Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed...Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed.In this research,the hydrodynamic performance,including capture width ratio(CWR),wave transmission coefficient,heave motion,and force coefficient,were studied and compared between the two types.A numerical simulation model based on the Navier-Stokes equation was employed.The effects of power take-off(PTO)damping coefficient,wave periods,and draft/displacement on the hydrodynamic performance of the two structure shapes were simulated and investigated.The results reveal that the L type performs better in shorter wave periods,and the trapezoidal type exhibits a higher CWR in intermediate wave periods.This study offers knowledge of the design and protection of the two WEC-FB types.展开更多
The turning performance of a ship is an important aspect of its maneuverability,and accurately predicting the hydrodynamic forces during ship turning motion is of great significance for the safe maneuvering design of ...The turning performance of a ship is an important aspect of its maneuverability,and accurately predicting the hydrodynamic forces during ship turning motion is of great significance for the safe maneuvering design of ships.This paper investigated the hydrodynamic performance of a KRISO container ship in steady turning using experimental and numerical approaches.The rotating arm tests were carried out in rotating arm basin of Zhejiang University,while the numerical simulations were conducted in commercial computational fluid dynamics software.Hydrodynamic forces and moments,hull surface wave height,wave patterns,and vorticity are studied under different velocities,radii,and drift angles.The results show that the increase in velocity has a significant impact on the forces and moments of the hull.The changes in longitudinal and transverse forces reflect the complex fluid dynamic interactions between the hull and water.Under conditions of small radius and large drift angle,the hull experiences greater forces and moments,indicating that stability and maneuverability will be more challenged during sudden turns.This study can provide experimental data and numerical simulation references for the research of ship turning maneuvers.展开更多
Obtaining unsteady hydrodynamic performance is of great significance for seaplane design.Common methods for obtaining unsteady hydrodynamic performance data include tank test and Computational Fluid Dynamics(CFD)numer...Obtaining unsteady hydrodynamic performance is of great significance for seaplane design.Common methods for obtaining unsteady hydrodynamic performance data include tank test and Computational Fluid Dynamics(CFD)numerical simulation,which are costly and time-consuming.Therefore,it is necessary to obtain unsteady hydrodynamic performance in a low-cost and high-precision manner.Due to the strong nonlinearity,complex data distribution,and temporal characteristics of unsteady hydrodynamic performance,the prediction of it is challenging.This paper proposes a Temporal Convolutional Diffusion Model(TCDM)for predicting the unsteady hydrodynamic performance of seaplanes given design parameters.Under the framework of a classifier-free guided diffusion model,TCDM learns the distribution patterns of unsteady hydrodynamic performance data with the designed denoising module based on temporal convolutional network and captures the temporal features of unsteady hydrodynamic performance data.Using CFD simulation data,the proposed method is compared with the alternative methods to demonstrate its accuracy and generalization.This paper provides a method that enables the rapid and accurate prediction of unsteady hydrodynamic performance data,expecting to shorten the design cycle of seaplanes.展开更多
To meet the intelligent detection needs of underwater defects in large hydropower stations,the hydrodynamic performance of a bionic streamlined remotely operated vehicle containing a thruster protective net structure ...To meet the intelligent detection needs of underwater defects in large hydropower stations,the hydrodynamic performance of a bionic streamlined remotely operated vehicle containing a thruster protective net structure is numerically simulated via computational fluid dynamics and overlapping mesh technology.The results show that the entity model generates greater hydrodynamic force during steady motion,whereas the square net model experiences greater force and moment during unsteady motion.The lateral and vertical force coefficients of the entity model are 4.32 and 3.13 times greater than those of the square net model in the oblique towing test simulation.The square net model also offers better static and dynamic stability,with a 24.5%increase in dynamic stability,achieving the highest lift-to-drag ratio at attack angles of 6°∼8°.This research provides valuable insights for designing and controlling underwater defect detection vehicles for large hydropower stations.展开更多
This paper presents a multi-module oscillating water column(OWC)wave energy converter(WEC)array system,comprising seven interconnected OWC modules.The modules are connected by elastic ropes with clumped weights positi...This paper presents a multi-module oscillating water column(OWC)wave energy converter(WEC)array system,comprising seven interconnected OWC modules.The modules are connected by elastic ropes with clumped weights positioned at the ropes'midpoints.Three distinct mooring systems are designed for this OWC array,and the impact of mooring configurations on the hydrodynamic responses of the OWCs and mooring tensions is thoroughly examined.Three-dimensional potential flow theory is applied to perform time domain analyses.The motion responses of representative modules,the tension of specific mooring lines,and the spacing between adjacent modules in the array system are investigated through a comprehensive coupled dynamic analysis in the time domain.Based on these analyses,recommendations are provided for the optimal mooring system configuration for the array system.展开更多
The main aims of this study are to investigate the hydrodynamic performance of an autonomous underwater vehicle(AUV),calculate its hydrodynamic coefficients,and consider the flow characteristics of underwater bodies.I...The main aims of this study are to investigate the hydrodynamic performance of an autonomous underwater vehicle(AUV),calculate its hydrodynamic coefficients,and consider the flow characteristics of underwater bodies.In addition,three important parts of the SUBOFF bare hull,namely the main body,nose,and tail,are modified and redesigned to improve its hydrodynamic performance.A three-dimensional(3D)simulation is carried out using the computational fluid dynamics(CFD)method.To simulate turbulence,the k-ωshear stress transport(SST)model is employed,due to its good prediction capability at reasonable computational cost.Considering the effects of the length-to-diameter ratio(LTDR)and the nose and tail shapes on the hydrodynamic coefficients,it is concluded that a hull shape with bullet nose and sharp tail with LTDR equal to 7.14 performs better than the SUBOFF model.The final proposed model shows lower drag by about 14.9%at u=1.5 m·s^-1.Moreover,it produces 8 times more lift than the SUBOFF model at u=6.1 m·s^-1.These effects are due to the attachment of the fluid flow at the tail area of the hull,which weakens the wake region.展开更多
The hydrodynamic performance of a bottom-hinged flap wave energy converter （WEC） is investigated through a frequency domain numerical model. The numerical model is verified through a two-dimensional analytic solutio...The hydrodynamic performance of a bottom-hinged flap wave energy converter （WEC） is investigated through a frequency domain numerical model. The numerical model is verified through a two-dimensional analytic solution, as well as the qualitative analysis on the dynamic response of avibrating system. The concept of ＂optimum density＂ of the bottom-hinged flap is proposed, and its analytic expression is derived as well. The frequency interval in which the optimum density exists is also obtained. The analytic expression of the optimum linear damping coefficient is obtained by a bottom-hinged WEC. Some basic dynamic properties involving natural period, excitation moment, pitch amplitude, and optimum damping coefficient are analyzed and discussed in detail. In addition, this paper highlights the analysis of effects on the conversion performance of the device exerted by some important parameters. The results indicate that ＂the optimum linear damping period of 5.0 s＂ is the most ideal option in the short wave sea states with the wave period below 6.0 s. Shallow water depth, large flap thickness and low flap density are advised in the practical design of the device in short wave sea states in order to maximize power capture. In the sea state with water depth of 5.0 m and wave period of 5.0 s, the results of parametric optimization suggest a flap with the width of 8.0 m, thickness of 1.6 m, and with the density as little as possible when the optimum power take-off （PTO） damping coefficient is adopted.展开更多
In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the...In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.展开更多
The unsteady performance of drag and double reverse propeller podded propulsors in open water was numerically simulated using a computational fluid dynamics （CFD） method. A moving mesh method was used to more realis...The unsteady performance of drag and double reverse propeller podded propulsors in open water was numerically simulated using a computational fluid dynamics （CFD） method. A moving mesh method was used to more realistically simulate propulsor working conditions, and the thrust, torque, and lateral force coefficients of both propulsors were compared and analyzed. Forces acting on different parts of the propulsors along with the flow field distribution of steady and unsteady results at different advance coefficients were compared. Moreover, the change of the lateral force and the difference between the abovementioned two methods were mainly analyzed. It was shown that the thrust and torque results of both methods were similar, with the lateral force results having the highest deviation展开更多
In the present paper,the hydrodynamic performance of stepped planing craft is investigated by computational fluid dynamics(CFD)analysis.For this purpose,the hydrodynamic resistances of without step,one-step,and two-st...In the present paper,the hydrodynamic performance of stepped planing craft is investigated by computational fluid dynamics(CFD)analysis.For this purpose,the hydrodynamic resistances of without step,one-step,and two-step hulls of Cougar planing craft are evaluated under different distances of the second step and LCG from aft,weight loadings,and Froude numbers(Fr).Our CFD results are appropriately validated against our conducted experimental test in National Iranians Marine Laboratory(NIMALA),Tehran,Iran.Then,the hydrodynamic resistance of intended planing crafts under various geometrical and physical conditions is predicted using artificial neural networks(ANNs).CFD analysis shows two different trends in the growth rate of resistance to weight ratio.So that,using steps for planing craft increases the resistance to weight ratio at lower Fr and decreases it at higher Fr.Additionally,by the increase of the distance between two steps,the resistance to weight ratio is decreased and the porpoising phenomenon is delayed.Furthermore,we obtained the maximum mean square error of ANNs output in the prediction of resistance to weight ratio equal to 0.0027.Finally,the predictive equation is suggested for the resistance to weight ratio of stepped planing craft according to weights and bias of designed ANNs.展开更多
The hydrodynamic performance of a hybrid CRP pod propulsion system was studied by RANS method with SST k ？？ turbulence model and sliding mesh. The effect of axial spacing on the hydrodynamic performance of the hybri...The hydrodynamic performance of a hybrid CRP pod propulsion system was studied by RANS method with SST k ？？ turbulence model and sliding mesh. The effect of axial spacing on the hydrodynamic performance of the hybrid CRP pod propulsion system was investigated numerically and experimentally. It shows that RANS with the sliding mesh method and SST k -ω turbulence model predicts accurately the hydrodynamic performance of the hybrid CRP pod propulsion system. The axial spacing has little influence on the hydrodynamic performance of the forward propeller, but great influence on that of the pod unit. Thrust coefficient of the pod unit declines with the increase of the axial spacing, but the trend becomes weaker, and the decreasing amplitude at the lower advance coefficient is larger than that at the higher advance coefficient. The thrust coefficient and open water efficiency of the hybrid CRP pod propulsion system decrease with the increase of the axial spacing, while the torque coefficient keeps almost constant. On this basis, the design principle of axial spacing of the hybrid CRP pod propulsion system was proposed.展开更多
A new numerical method was developed for predicting the steady hydrodynamic performance of ducted propellers. A potential based surface panel method was applied both to the duct and the propeller, and the interaction ...A new numerical method was developed for predicting the steady hydrodynamic performance of ducted propellers. A potential based surface panel method was applied both to the duct and the propeller, and the interaction between them was solved by an induced velocity potential iterative method. Compared with the induced velocity iterative method, the method presented can save programming and calculating time. Numerical results for a JD simplified ducted propeller series showed that the method presented is effective for predicting the steady hydrodynamic performance of ducted propellers.展开更多
A numerical approach based on the solution of the Reynolds-averaged Navier-Stokes(RANS) equations using the shear-stress transport(SST) turbulence model has been employed to investigate the hydrodynamic performance an...A numerical approach based on the solution of the Reynolds-averaged Navier-Stokes(RANS) equations using the shear-stress transport(SST) turbulence model has been employed to investigate the hydrodynamic performance and flow of tunnel thrusters.The flow passages between adjacent blades are discretized with prismatic cells so that the boundary layer flow is resolved down to the viscous sub-layer.The hydrodynamic performances predicted by the quasi-steady approach agree well with the experimental data for three impellers covering a range of blade area and pitch.Through analysis of the flow field,the reason why the hub of impeller also contributes to thrust which can amount to 40%—60% of the impeller thrust,and the mechanism of the impeller inducing an axial force on the hull are elucidated.展开更多
A hybrid, porous breakwater-Oscillating Water Column(OWC) Wave Energy Converter(WEC) system is put forward and its hydrodynamic performance is investigated using the fully nonlinear, open-source computational fluid dy...A hybrid, porous breakwater-Oscillating Water Column(OWC) Wave Energy Converter(WEC) system is put forward and its hydrodynamic performance is investigated using the fully nonlinear, open-source computational fluid dynamics(CFD) model, OpenFOAM. The permeable structure is positioned at the weather side of the OWC device and adjoined to its front wall. A numerical modelling approach is employed in which the interstices within the porous structure are explicitly defined. This permits the flow field development within the porous structure and at the OWC front wall to be observed. The WEC device is defined as a land-fixed, semi-submerged OWC chamber. A range of regular incident waves are generated at the inlet within the numerical tank. The OWC efficiency and the forces on the structure are examined. Results are compared for the simulation cases in which the porous component is present or absent in front of the OWC chamber. It is found that the incorporation of the porous component has minimal effect on the hydrodynamic efficiency of the OWC, reducing the efficiency by less than 5%. Nevertheless,the forces on the front wall of the OWC can be reduced by up to 20% at the higher wave steepness investigated,through inclusion of the porous structure at the OWC front wall. These findings have considerable implications for the design of hybrid OWC-breakwater systems, most importantly in terms of enhancing the durability and survivability of OWC WECs without significant loss of operational efficiency.展开更多
Fish are able to make good use of vortices.In a complex flow field,many fish continue to maintain both efficient cruising and maneuverability.Traditional man-made propulsion systems perform poorly in complex flow fiel...Fish are able to make good use of vortices.In a complex flow field,many fish continue to maintain both efficient cruising and maneuverability.Traditional man-made propulsion systems perform poorly in complex flow fields.With fish-like propulsion systems,it is important to pay more attention to complex flow fields.In this paper,the influence of vortices on the hydrodynamic performance of 2-D flapping-foils was investigated.The flapping-foil heaved and pitched under the influence of inflow vortices generated by an oscillating D-section cylinder.A numerical simulation was run based the finite volume method,using the computational fluid dynamics(CFD) software FLUENT with Reynolds-averaged Navier-Stokes(RANS) equations applied.In addition,dynamic mesh technology and post processing systems were also fully used.The calculations showed four modes of interaction.The hydrodynamic performance of flapping-foils was analyzed and the results compared with experimental data.This validated the numerical simulation,confirming that flapping-foils can increase efficiency by absorbing energy from inflow vortices.展开更多
A mathematical model of podded propulsors was established in order to investigate the influence of fins. The hydrodynamic performance of podded propulsors with and without fins was calculated, with interactions betwee...A mathematical model of podded propulsors was established in order to investigate the influence of fins. The hydrodynamic performance of podded propulsors with and without fins was calculated, with interactions between propellers and pods and fins derived by iterative calculation. The differential equation based on velocity potential was adopted and hyperboloidal panels were used to avoid gaps between surface panels. The Newton-Raphson iterative procedure was used on the trailing edge to meet the pressure Kutta condition. The velocity distribution was calculated with the Yanagizawa method to eliminate the singularity caused by use of the numerical differential. Comparisons of the performance of podded propulsors with different fins showed that the thrust of propeller in a podded propulsor with fins is greater. The resistance of the pod is also reduced because of the thrust of the fin. The hydrodynamic performance of a podded propulsor with two fins is found to be best, the performance of a podded propulsor with one fin is not as good as two fins, and the performance of the common type is the worst.展开更多
Articulated buoys become more and more popular by the marine management departments as a new type of aids to navigation, for they possess an excellent hydrodynamic performance with small static heel angle in wind and ...Articulated buoys become more and more popular by the marine management departments as a new type of aids to navigation, for they possess an excellent hydrodynamic performance with small static heel angle in wind and current and small rolling in wave and accurate position. The structure of articulated buoys and calculation method of their hydrodynamic performance are introduced in this paper. A scries of experiments has been conducted in the State Key Laboratory of Ocean Engineering of China and useful results achieved for providing a design optimization basis.展开更多
With the acceleration of marine construction in China,the exploitation and utilization of resources from islands and reefs are necessary.To prevent and dissipate waves in the process of resource exploitation and utili...With the acceleration of marine construction in China,the exploitation and utilization of resources from islands and reefs are necessary.To prevent and dissipate waves in the process of resource exploitation and utilization,a more effective method is to install floating breakwaters near the terrain of islands and reefs.The terrain around islands and reefs is complex,and waves undergo a series of changes due to the impact of the complex terrain in transmission.It is important to find a suitable location for floating breakwater systems on islands and reefs and investigate how the terrain affects the system’s hydrodynamic performance.This paper introduces a three-cylinder floating breakwater design.The breakwater system consists of 8 units connected by elastic structures and secured by a slack mooring system.To evaluate its effectiveness,a 3D model experiment was conducted in a wave basin.During the experiment,a model resembling the islands and reefs terrain was created on the basis of the water depth map of a specific region in the East China Sea.The transmission coefficients and motion responses of the three-cylinder floating breakwater system were then measured.This was done both in the middle of and behind the islands and reefs terrain.According to the experimental results,the three-cylinder floating breakwater system performs better in terms of hydrodynamics when it is placed behind the terrain of islands and reefs than in the middle of the same terrain.展开更多
The problem of the hydrodynamic interaction with the arc-shaped bottom-mounted breakwaters is investigated theoretically. The breakwater is assumed to be rigid, thin, impermeable and vertically located in a finite wat...The problem of the hydrodynamic interaction with the arc-shaped bottom-mounted breakwaters is investigated theoretically. The breakwater is assumed to be rigid, thin, impermeable and vertically located in a finite water depth. The fluid domain is divided into two sub-regions of inner and outer by an auxiliary circular interface. Linear theory is assumed and the eigenfunction expansion approach is used to determine the wave field. In order to examine the validity of the theoretical model, the analytical solutions are compared to agree well with published results with the same parameters. Numerical results including wave amplitude, surge pressure, and wave force are presented with different model parameters. The major factors including wave parameters, structure configuration, and water depth that affect the surge pressure, wave forces, and wave amplitudes are discussed and illustrated by some graphs and cloud maps.展开更多
Two-dimensional(2D)flume experiments are useful in investigating the performances of floating breakwaters(FBs),including hydrodynamic performances,motion responses,and mooring forces.Designing a reasonable gap between...Two-dimensional(2D)flume experiments are useful in investigating the performances of floating breakwaters(FBs),including hydrodynamic performances,motion responses,and mooring forces.Designing a reasonable gap between the flume wall and the FBs is a critical step in 2D flume tests.However,research on the effect of the gap on the accuracy of 2D FB experimental results is scarce.To address this issue,a numerical wave tank is developed using CFD to estimate the wave-FB interaction of a moored dual-cylindrical FB,and the results are compared to experimental data from a previously published work.There is good agreement between them,indicating that the numerical model is sufficiently accurate.The numerical model is then applied to explore the effect of gap diffraction on the performance of FBs in2D experiments.It was discovered that the nondimensional gap length L_(Gap)/W_(Pool)should be smaller than 7.5%to ensure that the relative error of the transmission coefficient is smaller than 3%.The influence of the gap is also related to the entering wave properties,such as the wave height and period.展开更多
基金Supported by Shandong Provincial Natural Science Foundation,China(ZR2020ME259)Open Fund of Shandong Key Laboratory of Civil Engineering Disaster Prevention and Mitigation(CDPM2021KF21).
文摘Two asymmetric types of floating breakwaters integrated with a wave energy converter(WEC-FBs),a floating square box with a triangle(trapezoidal type)or a wave baffle(L type)attached to its rear side,have been proposed.In this research,the hydrodynamic performance,including capture width ratio(CWR),wave transmission coefficient,heave motion,and force coefficient,were studied and compared between the two types.A numerical simulation model based on the Navier-Stokes equation was employed.The effects of power take-off(PTO)damping coefficient,wave periods,and draft/displacement on the hydrodynamic performance of the two structure shapes were simulated and investigated.The results reveal that the L type performs better in shorter wave periods,and the trapezoidal type exhibits a higher CWR in intermediate wave periods.This study offers knowledge of the design and protection of the two WEC-FB types.
基金supported by the China Scholarship Council(Grant No.202306320084).
文摘The turning performance of a ship is an important aspect of its maneuverability,and accurately predicting the hydrodynamic forces during ship turning motion is of great significance for the safe maneuvering design of ships.This paper investigated the hydrodynamic performance of a KRISO container ship in steady turning using experimental and numerical approaches.The rotating arm tests were carried out in rotating arm basin of Zhejiang University,while the numerical simulations were conducted in commercial computational fluid dynamics software.Hydrodynamic forces and moments,hull surface wave height,wave patterns,and vorticity are studied under different velocities,radii,and drift angles.The results show that the increase in velocity has a significant impact on the forces and moments of the hull.The changes in longitudinal and transverse forces reflect the complex fluid dynamic interactions between the hull and water.Under conditions of small radius and large drift angle,the hull experiences greater forces and moments,indicating that stability and maneuverability will be more challenged during sudden turns.This study can provide experimental data and numerical simulation references for the research of ship turning maneuvers.
基金supported by the Aeronautical Science Foundation of China(Nos.2018ZA52002,2019ZA052011)the National Natural Science Foundation of China(No.12472236).
文摘Obtaining unsteady hydrodynamic performance is of great significance for seaplane design.Common methods for obtaining unsteady hydrodynamic performance data include tank test and Computational Fluid Dynamics(CFD)numerical simulation,which are costly and time-consuming.Therefore,it is necessary to obtain unsteady hydrodynamic performance in a low-cost and high-precision manner.Due to the strong nonlinearity,complex data distribution,and temporal characteristics of unsteady hydrodynamic performance,the prediction of it is challenging.This paper proposes a Temporal Convolutional Diffusion Model(TCDM)for predicting the unsteady hydrodynamic performance of seaplanes given design parameters.Under the framework of a classifier-free guided diffusion model,TCDM learns the distribution patterns of unsteady hydrodynamic performance data with the designed denoising module based on temporal convolutional network and captures the temporal features of unsteady hydrodynamic performance data.Using CFD simulation data,the proposed method is compared with the alternative methods to demonstrate its accuracy and generalization.This paper provides a method that enables the rapid and accurate prediction of unsteady hydrodynamic performance data,expecting to shorten the design cycle of seaplanes.
基金supported by the National Key R&D Program of China(Grant No.2022YFB4703401).
文摘To meet the intelligent detection needs of underwater defects in large hydropower stations,the hydrodynamic performance of a bionic streamlined remotely operated vehicle containing a thruster protective net structure is numerically simulated via computational fluid dynamics and overlapping mesh technology.The results show that the entity model generates greater hydrodynamic force during steady motion,whereas the square net model experiences greater force and moment during unsteady motion.The lateral and vertical force coefficients of the entity model are 4.32 and 3.13 times greater than those of the square net model in the oblique towing test simulation.The square net model also offers better static and dynamic stability,with a 24.5%increase in dynamic stability,achieving the highest lift-to-drag ratio at attack angles of 6°∼8°.This research provides valuable insights for designing and controlling underwater defect detection vehicles for large hydropower stations.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52301322,52025112,and 52331011)Natural Science Foundation of Jiangsu Province(Grant No.BK20220653)。
文摘This paper presents a multi-module oscillating water column(OWC)wave energy converter(WEC)array system,comprising seven interconnected OWC modules.The modules are connected by elastic ropes with clumped weights positioned at the ropes'midpoints.Three distinct mooring systems are designed for this OWC array,and the impact of mooring configurations on the hydrodynamic responses of the OWCs and mooring tensions is thoroughly examined.Three-dimensional potential flow theory is applied to perform time domain analyses.The motion responses of representative modules,the tension of specific mooring lines,and the spacing between adjacent modules in the array system are investigated through a comprehensive coupled dynamic analysis in the time domain.Based on these analyses,recommendations are provided for the optimal mooring system configuration for the array system.
文摘The main aims of this study are to investigate the hydrodynamic performance of an autonomous underwater vehicle(AUV),calculate its hydrodynamic coefficients,and consider the flow characteristics of underwater bodies.In addition,three important parts of the SUBOFF bare hull,namely the main body,nose,and tail,are modified and redesigned to improve its hydrodynamic performance.A three-dimensional(3D)simulation is carried out using the computational fluid dynamics(CFD)method.To simulate turbulence,the k-ωshear stress transport(SST)model is employed,due to its good prediction capability at reasonable computational cost.Considering the effects of the length-to-diameter ratio(LTDR)and the nose and tail shapes on the hydrodynamic coefficients,it is concluded that a hull shape with bullet nose and sharp tail with LTDR equal to 7.14 performs better than the SUBOFF model.The final proposed model shows lower drag by about 14.9%at u=1.5 m·s^-1.Moreover,it produces 8 times more lift than the SUBOFF model at u=6.1 m·s^-1.These effects are due to the attachment of the fluid flow at the tail area of the hull,which weakens the wake region.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41206074 and 51205346)the Special Fund for Marine Renewable Energy (Grant Nos. GHME2011CX01 and GHME2011ZC05)
文摘The hydrodynamic performance of a bottom-hinged flap wave energy converter （WEC） is investigated through a frequency domain numerical model. The numerical model is verified through a two-dimensional analytic solution, as well as the qualitative analysis on the dynamic response of avibrating system. The concept of ＂optimum density＂ of the bottom-hinged flap is proposed, and its analytic expression is derived as well. The frequency interval in which the optimum density exists is also obtained. The analytic expression of the optimum linear damping coefficient is obtained by a bottom-hinged WEC. Some basic dynamic properties involving natural period, excitation moment, pitch amplitude, and optimum damping coefficient are analyzed and discussed in detail. In addition, this paper highlights the analysis of effects on the conversion performance of the device exerted by some important parameters. The results indicate that ＂the optimum linear damping period of 5.0 s＂ is the most ideal option in the short wave sea states with the wave period below 6.0 s. Shallow water depth, large flap thickness and low flap density are advised in the practical design of the device in short wave sea states in order to maximize power capture. In the sea state with water depth of 5.0 m and wave period of 5.0 s, the results of parametric optimization suggest a flap with the width of 8.0 m, thickness of 1.6 m, and with the density as little as possible when the optimum power take-off （PTO） damping coefficient is adopted.
基金supported by the National Key Technology R&D Program(No.2013BAD13B03)the Key R&D Project from Science and Technology Department of Zhejiang Province(Nos.2018C02026,2018C02040)+1 种基金the National Natural Science Foundation of China(No.31072246)the Fundamental Research Funds for the Central Universities(No.201564020)
文摘In the present work,the hydrodynamic performance of the double deflector rectangular cambered otter board was studied using wind tunnel experiment,flume tank experiment and numerical simulation.Results showed that the otter board had a good hydrodynamic performance with the maximum lift-to-drag ratio(K_(MAX) = 3.70).The flow separation occurred when the angle of attack(AOA) was at 45?,which revealed that the double deflector structure of the otter board can delay the flow separation.Numerical simulation results showed a good agreement with experiment ones,and could predict the critical AOA,which showed that it can be used to study the hydrodynamic performance of the otter board with the advantage of flow visualization.However,the drag coefficient in flume tank was much higher than that in wind tunnel,which resulted in a lower lift-to-drag ratio.These may be due to different fluid media between flume tank and wind tunnel,which result in the big difference of the vortexes around the otter board.Given the otter boards are operated in water,it was suggested to apply both flume tank experiment and numerical simulation to study the hydrodynamic performance of otter board.
基金Supported by National Natural Science Foundation of China （41176074, 51209048,51379043,51409063） High tech ship research project of Ministry of industry and technology （G014613002） The support plan for youth backbone teachers of Harbin Engineering University （HEUCFQ1408）
文摘The unsteady performance of drag and double reverse propeller podded propulsors in open water was numerically simulated using a computational fluid dynamics （CFD） method. A moving mesh method was used to more realistically simulate propulsor working conditions, and the thrust, torque, and lateral force coefficients of both propulsors were compared and analyzed. Forces acting on different parts of the propulsors along with the flow field distribution of steady and unsteady results at different advance coefficients were compared. Moreover, the change of the lateral force and the difference between the abovementioned two methods were mainly analyzed. It was shown that the thrust and torque results of both methods were similar, with the lateral force results having the highest deviation
文摘In the present paper,the hydrodynamic performance of stepped planing craft is investigated by computational fluid dynamics(CFD)analysis.For this purpose,the hydrodynamic resistances of without step,one-step,and two-step hulls of Cougar planing craft are evaluated under different distances of the second step and LCG from aft,weight loadings,and Froude numbers(Fr).Our CFD results are appropriately validated against our conducted experimental test in National Iranians Marine Laboratory(NIMALA),Tehran,Iran.Then,the hydrodynamic resistance of intended planing crafts under various geometrical and physical conditions is predicted using artificial neural networks(ANNs).CFD analysis shows two different trends in the growth rate of resistance to weight ratio.So that,using steps for planing craft increases the resistance to weight ratio at lower Fr and decreases it at higher Fr.Additionally,by the increase of the distance between two steps,the resistance to weight ratio is decreased and the porpoising phenomenon is delayed.Furthermore,we obtained the maximum mean square error of ANNs output in the prediction of resistance to weight ratio equal to 0.0027.Finally,the predictive equation is suggested for the resistance to weight ratio of stepped planing craft according to weights and bias of designed ANNs.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51479207 and 51179198)the High Technology Marine Scientific Research Project of the Ministry of Industry and Information Technology of China(Grant No.[2012]534)
文摘The hydrodynamic performance of a hybrid CRP pod propulsion system was studied by RANS method with SST k ？？ turbulence model and sliding mesh. The effect of axial spacing on the hydrodynamic performance of the hybrid CRP pod propulsion system was investigated numerically and experimentally. It shows that RANS with the sliding mesh method and SST k -ω turbulence model predicts accurately the hydrodynamic performance of the hybrid CRP pod propulsion system. The axial spacing has little influence on the hydrodynamic performance of the forward propeller, but great influence on that of the pod unit. Thrust coefficient of the pod unit declines with the increase of the axial spacing, but the trend becomes weaker, and the decreasing amplitude at the lower advance coefficient is larger than that at the higher advance coefficient. The thrust coefficient and open water efficiency of the hybrid CRP pod propulsion system decrease with the increase of the axial spacing, while the torque coefficient keeps almost constant. On this basis, the design principle of axial spacing of the hybrid CRP pod propulsion system was proposed.
基金Supported by the Open Research Foundation of State Key Laboratory of AUV,HEU under Grant No.2007015
文摘A new numerical method was developed for predicting the steady hydrodynamic performance of ducted propellers. A potential based surface panel method was applied both to the duct and the propeller, and the interaction between them was solved by an induced velocity potential iterative method. Compared with the induced velocity iterative method, the method presented can save programming and calculating time. Numerical results for a JD simplified ducted propeller series showed that the method presented is effective for predicting the steady hydrodynamic performance of ducted propellers.
文摘A numerical approach based on the solution of the Reynolds-averaged Navier-Stokes(RANS) equations using the shear-stress transport(SST) turbulence model has been employed to investigate the hydrodynamic performance and flow of tunnel thrusters.The flow passages between adjacent blades are discretized with prismatic cells so that the boundary layer flow is resolved down to the viscous sub-layer.The hydrodynamic performances predicted by the quasi-steady approach agree well with the experimental data for three impellers covering a range of blade area and pitch.Through analysis of the flow field,the reason why the hub of impeller also contributes to thrust which can amount to 40%—60% of the impeller thrust,and the mechanism of the impeller inducing an axial force on the hull are elucidated.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51679036 and 52011530183)Liaoning Revitalization Talents Program (Grant No. XLYC2002033)+1 种基金Liaoning BaiQianWan Talents Program (Grant No. 2020921007)EPSRC Project (Grant No. EP/R007519/1)
文摘A hybrid, porous breakwater-Oscillating Water Column(OWC) Wave Energy Converter(WEC) system is put forward and its hydrodynamic performance is investigated using the fully nonlinear, open-source computational fluid dynamics(CFD) model, OpenFOAM. The permeable structure is positioned at the weather side of the OWC device and adjoined to its front wall. A numerical modelling approach is employed in which the interstices within the porous structure are explicitly defined. This permits the flow field development within the porous structure and at the OWC front wall to be observed. The WEC device is defined as a land-fixed, semi-submerged OWC chamber. A range of regular incident waves are generated at the inlet within the numerical tank. The OWC efficiency and the forces on the structure are examined. Results are compared for the simulation cases in which the porous component is present or absent in front of the OWC chamber. It is found that the incorporation of the porous component has minimal effect on the hydrodynamic efficiency of the OWC, reducing the efficiency by less than 5%. Nevertheless,the forces on the front wall of the OWC can be reduced by up to 20% at the higher wave steepness investigated,through inclusion of the porous structure at the OWC front wall. These findings have considerable implications for the design of hybrid OWC-breakwater systems, most importantly in terms of enhancing the durability and survivability of OWC WECs without significant loss of operational efficiency.
基金Supported by the National Natural Science Foundation of China under Grant No.50579007,50879014the specialized research fund for the doctoral program of higher education under Grant No.200802170010
文摘Fish are able to make good use of vortices.In a complex flow field,many fish continue to maintain both efficient cruising and maneuverability.Traditional man-made propulsion systems perform poorly in complex flow fields.With fish-like propulsion systems,it is important to pay more attention to complex flow fields.In this paper,the influence of vortices on the hydrodynamic performance of 2-D flapping-foils was investigated.The flapping-foil heaved and pitched under the influence of inflow vortices generated by an oscillating D-section cylinder.A numerical simulation was run based the finite volume method,using the computational fluid dynamics(CFD) software FLUENT with Reynolds-averaged Navier-Stokes(RANS) equations applied.In addition,dynamic mesh technology and post processing systems were also fully used.The calculations showed four modes of interaction.The hydrodynamic performance of flapping-foils was analyzed and the results compared with experimental data.This validated the numerical simulation,confirming that flapping-foils can increase efficiency by absorbing energy from inflow vortices.
基金Supported by the National Natural Science Foundation of China under Grant No.10702016
文摘A mathematical model of podded propulsors was established in order to investigate the influence of fins. The hydrodynamic performance of podded propulsors with and without fins was calculated, with interactions between propellers and pods and fins derived by iterative calculation. The differential equation based on velocity potential was adopted and hyperboloidal panels were used to avoid gaps between surface panels. The Newton-Raphson iterative procedure was used on the trailing edge to meet the pressure Kutta condition. The velocity distribution was calculated with the Yanagizawa method to eliminate the singularity caused by use of the numerical differential. Comparisons of the performance of podded propulsors with different fins showed that the thrust of propeller in a podded propulsor with fins is greater. The resistance of the pod is also reduced because of the thrust of the fin. The hydrodynamic performance of a podded propulsor with two fins is found to be best, the performance of a podded propulsor with one fin is not as good as two fins, and the performance of the common type is the worst.
文摘Articulated buoys become more and more popular by the marine management departments as a new type of aids to navigation, for they possess an excellent hydrodynamic performance with small static heel angle in wind and current and small rolling in wave and accurate position. The structure of articulated buoys and calculation method of their hydrodynamic performance are introduced in this paper. A scries of experiments has been conducted in the State Key Laboratory of Ocean Engineering of China and useful results achieved for providing a design optimization basis.
基金financially supported by the China National Funds for Distinguished Young Scientists(Grant No.52025112).
文摘With the acceleration of marine construction in China,the exploitation and utilization of resources from islands and reefs are necessary.To prevent and dissipate waves in the process of resource exploitation and utilization,a more effective method is to install floating breakwaters near the terrain of islands and reefs.The terrain around islands and reefs is complex,and waves undergo a series of changes due to the impact of the complex terrain in transmission.It is important to find a suitable location for floating breakwater systems on islands and reefs and investigate how the terrain affects the system’s hydrodynamic performance.This paper introduces a three-cylinder floating breakwater design.The breakwater system consists of 8 units connected by elastic structures and secured by a slack mooring system.To evaluate its effectiveness,a 3D model experiment was conducted in a wave basin.During the experiment,a model resembling the islands and reefs terrain was created on the basis of the water depth map of a specific region in the East China Sea.The transmission coefficients and motion responses of the three-cylinder floating breakwater system were then measured.This was done both in the middle of and behind the islands and reefs terrain.According to the experimental results,the three-cylinder floating breakwater system performs better in terms of hydrodynamics when it is placed behind the terrain of islands and reefs than in the middle of the same terrain.
基金supported by the Major State Basic Research Development Program of China(973 Program,Grant Nos.2014CB046801 and 2014CB046804)the Foundation of the China Scholarship Council(Grant No.201203170143)
文摘The problem of the hydrodynamic interaction with the arc-shaped bottom-mounted breakwaters is investigated theoretically. The breakwater is assumed to be rigid, thin, impermeable and vertically located in a finite water depth. The fluid domain is divided into two sub-regions of inner and outer by an auxiliary circular interface. Linear theory is assumed and the eigenfunction expansion approach is used to determine the wave field. In order to examine the validity of the theoretical model, the analytical solutions are compared to agree well with published results with the same parameters. Numerical results including wave amplitude, surge pressure, and wave force are presented with different model parameters. The major factors including wave parameters, structure configuration, and water depth that affect the surge pressure, wave forces, and wave amplitudes are discussed and illustrated by some graphs and cloud maps.
基金financially supported by China National Funds for Distinguished Young Scientists(Grant No.52025112)the Key Projects of the National Natural Science Foundation of China(Grant No.52331011)。
文摘Two-dimensional(2D)flume experiments are useful in investigating the performances of floating breakwaters(FBs),including hydrodynamic performances,motion responses,and mooring forces.Designing a reasonable gap between the flume wall and the FBs is a critical step in 2D flume tests.However,research on the effect of the gap on the accuracy of 2D FB experimental results is scarce.To address this issue,a numerical wave tank is developed using CFD to estimate the wave-FB interaction of a moored dual-cylindrical FB,and the results are compared to experimental data from a previously published work.There is good agreement between them,indicating that the numerical model is sufficiently accurate.The numerical model is then applied to explore the effect of gap diffraction on the performance of FBs in2D experiments.It was discovered that the nondimensional gap length L_(Gap)/W_(Pool)should be smaller than 7.5%to ensure that the relative error of the transmission coefficient is smaller than 3%.The influence of the gap is also related to the entering wave properties,such as the wave height and period.
