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Joseph Katz - One of the best experts on this subject based on the ideXlab platform.
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MEASUREMENTS OF THE FLOW STRUCTURE AND TURBULENCE WITHIN A SHIP Bow Wave
Physics of Fluids, 1999Co-Authors: Gary I. Roth, Daniel T. Mascenik, Joseph KatzAbstract:Particle image velocimetry measurements around a 7-m-long ship model focus on the flow within the attached liquid sheet, upstream of the point at which the Bow Wave separates from the model. Performed in a towing basin at a Reynolds number of 1.6×107 and a Froude number of 0.30 (both based on ship length L), these measurements expand upon previous work by examining the Bow Wave flow at a higher Reynolds number than before. Further, the increased scale of the model and the flow allows finer observation of the flow structure. Individual vector maps show a growing region of negative vorticity originating at the toe of the Wave. This shear layer, which first appears at X/L=0.0619, penetrates further into the Wave as X/L increases but curves upward to remain close to the forward face. Positive vorticity appears on the top of the Wave and at the ship boundary. Repeated runs at X/L=0.0690 produce mean flow and turbulent stress data for this three-dimensional spilling Wave. Normal and shear Reynolds stresses are ...
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On the structure of Bow Waves on a ship model
Journal of Fluid Mechanics, 1997Co-Authors: Ronald R. Dong, Joseph Katz, Thomas T. HuangAbstract:Particle image velocitmetry (PIV) measurements and free-surface visualizations around a ship model focus on the flow within the attached liquid sheet, upstream of the point at which the Bow Wave separates from the model, the origin and structure of the Bow Wave and the flow downstream of the Wave crest. The measurements are performed at Reynolds numbers ranging between 2.8 x 10 6 and 7.4 x 10 6 and Froude numbers between 0.17 and 0.45 (both are based on ship length L). Representative velocity and vorticity distributions at Fr L = 0.28 and Fr L = 0.45 demonstrate the characteristic structure of mild and steep Waves, respectively. Very close to the Bow the attached sheet is thin and quite unsteady. With increasing distance from the nose the sheet becomes thicker and its development involves considerable vorticity production. In the mild case this vorticity is originated at the free surface, whereas in the steep Wave case, boundary layer separation occurs on the model, which also transports vorticity into the sheet. This vorticity and its associated induced lateral flow remain near the model downstream of the Bow Wave. By calculating the acceleration component tangent to the free surface of the sheet it is shown that the peaks in the near-surface vorticity appear in regions with high viscous flux of vorticity from the surface. Formation of a Bow Wave also involves considerable production of vorticity. Similar to two-dimensional breakers, the primary origin of this vorticity is at the toe of the breaker. However, unlike the two-dimensional cases, the region containing vorticity in the ship Wave does not appear as an extended shear layer. Instead, this vorticity is convected out of the plane of the laser sheet in a series of distinct vortex filaments. The ship Wave also has powerful counter-rotating vorticity concentrated near the Wave crest that has been observed in two-dimensional Waves, but not of the same strength. Breaking becomes weaker, i.e. there is less vorticity production, with increasing distance from the model, but it persists even at the 'tail' of the Bow Wave. The sites of vorticity entrainment of both signs are consistent with the computed near-surface acceleration. Estimates of the three-dimensional velocity distribution and head losses within the Wave are also provided.
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The flow structure around a surface piercing strut
Physics of Fluids, 1997Co-Authors: E. M. Pogozelski, Joseph Katz, T. T. HuangAbstract:The flow near a surface piercing, symmetric body with a long draft is examined. The experiments are performed in a towing tank at 0.05⩽FrL⩽0.51, primarily focusing on FrL=0.25, and include velocity measurements using PIV as well as video and film photography above and below the free surface. The Bow Wave is mild (no bubble entrainment) for Froude numbers below 0.35; however, Bow Wave breaking and vorticity entrainment at the toe of the Wave occur. Energy dissipation in the Bow Wave is significant and affects the flow behind it. At FrL⩾0.15, impingement of the flow on the model near x/L=0.41 generates a turbulent, bubbly wake. On the mid-body just behind this impingement is the origin of a second Wave, containing several regions of counter-rotating vorticity which entrain bubbles from the free surface. The Wave crest becomes milder and eventually irrotational with increasing distance from the model. At x/L=0.64, boundary layer separation begins at the intersection of the model and the free surface. The sep...
Donald A. Gurnett - One of the best experts on this subject based on the ideXlab platform.
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The whistler‐mode Bow Wave of an asteroid
Journal of Geophysical Research: Space Physics, 1995Co-Authors: Donald A. GurnettAbstract:The Galileo spacecraft has flown by two asteroids, Gaspra in 1990 and Ida in 1993. In both cases the magnetometer detected magnetic field perturbations that are believed to be produced by an interaction of the asteroid with the solar wind. Kivelson et al. have proposed that these perturbations are caused by whistler-mode Waves excited by the solar wind flow around the asteroid. This paper presents an analysis of whistler-mode Waves generated by the interaction of a small object with the solar wind. Three cases are considered, with the solar wind magnetic field (1) parallel, (2) perpendicular, and (3) at an arbitrary angle to the velocity vector. Using the Cerenkov condition and the quasi-longitudinal approximation for the whistler mode, the angular limits of the Wave pattern are determined. For the parallel case the Waves are confined to the upstream region, and for the perpendicular case the Waves are confined to two wedge-shaped regions extending downstream from the magnetic field line through the object. For intermediate magnetic field orientations the accessibility region maintains the wedge-shaped configuration, with the leading edge of the wedge roughly following the direction of the magnetic field. The outer boundary of the accessibility region is a caustic surface, along which large field amplitudes are expected, similar to the Bow Wave of a ship. In all cases the interaction involves a characteristic Wavelength, λc = ƒcc²/(ƒp²V), that is comparable to the size of an asteroid.
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On a remarkable similarity between the propagation of whistlers and the Bow Wave of a ship
Geophysical Research Letters, 1995Co-Authors: Donald A. GurnettAbstract:It is well known that lightning-generated whistlers propagate along the Earth's magnetic field lines within a cone that at low frequencies makes an angle of 19°28′ with respect to the local magnetic field. This angle turns out to be exactly the same as the half-angle of the Bow Wave of a ship in deep water. Both problems are complicated by the fact that the Wave propagation is dispersive. In this paper we show that these two seemingly unrelated problems can be understood using the same basic approach, which is to analyze the direction of the group velocity as a function of the Wave normal angle. This approach may have applications to other problems of geophysical interest, such as the Bow Wave generated by the interaction of a large object with a moving plasma.
D A Gurnett - One of the best experts on this subject based on the ideXlab platform.
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the whistler mode Bow Wave of an asteroid
Journal of Geophysical Research, 1995Co-Authors: D A GurnettAbstract:The Galileo spacecraft has flown by two asteroids, Gaspra in 1990 and Ida in 1993. In both cases the magnetometer detected magnetic field perturbations that are believed to be produced by an interaction of the asteroid with the solar wind. Kivelson et al. have proposed that these perturbations are caused by whistler-mode Waves excited by the solar wind flow around the asteroid. This paper presents an analysis of whistler-mode Waves generated by the interaction of a small object with the solar wind. Three cases are considered, with the solar wind magnetic field (1) parallel, (2) perpendicular, and (3) at an arbitrary angle to the velocity vector. Using the Cerenkov condition and the quasi-longitudinal approximation for the whistler mode, the angular limits of the Wave pattern are determined. For the parallel case the Waves are confined to the upstream region, and for the perpendicular case the Waves are confined to two wedge-shaped regions extending downstream from the magnetic field line through the object. For intermediate magnetic field orientations the accessibility region maintains the wedge-shaped configuration, with the leading edge of the wedge roughly following the direction of the magnetic field. The outer boundary of the accessibility region is a caustic surface, along which large field amplitudes are expected, similar to the Bow Wave of a ship. In all cases the interaction involves a characteristic Wavelength, λc = ƒcc²/(ƒp²V), that is comparable to the size of an asteroid.
Francis Noblesse - One of the best experts on this subject based on the ideXlab platform.
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An elementary analytical theory of overturning ship Bow Waves
European Journal of Mechanics - B Fluids, 2014Co-Authors: Francis Noblesse, Gérard Delhommeau, Patrick Queutey, Chi YangAbstract:a b s t r a c t A fully-analytical theory that approximately predicts the size, shape and thickness of the overturning detached Bow Wave, and the width of the Wavebreaking wake behind the plunging Bow Wave, generated by a ship with a fine Bow that advances (at constant speed along a straight path) in calm water is reported. The theory yields simple analytical 'cause-and-effect' relations that provide useful physical insight and explicitly relate a ship's speed, draft, and main parameters characterizing the Bow shape (entrance angles of the top and bottom waterlines, rake angle, flare) to the corresponding overturning Bow Wave and Wavebreaking wake. Qualitative comparisons with experimental observations and CFD calculations show that while the elementary analysis underlying the theory cannot be expected to yield accurate predictions, the theory predicts trends correctly and provides practical estimates of the influence of basic ship design parameters (speed, draft, Bow shape) on main characteristics of the overturning Bow Wave and the related Wavebreaking wake created by a ship Bow.
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Ship Bow Waves
Journal of Hydrodynamics, 2013Co-Authors: Francis Noblesse, Gérard Delhommeau, Hua Liu, Decheng Wan, Chi YangAbstract: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 determine 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 overturning 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.
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Evaluation of ship Waves at the free surface and removal of short Waves
European Journal of Mechanics - B Fluids, 2013Co-Authors: Francis Noblesse, Fuxin Huang, Chi YangAbstract:Abstract The dual basic tasks of evaluating ship Waves at the free surface and of removing unwanted short Waves are considered within the framework of the ‘free-surface Green function potential flow theory’, based on a Green function that satisfies the radiation condition and the Kelvin–Michell linearized boundary condition at the free surface. A practical approach based on parabolic extrapolation within an extrapolation layer bordering the free surface is used. The height of the extrapolation layer is defined explicitly via simple analytical relations in terms of the Froude number and the slenderness of the ship hull, and varies from the Bow to the stern. The Bow-to-stern variation is an important ingredient that accounts for the fact that Waves along the ship hull aft of the Bow Wave differ from the Bow Wave. Indeed, a ship Bow Wave is significantly higher and shorter than Waves aft of the Bow Wave, is affected by nearfield effects related to the rapid variation of the hull geometry at a ship Bow, and consequently contains more short Wave components. Illustrative calculations demonstrate the need for removing short ship Waves and the effectiveness of the approach based on parabolic extrapolation.
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Short-Wave Filter in Fourier Representation of Waves due to a Steadily Advancing Ship Hull
2012Co-Authors: Francis Noblesse, Fuxin Huang, Chi YangAbstract:Abstract : The dual basic tasks of evaluating ship Waves at the free surface and of removing unwanted short Waves are considered within the framework of the free-surface Green function potential flow theory', based on a Green function that satisfies the radiation condition and the Kelvin-Michell linearized boundary condition at the free surface. A practical approach based on parabolic extrapolation within an extrapolation layer bordering the free surface is used. The height of the extrapolation layer is defined explicitly via simple analytical relations in terms of the Froude number and the slenderness of the ship hull, and varies from the Bow to the stern. The Bow-to-stern variation is an important ingredient that accounts for the fact that Waves along the ship hull aft of the Bow Wave differ from the Bow Wave. Indeed, a ship Bow Wave is significantly higher and shorter than Waves aft of the Bow Wave, is affected by nearfield effects related to the rapid variation of the hull geometry at a ship Bow, and consequently contains more short Wave components.
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Analytical Bow Waves for fine ship Bows with rake and flare
Journal of Ship Research, 2011Co-Authors: Francis Noblesse, Gérard Delhommeau, Chi Yang, Hyun Yul Kim, Patrick QueuteyAbstract:The Bow Wave generated by a steadily advancing ship is considered for a family of fine ruled ship Bows with rake and flare. This family of ship Bows is defined in terms of four parameters: the ship draft D, the entrance angles α and α' at the top and bottom waterlines, and the rake angle 8. The corresponding Bow Wave similarly depends on four parameters: the draft-based Froude number Fand the three angles α, α', and δ. An extensive parametric study, based on thin-ship theory, is performed to explore the variations of the water height Z 0 at the ship stem X = 0, the location X 0 (measured from the ship stem) of the intersection of the Bow-Wave profile with the mean free-surface plane Z= 0, and the Bow-Wave profile, with respect to the four parameters F, α, α', and 8. This parametric study extends the previously reported similar study of the height Z b of the Bow Wave and the location X b of the Bow-Wave crest. These two complementary parametric studies yield simple analytical relations, which extend relations given previously for wedge-shaped ship Bows without rake or flare. In spite of their remarkable simplicity, the analytical relations given here yield Bow Waves that are comparable to computational fluid dynamics (CFD) Waves given by Euler-flow calculations. The analytical relations, which explicitly account for the influence of the four primary parameters F, α, α', and 8, can be used immediately—without hydrodynamic calculations—for ship design, notably at early design stages when the precise hull geometry is not yet known. The study also provides insight for ship Bow design. Specifically, it suggests that a Bow with positive rake and negative flare may be beneficial, and that a bulb located aft of the stem and integrated with the hull may be an advantageous alternative to a traditional bulb protruding ahead of the Bow, in agreement with the results of a hull-form optimization analysis.
Chi Yang - One of the best experts on this subject based on the ideXlab platform.
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An elementary analytical theory of overturning ship Bow Waves
European Journal of Mechanics - B Fluids, 2014Co-Authors: Francis Noblesse, Gérard Delhommeau, Patrick Queutey, Chi YangAbstract:a b s t r a c t A fully-analytical theory that approximately predicts the size, shape and thickness of the overturning detached Bow Wave, and the width of the Wavebreaking wake behind the plunging Bow Wave, generated by a ship with a fine Bow that advances (at constant speed along a straight path) in calm water is reported. The theory yields simple analytical 'cause-and-effect' relations that provide useful physical insight and explicitly relate a ship's speed, draft, and main parameters characterizing the Bow shape (entrance angles of the top and bottom waterlines, rake angle, flare) to the corresponding overturning Bow Wave and Wavebreaking wake. Qualitative comparisons with experimental observations and CFD calculations show that while the elementary analysis underlying the theory cannot be expected to yield accurate predictions, the theory predicts trends correctly and provides practical estimates of the influence of basic ship design parameters (speed, draft, Bow shape) on main characteristics of the overturning Bow Wave and the related Wavebreaking wake created by a ship Bow.
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Ship Bow Waves
Journal of Hydrodynamics, 2013Co-Authors: Francis Noblesse, Gérard Delhommeau, Hua Liu, Decheng Wan, Chi YangAbstract: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 determine 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 overturning 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.
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Evaluation of ship Waves at the free surface and removal of short Waves
European Journal of Mechanics - B Fluids, 2013Co-Authors: Francis Noblesse, Fuxin Huang, Chi YangAbstract:Abstract The dual basic tasks of evaluating ship Waves at the free surface and of removing unwanted short Waves are considered within the framework of the ‘free-surface Green function potential flow theory’, based on a Green function that satisfies the radiation condition and the Kelvin–Michell linearized boundary condition at the free surface. A practical approach based on parabolic extrapolation within an extrapolation layer bordering the free surface is used. The height of the extrapolation layer is defined explicitly via simple analytical relations in terms of the Froude number and the slenderness of the ship hull, and varies from the Bow to the stern. The Bow-to-stern variation is an important ingredient that accounts for the fact that Waves along the ship hull aft of the Bow Wave differ from the Bow Wave. Indeed, a ship Bow Wave is significantly higher and shorter than Waves aft of the Bow Wave, is affected by nearfield effects related to the rapid variation of the hull geometry at a ship Bow, and consequently contains more short Wave components. Illustrative calculations demonstrate the need for removing short ship Waves and the effectiveness of the approach based on parabolic extrapolation.
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Short-Wave Filter in Fourier Representation of Waves due to a Steadily Advancing Ship Hull
2012Co-Authors: Francis Noblesse, Fuxin Huang, Chi YangAbstract:Abstract : The dual basic tasks of evaluating ship Waves at the free surface and of removing unwanted short Waves are considered within the framework of the free-surface Green function potential flow theory', based on a Green function that satisfies the radiation condition and the Kelvin-Michell linearized boundary condition at the free surface. A practical approach based on parabolic extrapolation within an extrapolation layer bordering the free surface is used. The height of the extrapolation layer is defined explicitly via simple analytical relations in terms of the Froude number and the slenderness of the ship hull, and varies from the Bow to the stern. The Bow-to-stern variation is an important ingredient that accounts for the fact that Waves along the ship hull aft of the Bow Wave differ from the Bow Wave. Indeed, a ship Bow Wave is significantly higher and shorter than Waves aft of the Bow Wave, is affected by nearfield effects related to the rapid variation of the hull geometry at a ship Bow, and consequently contains more short Wave components.
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Analytical Bow Waves for fine ship Bows with rake and flare
Journal of Ship Research, 2011Co-Authors: Francis Noblesse, Gérard Delhommeau, Chi Yang, Hyun Yul Kim, Patrick QueuteyAbstract:The Bow Wave generated by a steadily advancing ship is considered for a family of fine ruled ship Bows with rake and flare. This family of ship Bows is defined in terms of four parameters: the ship draft D, the entrance angles α and α' at the top and bottom waterlines, and the rake angle 8. The corresponding Bow Wave similarly depends on four parameters: the draft-based Froude number Fand the three angles α, α', and δ. An extensive parametric study, based on thin-ship theory, is performed to explore the variations of the water height Z 0 at the ship stem X = 0, the location X 0 (measured from the ship stem) of the intersection of the Bow-Wave profile with the mean free-surface plane Z= 0, and the Bow-Wave profile, with respect to the four parameters F, α, α', and 8. This parametric study extends the previously reported similar study of the height Z b of the Bow Wave and the location X b of the Bow-Wave crest. These two complementary parametric studies yield simple analytical relations, which extend relations given previously for wedge-shaped ship Bows without rake or flare. In spite of their remarkable simplicity, the analytical relations given here yield Bow Waves that are comparable to computational fluid dynamics (CFD) Waves given by Euler-flow calculations. The analytical relations, which explicitly account for the influence of the four primary parameters F, α, α', and 8, can be used immediately—without hydrodynamic calculations—for ship design, notably at early design stages when the precise hull geometry is not yet known. The study also provides insight for ship Bow design. Specifically, it suggests that a Bow with positive rake and negative flare may be beneficial, and that a bulb located aft of the stem and integrated with the hull may be an advantageous alternative to a traditional bulb protruding ahead of the Bow, in agreement with the results of a hull-form optimization analysis.