Cobscook Bay regional and local (inset) model domains including schematic of ORPC TidGen™ unit (bottom left).

Cobscook Bay regional and local (inset) model domains including schematic of ORPC TidGen™ unit (bottom left).

In FY13, Sandia developed a framework to identify optimal placement locations—leading to marine hydrokinetic (MHK) current energy converter (CEC) device array configurations that will maximize energy production and minimize environmental effects. The CEC array optimization framework was applied to Cobscook Bay, Maine, the first deployment site of the Ocean Renewable Power Company’s (ORPC) TidGen CEC device.

The framework used a hydrodynamic modeling platform, known as SNL-EFDC, to investigate flow patterns before and after MHK array placements. In addition to maximizing device performance, the optimization framework also considered potential environmental effects to avoid conditions that may alter fish behavior and sediment-transport trends. Although the optimization framework’s usefulness was demonstrated in 2013, several questions remained regarding the hydrodynamic model’s sensitivity to setup and forcing conditions.

Three 5-CEC arrays investigated during FY13; unoptimized preliminary layout (left panel), an environmentally constrained optimized array (center panel), and a power optimized array without environmental constraints (right panel). The color contour shows percent change in velocity vs. baseline (no CEC devices). The placement footprint is outlined by a white rectangle. Cells with depths less than 23 m are blacked out as they are potentially too shallow for placement.

Currently, Sandia is testing the effects the model’s grid resolution has on device-performance and flow-pattern predictions. Original modeling efforts vertically resolved the water column with five layers. The coarse layering scheme was chosen to reduce computational demands for initial optimization framework development, where over 50 simulations were conducted. Sandia is now testing the hydrodynamic models sensitivity to vertical resolution by comparing model results between simulations with 3, 5, 15, and 25 vertical layers. We recently conducted the simulations and are now analyzing the results.

We are also investigating the model grid’s horizontal orientation to determine if any bias in grid/flow direction exists. The initial studies used a grid aligned with the net flow direction determined from one acoustic Doppler current profiler dataset. To the best of our knowledge, this dataset represents conditions within the site; however, we must still investigate grid-orientation bias. We are investigating the hydrodynamic model sensitivity by comparing simulations with grids orientated at +10°, +5°, –5°, and –10° with respect to the original orientation.