Note on wind drift in a channel in the presence of tidal currents

1953 ◽  
Vol 219 (1139) ◽  
pp. 426-446 ◽  
Keyword(s):  
Steady State ◽  
Drift Velocity ◽  
Wind Stress ◽  
Eddy Viscosity ◽  
Tidal Currents ◽  
Bottom Friction ◽  
Convergent Channel ◽  
Tidal Period ◽  
Uniform Channel ◽  
Wind Currents

In waters such as those surrounding the British Isles, wind currents appear as perturbations superimposed on the tidal currents. In treating this problem, it is assumed that the drift velocity is small compared with the amplitude of the tidal current. In this case, if the instantaneous value of the bottom friction is proportional to the square of the instantaneous velocity, the non-periodic component of friction, averaged over a tidal period, is linearly proportional to the drift velocity. It is assumed that the water is homogeneous and that, above a skin-friction layer close to the bottom, the eddy viscosity is constant with depth. In the steady state, the drift current due to a given wind stress is reduced in the presence of tidal currents. Steady-state solutions, involving the elevation of the surface as well as the currents, are given for a channel of uniform width and depth, a uniformly convergent channel and a non-uniform channel. Numerical calculations, based on the most probable estimates of wind stress, eddy viscosity and bottom friction available at present, are given for several particular cases. A discussion is given of their application to drift currents and surface gradients in the English Channel, a region in which it is proposed to carry out a programme of observations in the near future.

On the Role of Bottom Pressure Torques in Wind-Driven Gyres

2021 ◽  
Vol 51 (5) ◽  
pp. 1441-1464
Author(s):  
Andrew L. Stewart ◽  
James C. McWilliams ◽  
Aviv Solodoch
Keyword(s):  
Wind Stress ◽  
Bottom Friction ◽  
Bottom Pressure ◽  
Wind Stress Curl ◽  
Previous Theory ◽  
Model Experiments ◽  
Basin Scale ◽  
Vorticity Budget ◽  
Gyre Circulation

AbstractPrevious studies have concluded that the wind-input vorticity in ocean gyres is balanced by bottom pressure torques (BPT), when integrated over latitude bands. However, the BPT must vanish when integrated over any area enclosed by an isobath. This constraint raises ambiguities regarding the regions over which BPT should close the vorticity budget, and implies that BPT generated to balance a local wind stress curl necessitates the generation of a compensating, nonlocal BPT and thus nonlocal circulation. This study aims to clarify the role of BPT in wind-driven gyres using an idealized isopycnal model. Experiments performed with a single-signed wind stress curl in an enclosed, sloped basin reveal that BPT balances the winds only when integrated over latitude bands. Integrating over other, dynamically motivated definitions of the gyre, such as barotropic streamlines, yields a balance between wind stress curl and bottom frictional torques. This implies that bottom friction plays a nonnegligible role in structuring the gyre circulation. Nonlocal bottom pressure torques manifest in the form of along-slope pressure gradients associated with a weak basin-scale circulation, and are associated with a transition to a balance between wind stress and bottom friction around the coasts. Finally, a suite of perturbation experiments is used to investigate the dynamics of BPT. To predict the BPT, the authors extend a previous theory that describes propagation of surface pressure signals from the gyre interior toward the coast along planetary potential vorticity contours. This theory is shown to agree closely with the diagnosed contributions to the vorticity budget across the suite of model experiments.

Wind effects on the water in a narrow two-layered lake. Part I. Theoretical analysis. Part II. Analysis of observations from Windermere. Part III. Application of the theory to Windermere

1966 ◽  
Vol 259 (1102) ◽  
pp. 391-430 ◽  
Keyword(s):  
Wind Stress ◽  
Water Surface ◽  
Water Movement ◽  
Lower Layer ◽  
Longitudinal Section ◽  
Bottom Friction ◽  
Bottom Current ◽  
Numerical Application ◽  
Warm Surface Water ◽  
Temperature Observations

This paper presents a theoretical study of water movement in a long narrow lake subject to wind action during the summer season of thermal stratification. A model basin of uniform depth and width, consisting of two homogeneous layers of slightly different density, is considered. The motion of the water is assumed to be two dimensional in the vertical longitudinal section; geostrophic effects are ignored. The top and bottom layers in the model respectively represent the relatively warm surface water and the colder bottom water in the natural lake. Hydrodynamical equations are formulated in terms of the currents in the upper and lower layers, the elevation of the interface between the layers, and the elevation of the water surface. Solutions are sought to determine the dynamic response of the basin to an instantaneous rise in the wind stress applied tangentially over the surface. Three cases are considered corresponding to different frictional conditions at the bottom of the basin: (i) bottom friction zero, (ii) bottom friction proportional to the depth mean of the horizontal current in the lower layer, (iii) bottom current zero. It is assumed that internal friction is zero at the interface between the layers (this interface corresponds to the thermocline boundary in reality). Results obtained show that in the motion of the water there are ordinary and internal seiches characteristic of the two-layered model, together with a wind-driven circulation in the top layer. The theory is applied to determine vertical oscillations of the thermocline in an actual lake (Windermere) at one station, in response to a succession of wind pulses representing actual wind conditions over the lake. The oscillations thus obtained from theory compare satisfactorily with those derived from temperature observations taken in the lake. Depth-mean currents in the lake are deduced from theory, but there are no current measurements against which these values may be tested. The paper is divided into three parts. Part I deals with the development of the theory. Part II gives an account of actual physical conditions in Windermere, describing the analysis of temperature observations taken in the lake (yielding thermocline movements) and the analysis of wind records (yielding corresponding values of wind stress over the water surface). Part III is concerned with the numerical application of the theory to Windermere (under conditions described in part II), and gives general conclusions resulting from the entire work.

Depth Dependence of Physical Parameters Associated with Convection in the Solar Atmosphere

1971 ◽  
Vol 2 (1) ◽  
pp. 50-51
Author(s):  
B. E. Waters
Keyword(s):  
Steady State ◽  
Rayleigh Number ◽  
Eddy Viscosity ◽  
Convection Zone ◽  
Finite Amplitude ◽  
Physical Parameters ◽  
Solar Granulation ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Convective Phenomenon

It has been often suggested that the solar granulation is essentially a turbulent convective phenomenon. It is then worthwhile to investigate steady state, finite-amplitude convection in the outer layers of the solar convection zone. On the basis that the convection zone is turbulent, we will define an eddy viscosity; and for the present we will consider only the first 300 km of the convection zone. This value is predicted by van der Borght using an asymptotic analysis of convection at high Rayleigh number—provided we assume the horizontal dimension of the cellular pattern to be ˜1000 km.

Code Development and Validation of RANS Solvers for Flows Around Bluff Bodies

2002 ◽  
Author(s):  
Saud Khashan ◽  
Abdullatif M. Alteraifi
Keyword(s):  
Steady State ◽  
Eddy Viscosity ◽  
Turbulence Modeling ◽  
Streamwise Velocity ◽  
Numerical Dissipation ◽  
Bluff Bodies ◽  
Surface Pressure Distribution ◽  
Non Linear ◽  
Steady State Simulation ◽  
Marginal Improvement

A steady state simulation for the flow past a circular cylinder at the sub-critical Reynolds number of 3900 is conducted using a variety of non-linear eddy viscosity-based two-equation κ-ε models. Although, this simulation compromises the transient characteristics of the flow, the solution obtained using a steady state simulation showed qualitative relevance. Steady state results were closely comparable to the far more expensive and supposedly more correct time-averaged solutions obtained using transient simulations. The dissipative effect due to such turbulence modeling by far overweighs the effect of the numerical dissipation. Such dissipation dampened the intrinsic self-excited unsteadiness known to exist in such flow and enabled steady state-like solution. In-house developed finite volume based code along with a commercial finite-element code, were used. Qualitative agreement is attainable for the surface-pressure distribution over the cylinder and the centerline streamwise velocity in the wake regions. For this type of problems, the time-averaged solutions obtained using transient simulation that employs the non-linear eddy viscosity-based two-equation κ-ε type models, offered marginal improvement over those obtained using steady state simulations.

scholarly journals Townsend Discharges in Transverse Magnetic Fields

1983 ◽  
Vol 36 (6) ◽  
pp. 859 ◽  
Author(s):  
HA Blevin ◽  
MJ Brennan
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Magnetic Fields ◽  
Drift Velocity ◽  
Transverse Magnetic Field ◽  
Electron Concentration ◽  
Diffusion Coefficients ◽  
Concentration Distribution ◽  
Transverse Magnetic ◽  
Electron Drift

Expressions are derived for the electron concentration in Townsend discharges in the presence of a transverse magnetic field for both steady state and pulsed conditions. These results indicate that the two components of the electron drift velocity and the four diffusion coefficients required to describe the concentration distribution can be determined by observation of photons emitted from the discharge.

scholarly journals Freshwater Composition and Connectivity of the Connecticut River Plume During Ambient Flood Tides

2021 ◽  
Vol 8 ◽  
Author(s):  
Michael M. Whitney ◽  
Yan Jia ◽  
Kelly L. Cole ◽  
Daniel G. MacDonald ◽  
Kimberly D. Huguenard
Keyword(s):  
Mixing Time ◽  
Growth Period ◽  
Tidal Currents ◽  
Surface Flow ◽  
River Plume ◽  
Tidal River ◽  
Initial Growth ◽  
Connecticut River ◽  
Tidal Period ◽  
Source Waters

The Connecticut River plume interacts with the strong tidal currents of the ambient receiving waters in eastern Long Island Sound. The plume formed during ambient flood tides is studied as an example of tidal river plumes entering into energetic ambient tidal environments in estuaries or continental shelves. Conservative passive freshwater tracers within a high-resolution nested hydrodynamic model are applied to determine how source waters from different parts of the tidal cycle contribute to plume composition and interact with bounding plume fronts. The connection to source waters can be cut off only under low-discharge conditions, when tides reverse surface flow through the mouth after max ambient flood. Upstream plume extent is limited because ambient tidal currents arrest the opposing plume propagation, as the tidal internal Froude number exceeds one. The downstream extent of the tidal plume always is within 20 km from the mouth, which is less than twice the ambient tidal excursion. Freshwaters in the river during the preceding ambient ebb are the oldest found in the new flood plume. Connectivity with source waters and plume fronts exhibits a strong upstream-to-downstream asymmetry. The arrested upstream front has high connectivity, as all freshwaters exiting the mouth immediately interact with this boundary. The downstream plume front has the lowest overall connectivity, as interaction is limited to the oldest waters since younger interior waters do not overtake this front. The offshore front and inshore boundary exhibit a downstream progression from younger to older waters and decreasing overall connectivity with source waters. Plume-averaged freshwater tracer concentrations and variances both exhibit an initial growth period followed by a longer decay period for the remainder of the tidal period. The plume-averaged tracer variance is increased by mouth inputs, decreased by entrainment, and destroyed by internal mixing. Peak entrainment velocities for younger waters are higher than values for older waters, indicating stronger entrainment closer to the mouth. Entrainment and mixing time scales (1–4 h at max ambient flood) are both shorter than half a tidal period, indicating entrainment and mixing are vigorous enough to rapidly diminish tracer variance within the plume.

How changes in the crystal temperature and the doping concentration impact upon bulk wurtzite zinc oxide’s electron transport response

MRS Advances ◽  
2019 ◽  
Vol 4 (50) ◽  
pp. 2673-2678
Author(s):  
Poppy Siddiqua ◽  
Walid A. Hadi ◽  
Michael S. Shur ◽  
Stephen K. O’Leary
Keyword(s):  
Monte Carlo ◽  
Steady State ◽  
Electron Transport ◽  
Drift Velocity ◽  
Doping Concentration ◽  
Electron Drift ◽  
Crystal Temperature ◽  
Transient Transport ◽  
Transport Response ◽  
The Impact

ABSTRACTThe role that changes in the crystal temperature and the doping concentration play in shaping the character of the steady-state and transient transport response of electrons within bulk wurtzite zinc oxide will be examined. Monte Carlo electron transport simulations are drawn upon for the purposes of this analysis. We find that both the crystal temperature and the doping concentration greatly influence the character of the steady-state and transient electron transport response. In particular, for the case of steady-state electron transport, the peak drift velocity decreases by 30% as the crystal temperature is increased from 100 to 700 K, this decrease in velocity being only 20% as the doping concentration is increased from 1015 to 1019 cm-3. The impact on the transient electron drift velocity is not as acute.

Transient Lubricating Films With Inertia—Turbulent Flow

1984 ◽  
Vol 106 (1) ◽  
pp. 134-139 ◽  
Author(s):  
H. G. Elrod ◽  
I. Anwar ◽  
R. Colsher
Keyword(s):  
Steady State ◽  
Turbulent Flow ◽  
Stream Function ◽  
Velocity Gradient ◽  
Eddy Viscosity ◽  
Mean Velocity ◽  
Steady State Operation ◽  
Pressure Development ◽  
Transient And Steady State

This paper presents some new equations for the treatment of turbulent lubricating films when the effects of inertia cannot be neglected. The eddy-viscosity concept is used to represent the turbulent stresses in terms of mean-velocity gradient. Transient and steady-state operation are both considered by means of a generalized stream-function-pressure development.

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