现场海域水平、铅直扩散系数的推算

本文根据拉格朗日流与欧拉流自相关系数的相似关系和Kullenberg提出的半理论半经验公式,用渤中8号平台1987年1～2月和7～8月的实测资料,分别推算了水平、铅直扩散系数.推算结果表明,研究长时间水平扩散时,把潮流看作湍流,所求的扩散系数实际上是潮流扩散系数,其值在108cm2 /s范围内;研究短时间水平扩散时,把潮流看作平流,用傅里叶变换的长周期合成值从实测值中扣除,所求的扩散系数,可认为是湍流扩散系数,其值在104em2/s范围内.本海域铅直扩散系数值,冬季在3.8～4.2cm2/s范围内;夏季在0.0l～0.75cm2/s范围内.它与国外一些海区和以前文献中的估算值基本一致;它随风速、流的剪切增大而增大;随水柱的稳定度增大而减小;它在跃层处最小,在跃层以上和以下逐渐增大.     

现场海域水平扩散系数的探讨 Ⅱ．黄河三角洲埕北海域的计算

根据Ｔａｙｌｏｒ的湍流扩散理论和Ｈａｙ、Ｐａｓｑｕｉｌｌ提出的拉格朗日流和欧拉流的相关函数的相似性，用黄河三角洲埕北海域的实测资料，按四种不同方案计算出该海域的水平扩散系数和谱密度分布。指出：该海区潮流扩散系数主要受潮流的影响，其分布特征与潮流的分布基本一致，所求的水平扩散系数主要是由周期性的潮运动给予潮流扰动所致。方案４是通过富氏变换滤波消去了周期性潮流扰动，本方案计算的水平扩散系数是由周期为６ｈ以下的小尺度涡提供能量。     

利用“LGC2—1A”水中荧光计和荧光染料试验研究近岸海水的湍流扩散

本文介绍拖曳荧光计及荧光染料试验的工作原理及操作方法。在青岛胶州湾及朝连岛附近海域进行两次实地试验.观测污染物质的时、空分布,检验污染物在湍流扩散和输送间的关系,从而定出其水平扩散系数及变化。试验说明此海域污染水平扩散系数为10~3厘米~2/秒量级,为一般情况的(1/10),扩散能力较差,在此海域排污应加注意。     

极谱法同时测定各级络离子的稳定常数和扩散系数Ⅰ——亚铊离子与硫代硫酸根的络合反应

1.提出一个新的从极谱实验数据(扩散电流)同时求各级络离子的稳定常数和扩散系数的方法。在具体数学处理上,把法作了改进。 2.提出了一种校核上述计算结果准确性的方法。这也是一种当已知各级络离子的稳定常数(或扩散系数)后计算扩散系数(或稳定常数)的方法。 3.研究了亚铊离子与硫代硫酸根的络合反应。利用上述方法计算,证明溶液中存在有Tl~+、TlS_2O_3~-、Tl(S_2O_3)~(--)。其稳定常数和扩散系数分别为:K_1=27.8,D_1=1.11×10~(-5)cm~2/sec;K_2=13.9、D_2=8.24×10~(-6)cm~2/sec(25℃, μ=3.00,用NaClO_4维持。)。     

长江九江段水中污染物稀释扩散规律的研究

用罗丹明-B染料作示踪体研究了长江九江段溶解污染物质的扩散规律。该区为顺直河段,水流速度约为22—80cm/s,6kg罗丹明-B的扩散长度为3240m。在4级风下,在40Min内,D. F值从10~2变化到10~9,说明江水中污染物的扩散还是很快的。实验表明,污染物质的浓度变化与时间的2.9次方成反比。九江段的扩散系数为1.23m~2/s。九江市取水口上游500一1000m外贸货运码头所排放的污水和其它污染物质对取水口有一定的影响,必须对污物的排放加以限制。     

杭州湾潮波三维数值模拟

采用“σ坐标下的三维数值模式”来模拟杭州湾三维潮波运动,水平方向上以较小尺度的差分网格覆盖计算区,垂直方向上给予均匀的分层,对占本湾水位谱总能量80％的半日潮波M_2和半日潮波m_1((K_1+O_1)/2)两类进行了数值模拟。水平流动和潮位的计算结果与相应的实测值拟合良好。计算表明,水平潮流具有明显的往复流性质,主要呈东-西方向;流速自湾口向湾顶增加,M_2分潮流最大可达270cm/s左右,m_1分潮流最大可达24cm/s左右。在太阴时1和13时,于湾的中部偏南存在一个弱的逆时针向的大涡旋;在7和19时于上述位置存在一个弱的顺时针向的大涡旋。垂直流速振幅一般为10~(-2)—2×10~(-2)cm/s,最大可达2.5×10~(-2)cm/s,位于乍浦附近的底层水域中。     

丁字湾近岸海域潮汐、潮流和余流特征研究

利用丁字湾近岸海域2021年的最新观测资料,研究了潮汐、潮流和余流的基本特征和变化规律。得出如下结论：潮汐为正规半日潮,最大潮差405 cm,最小潮差69 cm,平均潮差248 cm,涨潮历时小于落潮历时。潮流为规则半日浅海潮流,最大涨潮流流速为67 cm/s,最大落潮流流速为72 cm/s。涨潮流历时小于落潮流历时。垂向来看,表层流速最大,中层次之,底层最小。海流的旋转谱分析的结果显示M₂分潮的谱峰值最高,运动形式为逆时针旋转流。余流,整体余流流速小于10 cm/s,表层余流最大,中层次之,底层最小。观测期间,长周期的风向和余流流向相反,因此风不是余流的控制因素。     

基于高频ADCP资料的磨刀门河口羽状流湍流动力特征

利用1 200 kHz的宽频RDI ADCP于2015年7月在磨刀门河口拦门沙前缘的浅水站和沿岸流影响的深水站进行座底观测,采样频率为1 Hz,数据经滤波去噪处理,应用方差方法分析了磨刀门的羽状流湍流动力特征。结果表明,磨刀门河口水流表现出3层流结构,峰值流速出现在表层的羽状流层,深水区雷诺应力量级为10-3~10-5 m2/s2,小于拦门沙前缘的湍流脉动强度;拦门沙前缘和深水区湍流动能密度参数的范围均在0.01~0.6 m2/s2左右,羽状流的湍动能比底边界层高一个数量级。拦门沙前缘羽状流的湍动能生成率量级约为10-3 W/kg,比底层大2~3个量级,且远强于深水区;垂直涡黏系数的大小约为0~0.15 m2/s。总的来说,羽状流表现出层化稳定、混合强烈,以及高的湍动能生成率,为羽状流携带高浊度悬沙离岸远距离搬运提供了湍流动力条件。     

渤海弱层化期湍流混合观测特征分析

利用2017年9月在渤海共享航次中取得的湍流混合直接观测数据,本文研究了渤海海域湍流混合的空间分布特征及有关的影响因素。9月观测海区水体垂向层结较弱,莱州湾受黄河冲淡水影响出现高温低盐结构,位于渤海中央浅滩南北两侧洼地的双中心冷水结构依旧存在。湍流观测结果表明湍动能耗散率在10~(-9)～10~(-5)W/kg之间变化,统计上满足对数正态分布。耗散率强值区出现在辽东湾及渤海湾湾口近岸处,相应的垂向湍扩散系数约为10~(-6)～10~(-2)m~2/s。垂向上,水体表、底层混合较强,进一步研究发现弱层化水体的平均湍动能耗散率〈ε〉与风速和正压潮流速的大小存在正相关关系。另一方面,耗散率ε与浮性频率N近似满足ε=2.0×10~(-8)+3.0×10~(-7)(N~2/N_0~2)~(-5)的拟合函数关系,反映了层化对水体垂向混合的抑制作用。     

利用高分辨率水体反射地震资料研究吕宋海峡以东黑潮区混合

混合过程是海洋中普遍存在的一种形式, 对气候变化、物质分布等起到了重要作用。地震海洋学是近十多年发展起来的一门新兴学科, 被广泛应用到物理海洋学问题的研究中, 具有高空间分辨率的突出优点。文章利用反射地震资料, 通过斜率谱方法, 分别获得了吕宋海峡以东黑潮区湍流段与内波段的耗散率及扩散率。结果显示, 在剖面深度200~800m的平均耗散率为10 ^-7.0W·kg ^-1, 平均扩散率为10 ^-3.3m ²·s ^-1, 比大洋统计均值10 ^-5.0m ²·s ^-1高约1~2个量级, 与前人在吕宋海峡的观测结果相一致。湍流段和内波段的扩散率空间分布差异较大: 湍流段扩散率高值区对应强流区域, 推测这里是中尺度涡边缘, 其次中尺度不稳定过程引起扰动增强, 进而引起湍流混合的加强; 内波段扩散率高值区出现在吕宋岛弧附近, 推测是内波遇到岛弧地形发生破碎, 进而引起强的内波混合。     

Effect of boundary geometries on tidal currents and tidal mixing

The effects of the coastal boundary geometries on the tidal currents and the tidal mixing are studied mainly on the basis of hydraulic model experiments. Mizushima-Nada Sea, which is located in the central part of Seto Inland Sea, and the whole Seto Inland Sea were chosen as the prototypes.Currents and eddies geometrically induced in the tidal currents and in the ocean currents have significant effects on the water exchange, from small scales to meso scales, in the bays and near-shore regions of the ocean.As to small scale phenomena near irregular coastal boundaries such as river mouths, headlands and harbors, tidal currents produce organized eddy currents of the width scale. They are important to the temporary flushing and the local redistribution of the river water or the waste water.As to phenomena of larger scales, the tidal currents produce rather steady residual circulations in each part of the Inland Sea, due to the non-linear effects of the oscillating component. They are controlled by the geometry of the sea as separated by a narrow strait. These horizontal circulations of about 20 km in scale become the main mechanism of the water exchange in the Inland Sea. The one-dimensional dispersion coefficient due to these circulations is proportional to the product of the diameter and the current velocity of the circulations. The proportional constant takes the value of 0.40.5.     

FVCOM模型关键参数的处理及其在涌潮模拟中的应用

通过改进海床阻力系数和设置合适的垂向紊动背景系数,应用FVCOM模型成功再现了钱塘江河口强涌潮的演进过程。海床阻力系数采用Manning公式形式,取值随水深、地形在0.000 2~0.002 9之间变化;垂向紊动背景系数取1×10^-4 m²/s。模拟结果较好地复演了涌潮到达时刻、涌潮高度及涌潮抬升过程、涌潮水平流速以及其沿垂向分布规律,表明阻力系数及垂向紊动背景系数等关键参数的改进和处理是合理的,可应用于涌潮三维潮流运动特征模拟。     

Structure of tidal mixing at the Hayasui Straits

Based on the observation at the Hayasui Straits, actual conditions of the tidal mixing, of two water masses separated by the strait, are investigated for the time scale shorter than the the tidal period. Analyses show that the tidal mixing of water masses occurs by the disintegration of mutually penetrating small masses of water, which have been produced by the reciprocating tidal motion of the water masses with some topographical effect, especially at the slack water as large tongues. The mutual penetration occurs rather horizontally, and some of these turbulent smaller masses of water keep their own properties for a rather long period of the order of three hours, without mixing even in the violent shear flows. Initial horizontal scale of these turbulent masses is estimated as of the order of three kilometers. These actual conditions reveal themselves as the macroscopic diffusion coefficient.     

Similitude of the hydraulic model experiment for tidal mixing

The treatment of diffusion due to the tidal current in the near-shore ocean, and the similitude in the hydraulic model experiment are studied.In broad and shallow tidal bays and in the coastal seawaters near irregular boundaries, horizontal eddy-currents induced geometrically and turbulence caused by their cascading have predominant effect on dispersion of river and waste waters. These turbulent diffusion processes are similarly reproduced in the Froude models of turbulent resume, by adding the similitude for the self-similar structure of the spectral density of turbulence, or the eddy diffusivity. The similitude means to take the scale ratios of the time and the vertical length as the two-thirds power of the scale ratio of the horizontal length.Similitudes are also derived for the system of the gravitational circulation, the stratification and the salt-mass transport in partially and well-mixed estuaries. Generally, the vertical eddy diffusivity must be exaggerated by a half power of the model distortion externally by some methods of agitation. When the tidal bay is broad and very shallow, the Rayleigh number and the Hansen number are small, and the effect of density current and stratification on the flushing is small. Instead the effect of local eddies, geometrically induced tidal residual circulations become predominant. In this special case, there is no need to satisfy the similitude for density difference and vertical shear effects on dispersion.     

现场海域水平扩散系数的探讨

根据Taylor的扩散理论,按Hay和Pasquill的拉格朗日流与欧拉流自相关函数相似的假定,用实测的长序列欧拉流资料,计算了不同时间尺度的水平扩散系数。     

渤海、黄海、东海M2潮汐潮流的三维数值模拟

利用建立的一种新的半隐半显三维数值格式,将渤海、黄海、东海作为一个整体,采用球面坐标系下的三维潮波方程组,考虑了引潮力的作用,数值模拟了渤海、黄海、东海的M₂分潮的潮汐与潮流,结果较好地体现了渤海、黄海、东海M₂分潮的特征.通过比较65个验潮站的实测值与计算值,所得计算结果的振幅差平均为6.4cm,相角差为6.1°,计算与实测符合良好.本文给出的问潮图与Fang于1986年给出的实测占数值综合结果基本一致.对选取的47个测流站,比较了各层潮流调和常数Ucosζ、Usinζ、Vcosη、Vsinη的计算值与实测值的偏差,偏差绝对值的平均在2.6～4.9cm/s之间.并比较分析了潮流的垂直结构,所得结果与实测符合较好.首次揭示出回流点的水平位置不随深度变化这一特性.最后给出了M₂分潮的潮能消耗.     

辽东湾中部西岸浅水海域冬季实测海流分析

2015年12月在辽东湾中部西岸浅水海域进行了8个站、连续半个月的坐底ADCP海流剖面观测,通过对分层潮流和余流分析,得到该海域的海流特征如下:1)实测海流以潮流特征占主导,潮流特征为规则半日潮流,优势分潮为M2;M2椭圆长轴大小为25~50 cm/s、方向多为NE-SW向,具有显著的往复流特征。2)观测期间的平均余流为1~10 cm/s,方向多为SW向,平均余流在水平和垂向上的空间差异明显,日均余流波动剧烈;表层余流方向与局地风向具有很好的同步一致性,且距岸较近站位的表层余流受风影响更大;中、底层余流与风的相关性较差。本文得到的余流方向不支持冬季辽东湾北部的边界顺时针环流的存在。     

Estuary/ocean exchange and tidal mixing in a Gulf of Maine Estuary: A Lagrangian modeling study

A Lagrangian particle method embedded within a 2-D finite element code, is used to study the transport and ocean–estuary exchange processes in the well-mixed Great Bay Estuarine System in New Hampshire, USA. The 2-D finite element model, driven by residual, semi-diurnal and diurnal tidal constituents, includes the effects of wetting and drying of estuarine mud flats through the use of a porous medium transport module. The particle method includes tidal advection, plus a random walk model in the horizontal that simulates sub-grid scale turbulent transport processes. Our approach involves instantaneous, massive [O(500,000)] particle releases that enable the quantification of ocean–estuary and inter-bay exchanges in a Markovian framework. The effects of the release time, spring–neap cycle, riverine discharge and diffusion strength on the intra-estuary and estuary–ocean exchange are also investigated.The results show a rather dynamic interaction between the ocean and the estuary with a fraction of the exiting particles being caught up in the Gulf of Maine Coastal Current and swept away. Three somewhat different estimates of estuarine residence time are calculated to provide complementary views of estuary flushing. Maps of residence time versus release location uncover a strong spatial dependency of residence time within the estuary that has very important ramifications for local water quality. Simulations with and without the turbulent random walk show that the combined effect of advective shear and turbulent diffusion is very effective at spreading particles throughout the estuary relatively quickly, even at low (1 m²/s) diffusivity. The results presented here show that a first-order Markov Chain approach has applicability and a high potential for improving our understanding of the mixing processes in estuaries.     

Experimental determination of small-scale turbulence coefficients in the near-surface layer of the sea

The results of numerous experiments on the diffusion of fluorescent dyes are presented. To determine the turbulent diffusion coefficients, the technique involving under water photography of a jet with the subsequent processing of negatives by a microphotometer was used. The vertical coefficients were found to be slightly larger (by about 20%) than the horizontal ones, with the scale of the phenomenon being 0.3–1 m. Empiric relationships have been derived for the turbulent diffusion vertical coefficient on the parameters of surface waves.Translated by V. Puchkin.