Benchmark Modeling of Wave Energy Arrays

1. Water Power Peer Review Ken Rhinefrank [Columbia Power Technologies, Inc.] [krhinefrank@columbiapwr.com] [November 2, 2011] Benchmark Modeling of the Near-field and Far-field Wave Effects of Wave Energy Arrays

2. Water Power Peer Review Project Team Columbia Power Technologies Ken Rhinefrank Pukha Lenee-Bluhm Erik Hammagren Oregon State University Merrick Haller Tuba Oskan-Haller Aaron Porter Ken Rhinefrank [Columbia Power Technologies, Inc.] [krhinefrank@columbiapwr.com] [November 2, 2011] Benchmark Modeling of the Near-field and Far-field Wave Effects of Wave Energy Arrays

3. Purpose, Objectives, & Integration • Numerous environmental uncertainties exist with wave energy converter designs. Such uncertainties can concern stakeholders and can to lead to a lengthy and expensive permitting process. One such concern is potential changes to the shoreline that may be caused by wave field modification induced by WEC devices. • Numerical wave prediction models that have been thoroughly validated with detailed observations can be used to show expected physical impacts at considered sites. For example, the validated model will enable us to assess ways to mitigate any unwanted effects through modifications in the array design.

4. Technical Approach Project Objectives • Collection of a benchmark data set for testing numerical models of wave-structure interaction • Development of a predictive understanding of the effects of an array of wave energy converters on the wave conditions. • Develop a methodology for estimating the potential for arrays of wave energy converters to change the near-shore current and sediment transport patterns.

5. Technical Approach Key project issues and approach The technical approach involves experimental design, setup, and testing at 1:33 scale. It also involves the development and validation of a numerical model and comparison of the numerical model with experimental results. This approach includes the following tasks • Experimental setup • Design & construction of 1:33 scale WEC array • Experimental tank testing of three different array configurations • Develop numerical model • Model/data comparisons • Develop validated parameterizations for WEC

6. Technical Approach • Experimental setup • Design & construction of 1:33 scale WEC array Wavemaker Offshore array Near-field array Far-field array WEC array (Manta-33)

7. Technical Approach 3. Experimental Tank Testing

8. Technical Approach 4. Develop Numerical Model SWAN modeling at lab scale Lab data SWAN output

9. Technical Approach Measured offshore and lee wave Power 5. Model/Data Comparisons

10. Technical Approach Preliminary Investigation Measured WEC Power vs. Measured Wave Power Loss 5. Model/Data Comparisons

11. Plan, Schedule, & Budget Schedule • Initiation date: January 1, 2010 • Planned completion date: December 31, 2011 • Requesting an extension to August 2012 to address the vast amounts of data that must be accurately post processed prior to finalizing the numerical models. • Milestones FY10 • 5 WEC design build test • Design tank experiment • Setup tank experiment and begin testing FY11 • Complete array experiment and process wave data • Begin Numerical Model development FY12 • Develop Numerical Model • Model Data Comparison

12. Plan, Schedule, & Budget • Go/no-go decision points - FY12 • Confirm validity of model for public distribution Budget: • Remaining budget will be utilized during numerical model development • 47% of budget utilized to date.

13. Accomplishments and Results • Five 1:33 scale models have been designed, built and tested in the Tsunami Wave Basin • Wave data has been post processed using proper calibration coefficients and checked for accuracy. • Preliminary investigation of the wave buoy array effects on the near-field and far-field wave climates has been made and clear indicators of energy absorption exist. • The remainder of the project will further develop and validate the numerical models that describe these affects on the wave climate.

14. Challenges to Date Quality control of hydrodynamic data has been challenging Causes: • Wave gauge calibration shift over testing period (Time-varying calibration coefficients) due to ionization changes in the water body. • Organizational structure of the dataset remains a challenge, owing to the sheer number of different permutations that were tested. • A large percentage (>90%) of the collected data has passed quality control. Solutions: • Comparing the outputs of an ultrasonic wave gauge and a collocated resistance wire wave gauge at a number of points in time, a time varying calibration coefficient function was developed. • Continue to scrutinize, understand and process data.

15. Challenges to Date Different damping characteristics of the individual WECs Causes: • Mechanical variation of damper over the test period Solutions: • An additional round of testing was performed to fully characterize each WEC • Characterize dampers pre and post testing • Treat each WEC as a heterogeneous point absorber rather than all the same

16. Challenges to Date Optical clarity issues degrading the stereo-video observations Causes: • Clear water Solution: • Pressurized particle seeding gun was built to launch seed material into the basin Tank resonant modes under some conditions Causes: • Reflection from beach and side walls Solution: • Presently being analyzed. • None-Would require substantial investment in beach and side wall energy absorption.

17. Next Steps • Develop Numerical Model • Model/Data Comparisons • Final report