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Ocean currents represent an alternative source of clean energy given their inherent reliability, persistence and sustainability. The general ocean circulation is characterized by large rotating ocean gyres resulting in rapid ocean currents along the western boundaries because of the Coriolis Effect. The Gulf Stream system is formed by the western boundary current of the North Atlantic Ocean flowing along the east coast of the United States, and is of particular interest as a potential energy resource for the United States. This study presents a national database of ocean current kinetic energy resource derived from seven years of numerical model simulations to help advance awareness and market penetration for ocean current energy. A web based GIS interface is provided for dissemination of the national energy resource data: http://www.oceancurrentpower.gatech.edu/ . The website includes GIS layers of computed monthly and yearly mean ocean current speed and associated power density along the coastlines of the United States, as well as joint and marginal probability histograms for current velocities at a variable horizontal resolution of 4–7 km. Various tools are provided for viewing, identifying, filtering and downloading the data from this website. The Gulf Stream system, especially the Florida Current, concentrates the highest kinetic power density ( > 2000 W / m 2 ). The majority of the kinetic power and its variability are only present in relatively shallow water given the strong correlation with the surface wind stress. The kinetic energy flux in the Florida Current is estimated over 30 years to provide temporal variability of the undisturbed kinetic energy with high statistical significance. Available power of approximately 5 GW associated with the undisturbed natural flow condition from the Gulf Stream system is predicted based on hypothetical turbine parameters. Successful development of renewable energy generation requires further studies to account for more precise technical, economic and environmental constraints. [ABSTRACT FROM AUTHOR]

The Gulf Stream system features some of the fastest and most persistent currents in the Atlantic Ocean and has long been identified as a promising target for renewable ocean current energy. This study investigates the theoretical energy potential of ocean currents for the Gulf Stream system. A simplified analytical model is calibrated and utilized to represent the quasi-geostrophic balance in the North Atlantic subtropical circulation. The effect of turbines is included in the model as additional turbine drag force. The energy equation in the system is derived and analyzed both locally and basin-wide. Basin-wide, energy production from surface wind stress is balanced by energy dissipation from natural friction and turbines. However, the pressure gradient is playing an important role in redistributing the energy in the local energy balance. It is found that increasing turbine drag does not necessarily increase total energy dissipation from turbines. The maximum energy dissipation by turbines is estimated to be approximately 44 GW, although electrical power output will be significantly reduced due to various engineering and technological constraints. The turbine drag has significant impact on the circulation system. The reduction of energy and volume fluxes in the circulation is featured for different levels of turbine drag. It is found that residual energy flux along the western boundary; can be significantly reduced under the peak energy dissipation by turbines, while reduction of volume flux is less extreme. [ABSTRACT FROM AUTHOR]

Abstract: The tidal stream power potential along the coast of the state of Georgia is evaluated based on numerical modeling and validated with the available data. The Georgia coast consists of a complex network of tidal rivers and inlets between barrier islands that funnel and locally amplify the strength of the ambient tidal currents in the region. The number of existing tidal current prediction locations is not sufficient to resolve the temporal and spatial changes in the current speeds and patterns. Therefore, the currents are modeled with the Regional Ocean Modeling System (ROMS) to determine the locations with high tidal stream power potential and the results are validated against measurements. The wetlands and the topographical features are integrated in the computational model with wetting and drying of computational cells. The locations with the largest mean tidal stream power density are identified and their characteristics are provided. The effect of power extraction on estuarine hydrodynamics is simulated by implementing an additional retarding force in the governing momentum equations in ROMS. Two different power extraction schemes are simulated at the Canoochee River. The first scheme involves extracting 20% of the original kinetic power across the entire cross-section of the river, and is found to have substantially lower impact on the original flow than the second scheme with 45% extraction. The summation of removed and residual kinetic powers is found to be larger than the original kinetic power in the cross-section, which is attributed to the recovery in the flow momentum through reorganization of stream flow energy. In both of the cases the major impact on the currents is limited to a partial reach of the river. The change in the maximum and minimum water levels is observed to be on the order of centimeters. [Copyright &y& Elsevier]

Abstract: Predictions of nearshore and surf zone processes are important for determining coastal circulation, impacts of storms, navigation, and recreational safety. Numerical modeling of these systems facilitates advancements in our understanding of coastal changes and can provide predictive capabilities for resource managers. There exists many nearshore coastal circulation models, however they are mostly limited or typically only applied as depth integrated models. SHORECIRC is an established surf zone circulation model that is quasi-3D to allow the effect of the variability in the vertical structure of the currents while maintaining the computational advantage of a 2DH model. Here we compare SHORECIRC to ROMS, a fully 3D ocean circulation model which now includes a three dimensional formulation for the wave-driven flows. We compare the models with three different test applications for: (i) spectral waves approaching a plane beach with an oblique angle of incidence; (ii) monochromatic waves driving longshore currents in a laboratory basin; and (iii) monochromatic waves on a barred beach with rip channels in a laboratory basin. Results identify that the models are very similar for the depth integrated flows and qualitatively consistent for the vertically varying components. The differences are primarily the result of the vertically varying radiation stress utilized by ROMS and the utilization of long wave theory for the radiation stress formulation in vertical varying momentum balance by SHORECIRC. The quasi-3D model is faster, however the applicability of the fully 3D model allows it to extend over a broader range of processes, temporal, and spatial scales. [Copyright &y& Elsevier]

The behavior of rip currents with changing bar and gap lengths was tested in a series of laboratory experiments using video-tracked floating drifters. Qualitatively, currents showed strong differences in overall character with changing topography. As narrow gaps became wider, the circulation tended to first travel parallel to the shoreline instead of immediately offshore, although strong offshore-directed flows were found for all topographies. Quantitatively, the width of the rip neck was found to increase slowly when compared to the increasing width of the rip channel. Maximum offshore and longshore velocities showed little dependence on bar or gap lengths, and were found to scale well with the predicted rate of generation of circulation. Finally, volumetric offshore flow rates through the rip channel showed no proportionality with the bar length as predicted by the mass transport hypothesis of rip current strength. [ABSTRACT FROM AUTHOR]

Waves, currents, and longshore sand transport are calculated locally as a function of position in the nearshore region using process based numerical models. The resultant longshore sand transport is then integrated across the nearshore to provide predictions of the total longshore transport of sand due to waves and longshore currents. Model results are in close agreement with the I1-P1 correlation described by Komar and Inman (1970) and the CERC (1984) formula. Model results also indicate that the proportionality constant in the l1-P2 formula depends weakly upon the sediment size, the shape of the beach profile, and the particular local sediment flux formula that is employed. Model results indicate that the various effects and influences of sediment size tend to cancel out, resulting in little overall dependence on sediment size. [ABSTRACT FROM AUTHOR]