A numerical simulation and an experimental study on vortex-induced motion（VIM） of a new type of deep draft multi-columns floating drilling production, storage and offloading（FDPSO） are presented in this paper. The...A numerical simulation and an experimental study on vortex-induced motion（VIM） of a new type of deep draft multi-columns floating drilling production, storage and offloading（FDPSO） are presented in this paper. The main dimension, the special variable cross-section column and the cabin arrangement of the octagonal pontoon are introduced based on the result. The numerical simulation is adapted to study the effects of current incidence angles and reduced velocities on this platform’s sway motion response. The 300 m water depth equivalent truncated mooring system is adopted for the model tests. The model tests are carried out to check the reliability of numerical simulation. The results consist of surge, sway and yaw motions, as well as motion trajectories. The maximum sway amplitudes for different types of offshore platform is also studied. The main results show that the peak frequencies of sway motion under different current incidence angles and reduced velocities vary around the natural frequency. The analysis result of flow field indicates that the change of distribution of vortex in vertical presents significant influences on the VIM of platform. The trend of sway amplitude ratio curve of this new type FDPSO differs from the other types of platform. Under 45° current incidence angle, the sway amplitude of this new type of FDPSO is much smaller than those of other types of offshore platform at 4.4 ≤ V;≤ 8.9. The typical ‘8’ shape trajectory does not appear in the platform’s motion trajectories.展开更多
A Deep Draft Semi-submersible （DDS） under certain flow conditions could be subjected to Vortex-Induced Motions （VIM）, which significantly influences the loads on and life fatigue of the moorings and the risers. To...A Deep Draft Semi-submersible （DDS） under certain flow conditions could be subjected to Vortex-Induced Motions （VIM）, which significantly influences the loads on and life fatigue of the moorings and the risers. To investigate the VIM of a DDS with four rectangular section columns in waves coupled with a uniform current, a numerical study using the computational fluid dynamics （CFD） method was conducted. The issues of the VIM of multi-column floaters can be con＇,＇eniently converted to the issues of oscillating cylinders in fluid cross flows. This paper looks into the CFD numerical simulation of infinite cylinders having rectangular sections in a two-dimensional sinusoidal time- dependent flow field coupled with a uniform current. The resulted hydrodynamic forces and motion responses in different oscillatory flows plus currents both aligned in the same direction for the incidence of 135° of the DDS relative to the flow are compared with the ones in current only cases. The results show that the VIM response of this geometric arrangement of a DDS with four rectangular columns in a current combined with oscillatory flows is more evident than that in the current only case. The oscillatory flows and waves have the significant influence on the VIM response, forces and trajectory, in-plane motions of the DDS.展开更多
Spar platforms could be subject to vortex-induced-motions(VIM) in certain current conditions.Lockin is a phenomenon which occurs in a range of reduced velocities in VIM.In this paper,a new concept of spar platform cal...Spar platforms could be subject to vortex-induced-motions(VIM) in certain current conditions.Lockin is a phenomenon which occurs in a range of reduced velocities in VIM.In this paper,a new concept of spar platform called cell-truss spar is studied using both computational fluid dynamics(CFD) and model test to investigate the VIM of the spar under different reduced velocities.The unique configuration of the cell-truss spar is carefully considered,and the unsteady flow around the spar is calculated and visualized in CFD simulations.A physical model with a scale ratio of 1:100 of the cell-truss spar is fabricated,and model tests are carried out in the current-generating ocean engineering basin.Many important parameters in VIM of the cell-truss spar are obtained,the occurrence of lock-in phenomenon is successfully simulated,and the mechanism and rules of lock-in are analyzed.展开更多
In this paper,numerical simulations on vortex-induced motions(VIM)of a semi-submersible at two different current headings are conducted over a wide range of current velocities.The simulations are performed with the co...In this paper,numerical simulations on vortex-induced motions(VIM)of a semi-submersible at two different current headings are conducted over a wide range of current velocities.The simulations are performed with the computational fluid dynamics(CFD)solver VIM-FOAM-SJTU which is an in-house solver developed based on the OpenFOAM framework.The turbulent flows are resolved with a shear stress transport-delayed detached eddy simulation(SST-DDES)model.Free decay tests for transverse and yaw motion are performed in calm still water to make sure the equivalent stiffness is setup correctly.Then the results of VIM,including motion response,forces and moments,and flow patterns are presented and analyzed carefully.Motions including transverse,in-line and yaw motion at different current headings and velocities are compared.Instantaneous vorticity in the wake regions at different time stamps are also illustrated for different current headings and velocities.展开更多
In this paper,numerical simulation is conducted via our in-house solver,vim-FOAM-SJTU,developed on open-source software,OpenFOAM.Flow around static rigid cylinders and elastically mounted rigid cylinder constrained to...In this paper,numerical simulation is conducted via our in-house solver,vim-FOAM-SJTU,developed on open-source software,OpenFOAM.Flow around static rigid cylinders and elastically mounted rigid cylinder constrained to free stream with free end are numerically investigated.Some significant conclusions are made by analyzing the different results between cases with and without free end.The turbulence model is implemented with a shear stress transport-based(SST-based)improved delayed detached eddy simulation(IDDES)approach in the vim-FOAM-SJTU.Firstly,The paper starts with the application of the vim-FOAM-SJTU solver to flow past fixed cylinder with free end at Reynolds number 43000.The numerical results are compared with experimental data.Comparison are satisfactory which implies the validity and accuracy of the current computational fluid dynamics(CFD)solver.The flow visualization in the vicinity of free-end is discussed.Subsequently,the solver is utilized to simulate the free end effect associated with the VIM of a cylinder submerged in current.The motion responses under different inflow velocities are studied.The relationship between transverse motion frequency,in-line motion frequency is discussed.Lastly,the effect of the free end on the vortex of the wake field is analyzed by comparing the 3-D vorticity diagrams of the free end cylinder.The responses of circular cylinder with or without free end are compared.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.51779109)the Natural Science Foundation of Jiangsu Province(Grant No.BK20171306)
文摘A numerical simulation and an experimental study on vortex-induced motion（VIM） of a new type of deep draft multi-columns floating drilling production, storage and offloading（FDPSO） are presented in this paper. The main dimension, the special variable cross-section column and the cabin arrangement of the octagonal pontoon are introduced based on the result. The numerical simulation is adapted to study the effects of current incidence angles and reduced velocities on this platform’s sway motion response. The 300 m water depth equivalent truncated mooring system is adopted for the model tests. The model tests are carried out to check the reliability of numerical simulation. The results consist of surge, sway and yaw motions, as well as motion trajectories. The maximum sway amplitudes for different types of offshore platform is also studied. The main results show that the peak frequencies of sway motion under different current incidence angles and reduced velocities vary around the natural frequency. The analysis result of flow field indicates that the change of distribution of vortex in vertical presents significant influences on the VIM of platform. The trend of sway amplitude ratio curve of this new type FDPSO differs from the other types of platform. Under 45° current incidence angle, the sway amplitude of this new type of FDPSO is much smaller than those of other types of offshore platform at 4.4 ≤ V;≤ 8.9. The typical ‘8’ shape trajectory does not appear in the platform’s motion trajectories.
基金supported by the National Natural Science Foundation of China(Grant No.51279104)a Research Project on High-Technology Ships by the Ministry of Industry and Information Technology
文摘A Deep Draft Semi-submersible （DDS） under certain flow conditions could be subjected to Vortex-Induced Motions （VIM）, which significantly influences the loads on and life fatigue of the moorings and the risers. To investigate the VIM of a DDS with four rectangular section columns in waves coupled with a uniform current, a numerical study using the computational fluid dynamics （CFD） method was conducted. The issues of the VIM of multi-column floaters can be con＇,＇eniently converted to the issues of oscillating cylinders in fluid cross flows. This paper looks into the CFD numerical simulation of infinite cylinders having rectangular sections in a two-dimensional sinusoidal time- dependent flow field coupled with a uniform current. The resulted hydrodynamic forces and motion responses in different oscillatory flows plus currents both aligned in the same direction for the incidence of 135° of the DDS relative to the flow are compared with the ones in current only cases. The results show that the VIM response of this geometric arrangement of a DDS with four rectangular columns in a current combined with oscillatory flows is more evident than that in the current only case. The oscillatory flows and waves have the significant influence on the VIM response, forces and trajectory, in-plane motions of the DDS.
基金the National High Technology Research and Development Program (863) of China(No. 2006AA09A107)the Key Fundamental Research Project of Science and Technology Commission of Shanghai Municipality (No. 07XD14018)
文摘Spar platforms could be subject to vortex-induced-motions(VIM) in certain current conditions.Lockin is a phenomenon which occurs in a range of reduced velocities in VIM.In this paper,a new concept of spar platform called cell-truss spar is studied using both computational fluid dynamics(CFD) and model test to investigate the VIM of the spar under different reduced velocities.The unique configuration of the cell-truss spar is carefully considered,and the unsteady flow around the spar is calculated and visualized in CFD simulations.A physical model with a scale ratio of 1:100 of the cell-truss spar is fabricated,and model tests are carried out in the current-generating ocean engineering basin.Many important parameters in VIM of the cell-truss spar are obtained,the occurrence of lock-in phenomenon is successfully simulated,and the mechanism and rules of lock-in are analyzed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51909160,52131102 and 51879159)the National Key Research and Development Program of China(Grant No.2019YFB1704200).
文摘In this paper,numerical simulations on vortex-induced motions(VIM)of a semi-submersible at two different current headings are conducted over a wide range of current velocities.The simulations are performed with the computational fluid dynamics(CFD)solver VIM-FOAM-SJTU which is an in-house solver developed based on the OpenFOAM framework.The turbulent flows are resolved with a shear stress transport-delayed detached eddy simulation(SST-DDES)model.Free decay tests for transverse and yaw motion are performed in calm still water to make sure the equivalent stiffness is setup correctly.Then the results of VIM,including motion response,forces and moments,and flow patterns are presented and analyzed carefully.Motions including transverse,in-line and yaw motion at different current headings and velocities are compared.Instantaneous vorticity in the wake regions at different time stamps are also illustrated for different current headings and velocities.
基金supported by the National Natural Science Foundation of China(Grant Nos.52131102,51909160 and 51879159)the National Key Research and Development Program of China(Grant No.2019YFB1704200).
文摘In this paper,numerical simulation is conducted via our in-house solver,vim-FOAM-SJTU,developed on open-source software,OpenFOAM.Flow around static rigid cylinders and elastically mounted rigid cylinder constrained to free stream with free end are numerically investigated.Some significant conclusions are made by analyzing the different results between cases with and without free end.The turbulence model is implemented with a shear stress transport-based(SST-based)improved delayed detached eddy simulation(IDDES)approach in the vim-FOAM-SJTU.Firstly,The paper starts with the application of the vim-FOAM-SJTU solver to flow past fixed cylinder with free end at Reynolds number 43000.The numerical results are compared with experimental data.Comparison are satisfactory which implies the validity and accuracy of the current computational fluid dynamics(CFD)solver.The flow visualization in the vicinity of free-end is discussed.Subsequently,the solver is utilized to simulate the free end effect associated with the VIM of a cylinder submerged in current.The motion responses under different inflow velocities are studied.The relationship between transverse motion frequency,in-line motion frequency is discussed.Lastly,the effect of the free end on the vortex of the wake field is analyzed by comparing the 3-D vorticity diagrams of the free end cylinder.The responses of circular cylinder with or without free end are compared.
