The Experts below are selected from a list of 162 Experts worldwide ranked by ideXlab platform
S. J. Arthur - One of the best experts on this subject based on the ideXlab platform.
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Bow shocks, Bow Waves, and dust Waves - III. Diagnostics
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: William J. Henney, S. J. ArthurAbstract:Stellar Bow shocks, Bow Waves, and dust Waves all result from the action of a star's wind and radiation pressure on a stream of dusty plasma that flows past it. The dust in these Bows emits prominently at mid-infrared wavelengths in the range 8 to 60 micron. We propose a novel diagnostic method, the tau-eta diagram, for analyzing these Bows, which is based on comparing the fractions of stellar radiative energy and stellar radiative momentum that is trapped by the Bow shell. This diagram allows the discrimination of wind-supported Bow shocks, radiation-supported Bow Waves, and dust Waves in which grains decouple from the gas. For the wind-supported Bow shocks, it allows the stellar wind mass-loss rate to be determined. We critically compare our method with a previous method that has been proposed for determining wind mass-loss rates from Bow shock observations. This comparison points to ways in which both methods can be improved and suggests a downward revision by a factor of two with respect to previously reported mass-loss rates. From a sample of 23 mid-infrared Bow-shaped sources, we identify at least 4 strong candidates for radiation-supported Bow Waves, which need to be confirmed by more detailed studies, but no strong candidates for dust Waves.
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Bow shocks Bow Waves and dust Waves ii beyond the rip point
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: W J Henney, S. J. ArthurAbstract:Dust Waves are a result of gas-grain decoupling in a stream of dusty plasma that flows past a luminous star. The radiation field is sufficiently strong to overcome the collisional coupling between grains and gas at a "rip-point", where the ratio of radiation pressure to gas pressure exceeds a critical value of roughly 1000. When the rip point occurs outside the hydrodynamic Bow shock, a separate dust wave may form, decoupled from the gas shell, which can either be drag-confined or inertia-confined, depending on the stream density and relative velocity. In the drag-confined case, there is a minimum stream velocity of roughly 60 km/s that allows a steady-state stagnant drift solution for the dust wave apex. For lower relative velocities, the dust dynamics close to the axis exhibit a limit cycle behavior (rip and snap back) between two different radii. Strong coupling of charged grains to the plasma's magnetic field can modify these effects, but for a quasi-parallel field orientation the results are qualitatively similar to the non-magnetic case. For a quasi-perpendicular field, on the other hand, the formation of a decoupled dust wave is strongly suppressed.
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Bow shocks Bow Waves and dust Waves i strong coupling limit
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: W J Henney, S. J. ArthurAbstract:Dust Waves and Bow Waves result from the action of a star's radiation pressure on a stream of dusty plasma that flows past it. They are an alternative mechanism to hydrodynamic Bow shocks for explaining the curved arcs of infrared emission seen around some stars. When gas and grains are perfectly coupled, for a broad class of stellar parameters, wind-supported Bow shocks predominate when the ambient density is below 100 per cubic cm. At higher densities radiation-supported Bows can form, tending to be optically thin Bow Waves around B stars, or optically thick Bow shocks around early O stars. For OB stars with particularly weak stellar winds, radiation-supported Bows become more prevalent.
Dick K P Yue - One of the best experts on this subject based on the ideXlab platform.
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computations of fully nonlinear three dimensional wave wave and wave body interactions part 2 nonlinear Waves and forces on a body
Journal of Fluid Mechanics, 2001Co-Authors: Yuming Liu, Ming Xue, Dick K P YueAbstract:The mixed-Eulerian–Lagrangian method using high-order boundary elements, described in Xue et al. (2001) for the simulation of fully nonlinear three-dimensional wave–wave and wave–body interactions, is here extended and applied to the study of two nonlinear three-dimensional wave–body problems: (a) the development of Bow Waves on an advancing ship; and (b) the steep wave diffraction and nonlinear high-harmonic loads on a surface-piercing vertical cylinder. For (a), we obtain convergent steady-state Bow wave profiles for a flared wedge, and the Wigley and Series 60 hulls. We compare our predictions with experimental measurements and find good agreement. It is shown that upstream influence, typically not accounted for in quasi-two-dimensional theory, plays an important role in Bow wave prediction even for fine Bows. For (b), the primary interest is in the higher-harmonic ‘ringing’ excitations observed and quantified in experiments. From simulations, we obtain fully nonlinear steady-state force histories on the cylinder in incident Stokes Waves. Fourier analysis of such histories provides accurate predictions of harmonic loads for which excellent comparisons to experiments are obtained even at third order. This confirms that ‘ringing’ excitations are directly a result of nonlinear wave diffraction.
James H. Duncan - One of the best experts on this subject based on the ideXlab platform.
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a parametric study of breaking Bow Waves using a 2d t technique
Journal of Fluid Mechanics, 2011Co-Authors: Eric Maxeiner, Mostafa Shakeri, James H. DuncanAbstract:A mechanical two-dimensional wave maker with a flexible surface was used to create Waves similar to those formed at the Bow of a moving ship. Utilizing the two-dimensional plus time (2D + T) approximation, the wave maker was programmed so that its deformable wave board created a time sequence of shapes that simulated the line of intersection between one side of the hull of a slender ship model moving at constant speed and an imaginary vertical plane oriented normal to the ship model track. However, instead of simulating a particular ship hull, the wave maker was set to produce a parametric set of flat plate motions that represent components of typical Bow shapes. The resulting surface Waves were measured using a cinematic laser-induced fluorescence technique and the resulting wave profiles were analysed. A large variation of wave crest shapes was observed. An assortment of wave characteristics including the maximum contact point height, maximum wave height and plunging jet geometry were measured and related to the corresponding wave maker motion parameters. Despite the variety of wave maker motions and resulting wave crest shapes, it was observed that the gross parameters describing the wave, such as the maximum wave height, maximum contact point height and wave phase speed, correlate strongly with the wave maker velocity along the water line. Details of the crest shape at the moment of incipient breaking showed a stronger dependence on the initial acceleration of the wave board.
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An experimental investigation of divergent Bow Waves simulated by a two-dimensional plus temporal wave marker technique
Journal of Fluid Mechanics, 2009Co-Authors: Mostafa Shakeri, Mohammadreza Tavakolinejad, James H. DuncanAbstract:Divergent ship Bow Waves were simulated experimentally with a two-dimensional wavemaker that employs a flexible wave board. The wavemaker was programmed so that the wave board created a time sequence of shapes that simulated the line of intersection between one side of the hull of a slender ship model moving at constant speed and an imaginary vertical plane oriented normal to the ship model track. The time history of the water surface shape was measured with a cinematic laser-induced fluorescence technique for eight Froude numbers ( F D = U / , where U is the forward speed of the equivalent three-dimensional ship model, g the acceleration of gravity and D the ship model draft). The Waves produced ranged from small-amplitude non-breaking Waves at the lowest Froude numbers to plunging breakers at the highest Froude numbers. These Waves are strongly forced and at the higher Froude numbers begin breaking before leaving the wave board. The time histories of various geometric characteristics of the water surface shape including the hull contact line, the wave crest, the plunging jet and the splash zone, which is here defined as both the turbulent zone on the front face of the wave in the spilling breakers and the turbulent zone generated ahead of the jet impact point in the plunging breakers, were measured. The phase speed of the primary wave generated during each run ranged from 2.56 U wl (where U wl is the maximum speed of the wave board at the undisturbed water level in the tank) at the lowest Froude number to about 1.7 U wl at the three highest Froude numbers. The maximum heights of the primary wave, the contact point on the wavemaker and the splash zone increased in a nearly linear fashion with increasing F D . In the cases with plunging jets, the jet tip trajectory was parabolic with a vertical acceleration ranging from 0.6 g at F D = 1.467 to 0.8 g at F D = 1.817 (the highest Froude number).
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Characteristics of Breaking Bow Waves Generated by a 2D+T Wave Maker
Volume 2: Fora, 2006Co-Authors: Mostafa Shakeri, Mohammadreza Tavakolinejad, Matthias Mayer, James H. DuncanAbstract:Ship Bow Waves simulated experimentally with a 2D+T wave maker were investigated experimentally. Wave profile measurements are presented for a range of equivalent full-scale ship speeds ranging from 16.5 to 27 knots. At the beginning of the wave maker motion, the water surface rises rapidly up the surface of the wave board which represents the hull of the equivalent ship model. The maximum rise height and the rate of rise increase with increasing equivalent ship speed. Later in the wave maker motion, this point of maximum water height moves away from the wave board and forms the primary crest in the wave pattern. This crest moves at a speed that is about 1.8 times the maximum speed of the wave board. At the higher speeds, this wave crest evolves into a strong plunging breaker with a jet that hits the water surface ahead of the breaker, creating a large splash and entraining large amounts of air. The temporal histories of various geometrical characteristics of the breaker are presented.Copyright © 2006 by ASME
R. Cointe - One of the best experts on this subject based on the ideXlab platform.
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New insight into the generation of ship Bow Waves
Journal of Fluid Mechanics, 2000Co-Authors: E. Fontaine, Odd M. Faltinsen, R. CointeAbstract:The generation of ship Bow Waves is studied within the framework of potential flow theory. Assuming the ship Bow to be slender, or thin, a pattern of the flow is derived using the method of matched asymptotic expansions. This method leads to the determination of three different zones in which three asymptotic expansions are performed and matched. To first order with respect to the slenderness parameter, the near-field flow appears to be two-dimensional in each transverse plane along the Bow. However, it is demonstrated that three-dimensional effects are important in front of the ship and must be taken into account in the composite solution. This leads to a three-dimensional correction to be added to the two-dimensional solution along the ship. The asymptotic approach is then applied to explain the structure of the Bow flow in connection with experimental observations and numerical simulations
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a slender body approach to nonlinear Bow Waves
Philosophical transactions - Royal Society. Mathematical physical and engineering sciences, 1997Co-Authors: E. Fontaine, R. CointeAbstract:The behaviour of the flow near the Bow of a slender ship is studied. The fluid is assumed to be perfect and incompressible and the flow to be irrotational. The formalism of matched asymptotic expansion is used to provide a consistent perturbation procedure for the simplification of the initial problem. The resulting nonlinear free surface problem describing the flow in the inner domain close to the Bow is solved numerically. Examples of solutions are given for the flows around a wedge shaped Bow and a prismatic planing hull.
Vito Despoja - One of the best experts on this subject based on the ideXlab platform.
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ab initio study of energy loss and wake potential in the vicinity of a graphene monolayer
Physical Review B, 2012Co-Authors: Vito Despoja, Kresimir Dekanic, Marijan Sunjic, Leonardo MarusicAbstract:A propagator of the dynamically screened Coulomb interaction in the vicinity of a graphene monolayer is calculated using ground-state Kohn-Sham orbitals, and the imaginary part of this propagator is used to calculate the energy-loss rate of a static blinking point charge due to excitation of electronic modes in graphene. Energy loss calculated for all (Q,ω) modes gives intensities of electronic excitations, including plasmon dispersions in graphene, with low-energy two-dimensional (2D) and high-energy π1, π2, and π+σ plasmons. Plasmon energies are in good agreement with experimental results. This spectral analysis also enables us to study the contribution of each plasmon mode to the stopping power and potential induced by a point charge moving parallel to the graphene. We find the Bow Waves that in pristine graphene appear for higher velocities (v≥2vF) and predominantly originate from excitation of π plasmons. Doping induces extra features which appear for lower v≈vF velocities and predominantly originate from the excitation of 2D or Drude plasmons.