共查询到20条相似文献，搜索用时 453 毫秒
1.
R. H. Wilkinson 《Geo-Marine Letters》1983,3(1):49-52
A logarithmic velocity profile is often fitted to velocity data in order to calculate the friction velocity (u *) and typify the surface texture by a roughness length (z o ). A method is given for estimating the errors in these parameters as calculated by this method. An example is given in which the size of the error is compared with the fluctuations that typically occur in the time seriesu *(t) andz o (t). 相似文献
2.
Jin Wu 《Journal of Oceanography》1988,44(5):254-260
Physical bases for nondimensional parameters,z
0/(u
2
*/g) andz
0/(u
*/), characterizing wind-wave interaction are discussed; data selected to support the latter are critically reviewed. Both parameters are herewith unified, with the former describing the primary growth of roughness length with wind and the latter the secondary effects due to waves. 相似文献
3.
When the nondimensional aerodynamic roughness parameter for the sea surface (gz
0/u
*
2,g being the acceleration of gravity,u
* the air friction velocity) is plotted as a function of the wave age, the data points in the diagram are distributed mostly in a triangle area between the Charnock formula and the Toba-Koga formula; the nondimensional roughness perameter is not expressed as a unique function of the wave age, but rather there seem to be multiple regimes. In order to investigate the cause of the data point scattering, a reanalysis was made of the 4.5-hour time series of the wind profile and wind-wave statistics which were obtained at an oceanographic tower station under the conditions of a winter monsoon wind having slightly fluctuating speed and steadily growing wind waves.It is concluded that the averaged variation ofz
0 is given by the Toba-Koga formula with a constant of value 0.015. However, as a result of the wind fluctuation on the time scales ranging from several minutes to an hour, data points show a conspicuous fluctuation on the nondimensional roughness parameter-wave age diagram in the direction transverse to the averaged variation. The variation inz
0 directly reflects the degree of over- or under-saturation in the high-frequency range of the wind-wave spectra. Physical interpretation of these variations is also presented. 相似文献
4.
M. V. Kurgansky 《Izvestiya Atmospheric and Oceanic Physics》2014,50(4):337-342
A model for the density Q of vertical mass flux of sand (dust) in the convective atmospheric boundary layer as a function of the number density N of convective elements (including vortices), friction velocity u *, and vertical (turbulent) buoyancy flux B is proposed. It is shown that the flux Q is proportional to the product of the square root of B and the sixth power of u *. This finding is consistent with empirical dependences Q(u *) reported in the literature. We discuss two methods for experimentally determining density N when the lifting of dust occurs, mainly due to (terrestrial and Martian) dust devils. 相似文献
5.
A new set of empirical formulas for the production rate and the number concentration of sea-water droplets on the sea surface are proposed, synthesizing past observation data of sea-salt particles in the sea and water droplets in wind-wave tanks. A new levelz
c
is introduced as the effective wind-sea surface where seawater droplets are produced. The new formulas are expressed in linear functions in logarithmic scales ofu*2/v
p
, a parameter to describe overall conditions of airsea boundary processes, whereu
* is the friction velocity of air,v the kinematic viscosity of air and
p
the peak angular frequency of wind-wave part of wave spectra. A model of coexistence of spray droplets and suspended particles near the sea surface is proposed. As for the independent parameter, a comparison between the uses ofu*2/v
p
and ofu
*
3 which was the traditional way of parameterization excluding wave measure, shows that the advantage of usingu*2/v
p
is statistically significant with a confidence limit 89% in F-test. 相似文献
6.
The paper discusses a method for the statistical evaluation of the vertical current velocity componentV
z(z) using data provided by profilers. The calculation of theV
z(z) profiles involves the determination of the root-mean-square deviation of the error of determination of the vetical current
velocity component at each level and the RMS deviation of the sample statistical variability of this quantity's estimates.
ProfilesV
z(z) have been computed for the north-western Black Sea using three surveys, with the involvement of an OLT profiler. The computations
have shownV
z(z) to have a two-layer structure, with zero being crossed in the main pycnocline. Such structure of the current velocity
vertical component is consistent with the hydrodynamic model of the field of currents induced by buoyancy fluxes through the
lateral boundaries of the basin. The availability of the zero values of the vertical current velocity in the pycnocline yields
a tool for gaining insight into the mechanism controlling the emergence of the oxic/anoxic interface and areas with sharp
vertical gradients of chemical and hydro-optical characteristics.
Translated by Vladimir A. Puchkin. 相似文献
7.
进一步研究强风条件下海-气湍流动量交换以及海浪特征,有助于提高数值天气模式对台风强度演变、移动路径以及恶劣海况的预报能力。依照前人的方法将台风分为风向与浪向(1)相同,(2)相反,和(3)交叉3个扇形区,并结合台风路径数据,得到了浮标数据相对于台风的方位。分别对3种类型的浮标数据进行分析,进而发现了波浪高度和相速度随风速增加而变化的规律。并利用GWW参数化方案计算出摩擦速度(u*)、拖曳系数(CDN)和粗糙长度(z0)。将这些结果与前人代表性的研究论文中所用观测数据和所得研究结论进行比较,结果表明二者有较强的一致性。该研究证明GWW参数化方案在强风条件下依然有很好的适用性。 相似文献
8.
K.F. Lambrakos 《Ocean Engineering》1985,12(4):271-291
Measurements of tidal current and wave velocity made at 0.69 and 1.85 m above a rough seafloor exhibit large current gradients (boundary layer) in the water column. The logarithmic boundary layer flow model was fitted to the measurements, and thus roughness (z0) and friction velocity (u*) parameters were derived. The roughness parameter values were generally consistent with the observed upstream physical roughness. The values of both parameters for conditions in the rough turbulence flow regime are generally larger (much larger for ebb) than earlier published values for similar measurements of currents in the absence of significant waves but are comparable to values from recent measurements of currents in the presence of storm waves. The high parameter values here appear to relate more to the magnitude of the current and to the upstream physical bottom roughness than to the magnitude of the seastate. Large boundary layers in the flow at the seabed have a profound effect on the design of offshore structures such as offshore pipelines. 相似文献
9.
Velocity profiles in a salt marsh canopy 总被引：7，自引：0，他引：7
Flow velocity profiles, measured in aSpartina anglica canopy in a laboratory flume, change with the location of measurement and plant stem density. The shear velocity above the canopy is larger than that within the canopy. The reduction ofu
* within the canopy will favor the deposition of cohesive sediment. The reducedu
* and flow turbulence within the canopy can enhance particle flocculation and settling velocity. The canopy exerts a strong influence on the concentration, settling velocity of the flocs, and deposition rate of the suspended sediment through effects on bed shear stress and turbulence of flow within the canopy. 相似文献
10.
A series of measurements of winds and wind-waves were carried out in wind-wave flumes. A data analysis based on the hypothesis
of local equilibrium yielded a new empirical formula on the controversial quantity of roughness heightz
0 over the water surface:
, where the nondimensional roughness height
is defined bygz
0/u
*
2 and the wave-wind parameterũ byω
p
u
*/g, g being the gravitational acceleration,u
* the friction velocity of air,ω
p
the peak frequency of wind-wave spectra. The obtained formula is compared with Charnock's (1955) and Toba's (1979) proposals;
is constant in the former and inversely proportional toũ in the latter. As in Toba's, this formula immediately leads to a practically important conclusion that the drag coefficientC
d
depends not merely on the usual variableU
10 (wind velocity at 10m height over the water surface), but also on the surface state represented by wind-waves. An explicit
expression is provided for the drag coefficient incorporating the wave-wind parameter; it covers the range ofC
d
calculated from most of the previous drag formulas, by varying the wave-wind parameter. 相似文献
11.
Dependence of Whitecap Coverage on Wind and Wind-Wave Properties 总被引：13，自引：0，他引：13
12.
Analysis is made of wind and wave data, which were obtained during the passage of Typhoon 8013 at an Ocean Data Buoy Station south of Honshu operated by the Japan Meteorological Agency, in order to investigate the wave dependence of sea-surface roughness parameter in the situation where wind waves are dominant with less significant swells. The data fit better the wave-dependent expression of the wind stress,z
0
p/u*=, than to Charnock's formula,gz
0/u*2=, wherez
0 is the roughness length,
p the angular frequency of the spectral peak of wind waves,u* the friction velocity of air,g the acceleration of gravity, and are non-dimensional constants. The results are very similar to those of our previous study using data from an oil producing platform in the Bass Strait, Australia, although the type of observation system and the synoptic situation of the winds and wind waves were totally different. 相似文献
13.
Observational data on air-sea boundary processes at the Shirahama Oceanographic Tower Station, Kyoto University, obtained in November, 1969, was analyzed and presented as an example representing the structure of growing wind-wave field. The condition was an ideal onshore wind, and the data contained continuous records of the wind speed at four heights, the wind direction, the air and water temperatures, the tides, and the growing wind waves, for more than six hours. The main results are as follows. Firstly, in both of the wind speed and the sea surface wind stress, rather conspicuous variations of about six-minute period were appreciable. Secondly, the three-seconds power law and its lemma expressed byH
*=BT
*3/2 and=2BT
*–1/2, respectively, are very well supported by the data, whereH
*(gH/u
*
2) andT
*(gT/u
*) are the dimensionless significant wave height and period, respectively, the wave steepness,u
* the friction velocity of air,g the acceleration of gravity, andB=0.062 is a universal constant. Thirdly, the spectral form for the high-frequency side of the spectral maximum is well expressed by the form of()=
sgu*–4, where is the angular frequency and() the spectral density. The value of
s is determined as 0.062±0.010 from the observational data. There is a conspicuous discrepancy between the spectral shape of wind waves obtained in wind-wave tunnels and those in the sea, the former containing well-defined higher harmonics of the spectral peak, and consequently there is an apparent difference in the values of
s also. However, it is shown that the discrepancy of
s may be eliminated by evaluating properly the energy level of the spectral form containing higher harmonics. 相似文献
14.
1. The adsorption action of basic zinc carbonate adsorbent on uranium in natural seawater can be expressed with the following formula of adsorption isotherm:C=k(U*)n = 8.51× 10-1(U*)0.49,where C is the concentration of uranium on adsorbent; U* is content of uranium in natural seawater employed.2. when the quantity of basic zinc carbonate adsorbent (T) is constant, with the increase of natural seawater quantity through the adsorption column (G), also increased are the adsorption content of uranium of the adsorbent (U), the concentration of uranium on the adsorbent (C) and the concentration of residual uranium (C0*) in natural seawater after adsorbing uranium, while the rate of recovery of uranium (R) is decreased. With the increase of (G) the coefficient of distribution (Kd) decreases to a certain value and then a little rises again. 相似文献
15.
海底沉积物再悬浮及其分布取决于海洋水动力、沉积物类型与床面形态之间复杂的相互作用,准确地理解和确定沉积物再悬浮过程对于沉积物输运的研究具有重要的意义。本文在祥云湾海洋牧场典型海域开展现场原位观测,获取研究区波浪、海流及悬浮沉积物浓度数据;分析了波、流作用下海底边界层悬浮沉积物垂向分布特征,并探究了海洋水动力和床面形态对悬浮沉积物垂向分布的影响。结果表明,研究区波流之间的相互作用不显著,沉积物再悬浮受控于风暴浪作用,风暴浪作用下底床切应力可以达到沉积物临界切应力的10～15倍,沉积物的再悬浮滞后于风暴浪作用2～3 h。在波浪荷载微小的情况下,悬浮沉积物垂向分布呈现"I"型,波浪荷载下,悬浮沉积物垂向分布呈现幂指函数分布,表现为"L"型;床面形态随波、流作用而演化,影响沉积物的再悬浮过程,u_(?w)/u_(?c)=1.00可作为波浪和海流起主导控制作用的床面形态的判别依据,纯波浪荷载作用下的u_(?w)/u_(?c)显著高于波浪主控作用下,但二者之间的界线随着波浪荷载的增加而升高。 相似文献
16.
Abstract The continental slope off the coast of Israel is riddled with numerous large slump scars at depths greater than 400 m. Recent scar slumps are situated in the steepest central portions of the continental slope (400–450 m depth, α=6°), frequently disfiguring older slump scars in its lower portions. The slumping materials were probably largely transported downslope in the form of density currents, and occasionally by sliding of large sediment chunks. Upslope retrogressive slumping phases progressively disfigure the shape of the slump scars until they totally disappear, causing net reduction of the thickness of the sedimentary column. To provide a basis for the quantitative analysis of slumping, laboratory vane tests, triaxial consolidated, undrained compression tests with pore‐pressure measurements, drained direct shear tests, and consolidation tests were performed oh undisturbed samples. Because the sediments consist of normally consolidated silty clays, the geotechnical properties measured on the core samples can be readily extrapolated for greater depths, assuming the sediments are homogeneous. Angles of internal friction measured by direct shearing under drained conditions are ?d =24°‐25°, designating the maximum possible angle of a stable infinite slope. These angles are appreciably higher than the steepest slopes in the investigated area, and a drained slumping mechanism is therefore considered unlikely. The slopes of the slump scar walls are about 20°; therefore, in the absence of active erosional, sedimentological, or tectonic agents, these walls have long‐term stability (drained shear). Undrained shear failure resulting in slope instability may be attributable to rapid changes in slope geometry (undercutting or oversteepening of the slope), fluctuations in pore pressure, or accelerations associated with earthquakes. Undrained shear‐strength parameters were determined by both laboratory consolidated‐un‐drained triaxial tests and by miniature vane shear tests. The angles of internal friction that were measured are ?cu =15°‐17°, and the cu/po values range between 0.22 and 0.75. An analysis of the force equilibrium within the sediments leads to the conclusion that horizontal earthquake‐induced accelerations, as little as 5–6% of gravity, are sufficient to cause slope failure in the steepest slope zone (400–450 m depth, α = 6°, cu /po =0.25). Collapse resulting from liquefaction is unlikely, as the sediments are normally consolidated silty clays with intermediate sensitivity, St =2–4. The existence of slump scars in the lower portion of the continental slope, characterized by gentle slopes (α=1°‐3°) and sediments with high shear strength (c u /p o=0.30–0.50) is attributed to large horizontal accelerations(k=12–16% of gravity). Owing to the wide range of geotechnical properties of the sediments (cu /po = 0.20–0.75) and the inclination of the continental slope (α=1°‐6°), the same earthquake may generate a wide range of horizontal accelerations in different portions of the continental slope, and slumping may occur wherever the stability equilibrium is disrupted. 相似文献
17.
Airy waves have a sinusoidal profile in deep water that can be modeled by a time series at any point x and time t, given by η(x,t) = (Ho/2) cos[2πx/Lo − 2πt/Tw], where Ho is the deepwater height, Lo is the deepwater wavelength, and Tw is the wave period. However, as these waves approach the shore they change in form and dimension so that this equation becomes invalid. A method is presented to reconstruct the wave profile showing the correct wavelength, wave height, wave shape, and displacement of the water surface with respect to the still water level for any water depth. 相似文献
18.
Various wind velocitiesu
*,U
/2,U
andU
10 are correlated to the measured growth rate of water waves , whereu
* is the friction velocity of the wind, andU
/2,U
andU
10 are the wind speeds respectively at the heights /2, and 10m above sea surface (: wave length). It is shown that within a range of the dimensionless wind speed, 0.1<u
* /C<0.6, there are no appreciable differences in the correlations, whereC is the phase velocity of water waves. The present relation between andU
shows qualitatively similar properties as the one obtained by Al'Zanaidi and Hui (1984); the growth rate for waves with rough surface is larger than that with smooth surface. However, our present relations give, for the both waves with different surface roughness, larger values by factors 1.71.8 than those given by Al'Zanaidi and Hui's relation. 相似文献
19.
Mikitoshi Hirabara Hiroshi Ishizaki Goro Yamanaka Hiroyuki Tsujino Ichiro Ishikawa 《Journal of Oceanography》2010,66(5):633-647
An analysis is presented of snapshot data (eastward and northward velocity components: u and v; tracer such as potential temperature: τ) from an eddy-resolving (Rgrid: 1/12°) ocean model experiment, in order to explore a method for improving eddy-permitting
model performance. Horizontal 3 × 3 R-grid averages give the eddy-permitting grid (P-grid: 1/4°) variables: 〈u〉, 〈v〉, and 〈τ〉, where 〈〉 denotes the spatial P-grid scale average. The difference between the horizontal tracer flux across the boundary
face of a P-grid and that across the corresponding faces of R-grids is estimated as F2E. It is found that the correlations among the gradients of u, v, and τ give a good approximation F2C to the estimated flux F2E. The approximated flux is a function of these gradients and the grid size. A method is presented for implementing the F2C for density to an eddying ocean model as an additional advection. Practical experiments were conducted with a realistic configuration.
It is shown that the zonal mean isotherms in the Kuroshio extension region are more flattened in the run using the proposed
method than in another run using the conventional horizontal biharmonic operator, suggesting that the additional flux correction
leads to an enhancement of sub-basin scale mixing. 相似文献
20.
Essential properties of Boussinesq equations for internal and surface waves in a two-fluid system 总被引：1，自引：0，他引：1
Boussinesq equations describing motions of internal waves in a two-fluid system with the presence of free surface are theoretically derived, and the associated essential properties are examined in this study. Eliminating the dependence on the vertical coordinate from all variables, four equations constitute the Boussinesq model with two flexible parameters, zu and zl, which indicate the specific elevations, respectively, in the upper and lower fluids. Similar to the Boussinesq model for a single-layer fluid, zu and zl are determined by matching the linear dispersion relation with Lamb's solution. This determines the optimal model. In the analysis stage, this problem is classified into two cases, the thicker-upper-layer case and the thicker-lower-case case, to avoid the possible divergence of wave properties as the thickness ratio grows. Since there exist two modes of motions that may be excited, cases of both modes are separately analyzed. Linear characteristics including the amplitude ratios and normalized particle velocities are analyzed. Second-order harmonic waves are examined to validate nonlinear behaviors of present model. Results of linear and nonlinear investigations show that the present model indeed extends the applicable range of traditional Boussinesq equations. 相似文献