Exploring Optimal Locations for Underwater Turbine Emplacement near Marine Navigation Passageways...
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Transcript of Exploring Optimal Locations for Underwater Turbine Emplacement near Marine Navigation Passageways...
Exploring Optimal Locations for Underwater Turbine Emplacement near Marine Navigation
Passageways
Steps to a “go” or “no” answer.
With Thanks to:MIT Sea Grant, the Chewonki Foundation, Mass Maritime Academy, Town of Hull, MAUSGS, Falmouth Scientific Inc.
Geoff Cowles, Dorothy Kelly, Peter Arnold, Stanley King, Tom Pham, Herman Gustafson, Jim Manning, Kurt Bornheim, Andy Stern, Neil Ganju, ….
Studies Done at Three Sites
The Three Sites
Mass. Maritime/Cape Cod Canal
The Three Sites
The Hull Gut
The Three Sites
The Sheepscot River
Site #3
The Sheepscot River
FERC Permit Area
Step 1
Hydrodynamic Modeling
The Island Tidal Node
Tidal Power Distribution
Tidal Power Distribution
Step 2
Spatial Velocity Survey
Surveyed Areas
Our sampling focused on five areas, indicated by the sampling sites (green dots) shown here. These areas were identified as high energy locations by a numerical model and by the data from a preliminary survey conducted on September 28.
The Surveying Equipment
Acoustic Doppler Current Profiler
(ADCP)R/V Seagull and Capt.
Stanley King
Surveyed Areas
The Best Area
Under the Bridge
The focus here will be on the tidal flows and tidal power near the Westport Island bridge.
Capturing the Tidal Cycle
Observations out of the Nav. Channel, but with bottom depth > 7m
The Tidal Cycle
The tidal velocity nicely follows a sinusoidal cycle, with maximum ebb (positive) and flood (negative) currents of slightly greater than 1 m/s. Velocities were somewhat higher directly underneath the bridge (by about 10 %), but this is a minor point.
Not the Strongest Tides of the Year
But wait! The timing of our survey was based on boat and personnel availability. Unfortunately, this availability did not coincide with a time of strong tides. In fact, our survey was conducted during unusually weak neap tides, as seen by highlighting the time of our survey (in red above) on a plot of tidal height at Wiscasset.
Extending the Analysis to Other Tides
With a little math, we can relate the maximum tidal velocity, Vmax, to the mean power density over the half tidal cycle. The formula is:
<F> = 2ρVmax3
3π
Assuming that Vmax is proportions to the height range, Hdiff, of a particular tide
Vmax = Hdiff*Vmax(Sept 30) 7 ft
Allows for the computation of the expected velocity and power distribution under the bridge.
For Vmax(Sept 30) = 1 m/s ; <F>year = 623 W/m2
Step 3
Evaluating the Bottom Conditions
-Side Scan Surveying
Maine DMR Side-Scan Survey April 5,2011
Refining the “Best Spot” Assessment
Step 4
Installing a Moored Velocity Profiler (e.g. ADCP) Near the Best Spot
ADCP
Conclusion
Conclusion
A four-step process:
1. Hydrodynamics modeling
2. Ship-board velocity surveying
3. Side-scan sonar surveying
4. Moored velocity profiling
Offers a cost-effective way to evaluate the tidal resource in a estuarine environment, with a “go” or
“no” assessment at each step