Slide 1

Andrew T. Myers, PhD, PE, Assistant Professor Vahid Valamanesh, Graduate Student Department of Civil and Environmental Engineering Northeastern University The Influence of Aerodynamic Damping in the Seismic Response of HAWTs Slide 2 Presentation Outline Motivation Dimensions of utility-scale HAWTs Vulnerability to earthquakes Derivation of aerodynamic damping Fore-aft direction Side-to-side direction Numerical example 1.5 MW NREL baseline turbine Conclusions Slide 3 Installed wind capacity map as of Jan 2011 United States National Seismic Hazard Map Motivation: Exposure of HAWTs to Earthquakes Slide 4 Approximate dimensions of a utility-scale HAWT First Period ~ 3 s Dimensions and Period of HAWTs Slide 5 No redundancy in the support structure Slender hollow sections (D/t as high as 280) Farms consisting of many nearly identical structures Large directional affect due to aerodynamic damping Side-to-sideFore-aft Vulnerability to Earthquakes Slide 6 Aerodynamic Damping of HAWTs in the Fore-Aft Direction Forces based on blade element momentum theory (BEM) Flexibility of rotor is omitted Wind direction is along fore-aft direction Steady wind First mode of vibration is considered Slide 7 Aerodynamic Damping of HAWTs in the Side-to-Side Direction Slide 8 Numerical Example 1.5 MW Baseline Turbine by NREL Power output1.5 MW Hub Height84 m Rotor Diameter70 m Number of Blades3 Max Rotational Speed20 rpm Cut in wind speed5 m/s Cut out wind speed25 m/s Nacelle Mass51 Ton Hub Mass15 Ton Tower Mass123 Ton Rotor Mass11 Ton Active Pitch ControlYes [Base image from Nuta, 2010] Slide 9 Numerical Example 1.5 MW Baseline Turbine by NREL Aerodynamic damping in the fore-aft direction with =20 rpm and =7.5 Slide 10 Numerical Example 1.5 MW Baseline Turbine by NREL Aerodynamic damping in the side-to-side direction with =20 rpm and =7.5 Slide 11 Aerodynamic damping in the fore-aft direction with =7.5 (left) and =20 rpm (right) Numerical Example 1.5 MW Baseline Turbine by NREL Slide 12 Aerodynamic damping in the side-to-side direction with =7.5 (left) and =20 rpm (right) Slide 13 FAST Derivation Numerical Example 1.5 MW Baseline Turbine by NREL Validation with FAST in the fore-aft direction with =7.5 and =20 rpm Slide 14 Numerical Example 1.5 MW Baseline Turbine by NREL Effect of aerodynamic damping on the seismic response with =20 rpm Slide 15 Conclusions Aerodynamic damping of operational wind turbines strongly depends on wind speed. For the considered example (1.5 MW turbine, = 20 rpm, = 7.5, wind speed between cut-in and cut-out): The fore-aft aerodynamic damping varies between 2.6% and 6.4% The side-to-side aerodynamic damping varies between -0.1% and 0.9% For this same operational case, the derivative of the lift coefficient with respect to the angle of attack is the most influential parameter in aerodynamic damping in the fore-aft direction The blade pitch angle and rotational speed also influence the aerodynamic damping in both the fore-aft and side-to-side directions The directional effect strongly influences the seismic response, with median spectral drift predicted to be as much as 70% larger in the side-to-side direction than in the fore-aft direction