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031,02-11-09,TID

This seminar discusses the modeling and effects of tidal energy extraction in Puget Sound, focusing on far-field, barotropic effects. It covers site characteristics, numerical solutions, boundary conditions, turbine models, and response to extraction. Comparisons with theoretical models are also presented.

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031,02-11-09,TID

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  1. Far-field Effects of Tidal Energy Extraction in Puget Sound ME 523: Energy and Environment Seminar February 11, 2008 Brian Polagye PhD Candidate University of Washington Department of Mechanical Engineering 031,02-11-09,TID

  2. Tidal Energy in Puget Sound • Modeling Extraction Effects • Model Application to Puget Sound

  3. Spieden Channel Guemes Channel San Juan Channel Deception Pass Project pending Race Rocks Demonstration turbine Admiralty Inlet Pilot project Marrowstone Island Demonstration array Agate Passage Preliminary permit returned Rich Passage Preliminary permit returned Tacoma Narrows No activity Tidal Energy Projects in Puget Sound 001,02-11-09,TID

  4. Tidal Energy Devices • (clockwise from left) • Verdant Power • Clean Current • Marine Current Turbines • Open Hydro 002,02-11-09,TID

  5. Admiralty Inlet Pilot Project Site Survey Area 003,02-11-09,TID

  6. Site Characteristics • Resource intensity • Seabed geology • Electrical interconnection • Existing uses • Environmental concerns • Long-term potential How do we measure this? 004,02-11-09,TID

  7. Tidal Energy in Puget Sound • Modeling Extraction Effects • Model Application to Puget Sound

  8. Problem Definition and Approach • Determine what effects extraction has on the natural environment, including changes to the resource. • Approach with numerical model that: • Captures basic physics of power extraction on the natural system. • Is sufficiently flexible to study a range of site types, tidal regimes, and turbine dynamics. • Performs these studies at low computational cost. • Focuses on far-field, barotropic effects. • Possible with a 1D, 2D, or 3D numerical models. 031,02-11-09,TID

  9. Governing Equations • Tidal streams characterized by energetic, bidirectional flow h Q • 1D shallow water equations appropriate to problem: 027,02-11-09,TID

  10. Numerical Solution • Many algorithms available to solve shallow water equations. For example, explicit algorithms include: • Lax • Leap Frog • MacCormack predictor-corrector • MacCormack algorithm (2nd order in time and space): (compact notation) (predictor) (corrector) (update) 027,02-11-09,TID

  11. Boundary Conditions • Three required properties: • Radiative: allow outgoing wave to pass without reflection • Active: admit incoming waves (e.g. tides) • Stable: maintain mean sea level over long simulation times • Obvious solution is to prescribe tidal elevation at boundary: • This is a clamped boundary and does not radiate outgoing waves. A better option is a Flather boundary (e.g. Blayo and Debreu 2005). 029,02-11-09,TID

  12. Channel Junctions Serial (1:1) Branching (1:2) Merging (2:1) 2 1 3 1 2 1 3 2 • 2 unknowns (velocity u and depth h) for each channel • Model by compatibility condition (e.g. for serial): (1) (3) (2) (4) 024,02-11-09,TID

  13. Turbine Model • Requirements (from 1D momentum theory): • Reflect drop in pressure over plane of extraction. • Reflect total dissipated power (power extracted + wake losses). • Assume: • Turbines are infinitesimally small in comparison to water depth. • Turbines are distributed uniformly on channel cross-section. • Wake region is infinitesimally short and dissipation may be modeled as a discontinuous decrease in power. • Implement similarly to a channel junction, (flood tide). 019,02-11-09,TID

  14. Steady State Extraction Δh = 0.5 m H = 50 m L = 5000 m Water Depth Velocity (no rows) Velocity (two rows) 026,02-11-09,TID

  15. Basic Channel Network Inlet Basin Constriction • Three channel segments • Kinetic power extraction by one or more rows of turbines in constrictions • Single constituent tidal forcing: • Analytical theory formulated for this configuration 025,02-11-09,TID

  16. 1. Response is a continuous function of power dissipated 2. Diminishing marginal benefit 3. Kinetic resource has limits Response to Extraction 005,02-11-09,TID

  17. Response to Extraction Basin Narrows Inlet 006,02-11-09,TID

  18. Maximum Flow (m3/s) Seawater Density (1024 kg/m3) Tidal Amplitude (m) 0.19 ≤ γ ≤ 0.26 Theoretical Response Gravity constant (9.81 m/s2) Source: Blanchfield et al. (2008) • Theory developed by Garrett and Cummins (2005) • Extended to ocean-basin system by Blanchfield et al. (2008) • Further extended by Karsten et al. (2008) during Bay of Fundy modeling 007,02-11-09,TID

  19. Comparison with Theory Some disagreement between model and theory… …but theory neglects important dynamics. • Comparison also in-line with site-specific 2D modeling results by Karsten et al. (2008) for Bay of Fundy 008,02-11-09,TID

  20. Conclusions from Basic Networks • Extraction of kinetic power alters: • Tidal range • Currents, transport, and kinetic power density • These changes have environmental, social, and economic consequences. • Changes are generally site-specific, and depend on: • Level of power extraction (small extraction, small impact) • Geometry of segments • Type of network (basic, branching, etc.) • Tidal regime • Device dynamics 009,02-11-09,TID

  21. Tidal Energy in Puget Sound • Modeling Extraction Effects • Model Application to Puget Sound

  22. Modeling Extraction in Puget Sound • Concerns that tidal energy extraction could exacerbate existing stresses (hypoxia) • Modeling goals: • In-stream power potential for Puget Sound • Optimal siting of arrays • Assumptions: • Flow dominantly 1D • Neglect salinity effects • Neglect small-scale features 010,02-11-09,TID

  23. Primary Semiduirnal Calibration Phase Lag (Model – Observations) Amplitude (Model/Observations) 011,02-11-09,TID

  24. Amplitude Calibration 012,02-11-09,TID

  25. Effect of Extraction on Transport Extraction from Admiralty Inlet 1 2 Extraction from Tacoma Narrows 4 6 Extraction from Both Sites 8 A B C D 014,02-11-09,TID

  26. Development Trade-Offs Resource Intensity More energetic resource in Tacoma Narrows Resource Size Larger potential resource in Admiralty Inlet Extraction in Tacoma Narrows has no significant effect on Hood Canal Impact on Hood Canal For same level of power generation, extraction in Admiralty Inlet has less effect on South Sound Impact on South Sound 016,02-11-09,TID

  27. Effects of Pilot Project Change in M2 Transport (%) Change in M2 Tidal Range (mm) 3 MW rated electrical capacity Power extraction from Admiralty Inlet Currently in permitting phase Immeasurable effects 017,02-11-09,TID

  28. Effects of Commercial Project Change in M2 Transport (%) Change in M2 Tidal Range (mm) 135 MW rated electrical capacity Power extraction from Admiralty Inlet Subject of feasibility study Measurable effects Significant effects? 018,02-11-09,TID

  29. Conclusions for Puget Sound • Tidal energy extraction can measurably change the tidal regime of Puget Sound. • Tidal energy extraction has the potential to provide significant quantities of predictable renewable energy to the region. • Insufficient information exists to perform a cost-benefit analysis. We can calculate the theoretical resource, but do not know what is recoverable. • Key next step is to determine the ecosystem implications for changes to the tidal regime. 023,02-11-09,TID

  30. Questions? This research is supported by Snohomish Public Utility District and the Electric Power Research Institute (EPRI) 020,02-11-09,TID

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