渤、黄、东海潮汐、潮流的数值模拟与研究

基于FVCOM海洋数值模式,采用高分辨率的三角形网格,对渤、黄、东海的潮汐、潮流进行数值模拟,并通过比较120个沿岸验潮站和14个潮流观测站的实测与模拟结果进行模型验证,两者符合较好。根据模拟结果,给出了四个主要分潮的潮汐同潮图和5m层潮流最大流速及最大潮流同潮时分布。渤、黄、东海共有5个半日分潮和3个全日分潮的独立旋转潮波系统,且都呈逆时针方向旋转;半日潮流和全日潮流各有12个圆流点;在冲绳岛和奄美岛两侧的4个半日潮流圆流点分别呈对称分布,其中有3个为本文首次给出;在日本九州岛西侧还新给出2个全日潮流圆流点。有关它们的存在性需要实测资料的进一步检验。     

长江口外潮汐精细化模型研究与精度分析

长江口外海上测量除受风浪影响较大外,最重要的问题是潮位控制非常困难。文中简要阐述了开展长江口外潮汐精细化模型研究的方法,介绍了利用潮汐精细化模型对长江口外航路任意点进行潮汐预报的方法,并通过实测数据进行了精度分析,提出了建议。     

The effects of blade twist and nacelle shape on the performance of horizontal axis tidal current turbines

The paper presents the effects of blade twist and nacelle shape on the performance of horizontal axis tidal current turbines using both analytical and numerical methods. Firstly, in the hydrodynamic design procedure, the optimal profiles of untwisted and twisted blades and their predicted theoretical turbine performance are obtained using the genetic algorithm method. Although both blade profiles produce desired rated rotational speed, the twisted blade achieves higher power and thrust performance. Secondly, numerical simulation is performed using sliding mesh technique to mimic rotating turbine in ANSYS FLUENT to validate the analytical results. The Reynolds-Averaged Navier-Stokes (RANS) approximation of the turbulence parameters is applied to obtain the flow field around the turbine. It is found that power and axial thrust force from BEMT (Blade Element Momentum Theory) method are under-predicted by 2% and 8% respectively, compared with numerical results. Afterwards, the downstream wake field of the turbine is investigated with two different nacelle shapes. It is found that the rotor performance is not significantly affected by the different nacelle shapes. However, the structural turbulence caused by the conventional nacelle is stronger than that by the NACA-profiled shape, and the former can cause detrimental effect on the performance of the downstream turbines in tidal farms.     

A novel time-series station in the Wadden Sea (NW Germany): First results on continuous nutrient and methane measurements

In autumn 2002 a time-series station was installed in the tidal inlet between the Islands of Langeoog and Spiekeroog (Southern North Sea, NW Germany) to continuously measure physical, chemical, and meteorological parameters, even during extreme weather conditions (gale-force storms, drifting ice). Inside the pole of the station sensor tubes are installed in direction of the prevailing tidal currents. The tubes are equipped with hydrographic sensors (pressure, temperature, conductivity) and allow retrieval of water for nutrient analysis by automated instruments located inside the pole. Dissolved methane and the nutrients ammonia, nitrite, nitrate, phosphate, and silicate are measured at the station.     

The impact of the M2 internal tide on data-assimilative model estimates of the surface tide

We use a synthetic data experiment to assess the accuracy of ocean tides estimated from satellite altimetry data, with emphasis on the impact of the phase-locked internal tide, which has a surface expression of several centimeters near its sites of genesis. Previous tidal estimates have regarded this signal as a random measurement error; however, it is deterministic and not scale-separated from the barotropic (surface) tide around complex bathymetric features. The synthetic data experiments show that the internal tide has a negligible impact on the barotropic tidal fields inferred under these circumstances, and the barotropic dissipation (a quadratic functional of the tidal fields) is in good agreement with the energetics of the three-dimensional regional primitive equations model which is the source of the synthetic data.     

Semidiurnal Dynamics of Salinity, Nutrients and Suspended Particulate Matter in an Estuary in the Seto Inland Sea, Japan, during a Spring Tide Cycle

The physical and chemical variability of the water column at subtidal station of an estuary in the Seto Inland Sea, Japan, was studied over a 24-hour period during a spring tide (tidal range ca. 2 m) in May 1995. Surface water and several depths through the water column were monitored every one and two hours, respectively. At each occasion, water temperature, salinity and dissolved oxygen concentration were measured and water samples were collected for the determination of nutrients and suspended particulate matter (SPM). Disruptive changes in the physical and chemical characteristics of the water was produced by the tidal cycle and the mixing of water masses of different origin. These changes were highly significant both spatially and temporally, yet with varying effects on physical parameters, nutrients and the different components of SPM. Significant differences in nutrient concentrations were also observed when the data-set was divided into ebb and flood components, irrespective of the depth. Nitrate and nitrite rose to 1.8 times higher during the flood. Spatial differences of SPM were less marked than those of nutrients, only particulate organic carbon (POC) being significantly higher at the surface than in the intermediate and the lower layer. Both POC and pheopigment concentrations increased markedly through the water column, being highest shortly before the lower low tide. In contrast, suspended solid (SS) content increased sharply after the lower low tide (>40 mg l⁻¹) and this coincided with a marked decrease of the C/SS content (<20 mg g⁻¹). The lagtime between POC and SS tidal transport was caused by particle resuspension from the exposed intertidal sediments as the tidal level rose, and particle transport selection in relation to the tidal state. This revised version was published online in August 2006 with corrections to the Cover Date.     

The intertidal erosion rate of cohesive sediment: a case study from Long Island Sound

Over the past decades, many attempts have been made to generate useful bottom erosion models for the study of cohesive sediment movement. This study addresses some of the key questions involved in determining the functional relationship between erosion rate and bottom shear stress. Current, wave, and turbidity data were collected from a bottom mounted instrument array in a moderately energetic estuarine environment. The bottom shear stress was calculated from a wave–current interaction model. The erosion rate was derived from the observed sediment concentration using a vertical mixing model. Examination of the relationship between erosion rate and bottom stress showed that the erosion rate varied at intertidal frequency. When averaged over the tidal fluctuation, the erosion rate remained approximately constant at low stress, but increased sharply when the shear stress rose above a critical value. This suggests two-stage erosion. The bed has a layered structure, in which a thin layer of loose, high water content material overlies a more consolidated bed. The top layer of high water content material (fluff) was easily disturbed and re-suspended by tidal currents, but the consolidated bottom layer was eroded only under conditions of high shear stress.     

风暴潮灾与月相

本文以实测资料为依据,统计分析了风暴潮灾、风暴潮、登陆台风、天文高潮等与月相的关系。统计资料表明,登陆台风和台风风暴潮发生在大(小)潮期的次数相对较多,略大于平均数,但它们与月相没有明显的因果关系,它们相对于月相的分布大致上是随机的,如果台风在天文大潮期间登陆,台风引起的暴潮与天文潮叠加后成灾的概率明显增大,但也不一定成灾;成了灾的,往往是风暴潮峰值适逢当日的天文高潮所致。     

Numerical modeling of long waves in shallow water using Incremental Differential Quadrature Method

Incremental Differential Quadrature Method (IDQM) as a rapid and accurate method for numerical simulation of Nonlinear Shallow Water (NLSW) waves is employed. To the best of authors’ knowledge, this is the first endeavor to exploit DQM in coastal hydraulics. The one-dimensional NLSW equations and related boundary conditions are discretized in space and temporal directions by DQM rules and the resulting system of equations are used to compute the state variables in the entire computational domain. It was found that the splitting of total simulation time into a number of smaller time increments, could significantly enhance the performance of the proposed method. Furthermore, results of this study show two main advantages for IDQM compared with other conventional methods, namely; unconditional stability and minimal computational effort. Indeed, using IDQM, one can use a few grid points (in spatial or time direction) without imposing any stability condition on the time step to obtain an accurate convergent solution.     

Impact of mega-scale sand extraction on tidal dynamics in semi-enclosed basins: An idealized model study with application to the Southern North Sea

Long-term considerations of repeated and increasing sand extraction on the Netherlands Continental Shelf (North Sea) may lead to the creation of a mega-scale extraction trench in front of the Dutch coast (length hundreds of km, width over 10 km, depth several m). We investigate the impact of such a huge topographic intervention on tidal dynamics, which is a key aspect in hydrodynamics, and indirectly also affecting morphodynamics and ecology.