scholarly journals Generation of Vortex Lattices at the Liquid–Gas Interface Using Rotating Surface Waves

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 74 ◽  
Author(s):  
Hua Xia ◽  
Nicolas Francois ◽  
Jean-Baptiste Gorce ◽  
Horst Punzmann ◽  
Michael Shats
Keyword(s):  
Relative Phase ◽  
Liquid Surface ◽  
Standing Waves ◽  
Stokes Drift ◽  
Vortex Lattices ◽  
Rotating Surface ◽  
A Cell ◽  
Drift Orbits ◽  
Vortex Crystal ◽  
The Waves

In this paper, we demonstrate experimentally that by generating two orthogonal standing waves at the liquid surface, one can control the motion of floating microparticles. The mechanism of the vortex generation is somewhat similar to a classical Stokes drift in linear progression waves. By adjusting the relative phase between the waves, it is possible to generate a vortex lattice, seen as a stationary horizontal flow consisting of counter-rotating vortices. Two orthogonal waves which are phase-shifted by π / 2 create locally rotating waves. Such waves induce nested circular drift orbits of the surface fluid particles. Such a configuration allows for the trapping of particles within a cell of the size about half the wavelength of the standing waves. By changing the relative phase, it is possible to either create or to destroy the vortex crystal. This method creates an opportunity to confine surface particles within cells, or to greatly increase mixing of the surface matter over the wave field surface.

scholarly journals Phase shift in skyrmion crystals

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Satoru Hayami ◽  
Tsuyoshi Okubo ◽  
Yukitoshi Motome
Keyword(s):  
Phase Shift ◽  
Relative Phase ◽  
Exchange Interactions ◽  
Thermal Fluctuations ◽  
Coupled Systems ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Spin Density Waves ◽  
Vortex Crystal ◽  
Spin Texture

AbstractThe magnetic skyrmion crystal is a periodic array of a swirling topological spin texture. Since it is regarded as an interference pattern by multiple helical spin density waves, the texture changes with the relative phase shifts among the constituent waves. Although such a phase degree of freedom is relevant to not only magnetism but also transport properties, its effect has not been elucidated thus far. We here theoretically show that a phase shift in the skyrmion crystals leads to a tetra-axial vortex crystal and a meron-antimeron crystal, both of which show a staggered pattern of the scalar spin chirality and give rise to nonreciprocal transport phenomena without the spin-orbit coupling. We demonstrate that such a phase shift can be driven by exchange interactions between the localized spins, thermal fluctuations, and long-range chirality interactions in spin-charge coupled systems. Our results provide a further diversity of topological spin textures and open a new field of emergent electromagnetism by the phase shift engineering.

scholarly journals Mutual Interaction between Surface Waves and Langmuir Circulations Observed in Wave-Resolving Numerical Simulations

2020 ◽  
Vol 50 (8) ◽  
pp. 2323-2339
Author(s):  
Yasushi Fujiwara ◽  
Yutaka Yoshikawa
Keyword(s):  
Surface Waves ◽  
Friction Velocity ◽  
Phase Speed ◽  
Mutual Interaction ◽  
Stokes Drift ◽  
Horizontal Shear ◽  
Budget Analysis ◽  
Vorticity Budget ◽  
Langmuir Circulations ◽  
The Waves

AbstractWave-resolving simulations of monochromatic surface waves and Langmuir circulations (LCs) under an idealized condition are performed to investigate the dynamics of wave–current mutual interaction. When the Froude number (the ratio of the friction velocity of wind stress imposed at the surface and wave phase speed) is large, waves become refracted by the downwind jet associated with LCs and become amplitude modulated in the crosswind direction. In such cases, the simulations using the Craik–Leibovich (CL) equation with a prescribed horizontally uniform Stokes drift profile are found to underestimate the intensity of LCs. Vorticity budget analysis reveals that horizontal shear of Stokes drift induced by the wave modulation tilts the wind-driven vorticity to the downwind direction, intensifying the LCs that caused the waves to be modulated. Such an effect is not reproduced in the CL equation unless the Stokes drift of the waves modulated by LCs is prescribed. This intensification mechanism is similar to the CL1 mechanism in that the horizontal shear of the Stokes drift plays a key role, but it is more likely to occur because the shear in this interaction is automatically generated by the LCs whereas the shear in the CL1 mechanism is retained only when a particular phase relation between two crossing waves is kept locked for many periods.

scholarly journals Demonstration and application of diffusive and ballistic wave propagation for drone-to-ground and drone-to-drone wireless communications

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Peter J. Burke
Keyword(s):  
Wave Propagation ◽  
Electromagnetic Wave ◽  
Path Loss ◽  
Base Station ◽  
Physical Models ◽  
Mapping Technology ◽  
Aerial Vehicle ◽  
A Cell ◽  
Independent Path ◽  
The Waves

Abstract In order to determine how an electromagnetic wave propagates from a base station to a cell phone or a wirelessly connected device, we use a novel Unmanned Aerial Vehicle (UAV) mapping technology to map the cellular network coverage at various altitudes in various terrains (flat, hilly, mountainous). For the flat terrains, the waves are shown to propagate ballistically: They have an altitude independent path loss consistent with minimal scatter in the propagation from transmitter to (aerial) receiver. In mountainous terrain, the waves are shown to propagate in the diffuse regime, and demonstrate a 10 dB increase in received signal intensity per 100′ of altitude gain, up to 400′. In the intermediate case, evidence of coherent wave interference is clearly observed in altitude independent interference patterns. These general observations can be used to build a physical or empirical model for drone-to-ground and drone-to-drone propagation, for which existing models are shown to fail. While important for building physical models of wave propagation in wireless networks, this method can be used more generally to determine the magnitude and phase of an electromagnetic wave at every point in space, as well as usher in the era of drone-to-ground and drone-to-drone communications.

On Lagrangian drift in shallow-water waves on moderate shear

2010 ◽  
Vol 660 ◽  
pp. 221-239 ◽  
Author(s):  
W. R. C. PHILLIPS ◽  
A. DAI ◽  
K. K. TJAN
Keyword(s):  
Boundary Layer ◽  
Shear Flow ◽  
Shallow Water ◽  
Water Waves ◽  
Stokes Drift ◽  
Shallow Water Waves ◽  
Sea Floor ◽  
Langmuir Circulations ◽  
A Minor ◽  
The Waves

The Lagrangian drift in anO(ϵ) monochromatic wave field on a shear flow, whose characteristic velocity isO(ϵ) smaller than the phase velocity of the waves, is considered. It is found that although shear has only a minor influence on drift in deep-water waves, its influence becomes increasingly important as the depth decreases, to the point that it plays a significant role in shallow-water waves. Details of the shear flow likewise affect the drift. Because of this, two temporal cases common in coastal waters are studied, viz. stress-induced shear, as would arise were the boundary layer wind-driven, and a current-driven shear, as would arise from coastal currents. In the former, the magnitude of the drift (maximum minus minimum) in shallow-water waves is increased significantly above its counterpart, viz. the Stokes drift, in like waves in otherwise quiescent surroundings. In the latter, on the other hand, the magnitude decreases. However, while the drift at the free surface is always oriented in the direction of wave propagation in stress-driven shear, this is not always the case in current-driven shear, especially in long waves as the boundary layer grows to fill the layer. This latter finding is of particular interest vis-à-vis Langmuir circulations, which arise through an instability that requires differential drift and shear of the same sign. This means that while Langmuir circulations form near the surface and grow downwards (top down), perhaps to fill the layer, in stress-driven shear, their counterparts in current-driven flows grow from the sea floor upwards (bottom up) but can never fill the layer.

Attenuated wave-induced drift in a viscous rotating ocean

1983 ◽  
Vol 137 ◽  
pp. 115-129 ◽  
Author(s):  
Jan Erik Weber
Keyword(s):  
Mass Transport ◽  
Stokes Drift ◽  
Lagrangian Description ◽  
Rotating Fluid ◽  
Periodic Surface ◽  
Continuous Energy ◽  
Spatially Periodic ◽  
Wave Induced ◽  
The Waves ◽  
Associated Mass

Mean drift currents due to spatially periodic surface waves in a viscous rotating fluid are investigated theoretically. The analysis is based on the Lagrangian description of motion. The fluid is homogeneous, the depth is infinite, and there is no continuous energy input at the surface. Owing to viscosity the wave field and the associated mass transport will attenuate in time. For the non-rotating case the present approach yields the time-decaying Stokes drift in a slightly viscous ocean. The analysis shows that the drift velocities are finite everywhere. In a rotating fluid it is found that the effect of viscosity implies a non-zero net mass transport associated with the waves, as opposed to the result of no net transport obtained from inviscid theory (Ursell 1950).

Broadband Random Phase Diffuser for Ultrasonic Imaging

1979 ◽  
Vol 1 (4) ◽  
pp. 325-332
Author(s):  
Gerard A. Alphonse ◽  
David Vilkomerso
Keyword(s):  
Solid Angle ◽  
Random Phase ◽  
Ultrasonic Imaging ◽  
Standing Waves ◽  
Acoustic Imaging ◽  
Point Sources ◽  
Phase Plate ◽  
Reflected Waves ◽  
Large Aperture ◽  
The Waves

In reflective imaging, waves must be scattered by the object over a broad solid angle so that some of the reflected waves impinge upon the collecting aperture. Surfaces such as biological specimens under study in acoustic imaging are considered smooth at the wavelengths used (e.g., 1 mm) and therefore act as specular reflectors. In order to obtain reflection over a broad spatial range, large aperture, sector or compound scanning are used. In certain types of systems, diffuse insonification is sometimes used by imaging a raster of random phase points onto the surface. However interference between the waves from these point sources produces random fringes or “speckle-like” patterns overlaying the image. In optics these fringes have been reduced by rotating the diffuser. A similar approach has been taken here. This paper describes a simple random phase plate having two levels, 0° and 180 phase that can, by rotation, change the relative phases of the diffuse insonification points so as to reduce the speckle-like effect in the image. The temporal bandwidth of the random phase plate is narrow because of standing waves in it. To reduce standing waves the diffuser is intimately coupled to a wedged transducer. This combination is used to obtain diffuse insonification with broad spatial and temporal bandwidth.

scholarly journals Wave-induced Lagrangian drift in a porous seabed

2021 ◽  
Author(s):  
Jan Erik H. Weber ◽  
Peygham Ghaffari
Keyword(s):  
Porous Layer ◽  
Fluid Layer ◽  
Lagrangian Formulation ◽  
Stokes Drift ◽  
Porous Bed ◽  
Wave Approximation ◽  
Long Wave ◽  
The Mean ◽  
Long Wave Approximation ◽  
The Waves

AbstractThe mean drift in a porous seabed caused by long surface waves in the overlying fluid is investigated theoretically. We use a Lagrangian formulation for the fluid and the porous bed. For the wave field we assume inviscid flow, and in the seabed, we apply Darcy’s law. Throughout the analysis, we assume that the long-wave approximation is valid. Since the pressure gradient is nonlinear in the Lagrangian formulation, the balance of forces in the porous bed now contains nonlinear terms that yield the mean horizontal Stokes drift. In addition, if the waves are spatially damped due to interaction with the underlying bed, there must be a nonlinear balance in the fluid layer between the mean surface gradient and the gradient of the radiation stress. This causes, through continuity of pressure, an additional force in the porous layer. The corresponding drift is larger than the Stokes drift if the depth of the porous bed is more than twice that of the fluid layer. The interaction between the fluid layer and the seabed can also cause the waves to become temporally attenuated. Again, through nonlinearity, this leads to a horizontal Stokes drift in the porous layer, but now damped in time. In the long-wave approximation only the horizontal component of the permeability in the porous medium appears, so our analysis is valid for a medium that has different permeabilities in the horizontal and vertical directions. It is suggested that the drift results may have an application to the transport of microplastics in the porous oceanic seabed.

Mathematical modeling of a well performance in view of nonequilibrium relative phase permeability

2020 ◽  
Vol 6 (1) ◽  
pp. 208-217
Author(s):  
Alexander V. Ivanov ◽  
Sergey V. Stepanov
Keyword(s):  
Relative Phase ◽  
Oil Field ◽  
Well Performance ◽  
Mathematical Methods ◽  
Hydrodynamic Models ◽  
Phase Permeability ◽  
Relative Phase Permeability ◽  
A Cell ◽  
Relationship Of ◽  
The Relationship

As it is well known, mesh refinement of hydrodynamic models to improve accuracy of well performance modeling results in a significant increase of the calculation time. That explains the relevance of developing mathematical methods that can increase the modeling adequacy without a detailed computation mesh. This article discusses using a well correcting function (CF) that presents the coordinated performance of a watercut in a calculated cell and a well. The distinctive feature of the introduced CF lies in it being defined by the saturation structure of the calculated cell which accounts for the disequilibrium of the relative phase permeability (RFP) function. At the same time, the RFP disequilibrium follows Barenblat’s model. This method is presented as a computer program, which has helped to determine that the watercut in a cell gravitates towards the well watercut when the redistribution time rises. This behavior agrees with the saturation contour, which accounts for the relationship of the width of stabilized zone with the driving velocity. The selection of CF was tested on four wells working in horizons AV1(3) of the Samotlor Oil Field. The retrospective analysis shows, that this method can be used for increasing the accuracy of well modeling.

Seismic seiches in Norway and England during the Assam earthquake of August 15, 1950*

1955 ◽  
Vol 45 (2) ◽  
pp. 93-113
Author(s):  
Anders Kvale
Keyword(s):  
Standing Waves ◽  
Vertical Direction ◽  
Maximum Amplitude ◽  
Long Waves ◽  
Water Reservoirs ◽  
Lisbon Earthquake ◽  
Seismological Observatory ◽  
Progressive Waves ◽  
The Waves ◽  
East West

Abstract During the Assam earthquake of August 15, 1950, unusual waves were observed in at least 37 localities in fjords and lakes in Norway. Reports from 29 of these are discussed in this paper. In most places the waves were standing waves, with periods of 1 to 3 minutes and amplitudes of 5 to 100 cm. and began when the acceleration at the seismological observatory in Bergen surpassed 20 milligals in the east-west direction and 40 milligals in the vertical direction. The movements generally ceased when the acceleration decreased to below 10 milligals. The main periods of the long waves declined during this period from about 30 to 15 seconds, but the seismograms also indicate longer periods, of about 1 to 3 minutes, which may have some connection with the seiches. The calculated periods for the basins where waves were observed are, assuming one node, in most places between 1 and 3 minutes. In England, standing oscillations were recorded in water reservoirs at Margate, Chichester, and Portsmouth during the earthquake. The periods cannot be determined from the records, but the calculated periods vary from 15 to 25 seconds, which corresponds fairly closely with the 22 seconds given by Kew Observatory as the period of the long waves of the earthquake. The maximum amplitude in the reservoirs was 2 inches. Seiches in Norway during the Lisbon earthquake of November 1, 1755, and progressive waves during the Kansu earthquake of December 16, 1920, are briefly discussed.

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