The present study investigates the effect of moorings on hybrid floating breakwaters of different configurations based on potential flow theory.The mooring analysis is performed for the regular wave incidence for five...The present study investigates the effect of moorings on hybrid floating breakwaters of different configurations based on potential flow theory.The mooring analysis is performed for the regular wave incidence for five different shapes of hybrid floating breakwaters,namely,rectangular,box,H,Π,and trapezoidal,integrated with a single J-shaped oscillating water column(OWC).The mooring lines are considered to be nonlinear catenary sections that are analysed for open mooring and cross mooring configuration.The hydrodynamic analysis is performed using Ansys-AQWA and the effectiveness of the moorings is evaluated in terms of the mooring line tension and the floating structure’s motion response,and comparisons are made for the influence of different mooring configurations and the implications of changing the design of the hybrid floating breakwater.The regular gravity wave frequency range is taken into consideration and the hydrodynamic properties are reported for the entire range of regular wave frequencies.Additionally,for a few chosen wave frequencies the analysis of structural forces and moment is performed for long and short waves.The study suggests that a hydrodynamically stable hybrid floating structure integrated with an oscillating water column can provide good and effective wave energy conversion and wave attenuation.Thus,with the help of the findings of the present study,the researchers will be able to examine the stability of hybrid floating breakwater structures under the action of regular waves with normal incidence.展开更多
Mooring cable tension is a crucial parameter for evaluating the safety and reliability of a floating platform mooring system.The real-time mooring tension in an actual marine environment has always been essential data...Mooring cable tension is a crucial parameter for evaluating the safety and reliability of a floating platform mooring system.The real-time mooring tension in an actual marine environment has always been essential data that mooring system designers aim to acquire.To address the need for long-term continuous monitoring of mooring tension in deep-sea marine environments,this paper presents a mooring cable tension monitoring method based on the principle of direct mechanical measurement.The developed tension monitoring sensors were installed and applied in the mooring system of the"Yongle"scientific experimental platform.Over the course of one year,a substantial amount of in-situ tension monitoring data was obtained.Under wave heights of up to 1.24 m,the mooring tension on the floating platform reached 16.5 tons.Through frequency domain and time domain analysis,the spectral characteristics of mooring tension,including waveinduced force,slow drift force,and mooring cable elastic restoring force,were determined.The mooring cable elastic restoring force frequency was approximately half of that of the wave signal.Due to the characteristics of the hinge connection structure of the dual module floating platform,under some specific working conditions the wave-induced force was the maximum of the three different frequency forces,and restoring force was the smallest.展开更多
Floating breakwaters(FBs)are commonly employed for the protection of coastal installations.In this work,a convextype floating breakwater(FB)is proposed,and its hydrodynamic characteristics are studied through systemat...Floating breakwaters(FBs)are commonly employed for the protection of coastal installations.In this work,a convextype floating breakwater(FB)is proposed,and its hydrodynamic characteristics are studied through systematic laboratory experiments.Two different deck widths and two different mooring systems are set in the experiment.The transmission coefficients,reflection coefficients,motion responses and mooring forces of convex-type FBs are obtained in experiments.The influences of the deck width and mooring system on the hydrodynamic characteristics of the proposed FB are analyzed and compared.The experimental results show that the reflection coefficient and mooring force of the convex-type FB with a cross-mooring system are significantly larger than those of the convextype FB with a parallel-mooring system.A convex-type FB with a larger deck width has a higher reflection coefficient.The convex-type FBs with cross-and parallel-mooring systems have similar surge and heave motions,but the cross-mooring results in small roll motion.In addition,reliable prediction formulas for the transmission coefficient of convex-type FBs with different mooring systems have been developed,which are important for engineering design.展开更多
In the process of developing oil and gas resources in the Arctic,the impact of icebergs can pose a considerable threat to the structural safety of semi-submersible mooring platforms in ice regions.On the basis of the ...In the process of developing oil and gas resources in the Arctic,the impact of icebergs can pose a considerable threat to the structural safety of semi-submersible mooring platforms in ice regions.On the basis of the arbitrary Lagrangian Eulerian(ALE)algorithm,a numerical model for the interaction between an iceberg and a semi-submersible mooring platform is built in this work.First,a mooring system with a link element is designed and validated.An ice material model for the target iceberg is built and validated.A numerical model for the interaction between an iceberg and a semi-submersible mooring platform is then built.A parametric study(cable angle,tension angle and number of cables)is carried out to study the performance of the mooring system.The collision process between the semi-submersible mooring platform and the iceberg in the polar marine environment can be predicted by the present numerical model,and then the optimal mooring arrangement scheme can be obtained.The research results in this work can provide a reference for the design of mooring systems.展开更多
This study employs the Smoothed Particle Hydrodynamics(SPH)method to develop a computational fluid dynamics(CFD)model for analyzing the interaction between rogue waves and mooring systems.Four floating body configurat...This study employs the Smoothed Particle Hydrodynamics(SPH)method to develop a computational fluid dynamics(CFD)model for analyzing the interaction between rogue waves and mooring systems.Four floating body configurations are investigated:(1)dual rectangular prisms,(2)rectangular prism–sphere composites,(3)sphere–rectangular prism composites,and(4)dual spheres.These configurations are systematically evaluated under varying mooring conditions to assess their hydrodynamic performance and wave attenuation capabilities.The model accurately captures the complex fluid–structure interaction dynamics between moored floating breakwaters and incident wave fields.Among the configurations,the dual rectangular prism system demonstrates superior performance in both wave dissipation and mooring force reduction.Under conditions involving dual wave makers,the influence of floating body shape and number on wave height is found to be minimal.However,dual-body arrangements consistently outperform single-body setups in terms of both energy dissipation and structural stability.From a cost-efficiency perspective,the configuration comprising two rectangular prisms connected via a single mooring system offers significant advantages in material usage and deployment feasibility.展开更多
With the development of marine resources,a dual-platform joint operation has been paid more attention.In this paper,the mooring layout space and relative motion limitation of the dual-platform berthing operation were ...With the development of marine resources,a dual-platform joint operation has been paid more attention.In this paper,the mooring layout space and relative motion limitation of the dual-platform berthing operation were fully considered.A new hybrid mooring system with“X+buoy”combination was designed based on the characteristics of catenary and tension mooring.The hydrodynamic characteristics of the new mooring system were analyzed by combining numerical simulation with model experiment.Under the regular and freak waves with different wave heights and periods,the time-domain full-coupling analysis method was used to study the hydrodynamic characteristics of the mooring system.It can be found that the arrangement of dual-platform under 0◦wave direction is optimal,and the“X+buoy”combined mooring system designed in this paper has a good follow-up between the two platforms under different regular and freak waves.The relative motion response between the two platforms can be effectively controlled,and finally the positioning of the dual-platform joint operation is realized.Research results of this paper provide a theoretical basis and technical support for the hydrodynamic performance analysis and safety assessment of deep-sea offshore platforms in China.展开更多
Utilizing computational fluid dynamics(CFD),this study analyzes the relative pitching motion amplitude and conversion efficiency of the parallelogram raft wave energy converter(R-WEC)under wave current conditions,exam...Utilizing computational fluid dynamics(CFD),this study analyzes the relative pitching motion amplitude and conversion efficiency of the parallelogram raft wave energy converter(R-WEC)under wave current conditions,examining the effects of power take-off(PTO)parameters,wave parameters,and flow velocity on R-WEC hydrodynamic performance.The research includes an analysis of a single point mooring system to determine optimal mooring conditions.Through comparative analysis of energy conversion efficiency across 10 single mooring modes and nine double-mooring modes,the study evaluates their impact on the R-WEC.Findings demonstrate that flow velocity adversely affects wave energy capture.Energy conversion efficiency exhibits an initial increase followed by a decrease as damping coefficient or wave frequency coefficient increases.An optimal anchor chain unit mass coefficient exists that maximizes R-WEC energy conversion efficiency.The dual mooring system demonstrates marginally enhanced energy conversion efficiency compared with single mooring,with specific impacts on R-wave energy converters(WECs)documented.These findings provide valuable reference data for R-WEC design optimization and operational strategies to enhance conversion efficiency.展开更多
The dynamic response of moored crane-ship is studied. Governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange’s equations. The boom i...The dynamic response of moored crane-ship is studied. Governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange’s equations. The boom is modeled based on finite element method, while the payload is modeled as a planar pendulum of point mass. The dynamic response was studied using numerical method. The calculation results show that the large-amplitude responses occur at wave periods near the natural period of the payload. Load swing angle is smaller for crane-ship with flexible boom, in comparison with rigid boom. The ship surge mo- tions have large vibrations for crane-ship with flexible boom, which were not observed for a rigid boom. The analysis identifies the significance of key parameters and reveals how the system design can be adjusted to avoid critical conditions.展开更多
Much attention should be paid to a large FPSO moored permanently in an oil field with water depth of only about 20 m, since shallow water effects on the hydrodynamics may bring about collision and damage. A 160kDWT FP...Much attention should be paid to a large FPSO moored permanently in an oil field with water depth of only about 20 m, since shallow water effects on the hydrodynamics may bring about collision and damage. A 160kDWT FPSO with a permanent soft yoke mooring system is investigated with various shallow water depths and focuses are the low frequency surge motion and mooring load. Computation for the FPSO system is made based on linear 3-D potential fluid theory and time-domain numerical simulation method. Corresponding model test is carried out in the ocean engineering basin of Shanghai Jiao Tong University. It is shown that, in the surge natural period, low frequency surge motion and mooring force increase remarkably with the decrease of water depth. Especially, the smaller the ratio of water depth and draught is, the quicker the increase is. The shallow water effects should be taken into account carefully for determining the design load of a single point mooring system.展开更多
There is a need to obtain the hydrologic data including ocean current, wave, temperature and so on in the South China Sea. A new profiling instrument which does not suffer from the damage due to nature forces or incid...There is a need to obtain the hydrologic data including ocean current, wave, temperature and so on in the South China Sea. A new profiling instrument which does not suffer from the damage due to nature forces or incidents caused by passing ships, is under development to acquire data from this area. This device is based on a taut single point mid-water mooring system. It incorporates a small, instrumented vertically profiling float attached via an electromechanical cable to a winch integral with the main subsurface flotation. On a pre-set schedule, the instrument float with sensors is winched up to the surface if there is no ship passing by, which is defined by an on-board miniature sonar. And it can be. inunediately winched down to a certain depth if the sonar sensor finds something is coming. Since, because of logistics, the area can only be visited once for a long time and a minimum of 10 times per day profiles are desired, energy demands are severe. To respond to these concerns, the system has been designed to conserve a substantial portion of the potential energy lost during the ascent phase of each profile and subsequently use this energy to pull the instrument down. Compared with the previous single-point layered measuring mode, it is advanced and economical. At last the paper introduces the test in the South China Sea.展开更多
A three-dimensional high-order panel method based on non-uniform rational B-spline(NURBS) is developed for predicting the hydrodynamic interaction forces on a moored ship induced by a passing ship in shallow water. An...A three-dimensional high-order panel method based on non-uniform rational B-spline(NURBS) is developed for predicting the hydrodynamic interaction forces on a moored ship induced by a passing ship in shallow water. An NURBS surface is used to precisely represent the hull geometry. Velocity potential on the hull surface is described by B-spline after the source density distribution on the boundary surface is determined. A collocation approach is applied to the boundary integral equation discretization. Under the assumption of low passing speed, the effect of free surface elevation is neglected in the numerical calculation, and infinite image method is used to deal with the finite water depth effect. The time stepping method is used to solve the velocity potential at each time step. Detailed convergence study with respect to time step, panel size and Green function is undertaken. The present results of hydrodynamic forces are compared with those obtained by slender-body theory to show the validity of the proposed numerical method. Calculations are conducted for different water depths and lateral distances between ships, and the detail results are presented to demonstrate the effects of these factors.展开更多
A three-dimensional method of calculating wave loads of turret moored FPSO (Flo ating Production Storage and Offloading) tankers is presented. The linearized restoring forces acting on the ship hull by the mooring sys...A three-dimensional method of calculating wave loads of turret moored FPSO (Flo ating Production Storage and Offloading) tankers is presented. The linearized restoring forces acting on the ship hull by the mooring system are calculated according to the catenary theory, which are expressed as the function of linear stiffness coefficients and the displacements of the upper ends of mooring chains. The hydrodynamic coefficients of the ship are calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for ships with a low forward speed. The equations of ship motions are established with the effect of the restoring forces from the mooring system included as linear stiffness coefficients. The equations of motions are solved in frequency domain, and the responses of wave-induced motions and loads on the ship can be obtained. A computer pro gram based on this method has been developed,and some calculation examples are illustrated. Analysis results show that the method can give satisfying prediction of wave loads.展开更多
Moored structures are suitable for operations in ice-covered regions owing to their security and efficiency.This paper aims to present a new method for simulating the ice load and mooring force on the moored structure...Moored structures are suitable for operations in ice-covered regions owing to their security and efficiency.This paper aims to present a new method for simulating the ice load and mooring force on the moored structure during ice-structure interaction with a spherical Discrete Element Method(DEM).In this method,the level ice and mooring lines consist of bonded sphere elements arranged in different patterns.The level ice model has been widely validated in simulation of the ice load of fixed structures.In the mooring line simulation,a string of spherical elements was jointed with the parallel bond model to simulate the chains or cable structure.The accuracy of the mooring line model was proved by comparing the numerical results with the nonlinear FEM results and model towing experiment results.The motion of the structure was calculated in the quaternion method,considering the ice load,mooring force,and hydrodynamic force.The hydrodynamic force comprised wave-making damping,current drag,and buoyancy force.Based on the proposed model,the interaction of a semi-submersible structure with level ice was simulated,and the effect of ice thickness on the ice load was analyzed.The numerical results show that the DEM method is suitable to simulate the ice load and mooring force on moored floating structures.展开更多
Hydrodynamic performance of an ultra deep turret-moored Floating Liquefied Natural Gas （FLNG） system is investigated. Hydrodynamic modeling of a turret-moored FLNG system, in consideration of the coupling effects of...Hydrodynamic performance of an ultra deep turret-moored Floating Liquefied Natural Gas （FLNG） system is investigated. Hydrodynamic modeling of a turret-moored FLNG system, in consideration of the coupling effects of the vessel and its mooring lines, has been addressed in details. Based on the boundary element method, a 3-D panel model of the FLNG vessel and the related free water surface model are established, and the first-order and second-order mean-drift wave loads and other hydrodynamic coefficients are calculated. A systematic model test program consisting of the white noise wave test, offset test and irregular wave test combined with current and wind, etc. is performed to verify the numerical model. Owing to the depth limit of the water basin, the model test is carried out for the hydrodynamics of the FLNG coupled with only the truncated mooring system. The numerical simulation model features well the hydrodynamic performance of the FLNG system obtained from the model tests. The hydrodynamic characteristics presented in both the numerical simulations and the physical model tests would serve as the guidance for the ongoing project of FLNG system.展开更多
In this paper, the motions are studied of a multi-body which is composed of two plates hinged together and moored by eight mooring lines in regular waves. The experimental results are compared with computational resul...In this paper, the motions are studied of a multi-body which is composed of two plates hinged together and moored by eight mooring lines in regular waves. The experimental results are compared with computational results. The linear potential theory and the perturbation method are combined to study this complicated system. The former is used to calculate the wave forces acting on the plates and the motion responses of them, while the latter is used to describe the dynamic character of the eight mooring lines coupled with the two hinged plates. Some response results of each plate are presented and comparisons between calculated results and experimental data are given. All the calculations are confined to regular beam waves.展开更多
With the floating structures pushing their activities to the ultra-deep water, model tests have presented a challenge due to the limitation of the existing wave basins. Therefore, the concept of truncated mooring syst...With the floating structures pushing their activities to the ultra-deep water, model tests have presented a challenge due to the limitation of the existing wave basins. Therefore, the concept of truncated mooring system is implemented to replace the full depth mooring system in the model tests, which aims to have the same dynamic responses as the full depth system. The truncated mooring system plays such a significant role that extra attention should be paid to the mooring systems with large truncation factor. Three different types of large truncation factor mooring system are being employed in the simulations, including the homogenously truncated mooring system, non-homogenously truncated mooring system and simplified truncated mooring system. A catenary moored semi-submersible operating at 1000 m water depth is presented. In addition, truncated mooring systems are proposed at the truncated water depth of 200 m. In order to explore the applicability of these truncated mooring systems, numerical simulations of the platform’s surge free decay interacting with three different styles of truncated mooring systems are studied in calm water. Furthermore, the mooring-induced damping of the truncated mooring systems is simulated in the regular wave. Finally, the platform motion responses and mooring line dynamics are simulated in irregular wave. All these simulations are implemented by employing full time domain coupled dynamic analysis, and the results are compared with those of the full depth simulations in the same cases. The results show that the mooring-induced damping plays a significant role in platform motion responses, and all truncated mooring systems are suitable for model tests with appropriate truncated mooring line diameters. However, a large diameter is needed for simplified truncated mooring lines. The suggestions are given to the selection of truncated mooring system for different situations as well as to the truncated mooring design criteria.展开更多
In the paper, a comprehensive numerical study on the moored system is performed in time domain. The moored system, which is composed of the floating body sub system and the mooring line sub system, is calculated as ...In the paper, a comprehensive numerical study on the moored system is performed in time domain. The moored system, which is composed of the floating body sub system and the mooring line sub system, is calculated as a whole system by coupling. A time domain method is applied to the analysis of the mooring line sub system, and at the same time, an indirect time domain method translated from frequency domain to time domain is developed to calculate the floating body sub system. In the end, an FPSO vessel is calculated as a numerical example by the present method. A comparison of the result of the model test and that of the numerical method indicates that the present method is exact and effective.展开更多
文摘The present study investigates the effect of moorings on hybrid floating breakwaters of different configurations based on potential flow theory.The mooring analysis is performed for the regular wave incidence for five different shapes of hybrid floating breakwaters,namely,rectangular,box,H,Π,and trapezoidal,integrated with a single J-shaped oscillating water column(OWC).The mooring lines are considered to be nonlinear catenary sections that are analysed for open mooring and cross mooring configuration.The hydrodynamic analysis is performed using Ansys-AQWA and the effectiveness of the moorings is evaluated in terms of the mooring line tension and the floating structure’s motion response,and comparisons are made for the influence of different mooring configurations and the implications of changing the design of the hybrid floating breakwater.The regular gravity wave frequency range is taken into consideration and the hydrodynamic properties are reported for the entire range of regular wave frequencies.Additionally,for a few chosen wave frequencies the analysis of structural forces and moment is performed for long and short waves.The study suggests that a hydrodynamically stable hybrid floating structure integrated with an oscillating water column can provide good and effective wave energy conversion and wave attenuation.Thus,with the help of the findings of the present study,the researchers will be able to examine the stability of hybrid floating breakwater structures under the action of regular waves with normal incidence.
文摘Mooring cable tension is a crucial parameter for evaluating the safety and reliability of a floating platform mooring system.The real-time mooring tension in an actual marine environment has always been essential data that mooring system designers aim to acquire.To address the need for long-term continuous monitoring of mooring tension in deep-sea marine environments,this paper presents a mooring cable tension monitoring method based on the principle of direct mechanical measurement.The developed tension monitoring sensors were installed and applied in the mooring system of the"Yongle"scientific experimental platform.Over the course of one year,a substantial amount of in-situ tension monitoring data was obtained.Under wave heights of up to 1.24 m,the mooring tension on the floating platform reached 16.5 tons.Through frequency domain and time domain analysis,the spectral characteristics of mooring tension,including waveinduced force,slow drift force,and mooring cable elastic restoring force,were determined.The mooring cable elastic restoring force frequency was approximately half of that of the wave signal.Due to the characteristics of the hinge connection structure of the dual module floating platform,under some specific working conditions the wave-induced force was the maximum of the three different frequency forces,and restoring force was the smallest.
基金financially supported by the National Natural Science Foundation of China(Grant No.52088102)New Cornerstone Science Foundation through the XPLORER PRIZE.
文摘Floating breakwaters(FBs)are commonly employed for the protection of coastal installations.In this work,a convextype floating breakwater(FB)is proposed,and its hydrodynamic characteristics are studied through systematic laboratory experiments.Two different deck widths and two different mooring systems are set in the experiment.The transmission coefficients,reflection coefficients,motion responses and mooring forces of convex-type FBs are obtained in experiments.The influences of the deck width and mooring system on the hydrodynamic characteristics of the proposed FB are analyzed and compared.The experimental results show that the reflection coefficient and mooring force of the convex-type FB with a cross-mooring system are significantly larger than those of the convextype FB with a parallel-mooring system.A convex-type FB with a larger deck width has a higher reflection coefficient.The convex-type FBs with cross-and parallel-mooring systems have similar surge and heave motions,but the cross-mooring results in small roll motion.In addition,reliable prediction formulas for the transmission coefficient of convex-type FBs with different mooring systems have been developed,which are important for engineering design.
基金financially supported by the Open Project Program of Shandong Marine Aerospace Equipment Technological Innovation Center,Ludong University(Grant Nos.MAETIC202209 and MAETIC202201)Shandong Provincial Natural Science Foundation(Grant No.ZR2022QE092)+2 种基金China Postdoctoral Science Foundation(Grant No.2023M730829)Open Fund of the State Key Laboratory of Industrial Equipment Structural Analysis(Grant No.GZ23109)the National Natural Science Foundation of China(Grant Nos.52001284 and 52192694).
文摘In the process of developing oil and gas resources in the Arctic,the impact of icebergs can pose a considerable threat to the structural safety of semi-submersible mooring platforms in ice regions.On the basis of the arbitrary Lagrangian Eulerian(ALE)algorithm,a numerical model for the interaction between an iceberg and a semi-submersible mooring platform is built in this work.First,a mooring system with a link element is designed and validated.An ice material model for the target iceberg is built and validated.A numerical model for the interaction between an iceberg and a semi-submersible mooring platform is then built.A parametric study(cable angle,tension angle and number of cables)is carried out to study the performance of the mooring system.The collision process between the semi-submersible mooring platform and the iceberg in the polar marine environment can be predicted by the present numerical model,and then the optimal mooring arrangement scheme can be obtained.The research results in this work can provide a reference for the design of mooring systems.
基金funding from the National Natural Science Foundation of China(No.12462028).
文摘This study employs the Smoothed Particle Hydrodynamics(SPH)method to develop a computational fluid dynamics(CFD)model for analyzing the interaction between rogue waves and mooring systems.Four floating body configurations are investigated:(1)dual rectangular prisms,(2)rectangular prism–sphere composites,(3)sphere–rectangular prism composites,and(4)dual spheres.These configurations are systematically evaluated under varying mooring conditions to assess their hydrodynamic performance and wave attenuation capabilities.The model accurately captures the complex fluid–structure interaction dynamics between moored floating breakwaters and incident wave fields.Among the configurations,the dual rectangular prism system demonstrates superior performance in both wave dissipation and mooring force reduction.Under conditions involving dual wave makers,the influence of floating body shape and number on wave height is found to be minimal.However,dual-body arrangements consistently outperform single-body setups in terms of both energy dissipation and structural stability.From a cost-efficiency perspective,the configuration comprising two rectangular prisms connected via a single mooring system offers significant advantages in material usage and deployment feasibility.
基金the National Natural Science Foundation of China(No.52071161)。
文摘With the development of marine resources,a dual-platform joint operation has been paid more attention.In this paper,the mooring layout space and relative motion limitation of the dual-platform berthing operation were fully considered.A new hybrid mooring system with“X+buoy”combination was designed based on the characteristics of catenary and tension mooring.The hydrodynamic characteristics of the new mooring system were analyzed by combining numerical simulation with model experiment.Under the regular and freak waves with different wave heights and periods,the time-domain full-coupling analysis method was used to study the hydrodynamic characteristics of the mooring system.It can be found that the arrangement of dual-platform under 0◦wave direction is optimal,and the“X+buoy”combined mooring system designed in this paper has a good follow-up between the two platforms under different regular and freak waves.The relative motion response between the two platforms can be effectively controlled,and finally the positioning of the dual-platform joint operation is realized.Research results of this paper provide a theoretical basis and technical support for the hydrodynamic performance analysis and safety assessment of deep-sea offshore platforms in China.
基金supported by the National Natural Science Foundation of China(Grant Nos.52071348 and 51979129)。
文摘Utilizing computational fluid dynamics(CFD),this study analyzes the relative pitching motion amplitude and conversion efficiency of the parallelogram raft wave energy converter(R-WEC)under wave current conditions,examining the effects of power take-off(PTO)parameters,wave parameters,and flow velocity on R-WEC hydrodynamic performance.The research includes an analysis of a single point mooring system to determine optimal mooring conditions.Through comparative analysis of energy conversion efficiency across 10 single mooring modes and nine double-mooring modes,the study evaluates their impact on the R-WEC.Findings demonstrate that flow velocity adversely affects wave energy capture.Energy conversion efficiency exhibits an initial increase followed by a decrease as damping coefficient or wave frequency coefficient increases.An optimal anchor chain unit mass coefficient exists that maximizes R-WEC energy conversion efficiency.The dual mooring system demonstrates marginally enhanced energy conversion efficiency compared with single mooring,with specific impacts on R-wave energy converters(WECs)documented.These findings provide valuable reference data for R-WEC design optimization and operational strategies to enhance conversion efficiency.
基金Project supported by the National Natural Science Foundation of China (No. 50675077)the Research Fund for the Doctoral Program of Higher Education of China (No. 20050487047)
文摘The dynamic response of moored crane-ship is studied. Governing equations for the dynamic response of a crane-ship coupled with the pendulum motion of the payload are derived based on Lagrange’s equations. The boom is modeled based on finite element method, while the payload is modeled as a planar pendulum of point mass. The dynamic response was studied using numerical method. The calculation results show that the large-amplitude responses occur at wave periods near the natural period of the payload. Load swing angle is smaller for crane-ship with flexible boom, in comparison with rigid boom. The ship surge mo- tions have large vibrations for crane-ship with flexible boom, which were not observed for a rigid boom. The analysis identifies the significance of key parameters and reveals how the system design can be adjusted to avoid critical conditions.
基金This work was financially supported bythe National High Technology and Development Programof China (Grant No.2004AA616180)
文摘Much attention should be paid to a large FPSO moored permanently in an oil field with water depth of only about 20 m, since shallow water effects on the hydrodynamics may bring about collision and damage. A 160kDWT FPSO with a permanent soft yoke mooring system is investigated with various shallow water depths and focuses are the low frequency surge motion and mooring load. Computation for the FPSO system is made based on linear 3-D potential fluid theory and time-domain numerical simulation method. Corresponding model test is carried out in the ocean engineering basin of Shanghai Jiao Tong University. It is shown that, in the surge natural period, low frequency surge motion and mooring force increase remarkably with the decrease of water depth. Especially, the smaller the ratio of water depth and draught is, the quicker the increase is. The shallow water effects should be taken into account carefully for determining the design load of a single point mooring system.
基金The project was financially supported by the High Tech Research and Development (863) Program (Grant No2005AA604220)by a grant from China National Offshore Oil Corporation (Grant No051100036)
文摘There is a need to obtain the hydrologic data including ocean current, wave, temperature and so on in the South China Sea. A new profiling instrument which does not suffer from the damage due to nature forces or incidents caused by passing ships, is under development to acquire data from this area. This device is based on a taut single point mid-water mooring system. It incorporates a small, instrumented vertically profiling float attached via an electromechanical cable to a winch integral with the main subsurface flotation. On a pre-set schedule, the instrument float with sensors is winched up to the surface if there is no ship passing by, which is defined by an on-board miniature sonar. And it can be. inunediately winched down to a certain depth if the sonar sensor finds something is coming. Since, because of logistics, the area can only be visited once for a long time and a minimum of 10 times per day profiles are desired, energy demands are severe. To respond to these concerns, the system has been designed to conserve a substantial portion of the potential energy lost during the ascent phase of each profile and subsequently use this energy to pull the instrument down. Compared with the previous single-point layered measuring mode, it is advanced and economical. At last the paper introduces the test in the South China Sea.
基金the National Natural Science Foundation of China(Nos.51179019 and 51309152)
文摘A three-dimensional high-order panel method based on non-uniform rational B-spline(NURBS) is developed for predicting the hydrodynamic interaction forces on a moored ship induced by a passing ship in shallow water. An NURBS surface is used to precisely represent the hull geometry. Velocity potential on the hull surface is described by B-spline after the source density distribution on the boundary surface is determined. A collocation approach is applied to the boundary integral equation discretization. Under the assumption of low passing speed, the effect of free surface elevation is neglected in the numerical calculation, and infinite image method is used to deal with the finite water depth effect. The time stepping method is used to solve the velocity potential at each time step. Detailed convergence study with respect to time step, panel size and Green function is undertaken. The present results of hydrodynamic forces are compared with those obtained by slender-body theory to show the validity of the proposed numerical method. Calculations are conducted for different water depths and lateral distances between ships, and the detail results are presented to demonstrate the effects of these factors.
文摘A three-dimensional method of calculating wave loads of turret moored FPSO (Flo ating Production Storage and Offloading) tankers is presented. The linearized restoring forces acting on the ship hull by the mooring system are calculated according to the catenary theory, which are expressed as the function of linear stiffness coefficients and the displacements of the upper ends of mooring chains. The hydrodynamic coefficients of the ship are calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for ships with a low forward speed. The equations of ship motions are established with the effect of the restoring forces from the mooring system included as linear stiffness coefficients. The equations of motions are solved in frequency domain, and the responses of wave-induced motions and loads on the ship can be obtained. A computer pro gram based on this method has been developed,and some calculation examples are illustrated. Analysis results show that the method can give satisfying prediction of wave loads.
基金This study is financially supported by the National Natural Science Foundation of China(Grant Nos.11872136,U20A20327 and 42176241).
文摘Moored structures are suitable for operations in ice-covered regions owing to their security and efficiency.This paper aims to present a new method for simulating the ice load and mooring force on the moored structure during ice-structure interaction with a spherical Discrete Element Method(DEM).In this method,the level ice and mooring lines consist of bonded sphere elements arranged in different patterns.The level ice model has been widely validated in simulation of the ice load of fixed structures.In the mooring line simulation,a string of spherical elements was jointed with the parallel bond model to simulate the chains or cable structure.The accuracy of the mooring line model was proved by comparing the numerical results with the nonlinear FEM results and model towing experiment results.The motion of the structure was calculated in the quaternion method,considering the ice load,mooring force,and hydrodynamic force.The hydrodynamic force comprised wave-making damping,current drag,and buoyancy force.Based on the proposed model,the interaction of a semi-submersible structure with level ice was simulated,and the effect of ice thickness on the ice load was analyzed.The numerical results show that the DEM method is suitable to simulate the ice load and mooring force on moored floating structures.
基金supported by the Science Foundation of the Science and Technology Commission of Shanghai Municipality(Grant No. 11ZR1417800)the National Natural Science Foundation of China (Grant No. 50879045)
文摘Hydrodynamic performance of an ultra deep turret-moored Floating Liquefied Natural Gas （FLNG） system is investigated. Hydrodynamic modeling of a turret-moored FLNG system, in consideration of the coupling effects of the vessel and its mooring lines, has been addressed in details. Based on the boundary element method, a 3-D panel model of the FLNG vessel and the related free water surface model are established, and the first-order and second-order mean-drift wave loads and other hydrodynamic coefficients are calculated. A systematic model test program consisting of the white noise wave test, offset test and irregular wave test combined with current and wind, etc. is performed to verify the numerical model. Owing to the depth limit of the water basin, the model test is carried out for the hydrodynamics of the FLNG coupled with only the truncated mooring system. The numerical simulation model features well the hydrodynamic performance of the FLNG system obtained from the model tests. The hydrodynamic characteristics presented in both the numerical simulations and the physical model tests would serve as the guidance for the ongoing project of FLNG system.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.50009005 and No.50039010)
文摘In this paper, the motions are studied of a multi-body which is composed of two plates hinged together and moored by eight mooring lines in regular waves. The experimental results are compared with computational results. The linear potential theory and the perturbation method are combined to study this complicated system. The former is used to calculate the wave forces acting on the plates and the motion responses of them, while the latter is used to describe the dynamic character of the eight mooring lines coupled with the two hinged plates. Some response results of each plate are presented and comparisons between calculated results and experimental data are given. All the calculations are confined to regular beam waves.
基金financially supported by the National Natural Science Foundation of China(Grant No.51379095)
文摘With the floating structures pushing their activities to the ultra-deep water, model tests have presented a challenge due to the limitation of the existing wave basins. Therefore, the concept of truncated mooring system is implemented to replace the full depth mooring system in the model tests, which aims to have the same dynamic responses as the full depth system. The truncated mooring system plays such a significant role that extra attention should be paid to the mooring systems with large truncation factor. Three different types of large truncation factor mooring system are being employed in the simulations, including the homogenously truncated mooring system, non-homogenously truncated mooring system and simplified truncated mooring system. A catenary moored semi-submersible operating at 1000 m water depth is presented. In addition, truncated mooring systems are proposed at the truncated water depth of 200 m. In order to explore the applicability of these truncated mooring systems, numerical simulations of the platform’s surge free decay interacting with three different styles of truncated mooring systems are studied in calm water. Furthermore, the mooring-induced damping of the truncated mooring systems is simulated in the regular wave. Finally, the platform motion responses and mooring line dynamics are simulated in irregular wave. All these simulations are implemented by employing full time domain coupled dynamic analysis, and the results are compared with those of the full depth simulations in the same cases. The results show that the mooring-induced damping plays a significant role in platform motion responses, and all truncated mooring systems are suitable for model tests with appropriate truncated mooring line diameters. However, a large diameter is needed for simplified truncated mooring lines. The suggestions are given to the selection of truncated mooring system for different situations as well as to the truncated mooring design criteria.
文摘In the paper, a comprehensive numerical study on the moored system is performed in time domain. The moored system, which is composed of the floating body sub system and the mooring line sub system, is calculated as a whole system by coupling. A time domain method is applied to the analysis of the mooring line sub system, and at the same time, an indirect time domain method translated from frequency domain to time domain is developed to calculate the floating body sub system. In the end, an FPSO vessel is calculated as a numerical example by the present method. A comparison of the result of the model test and that of the numerical method indicates that the present method is exact and effective.
