Tidal Current Distribution Research Articles

Assessment of Tidal Current Energy Resources in the Pearl River Estuary Using a Numerical Method

In this paper, a numerical method is employed to assess tidal current energy resources in the Pearl River Estuary, China. The numerical model for tidal current simulation in the estuary is developed based on the MIKE 21 model, which enables numerical simulations in estuaries, coastal areas, and oceans. The model has a grid resolution that varies from about 2500 m at the open boundary to 500–1000 m inside the estuary. Extensive model validation is performed by comparing the model predictions with field observations of tidal level and velocity at various stations in the Pearl River Estuary. The tidal characteristics are thoroughly analyzed. Energy fluxes and power densities are calculated along selected cross sections to evaluate the feasibility of tidal energy development in the Pearl River Estuary. The results indicate that the distribution of annual average tidal current power density in the Pearl River Estuary generally aligns with the spatial distribution of tidal currents. The annual average power density of tidal energy is typically below 0.10 kW/m2. The theoretical potential of tidal current energy resources in the Pearl River Estuary is assessed to be approximately 11,000 kW.

Numerical modelling of a Macrotidal Bay over the last 9,000 years: An interdisciplinary methodology to understand the influence of sea-level variations on tidal currents in the Bay of Brest

Estuaries play a major role in the transfer of sediments from the continents to the shelves and deep ocean basins. Their position at the interface between land and sea promotes them as a key area for the understanding of ocean sediment supply, but yet long-term evolution remains poorly understood. The main reasons of the lack of knowledge about estuaries filling are the lack of hydrodynamic data in the past and the temporal application of numerical models. Oceanographers and geologists have developed numerical models to simulate currents and sedimentation. On one hand, hydro-sediment models allow a good physical representation of estuarine hydrodynamic processes and their impact on sedimentation, but only over time-scale spanning years to decades. On the other hand, stratigraphic diffusive models aim to study the impact of various geological processes on sedimentary basins over millions of years, but they are unable to describe in detail the tidal hydrodynamic processes that govern estuaries.In response to this timescale issue, this study presents a first step attempt to explore the evolution of tidal current distribution in relation with Holocene eustatic variations and seafloor evolution. Here we focus on a macro-tidal estuary, the bay of Brest, where tidal processes dominate, as the estuary is naturally protected from ocean swells. This paper aims to set up a methodology to simulate the (past) tidal currents over a long time period and correlate them with sedimentary data. Major changes in deposit dynamics are first identified from cores and seismic data, and the corresponding paleo-topographies and paleo-sea-levels are rebuilt. A process-based hydrodynamic model (MARS3D) is then used to test the impacts of these paleo-bathymetries on hydrodynamics over a 1-year time span. Four scenarii have been considered, representing four key stages of the Holocene transgression in the Bay of Brest.The simulated barotropic currents distributions were analysed and bottom currents impact on the seafloor compared with sedimentary records to understand past hydrodynamic context and associated sediment spatial distribution over geological time scale. Hydrodynamic simulations and sediments records are linked, in order to propose a reconstruction of the tidal influence on sediments over the last 9000 years. The results show changes of the tidal patterns related to the paleoenvironmental evolution (bathymetry and sea-level variations). Even if a hydro-sediment model would be needed to make a direct correlation between simulated currents and sediment records, this successful application in the Bay of Brest shows that discontinuous modelling can help to understand tidal current evolution and their impact on sediment distribution over long periods.

Heterogeneous Characteristics of Power Flow and Its Mathematical Representation Based on Gini Coefficient

The heterogeneous characteristics of the components of complex power grids in terms of operating conditions, grid structure, status, etc., will play a negative role in fuel grid cascading failures, thus posing a serious threat to grid security. This paper analyzes the heterogeneity of complex power grids in terms of tidal current operation, mainly as the trend distribution curve exhibits exponential and power-law characteristics in semi-logarithmic and double-log curves. Based on the Lorentz curve and the Gini coefficient concept in economics, it is proposed that the Gini coefficient can be used as a characterization index for the heterogeneity of tidal current distribution.

Tidal influences on a future evolution of the Filchner–Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

Abstract. Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner–Ronne Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the ice shelf and tides along the open boundaries. Our results show regionally dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed ice streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness (wct) and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded ice sheet as individual ice-stream grounding zones experience different responses to warming of the ocean inflow.

High-precision measurement of tidal current structures using coastal acoustic tomography

A high-precision coastal acoustic tomography (CAT) experiment for reconstructing the current variation in Dalian Bay (DLB) was successfully conducted by 11 coastal acoustic tomography systems during March 7–8, 2015. The horizontal distributions of tidal currents and residual currents were mapped well by the inverse method, which used reciprocal travel time data along 51 successful sound transmission rays. The semi-diurnal tide is dominant in DLB, with a maximum speed of 0.69 m s−1 at the eastern and southwestern parts near the bay mouth that gradually decreases toward the inner bay with an average velocity of 0.31 m s−1. The residual current enters the observational domain from the two flanks of the bay mouth and flows out in the inner bay. One anticyclone and one cyclone were noted inside DLB as was one cyclone at the bay mouth. The maximum residual current in the observational domain reached 0.11 m s−1, with a mean residual current of 0.03 m s−1. The upper 15-m depth-averaged inverse velocities were in excellent agreement with the moored Acoustic Doppler Current Profiler (ADCP) at the center of the bay, with a root–mean–square difference (RMSD) of 0.04 m s−1 for the eastward and northward components. The precision of the present tomography measurements was the highest thus far owing to the largest number of transmission rays ever recorded. Sensitivity experiments showed that the RMSD between CAT and moored-ADCP increased from 0.04 m s−1 to 0.08 m s−1 for both the eastward and northward velocities when reducing the number of transmission rays from 51 to 11. The observational accuracy was determined by the spatial resolution of acoustic ray in the CAT measurements. The cost-optimal scheme consisted of 29 transmission rays with a spatial resolution of acoustic ray of 2.03 km2/raynumbers. Moreover, a dynamic analysis of the residual currents showed that the horizontal pressure gradient of residual sea level and Coriolis force contribute 38.3% and 36.0%, respectively. This indicates that the two terms are the dominant factors of the residual currents in DLB.

Tidal stream characteristics on the coast of Cape Fuguei in northwestern Taiwan for a potential power generation site

Sites of high tidal current power potential are mostly found at narrow tidal passages or channels. Not many coastal sites with unbounded ocean with high tidal current speed have been reported. The coastal sea near the Cape Fuguei in northwestern Taiwan is such a site with a high tidal power potential. The purpose of this study is to investigate the tidal current speed at this location for assessing the tidal current power potential. In-situ and remote sensing instruments were deployed simultaneously to measure the temporal and spatial distributions of tidal currents. An Acoustic Doppler Current Profiler (ADCP) was deployed at a 26m depth site and an X-band marine radar was installed at a coastal building. Two measurements lasting over one month were done. Both instruments showed the maximum current speed at the surface was more than 3.5m/s in the measurement period. ADCP measurements showed that the time mean speed in the upper layer (−1.7 to −6m) was 1.5m/s. The current speed decreased with depth slightly. It was also found from both ADCP and radar measurements that in the surface layer, the probability of duration for current speed exceeding 1m/s was more than 70%. In addition, radar measurement showed that the average surface current speed at the area from 2km offshore out to 4km (radar offshore limit) was more than 1m/s. The size of this area is more than 15km2. Our investigations indicated that this area has a high tidal power potential for current turbine deployments.

Tidal and nontidal exchange at a subtropical inlet: Destin Inlet, Northwest Florida

A tidal-cycle study at Destin Inlet, Northwest Florida, investigated intratidal and residual flow structures for the first time across the inlet. Underway current velocity profiles were combined with hydrographic station profiles at neap tides to document the appearance of tidal fronts, the distribution of tidal currents across two cross-sections, and the residual, or non-tidal, flow structure at the same cross-sections. Intratidal variations of water density and velocity showed the presence of fronts both in 1) late ebb-early flood and 2) late flood-early ebb tidal stages. Late ebb-early flood tidal intrusion fronts brought about depth-independent changes in water density >10 kg/m3 in <2 h. Their counterparts, late flood-early ebb plume-like fronts, produced similar magnitude of variations in density but were depth-dependent. Diurnal tidal current distributions across the inlet followed a general behavior of a damped wave with strongest currents appearing near the surface and near the deepest part of the cross-sections (thalweg). However, curvature effects seemed to modify this behavior locally by shifting the maximum tidal current away from the thalweg. Frictional and curvature effects on the diurnal flows were confirmed by an analytical solution for tidal currents. The observed density gradients drove residual flows that were vertically sheared, with outflow at the surface and inflow near the bottom. Such residual flow distributions were reproduced by an analytical solution that diagnosed the flow structure as inherent of a dynamically narrow inlet with relatively weak frictional effects.

Study on the Interaction between Offshore Constructions and Marine Environment

The appearance of the offshore constructions will affect the hydrodynamic environment greatly. The direct effect is the change of hydrodynamic environment, which will affect the silt migration path and cause local scour. So a local refined calculation model of tidal distribution is developed in this paper to study the tidal current distribution and sediment scouring and deposition around the offshore constructions. Then an artificial island at Shengli Oil filed is taken for example. The developed model above is adopted to simulate the tidal distribution and local scouring change before and after the construction of the artificial island. The results of calculation show that excessive flow velocity appears near the construction, which cause sever local scour. And the calculation results can also provide technical support for the safety evaluation of the offshore constructions.

Analysis for TCSC Steady-State Characteristics

When the TCSC steady-state operation, the thyristor turn-on and turn-off time is definite, the changing for TCSC electric capacity voltage and thyristor electric current is with the periodicity and symmetry.Thyristor controlled series compensation technology is fixed series compensation technology foundation, which is meet the needs for adaptation electrical power system operation control developing. With changes the triggering angle for thyristor suitably, then can realize the TCSC equivalent reactance fast, continuously and adjusts smoothly, provides the controllable series compensation for the system, as to achieve increases the system transmitting capacity, enhance the transition condition stability, the damping power oscillation, and the purpose for improvement system tidal current distribution. Although in the entire time axis, obtains the analytic expression for TCSC running status variable is difficulty, but as long as had determined the analytic expression for various electrical quantity in a power frequency cycle, according to the stable state movement's symmetry and periodicity, we can determine the steady state profile that in the entire time axis, and then analyses the TCSC electric circuit’s steady-state characteristic with the time domain computation method. In this paper, topological analysis for TCSC operation established by formula, and then carries on the time domain partition to the TCSC electric circuit solution, finally obtains the steady state fundamental frequency impedance model for TCSC. This paper steady-state characteristic analysis is mainly carries on the topological analysis method to the TCSC main circuit, then establishes the stable state base frequency impedance model for TCSC, and analyses the resonance question for TCSC simultaneously. Then studies TCSC the steady- state characteristic, and with modeling and simulation on them to do further research and analysis, and utilizes the solution method for transformation territory, namely applies the Laplace transform solution equation of state. Thus can be obtained the zero-input response and zero status response formula for system.

A new high‐resolution unstructured grid finite volume Arctic Ocean model (AO‐FVCOM): An application for tidal studies

A spherical coordinate version of the unstructured grid 3‐D FVCOM (finite volume coastal ocean model) has been applied to the Arctic Ocean to simulate tides with a horizontal resolution ranging from 1 km in the near‐coastal areas to 15 km in the deep ocean. By accurately resolving the irregular coastlines and bathymetry in the Arctic Ocean coastal regions, this model reproduces the diurnal (K1 and O1) and semidiurnal (M2 and S2) tidal wave dynamics and captures the complex tidal structure along the coast, particularly in the narrow straits of the Canadian Archipelago. The simulated tidal parameters (harmonic constituents of sea surface elevation and currents) agree well with the available observational data. High‐resolution meshes over the continental shelf and slope capture the detailed spatial structure of topographic trapped shelf waves, which are quite energetic along the Greenland, Siberia, and Spitsbergen continental slope and shelf break areas. Water stratification influences the vertical distribution of tidal currents but not the water transport and thus tidal elevation. The comparison with previous finite difference models suggests that horizontal resolution and geometric fitting are two prerequisites to simulate realistically the tidal energy flux in the Arctic Ocean, particularly in the Canadian Archipelago.

Observations of sediment resuspension and settling off the mouth of Jiaozhou Bay, Yellow Sea

We deployed bottom-mounted quadrapod equipped with acoustic Doppler current profiler (ADCP), acoustic Doppler velocimeter (ADV), and optical backscatter sensor (OBS) over two semidiurnal tidal cycles along the western coast of the Yellow Sea, China. In combination with shipboard profiling of CTD and LISST-100, we resolved the temporal and spatial distributions of tidal currents, turbulent kinetic energy (TKE), suspended sediment concentration (SSC) and particle size distributions. During the observations, tidal-induced bottom shear stress was the main stirring factor. However, weak tidal flow during the ebb phase was accompanied by two large SSC and median size events. The interactions of seiche-induced oscillations with weak ebb flow induced multiple flow reversals and provided a source of turbulence production, which stripped up the benthic fluff layers (only several millimeters) around the Jiaozhou Bay mouth. Several different methods for inferring mean suspended sediment settling velocity agreed well under peak currents, including estimates using LISST-based Stokes’ settling law, and ADCP-based Rouse profiles, ADV-based inertial-dissipation balance and Reynolds flux. Suspended particles in the study site can be roughly classified into two types according to settling behavior: a smaller, denser class consistent with silt and clay and a larger, less dense class consistent with loosely aggregated flocs. In the present work, we prove that acoustic approaches are robust in simultaneously and non-intrusively estimating hydrodynamics, SSC and settling velocities, which is especially applicable for studying sediment dynamics in tidal environments with moderate concentration levels.

Analysis of the Characteristics of Tidal Current at Kurushima Strait-Field Observations and Numerical Simulation of 3D-Flow

This study presents the results of analysis of the field observations and the numerical simulation of tidal currents in the Kurushima Strait. The field data measured tidal currents at the two points near the Strait for fifteen days and measured vertical distributions of tidal currents in the west channel of the Strait for 10 hours in one day. The numerical simulation is performed by a multi-level model of tide and tidal currents as horizontal eddy viscosity terms, described with the Smagorinsky's formulas, are incorporated. The specific peculiarities of the complex coastal line and bottom topography of the Strait are taken into account in the model. The tidal current fields are reproduced by the model. Several components of tidal currents and the location of streaks, generated in the Strait, can be predicted by the numerical simulation.

Application of eddy viscosity closure models for the M 2 tide and tidal currents in the Yellow Sea and the East China Sea

A three-dimensional mode-splitting, σ-coordinate barotropic finite-difference model, with subgrid scale diffusion represented using a range of eddy viscosity closure models, is used to examine M 2 tidal elevation and currents in the Yellow Sea and the East China Sea. Four eddy viscosity formulations are considered: q 2- q 2 l turbulence energy model (Blumberg and Mellor, 1987), Prandtl mixing length model, Davies and Furnes’ (1980) simple flow-related model with mixing length which includes the bottom boundary layer thickness, and a time and space invariant eddy viscosity with 650 cm 2/s. The bottom friction at the sea bed is given in a quadratic form using a constant bottom friction coefficient, c f and near-bottom velocities. A series of M 2 tide model runs were carried out and optimal values of c f were determined through the comparison with tidal elevation amplitudes and phases at 203 stations. From these comparisons it is shown that the M 2 tidal charts computed with a range of eddy viscosity formulations are in good agreement with each other when optimal values of c f are chosen; comparing with M 2 tidal current amplitudes and phases at 15 stations, it is shown that tidal current distributions and its profiles are in reasonably good agreement with winter-time observations in the central part of the Yellow Sea; relatively poor results are obtained near the Chinese coast where non-tidal effects such as abrupt changes in tidal current phase in the vertical due to large freshwater discharge are pronounced. It is noted that the bottom friction coefficient has a major influence on tidal elevation and tidal currents and optimal values of bottom friction coefficient are closely related to the near-bottom eddy viscosity. The considered eddy viscosity closure models appear to work well for tidal problem when the bottom friction parameter is optimized. Results indicate that for a barotropic tide the Prandtl mixing length model which can account of the boundary layer thickness could be an useful alternative to a highly complex q 2- q 2 l model.

The influence of wind and wind wave turbulence upon tidal currents: Taylor's problem in three dimensions with wind forcing

A three-dimensional model of the North Sea, represented by a rectangular basin of constant depth, or shallowing in the south, open at its northern end, is used to examine the influence of enhanced turbulence and bottom friction due to wind induced currents and wind waves upon the position of M 2 tidal amphidromes and tidal current distributions over the North Sea. Calculations show that enhanced levels of turbulence associated with the wind and with the wind induced currents significantly influence the profile of the M 2 tidal current, and also affect the higher tidal harmonics. Enhanced bed friction associated with increased turbulence due to wind waves can have a significant effect upon the currents, particularly in shallow water. The influence of a time varying eddy viscosity, depending upon the magnitude of the current in coupling tidal and wind induced currents, and producing higher tidal harmonics, is examined using a single point model in the vertical. By using this combination of a three-dimensional model and a single point model in the vertical, the mechanisms affect the coupling of wind and tidal currents can be understood.

The influence of bottom and internal friction upon tidal currents: Taylor's problem in three dimensions

Idealised calculations using a three-dimensional model of the North Sea, represented by a flat bottom rectangular basin, open at its northern end, are used to examine the influence of bottom topography, internal friction (parameterised using an eddy viscosity formulation) and bottom friction upon the position of M 2 tidal amphidromes and tidal current distributions over the North Sea. Calculations show that the bottom slope of the North Sea, from deep in the north to shallow in the south, together with the coefficient of bottom friction, influence the position of the tidal amphidromes. In a three-dimensional model, it is not just bottom friction which influences the position of tidal amphidromes, but also the magnitude of eddy viscosity. In the case of a no-slip condition applied at the sea bed, the magnitude of near-bed viscosity has a major influence upon the position of tidal amphidromes, and tidal current profiles. In a non-linear model in which bed stress and eddy viscosity magnitude depend upon the total tidal current, calculations show that enhanced levels of turbulence due to the M 2 tide have a significant influence upon other tidal constituents (e.g. the S 2 tide). By using a combination of a single point model in the vertical, based upon a rotary decomposition of the tide, and the full three-dimensional model of the basin, significant insight into the parameters (e.g. water depth, bottom friction, internal friction and tidal frequency) influencing the spatial distribution of tidal ellipses, and the profile of tidal currents is obtained.

Is the activity of benthic suspension feeders a factor controlling water quality in the Bay of Brest?

In the Bay of Brest, France, suspension feeders are broadly dominant in the trophic structure of macrobenthic assemblages in terms of species number, number of individuals and biomass. A succession of species exists on an east-west gradient, which is an ecological continuum from a 20 m depth marine environment with coarse and clean sedirnents. The abundance of biogenic substrates (shells, calcareous algae, etc.) on the sediment surface favours a high development of sessile epifauna. Some species, such as Crepicula fornicata, Ascidiella aspersa, Ficulina ficus, Ophiothrix fragilis and Ophiocomina nigra, can locally proliferate, reaching 100 g ODW (organic dry wt) m-2. Fertilization of the bay by streams loaded with nutrients induces a very high primary production (280 g C m-' yr-l) characterized by high annual and seasonal variability of phytoplanktonic blooms. However, so far, eutrophication has not been observed. While water renewal by tidal currents is one important factor in the control of eutrophication, suspension feeder activity is undoubtedly another effective control factor. Benthic suspension feeders can filter 7.18 X 10' m3 daily, which represents ca 30% of the total volume of the bay. The phytoplankton production is easily accessible to the benthos because of the relatively long water residence time and the high tidal current mixing. Spatial distribution of populations was found to be related to the tidal current distribution.

On the vertical structure of tidal currents in a homogeneous sea

The vertical variation of tidal currents caused by friction at the sea-bed is investigated in both qualitative and quantitative ways with the Coriolis force being taken into account. The simple model with the assumption of constant eddy viscosity is employed to study the effects of friction on the vertical structure of tidal currents. The model explains these effects in vertical change of the maximum velocity, the ellipticity (the ratio of the minor to the major axis) of current ellipse, the time and the direction of the maximum velocity, and the ratio of diurnal current to semidiurnal current. To reach a quantitative agreement with the data observed by Bowden & Fairbairn in the Irish Sea, the mixing length theory is applied to numerical calculation of the vertical distribution of tidal currents with a finite difference scheme. A fair agreement with the observations is obtained in the calculation. The results show the following features: (1) the vertical profile of amplitude of the main component for the current is almost logarithmic throughout the depth; (2) the corresponding profde for the shearing stress is almost linear with depth; (3) the maximum stress lags the maximum velocity with the delay increasing with elevation; (4) the eddy viscosity coefficient has its maximum around the mid-depth; and (5) the vertically averaged viscosity lags the velocity magnitude. The dependence of the quadratic resistance coefficient and the coefficient k defined by Bowden's formulav̄=κhū(h— depth, v̄ and ū— depth-averaged eddy viscosity and velocity) on the roughness length is given for a steady flow in a non-rotating system. The numerical solution shows that these relations can be approximately applied to the tidal currents in shallow waters.

A mixing‐length theory of tidal flushing

The salinity distribution in an idealized estuary where mining is predominantly due to the tides is computed, using an eddy diffusivity based on the distribution of tidal currents and excursions. Comparison is made to the salinity distribution in real estuaries.