  A single-layer, quasi-geostrophic (QG), large-scale ocean circulation model
is developed in this paper to study available ocean current energy potentials
harnessed by using the ocean current turbines. Power extraction is modeled by
adding a parameterized Rayleigh friction term in the barotropic vorticity
equation. Numerical assessments are performed by simulating a set of
mid-latitude ocean basins in the beta plane, which are standard prototypes of
more realistic ocean dynamics considering inter-decadal variability in
turbulent equilibrium. A sensitivity analysis with respect to the turbine
parameters is performed for various physical conditions. Results show that the
proposed model captures the quasi-stationary ocean dynamics and provides the
four-gyre circulation patterns in time mean. After an initial spin-up process,
the proposed model reaches a statistically steady state at an average maximum
speed between 1.5 m/s and 2.5 m/s, which is close to the observed maximum zonal
velocities in the western boundary currents. The probability density function
of the available power over a long time period is computed for a wide range of
parameters. Numerical results shows that 10 GW mean power can be extracted from
the turbines distributed over a length scale of 100 km along the western
boundaries. However, it is demonstrated that bigger turbine areas would alter
the flow patterns and energetics due to excessive dissipation. An increase in
the turbine area results in an increase in the available power ranging from 8
to 22 GW depending on the values of turbine modeling parameters. This first
step in the numerical assessment of the proposed QG model shows that the
present framework could represent a viable tool for evaluating energy
potentials in a highly turbulent flow regime.
