In this paper, the effects of a quay or a solid jetty on hydrodynamic coefficients and vertical wave excitation forces on a ship with or without forward speed are discussed. A modified simple Green function technique ...In this paper, the effects of a quay or a solid jetty on hydrodynamic coefficients and vertical wave excitation forces on a ship with or without forward speed are discussed. A modified simple Green function technique is used to calculate the 2D coefficients while the strip theory is used to calculate the 3D coefficients. Wave excitation forces are also calculated with the strip theory. Numerical results are provided for hydrodynamic coefficients and vertical wave excitation forces on a 200 000 DWT tanker ship. It is found that the quay has a considerable effect on the hydrodynamic coefficients and wave excitation forces for a ship.展开更多
-The hydrodynamic coefficients for each of two piles and three piles in both side-by-side arrangement and tandem arrangement under the action of irregular waves are experimentally investigated. These coefficients vary...-The hydrodynamic coefficients for each of two piles and three piles in both side-by-side arrangement and tandem arrangement under the action of irregular waves are experimentally investigated. These coefficients vary with the KC number, the relative pile spacing, the number of piles and the pile location, and their relationships are presented in this paper. They can be used in Morison Equation and other equations to calculate directly the in-line wave forces and the transverse forces on each pile in array.展开更多
The hydrodynamic coefficients C-d and C-m are not only dependent on the size of slender cylinder, its location in water, KC number and Re number, but also vary with environmental conditions, i.e., in regular waves or ...The hydrodynamic coefficients C-d and C-m are not only dependent on the size of slender cylinder, its location in water, KC number and Re number, but also vary with environmental conditions, i.e., in regular waves or in irregular waves, in pure waves or in wave-current coexisting field. In this paper, the normalization of hydrodynamic coefficients for various environmental conditions is discussed. When a proper definition of KC number and proper characteristic values of irregular waves are used, a unified relationship between C-d, C-m and KC number for regular waves, irregular waves, pure waves and wave-current coexisting field can be obtained.展开更多
Aiming at the demand for optimization of hydrodynamic coefficients in submarine's motion equations,an adaptive weight immune genetic algorithm was proposed to optimize hydrodynamic coefficients in motion equations...Aiming at the demand for optimization of hydrodynamic coefficients in submarine's motion equations,an adaptive weight immune genetic algorithm was proposed to optimize hydrodynamic coefficients in motion equations.Some hydrodynamic coefficients of high sensitivity to control and maneuver were chosen as the optimization objects in the algorithm.By using adaptive weight method to determine the weight and target function,the multi-objective optimization could be translated into single-objective optimization.For a certain kind of submarine,three typical maneuvers were chosen to be the objects of study:overshoot maneuver in horizontal plane,overshoot maneuver in vertical plane and turning circle maneuver in horizontal plane.From the results of computer simulations using primal hydrodynamic coefficient and optimized hydrodynamic coefficient,the efficiency of proposed method is proved.展开更多
The purpose of this paper is to find some better methods for calculating in-line forces on a vertical circular cylinder and for analysing the hydrodynamic coefficients C_D and C_M in wave-current co-existing field. In...The purpose of this paper is to find some better methods for calculating in-line forces on a vertical circular cylinder and for analysing the hydrodynamic coefficients C_D and C_M in wave-current co-existing field. In this pa- per, in order to calculate hydrodynamic forces, the authors try to find a way of applying a great number of the re- sults about C_D and C_M for wave-only field in the case of wave-current co-existing field, and the results about C_D and C_M obtained in regular waves in the ease of irregular waves. Such a way may be of significance in engineering and further research.展开更多
The hydrodynamic characteristics of heave plates with different form edges of Truss Spar Platform are studied in this paper. Numerical simulations are carried out for the plate forced oscillation by the dynamic mesh m...The hydrodynamic characteristics of heave plates with different form edges of Truss Spar Platform are studied in this paper. Numerical simulations are carried out for the plate forced oscillation by the dynamic mesh method and user defined fimctions of FLUENT. The added mass coefficient Cm and the damping coefficient Cd of heave plate with tapering condition and the chamfer condition are calculated. The results show that, in a certain range, the hydrodynamic performance of heave plate after being tapered is better.展开更多
This paper presents the features of newly designed hydrodynamics test for the scaled model of 4500 m deepsea open-framed remotely operated vehicle (ROV), which is being researched and developed by Shanghai Jiao Tong...This paper presents the features of newly designed hydrodynamics test for the scaled model of 4500 m deepsea open-framed remotely operated vehicle (ROV), which is being researched and developed by Shanghai Jiao Tong University. Accurate hydrodynamics coefficients measurement and spatial modeling of ROV are significant for the maneuverability and control algorithm. The scaled model of ROV was constructed by 1:1.6. Hydrodynamics coefficients were measured through VPMM and LAHPMM towing test. And dynamics model was derived as a set of equations, describing nonlinear and coupled 5-DOF spatial motions. Rotation control motion was simulated to verify spatial model proposed. Research and application of hydrodynamics coefficients are expected to enable ROV to overcome uncertainty and disturbances of deepsea environment, and accomplish some more challengeable and practical missions.展开更多
-A composite pipeline is defined as a pipeline system composed of one big pipe and one or several small pipes. Based on the theory of wave- current interaction and physical model test, the hydrodynamic characteristics...-A composite pipeline is defined as a pipeline system composed of one big pipe and one or several small pipes. Based on the theory of wave- current interaction and physical model test, the hydrodynamic characteristics of the submarine composite pipeline in wave-current coexisting field (both regular and irregular waves) are investigated. The so-called 'modified diameter method' is used for analyzing the in-fine hydrodynamic coefficients of the composite pipeline, which are well related to KC number. The comparison of test data for regular and irregular waves shows that in the region of 90 > KC> 20, the results in these two cases can be unified. The effect of water depth is analyzed in details. The relationships between CD, CM and KC , which are based on the results of present research, may be used as a reference in engineering design.展开更多
This paper investigates the effects of structure parameters on dynamic responses of submerged floating tunnel (SFT) under hydrodynamic loads. The structure parameters includes buoyancy-weight ratio (BWR), stiffnes...This paper investigates the effects of structure parameters on dynamic responses of submerged floating tunnel (SFT) under hydrodynamic loads. The structure parameters includes buoyancy-weight ratio (BWR), stiffness coefficients of the cable systems, tunnel net buoyancy and tunnel length. First, the importance of structural damp in relation to the dynamic responses of SPT is demonstrated and the mechanism of structural damp effect is discussed. Thereafter, the fundamental structure parameters are investigated through the analysis of SFT dynamic responses under hydrodynamic loads. The results indicate that the BWR of SFT is a key structure parameter. When BWR is 1.2, there is a remarkable trend change in the vertical dynamic response of SFT under hydrodynamic loads. The results also indicate that the ratio of the tunnel net buoyancy to the cable stiffness coefficient is not a characteristic factor affecting the dynamic responses of SFT under hydrodynamic loads.展开更多
In this paper, the hydrodynamic coefficients of a horizontal semi-immersed cylinder in steady current and oscillatory flow combining with constant current are obtained via forced oscillation experiments in a towing ta...In this paper, the hydrodynamic coefficients of a horizontal semi-immersed cylinder in steady current and oscillatory flow combining with constant current are obtained via forced oscillation experiments in a towing tank. Three nondimensional parameters(Re, KC and Fr) are introduced to investigate their effects on the hydrodynamic coefficients.The experimental results show that overtopping is evident and dominates when the Reynolds number exceeds 5×105 in the experiment. Under steady current condition, overtopping increases the drag coefficient significantly at high Reynolds numbers. Under oscillatory flow with constant current condition, the added mass coefficient can even reach a maximum value about 3.5 due to overtopping while the influence of overtopping on the drag coefficient is minor.展开更多
For active wave absorbers in force-control mode,the optimal feedback(control)force provided by the control system depends on the hydrodynamic forces.This work investigates a piston-type wave absorber with different dr...For active wave absorbers in force-control mode,the optimal feedback(control)force provided by the control system depends on the hydrodynamic forces.This work investigates a piston-type wave absorber with different draft-to-water depth ratios,focusing on the frequency-dependent hydrodynamic coefficients,wave absorption efficiency,wave absorber displacement and velocity,and control force.Analytical results were derived based on potential flow theory,confirming that regular incident waves can be fully absorbed by the piston-type active wave absorber at any draft ratio by optimizing the control force.The results for the wave tank with a typical water depth of 3 m were studied in detail.The draft ratio has a strong influence on the hydrodynamic coefficients.At the maximum wave absorption efficiency,the displacement and velocity amplitudes are sensitive to the draft ratio in the low-frequency region,increase with decreasing draft ratio,and are independent of the mass of the wave absorber.The control force required can be extremely large for a draft ratio greater than 1/3.The control force increases significantly as the draft ratio increases.The mass of the wave absorber has a weak influence on the control force.A time-domain numerical method based on the boundary element method was developed to verify the analytical solutions.Perfect agreements between the analytical solutions and the numerical results were obtained.展开更多
The Reynolds-averaged Navier–Stokes(RANS)equation was solved using computational fluid dynamics to study the effect of the circulating tank wall on the hydrodynamic coefficient of an autonomous underwater vehicle(AUV...The Reynolds-averaged Navier–Stokes(RANS)equation was solved using computational fluid dynamics to study the effect of the circulating tank wall on the hydrodynamic coefficient of an autonomous underwater vehicle(AUV).Numerical results were compared with the experimental results in the circulating water tank of Harbin Engineering University.The numerical results of the model with different scale ratios under the same water in the flume were studied to investigate the effect of blockage on the hydrodynamic performance of AUV in the circulating flume model test.The results show that the hydrodynamic coefficient is stable with the scale reduction of the model.The influence of blocking effect on AUV is given by combining theoretical calculation with experiment.展开更多
The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device o...The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device on a plane incident wave is solved by the use of an eigenfunction expansion method, and a new analytical expression for the radiation velocity potential is obtained. The wave excitation force is calculated via the known incident wave potential and the radiation potential with a theorem of Haskind employed. To verify the correctness of this method, an example is computed respectively through the bound element method and analytical method. Results show that two numerical methods. are in good agreement, which shows that the present method is applicable. In addition, the trends of hydrodynamic coefficients and wave force are analyzed under different conditions by use of the present analytical method.展开更多
A plate submerged at a certain depth underneath the sea surface has been proposed as a structure type for different purposes, including motion response reduction, wave control, and wave energy harvesting. In the prese...A plate submerged at a certain depth underneath the sea surface has been proposed as a structure type for different purposes, including motion response reduction, wave control, and wave energy harvesting. In the present study, the three-dimensional wave radiation problem is investigated in the context of the linear potential theory for a submerged ring plate in isolation or attached to a floating column as an appendage. In the latter case, the ring plate is attached at a certain distance above the column bottom. The structure is assumed to undergo a heave motion. An analytical model is developed to solve the wave radiation problem via the eigenfunction expansion method in association with the region-matching technique. With the velocity potential being available, the hydrodynamic coefficients, such as added mass and radiation damping, are obtained through the direct pressure integration. An alternative solution of radiation damping has also been developed in this study, in which the radiation damping is related to the Kochin function in the wave radiation problem. After validating the present model, numerical analysis is performed in detail to assess the influence of various plate parameters, such as the plate size and submergence depth. It is noted that the additional added mass due to the attached ring plate is larger than that when the plate is in isolation. Meanwhile, the radiation damping of the column for the heave motion can vanish at a specific wave frequency by attaching a ring plate, corresponding to a condition that there exist no progressive waves in the exterior region.展开更多
Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step fi...Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re -- 200 for various dimensionless ratios of 0.25 ≤ G/D ≤2.0 and 1.0 ≤ L/D ≤ 4.0, where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of G/D and L/D on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of G/D and L/D. For very small values of G/D, the vortex shedding is completely suppressed, resulting in the root mean square (RMS) values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of G/D and L/D. It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients.展开更多
Vortex-induced motion is based on the complex characteristics of the flow around the tension leg platform (TLP) hull. By considering the flow field of the South China Sea and the configuration of the platform, three...Vortex-induced motion is based on the complex characteristics of the flow around the tension leg platform (TLP) hull. By considering the flow field of the South China Sea and the configuration of the platform, three typical flow velocities and three flow directions are chosen to study the numerical simulation of the flow field characteristics around the TLP hull. Reynolds-averaged Navier-Stokes equations combined with the detached eddy simulation turbulence model are employed in the numerical study. The hydrodynamic coefficients of columns and pontoons, the total drag and lift coefficients of the TLP, the formation and development of the wake, and the vorticity iso-surfaces for different inlet velocities and current directions are discussed in this paper. The average value of the drag coefficient of the upstream columns is considerably larger than that of the downstream columns in the inlet direction of 0°. Although the time history of the lift coefficient demonstrates a "beating" behavior, the plot shows regularity in general. The Strouhal number decreases as the inlet velocity increases from the power spectral density plot at different flow velocities. The mean root values of the lift and drag coefficients of the front column decrease as the current direction increases. Under the symmetrical configuration of 45°, the streamwise force on C4 is the smallest, whereas the transverse force is the largest. The broken vortex conditions in current directions of 22.5° and 45° are more serious than that in the current direction of 0°. In addition, turbulence at the bottom of the TLP becomes stronger when the current direction changes from 0° to 45°. However, a high inlet velocity indicates a large region influenced by the broken vortex and shows the emergence of the wake behind the TLP under the same current angle.展开更多
The submarine Hydrodynamic coefficients are predicted by numerical simulations. Steady and unsteady Reynolds Averaged Navier-Stokes (RANS) simulations are carried out to numerically simulate the oblique towing exper...The submarine Hydrodynamic coefficients are predicted by numerical simulations. Steady and unsteady Reynolds Averaged Navier-Stokes (RANS) simulations are carried out to numerically simulate the oblique towing experiment and the Planar Motion Mechanism (PMM) experiment performed on the SUBOFF submarine model. The dynamic mesh method is adopted to simulate the maneuvering motions of pure heaving, pure swaying, pure pitching and pure yawing. The hydrodynamic forces and moments acting on the maneuvering submarine are obtained. Consequently, by analyzing these results, the hydrodynamic coefficients of the submarine maneuvering motions can be determined. The computational results are verified by comparison with experimental data, which show that this method can be used to estimate the hydrodynamic derivatives of a fully appended submarine.展开更多
The boundary hydrodynamic interaction of a 3-D oval body was experimentally surveyed for different cases. The regression method was employed to fred the experimental formulae of hydrodynamic coefficients relating to t...The boundary hydrodynamic interaction of a 3-D oval body was experimentally surveyed for different cases. The regression method was employed to fred the experimental formulae of hydrodynamic coefficients relating to the attack angle, clearance to wall, and moving speed. The mechanism of interaction was discussed. The experimental results show that there exists a lifting effect, similar to wings in flow. The lifting effect is remarkable. The boundary hydrodynamic interaction of the small aspect ratio model is almost linearly dependent on the attack angle, but the effect of the moving speed of the body on the hydrodynamic coefficients is very small. The effect of clearance is related to the geometric shape. The boundary hydrodynamic interaction always enhances the lifting effect if the clearance is small.展开更多
Euler-Euler two-fluid model is used to simulate the hydrodynamics of gas-solid flow in a bubbling flu- idized bed with Geldert B particles where the solid property is calculated by applying the kinetic theory of granu...Euler-Euler two-fluid model is used to simulate the hydrodynamics of gas-solid flow in a bubbling flu- idized bed with Geldert B particles where the solid property is calculated by applying the kinetic theory of granular flow (KTGF). Johnson and Jackson wall boundary condition is used for the particle phase, and different amount of slip between particle and wall is given by varying the specularity coefficient (φ) from 0 to 1. The simulated particle velocity, granular temperature and particle volume fraction are compared to investigate the effect of different wall boundary conditions on the hydrodynamic behavior, Some of the results are also compared with the available experimental data from the literature. It was found that the model predictions are sensitive to the specularity coefficient. The hydrodynamic behavior deviated sig- nificantly for φ = 0 and φ = 0.01 with maximum deviation found at φ = 0 i.e. free-slip condition. However, the overall bed height predicted by all the conditions is similar.展开更多
Hydrodynamic dispersion is a measure for describing the process of solute transport in porous media.Characterizing the dispersion of water flow within gravel is essential for the prediction of solute transport especia...Hydrodynamic dispersion is a measure for describing the process of solute transport in porous media.Characterizing the dispersion of water flow within gravel is essential for the prediction of solute transport especially nonpoint source pollutants migration in alpine watersheds where the land surface is typically covered with gravel.In this study,an integrated model and experimental method using an electrolyte tracer is proposed for determination of the hydrodynamic dispersion coefficient.Two experimental scenarios were designed to measure electrolyte tracer transport processes in both free water flow and gravel layer flow under different slope gradients and transport distances.Subsequently,the measured data were used to simultaneously calculate both the hydrodynamic dispersion coefficient and flow velocity by fitting the experimental data with the mathematical model.Dispersivity,as a critical feature of hydrodynamic dispersion,was determined as well under the two specified scenarios.Finally,the impact mechanisms of the gravel layer and factors related to the dispersion processes were comprehensively analyzed.The results indicate that the presence of a gravel layer significantly reduces flow velocity and the hydrodynamic dispersion coefficient,but increases solute dispersivity.For the flow within gravel layers,with much lower velocity,the positive effect of the gravel layer on dispersivity may be neutralized or even surpassed by the negative effect of flow velocity.The results should be helpful in characterizing the dispersion processes of water flow within gravel layer and hence in predicting solute transport,especially in nonpoint source pollutants migration in alpine watersheds where the land surface is richly covered with gravel.展开更多
文摘In this paper, the effects of a quay or a solid jetty on hydrodynamic coefficients and vertical wave excitation forces on a ship with or without forward speed are discussed. A modified simple Green function technique is used to calculate the 2D coefficients while the strip theory is used to calculate the 3D coefficients. Wave excitation forces are also calculated with the strip theory. Numerical results are provided for hydrodynamic coefficients and vertical wave excitation forces on a 200 000 DWT tanker ship. It is found that the quay has a considerable effect on the hydrodynamic coefficients and wave excitation forces for a ship.
文摘-The hydrodynamic coefficients for each of two piles and three piles in both side-by-side arrangement and tandem arrangement under the action of irregular waves are experimentally investigated. These coefficients vary with the KC number, the relative pile spacing, the number of piles and the pile location, and their relationships are presented in this paper. They can be used in Morison Equation and other equations to calculate directly the in-line wave forces and the transverse forces on each pile in array.
基金National Natural Science Foundation of China(No.59779005)
文摘The hydrodynamic coefficients C-d and C-m are not only dependent on the size of slender cylinder, its location in water, KC number and Re number, but also vary with environmental conditions, i.e., in regular waves or in irregular waves, in pure waves or in wave-current coexisting field. In this paper, the normalization of hydrodynamic coefficients for various environmental conditions is discussed. When a proper definition of KC number and proper characteristic values of irregular waves are used, a unified relationship between C-d, C-m and KC number for regular waves, irregular waves, pure waves and wave-current coexisting field can be obtained.
文摘Aiming at the demand for optimization of hydrodynamic coefficients in submarine's motion equations,an adaptive weight immune genetic algorithm was proposed to optimize hydrodynamic coefficients in motion equations.Some hydrodynamic coefficients of high sensitivity to control and maneuver were chosen as the optimization objects in the algorithm.By using adaptive weight method to determine the weight and target function,the multi-objective optimization could be translated into single-objective optimization.For a certain kind of submarine,three typical maneuvers were chosen to be the objects of study:overshoot maneuver in horizontal plane,overshoot maneuver in vertical plane and turning circle maneuver in horizontal plane.From the results of computer simulations using primal hydrodynamic coefficient and optimized hydrodynamic coefficient,the efficiency of proposed method is proved.
文摘The purpose of this paper is to find some better methods for calculating in-line forces on a vertical circular cylinder and for analysing the hydrodynamic coefficients C_D and C_M in wave-current co-existing field. In this pa- per, in order to calculate hydrodynamic forces, the authors try to find a way of applying a great number of the re- sults about C_D and C_M for wave-only field in the case of wave-current co-existing field, and the results about C_D and C_M obtained in regular waves in the ease of irregular waves. Such a way may be of significance in engineering and further research.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51079097 and 50879057)Science Fund for Creative Research Groups of the National Natural Science Foundation of China (Grant No. 51021004)
文摘The hydrodynamic characteristics of heave plates with different form edges of Truss Spar Platform are studied in this paper. Numerical simulations are carried out for the plate forced oscillation by the dynamic mesh method and user defined fimctions of FLUENT. The added mass coefficient Cm and the damping coefficient Cd of heave plate with tapering condition and the chamfer condition are calculated. The results show that, in a certain range, the hydrodynamic performance of heave plate after being tapered is better.
基金financially supported by the National High Technology Research and Development Program of China(863 Program,Grant No.2008AA092301)
文摘This paper presents the features of newly designed hydrodynamics test for the scaled model of 4500 m deepsea open-framed remotely operated vehicle (ROV), which is being researched and developed by Shanghai Jiao Tong University. Accurate hydrodynamics coefficients measurement and spatial modeling of ROV are significant for the maneuverability and control algorithm. The scaled model of ROV was constructed by 1:1.6. Hydrodynamics coefficients were measured through VPMM and LAHPMM towing test. And dynamics model was derived as a set of equations, describing nonlinear and coupled 5-DOF spatial motions. Rotation control motion was simulated to verify spatial model proposed. Research and application of hydrodynamics coefficients are expected to enable ROV to overcome uncertainty and disturbances of deepsea environment, and accomplish some more challengeable and practical missions.
文摘-A composite pipeline is defined as a pipeline system composed of one big pipe and one or several small pipes. Based on the theory of wave- current interaction and physical model test, the hydrodynamic characteristics of the submarine composite pipeline in wave-current coexisting field (both regular and irregular waves) are investigated. The so-called 'modified diameter method' is used for analyzing the in-fine hydrodynamic coefficients of the composite pipeline, which are well related to KC number. The comparison of test data for regular and irregular waves shows that in the region of 90 > KC> 20, the results in these two cases can be unified. The effect of water depth is analyzed in details. The relationships between CD, CM and KC , which are based on the results of present research, may be used as a reference in engineering design.
基金the National Natural Science Foundation of China (10532070)Chinese Academy of Sciences (KJCX2-YW-L07)
文摘This paper investigates the effects of structure parameters on dynamic responses of submerged floating tunnel (SFT) under hydrodynamic loads. The structure parameters includes buoyancy-weight ratio (BWR), stiffness coefficients of the cable systems, tunnel net buoyancy and tunnel length. First, the importance of structural damp in relation to the dynamic responses of SPT is demonstrated and the mechanism of structural damp effect is discussed. Thereafter, the fundamental structure parameters are investigated through the analysis of SFT dynamic responses under hydrodynamic loads. The results indicate that the BWR of SFT is a key structure parameter. When BWR is 1.2, there is a remarkable trend change in the vertical dynamic response of SFT under hydrodynamic loads. The results also indicate that the ratio of the tunnel net buoyancy to the cable stiffness coefficient is not a characteristic factor affecting the dynamic responses of SFT under hydrodynamic loads.
基金financially supported by the SINTEF Fisheries and Aquaculture of Norway and the National Natural Science Foundation of China(Grant No.51490674)
文摘In this paper, the hydrodynamic coefficients of a horizontal semi-immersed cylinder in steady current and oscillatory flow combining with constant current are obtained via forced oscillation experiments in a towing tank. Three nondimensional parameters(Re, KC and Fr) are introduced to investigate their effects on the hydrodynamic coefficients.The experimental results show that overtopping is evident and dominates when the Reynolds number exceeds 5×105 in the experiment. Under steady current condition, overtopping increases the drag coefficient significantly at high Reynolds numbers. Under oscillatory flow with constant current condition, the added mass coefficient can even reach a maximum value about 3.5 due to overtopping while the influence of overtopping on the drag coefficient is minor.
文摘For active wave absorbers in force-control mode,the optimal feedback(control)force provided by the control system depends on the hydrodynamic forces.This work investigates a piston-type wave absorber with different draft-to-water depth ratios,focusing on the frequency-dependent hydrodynamic coefficients,wave absorption efficiency,wave absorber displacement and velocity,and control force.Analytical results were derived based on potential flow theory,confirming that regular incident waves can be fully absorbed by the piston-type active wave absorber at any draft ratio by optimizing the control force.The results for the wave tank with a typical water depth of 3 m were studied in detail.The draft ratio has a strong influence on the hydrodynamic coefficients.At the maximum wave absorption efficiency,the displacement and velocity amplitudes are sensitive to the draft ratio in the low-frequency region,increase with decreasing draft ratio,and are independent of the mass of the wave absorber.The control force required can be extremely large for a draft ratio greater than 1/3.The control force increases significantly as the draft ratio increases.The mass of the wave absorber has a weak influence on the control force.A time-domain numerical method based on the boundary element method was developed to verify the analytical solutions.Perfect agreements between the analytical solutions and the numerical results were obtained.
基金Supported by the National Natural Science Foundation of China(Grant No.51909040)the Fund of Science and Technology on Underwater Vehicle Technology(Grant No.JCKYS2022SXJQR-11)+1 种基金the Heilongjiang Provincial Natural Science Foundation of China(Grant No.LH2020E073)the Key Technology Research and Development Program of Shandong(Grant No.2020CXGC010702).
文摘The Reynolds-averaged Navier–Stokes(RANS)equation was solved using computational fluid dynamics to study the effect of the circulating tank wall on the hydrodynamic coefficient of an autonomous underwater vehicle(AUV).Numerical results were compared with the experimental results in the circulating water tank of Harbin Engineering University.The numerical results of the model with different scale ratios under the same water in the flume were studied to investigate the effect of blockage on the hydrodynamic performance of AUV in the circulating flume model test.The results show that the hydrodynamic coefficient is stable with the scale reduction of the model.The influence of blocking effect on AUV is given by combining theoretical calculation with experiment.
基金The Sino-Denmark Cooperation Research on high efficient MW wave power device under contractNo.2007DFA60490the National High-Teach Research and Development Program of China (863 Program) under contract No.2006AA05Z426the National Natural Science Foundation of China under contract No. 50679078
文摘The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device on a plane incident wave is solved by the use of an eigenfunction expansion method, and a new analytical expression for the radiation velocity potential is obtained. The wave excitation force is calculated via the known incident wave potential and the radiation potential with a theorem of Haskind employed. To verify the correctness of this method, an example is computed respectively through the bound element method and analytical method. Results show that two numerical methods. are in good agreement, which shows that the present method is applicable. In addition, the trends of hydrodynamic coefficients and wave force are analyzed under different conditions by use of the present analytical method.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51809037,51879039 and51490672)the Fundamental Research Funds for the Central Universities(Grant No.DUT16RC(4)048)
文摘A plate submerged at a certain depth underneath the sea surface has been proposed as a structure type for different purposes, including motion response reduction, wave control, and wave energy harvesting. In the present study, the three-dimensional wave radiation problem is investigated in the context of the linear potential theory for a submerged ring plate in isolation or attached to a floating column as an appendage. In the latter case, the ring plate is attached at a certain distance above the column bottom. The structure is assumed to undergo a heave motion. An analytical model is developed to solve the wave radiation problem via the eigenfunction expansion method in association with the region-matching technique. With the velocity potential being available, the hydrodynamic coefficients, such as added mass and radiation damping, are obtained through the direct pressure integration. An alternative solution of radiation damping has also been developed in this study, in which the radiation damping is related to the Kochin function in the wave radiation problem. After validating the present model, numerical analysis is performed in detail to assess the influence of various plate parameters, such as the plate size and submergence depth. It is noted that the additional added mass due to the attached ring plate is larger than that when the plate is in isolation. Meanwhile, the radiation damping of the column for the heave motion can vanish at a specific wave frequency by attaching a ring plate, corresponding to a condition that there exist no progressive waves in the exterior region.
基金supported by the National Natural Science Foundation of China(Grants No.51409035,51279029,and 51490673)the Open Fund from the Key Laboratory of Harbor,Waterway and Sedimentation Engineering of Ministry of Communications,Nanjing Hydraulic Research Institute
文摘Fluid flow past twin circular cylinders in a tandem arrangement placed near a plane wall was investigated by means of numerical simulations. The two-dimensional Navier-Stokes equations were solved with a three-step finite element method at a relatively low Reynolds number of Re -- 200 for various dimensionless ratios of 0.25 ≤ G/D ≤2.0 and 1.0 ≤ L/D ≤ 4.0, where D is the cylinder diameter, L is the center-to-center distance between the two cylinders, and G is the gap between the lowest surface of the twin cylinders and the plane wall. The influences of G/D and L/D on the hydrodynamic force coefficients, Strouhal numbers, and vortex shedding modes were examined. Three different vortex shedding modes of the near wake were identified according to the numerical results. It was found that the hydrodynamic force coefficients and vortex shedding modes are quite different with respect to various combinations of G/D and L/D. For very small values of G/D, the vortex shedding is completely suppressed, resulting in the root mean square (RMS) values of drag and lift coefficients of both cylinders and the Strouhal number for the downstream cylinder being almost zero. The mean drag coefficient of the upstream cylinder is larger than that of the downstream cylinder for the same combination of G/D and L/D. It is also observed that change in the vortex shedding modes leads to a significant increase in the RMS values of drag and lift coefficients.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51309123 and 51279104)the Jiangsu Province Natural Science Research Projects in Colleges and Universities(Grant No.13KJB570002)+2 种基金the Open Foundation of State Key Laboratory of Ocean Engineering(Grant No.1407)the"Qing Lan Project"of Colleges and Universities in Jiangsu Provincethe Academic Program Development of Jiangsu Higher Education Institutions(Grant No.APD)
文摘Vortex-induced motion is based on the complex characteristics of the flow around the tension leg platform (TLP) hull. By considering the flow field of the South China Sea and the configuration of the platform, three typical flow velocities and three flow directions are chosen to study the numerical simulation of the flow field characteristics around the TLP hull. Reynolds-averaged Navier-Stokes equations combined with the detached eddy simulation turbulence model are employed in the numerical study. The hydrodynamic coefficients of columns and pontoons, the total drag and lift coefficients of the TLP, the formation and development of the wake, and the vorticity iso-surfaces for different inlet velocities and current directions are discussed in this paper. The average value of the drag coefficient of the upstream columns is considerably larger than that of the downstream columns in the inlet direction of 0°. Although the time history of the lift coefficient demonstrates a "beating" behavior, the plot shows regularity in general. The Strouhal number decreases as the inlet velocity increases from the power spectral density plot at different flow velocities. The mean root values of the lift and drag coefficients of the front column decrease as the current direction increases. Under the symmetrical configuration of 45°, the streamwise force on C4 is the smallest, whereas the transverse force is the largest. The broken vortex conditions in current directions of 22.5° and 45° are more serious than that in the current direction of 0°. In addition, turbulence at the bottom of the TLP becomes stronger when the current direction changes from 0° to 45°. However, a high inlet velocity indicates a large region influenced by the broken vortex and shows the emergence of the wake behind the TLP under the same current angle.
基金Project supported by the National Natural Science Foundation of China(Grant No.11272213)
文摘The submarine Hydrodynamic coefficients are predicted by numerical simulations. Steady and unsteady Reynolds Averaged Navier-Stokes (RANS) simulations are carried out to numerically simulate the oblique towing experiment and the Planar Motion Mechanism (PMM) experiment performed on the SUBOFF submarine model. The dynamic mesh method is adopted to simulate the maneuvering motions of pure heaving, pure swaying, pure pitching and pure yawing. The hydrodynamic forces and moments acting on the maneuvering submarine are obtained. Consequently, by analyzing these results, the hydrodynamic coefficients of the submarine maneuvering motions can be determined. The computational results are verified by comparison with experimental data, which show that this method can be used to estimate the hydrodynamic derivatives of a fully appended submarine.
文摘The boundary hydrodynamic interaction of a 3-D oval body was experimentally surveyed for different cases. The regression method was employed to fred the experimental formulae of hydrodynamic coefficients relating to the attack angle, clearance to wall, and moving speed. The mechanism of interaction was discussed. The experimental results show that there exists a lifting effect, similar to wings in flow. The lifting effect is remarkable. The boundary hydrodynamic interaction of the small aspect ratio model is almost linearly dependent on the attack angle, but the effect of the moving speed of the body on the hydrodynamic coefficients is very small. The effect of clearance is related to the geometric shape. The boundary hydrodynamic interaction always enhances the lifting effect if the clearance is small.
基金the support of Department of Science&Technology(Govt.of India)through PURSE scheme
文摘Euler-Euler two-fluid model is used to simulate the hydrodynamics of gas-solid flow in a bubbling flu- idized bed with Geldert B particles where the solid property is calculated by applying the kinetic theory of granular flow (KTGF). Johnson and Jackson wall boundary condition is used for the particle phase, and different amount of slip between particle and wall is given by varying the specularity coefficient (φ) from 0 to 1. The simulated particle velocity, granular temperature and particle volume fraction are compared to investigate the effect of different wall boundary conditions on the hydrodynamic behavior, Some of the results are also compared with the available experimental data from the literature. It was found that the model predictions are sensitive to the specularity coefficient. The hydrodynamic behavior deviated sig- nificantly for φ = 0 and φ = 0.01 with maximum deviation found at φ = 0 i.e. free-slip condition. However, the overall bed height predicted by all the conditions is similar.
基金This work was supported by the National Natural Science Foundation of China(Grant no.41571274 and 41230746)the Foundation of State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau under project(Grant no.10501-1209).
文摘Hydrodynamic dispersion is a measure for describing the process of solute transport in porous media.Characterizing the dispersion of water flow within gravel is essential for the prediction of solute transport especially nonpoint source pollutants migration in alpine watersheds where the land surface is typically covered with gravel.In this study,an integrated model and experimental method using an electrolyte tracer is proposed for determination of the hydrodynamic dispersion coefficient.Two experimental scenarios were designed to measure electrolyte tracer transport processes in both free water flow and gravel layer flow under different slope gradients and transport distances.Subsequently,the measured data were used to simultaneously calculate both the hydrodynamic dispersion coefficient and flow velocity by fitting the experimental data with the mathematical model.Dispersivity,as a critical feature of hydrodynamic dispersion,was determined as well under the two specified scenarios.Finally,the impact mechanisms of the gravel layer and factors related to the dispersion processes were comprehensively analyzed.The results indicate that the presence of a gravel layer significantly reduces flow velocity and the hydrodynamic dispersion coefficient,but increases solute dispersivity.For the flow within gravel layers,with much lower velocity,the positive effect of the gravel layer on dispersivity may be neutralized or even surpassed by the negative effect of flow velocity.The results should be helpful in characterizing the dispersion processes of water flow within gravel layer and hence in predicting solute transport,especially in nonpoint source pollutants migration in alpine watersheds where the land surface is richly covered with gravel.