共查询到20条相似文献，搜索用时 31 毫秒
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2.
钱塘江涌潮具有动力作用强和流速变化快等特点。涌潮水流紊动复杂,流速的垂向分布和紊动强度息息相关。通过涌潮水流实测资料的分析可以发现,涌潮作用下流速垂向分布在底部和上层存在差异。为研究涌潮作用下流速垂向分布的特征,应用基于非结构网格下有限体积法模型FVCOM对钱塘江涌潮河段水流运动进行三维数值模拟。考虑到涌潮紊动作用复杂且对流速的垂向分布起着重要影响,采用不同的湍流模式对涌潮传播过程中水流的运动特征开展研究。通过与涌潮河段实测资料的验证,复演涌潮到达前后水流运动特征,给出涌潮水流湍动能的变化过程。研究成果有助于深入认识涌潮水流紊动特征和流速的分布规律,为涌潮作用下物质输运的研究提供基础。 相似文献
3.
The combined tidal and wind driven flow and resulting sediment transport in the ocean over a flat bottom at intermediate water depth has been investigated, using a simple one dimensional two-equation turbulence closure model. This model has been verified against field measurements of a tidal flow in the Celtic Sea. The tidal velocity ellipses and the time series of the horizontal velocity components at given elevations above the bottom are well predicted through the water column although there are some deviations between the predicted and measured velocities near the bottom due to the uncertainty of the bottom roughness. For the combined tidal and wind driven flows the velocity profiles, turbulent kinetic energy profiles and surface particle trajectories are predicted for weak and strong winds. Furthermore, the bottom shear stress and the resulting bedload transport have been predicted; the parts of the particle trajectories in the close vicinity of the bottom where the bedload transport exists are displayed. Finally, the direction and magnitude of the surface drift, the depth-averaged mean velocity and the mean bedload transport are given, and the effect of the bottom roughness on the sea surface drift is investigated. 相似文献
4.
The boundary layer characteristics beneath waves transforming on a natural beach are affected by both waves and wave-induced
currents, and their predictability is more difficult and challenging than for those observed over a seabed of uniform depth.
In this research, a first-order boundary layer model is developed to investigate the characteristics of bottom boundary layers
in a wave–current coexisting environment beneath shoaling and breaking waves. The main difference between the present modeling
approach and previous methods is in the mathematical formulation for the mean horizontal pressure gradient term in the governing
equations for the cross-shore wave-induced currents. This term is obtained from the wave-averaged momentum equation, and its
magnitude depends on the balance between the wave excess momentum flux gradient and the hydrostatic pressure gradient due
to spatial variations in the wave field of propagating waves and mean water level fluctuations. A turbulence closure scheme
is used with a modified low Reynolds number k-ε model. The model was validated with two published experimental datasets for normally incident shoaling and breaking waves
over a sloping seabed. For shoaling waves, model results agree well with data for the instantaneous velocity profiles, oscillatory
wave amplitudes, and mean velocity profiles. For breaking waves, a good agreement is obtained between model and data for the
vertical distribution of mean shear stress. In particular, the model reproduced the local onshore mean flow near the bottom
beneath shoaling waves, and the vertically decreasing pattern of mean shear stress beneath breaking waves. These successful
demonstrations for wave–current bottom boundary layers are attributed to a novel formulation of the mean pressure gradient
incorporated in the present model. The proposed new formulation plays an important role in modeling the boundary layer characteristics
beneath shoaling and breaking waves, and ensuring that the present model is applicable to nearshore sediment transport and
morphology evolution. 相似文献
5.
Andrs E. Tejada-Mart&#x; nez Chester E. Grosch Ann E. Gargett Jeff A. Polton Jerome A. Smith J.A. MacKinnon 《Ocean Modelling》2009,30(2-3):115-142
A three-dimensional numerical model for large-eddy simulation (LES) of oceanic turbulent processes is described. The numerical formulation comprises a spectral discretization in the horizontal directions and a high-order compact finite-difference discretization in the vertical direction. Time-stepping is accomplished via a second-order accurate fractional-step scheme. LES subgrid-scale (SGS) closure is given by a traditional Smagorinsky eddy-viscosity parametrization for which the model coefficient is derived following similarity theory in the near-surface region. Alternatively, LES closure is given by the dynamic Smagorinsky parametrization for which the model coefficient is computed dynamically as a function of the flow. Validation studies are presented demonstrating the temporal and spatial accuracy of the formulation for laminar flows with analytical solutions. Further validation studies are described involving direct numerical simulation (DNS) and LES of turbulent channel flow and LES of decaying isotropic turbulence. Sample flow problems include surface Ekman layers and wind-driven shallow water flows both with and without Langmuir circulation (LC), generated by wave effects parameterized via the well-known Craik–Leibovich (C–L) vortex force. In the case of the surface Ekman layers, the inner layer (where viscous effects are important) is not resolved and instead is parameterized with the Smagorinsky models previously described. The validity of the dynamic Smagorinsky model (DSM) for parameterizing the surface inner layer is assessed and a modification to the surface stress boundary condition based on log-layer behavior is introduced improving the performance of the DSM. Furthermore, in Ekman layers with wave effects, the implicit LES grid filter leads to LC subgrid-scales requiring ad hoc modeling via an explicit spatial filtering of the C–L force in place of a suitable SGS parameterization. 相似文献
6.
对夏季北黄海南部一定点高分辨率连续ADCP(Acoustic Doppler Current Profiler)海流实测资料,使用调和分析方法分解成3部分:不随时间变化的定常余流,周期性潮流和剩余流,再将潮流分解为正压潮流和斜压潮流。通过对实测海流中各组分的分析,结合同时期卫星反演海面风场资料,温度、盐度断面调查资料,得到以下结论:夏季该站点上层定常余流的主导动力控制因素是风应力,上层表现出明显的Ekman风海流特征,中、下层流速方向与表层流向基本成反向,体现出"上进下出"的垂向空间结构,定常流速最大位于近表层,可以达到5cm/s以上;各层的潮流类型均为正规半日潮流,主要半日潮潮流椭圆长轴的方向基本上呈东南-西北方向,其椭率在近底层达到最大值,中、上层较小;从能量角度分析该站点各海流组分,潮流与剩余流所占能量较大,平均起来看,潮流能量占测量海流能量的77%,而定常余流仅占0.6%,该点的斜压潮流较弱,平均斜压潮流能量仅占正压潮流能量的5%。 相似文献
7.
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
8.
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
9.
The results obtained from both atmospheric and laboratory measurements and from LES data show that, in the stably stratified
flows of the atmospheric boundary layer, turbulent mixing occurs at gradient Richardson numbers Ri
g
that significantly exceed one: the inverse turbulent Prandtl number Pr
t
−1 decreases with an increase in the thermal flow stability. The decreasing trend of the inverse turbulent Ptandtl number is
reproduced in a stably stratified atmospheric boundary layer in agreement with measurement data with the aid of an improved
three-parameter turbulence model. In this model, a modified model that takes into account the effect of stratification in
the expression for the time scale of the scalar field is used for the pressure-scalar correlation. 相似文献
10.
对长江口2002年和2003年共4个潮周期的数据进行了分析,通过流速对数剖面公式计算边界层参数,并对各个潮周期内的边界层参数的变化规律进行了分析,同时也对悬沙输送可能对垂向水流结构以及边界层参数造成的影响进行了探讨。结果表明,悬沙的时间分布特征对温度、盐度、水体密度的分布格局有重要影响,主要表现在水体的Rf值普遍较高,分层稳定。此外,悬沙也可影响边界层参数,从而对水流结构产生影响。由于水体的层化作用,使层间的摩擦阻力增大,相当于在垂向上产生不同内边界层,因而影响了流速在垂向上的变化。 相似文献
11.
Contrasts between estuarine and river systems in near-bed turbulent flows in the Zhujiang (Pearl River) Estuary, China 总被引：5，自引：0，他引：5
A bottom-mounted instrumental tripod was deployed in the tidally energetic Zhujiang (Pearl River) Estuary to examine the contrasting properties of the bottom boundary layer (BBL) flows between estuarine and tide-affected river systems. Three aspects of the BBL flows were investigated to understand the mechanism of the turbulence responses to the large-scale ambient forcing: the flow structures (profile, anisotropy, and spectra), shearing strains and stresses, and the balance of turbulent kinetic energy (TKE). Single log-law profiles and turbulence anisotropy predominated in the two systems, but the non-log regime and stronger anisotropy occurred more frequently at the slack tide in the estuary. The ADV-based turbulence intensities and shearing strains both exceeded their low-frequency counterparts (frictional velocities and mean shears) derived from the logarithmic law. On the contrary, the ADV-based Reynolds stresses were smaller than the log profile-derived bottom stresses, so the hypothesis of a constant stress layer cannot be well satisfied, especially in the river. The bandwidth of the inertial subrange in the river was of one decade larger than in the estuary. The balance between shear production and viscous dissipation was better achieved in the straight river. This first-order balance was significantly broken in the estuary and in the meandering river, by non-shear production/dissipation due to wave-induced fluctuations or salinity/sediment stratification. All these disparities between two systems in turbulence properties are essentially controlled by the anisotropy induced by the large-scale processes such as secondary currents, density stratification. In conclusion, the acceleration of unsteady flows determines the profile structure of the BBL flow, and turbulence anisotropy results in the invalidation of the phenomenological relations such as the constant stress hypothesis and the first-order TKE balance. 相似文献
12.
北仑河口水动力状况复杂,受入海径流、潮汐、波浪、沿岸流、风应力等多种因子的共同影响.对北仑河口S1、S2站长序列的海流剖面资料进行数学统计、潮流调和分析和数字滤波,探讨其潮流特征和余流形成机制.分析结果表明:北仑河口潮流性质主要为不规则全日潮流;观测期间S1站实测涨、落潮最大流速分别为39、83 cm/s,S2站分别为52、44 cm/s.研究海域余流流速从表层往底层逐渐减小,其中S1站余流流速主要介于5～10 cm/s之间,流向集中在S-SW向,S2站主要介于0～5 cm/s之间,表、中层以NNE-ENE向为主,底层以偏W向为主.风应力是调查区表层与近表层余流形成的主导因素;西向沿岸流对调查区的余流也有较明显的作用;径流对调查区的S1站有一定的影响,但对S2站影响很小;潮致余流对调查区的余流贡献较小. 相似文献
13.
Large eddy simulation of turbulence in ocean surface boundary layer at Zhangzi Island offshore 总被引：1，自引：0，他引：1
This study uses a large eddy simulation （LES） model to investigate the turbulence processes in the ocean surface boundary layer at Zhangzi Island offshore. Field measurements at Zhangzi Island （39°N, 122°E） during July 2009 are used to drive the LES model. The LES results capture a clear diurnal cycle in the oceanic turbulence boundary layer. The process of the heat penetration and heat distribution characteristics are analyzed through the heat flux results from the LES and their differences between two diurnal cycles are discussed as well. Energy balance and other dynamics are investigated which show that the tide-induced shear production is the main source of the turbulence energy that balanced dissipation. Momentum flux near the surface shows better agreement with atmospheric data computed by the eddy correlation method than those computed by bulk formula. 相似文献
14.
Modelling of undertow by a one-equation turbulence model 总被引：1，自引：0，他引：1
15.
潮流的流速分布和湍流切应力的分布密切相关。为了研究潮流湍流切应力的特征和变化规律,本文从潮流运动方程推导出随潮流呈周期性变化的湍流切应力随深度的分布表达式。从江苏近海现场实测流速剖面中计算得到一个潮周期内的湍流切应力的变化过程。通过将实测值与本文理论解的比较发现,计算值能很好地反映出实测值的变化特征,尤其是能正确地反映潮流在加速和减速过程中,湍流切应力偏离线性分布呈现上凹和下凹的现象,以及只有在加减速转换的时候切应力才呈现线性分布的特点。最后,通过分析湍流切应力振幅及相位沿水深的变化情况,认为反映潮流周期、涡粘性和水深之间关系的参数Ri是决定湍流切应力弯曲程度及分布形态的重要参数。对于近海潮流,水深是影响湍流切应力偏离线性程度的主要因素。 相似文献
16.
Alan M. Davies Jiuxing Xing John M. Huthnance Philip Hall Laurenz Thomsen 《Progress in Oceanography》2002,52(2-4)
A three dimensional time-dependent baroclinic hydrodynamic model, including sediment transport and incorporating a turbulence energy sub-model, is used in cross sectional form to examine sediment movement at the shelf edge off North West Iberia at 42°40.5’N where measurements were made as part of the OMEX-II programme. These calculations are complemented by a simpler, in essence time-independent model, which is used to examine the sensitivity of the sediment distribution over the slope (from a shelf-break source) to changes in the specified values of horizontal and vertical diffusion coefficients. The philosophy of the paper is to use idealized tidal, wind and wind wave forcing to examine changes in sediment distribution resulting from these processes. Calculations with the time-dependent and steady state models give insight into both the role of events and long-term effects. The steady state model focuses on the off-shelf region, whilst the time-dependent model considers on-shelf events.Tidal calculations showed that for the stratification used here the internal tide in the OMEX region was primarily confined to the shelf edge and ocean. A mean on-shelf sediment transport in the surface layer and off-shelf transport at the bed was found. Across-shelf circulations produced by up-welling/down-welling favourable winds gave rise to on-shelf/off-shelf currents in the bottom boundary layer with an opposite flow in the surface layer. In the case of an up-welling favourable wind, sediment suspension was at a maximum in the near coastal region, with sediment being advected off shore in the surface layer. With a down-welling favourable wind, surface sediment was advected towards the shore, but there was offshore transport at the bed. Near the shelf edge any upwelling flow had the tendency to return this sediment to the surface layer from whence it was transported on-shore. So in essence the sediment was trapped within an on-shelf circulation cell. Wind waves effects increased the total bed stress and hence the sediment concentration and its transport, although its pattern was determined by tidal and wind forcing.The time independent model with increased/decreased lateral diffusivity gave an enhanced/reduced horizontal sediment distribution for a given settling velocity. As the settling velocity increases, the down-slope movement of sediment is increased, with a reduction in the thickness of the near-bed sediment layer, but with little change in its horizontal extent. 相似文献
17.
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
18.
A high-quality experimental study including a large number of tests which correspond to full-scale coastal boundary layer flows is conducted using an oscillating water tunnel for flow generations and a Particle Image Velocimetry system for velocity measurements. Tests are performed for sinusoidal, Stokes and forward-leaning waves over three fixed bottom roughness configurations, i.e. smooth, “sandpaper” and ceramic-marble bottoms. The experimental results suggest that the logarithmic profile can accurately represent the boundary layer flows in the very near-bottom region, so the log-profile fitting analysis can give highly accurate determinations of the theoretical bottom location and the bottom roughness. The first-harmonic velocities of both sinusoidal and nonlinear waves, as well as the second-harmonic velocities of nonlinear waves, exhibit similar patterns of vertical variation. Two dimensionless characteristic boundary layer thicknesses, the elevation of 1% velocity deficit and the elevation of maximum amplitude, are found to have power-law dependencies on the relative roughness for rough bottom tests. A weak boundary layer streaming embedded in nonlinear waves and a small but meaningful third-harmonic velocity embedded in sinusoidal waves are observed. They can be only explained by the effect of a time-varying turbulent eddy viscosity. The measured period-averaged vertical velocities suggest the presence of Prandtl's secondary flows of the second kind in the test channel. Among the three methods to infer bottom shear stress from velocity measurements, the Reynolds stress method underestimates shear stress due to missed turbulent eddies, and the momentum integral method also significantly underestimates bottom shear stress for rough bottom tests due to secondary flows, so only the log-profile fitting method is considered to yield the correct estimate. The obtained bottom shear stresses are analyzed to give the maximum and the first three harmonics, and the results are used to validate some existing theoretical models. 相似文献
19.
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
20.
Shallow-water-boundary layers are affected by current, waves, bottom topography, and stratification. Precise turbulence measurements through such regions are difficult. A deployment of a BASS (Benthic Acoustic Stress Sensor) tripod in November 1997 in the North Sea in 15 m of water provides a data set to examine turbulent boundary layer models. The deployment spanned both calm and storm sea conditions, had strong tidal currents, the location was uniform horizontally, and the bottom-boundary layer was well mixed in temperature. Estimates of stress derived from the covariance, log-fit, drag-law, and inertial-dissipation method have been compared. The covariance stress estimate had the largest sample to sample scatter, but from theoretical considerations should give the best estimate in stratified flow. The drag-law estimate gave the least sampling variability but suffers from the user having to measure a drag coefficient by some other method. The inertial-dissipation method was more tolerant to sensor misalignment, had the second greatest sampling variability, and could not be used to measure stress during slack tide. Averaging many semidiurnal tidal cycles showed greater tidal asymmetry of the log-fit stress than the covariance or inertial-dissipation stress estimates. Turbulent energy generation and dissipation were measured and balanced individually for the upper two sensors and followed a one-over-height-above-bottom profile 相似文献