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Increasing energy consumption and decreasing reserves of fossil fuels have led to growing interest in renewable energy from the ocean. Ocean currents are an alternative source of clean energy due to their inherent reliability, persistence and sustainability. General ocean circulations exist in the form of large rotating ocean gyres, and feature extremely rapid current flow in the western boundaries due to the Coriolis effect. The Gulf Stream system is formed by the western boundary current of the North Atlantic Ocean that flows along the east coastline of the United States, and therefore is of particular interest as a potential energy resource for the United States. The theoretical energy balance in the Gulf Stream system is examined using the two-dimensional ocean circulation equations based on the assumptions of the Stommel model for subtropical gyres with the quasi-geostrophic balance between pressure gradient, Coriolis force, wind stress and friction driving the circulation. To represent flow dissipation due to turbines a spatially varying turbine drag coefficient is formulated and a finite difference numerical approach is utilized to obtain an implicit solution of the model. The results show that considering extraction over a region representing the entire Florida Current portion of the Gulf Stream system, the average power dissipated ranges between 4 and 6 GW with a mean around 5.1 GW. This corresponds to an average of approximately 45 TWh/yr. However, if the extraction area approximates the entire portion of the Gulf Stream within 200 miles of the US coastline, the average power dissipated becomes 18.6 GW or 163 TWh/yr. The impact of the localized turbine drag on the hydrodynamics is primarily within the turbine region. The extra drag force from turbines slows down the current velocity and leads to redirection of the Gulf Stream flow. It also results in a sea surface drop in the turbine region. Localized turbine drag significantly reduces residual kinetic energy flux in the circulation. However, its influence on the residual volume flux depends on the area of the turbine region. [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: The wave power potential along the southeast Atlantic coast of the United States of America bounded by latitudes 27° N and 38° N and longitudes 82° W and 72° W (i.e. North Carolina, South Carolina, Georgia, and northern Florida) is investigated. The available data from National Data Buoy Center wave stations in the given area are examined. Temporal trends of the wave heights, wave periods and the wave power are analyzed for a time scale of weeks. The time series from the wave stations are downsampled with a 15-day moving average filter with near 50% overlapping to study the seasonal trends. Power calculated from hourly significant wave heights and average wave periods is compared to power calculated using spectral wave density. It is found that a factor of 0.61 needs to be applied to the wave power calculated from hourly significant wave heights and average periods in order to get the same results with the power calculated from spectral wave density. The mean power within 50km of the shore is determined to be ∼9kW/m, whereas higher power (∼15kW/m) is available further offshore. [Copyright &y& Elsevier]