Ground-effect vehicles flying close to water or ground often employ ram wings which generate aerodynamic lift primarily on their lower surfaces.The subject of this paper is the 3-DOF modeling of roll,heave,and pitch m...Ground-effect vehicles flying close to water or ground often employ ram wings which generate aerodynamic lift primarily on their lower surfaces.The subject of this paper is the 3-DOF modeling of roll,heave,and pitch motions of such a wing in the presence of surface waves and other ground non-uniformities.The potential-flow extreme-ground-effect theory is applied for calculating unsteady pressure distribution under the wing which defines instantaneous lift force and moments.Dynamic simulations of a selected ramwing configuration are carried out in the presence of surface waves of various headings and wavelengths,as well as for transient flights over a ground obstacle.The largest amplitudes of the vehicle motions are observed in beam waves when the periods of the encounter are long.Nonlinear effects are more pronounced for pitch angles than for roll and heave.The present method can be adapted for modeling of air-supported lifting surfaces on fast marine vehicles.展开更多
Injecting air under hulls of marine vessels can lead to reduction of their hydrodynamic resistance.Since experimental development of air-assisted hulls usually requires a large number of tests,numerical simulations of...Injecting air under hulls of marine vessels can lead to reduction of their hydrodynamic resistance.Since experimental development of air-assisted hulls usually requires a large number of tests,numerical simulations of air-ventilated water flows can potentially accelerate the design process.In this study,computational modeling has been carried out for the previously tested simplified hull form with an air cavity formed behind a step.To achieve proper agreement with experimental results,it is established that a sufficiently fine numerical mesh needs to be generated at the cavity re-attachment to the hull and the sharpening treatment of the air-water interface must be included.It is also shown how the cavity length can be manipulated by changing inclination of the cavity-originating step.展开更多
Shallow hydrofoils are known to produce lower lift in normal operating conditions in comparison with deep hydrofoils.However,the maximum lift capability of shallow hydrofoils at moderate speeds,which is important for ...Shallow hydrofoils are known to produce lower lift in normal operating conditions in comparison with deep hydrofoils.However,the maximum lift capability of shallow hydrofoils at moderate speeds,which is important for transitional regimes of hydrofoil boats,is studied insufficiently.In this work,two-dimensional flow around a high-lift hydrofoil at a moderate Froude number is numerically simulated in a broad range attack angles up to the stall occurrence in both single-phase fluid and in the vicinity of free surface.It is found that nearly the same maximum lift coefficient can be produced by the shallow foil in the modeled condition as by the deep foil,but much higher attack angle is required near the free surface,which also results in larger drag.Additionally,it is shown that higher Reynolds numbers lead to higher lift coefficients,especially at large attack angles.展开更多
Hydrodynamics of planing hulls is affected by proximity to the seabed floor in shallow waters.In this study,a three-dimensional steady linearized model based on the potential theory is applied to model flat planing su...Hydrodynamics of planing hulls is affected by proximity to the seabed floor in shallow waters.In this study,a three-dimensional steady linearized model based on the potential theory is applied to model flat planing surfaces at finite water depth and finite Froude numbers.Modeling results for shallow waters agree with experimental data in the subcritical and supercritical regimes sufficiently far from the critical speed that corresponds to the depth Froude number of unity.At the critical speed,nonlinear and unsteady effects become important,and a different modeling approach is required.展开更多
文摘Ground-effect vehicles flying close to water or ground often employ ram wings which generate aerodynamic lift primarily on their lower surfaces.The subject of this paper is the 3-DOF modeling of roll,heave,and pitch motions of such a wing in the presence of surface waves and other ground non-uniformities.The potential-flow extreme-ground-effect theory is applied for calculating unsteady pressure distribution under the wing which defines instantaneous lift force and moments.Dynamic simulations of a selected ramwing configuration are carried out in the presence of surface waves of various headings and wavelengths,as well as for transient flights over a ground obstacle.The largest amplitudes of the vehicle motions are observed in beam waves when the periods of the encounter are long.Nonlinear effects are more pronounced for pitch angles than for roll and heave.The present method can be adapted for modeling of air-supported lifting surfaces on fast marine vehicles.
基金the U.S.National Science Foundation under Grant no.1800135.
文摘Injecting air under hulls of marine vessels can lead to reduction of their hydrodynamic resistance.Since experimental development of air-assisted hulls usually requires a large number of tests,numerical simulations of air-ventilated water flows can potentially accelerate the design process.In this study,computational modeling has been carried out for the previously tested simplified hull form with an air cavity formed behind a step.To achieve proper agreement with experimental results,it is established that a sufficiently fine numerical mesh needs to be generated at the cavity re-attachment to the hull and the sharpening treatment of the air-water interface must be included.It is also shown how the cavity length can be manipulated by changing inclination of the cavity-originating step.
基金This material is based upon research supported by the U.S.Office of Naval Research under Award(Grant No.N 00014-17-1-2553).
文摘Shallow hydrofoils are known to produce lower lift in normal operating conditions in comparison with deep hydrofoils.However,the maximum lift capability of shallow hydrofoils at moderate speeds,which is important for transitional regimes of hydrofoil boats,is studied insufficiently.In this work,two-dimensional flow around a high-lift hydrofoil at a moderate Froude number is numerically simulated in a broad range attack angles up to the stall occurrence in both single-phase fluid and in the vicinity of free surface.It is found that nearly the same maximum lift coefficient can be produced by the shallow foil in the modeled condition as by the deep foil,but much higher attack angle is required near the free surface,which also results in larger drag.Additionally,it is shown that higher Reynolds numbers lead to higher lift coefficients,especially at large attack angles.
文摘Hydrodynamics of planing hulls is affected by proximity to the seabed floor in shallow waters.In this study,a three-dimensional steady linearized model based on the potential theory is applied to model flat planing surfaces at finite water depth and finite Froude numbers.Modeling results for shallow waters agree with experimental data in the subcritical and supercritical regimes sufficiently far from the critical speed that corresponds to the depth Froude number of unity.At the critical speed,nonlinear and unsteady effects become important,and a different modeling approach is required.
