering domain is described through the process of modelling the response of catenary-moored wave-energy converters in the ‘free-to-use’ OpenModelica simulation environment and its associated OMEdit graphical user interface. A wave energy conversion concept is presented, followed by the implementation of Modelica component models and functions to simulate wave, current, and mooring loads on a cylindrical floating object. The irregular sea surface is specified using the Pierson-Moskowitz spectrum and the heave force on the buoy is determined based on the Froude-Krylov formulation. Mooring load formulation is based on the catenary theory. Combined wave and current loads on the buoy and on the mooring chain are arrived at using the Morison equation. The results are verified with the commercial software Orcaflex, and the preliminary OceanEngineering library is made available for download. The integrated simulation of the multiphysical wave energy buoy system is then carried out to determine the energy harvest potential, and results discussed. An alternative design is then suggested and simulated to demonstrate the advantages of using the component-based approach.
{"title":"Towards the Development of an Ocean Engineering Library for OpenModelica","authors":"Savin Viswanathan, C. Holden","doi":"10.1115/omae2019-95054","DOIUrl":"https://doi.org/10.1115/omae2019-95054","url":null,"abstract":"\u0000 The development of component models to populate a proposed OpenModelica standard library for the ocean engineering domain is described through the process of modelling the response of catenary-moored wave-energy converters in the ‘free-to-use’ OpenModelica simulation environment and its associated OMEdit graphical user interface. A wave energy conversion concept is presented, followed by the implementation of Modelica component models and functions to simulate wave, current, and mooring loads on a cylindrical floating object. The irregular sea surface is specified using the Pierson-Moskowitz spectrum and the heave force on the buoy is determined based on the Froude-Krylov formulation. Mooring load formulation is based on the catenary theory. Combined wave and current loads on the buoy and on the mooring chain are arrived at using the Morison equation. The results are verified with the commercial software Orcaflex, and the preliminary OceanEngineering library is made available for download. The integrated simulation of the multiphysical wave energy buoy system is then carried out to determine the energy harvest potential, and results discussed. An alternative design is then suggested and simulated to demonstrate the advantages of using the component-based approach.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116558180","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 is concerned with a methodology for defining metocean criteria for the analysis of subsea pipelines. The approach that has been developed incorporates the statistical dependence between wave and current loading. The method achieves this through a combination of the application of the conditional extreme value model of Heffernan and Tawn (2004) and clustering algorithms. This is particularly important in regions where the currents are largely wind driven as there can be a strong correlation between the two. The results can be used to assess fatigue damage from vortex-induced-vibrations and wave loading. The same model can be used to derive deterministic design events. The method is applied to a pipeline in the Caspian Sea. The results are compared to models that assume either independence or a perfect correlation between waves and currents. It is shown that simpler models that do not accurately model the dependence between the waves and the currents can provide estimates of fatigue damage that are an order of magnitude too high or too low.
{"title":"Metocean Criteria for the Fatigue Analysis of Subsea Pipelines","authors":"R. Gibson, M. Christou","doi":"10.1115/omae2019-96363","DOIUrl":"https://doi.org/10.1115/omae2019-96363","url":null,"abstract":"\u0000 This paper is concerned with a methodology for defining metocean criteria for the analysis of subsea pipelines. The approach that has been developed incorporates the statistical dependence between wave and current loading. The method achieves this through a combination of the application of the conditional extreme value model of Heffernan and Tawn (2004) and clustering algorithms. This is particularly important in regions where the currents are largely wind driven as there can be a strong correlation between the two. The results can be used to assess fatigue damage from vortex-induced-vibrations and wave loading. The same model can be used to derive deterministic design events. The method is applied to a pipeline in the Caspian Sea. The results are compared to models that assume either independence or a perfect correlation between waves and currents. It is shown that simpler models that do not accurately model the dependence between the waves and the currents can provide estimates of fatigue damage that are an order of magnitude too high or too low.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"1684 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129374911","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. Kristoffersen, H. Bredmose, C. Georgakis, L. Tao
The spatial localized influence of wind on wave induced load on a flexible cylinder has been assessed throughout a test series conducted in a wave-wind-current flume at Newcastle University. The tests are motivated from other experimental and numerical investigations showing air flow separation on the leeward side of steep waves that can lead to added wind energy transfer, which could suggest an increase in the impulsive wave loading. The waves are generated as focused waves, resulting in a plunging breaker, leading to an impulsive wave load. The test model was equipped with a load cell measuring the connection load. Due to the flexibility of the cylinder, the measured force response shows oscillations and dynamic amplification of the load. The maxima of the force responses are compared for the tests with and without wind. Another measure for comparison is the local and short-lived impulse, which is responsible for the amplification. This impulsive load is estimated from the load cell and acceleration measurements. For the tests in this study, the introduction of wind over the breaking waves does for some cases lead to a slight increase in the peak of the impulsive load and thereby the load response, although large scattering is present. Further investigations are needed to verify this effect. Some differences in the time series of the free surface elevation are observed when wind is present, but the maximum of the surface elevation does not change notably, and the slope is only minimally changed, meaning that this should not give basis for the differences in the loads.
{"title":"Preliminary Experimental Study on the Influence of the Local Wind Field on Forces From Breaking Waves on a Circular Cylinder","authors":"J. Kristoffersen, H. Bredmose, C. Georgakis, L. Tao","doi":"10.1115/omae2019-95179","DOIUrl":"https://doi.org/10.1115/omae2019-95179","url":null,"abstract":"\u0000 The spatial localized influence of wind on wave induced load on a flexible cylinder has been assessed throughout a test series conducted in a wave-wind-current flume at Newcastle University. The tests are motivated from other experimental and numerical investigations showing air flow separation on the leeward side of steep waves that can lead to added wind energy transfer, which could suggest an increase in the impulsive wave loading. The waves are generated as focused waves, resulting in a plunging breaker, leading to an impulsive wave load. The test model was equipped with a load cell measuring the connection load. Due to the flexibility of the cylinder, the measured force response shows oscillations and dynamic amplification of the load. The maxima of the force responses are compared for the tests with and without wind. Another measure for comparison is the local and short-lived impulse, which is responsible for the amplification. This impulsive load is estimated from the load cell and acceleration measurements. For the tests in this study, the introduction of wind over the breaking waves does for some cases lead to a slight increase in the peak of the impulsive load and thereby the load response, although large scattering is present. Further investigations are needed to verify this effect. Some differences in the time series of the free surface elevation are observed when wind is present, but the maximum of the surface elevation does not change notably, and the slope is only minimally changed, meaning that this should not give basis for the differences in the loads.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128948001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：