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11.
A multi-limit formulation for the equilibrium depth of a stably stratified boundary layer 总被引：1，自引：0，他引：1
Currently no expression for the equilibrium depth of the turbulent stably-stratified boundary layer is available that accounts
for the combined effects of rotation, surface buoyancy flux and static stability in the free flow. Various expressions proposed
to date are reviewed in the light of what is meant by the stable boundary layer. Two major definitions are thoroughly discussed.
The first emphasises turbulence and specifies the boundary layer as a continuously and vigorously turbulent layer adjacent
to the surface. The second specifies the boundary layer in terms of the mean velocity profile, e.g. by the proximity of the
actual velocity to the geostrophic velocity. It is shown that the expressions based on the second definition are relevant
to the Ekman layer and portray the depth of the turbulence in the intermediate regimes, when the effects of static stability
and rotation essentially interfere. Limiting asymptotic regimes dominated by either stratification or rotation are examined
using the energy considerations. As a result, a simple equation for the depth of the equilibrium stable boundary layer is
developed. It is valid throughout the range of stability conditions and remains in force in the limits of a perfectly neutral
layer subjected to rotation and a rotation-free boundary layer dominated by surface buoyancy flux or stable density stratification
at its outer edge. Dimensionless coefficients are estimated using data from observations and large-eddy simulations. Well-known
and widely used formulae proposed earlier by Zilitinkevich and by Pollard, Rhines and Thompson are shown to be characteristic
of the above interference regimes, when the effects of rotation and static stability (due to either surface buoyancy flux,
or stratification at the outer edge of the boundary layer) are roughly equally important. 相似文献
12.
During spring and autumn, many lakes in temperate latitudes experience intensive convective mixing in the vertical, which leads to almost isothermal conditions with depth. Thus the regime of turbulence appears to be similar with that characteristic of convective boundary layers in the atmosphere. In the present paper a simple analytical approach, based on boundary-layer theory, is applied to convective conditions in lakes. The aims of the paper are firstly to analyze in detail the temperature distribution during these periods, and secondly to investigate the current system, created by the horizontal temperature gradient and wind action. For these purposes, simple analytical solutions for the current velocities are derived under the assumption of depth-constant temperatures. The density-induced current velocities are shown to be small, in the order of a few mm/sec. The analytical model of wind-driven currents is compared with field data. The solution is in good qualitative agreement with observed current velocities under the condition that the wind field is steady for a relatively long time and that residual effects from former wind events are negligible.The effect of the current system on an approximately depth-constant temperature distribution is then checked by using the obtained current velocity fields in the heat transfer equation and deriving an analytical solution for the corrected temperature field. These temperature corrections are shown to be small, which indicates that it is reasonable to describe the temperature distribution with vertical isotherms.Notation
T
temperature
-
t
time
-
x, y, z
cartesian coordinates
-
molecular viscosity
-
h
,
v
horizontal and vertical turbulent viscosity
-
K
h
,K
v
horizontal and vertical turbulent conductivity
-
Q
heat flux through the water surface
-
D
depth
-
u, v, w
average current velocity components inx, y andz directions
-
f
Coriolis parameter
-
p
pressure
-
density
-
g
gravity acceleration
-
a
constant in the freshwater state equation
-
h
s
deviation from the average water surface elevation
-
L
*,H
*
length and depth scale
-
U
*,W
*
horizontal and vertical velocity scale
- T
temperature difference scale
-
bottom slope
-
u
*
friction velocity at the water surface
-
von Karman constant
-
L
Monin-Obukhov length scale
-
buoyancy parameter
-
l
turbulence length scale
-
C
1,C
2,C
3
dimensionless constants in the expressions for the vertical turbulent viscosity
- ,
dimensionless vertical coordinate and dimensionless local depth
-
angle between surface stress direction andx-axis
-
T
bx
,T
by
bottom stress components
-
c
bottom drag coefficient 相似文献
13.
14.
The sandhopper Talitrus saltator (Crustacea: Amphipoda) as a biomonitor of trace metal bioavailabilities in European coastal waters 总被引：1，自引：0，他引：1
Fialkowski W Calosi P Dahlke S Dietrich A Moore PG Olenin S Persson LE Smith BD Spegys M Rainbow PS 《Marine pollution bulletin》2009,58(1):39-44
The amphipod crustacean Talitrus saltator is an established, easily accessible, biomonitor of trace metal bioavailabilities in coastal waters. We have carried out a geographically widespread collection of T. saltator from European shores, stretching from the north-west Atlantic through the Baltic to the Mediterranean. A primary aim of the work was to establish a database of accumulated trace metal concentrations (Cd, Cr, Cu, Fe, Mn and Zn) in this biomonitor. Statistical analysis has shown significant geographical differences in the bioavailabilities of all the metals, the most distinct being copper, iron and manganese. It has proved possible to identify unusually high accumulated concentrations of Cd, Cr, Cu, Fe, Mn and Zn in this biomonitor, indicative of high metal bioavailability at a particular site. These may serve as reference points for future biomonitoring programmes seeking to identify metal contamination in coastal waters. 相似文献
15.
Sergej Zilitinkevich 《Boundary-Layer Meteorology》1994,70(1-2):51-78
During the last two decades, different scalings for convective boundary layer (CBL) turbulence have been proposed. For the shear-free regime, Deardorff (1970) introduced convective velocity and temperature scales based on the surface potential temperature flux,Q
s
, the buoyancy parameter, , and the time-dependent boundary-layer depth,h. Wyngaard (1983) has proposed decomposition of turbulence into two components, bottom-up (b) and top-down (t), the former characterized byQ
s
, the latter, by the potential temperature flux due to entrainment,Q
h
. Sorbjan (1988) has devised height-dependent velocity and temperature scales for both b- and t-components of turbulence.Incorporating velocity shear, the well known similarity theory of Monin and Obukhov (1954) has been developed for the atmospheric surface layer. Zilitinkevich (1971, 1973) and Betchov and Yaglom (1971) have elaborated this theory with the aid of directional dimensional analysis for a particular case when different statistical moments of turbulence can be alternatively attributed as being of either convective or mechanical origin.In the present paper, we attempt to create a bridge between the two approaches pointed out above. A new scaling is proposed on the basis of, first, decomposition of statistical moments of turbulence into convective (c), mechanical (m) and covariance (c&m) contributions using directional dimensional analysis and, second, decomposition of these contributions into bottom-up and top-down components using height-dependent velocity and temperature scales. In addition to the statistical problem, the scaling suggests a new approach of determination of mean temperature and velocity profiles with the aid of the budget equations for the mean square fluctuations.Notation ATL
alternative turbulence layer
- CBL
convective boundary layer
- CML
convective and mechanical layer
- FCL
free convection layer
- MTL
mechanical turbulence layer 相似文献
16.
The motion of Adria, the largest lithospheric fragment in the Central Mediterranean region, has played an important role in the tectonic development of the surrounding mountain chains and even of distant areas, like the Eastern Alps or the Pannonian basin. The available paleomagnetic data were insufficient to constrain this motion, except in a general way. In this paper, new paleomagnetic results are presented from one of the stable parts of Adria which emerge from the Adriatic Sea. The results were obtained on weakly magnetic platform carbonates of the mud-supported type, collected from 21 geographically distributed localities.The results, combined with mean paleomagnetic directions from selected localities from a pioneer study in Istria that were chosen using statistical criteria, were divided into three age groups (Tithonian–Aptian, Albian–Cenomanian, Turonian–Coniacian). The paleomagnetic poles calculated for each of them (Tithonian–Aptian): λ(N) = 47°, (E) = 275°, k = 67, α95 = 9.4°, N = 5; Albian-Cenomanian: λ(N) = 58°, (E) = 253°, k = 145, α95 = 4.3°, N = 9; Turonian–Coniacian: λ(N) = 63°, (E) = 261°, k = 50, α95 = 7.3°, N = 9) reveal a moderate shift during the Cretataceous, which is comparable with that calculated from the African reference poles. However, the Istrian apparent polar wander path is slightly displaced from the African curve, as a consequence of about 10° counterclockwise rotation of Istria, with respect to Africa. This rotation angle is more that 10° smaller than the difference measured for the Mid-Late Eocene between the paleomagnetic direction of platform carbonates from Istria and the African reference direction. This difference may be the consequence of a small clockwise rotation of Istria, with respect to Africa, most probably at the end of Cretaceous. 相似文献
17.
The concept of biotope in marine ecology and coastal management 总被引：3，自引：0，他引：3
The term "biotope" was introduced by a German scientist, Dahl in 1908 as an addition to the concept of "biocenosis" earlier formulated by M?bius (1877). Initially it determined the physical-chemical conditions of existence of a biocenosis ("the biotope of a biocenosis"). Further, both biotope and biocenosis were respectively considered as abiotic and biotic parts of an ecosystem. This notion ("ecosystem = biotope + biocenosis") became accepted in German, French, Russian and other European "continental" ecological literature. The new interpretation of the term ("biotope = habitat + community") appeared in the United Kingdom in the early 1990s while classifying "marine habitats" of the coastal zone. Since then, this meaning was also used in international European environmental documents. This paper examines the evolution of the biotope notion. It is concluded that the contemporary concept is robust and may be used not only for the classification and mapping but also for functional marine ecology and coastal zone management. 相似文献
18.
Anurag Gupta Somnath Chattopadhyaya Sergej Hloch 《Rock Mechanics and Rock Engineering》2013,46(1):169-177
Mining and petroleum drill bits are subjected to highly abrasive rock and high-velocity fluids that cause severe wear and erosion in service. To augment the rate of penetration and minimize the cost per foot, such drill bits are subjected to increasing rotary speeds and weight. A rotary/percussive drill typically hits the rock 50 times per second with hydraulic impact pressure of about 170–200 bar and feed pressure of about 90–100 bar, while rotating at 75–200 rpm. The drill rig delivers a high-velocity flow of drilling fluid onto the rock surface to dislodge cuttings and cool the bit. The impingement of high-velocity drilling fluid with entrained cuttings accelerates the erosion rate of the bit. Also, high service temperature contributes to softening of the rock for increased penetration. Hence, there is a need to optimize the drilling process and balance the wear rate and penetration rate simultaneously. This paper presents an experimental scanning electron microscopy (SEM) study of electroplated (nickel-bonded) diamond drills for different wear modes. 相似文献
19.
We discuss the materials of model experiments concerning the behavior of different constructions of prototypes of buoy carriers
for buoy stations subjected to forcing of wind, waves, and surface currents. 相似文献
20.
In this paper we revise the similarity theory for the stably stratified atmospheric boundary layer (ABL), formulate analytical
approximations for the wind velocity and potential temperature profiles over the entire ABL, validate them against large-eddy
simulation and observational data, and develop an improved surface flux calculation technique for use in operational models. 相似文献