Cyclic loadings produce progressive damage that can ultimately result in wind turbine structural failure. There are many issues that must be dealt with in turning load measurements into estimates of component fatigue life. This paper deals with how the measured loads can be analyzed and processed to meet the needs of both fatigue life calculations and reliability estimates. It is recommended that moments of the distribution of rainflow-range load amplitudes be calculated and used to characterize the fatigue loading. These moments reflect successively more detailed physical characteristics of the loading (mean, spread, tail behavior). Moments can be calculated from data samples and functional forms can be fitted to wind conditions, such as wind speed and turbulence intensity, with standard regression techniques. Distributions of load amplitudes that accurately reflect the damaging potential of the loadings can be estimated from the moments at any wind condition of interest. Fatigue life can then be calculated from the estimated load distributions, and the overall, long-term, or design spectrum can be generated for any particular wind-speed distribution. Characterizing the uncertainty in the distribution of cyclic loads is facilitated by using a small set of descriptive statistics for which uncertainties can be estimated. The effects of loading parameter uncertainty can then be transferred to the fatigue life estimate and compared with other uncertainties, such as material durability.

1.
Barnard, J. C., and Wendell, L. L., 1997, “A Simple Method of Estimating Wind Turbine Blade Fatigue at Potential Wind Turbine Sites,” ASME JOURNAL OF SOLAR ENERGY ENGINEERING, Vol. 119, No. 2, Aug. 1997.
2.
Connell, J. R., Morris, V. R., Powell, D. C., and Glower, G. L., 1988, “The PNL Single-Tower Measurement Model of Rotationally Sampled Turbulent Wind, With User’s Guide for STRS2PC,” PNL-6580, Pacific Northwest Laboratories, Richland, WA.
3.
IEA, 1990, Expert Group Study on Recommended Practices for Wind Turbine Testing and Evaluation, 3. Fatigue Loads, 2. Edition 1990, P. H. Madsen, ed., International Energy Agency Programme for Research and Development on Wind Energy Conversion Systems, Riso National Laboratory, Denmark.
4.
Jackson, K., 1992, “Deriving Fatigue Design Loads from Field Test Data,” Proc. WindPower ’92, American Wind Energy Association, pp. 313–320.
5.
Kashef, T., and Winterstein, S. R., 1998, “Relating Turbulence to Wind Turbine Blade Loads: Parametric Study with Multiple Regression Analysis,” Proceedings, 1998 ASME Wind Energy Symposium, W. Musial, and D. Berg, eds., Presented at the 36th AIAA Aerospace Sciences Meeting and Exhibit, AIAA-98-0057, Reno, NV, Jan. 12–15, 1998.
6.
Kelley, N. D., 1993, “The Identification of Inflow Fluid Dynamics Parameters That Can Be Used to Scale Fatigue Loading Spectra of Wind Turbine Structural Components,” NREL/TP-442-6008, National Renewable Energy Laboratory, Golden, CO.
7.
Lange, C. H., and Winterstein, S. R., 1996, “Fatigue Design of Wind Turbine Blades; Load and Resistance Factors from Limited Data,” Energy Week–Wind Energy Symposium, L. L. Schluter ed., ASME, SED Vol. 17, 1996.
8.
Lange, C. H., 1996, “Probabilistic Fatigue Methodology and Wind Turbine Reliability,” SAND96-1246, UC-1211, Contractor Report, Sandia National Laboratories, Albuquerque, NM.
9.
Neter, J., Kutner, M. H., Nachtsheim, C. J., and Wasserman, W., 1996, Applied Linear Statistical Models, 4th edition, Irwin.
10.
Ronold, K. O., Wedel-Heinen, J., Christensen, C. J., and Jorgensen, E., 1994,“Reliability Based Calibration of Partial Safety Factors for Design of Wind Turbine Rotor Blades Against Fatigue,” Proc., 5th European Wind Energy Conf., Vol. II, Thessaloniki, Greece, pp. 927–933.
11.
SAE, 1988, Fatigue Design Handbook, 2nd edition, R. E. Rice, ed., AE-10, Society of Automotive Engineers, Warrendale, PA.
12.
Schluter, L. L., and Sutherland, H. J., 1990, “Rainflow Counting Algorithm for the LIFE2 Fatigue Analysis Code,” Proc., Ninth ASME Wind Energy Symposium, D. E. Berg, ed., ASME SED Vol. 9, Jan. 1990, pp. 121–123.
13.
Sutherland, H. J., 1989, “Analytical Framework for the LIFE2 Computer Code,” SAND89-1397, Sandia National Laboratories, Albuquerque, NM.
14.
Sutherland, H. J., and Wilson, T. A., 1996, “A Generalized Fitting Technique for the LIFE2 Fatigue Analysis Code,” SAND96-1992, UC-1211, Sandia National Laboratories, Albuquerque, NM.
15.
Veers
P. S.
,
1982
, “
Blade Fatigue Life Assessment with Application to VAWTs
,”
ASME JOURNAL OF SOLAR ENERGY ENGINEERING
, Vol.
104
, No.
2
, pp.
106
111
, May 1982.
16.
Veers, P. S., Winterstein, S. R., Lange, C. H., and Wilson, T. A., 1994, “User’s Manual for FAROW: Fatigue and Reliability of Wind Turbine Components,” SAND94-2460, Sandia National Laboratories, Albuquerque, NM.
17.
Winterstein, S. R., and Lange, C. H., 1995, “Load Models for Fatigue Reliability from Limited Data,” Wind Energy-1995, W. Musial, ed., ASME, SED Vol. 16, 1995.
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