Development of an MHK Model for In-stream Energy Removal and Environmental Effects

1. Water Power Peer Review Development of an MHK Model for the Assessment of In-stream Energy Removal and Environmental Effects Dr. Zhaoqing Yang Pacific Northwest National Laboratory zhaoqing.yang@pnnl.gov 206-528-3057 November 3, 2011 2.1.3: Effects on Physical Systems

2. Purpose, Objectives, & Integration • Extraction of in-stream energy needs state-of-the-art numerical models to enhance our understanding • Resource characterization – maximum energy potential • Technology and environmental barriers • Processes at various spatial and temporal scales • Development of an MHK model to assess • Resource characterization • Effects on physical environment at local and system wide scales • Optimal siting and array configuration • Results of the MHK model can be used for • Categorizing and evaluating effects of stressors • Assessing environmental risks to aquatic biota and habitats

3. Technical Approach • 3D Finite Volume Coastal Ocean Model (FVCOM) • Unstructured grid – well suited for complex geometry and various scales • Parallel computing – large domain and number of tidal turbines • Water quality • Sediment transport • WRF met forcing • Coupled SWAVE • Public domain Cell size ~ 15m Turbines Velocity Field

4. Technical Approach Momentum sink approach (retarding force) • Modification of momentum governing equations • Turbine representation • Turbine blades • Supporting structures • Turbine foundations

5. Technical Approach Validation to analytical solution (2D mode) • Idealized tidal channel and bay with realistic dimensions and forcing • Open boundary M2 tide (2m range) • User-friendly MHK parameter input • Turbine elevation from seabed • Turbine diameter • Turbine thrust coefficient • Turbine blade drag coefficient • Areas of supporting poles and base • Drag coefficients for poles and base

6. Plan, Schedule, & Budget Schedule • Initiation date: October 1, 2009 • Milestones: • FY10 Q2: Refinement/validation of Puget Sound models • FY10 Q4: Online dissemination of model results for the real-time Puget Sound Operational Forecast System (PS-OPF) • FY11 Q2: MHK model development • FY11 Q3: MHK model validation • FY11 Q4: Analysis of effects on flux, flushing, and array configurations Plan • Planned completion date: September 30, 2012 • Analysis of MHK effects on water quality, sediment transport and food web Budget

7. Accomplishments and Results • MHK model results agree well with analytical solution • Diminishing return of extractable power occurs when volume flux reduces by 42% • MHK model is also validated with widely used bottom drag approach in 2-D mode Flood Tide Flood Tide Reduced current speed with turbines Tidal currents without turbines

8. Accomplishments and Results • Three-dimensional effects • Volume flux reduction at maximum extractable power is smaller in 3D than that in 2D mode • Maximum extractable power varies with turbine height due to 3D structure of velocity profiles Extractable Power and Volume Flux Reduction in 3D mode Maximum Power 33% Reduction

9. Accomplishments and Results • MHK effects on flushing time of the bay • Model results show that MHK devices have greater effect on the relative change in flushing time than the change in volume flux • Relative change of flushing time increases exponentially as a function of percentage reduction of the volume flux

10. Accomplishments and Results • Effects of different array configurations • “Optimal” vs. practical constraints • Placement of turbines in the channel • Extracted power, volume flux, flushing time, etc. Extracted power: 207 MW Extracted power: 171 MW Dye concentration for center configuration (408 turbines) Dye concentration for side configuration (408 turbines) Velocity for MHK Side Configuration Velocity for MHK Center Configuration

11. Accomplishments and Results • The MHK model can be applied to river and ocean current environments • Cumulative effect and interaction of multiple projects • Change of hydrodynamic conditions at local and system scales • Model setup for an idealized river connected to a bay • Bay depth = 200m; length = 100km; width = 750m; slope = 5x10-4 • Forcing: M2 tide (1.0m tidal range); river flow = 15,000 m3 • Grid size varies from 36 m (river) to 580 m (bay) • 10 projects along the river with 90 turbines per project Tide River inflow Bottom elevation = 50m

12. Accomplishments and Results • MHK effects at local and system scales • Slow down the river • Increase water level • Local variations Without Turbine Velocity (m/s) Upstream Downstream With Turbine Without Turbine Water Depth (m) With Turbine

13. Challenges to Date • Further model validation and application • Long-term physical and biogeochemical data with MHK devices installed • Tidal turbine parameterizations (collaboration with developers) • Model simulations in real world, even pilot-scale study (e.g., Puget Sound) • Need of theoretical analysis • Alternative for model validation • General guidance to the relationship between energy extraction, turbine size, circulation and transport processes • Balancing energy extraction and environmental effects • Integration of other environmental stressors • Regulatory criteria for environmental impacts Predicted tidal currents with PNNL Puget Sound model

14. Next Steps (FY12) • Modeling analysis of MHK effects on water quality • Development of a generic, good baseline condition of water quality model • Realistic atmospheric forcing, heat flux and boundary conditions • Simulation of salinity, temperature, and algal/nutrient dynamics • Long-term simulations (seasonal variations) – high performance computing • MHK effects on sediment transport and food web • Analysis of MHK effects on relative changes of deposition/erosion patterns • Food web – what is the main physical driving force, temperature? • Future research • Modeling analysis in the real world (tides and river) • Hydrodynamics (far-field effects: tide flats) • Water quality – mixing and hypoxia • Ocean currents (FVCOM in modeling test bed project for Gulf of Mexico)