共查询到20条相似文献，搜索用时 15 毫秒
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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
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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
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《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
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基于2005年胶南近岸海域海流的周日连续观测资料,对该海域观测日期内的海流特征、潮流性质及余流特点进行了初步分析;进而在实测资料分析的基础上,利用分步杂交法对潮流场进行了数值模拟计算,展现了M2分潮的潮波系统、潮流椭圆分布、最大流速分布及逐时潮流场。数值计算结果与实测资料分析结果相一致,较好地反映出该海域M2分潮潮流场时空分布的基本特征,对该海域的水动力状况有了更进一步了解,为胶南近岸海域的环境保护规划的制定提供了一定条件下的科学依据。 相似文献
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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
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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
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《Coastal Engineering》2006,53(10):845-855
This paper presents a study of wave damping over porous seabeds by using a two-dimensional numerical model. In this model, the flow outside of porous media is described by the Reynolds Averaged Navier–Stokes equations. The spatially averaged Navier–Stokes equations, in which the presence of porous media is considered by including additional inertia and nonlinear friction forces, is derived and implemented for the porous flow. Unlike the earlier models, the present model explicitly represents the flow resistance dependency on Reynolds number in order to cover wider ranges of porous flows. The numerical model is validated against available theories and experimental data. The comparison between the numerical results and the theoretical results indicates that the omission or linearization of the nonlinear resistance terms in porous flow models, which is the common practice in most of analytical models, can lead to significant errors in estimating wave damping rate. The present numerical model is used to simulate nonlinear wave interaction with porous seabeds and it is found that the numerical results compare well with the experimental data for different wave nonlinearity. The additional numerical tests are also conducted to study the effects of wavelength, seabed thickness and Reynolds number on wave damping. 相似文献
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Anh Duc Nguyen Hubert H.G. Savenije Duc Nghia Pham Duc Thang Tang 《Estuarine, Coastal and Shelf Science》2008
The fresh water discharge is an important parameter for modelling salt intrusion in an estuary. In alluvial converging estuaries during periods of low flow, when salinity is highest, the river discharge is generally small compared to the tidal flow. This makes the determination of the fresh water discharge a challenging task. Even if discharge observations are available during a full tidal cycle, the fresh water discharge is seldom much larger than the measurement error in the tidal discharge. Observations further upstream, outside the tidal region, do not always reflect the actual flow in the saline area due to withdrawals or additional drainage. Discharge computation is even more difficult in a complex system such as the Mekong Delta, which is a multi-channel estuary consisting of many branches, over which the freshwater discharge distribution cannot be measured directly. This paper presents a new approach to determine the freshwater discharge distribution over the branches of the Mekong Delta by means of an analytical salt intrusion model, based on measurements made during the dry season of 2005 and 2006. It appears that the analytical model agrees well with observations and with a hydraulic model. This paper demonstrates that with relatively simple and appropriate salinity measurements and making use of the analytical salt intrusion model, it is possible to obtain an accurate discharge distribution over the branches of a complex estuary system. This makes the analytical model a powerful tool to analyze the water resources in tidal regions. 相似文献
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Numerical study on the characteristics of flow field and wave propagation near submerged breakwater on slope 总被引：2，自引：1，他引：1
In this study,characteristics of flow field and wave propagation near submerged breakwater on a sloping bed are investigated with numerical model. The governing equations of the vertical twodimensional model are Reynolds Averaged Navier Stokes equations. The Reynolds stress terms are closed by a nonlinear k ε turbulence transportation model. The free surface is traced through the PILC-VOF method. The proposed numerical model is verified with experimental results. The numerical result shows that the wave profile may become more asymmetrical when wave propa-gates over breakwater. When wave crest propagates over breakwater,the anticlockwise vortex may generate. On the contrary,when wave hollow propagates over breakwater,the clockwise vortex may generate. Meanwhile,the influenced zone of vortex created by wave crest is larger than that created by wave hollow. All the maximum values of the turbulent kinetic energy,turbulent dissi-pation and eddy viscosity occur on the top of breakwater. Both the turbulent dissipation and eddy viscosity increase as the turbulent kinetic energy increases. Wave energy may rapidly decrease near the breakwater because turbulent dissipation increases and energy in lower harmonics is transferred into higher harmonics. 相似文献
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在海洋流场数值计算中，当流场中建筑物尺度相对平面网格步长太小时，计算中难以引进其作用，在所得计算结果中难以反映其影响。本文依据流量连续、能量守恒规律，通过水力学物模实验，求得建筑物存在情况下的谢才系数Ｃ，解决了计算中的难题。 相似文献
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在海堤建设等人类活动和三角洲蚀淤等自然演变的共同作用下,黄河三角洲岸线水深近年来发生了剧烈变化,同时也将引起邻近海域潮波系统及物质输运路径的重要变化。本文基于FVCOM数值模式,建立了黄河三角洲及邻近海域三维高分辨率潮汐、潮流及拉格朗日粒子追踪数值模型。通过与环渤海长期验潮站的潮汐调和常数、黄河三角洲临时潮位站和测流站的实测资料对比,模型结果验证良好,能较好反映黄河三角洲及邻近海域潮汐、潮流运动特征,并获得了2019年M2分潮无潮点位置。通过设置1980年、2019年黄河三角洲岸线自然演变、海堤建设及相应水深地形变化的5个数值实验,结果表明：在人类活动与自然演变共同驱动下,黄河三角洲海域的M2分潮无潮点向东南方向移动,主要影响因素为水深。黄河口向海延伸和海堤丁坝建设导致的岸线变化,对无潮点位置影响较小,但在该凸出岸段两侧形成余流流涡,使得黄河入海物质在莱州湾内停留时间变长,向渤海输运扩散的时间推迟。 相似文献
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柱体绕流问题是流体力学领域一个非常经典的问题。当流体流经柱体时,由于黏性的存在,会发生许多复杂的流动现象,如流动分离、涡旋周期性生成与脱落等,经常被作为标准验证算例。同时,柱体绕流广泛存在于实际工程中,并在一定工况下可能对工程产生巨大危害,因此对柱体绕流进行深入研究具有重要意义。研究中,拟将一种无网格类方法——半隐式移动粒子方法(moving particle semi-implicit method,简称MPS)引入到柱体绕流问题的数值研究中,并对不同雷诺数下二维方柱绕流问题进行数值模拟。首先,使用基于MPS方法自主开发的MLParticle-SJTU求解器,结合入口边界条件和出口边界条件,模拟了雷诺数Re分别为40、200和1 000时均匀来流条件下的方柱绕流。随后,将模拟的绕流结果与文献中试验和数值计算结果进行了对比,结果吻合较好,并且在雷诺数为200和1 000时,可以清晰地捕捉到方柱尾流中的卡门涡街现象,验证了MPS方法在柱体绕流问题模拟上的有效性和适用性。 相似文献
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根据湍流封闭理论,建立一种适用于正压浅海湍流运动的雷诺应力封闭模型(RSM),以代替目前三维浅海动力学模型中普遍采用的湍粘性系数的传统假设。通过直接建立并模化f—平面上正压海洋的雷诺应力传输方程,分别得到的微分形式和代数形式的RSM方程组。并讨论了进行数值计算所需要的边界条件。利用该模型可以进一步研究浅海潮流、风暴潮流及风海流等浅海流动的三维结构和湍流特性。 相似文献
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Based on the one-dimensional salinity transport equation with constant diffusion coefficient, and separated water flow velocity into runoff and tidal current with the single-frequency in an idealized estuary, the simplest unsteady analytical so- lution of salinity intrusion is deduced and the estimation formula of diffusion coefficient is obtained in this paper. The unsteady solution indicates that salinity process in estuaries results from the interaction of runoff and tidal current, and its amplitude is in direct proportion to the product of the velocity of runoff water and the amplitude of tidal flow velocity and in inverse proportion to the diffusion coefficient and the tidal angular frequency, and its phase lag tidal flow with 7/2 which reveals the basic features of the maximum salinity appearing after flood slack and the minimum salinity appearing before ebb slack under the effect of runoff （the advance or lag time is relative to the magnitude of runoff and tidal flow）. According to the measured flow velocity and salinity data, the salinity diffusion coefficient could be estimated. Finally, with the field data of observing sites on the deepwater navigation channel of the Yangtze Estuary, the diffusion coefficient is calculated and a comparative analysis of simulated and measured of salinity process is made. The results show that the solution can comprehensively reflects the basic characteristics and processes of salinity intrusion under the interaction of runoff and tidal flow in estuaries. The solution is not only suitable for theoretical research, but also convenient for estimating reasonable physical parameters and giving the initial condition in the salinity intrusion numerical simulation. 相似文献
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Quasi-3D Numerical Simulation of Tidal Hydrodynamic Field 总被引：2，自引：0，他引：2
SONG Zhiyao XUE Hongchao YAN Yixin MAO Lihua XU Fumin
Doctor Senior Engineer College of Harbor Waterway Coastal Engineering Hohai University 《中国海洋工程》1999,(3)
Based on the 2D horizontal plane numerical model,a quasi-3D numerical model is establishedfor coastal regions of shallow water.The characteristics of this model are that the velocity profiles can be ob-tained at the same time when the equations of the value of difference between the horizontal current velocityand its depth-averaged velocity in the vertical direction are solved and the results obtained are consistent withthe results of the 2D model.The circulating flow in the rectangular area induced by wind is simulated and ap-plied to the tidal flow field of the radial sandbanks in the South Yellow Sea.The computational results fromthis quasi-3D model are in good agreement with analytical results and observed data.The solution of the finitedifference equations has been found to be stable,and the model is simple,effective and practical. 相似文献