HomeMy WebLinkAboutUAA Letter
School of Engineering
3211 Providence Drive, Anchorage, AK 99508
Nov. 10, 2008
Monty Worthington
Alaska Projects Manager
ORPC Alaska, LLC
911 w. 8TH Ave., Suite 205
Anchorage, AK 99501
Dear Monty,
The UAA School of Engineering is excited about the opportunity to work with Ocean
Renewable Power on this project to begin to develop renewable tidal energy in Cook
Inlet, Alaska. UAA will support this project by developing DELFT3D flow and sediment
transport models to assist in the siting of the in-line turbine(s).
DELFT3D is a state-of-the-art flow (velocity, water elevation), wave, sediment transport,
and morphologic change model that was developed by Delft Hydraulics. For this
application, the main focus will be on flow velocity and sediment transport. The model
uses the equations of motion in order to determine the distribution of velocity and water
elevation during a prescribed period of time. The model can operate in the 2D (depth-
averaged) mode or in the 3D mode where velocity variation with depth as well as
horizontal position is determined. The model requires bathymetric and bottom roughness
data and will be “forced” by boundary conditions. For upper Cook Inlet, there would be a
tidal boundary condition (on the ocean side of the study domain, e.g., Seldovia) as well as
discharge boundary conditions associated with the major river inflows. The tidal
boundary condition would be enforced by controlling the water level at the boundary
using either historic water level measurements at the boundary or using tidal constituents.
The Delft3D model will be calibrated using a combination of existing velocity/water
level data and using data collected for this project. The Knik Arm Crossing project
(HDR, URS, ENTRIX, UAA 2005) collected ADCP velocity data at two fixed locations
by the site of the proposed bridge (by Point McKenzie) for over 1 month. In addition,
velocity data was collected in that area using a moving boat. The model could be
calibrated with this data in order obtain accurate velocity predictions by Point McKenzie.
However, ORP is also interested in the possibility of placing the in-line turbine by Fire
Island. Hence, it would be advisable to collect about 1 month of ADCP data at one or
more locations there for calibration purposes. Calibration would involve making
adjustments to the bathymetry data or the bottom roughness until the model accurately
predicts the velocity or water level. The calibrated velocity model would provide accurate
velocity predictions in the vicinity of the locations where calibration data were collected.
However, additional velocity data from a roving boat could also be collected to verify the
model’s calculations. Based on the velocity calculations, the potential in-line power can
be readily calculated throughout the study domain.
School of Engineering
3211 Providence Drive, Anchorage, AK 99508