Slide 1

Andrew T. Myers, PhD, PE, Assistant ProfessorVahid Valamanesh, Graduate StudentDepartment of Civil and Environmental EngineeringNortheastern University

The Influence of Aerodynamic Damping in the Seismic Response of HAWTs

1Presentation OutlineMotivation

Dimensions of utility-scale HAWTs

Vulnerability to earthquakes

Derivation of aerodynamic damping Fore-aft directionSide-to-side direction

Numerical example 1.5 MW NREL baseline turbine

Conclusions

2

Installed wind capacity map as of Jan 2011

United States National Seismic Hazard MapMotivation: Exposure of HAWTs to Earthquakes3

Approximate dimensions of a utility-scale HAWTFirst Period ~ 3 s

Dimensions and Period of HAWTs4No redundancy in the support structureSlender hollow sections (D/t as high as 280)Farms consisting of many nearly identical structuresLarge directional affect due to aerodynamic damping

Side-to-sideFore-aftVulnerability to Earthquakes5Aerodynamic Damping of HAWTs in the Fore-Aft DirectionForces 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

6

Aerodynamic Damping of HAWTs in the Side-to-Side Direction7Numerical Example 1.5 MW Baseline Turbine by NRELPower output1.5 MWHub Height84 mRotor Diameter70 mNumber of Blades3Max Rotational Speed20 rpmCut in wind speed5 m/sCut out wind speed25 m/sNacelle Mass51 TonHub Mass15 TonTower Mass123 TonRotor Mass11 TonActive Pitch ControlYes

[Base image from Nuta, 2010]8

Numerical Example 1.5 MW Baseline Turbine by NREL

Aerodynamic damping in the fore-aft direction with W=20 rpm and b=7.59Numerical Example 1.5 MW Baseline Turbine by NREL

Aerodynamic damping in the side-to-side direction with W=20 rpm and b=7.5

10 Aerodynamic damping in the fore-aft direction with b=7.5 (left) and W=20 rpm (right)

Numerical Example 1.5 MW Baseline Turbine by NREL

11 Numerical Example 1.5 MW Baseline Turbine by NREL

Aerodynamic damping in the side-to-side direction with b=7.5 (left) and W=20 rpm (right)

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FAST Derivation Numerical Example 1.5 MW Baseline Turbine by NRELValidation with FAST in the fore-aft direction with b=7.5 and W=20 rpm13Numerical Example 1.5 MW Baseline Turbine by NREL

Effect of aerodynamic damping on the seismic response with W=20 rpm14ConclusionsAerodynamic damping of operational wind turbines strongly depends on wind speed. For the considered example (1.5 MW turbine, W = 20 rpm, b = 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 direction15