How to evaluate time-domain Green function and its gradients efficiently is the key problem to analyze ship hydrodynamics in time domain. Based on the Bessel function, an Ordinary Differential Equation （ODE） was der...How to evaluate time-domain Green function and its gradients efficiently is the key problem to analyze ship hydrodynamics in time domain. Based on the Bessel function, an Ordinary Differential Equation （ODE） was derived for time-domain Green function and its gradients in this paper. A new efficient calculation method based on solving ODE is proposed. It has been demonstrated by the numerical calculation that this method can improve the precision of the time-domain Green function. Numeiical research indicates that it is efficient to solve the hydrodynamic problems.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
A domain decomposition and matching method in the time-domain is outlined for simulating the motions of ships advancing in waves. The flow field is decomposed into inner and outer domains by an imaginary control surfa...A domain decomposition and matching method in the time-domain is outlined for simulating the motions of ships advancing in waves. The flow field is decomposed into inner and outer domains by an imaginary control surface, and the Rankine source method is applied to the inner domain while the transient Green function method is used in the outer domain. Two initial boundary value problems are matched on the control surface. The corresponding numerical codes are developed, and the added masses, wave exciting forces and ship motions advancing in head sea for Series 60 ship and S175 containership, are presented and verified. A good agreement has been obtained when the numerical results are compared with the experimental data and other references. It shows that the present method is more efficient because of the panel discretization only in the inner domain during the numerical calculation, and good numerical stability is proved to avoid divergence problem regarding ships with flare.展开更多
A 3-D time domain method is developed to investigate the gap influence on the wave threes for 3-D multiple floating structures. Special hydrodynamic resonance due to small gaps between multiple floating structures on ...A 3-D time domain method is developed to investigate the gap influence on the wave threes for 3-D multiple floating structures. Special hydrodynamic resonance due to small gaps between multiple floating structures on wave forces is examined. Strong and complicate hydrodynamic interactions between the floating bodies are observed and the numerical computations have proved the existence of the sharp peak force response on each floating body at some special resonant wave numbers. By comparison with the results from the frequency domain technique, the results obtained from the time domain method reveal the similar resonant phenomena and hydrodynamic interaction. The resonant wave numbers are also proved around kL-nπ （n = 1,2 ……∞） with a corresponding frequency shift. The strong hydrodynamic interaction feature is practically significant for the design of module structures and the links （connection） in whole the floating body system.展开更多
In this paper, an inner turret moored FPSO which works in the water of 320 m depth, is selected to study the socalled ＂passively-truncated ＋ numerical-simulation＂ type of hybrid model testing technique while the tn...In this paper, an inner turret moored FPSO which works in the water of 320 m depth, is selected to study the socalled ＂passively-truncated ＋ numerical-simulation＂ type of hybrid model testing technique while the tnmcated water depth is 160 m and the model scale ）, = 80. During the investigation, the optimization design of the equivalent-depth truncated system is performed by using the similarity of the static characteristics between the truncated system and the full depth one as the objective function. According to the truncated system, the corresponding physical test model is made. By adopting the coupling time domain simulation method, the tnmcated system model test is numerically reconstructed to carefully verify the computer simulation software and to adjust the corresponding hydrodynamic parameters. Based on the above work, the numerical extrapolation to the full depth system is performed by using the verified computer software and the adjusted hydrodyrmmic parameters. The full depth system model test is then performed in the basin and the results are compared with those from the numerical extrapolation. At last, the implementation procedure and the key technique of the hybrid model testing of the deep-sea platforms are summarized and printed. Through the above investigations, some beneficial conclusions are presented.展开更多
Influence of gaps on hydrodynamic interactions of multiple floating structures is considered in the present investigation. Strong and complicate hydrodynamic interactions between the floating bodies are observed and t...Influence of gaps on hydrodynamic interactions of multiple floating structures is considered in the present investigation. Strong and complicate hydrodynamic interactions between the floating bodies are observed and the numerical computations have showed the existence of the sharp peak force response on each floating body at some special resonant wave numbers, which are also proved to be around kL =nπ （n= 1, 2, ...,∞） with a corresponding frequency shift. Width and depth of a gap also give influences on the resonant frequency and resonant amplitude of added mass and damping forces due to the radiation motions of the multiple bodies. The strong hydrodynamic interaction feature may have a big influence on the integrated loads of multiple floating structures system.展开更多
To understand the mooring energy during Fositioning, the expressions of four items concerning mooring line energy are presented based on a finite element model, including gravitational and elastic potential energy, ki...To understand the mooring energy during Fositioning, the expressions of four items concerning mooring line energy are presented based on a finite element model, including gravitational and elastic potential energy, kinetic energy and dissipated energy due to mooting-induced damping. In a static case, the force calculated from the derivative of potential energy with respect to distance is compared with that of direct calculation. The results are tbund fit well, which indicates the law of conservation of energy and also shows the correctness of the potential energy results. For the cases of a single mooring line with the attaclunent point oscillating with different amplitudes in horizontal or vertical direction （corresponding to surge and roll motions respectively）, and the case of the mooring line with a horizontal bicbromatic oscillation on the attachment point, the time history of the first three items are calculated and analyzed, also, the indicator diagram tbr mooring-induced damping are given. These results reveal the energy state of the mooring line and can provide a better understanding of how the mooring line works.展开更多
The generation of unsteady interfacial gravity waves by a singularity immersed in two semi-infinite fluids was analytically investigated in detail by the methods of integral transform and of stationary-phase analysis....The generation of unsteady interfacial gravity waves by a singularity immersed in two semi-infinite fluids was analytically investigated in detail by the methods of integral transform and of stationary-phase analysis. The fluids were assumed to be initially stationary, immiscible, inviscid and incompressible. The disturbed flows, generated by an impulsive and oscillatory source/dipole immersed above or be neath the interface, were governed by the I.aplace equations. The kinematic and dynamic boundary conditions on the interface were linearized for the small-amplitude waves. By means of the stationary phase analysis on the exact integral form solutions, the asymptotic representations for the interracial waves were derived for large time with a fixed distance to time ratio. The relation between a submerged singularity and a sur face pressure point was discussed. It is found that the local wavelength and the local wave period of the interracial waves are elongated in comparison with those of free-surface waves for a single fluid.展开更多
The time-domain calculations of retard function and ship motions in waves by the direct time-domain method （DTM） and the frequency to time-domain transformation method （FTTM） are compared and analyzed. A Wigley-hu...The time-domain calculations of retard function and ship motions in waves by the direct time-domain method （DTM） and the frequency to time-domain transformation method （FTTM） are compared and analyzed. A Wigley-hull-form ship and an $60 ship moving in waves are examined, and the corresponding retard functions are in good agreement with those given by DTM and FTTM. The comparison of retard functions in different forward speeds by the two methods is observed, and the results of ship motions in forward speed are also compared with the experimental data. On this basis, the advantage and disadvantage of them are discussed.展开更多
基金This work was financially supported by Key Program of the National Natural Science Foundation of China(No.50639020)the National High Technology Research and Development Program of China(863Program)(No.2006AA09Z332)
文摘How to evaluate time-domain Green function and its gradients efficiently is the key problem to analyze ship hydrodynamics in time domain. Based on the Bessel function, an Ordinary Differential Equation （ODE） was derived for time-domain Green function and its gradients in this paper. A new efficient calculation method based on solving ODE is proposed. It has been demonstrated by the numerical calculation that this method can improve the precision of the time-domain Green function. Numeiical research indicates that it is efficient to solve the hydrodynamic problems.
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financially supported by the National Basic Research Program of China(973 Program,Grant No.2014CB046203)
文摘A domain decomposition and matching method in the time-domain is outlined for simulating the motions of ships advancing in waves. The flow field is decomposed into inner and outer domains by an imaginary control surface, and the Rankine source method is applied to the inner domain while the transient Green function method is used in the outer domain. Two initial boundary value problems are matched on the control surface. The corresponding numerical codes are developed, and the added masses, wave exciting forces and ship motions advancing in head sea for Series 60 ship and S175 containership, are presented and verified. A good agreement has been obtained when the numerical results are compared with the experimental data and other references. It shows that the present method is more efficient because of the panel discretization only in the inner domain during the numerical calculation, and good numerical stability is proved to avoid divergence problem regarding ships with flare.
基金the National Natural Science Foundation of China (Grant No. 50639020)the National High Technology Research and Development Program of China (863 Program, Grant No. 2006AA09Z332).
文摘A 3-D time domain method is developed to investigate the gap influence on the wave threes for 3-D multiple floating structures. Special hydrodynamic resonance due to small gaps between multiple floating structures on wave forces is examined. Strong and complicate hydrodynamic interactions between the floating bodies are observed and the numerical computations have proved the existence of the sharp peak force response on each floating body at some special resonant wave numbers. By comparison with the results from the frequency domain technique, the results obtained from the time domain method reveal the similar resonant phenomena and hydrodynamic interaction. The resonant wave numbers are also proved around kL-nπ （n = 1,2 ……∞） with a corresponding frequency shift. The strong hydrodynamic interaction feature is practically significant for the design of module structures and the links （connection） in whole the floating body system.
基金This work was financially supported by the National Natural Science Foundation of China (Grant No10602055)Nature Science Foundation of China Jiliang University (Grant No XZ0501)
文摘In this paper, an inner turret moored FPSO which works in the water of 320 m depth, is selected to study the socalled ＂passively-truncated ＋ numerical-simulation＂ type of hybrid model testing technique while the tnmcated water depth is 160 m and the model scale ）, = 80. During the investigation, the optimization design of the equivalent-depth truncated system is performed by using the similarity of the static characteristics between the truncated system and the full depth one as the objective function. According to the truncated system, the corresponding physical test model is made. By adopting the coupling time domain simulation method, the tnmcated system model test is numerically reconstructed to carefully verify the computer simulation software and to adjust the corresponding hydrodynamic parameters. Based on the above work, the numerical extrapolation to the full depth system is performed by using the verified computer software and the adjusted hydrodyrmmic parameters. The full depth system model test is then performed in the basin and the results are compared with those from the numerical extrapolation. At last, the implementation procedure and the key technique of the hybrid model testing of the deep-sea platforms are summarized and printed. Through the above investigations, some beneficial conclusions are presented.
文摘Influence of gaps on hydrodynamic interactions of multiple floating structures is considered in the present investigation. Strong and complicate hydrodynamic interactions between the floating bodies are observed and the numerical computations have showed the existence of the sharp peak force response on each floating body at some special resonant wave numbers, which are also proved to be around kL =nπ （n= 1, 2, ...,∞） with a corresponding frequency shift. Width and depth of a gap also give influences on the resonant frequency and resonant amplitude of added mass and damping forces due to the radiation motions of the multiple bodies. The strong hydrodynamic interaction feature may have a big influence on the integrated loads of multiple floating structures system.
基金supported by the Key Program of the National Natural Science Foundation of China (GrantNo.50639020)the National High Technology Research and Development Program of China (863 Program,Grant No.2006AA09Z332)
文摘To understand the mooring energy during Fositioning, the expressions of four items concerning mooring line energy are presented based on a finite element model, including gravitational and elastic potential energy, kinetic energy and dissipated energy due to mooting-induced damping. In a static case, the force calculated from the derivative of potential energy with respect to distance is compared with that of direct calculation. The results are tbund fit well, which indicates the law of conservation of energy and also shows the correctness of the potential energy results. For the cases of a single mooring line with the attaclunent point oscillating with different amplitudes in horizontal or vertical direction （corresponding to surge and roll motions respectively）, and the case of the mooring line with a horizontal bicbromatic oscillation on the attachment point, the time history of the first three items are calculated and analyzed, also, the indicator diagram tbr mooring-induced damping are given. These results reveal the energy state of the mooring line and can provide a better understanding of how the mooring line works.
文摘The generation of unsteady interfacial gravity waves by a singularity immersed in two semi-infinite fluids was analytically investigated in detail by the methods of integral transform and of stationary-phase analysis. The fluids were assumed to be initially stationary, immiscible, inviscid and incompressible. The disturbed flows, generated by an impulsive and oscillatory source/dipole immersed above or be neath the interface, were governed by the I.aplace equations. The kinematic and dynamic boundary conditions on the interface were linearized for the small-amplitude waves. By means of the stationary phase analysis on the exact integral form solutions, the asymptotic representations for the interracial waves were derived for large time with a fixed distance to time ratio. The relation between a submerged singularity and a sur face pressure point was discussed. It is found that the local wavelength and the local wave period of the interracial waves are elongated in comparison with those of free-surface waves for a single fluid.
文摘The time-domain calculations of retard function and ship motions in waves by the direct time-domain method （DTM） and the frequency to time-domain transformation method （FTTM） are compared and analyzed. A Wigley-hull-form ship and an $60 ship moving in waves are examined, and the corresponding retard functions are in good agreement with those given by DTM and FTTM. The comparison of retard functions in different forward speeds by the two methods is observed, and the results of ship motions in forward speed are also compared with the experimental data. On this basis, the advantage and disadvantage of them are discussed.
