Wave energy converter effects on wave and sediment circulation

Transcription

1 Wave energy converter effects on wave and sediment circulation Grace Chang and Craig Jones Integral Consulting Inc. Jesse Roberts, Kelley Ruehl, and Chris Chartrand Sandia National Laboratories

2 Integral Consulting Inc. Health Environment Technology Sustainability Multidisciplinary science and engineering consulting Practice areas focused in supporting Marine Renewable Energy Development and application of innovative technology and modeling tools Perform environmental and ecosystem risk assessments

3 Introduction Wave energy converter (WEC) arrays have the potential to alter nearshore wave propagation and circulation patterns o o o Sediment transport Ecological processes Socioeconomic services Wave model simulations can provide environmental assessments of WEC arrays

4 Objectives Evaluate a modified version of the wave modeling tool, SWAN Simulate wave propagation through hypothetical WEC arrays Perform model sensitivity analysis to examine effects of WEC characteristics on nearfield and far-field wave conditions Evaluate changes in sediment transport patterns Pacific Energy Ventures (WET-NZ)

5 Physical Assessment Tools MetOcean data: Geophysical Surveys Wave and Current Measurement Wind Measurement Geotechnical data: Sediment Erosion Rates Other Seabed Parameters Modeling Tools: Wave and circulation High-fidelity CFD Sediment Transport Water Quality

6 Model Modifications Spectral wave models use a total spectral transmission WEC energy absorption varies over frequency Sandia National Laboratories included a frequency dependent power absorption for WEC obstacles (Chartrand and Ruehl) Smith, H., C. Pearce, D. Millar (2012) Further analysis of change in nearshore wave climate due to an offshore wave farm: An enhanced case study for the Wave Hub site, Renew. Energ., 40,

7 SWAN Model Investigation Deep-water waves propagated from offshore Monterey Bay to Santa Cruz, California Nested model domain Monterey Bay: 100 m grid resolution Santa Cruz: 20 m grid resolution

8 SWAN Model Validation Monterey Bay: NOAA NDBC buoy Santa Cruz: Datawell Waverider Monterey Bay Santa Cruz RMSE SI ME RMSE SI ME H s T p MWD

9 SNL-SWAN User-specified power matrix for WEC devices SNL-SWAN calculates frequency dependent transmission coefficient associated with specific WECs Babarit, A., J. Hals, M.J. Muliawan, A. Kurniawan, T. Moan, and J. Krokstad (2012) Numerical benchmarking study of a selection of wave energy converters, Renew. Energ., 41,

10 SNL-SWAN: Sensitivity Analysis Understand model behavior related to: Eight different WEC types Size of Array o 10, 50, or 100 WECs WEC spacing o 4, 6, or 8 diameter spacing (center-tocenter) Oscillating Flap Oscillating Water Column Babarit, A., J. Hals, M.J. Muliawan, A. Kurniawan, T. Moan, and J. Krokstad (2012) Numerical benchmarking study of a selection of wave energy converters, Renew. Energ., 41,

11 SNL-SWAN: Model Set-Up Results evaluated near-shore Santa Cruz Model simulations with WECs compared to simulations without WECs (baseline)

12 SNL-SWAN: Results 9.5 m oscillating flap 20 m two-body heave 26 m oscillating flap 50 m oscillating water column

13 SNL-SWAN: Results Most sensitive to WEC device type and number of WECs in an array Relatively insensitive to WEC spacing

14 Summary In general, <15% differences in modeled H s in the presence and absence of WECs Largest difference (30%) for the 26 m oscillating flap, 100 devices in the array 50 m oscillating water column wave reduction potential relatively small Wave directions and periods insensitive to WEC characteristics; however likely related to model parameters (frequency and directional binning)

15 Modeling Wave Driven Circulation Hydrodynamics Model The SNL-EFDC three-dimensional, vertically hydrostatic, free surface, hydrodynamic model Incorporation of Wave Effects Wave generated radiation shear stresses from SNL- SWAN are incorporated as a source of shear momentum equations The wave dissipation is incorporated as a source term in the turbulent transport equations

16 Processes Controlling Wave Driven Circulation Radiation Shear Stress Waves in the nearshore cause an excess flow of momentum defined as the radiation shear stress. The change in momentum as waves move towards shore is balanced by a pressure gradient (wave set-up) and wave induced velocities. (Longuet-Higgins, 1970) Energy Dissipation Energy dissipation is due to loss of energy in a wave from the wave boundary layer and wave breaking and happens in the form of turbulence generation. The turbulence generated governs the exchange of momentum in the nearshore.

17 Hydrodynamic Model Validation A 10 km by 10 km domain was used A nearshore ADCP was used to measure currents Drifter studies were used to compare nearshore circulation

18 Seabed Risk Assessment Bathymetry, modeled waves and currents, and seabed characteristics are integrated in a classification system A scoring criteria defines the risk to offshore environment due to seabed stability alterations How big is the change?

19 Sediment Mobility Evaluation Spatial maps of sediment mobility can be produced from the assessment model and compared with multibeam surveys The results have excellent spatial consistency

20 Example Evaluation Spatial maps of stability and mobility potential are developed from the risk assessment Comparisons of baseline (above) and array (below) scenarios can be made to evaluate impacts on array infrastructure and the local environment Location of MHK array

21 Monterey Bay WEC Physical Environmental Effects Small Array Near-Field Deep water physical effects are negligible for surface following WEC Potential to impact near-field benthic communities and fish behavior dependent on mooring system Low Small Array Far-Field Minor alterations to sediment transport patterns» Potential for Moderate near shore sediment transport alteration Negligible alterations in circulation Low to Moderate far-field environmental effect

22 Summary Leveraged decades of hydrodynamic model development Enhancing models and developing unique analytical methods Quantitative methods can be used to evaluate the effects of MHK arrays in nearshore coastal regions and rivers Small arrays (~10) of WEC devices have minimal effect on the physical environment SITE SPECIFIC As array size increases, effects increase and require further study Initial evaluation strongly suggests adaptive management strategies Further site specific evaluation in regions where arrays are presently installed will help to validate and streamline tools and techniques

23 Acknowledgments Sandia National Laboratories Wind and Water Power Technologies Office U.S. Department of Energy CEROS US Navy Craig Jones: Grace Chang: