Loads Measurement and Validation of a 2.1-kW HAWT on a Fiberglass Composite Tower Scott Dana, Rick Damiani, Jeroen van Dam

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1 Loads Measurement and Validation of a 2.1-kW HAWT on a Fiberglass Composite Tower Scott Dana, Rick Damiani, Jeroen van Dam Small Wind Conference 2016 June 13 th June 15 th

2 Motivation Ongoing efforts to improve system dynamic modeling and prediction Assess common industry practice loads derivation methods Evaluate IEC Simplified Loads Approach Address fatigue loads more comprehensively 2

3 Design Load Derivation Methods 1. Full-Scale Loads Measurements (Field) A 2.1-kW, free yaw, variable-speed, downwind machine An AnemErgonics, LLC 18-m multisection fiberglass composite tower Meteorological data recorded at hub height Tower strain measured at 0.8 m above tower hinge plate Full bending bridges in two orthogonal directions 2. Aeroelastic Modeling (FAST) FAST v 7.02 utilized Turbulent wind files, 3 seeds, with reference wind speeds of 2, 4,24, 26 m/s Turbulence intensity of 18% Air density of 1.0 kg/m 3 to match site conditions Tower drag not modeled 3. Simplified Loads Approach (SLA) IEC design load cases (DLCs) A (fatigue), H, and I (ultimate loads) Input parameters derived from the FAST model, preliminary test results, and turbine dimensions SLA load components used to determine the tower-base bending moment 3

Full-Scale Loads Measurements Approach Wind Vane Primary Anemometer Reference Anemometer Temperature and Pressure Measurement sector of 223 to 333 of true north following IEC

(from true North) X Bending Bridge 5 Y Bending Bridge Tower Strain full bridge orientation and loads configuration Tower-Base Bending Bridge Location Met tower and instrumentation

4 Full-Scale Loads Measurements Approach Wind Vane Primary Anemometer Reference Anemometer Temperature and Pressure Measurement sector of 223 to 333 of true north following IEC Measurement methods and loads processing following IEC Coordinate transformation applied to loads M y 285 X (approximate prevailing wind direction) 195 Y M x 15 (from true North) X Bending Bridge 5 Y Bending Bridge Tower Strain full bridge orientation and loads configuration Tower-Base Bending Bridge Location Met tower and instrumentation used for field test campaign (Photo by Scott Dana, NREL) Test article used for full-scale loads measurement with identification of tower strain gage locations (Photo by Rick Damiani, NREL) 4

Measurement Data Acquisition System DAS Enclosure NI cdaq Chassis and Input Modules Sampled at 35 khz Stored at 0 Hz 1,332 -Minute data files within

5 Measurement Data Acquisition System DAS Enclosure NI cdaq Chassis and Input Modules Sampled at 35 khz Stored at 0 Hz 1,332 -Minute data files within measurement sector for Loads Calculations 3,482 -Minute data files for Fatigue Calculations (all operating data) Communication one-line for tower loads DAS 5

6 Bending Moment [knm] Simplified Loads Approach Maximum Bending Moments SLA DLCs for tower analysis: IEC DLC H Extreme wind speed of 59.5 m/s A normally parked turbine Total Moment = 80 knm IEC DLC I 42.5 m/s wind speed Maximum exposure (yaw mechanism failure) A no-yaw-error configuration in this case Total Moment = 47 knm knm 47 knm Rotor Drag Nacelle Drag Tower Drag 0 Load Case H Load Case I Component-drag contributions to the total combined tower-base bending moment for DLCs H and I DLC H develops the greatest bending moment Tower Design Driver 6

7 FAST and Field Bending Moments Results Bending Moment [kn-m] Bending Moment [kn-m] Field Max Field Mean Field Min FAST Max FAST Mean FAST Min Wind Speed [m/s] Ten-minute statistical comparison of the Field and FAST tower-base ultimate loads in the fore-aft (top) and side-to-side (bottom) directions Deviation between Field and FAST is likely a result of the actual turbine control system mitigating loads at high wind speeds (18 m/s and above) For the captured wind speeds FAST and field loads are within the load envelope of DLCs H and I Less than 47 knm (DLC I) Loads extrapolation of the field-measured loads is required for a proper comparison with SLA results a future work item of this study. 7

8 Load Range DEL Bending Moment [knm] Fatigue Loads Comparison Damage Equivalent Loads m = 3 m = 6 m = Field Fore-Aft FAST Fore-Aft SLA Fore-Aft Three different S-N curves Rayleigh distribution of wind speed 20-year design life SLA DELs by IEC DLC A Peak-to-peak thrust load 20-yr # of rated rotor speed Tower-base 1-Hz lifetime (20 years); DELs at zero mean for Field, FAST, and SLA with S-N curves with inverse exponent values (m) of Illustration 3, 6, and of the effect of a chosen S-N curve slope on the DEL for a high load range (S FAST ) at a low number of cycles (N FAST ) and vice versa (S SLA, N SLA ) S FAST m = Significant effect of material properties S-N curve exponent! S SLA m = 3 N FAST N eq N SLA Cycles 8

9 Fatigue Loads Comparison Continued min DEL [knm] Fore-aft Field Fore-aft FAST Although similar, FAST s over-prediction of high-range loads compared to the Field spectra are demonstrated. This outcome is consistent with the ultimate loads comparison. Fore-aft Field Fore-aft FAST SLA Value Wind Speed [m/s] Short-term ( minute) fore-aft tower-base bending moment DELs versus the mean wind speed for an S-N curve with m = The SLA DLC A yields a single fatigue load range value of knm, with a cycle count of.4e9. Load Range [knm] Cumulative Cycles Load range = knm Cycle Count =.4e9 Fore-aft tower-base bending moment cumulative fatigue spectra comparison of field-measured loads and FAST predictions 9

10 Final Remarks This study focused on tower-base bending moments of a horizontal-axis wind turbine to provide an indication of the overall performance of the load derivation methods. Notable outcomes include the following: The SLA DELs are different than those calculated from the Field and FAST data; o o High dependence on the assumed S-N curve slope and the number of cycles. SLA DEL more conservative for steel (m = 3 to 6) and less conservative for composites (m =). Better agreement between the field and FAST predictions for side-to-side than for fore-aft bending at high wind speeds; o Likely caused by a lower fidelity turbine control model used in the FAST simulations. The fatigue spectra reveals FAST s over-prediction of large cycles. SLA does not comprehensively address fatigue; o Conservative and coarse one load range at one cycle count. We recommend that this study be repeated with wind turbines of different configurations and sizes, and that field load extrapolation be conducted.

11 Acknowledgements The Authors of this work would like to sincerely thank Paul Migliore of AnemErgonics for allowing his tower and turbine to be used for the field measurement campaign of this study. The Presenter would like to thank Rick and Jeroen for their excellent mentorship and guidance throughout the project. 11

12 Thank you! Questions?

Possible Approaches to Turbine Structural Design

1 Possible Approaches to Turbine Structural Design Rick Damiani, Ph.D., P.E. Jeroen van Dam National Wind Technology Center NREL - 11/13/14 Turbine Design Possible Approaches It is some sort of tragedy