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1.
Study on the double-logarithmic profile of tidal flow velocity in the near-bed layers 总被引:1,自引:0,他引:1
Tidal current velocity profile in the near-bed layers has been widely studied. The results showed that velocity profile in the near-bed layer obviously departure from the traditional logarithmic profile, due to the acceleration or deceleration. Although the logarithmic linear profile can reduce the rate of deviation from this, only it is a lower-order approximate solution. In this paper, considering the unsteady and non-linear features of tidal motion, the double logarithmic profile near-bed layers in estuarine and coastal waters is established on the assumption that the turbulent shear stress along the water depth was parabolic distribution, and on the basis of Prandtl''s mixing length theory and von Karman''s self-similar theory. Having been verified the data observed at the West Solent in the south of England, and comparison of the logarithmic linear profile, it found that the double logarithmic profile is more precious than the latter. At last, the discussed results showed that:(1) The parabolic distribution of the tidal shear stresses verified good by the field data and experimental data, can be better reflected the basic features of the tidal shear stress deviating from linear distribution that is downward when to accelerate, upward when to decelerate. (2) The traditional logarithmic velocity profile is the zero-order approximation solution of the double logarithmic profile, the logarithmic linear profile is the first order, and the logarithmic parabolic profile is the second order. (3) Ignoring the conditions of diffusion and convection in the tidal movement, the double logarithmic profile can reflect the tidal properties of acceleration or deceleration, so that the calculation of the friction velocity and roughness length are more reasonable. When the acceleration or the deceleration is about zero, the double logarithmic profile becomes the logarithmic profile. 相似文献
2.
本文提出仅需若干特定层次的风速与气温的观测(或计算)值便可算出大气稳定度的5个简化式。计算结果显示:(1)所论海区可沿用风速的对数律,而(气温—表面水温)的对数律是有条件地被采用;(2)R_1=R_2,R_1=ζ_2和ζ_3=ζ_2。 相似文献
3.
Study on the Log-Linear Velocity Profile of Near-Bed Tidal Current in Estuarine and Coastal Waters 总被引:2,自引:1,他引:2
Many observed data show that the near-bed tidal velocity profile deviates from the usual logarithmic law. The amount of deviation may not be large, but it results in large errors when the logarithmic velocity profile is used to calculate the bed roughness height and friction velocity (or shear stress). Based on their investigation, Kuo et al. (1996) indicate that the deviation amplitude may exceed 100%. On the basis of fluid dynamic principle, the profile of the near-bed tidal velocity in estuarine and coastal waters is established by introducing Prandtl' s mixing length theory and Von Kannan selfsimilarity theory. By the fitting and calculation of the near-bed velocity profde data observed in the west Solent, England, the results are compared with those of the usual logarithmic model, and it is shown that the present near-bed tidal velocity profile model has such advantages as higher fitting precision, and better inner consistency between the roughness height and friction velocity. The calculated roughness height and friction velocity are closer to reality. The conclusions are validated that the logarithmic model underestimates the roughness height and friction velocity during tidal acceleration and overestimates them during tidal deceleration. 相似文献
4.
沿岸流流速垂向分布的实验研究 总被引:1,自引:0,他引:1
进行了沿岸流模型实验,测量沿岸流流速的垂向分布.采用Faria等(1996)的方法对实验结果进行了分析,将水深分为上层和下层两部分:下层采用对数分布来表达沿岸流的垂向分布;上层考虑了波浪引起的自由表面的波动,使流速分布包括了修正的对数分布和质量输移速度两部分.对实验结果得到的相对粗糙度与sleath(1991)的经验公式结果进行了对比,也对摩阻流速结果与已有经验公式计算结果的进行了对比. 相似文献
5.
The combined wave-current flow has been solved by researchers by assuming wave over either depthwise constant or linear current
profile. Some complicated nonlinear current profiles have also been considered to simulate various shear currents. We consider
a nonlinear current vertically logarithmic in nature and examine its interaction with a periodic surface wave. The Navier-Stokes
equations for incompressible flow are solved for the current part and by using periodic boundary conditions. The effect of
logarithmic current on wave components is assessed. The corresponding celerity and dispersion equation yields a close-form
solution for the shallow-wave approximation. Several comparative trends between wave-only, wave with log current, and wave
with constant current for the wave following/opposing these currents have been discussed. The flow properties of the first
order are presented which can be applicable to the real inland and coastal flows, where progressive waves are ubiquitous over
a depthwise logarithmic current. The work is further extended to the second-order semiempirical wave component by using past
experimental data on the wave spectrum of combined flow.
Published in Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 20–40, May–June, 2008. 相似文献
6.
江苏大丰地区潮滩由于水深较浅,潮流、波浪等动力较强,整个水层可视为边界层,其主体部分是对数层,即水流流速在垂向上呈对数分布。在潮流的加减速阶段,流速剖面将可能偏离对数分布,从而使对数剖面法计算出来的边界层参数造成误差。使用MIDAS-400用户化数据采集系统,在大丰潮滩获得了多层流速、浊度等同步高频观测数据,基于修正后的von Karman-Prandtl模型对u-lnz进行回归分析、数据内部一致性分析来定义流速对数剖面并与未修正前经典理论得到的边界层参数进行比较。分析结果表明,修正后的流速剖面更符合实际情况,边界层参数除了受水流加速度的影响外,还和沙纹等因素有关。另外,边界层参数的变化量与特征加速度负相关。 相似文献
7.
《Coastal Engineering》1999,36(3):263-269
Using the logarithmic wind profile and typical values of dimensionless sea roughness for different sea states, simple power expressions are derived for the wind profile over water. The power expressions are useful for correcting measured wind speed data at a given elevation (up to an elevation of 60 m) to the standard elevation of 10 m commonly used in coastal engineering studies. The analysis shows that the 1/7 power expression (suggested in [U.S. Army Corps of Engineers, 1984. Shore Protection Manual, Vol. 1. Coastal Engineering Research Center, Vicksburg, USA.] and commonly used today) is a good approximation (<3% error) of the logarithmic profile for various sea states up to an elevation of 20 m. Above this elevation, the 1/7 power expression underestimates the wind speed for moderate to fully developed sea states. 相似文献
8.
A method for evaluating statistical errors associated with logarithmic velocity profiles 总被引:3,自引:0,他引:3
R. H. Wilkinson 《Geo-Marine Letters》1984,3(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
9.
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
10.
New CTD-XBT (T-7 probe) comparison data are analyzed, which provide additional evidence of XBT depth error and support previous results (Hanawa and Yoritaka, 1987; Hanawa and Yoshikawa, 1991). The depth difference between the corrected and uncorrected data is about 26 m at 750 m. In the present study, new data processing procedures by which the depth errors are automatically detected, are developed and adopted. In the new method, first, temperature gradients (TG) of XBT and CTD profiles are calculated. Then, 20 m segment of the XBT-TG profile which should fit to the CTD-TG profile of 20 m segment to be referred to is searched in the XBT-TG profile. Actually, this is achieved by shifting the XBT-TG profile of 20 m segment so as to minimize the area surrounded by both TG profiles. The shifted depth of XBT-TG profile for CTD-TG profile can be regarded as the XBT depth error. This processing is repeated at intervals of 5 m from 10 m to 790 m of CTD-TG profile. The relationship between the scatter of the quadratic depth-time equation coefficients and the depth error is also discussed. It is shown that when the two coefficients have a certain relationship, the depth differences between the plural depth-time equations are small, even if the two coefficients of those equations have apparently very different values.This paper was presented and discussed in the Ad Hoc Meeting of the IGOSS Task Team on Quality Control for Automated System, held in Marion, Massachusetts,U.S.A. in June 3–6, 1991. 相似文献
11.
Frequency distribution characteristics of trace elements Fe. Mn, Zn, Cu. Sr and Ba are studied for the marine organisms collected from typical Chinese coastal waters and compared with those of major elements Ca and Mg. Nearly all the distributions for trace elements in macroalgae, benthic molluscs, crustaceans, cephalopods and different tissues of fish (muscle, liver and bone ) are found to show some degree of positive skewness, indicating a relatively large number of marine organisms with low concentrations for a particular element and only a few organisms with disproportionately high concentrations. Their distribution types are generally logarithmic normal distribution or nearly logarithmic normal distribution. Distribution of Ca is similar to that of trace elements, while Mg shows normal distribution. Average elemental concentrations of major types of organisms are calculated based on their frequency distributions. 相似文献
12.
13.
江苏大丰潮间带粉砂滩的潮流边界层特征 总被引:4,自引:0,他引:4
对江苏大丰潮间带粉砂滩的潮流观测数据,运用Karman-parndtl模型分析了流速对数剖面的出现频率和边界层参数(摩阻流速与粗糙长度)。结果表明,不同时间尺度(10^1-10^3s)的平均流速对计算u-lnz线性关系出现频率的影响不大,而不同层位组合的影响较为显著,影响流速对数剖面分布的自然因素为波浪、风、潮流旋转、表底层流向差异、滩面坡度和水流加减速等。相邻层位的流速在时间序列上存在很高的线性关系,回归直线的斜率与水层距底床的高度、粗糙长度和摩阻流速有关。涨潮阶段床面粗糙长度大于落潮阶段,涨潮阶段摩阻流速小于落潮阶段。 相似文献
14.
15.
A. V. Glazunov 《Izvestiya Atmospheric and Oceanic Physics》2006,42(3):282-299
The neutrally stratified boundary layer over a smooth rough surface is consider. The turbulent flow is simulated using a finite-difference eddy-resolving model of the atmospheric boundary layer (ABL). The model includes different turbulence closure schemes and numerical approximations for advection components of the momentum balance equation. We investigate the quality of reproduction of spectral characteristics of the turbulent flow and the model’s capabilities to reproduce the observed profile of mean wind velocity near the rough surface. It is shown that the best result is obtained by coupling a numerical scheme of higher order of accuracy with a mixed closure scheme based on an adaptive estimation of the mixing length for subgrid-scale fluctuations. Here, we are able to reproduce the asymptotics of the fluctuation spectrum of the longitudinal component of wind velocity near the surface and within the boundary layer as well as the logarithmic profile of mean velocity near the surface. 相似文献
16.
17.
《Estuarine, Coastal and Shelf Science》2005,62(1-2):193-204
A three-dimensional Large Eddy Simulation (LES) model is used to simulate oscillating tidal boundary layers and test previous results obtained from one-dimensional boundary layer models and turbulence measurements in tidal channels. The LES model produces low-order turbulence statistics in agreement with the semi-analytic theory and observations. It shows a logarithmic layer in the mean velocity profile and a linear distribution of Reynolds stress with water depth. However, the eddy viscosity profile predicted by the LES model is not parabolic but better matches a parabolic profile modified by wake effect observed in the outer part of depth-limited steady boundary layers. Low-order turbulence statistics can be scaled by the instantaneous friction velocity at the bottom boundary. Although turbulence intensities in three directions fluctuate over a tidal cycle, their normalized values are in good agreement with those determined from laboratory experiments of steady open-channel flows. The LES model confirms that tidal turbulence is in quasi-equilibrium. However, it also demonstrates the importance of flow acceleration/deceleration term in the depth-integrated momentum balance for the mean flow. Phase differences are found between flows at different heights above the bottom boundary. 相似文献
18.
The abandoned Yellow River Delta coast is a typical erodible silty and muddy coast in China. The paper analyses the marine dynamic characteristics and the mechanism of beach erosion of this area. Analysis and calculation show that in this sea area wave and tidal current action should be considered. Based on the above analysis, an equilibrium beach profile calculation model is developed, in which the wave-current interaction is considered while sediment supply and sediment re-deposition are neglected. The model consists of four parts: (1) calculation of wave parameters, (2) calculation of velocity due to wave-current interaction at different water depth, (3) calculation of friction velocity and shear stress at different water depths, and (4) calculation of the amount of sediment erosion, erosion intensity and variation of beach profile. Calculated results are in good agreement with observed data. Finally, the evolution tendency is discussed and the equilibrium beach profile of this coast is calculated. B 相似文献
19.
应用Dean,Bodge和Lee近岸平衡剖面模式,对粤东靖海波控弧形海湾两条近岸剖面作了分析对比。结果显示拟合的Dean模式与实际剖面偏差明显,由Bodge模式计算的四度,北剖面小于南剖面,此与沿岸滩面坡度变化趋势一致,由tee模式拟合的结果导出的波周期与实测值相近。文中讨论了海岸反射性与剖面凹度、剖面变化截止水深与泥沙运动的关系。 相似文献
20.
1 .IntroductionTheZhapuPortissituatedonthenorthbankoftheHangzhouBay ,nearZhapuTowninPinghuCity ,Zhejiangprovince .Asthefirststepofconstruction ,reclamationwasaccomplishedinthehinter landoftheharbor.Theborderdikeofafulllengthof 1 2 71mislocatedinthetidalregionoftheHangzhouBay .ThepreliminarydesignofthisprojectwascompletedinJune 1 986 ,anditsconstructionbeganinJuly 1 986 ,andwascompletedinMarch 1 991 .TheseadikewasbuiltontheQ4marinedepositofsaturatedsoftclaywithathicknessofabout2 7mandgeo… 相似文献