Numerical Simulation of the Three-Dimensional Wave-Induced Currents on Unstructured Grid

By coupling the three-dimensional hydrodynamic model with the wave model, numerical simulations of the three-dimensional wave-induced current are carried out in this study. The wave model is based on the numerical solution of the modified wave action equation and eikonal equation, which can describe the wave refraction and diffraction. The hydrodynamic model is driven by the wave-induced radiation stresses and affected by the wave turbulence. The numerical implementation of the module has used the finite-volume schemes on unstructured grid, which provides great flexibility for modeling the waves and currents in the complex actual nearshore, and ensures the conservation of energy propagation. The applicability of the proposed model is evaluated in calculating the cases of wave set-up, longshore currents, undertow on a sloping beach, rip currents and meandering longshore currents on a tri-cuspate beach. The results indicate that it is necessary to introduce the depth-dependent radiation stresses into the numerical simulation of wave-induced currents, and comparisons show that the present model makes better prediction on the wave procedure as well as both horizontal and vertical structures in the wave-induced current field.     

磨刀门河口枯季波生流场数值模拟研究

本文建立曲线坐标系下的双曲型缓坡方程波浪模型和考虑波浪辐射应力影响的深度平均2D潮流数学模型,首次研究了磨刀门河口2011年地形条件下的枯季波生流场。受波浪作用影响,落潮阶段,波浪作用方向与流向相反,在波浪顶托效应下拦门沙沙脊及外坡处流速普遍减小,形成两个主要回流区,口门外东西两侧浅滩处流速也减小,东西两汊及横洲深槽流速增大;涨潮阶段,波浪作用方向与流向相同,拦门沙沙脊及外坡处流速增大,沙脊处出现冲越流,口门两侧浅滩处流速增大,横洲深槽流速减小。     

Modelling of the barotropic processes in the Bohai Sea

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Quasi-three-dimensional modelling of the morphology of longshore bars

A morphological quasi-three-dimensional (Q3D) area model for barred coasts has been developed. The model combines a two-dimensional depth integrated model for wave-driven currents with a model for undertow circulation currents. The combined model makes a simultaneous simulation of the bar-forming processes associated with the undertow and the horizontal wave-driven circulation currents, which may cause instabilities of the bar and the formation of rip channels. Situations with normal and oblique wave incidence are considered. Compared to the depth integrated approach the Q3D model produces less pronounced alongshore irregularities for obliquely incident waves. For normal incident waves the Q3D model produces a crescentic bar while the depth integrated model predicts almost straight sections of the bar interrupted by rip channels. The sensitivity to variation of wave angle and beach slope is further investigated.     

Coupled modeling of currents and wind waves in the Kerch Strait

We present a numerical model of the dynamics of the Kerch Strait allowing one to perform the coordinated analysis of the fields of currents and wind waves. The model includes the spectral wave module and the hydrodynamic block of currents. The influence of waves on the currents is taken into account in the hydrodynamic block both via the surface and bottom tangential stresses and via the radiation stresses. In order to take into account the inverse influence of currents upon the waves, we use the fields of currents and sea level from the hydrodynamic block in the wave module. The specific features of the structure of currents and wind waves in the strait are studied for the typical wave situations. The results of the coupled and separate simulation are compared and the importance of taking into account the mechanisms of interaction between waves and currents in the analysis of the dynamic processes in the strait is demonstrated. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 3–20, September–October, 2007.     

An extended variable-grid global ocean circulation model and its preliminary results of the equatorial Pacific circulation

1IntroductionThetropicalPacificOceanplaysanimpor-tantroleintheclimatevariabilitiessuchasElNi-no-SouthernOscillation(ENSO)phenomenon(Chao,1993).ManystudieshavefoundthatthetropicalPacificvariabilitiescanhavesignifi-cantinfluenceontheoceancirculationintheseasadjacenttoChina(Yu,1985;Chaoetal.,1996;Wangetal.,2002).TheseaareaadjacenttoChinaischaracterizedbyitscomplextopog-raphyandnumerousnarrowstraits,andthusre-quiresafinegridtoresolve.Tostudytheinter-actionbetweenthetropicalPacificandChinas…     

广东省14个海滩裂流类型及统计特征分析

裂流是沿海地区频发的一种高速离岸流。根据Castelle的裂流分类模型对广东省14个海滩的Google Earth影像进行了解译分类,对裂流分类模型在遥感影像中的应用进行了探讨。结果表明:在高风险月份,海滩裂流的组成较为单一,混合型裂流少,水深控制的裂流占据主导地位,裂流数量总体维持在较高水平;在中风险月份,水动力控制的裂流和混合型裂流的比例增加,水深控制的裂流仍然占有一定比例;在低风险月份,裂流很少出现,甚至无裂流发生。裂流的类型与海滩的状态密切相关。对于海湾中的海滩,海湾长度影响裂流的数量,海湾凹入度影响不同类型裂流的组成比例。考虑到实验条件的限制,这一规律需要后续结合实际地形地貌进行更细致和深入的研究和验证。按照本文解译标准得出的分类结果,与前人提出的裂流风险性评价模型吻合度较高,进一步说明了该解译标准的有效性,为今后对海滩裂流的研究和分类工作提供了一定的参考。     

Investigation of the influence of cyclonic disturbances on the dynamic processes and the evolution of impurities in the Sea of Azov in the presence of stationary currents

A three-dimensional nonlinear mathematical model is used to study the dynamic processes under the action of cyclonic disturbances in the field of stationary wind in the Sea of Azov and the specific features of transformation of the impurities. The results of numerical calculations enable us to conclude that the maximum velocities of currents generated by a cyclone depend on the direction of its motion. It is shown that the cyclones moving westward generate currents with higher maximum velocities than the cyclones of other directions. It is also demonstrated that the motion of atmospheric disturbances leads to a significant enlargement of the area of propagation of pollutants as compared with the case of action solely of stationary currents. The influence of the velocities of stationary currents on the maximum current velocities caused by the passage of a cyclone is also analyzed.     

Estimates of winter currents on the Israeli continental shelf

A simplified analytical model for continental shelf wind-driven currents is adopted. The calculated results compare favorably with extensive field measurements from two separate sources. The model is used to hindcast the current climatology on the Israeli continental shelf. The maximum northward/southward alongshore currents at 10-m water depth, with a return period of 100 years, are found to be 1.28 and 0.53 m/s, respectively.     

Diurnal wind and nonlinear interaction between inertial and tidal currents in the South China Sea during the passage of Typhoon Conson

Diurnal wind （DW） and nonlinear interaction between inertial and tidal currents near the Xisha Islands of the South China Sea （SCS） during the passage of Typhoon Conson （2010） are investigated using observational data and a damped slab model. It is found that the DWs, which are dominated by clockwise wind components, are prominent at our observational site. The DWs increase after the passage of the typhoon from 1 to about 4 m/s, which may be due to the decrease of the sea surface temperature caused by the passage of the typhoon. Kinetic energy spectra and bicoherence methods reveal nonlinear interactions between the inertial currents and the 2MK3 tidal constituent at our observational site. The slab damped model reproduces the inertial currents successfully induced by the total observed winds, and it is shown that the inertial currents induced by DWs are positively proportional to the DWs speed. Even though the observed inertial currents are distinct, the proportion of inertial currents induced by DWs to those induced by the total observed winds is just 0.7%/4% before/after the passage of typhoon. This shows that the inertial currents induced by the DWs are unimportant near the Xisha Islands during the typhoon season.     

基于间断有限元方法的三维近岸波生流数值模型建立

在三维水动力模型中引入三维辐射应力,水滚影响以及波浪附加紊动效应,并基于间断有限元方法建立了非结构化网格三维波生流数值模型。采用实验室内斜坡地形条件下正向入射波在破波带附近产生的近底回流和斜向入射波产生的沿岸流对模型进行了验证。结果表明,计算值与实测值吻合程度较好,该模型可以较好地描述三维近岸波生流。     

Numerical study of the storm-induced circulation on the Scotian Shelf during Hurricane Juan using a nested-grid ocean model

A nested-grid ocean circulation modelling system is used to assess the upper ocean response of the Scotian Shelf and adjacent slope to Hurricane Juan in September 2003. The nested-grid system consists of a fine-grid inner model covering the Scotian Shelf/slope and a coarse-grid outer model covering the northwest Atlantic Ocean. The model-calculated upper ocean response to Hurricane Juan is characterized by large divergent surface currents forced by the local wind forcing under the storm, and intense near-inertial currents in the wake of the storm. The sea surface temperature (SST) cooling produced by the model is biased to the right of the storm track and agrees well with a satellite-derived analysis. Over the deep water, off the Scotian Shelf, some of the near-inertial energy input by the storm is advected eastward by the Gulf Stream away from the storm track. The hurricane also generates shelf waves that propagate equatorward with the coastline on their right. In comparison with the outer model results, the inner model captures more meso-scale structures, greater SST cooling and stronger near-inertial currents in the study region.     

Bashi channel,Luzon strait: A hydraulic model experiment of the tidal current

Bottom current conditions due to tidal currents in the area of the Bashi Channel, Luzon Strait, are examined using a scaled hydraulic model in a uni-directional flow channel. The geometrical model is scaled in both the similitude of Froude's Number and the similitude of the four-thirds power law of eddy viscosity. The currents obtained from the experiment seem to be consistent in order of magnitude with the estimated currents based on observations made by Offshore Environmental System Ltd. In a quasi-steady tidal phase, formation of a strong core flow is found in the Bashi Channel. It can be explained by a simple theoretical model in which the formation of the strong current is attributed to the submarine topography of the Luzon Strait.     

Numerical Study of Influence of Currents on Nonlinear Focusing Waves

In this paper,a numerical model for nonlinear wave propagation in currents is formulated by a set of enhanced fully nonlinear Boussinesq equations with ambient currents.This model is verified by comparison with the published results.Then the influence of currents on nonlinear focusing waves is studied by use of the numerical model.It is found that the effect of currents on the surface elevations at the focal location is negligible.Following currents can augment the maximum crest of focusing wave while decre...     

A numerical experiment on the variations of western boundary currents: Part I. Formation of western boundary currents

A numerical experiment is made using a barotropic model for the western boundary currents. The time-dependent, non-linear vorticity equation is integrated with and without the variable of bottom topography. The inertial and frictional boundary flow is resolved with a fine grid size of 10 km. Connection of the western boundary currents with the general circulation is facilitated by giving the fixed Sverdrup transport at the eastern boundary of the model (400 km offshore).For the flat bottom topography, steady flow forRe=35 shows dynamical balance essentially of a frictional model. The transient response leading to the formation of the western boundary currents in the model seems to support theLighthill's theory (1969). ForRe=350, unsteady features revealed byBryan (1963) is re-established. A phenomenon of barotropic instability is also observed with sufficient resolution. For the model with a continental slope the steady flow is also obtained forRe=35. The boundary currents flow over the continental slope, deviating offshore as they flow northward.     

A swell model of the German Bight

A numerical model is presented, which investigates the contribution of wave-induced currents to the tidal residual circulation in the German Bight. The momentum transfer, by swell decaying to the mean circulation, is calculated including wave-current interaction without refraction. The model couples deep-water and shallow-water energy dissipation mechanisms such as wave attenuation and wave breaking. The model computes wave set-up, wave set-down and a longshore current as well. The pure wave-induced circulation is calculated, and also the residual circulation due to the interaction between waves and tide. The results suggest that the wave-induced currents can be neglected for the calculation of transport of near-surface pollutants.     

Lagrangian Transport by Currents Variable in Time in the Model of Wind-Induced Circulation of the Black Sea

We construct a simple model of seasonal variability of circulation in the Black Sea, which satisfactorily explains the data of altimetric satellite observations. The model is used to describe the nonstationary wind-induced currents in a round basin and study the trajectories of water particles in the surface layer of the sea. It is shown that, for nonstationary currents, these trajectories can be quite complicated. It is also assumed that Lagrangian mixing can be caused by the complex trajectories of water particles.     

潮汐和风对马六甲海峡海流的影响

基于非结构有限体积法海洋模型FVCOM(Finite-Volume Community Ocean Model), 建立了马六甲海峡及其毗邻海域高分辨率水动力数值模型, 研究了风和潮流作用下的余环流结构以及水体输运特征。结果表明, 马六甲海峡航道中央潮流运动以往复流为主, 边缘存在旋转流; 主要研究区域内落潮流速略大于涨潮流速, 东南窄道处流速最大; 因峡道束窄变浅, 在涨落潮过程中潮流发生汇聚与分离; 主要研究区域东南段存在3个显著的潮致余环流; 东北季风驱动时模型响应为海峡海流整体向西北方向流动, 西南季风时反之; 季风期间潮致表层余环流结构被破坏, 但底层余流仍存在水平环流结构, 且随着风速增加, 底层余环流的数目、大小、形状、位置均会产生变化; 季风过渡期余环流结构也会发生部分改变, 尤其是小潮期间风场影响效果显著。     

Application of Two Turbulence Closure Schemes in the Modelling of Tidal Currents and Salinity in the Hooghly Estuary

This paper has two purposes. The first is to study the circulation and salinity in Hooghly Estuary, along the east coast of India and the second is to compare the performance of two turbulence closure schemes by modelling it. A breadth averaged numerical model using a sigma co-ordinate system in the vertical is briefly described. Vertical diffusion of momentum and salt are parameterized by a simple first-order turbulent closure or by a one equation model for turbulent kinetic energy (TKE) which uses a specified mixing length. The results are compared with the available neap and spring tide observations along the estuary for both low and high discharge periods.The computed elevations and currents are in reasonable agreement with the observations showing no major differences in vertical current profiles by both the turbulent schemes. However, there is a slight under-prediction of bottom currents. The salinity profiles predicted by TKE model show better matching with observations. Statistical tests are also conducted to study the comparative performance of the turbulent closure schemes. The maintenance of two layer structure in residual currents and salt variability are also studied by using the model.     

Sources of water in the Taiwan Strait

The conveyor of the source water that feeds into the Taiwan Strait (TS), particularly from the south, is investigated using historical CTD (Conductivity-Temperature-Depth) data and a North Pacific Ocean and East Asian seas coupled model. The modeled currents and drifter trajectories suggest that the Kuroshio Branch Water (KBW) rarely flows directly into the TS from the Luzon Strait (LS) in winter; instead the massive westward movement of the Kuroshio conveys high salinity water to the southeastern TS through a loop-like route. In summer, the modeled flow fields suggest that the Kuroshio surface currents hardly intrude into the TS directly from the LS. Observations and model results show that the monsoon-driven northeastwardflowing currents in the northern South China Sea transport relatively low salinity water through the entire TS.