A pair of Langmuir cells in a laboratory tank (I) wind-only experiment

1992 ◽  
Vol 48 (1) ◽  
pp. 37-57 ◽  
Author(s):  
Shinjiro Mizuno ◽  
Zhan Cheng
Keyword(s):  
Laboratory Tank ◽  
Langmuir Cells

Langmuir turbulence in the ocean

1997 ◽  
Vol 334 ◽  
pp. 1-30 ◽  
Author(s):  
JAMES C. McWILLIAMS ◽  
PETER P. SULLIVAN ◽  
CHIN-HOH MOENG
Keyword(s):  
Volume Transport ◽  
Stokes Drift ◽  
Equilibrium Solutions ◽  
Vertical Fluxes ◽  
Averaged Equations ◽  
Large Eddy ◽  
Convergence Zones ◽  
The Right ◽  
Langmuir Cells ◽  
Oceanic Currents

Solutions are analysed from large-eddy simulations of the phase-averaged equations for oceanic currents in the surface planetary boundary layer (PBL), where the averaging is over high-frequency surface gravity waves. These equations have additional terms proportional to the Lagrangian Stokes drift of the waves, including vortex and Coriolis forces and tracer advection. For the wind-driven PBL, the turbulent Langmuir number, Latur = (U∗/Us)1/2, measures the relative influences of directly wind-driven shear (with friction velocity U∗) and the Stokes drift Us. We focus on equilibrium solutions with steady, aligned wind and waves and a realistic Latur = 0.3. The mean current has an Eulerian volume transport to the right of the wind and against the Stokes drift. The turbulent vertical fluxes of momentum and tracers are enhanced by the presence of the Stokes drift, as are the turbulent kinetic energy and its dissipation and the skewness of vertical velocity. The dominant coherent structure in the turbulence is a Langmuir cell, which has its strongest vorticity aligned longitudinally (with the wind and waves) and intensified near the surface on the scale of the Stokes drift profile. Associated with this are down-wind surface convergence zones connected to interior circulations whose horizontal divergence axis is rotated about 45° to the right of the wind. The horizontal scale of the Langmuir cells expands with depth, and there are also intense motions on a scale finer than the dominant cells very near the surface. In a turbulent PBL, Langmuir cells have irregular patterns with finite correlation scales in space and time, and they undergo occasional mergers in the vicinity of Y-junctions between convergence zones.

Mating Behavior of the Rock Crab, Cancer irroratus

1978 ◽  
Vol 35 (10) ◽  
pp. 1385-1388 ◽  
Author(s):  
R. W. Elner ◽  
A. B. Stasko
Keyword(s):  
Key Words ◽  
Mating Behavior ◽  
Cancer Irroratus ◽  
Rock Crab ◽  
Laboratory Tank

A pair of rock crabs, Cancer irroratus, in mating embrace an hour after being placed in a laboratory tank, was observed intermittently until ecdysis of the female and copulation of the pair, and then until escape of the female 27 d after ecdysis. When separated from the mating embrace, the hard-shelled female sought out the male. Approach of female ecdysis was indicated by protrusion of a soft spherical bulge at the rear of the epimeral line. Details of the immediate pre- and postcopulatory behavior were observed continuously from 26 min before to 150 min after copulation. The female was first noted separated from the male 7 h after copulation. Periods of separation increased until mating interactions were completely abandoned 5 d after copulation. A second pair subsequently observed confirmed the above. Mating embrace was also observed between a hard-shelled male and a hard-shelled female that already had sperm plugs. Key words: Crustacea, crabs, copulation, molt indicators

scholarly journals THE ONE-DIMENSIONAL WAVE SPECTRA AT LIMITED FETCH

1972 ◽  
Vol 1 (13) ◽  
pp. 13
Author(s):  
Hisashi Mitsuyasu
Keyword(s):  
Similarity Theory ◽  
Wind Waves ◽  
Laboratory Data ◽  
Peak Frequency ◽  
Wave Spectra ◽  
One Dimensional ◽  
Wide Range ◽  
Laboratory Tank ◽  
The One ◽  
Dimensional Wave

The data for the spectra of wind-generated waves measured in a laboratory tank and in a bay are analyzed using the similarity theory of Kitaigorodski, and the one-dimensional spectra of fetch-limited wind waves are determined from the data. The combined field and laboratory data cover such a wide range of dimensionless fetch F (= gF/u2 ) as F : 102 ~ 10 . The fetch relations for the growthes of spectral peak frequency u)m and of total energy E of the spectrum are derived from the proposed spectra, which are consistent with those derived directly from the measured spectra.

Acoustic Study of Wave-Breaking to Enhance the Understanding of Wave Physics

2020 ◽  
Author(s):  
Michael Odzer ◽  
Kristina Francke
Keyword(s):  
Wave Breaking ◽  
Ocean Waves ◽  
Breaking Waves ◽  
Video Data ◽  
Wave Tank ◽  
Potential Applications ◽  
Audio Data ◽  
Video And Audio ◽  
Bubble Sizes ◽  
Laboratory Tank

Abstract The sound of waves breaking on shore, or against an obstruction or jetty, is an immediately recognizable sound pattern which could potentially be employed by a sensor system to identify obstructions. If frequency patterns produced by breaking waves can be reproduced and mapped in a laboratory setting, a foundational understanding of the physics behind this process could be established, which could then be employed in sensor development for navigation. This study explores whether wave-breaking frequencies correlate with the physics behind the collapsing of the wave, and whether frequencies of breaking waves recorded in a laboratory tank will follow the same pattern as frequencies produced by ocean waves breaking on a beach. An artificial “beach” was engineered to replicate breaking waves inside a laboratory wave tank. Video and audio recordings of waves breaking in the tank were obtained, and audio of ocean waves breaking on the shoreline was recorded. The audio data was analysed in frequency charts. The video data was evaluated to correlate bubble sizes to frequencies produced by the waves. The results supported the hypothesis that frequencies produced by breaking waves in the wave tank followed the same pattern as those produced by ocean waves. Analysis utilizing a solution to the Rayleigh-Plesset equation showed that the bubble sizes produced by breaking waves were inversely related to the pattern of frequencies. This pattern can be reproduced in a controlled laboratory environment and extrapolated for use in developing navigational sensors for potential applications in marine navigation such as for use with autonomous ocean vehicles.

Langmuir turbulence in shallow water. Part 1. Observations

2007 ◽  
Vol 576 ◽  
pp. 27-61 ◽  
Author(s):  
ANN E. GARGETT ◽  
JUDITH R. WELLS
Keyword(s):  
Shallow Water ◽  
Turbulent Flows ◽  
Deep Water ◽  
Vertical Velocity ◽  
Surface Stress ◽  
Large Eddy Simulations ◽  
Wave Groups ◽  
Large Eddy ◽  
Langmuir Circulations ◽  
Langmuir Cells

During extended deployment at an ocean observatory off the coast of New Jersey, a bottom-mounted five-beam acoustic Doppler current profiler measured large-scale velocity structures that we interpret as Langmuir circulations filling the entire water column. These circulations are the large-eddy structures of wind-wave-driven turbulent flows that occur episodically when a shallow water column experiences prolonged strong wind forcing. Many observational characteristics agree with former descriptions of Langmuir circulations in deep water. The three-dimensional velocity field reveals quasi-organized structures consisting of pairs of surface-intensified counter-rotating vortices, aligned approximately downwind. Maximum downward velocities are stronger than upward velocities, and the downwelling region of each cell, defined as a pair of vortices, is narrower than the upwelling region. Maximum downward vertical velocity occurs at or above mid-depth, and scales approximately with wind speed. The estimated crosswind scale of cells is roughly 3–6 times their vertical scale, set under these conditions by water depth. The long axis of the cells appears to lie at an angle ∼10°–20° to the right of the wind. A major difference from deep-water observations is strong near-bottom intensification of the downwind ‘jets’ found typically centred over downwelling regions. Accessible observational features such as cell morphology and profiles of mean velocities, turbulent velocity variances, and shear stress components are compared with the results of associated large-eddy simulations (reported in Part 2) of shallow water flows driven by surface stress and the Craik–Leibovich vortex forcing generally used to represent generation of Langmuir cells. A particularly sensitive diagnostic for identification of Langmuir circulations as the energy-containing eddies of the turbulent flow is the depth trajectory of invariants of the turbulent stress tensor, plotted in the Lumley ‘triangle’ corresponding to realizable turbulent flows. When Langmuir structures are present in the observations, the Lumley map is distinctly different from that of surface-stress-driven Couette flow, again in agreement with the large-eddy simulations (LES). Unlike the LES, observed velocity fields contain two distinct and significant scales of variability, documented by wavelet analysis of observational records of vertical velocity. Variability with periods of many minutes is that expected from Langmuir cells drifting past the instrument at the slowly time-varying crosswind velocity. Shorter period variability, of the order of 1–2 min, has roughly the observed periodicity of surface wave groups, suggesting a connection with the wave groups themselves and/or the wave breaking associated with them in high wind conditions.

Turbulent convection into a linearly stratified fluid: the generation of ‘subsurface anticyclones’

1998 ◽  
Vol 354 ◽  
pp. 101-121 ◽  
Author(s):  
SIAVASH NARIMOUSA
Keyword(s):  
Convective Flow ◽  
Three Dimensional ◽  
Turbulent Convection ◽  
Ambient Fluid ◽  
Coriolis Parameter ◽  
Central Arctic Ocean ◽  
Convective Processes ◽  
Swirl Velocity ◽  
Laboratory Tank ◽  
Negative Buoyancy

Penetrative turbulent convection from a localized circular top source into a rotating, linearly stratified ambient fluid of strength N has been investigated in a laboratory tank. Initially, the induced three-dimensional convective flow penetrated rapidly into the stratified water column until it reached an equilibrium depth at which the convective flow began to propagate radially outward. At this stage, the usual cyclonic vortices were generated around the convection source at the edge of the radially propagating flow. Soon after, a thin ‘subsurface anticyclone’ was formed at the level of equilibrium depth beneath the convection source. Later, this anticyclone dominated the central part of the convective regime and did not allow new cyclones to be injected into the system. After reaching its maximum mean diameter Da/R ≈10(R0;R)2/3 and swirl velocity va ≈(B0R)1/3, an anticyclone became unstable and split into two new vortices that left the area beneath the source, allowing a new anticyclone to form at its original place (here, R0,R =(B0/f3R2) 1/2 is the Rossby number based on R the radius of the source, B0 is the surface negative buoyancy flux, and f is the Coriolis parameter). These observations provide crucial evidence that many of the ‘subsurface anticyclonic’ vortices detected in the stratified pycnocline of the central Arctic Ocean are indeed generated as a result of convective processes occurring in this region.

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