Laboratory study of wave and turbulence velocities in a broad-banded irregular wave surf zone

The characteristics of wave and turbulence velocities created by a broad-banded irregular wave train breaking on a 1:35 slope were studied in a laboratory wave flume. Water particle velocities were measured simultaneously with wave elevations at three cross-shore locations inside the surf zone. The measured data were separated into low-frequency and high-frequency time series using a Fourier filter. The measured velocities were further separated into organized wave-induced velocities and turbulent velocity fluctuations by ensemble averaging. The broad-banded irregular waves created a wide surf zone that was dominated by spilling type breakers. A wave-by-wave analysis was carried out to obtain the probability distributions of individual wave heights, wave periods, peak wave velocities, and wave-averaged turbulent kinetic energies and Reynolds stresses. The results showed that there was a consistent increase in the kurtosis of the vertical velocity distribution from the surface to the bottom. The abnormally large downward velocities were produced by plunging breakers that occurred from time to time. It was found that the mean of the highest one-third wave-averaged turbulent kinetic energy values in the irregular waves was about the same as the time-averaged turbulent kinetic energy in a regular wave with similar deep-water wave height to wavelength ratio. It was also found that the correlation coefficient of the Reynolds stress varied strongly with turbulence intensity. Good correlation between u′ and w′ was obtained when the turbulence intensity was high; the correlation coefficient was about 0.3–0.5. The Reynolds stress correlation coefficient decreased over a wave cycle, and with distance from the water surface. Under the irregular breaking waves, turbulent kinetic energy was transported downward and landward by turbulent velocity fluctuations and wave velocities, and upward and seaward by the undertow. The undertow in the irregular waves was similar in vertical structure but lower in magnitude than in regular waves, and the horizontal velocity profiles under the low-frequency waves were approximately uniform.     

天然感潮河道水流紊动特性分析

采用多谱勒三相流速仪，在长江口徐六泾水文观测断面分别进行了涨潮、落潮时中泓与近岸垂线的流速观测，根据这些观测资料，对天然感潮河段潮流紊动的周期、频率、概率密度函数等进行了定量的数学描述，并对时均流速、紊动强度、雷诺应力等沿垂线分布进行了分析计算。     

Vertical Structure of Currents in Northern Black Sea,October 2016

The paper presents the results of an analysis of hydrological data obtained on cruise 89 of the R/V Professor Vodyanitskii from September 30 through October 19, 2016, in the central area of the northern Black Sea. Currents were measured using a lowered acoustic Doppler current profiler (LADCP) to a depth of 350 m. Examples of the current velocity profiles and conditional density at individual stations are presented. The averaged characteristics of the vertical current structure in the seasonal and permanent pycnoclines are discussed. The isopycnally averaged kinetic energy (KE) demonstrates an almost linear dependence on the conditional density (σ_θ). In the seasonal pycnocline, EK = 0.2–0.013σ_θ; in the permanent pycnocline, EK = 0.12–0.007σ_θ. An interpretation is given for the variability of the kinetic energy with depth. It is shown that the maxima of the averaged vertical shear profile correspond to the occurrence depth of the seasonal and permanent pycnoclines. The mean Richardson number has a value of ~10 in the upper sea layer and decreases with depth, assuming a value of ~3 at the 300 m horizon. The estimate for the vertical turbulent diffusion coefficient from the simplified model shows its increase with depth.     

Experimental and numerical study of current-induced artificial upwelling

The aim of the current paper is to investigate hydrodynamic characteristics of the artificial upwelling induced by ocean currents. Experiments were performed in a flume at different density difference heads, horizontal current velocities and upwelling pipe diameters. A three-dimensional computational fluid dynamics (CFD) model was employed on wider range of parameters for further analysis. The performance of the numerical model has been confirmed by the experimental findings. The present results show that the volume flow rate of current-induced artificial upwelling is influenced by geometrical parameters and inclination angle of the pipe, the horizontal current velocity and vertical distribution of water density. In ideal two-layer density stratified water, the critical current velocity to generate upwelling linearly increases with the increase of the density difference, and the maximum rising height for upwelling is inversely proportional to the density difference. Feasibility analysis was taken by using current and density profiles of the East China Sea near Dongji Islands, which provides an useful reference for engineering practice.     

东大港水道流速垂线分布探讨

对辐射沙洲海域东大港水道4号站位连续2个潮次的流速测量资料进行了分析、研究,拟合给出了流速垂线分布关系,并根据实际测量资料率定了该站位各时刻6个水层的浑水水流的尾流函数项表达式,这些表达式表明浑水水流的尾流函数项是相对深度和摩阻速度的函数。     

On the theory of calculation of currents in the world's ocean straits

The paper considers the statement of the problem on quasi-stationary diagnosis of currents, temperature, salinity, and density fields for multiply connected areas with fluid boundaries. The principles of self-similar parameterization over the vertical axis are applied by introducing models for the vertical substance distribution, which have two regularly varying functions. The problem is reduced to handling a set of Poisson equations, enabling the boundary conditions to be automatically determined at the island shores. A scheme is presented for calculating current velocity components at an arbitrarily oriented transect. Several examples of current velocity computation for the topographically complex oceanic areas are given which support the data collectedin situ. Translated by Vladimir A. Puchkin.     

西洋东大港水道流速垂线分布研究

对辐射沙洲海域东大港4#站位连续2个潮周期的流速测量资料进行了分析、研究,拟合给出了流速垂线分布关系,并根据实际测量资料确定了该站位6个水层的浑水水流尾流函数项表达式。这些表达式表明浑水水流尾流函数是相对深度和摩阻速度的函数。探讨分析了尾流函数的空间分布和潮周期过程。非恒定流的水流尾流函数项的准确表达,对于揭示含沙水流流速结构及水、沙相影响作用规律将起到启发和推动作用。     

Vertical structure of the field of current velocities in the northwest part of the Black Sea based on the <Emphasis Type="Italic">LADCP</Emphasis> data for May 2004

The profiles of absolute current velocity obtained by using a lowered acoustic doppler current profiler (LADCP) are presented. In the course of the BSERP-3 expedition, the measurements were carried out in the regions of the Rim Current, anticyclonic eddy, and northwest shelf. In the core of the Rim Current, a unidirectional motion of waters is traced in layers below the main pycnocline down to depths greater than 500 m. Its characteristic velocity can be as high as 0.08 m/sec. It is shown that the direct action of the eddy is detected in the shelf region at distances larger than 20 km from the outer edge of the shelf in the zone bounded by an isobath of 100 m. The formation of multilayer vertical structures in the field of current velocities is revealed in the region of interaction of the anticyclonic eddy with irregularities of the bottom on the side of the shelf. A two-layer structure of currents with specific features in the layer of formed seasonal pycnocline is observed in the region of the shelf down to an isobath of 100 m. The profiles of the moduli of vertical shears of currents averaged over the casts ensemble are presented for the abyssal and shelf parts of the sea. It is shown that the shears induced by the geostrophic currents and wave processes in the region of the main pycnocline are comparable. Below the pycnocline, the shears are mainly determined by the wave processes. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 25–37, November–December, 2008.     

波流耦合作用下渤海及北黄海风暴潮增水及海浪过程的数值模拟

本文基于三维波流耦合FVCOM-SWAVE数值模式,采用Jelesnianski参数化风场与再分析数据集ECMWF风场数据叠加而成的合成风场作为外力驱动力,模拟了1818号"温比亚"台风引起北黄海及渤海海域风暴潮增减水及波浪的生长与消减过程,进而分析该海域在"温比亚"台风作用下波浪对流速垂向分布的影响。研究结果表明:合成风场得到的风速最大值及出现时刻与实测数据符合较好,合成风场较为合理,能够为模拟波流耦合机制下海域水动力变化提供准确的风场条件;几个测站的风暴潮增水模拟结果与实测数据较为吻合,FVCOM-SWAVE耦合系统合理地再现了"温比亚"台风在黄渤海引发的风暴潮增水以及台风浪过程。此外,计算结果显示"温比亚"期间黄渤海海域最大有效波高分布于台风中心外围,且位于台风前进方向上,波浪最大有效波高值与台风强度有关;在台风过境期间,波流相互作用对近岸海域流速的垂向分布具有一定影响,考虑波流相互作用可有效提高台风风暴潮数值模拟精度。研究结果对台风灾害预报、防灾减灾及港口建筑选址具有一定的参考意义。     

On the application of a turbulence closure modified model to the description of the density jump evolution in a stably stratified medium

The self-similar turbulent density jump evolution has been studied in the scope of a turbulence closure modernized theory which takes into account the anisotropy and mutual transformation of the turbulent fluctuation kinetic and potential energy for a stably stratified fluid. The numerical calculation, performed using the equations for the average density and kinetic and potential energies of turbulent fluctuations, indicates that the vertical profiles of the buoyancy frequency, turbulence scale, and kinetic and potential energies drastically change when the turbulence anisotropy is strong. The vertical profiles of the corresponding energy and spatial discontinuity parameters, calculated at a weaker anisotropy, indicate that similar drastic changes are absent and a qualitative agreement exists with the known analytical solution, which describes the density jump evolution in a freshwater basin and was obtained previously [5, 8] in the scope of a turbulence local-similarity hypothesis applied in combination with the budget equation for the turbulent fluctuation kinetic energy.     

A method of submersion in the problem on the determination of dispersion curves of internal waves in the presence of a current with vertical velocity shear

The previously proposed method [1] of submerging aimed at determining internal wave dispersion characteristics is generalized to consider the case of a background horizontal flow with a vertical velocity shear. The results of calculating, dispersion curves of discrete spectrum modes for the profiles of the Brunt-Väisälä frequency and the mean current velocity are given; they agree well with the results of studies carried out in ref. [5].Translated by Mikhail M. Trufanov.     

长江口南港底部边界层特征的观测与分析

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。     

深海垂向流速剖面数值模拟

运用CFD软件对深海各种不同的垂向流速剖面进行数值模拟,分析研究试验区域内水流在空间上的流速分布情况以及湍流强度的变化,并与目标流速进行了比较.结合模型试验,表明数值模拟的结果是可靠的,造流系统能够较为准确地模拟出不同垂向流速剖面的海流,满足深水试验池对深海海流的模拟要求.     

东大港与豆腐渣腰门交汇区潮流动力特征分析

对江苏省辐射沙洲海域东大港与豆腐渣水道交汇处5号站位连续两个潮次流速测量资料进行分析,对该交汇区域的潮流特征和潮流过程有了近一步认识,拟合给出了潮汐过程流速垂线分布表达式。     

Current Dynamics of Estuarine Circulation in the Lateral Boundary Layer

High spatial resolution measurements of current velocity performed by the shipboard mounted Acoustic Doppler Current Profiler (ADCP) in the lateral boundary layer of the southern Gulf of Finland during two 5-day periods are described and analysed with a focus on the dominant dynamics. The measurement site represents a small (15×20 km), relatively deep (up to 100 m) bay opened to large-scale estuarine circulation. The measurement period was characterized by calm winds and a strong seasonal pycnocline (Brunt-Väisälä frequencyN=6–9*10⁻² s⁻¹). The quasi-steady velocity field revealed polarization of currents along the shore whereas an intensive baroclinic coastal jet was observed over a cross-shore scale of 1–2 km. The level of vertical separation of the alongshore flow coincided with the pycnocline at the coast, but was shifted below it in the offshore region. The cross-shore flow was considerably weaker and showed a three-layer structure with an opposite phase between the first and second surveys. It is suggested that the observed jet resembles a non-locally forced eastward propagating coastally trapped wave. In the offshore area the alongshore flow field satisfies local geostrophic balance quite well, except in the pycnocline where strong vertical stratification exerts considerable vertical stress. As vertical velocity shear is well correlated with vertical stratification, the horizontal advection prevails over vertical mixing. Horizontal inhomogeneities of density distribution are partly explained by vertical velocities with an estimated magnitude of less than 0·6 mm/s and the spatial pattern following bottom topography.     

海流流速计算的研究

由于大范围同步连续观测海流流速很困难,这才产生建立一定的理论及方法认真计算海流流速的要求.可是,过去沿用至今的动力计算[1],方法虽简便,但只能计算因密度分布所生的梯度流(或地转流),且存在着既不考虑风力,又不顾及湍流摩擦力,再加无运动面难以确定,即令设法作出浅海订正,其结果又往往与事实不符等根本性缺陷;而如籍Ekman漂流理论计算海流,又仅能计算因风所生的漂流,且还存在着既不考虑海水密度分布,又视海面无倾斜,再加湍流动力粘滞系量难以确定等与实际相差较远的理论依据.近代兴起的一些海流数值计算,又往往都局限于全流或深度平均流速的计算.因此,建立一种既考虑到海洋内部海水分布,又考虑到海面风力外加海面大气压力作用,顾及到海洋中湍流摩擦力,又体现流速随深度变化,而更重要的是应用起来简易的计算海流流速的理论及方法,便成为很需要解决的问题了.     

基于潜标观测的吕宋海峡以东深海海流的低频变异

本文利用在菲律宾海布放的一套锚系潜标获取的长时间海流和水温观测数据,分析了吕宋海峡以东的深海海洋环境特征,着重阐释了该海域海流的全水深垂向结构及其低频变化特征。研究表明,表层(100～160 m)平均流向为西偏北,流速约为12.5 cm/s;中层(810 m)的平均流为西向,流速为2.6 cm/s;深层(1 550 m和2 560 m)的平均流速在1 cm/s以内,近底(4 040 m)的流向为较稳定的西南向,流速为2.3 cm/s。上层海流的动能比中层和深层大1～2个量级,总动能、平均动能、涡动动能均在表层最大,中层次之、深层最小,各层次涡动能均大于平均动能。中上层海流的低频变化具有极高的相似性,全年为81～85 d的周期振荡;近底层海流则不同,变化周期约为51 d。     

The high-resolution vertical structure of internal tides and near-inertial waves measured with an ADCP over the continental slope in the Bay of Biscay

ADCP measurements of the velocity structure in the permanent thermocline at two locations over the continental slope in the Bay of Biscay are presented. The vertical variation of the contribution of the inertia-gravity waveband to the kinetic energy, vertical motion, and current shear are analysed. The semi-diurnal tides together with near-inertial waves appear to provide over 70% of the high-frequency kinetic energy (>1/3 cpd). Over the vertical range of the ADCP observations the phase of the harmonic M₂ tide changes up to 155°, while the kinetic energy varies in the vertical by a factor of 3.8, showing the importance of the contribution of internal waves to the observed tidal motion. Both semi-diurnal internal tidal waves and near-inertial waves have a vertically restricted distribution of the variance of the horizontal and vertical velocity, as in internal wave beams. The short-term 14-day averaged amplitude and phase lag of the M₂ tide shows large temporal changes, with a characteristic 40–45 day time scale. These changes are probably related to variations in generation sites and propagation paths of the internal tide, because of changes in the temperature and salinity stratification due to the presence of meso-scale eddies. The relatively large shear in the inertia-gravity wave band, mainly at near-inertial frequencies, supports low-gradient Richardson numbers that are well below 1 for nearly half of the time. This implies that the large shear may support turbulent mixing for a large part of the time.     

Distribution of eddy scales for wave current combined flow

This paper illustrates the modulation of the eddy scale distribution due to superimposition of surface wave on only current flow. Time series data of three-dimensional velocity components were measured in a laboratory flume by a three-dimensional (3D) 16-MHz micro-acoustic Doppler velocimeter (Micro-ADV). The velocity time series of only current case and waves following the current were analysed to obtain the phase-averaged mean velocities, turbulent intensities, and Reynolds stress. The probability density function of phase-averaged stream-wise and vertical velocity fluctuations showed bimodal oscillations towards the free surface for higher frequency surface waves. It was revealed that surface waves along the current effectively decrease the intermittency of turbulence of the only current flow. Surface wave changed the intermittent structure of only current flow by modulation of the energy cascade mechanism of the only current flow by introduction of wave induced length scales. Also the scale of the finer dissipative eddies were prominently enhanced by the increase in surface wave frequency. Wavelet analysis of time series of velocity signals provided information on the eddy scale and their frequency of occurrence. It was found that the large eddies are carried by the crest regions of the progressive wave while the small scale eddies are carried by the trough regions.