Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(...Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(SPH)method under the Lagrange framework is adopted to simulate the breaking bow wave of the KCS ship model.In order to improve the computational efficiency,the inflow and outflow boundary model is used to establish a numerical tank of current,and a numerical treatment for free surface separation is implemented.Numerical simulations are carried out at Fr=0.35,0.40,0.5,0.6,and different types of wave breaking such as spilling breaker,plunging breaker,and scars are captured by the SPH method,which is consistent with the experimental result,demonstrating that the present SPH method can be robust and reliable in accurately predicting the breaking bow wave phenomenon of high-speed ships.Furthermore,the wave elevation and velocity field in the bow wave region are analyzed,and the evolution of the bow wave breaking is provided.展开更多
The bow wave generated by a ship hull that advances at constant speed in calm water is considered. The bow wave only depends on the shape of the ship bow （not on the hull geometry aft of the bow wave）. This basic pr...The bow wave generated by a ship hull that advances at constant speed in calm water is considered. The bow wave only depends on the shape of the ship bow （not on the hull geometry aft of the bow wave）. This basic property makes it possible to de- termine the bow waves generated by a canonical family of ship bows defined in terms of relatively few parameters. Fast ships with fine bows generate overturning bow waves that consist of detached thin sheets of water, which are mostly steady until they hit the main free surface and undergo turbulent breaking up and diffusion. However, slow ships with blunt bows create highly unsteady and turbulent breaking bow waves. These two alternative flow regimes are due to a nonlinear constraint related to the Bernoulli relation at the free surface. Recent results about the ove^urning and breaking bow wave regimes, and the boundary that divides these two basic flow regimes, are reviewed. Questions and conjectures about the energy of breaking ship bow waves, and free-surface effects on flow circulation, are also noted.展开更多
In a probe and drogue aerial refueling system, the bow wave of the receiver aircraft will produce a strong aerodynamic effect on the drogue once the receiver follows the drogue at a close distance. It is a major diffi...In a probe and drogue aerial refueling system, the bow wave of the receiver aircraft will produce a strong aerodynamic effect on the drogue once the receiver follows the drogue at a close distance. It is a major difficulty of docking control in the probe and drogue refueling. This paper analyses the bow wave effect and presents a simple method to model it. Firstly, the inviscid flow around the receiver is modeled based on the stream function defined by basic stream singularities. Secondly, a correction function is developed to eliminate the error caused by the absence of air vis- cosity. Then, the aerodynamic coefficients are used to calculate the induced aerodynamic force on the drogue. The obtained model is in an analytical form that can be easily applied to the controller design and the real-time simulations. In the verification part, computational fluid dynamics （CFD） simulation tests are conducted to validate the obtained flow fields and aerodynamic forces. Finally, the modeling method is applied to an F-16 receiver aircraft in a previously developed autonomous aerial refueling simulation system. The simulations results are analyzed and compared with the NASA flight-test data, which demonstrates the effectiveness of the proposed method.展开更多
Bow wave breaking is a common phenomenon during ship navigation,especially at a high speed,involving complex physical mechanism such as interface mixing,air entrainment,and jet splashing.This study uses the delayed de...Bow wave breaking is a common phenomenon during ship navigation,especially at a high speed,involving complex physical mechanism such as interface mixing,air entrainment,and jet splashing.This study uses the delayed detached eddy simulation(DDES)turbulence model on the OpenFOAM platform to simulate flow around a KRISO Container Ship(KCS)model for a Froude number of 0.35,examining trim angles of 0°,0.5°,1°.This paper analyzes the statistical and power spectral density(PSD)characteristics of bow wave heights.The analysis shows root mean square(rms)and mean difference between top and bottom views indicate wave breaking.As the trim angle increases,peaks of rms in the bottom view become much higher than that in the top view,reaching 38%at 1°.PSD analysis reveals that resistance and wave height periods differ by no more than 5%,with small-scale structures like jetting and splashing causing non-dominant periodic and high-frequency wave height variations.展开更多
Ship bow wave breaking contains complex flow mechanism,which is very important for ship performance.In this study,a practical numerical simulation scheme for bow wave breaking is proposed and the scheme is applied to ...Ship bow wave breaking contains complex flow mechanism,which is very important for ship performance.In this study,a practical numerical simulation scheme for bow wave breaking is proposed and the scheme is applied to the simulation of bow wave breaking of KCS ship model with Fr=0.26,0.30,0.35,0.40,analyzing the impact of speed on the bow wave breaking.The results indicate that an increase in speed leads to a significant rise in viscous pressure resistance and more pronounced bow wave breaking.Moreover,it is found that the traditional wave height function in OpenFOAM is not suitable for detailed studies of bow wave breaking.This study extracts different free surfaces through top and bottom views to further analyze the free surface overturning,droplet splashing,and cavity entrainment in bow wave breaking.Additionally,the spatial and temporal distribution of cavities at Fr=0.40 is analyzed,revealing that cavity distribution is closely related to vortex structures and exhibits a periodic pulsation characteristic of approximately 12 s.展开更多
Ship bow wave breaking is a common phenomenon during navigation,involving complex multi-scale flow interactions.However,the understanding of this intense free surface flow issue is not sufficiently deep,especially reg...Ship bow wave breaking is a common phenomenon during navigation,involving complex multi-scale flow interactions.However,the understanding of this intense free surface flow issue is not sufficiently deep,especially regarding the lack of research on the impact of scale effects on bow wave breaking.This paper focuses on the benchmark ship model KCS and conducts numerical simulations and comparative analyses of bow wave breaking for three model scales under the condition of Fr=0.35.The numerical calculations were performed using the in-house computational fluid dynamics(CFD)solver naoe-FOAM-SJTU,which is developed on the open source platform OpenFOAM.Delayed detached eddy simulation(DDES)method is utilized to calculate the viscous flow field around the ship hull.The present method was validated through measurement data of wave profiles and wake flows obtained from model tests.Flow field results for three different scales,including bow wave profiles,vorticity at various sections,and wake distribution,were presented and analyzed.The results indicate that there is small difference in the bow wave overturning and breaking for the first two occurrences across different scales.However,considerable effects of scale are observed on the temporal and spatial variations of the free surface breaking pattern after the second overturning.The findings of this study can serve as valuable data references for the analysis of scale effects in ship bow wave breaking phenomena.展开更多
Trails induced by air entrainment of bow wave breaking can be observed clearly around an advancing ship,making it prong to be detected and causing reduction in hydrodynamic performance.In breaking bow wave region,diff...Trails induced by air entrainment of bow wave breaking can be observed clearly around an advancing ship,making it prong to be detected and causing reduction in hydrodynamic performance.In breaking bow wave region,different scale of coherent vortex structures related closely to the air entrainment are generated.The formation and evolution of bubble clouds can be accounted partly by the swirling vortex flow of the jet plunging.In this work,high-fidelity simulation of the bow wave breaking around a rectangular thin plate is performed with the in-house code BAMR-SJTU.A Liutex force model is constructed to investigate the interaction between the free surface and vortices,and to explore the possibility of alleviating or controlling the air entrainment.This study is the first attempt to manipulate vortices corresponding to the air entrainment of the bow wave breaking.Some typical vortex structures based on the Liutex vortex identification method and the distribution of the vortex force are presented.Comparison of the vortex structures and the entrapped bubbles is conducted to illustrate the efficiency of Liutex force model in air entrainment control.展开更多
For the general case of a spatial isoenergetic flow of ideal gas,Helmholtz’s theorems are generalized and the speed with which vortex tubes move is found,keeping the intensity.It is shown that along the streamline wi...For the general case of a spatial isoenergetic flow of ideal gas,Helmholtz’s theorems are generalized and the speed with which vortex tubes move is found,keeping the intensity.It is shown that along the streamline without stagnation point,vorticity either is equal to zero everywhere,or it is non zero at all.The pattern of vortex lines behind the three-dimensional detached bow shock wave is specified.展开更多
Navier-Stokes equations are solved to obtain the near field flow and to reveal the generation of droplets due to the breaking of the bow wave. With an adaptive refinement of the Octree mesh, the fine scale flow charac...Navier-Stokes equations are solved to obtain the near field flow and to reveal the generation of droplets due to the breaking of the bow wave. With an adaptive refinement of the Octree mesh, the fine scale flow characteristics, the wave breaking and the splashing are well simulated. For high-speed ships, the V-shape ship wave pattern with the angle smaller than the classical Kelvin angle is confirmed by the present numerical results, which can also be applied to the catamaran. Comparisons of the vertical velocity distributions induced by the mono-hull ship and the catamaran are made at different locations in the wake regions.展开更多
In this paper, some preliminary calculations and the experiments were performed to figure out the flow field, in which some rods were normally inserted into the main flow surrounded by a porous cavity. As a result, it...In this paper, some preliminary calculations and the experiments were performed to figure out the flow field, in which some rods were normally inserted into the main flow surrounded by a porous cavity. As a result, it is found that the starting shock wave severely interacts with the rods, the bow shock wave, its reflections, and the porous wall, which are numerically well predicted at some conditions. Moreover, inserting the rods makes the pressure on the upper wall in the porous region increase when the main flow in the porous region is completely supersonic. The calculations also suggest that three rods cause the widest suction area.展开更多
Computations of far-field ship waves,based on linear potential flow theory and the Hogner approximation,are reported for monohull ships and catamarans.Specifically,far-field ship waves are computed for six monohull sh...Computations of far-field ship waves,based on linear potential flow theory and the Hogner approximation,are reported for monohull ships and catamarans.Specifically,far-field ship waves are computed for six monohull ships at four Froude numbers F≡V/√gL=0.58,0.68,0.86,1.58 and for six catamarans with nondimensional hull spacing s≡S/L=0.25 at two Froude numbers F s≡V/√gS=1 and 2.5.Here,g is the gravitational acceleration,V and L denote the ship speed and length,and S is the separation distance between the twin hulls of a catamaran.The computations show that,although the amplitudes of the waves created by a ship are strongly influenced by the shape of the ship hull,as well known,the ray angles where the largest waves are found are only weakly influenced by the hull shape and indeed are mostly a kinematic feature of the flow around a ship hull.An important practical consequence of this flow feature is that the apparent wake angle of general monohull ships or catamarans(with arbitrarily-shaped hulls)can be estimated,without computations,by means of simple analytical relations;these relations,obtained elsewhere via parametric computations,are given here.Moreover,the influence of the two parameters F s and s that largely determine the ray angles of the dominant waves created by a catamaran is illustrated via computations for three catamarans with hull spacings s=0.2,0.35,0.5 at four Froude numbers F s=1,1.5,2,2.5.These computations confirm that the largest waves created by wide and/or fast catamarans are found at ray angles that only depend on F s(i.e.that do not depend on the hull spacing s)in agreement with an elementary analysis of lateral interference between the dominant waves created by the bows(or sterns)of the twin hulls of a catamaran.The dominant-waves ray angles predicted by the theory of wave-interference effects for monohull ships and catamarans are also compared with the observations of narrow Kelvin ship wakes reported by Rabaud and Moisy,and found to be consistent with these observations.展开更多
基金The Guangdong Basic and Applied Basic Research Foundation(2024B1515020107)the National Natural Science Foundation of China(Grant Nos.52171329)+1 种基金the State Key Laboratory of Disaster Prevention&Mitigation of Explosion&Impact(Grant No.NOLGD-SKL-202201)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.231gbi023).
文摘Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(SPH)method under the Lagrange framework is adopted to simulate the breaking bow wave of the KCS ship model.In order to improve the computational efficiency,the inflow and outflow boundary model is used to establish a numerical tank of current,and a numerical treatment for free surface separation is implemented.Numerical simulations are carried out at Fr=0.35,0.40,0.5,0.6,and different types of wave breaking such as spilling breaker,plunging breaker,and scars are captured by the SPH method,which is consistent with the experimental result,demonstrating that the present SPH method can be robust and reliable in accurately predicting the breaking bow wave phenomenon of high-speed ships.Furthermore,the wave elevation and velocity field in the bow wave region are analyzed,and the evolution of the bow wave breaking is provided.
文摘The bow wave generated by a ship hull that advances at constant speed in calm water is considered. The bow wave only depends on the shape of the ship bow （not on the hull geometry aft of the bow wave）. This basic property makes it possible to de- termine the bow waves generated by a canonical family of ship bows defined in terms of relatively few parameters. Fast ships with fine bows generate overturning bow waves that consist of detached thin sheets of water, which are mostly steady until they hit the main free surface and undergo turbulent breaking up and diffusion. However, slow ships with blunt bows create highly unsteady and turbulent breaking bow waves. These two alternative flow regimes are due to a nonlinear constraint related to the Bernoulli relation at the free surface. Recent results about the ove^urning and breaking bow wave regimes, and the boundary that divides these two basic flow regimes, are reviewed. Questions and conjectures about the energy of breaking ship bow waves, and free-surface effects on flow circulation, are also noted.
基金supported by the National Natural Science Foundation of China(Nos.61473012 and 51375462)
文摘In a probe and drogue aerial refueling system, the bow wave of the receiver aircraft will produce a strong aerodynamic effect on the drogue once the receiver follows the drogue at a close distance. It is a major difficulty of docking control in the probe and drogue refueling. This paper analyses the bow wave effect and presents a simple method to model it. Firstly, the inviscid flow around the receiver is modeled based on the stream function defined by basic stream singularities. Secondly, a correction function is developed to eliminate the error caused by the absence of air vis- cosity. Then, the aerodynamic coefficients are used to calculate the induced aerodynamic force on the drogue. The obtained model is in an analytical form that can be easily applied to the controller design and the real-time simulations. In the verification part, computational fluid dynamics （CFD） simulation tests are conducted to validate the obtained flow fields and aerodynamic forces. Finally, the modeling method is applied to an F-16 receiver aircraft in a previously developed autonomous aerial refueling simulation system. The simulations results are analyzed and compared with the NASA flight-test data, which demonstrates the effectiveness of the proposed method.
基金Project supported by the National Natural Science Foundation of China(Grant No.52131102)supported by the Research and Application Demonstration Project of Key Technologies for Safeguarding of Container vessels in Ningbo Zhoushan Port Based on Intelligent Navigation(Grant No.ZJHG-FW-2024-27).
文摘Bow wave breaking is a common phenomenon during ship navigation,especially at a high speed,involving complex physical mechanism such as interface mixing,air entrainment,and jet splashing.This study uses the delayed detached eddy simulation(DDES)turbulence model on the OpenFOAM platform to simulate flow around a KRISO Container Ship(KCS)model for a Froude number of 0.35,examining trim angles of 0°,0.5°,1°.This paper analyzes the statistical and power spectral density(PSD)characteristics of bow wave heights.The analysis shows root mean square(rms)and mean difference between top and bottom views indicate wave breaking.As the trim angle increases,peaks of rms in the bottom view become much higher than that in the top view,reaching 38%at 1°.PSD analysis reveals that resistance and wave height periods differ by no more than 5%,with small-scale structures like jetting and splashing causing non-dominant periodic and high-frequency wave height variations.
基金Project supported by the National Natural Science Foundation of China(Grant No.52131102).
文摘Ship bow wave breaking contains complex flow mechanism,which is very important for ship performance.In this study,a practical numerical simulation scheme for bow wave breaking is proposed and the scheme is applied to the simulation of bow wave breaking of KCS ship model with Fr=0.26,0.30,0.35,0.40,analyzing the impact of speed on the bow wave breaking.The results indicate that an increase in speed leads to a significant rise in viscous pressure resistance and more pronounced bow wave breaking.Moreover,it is found that the traditional wave height function in OpenFOAM is not suitable for detailed studies of bow wave breaking.This study extracts different free surfaces through top and bottom views to further analyze the free surface overturning,droplet splashing,and cavity entrainment in bow wave breaking.Additionally,the spatial and temporal distribution of cavities at Fr=0.40 is analyzed,revealing that cavity distribution is closely related to vortex structures and exhibits a periodic pulsation characteristic of approximately 12 s.
基金Project supported by the National Natural Science Foundation of China(Grant No.52131102).
文摘Ship bow wave breaking is a common phenomenon during navigation,involving complex multi-scale flow interactions.However,the understanding of this intense free surface flow issue is not sufficiently deep,especially regarding the lack of research on the impact of scale effects on bow wave breaking.This paper focuses on the benchmark ship model KCS and conducts numerical simulations and comparative analyses of bow wave breaking for three model scales under the condition of Fr=0.35.The numerical calculations were performed using the in-house computational fluid dynamics(CFD)solver naoe-FOAM-SJTU,which is developed on the open source platform OpenFOAM.Delayed detached eddy simulation(DDES)method is utilized to calculate the viscous flow field around the ship hull.The present method was validated through measurement data of wave profiles and wake flows obtained from model tests.Flow field results for three different scales,including bow wave profiles,vorticity at various sections,and wake distribution,were presented and analyzed.The results indicate that there is small difference in the bow wave overturning and breaking for the first two occurrences across different scales.However,considerable effects of scale are observed on the temporal and spatial variations of the free surface breaking pattern after the second overturning.The findings of this study can serve as valuable data references for the analysis of scale effects in ship bow wave breaking phenomena.
基金Project supported by the National Key Research and Development Program of China(Grant No.2019YFB1704200)the National Natural Science Foundation of China(Grant Nos.51879159,52131102).
文摘Trails induced by air entrainment of bow wave breaking can be observed clearly around an advancing ship,making it prong to be detected and causing reduction in hydrodynamic performance.In breaking bow wave region,different scale of coherent vortex structures related closely to the air entrainment are generated.The formation and evolution of bubble clouds can be accounted partly by the swirling vortex flow of the jet plunging.In this work,high-fidelity simulation of the bow wave breaking around a rectangular thin plate is performed with the in-house code BAMR-SJTU.A Liutex force model is constructed to investigate the interaction between the free surface and vortices,and to explore the possibility of alleviating or controlling the air entrainment.This study is the first attempt to manipulate vortices corresponding to the air entrainment of the bow wave breaking.Some typical vortex structures based on the Liutex vortex identification method and the distribution of the vortex force are presented.Comparison of the vortex structures and the entrapped bubbles is conducted to illustrate the efficiency of Liutex force model in air entrainment control.
文摘For the general case of a spatial isoenergetic flow of ideal gas,Helmholtz’s theorems are generalized and the speed with which vortex tubes move is found,keeping the intensity.It is shown that along the streamline without stagnation point,vorticity either is equal to zero everywhere,or it is non zero at all.The pattern of vortex lines behind the three-dimensional detached bow shock wave is specified.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11272210,51379123)the National Basic Research Development Program of China(973 Pro-gram,Grant No.2014CB046200)
文摘Navier-Stokes equations are solved to obtain the near field flow and to reveal the generation of droplets due to the breaking of the bow wave. With an adaptive refinement of the Octree mesh, the fine scale flow characteristics, the wave breaking and the splashing are well simulated. For high-speed ships, the V-shape ship wave pattern with the angle smaller than the classical Kelvin angle is confirmed by the present numerical results, which can also be applied to the catamaran. Comparisons of the vertical velocity distributions induced by the mono-hull ship and the catamaran are made at different locations in the wake regions.
文摘In this paper, some preliminary calculations and the experiments were performed to figure out the flow field, in which some rods were normally inserted into the main flow surrounded by a porous cavity. As a result, it is found that the starting shock wave severely interacts with the rods, the bow shock wave, its reflections, and the porous wall, which are numerically well predicted at some conditions. Moreover, inserting the rods makes the pressure on the upper wall in the porous region increase when the main flow in the porous region is completely supersonic. The calculations also suggest that three rods cause the widest suction area.
文摘Computations of far-field ship waves,based on linear potential flow theory and the Hogner approximation,are reported for monohull ships and catamarans.Specifically,far-field ship waves are computed for six monohull ships at four Froude numbers F≡V/√gL=0.58,0.68,0.86,1.58 and for six catamarans with nondimensional hull spacing s≡S/L=0.25 at two Froude numbers F s≡V/√gS=1 and 2.5.Here,g is the gravitational acceleration,V and L denote the ship speed and length,and S is the separation distance between the twin hulls of a catamaran.The computations show that,although the amplitudes of the waves created by a ship are strongly influenced by the shape of the ship hull,as well known,the ray angles where the largest waves are found are only weakly influenced by the hull shape and indeed are mostly a kinematic feature of the flow around a ship hull.An important practical consequence of this flow feature is that the apparent wake angle of general monohull ships or catamarans(with arbitrarily-shaped hulls)can be estimated,without computations,by means of simple analytical relations;these relations,obtained elsewhere via parametric computations,are given here.Moreover,the influence of the two parameters F s and s that largely determine the ray angles of the dominant waves created by a catamaran is illustrated via computations for three catamarans with hull spacings s=0.2,0.35,0.5 at four Froude numbers F s=1,1.5,2,2.5.These computations confirm that the largest waves created by wide and/or fast catamarans are found at ray angles that only depend on F s(i.e.that do not depend on the hull spacing s)in agreement with an elementary analysis of lateral interference between the dominant waves created by the bows(or sterns)of the twin hulls of a catamaran.The dominant-waves ray angles predicted by the theory of wave-interference effects for monohull ships and catamarans are also compared with the observations of narrow Kelvin ship wakes reported by Rabaud and Moisy,and found to be consistent with these observations.
