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Title: Advances in the Assessment of Wind Turbine Operating Extreme Loads via More Efficient Calculation Approaches

Abstract

A new adaptive stratified importance sampling (ASIS) method is proposed as an alternative approach for the calculation of the 50 year extreme load under operational conditions, as in design load case 1.1 of the the International Electrotechnical Commission design standard. ASIS combines elements of the binning and extrapolation technique, currently described by the standard, and of the importance sampling (IS) method to estimate load probability of exceedances (POEs). Whereas a Monte Carlo (MC) approach would lead to the sought level of POE with a daunting number of simulations, IS-based techniques are promising as they target the sampling of the input parameters on the parts of the distributions that are most responsible for the extreme loads, thus reducing the number of runs required. We compared the various methods on select load channels as output from FAST, an aero-hydro-servo-elastic tool for the design and analysis of wind turbines developed by the National Renewable Energy Laboratory (NREL). Our newly devised method, although still in its infancy in terms of tuning of the subparameters, is comparable to the others in terms of load estimation and its variance versus computational cost, and offers great promise going forward due to the incorporation of adaptivity into themore » already powerful importance sampling concept.« less

Authors:
; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Wind and Water Technologies Office (EE-4W)
OSTI Identifier:
1357742
Report Number(s):
NREL/CP-2C00-67470
DOE Contract Number:
AC36-08GO28308
Resource Type:
Conference
Resource Relation:
Conference: Presented at the AIAA SciTech Forum: 35th Wind Energy Symposium, 9-13 January 2017, Grapevine, Texas
Country of Publication:
United States
Language:
English
Subject:
17 WIND ENERGY; wind turbines; load calculation; extreme load

Citation Formats

Graf, Peter, Damiani, Rick R., Dykes, Katherine, and Jonkman, Jason M.. Advances in the Assessment of Wind Turbine Operating Extreme Loads via More Efficient Calculation Approaches. United States: N. p., 2017. Web. doi:10.2514/6.2017-0680.
Graf, Peter, Damiani, Rick R., Dykes, Katherine, & Jonkman, Jason M.. Advances in the Assessment of Wind Turbine Operating Extreme Loads via More Efficient Calculation Approaches. United States. doi:10.2514/6.2017-0680.
Graf, Peter, Damiani, Rick R., Dykes, Katherine, and Jonkman, Jason M.. Mon . "Advances in the Assessment of Wind Turbine Operating Extreme Loads via More Efficient Calculation Approaches". United States. doi:10.2514/6.2017-0680.
@article{osti_1357742,
title = {Advances in the Assessment of Wind Turbine Operating Extreme Loads via More Efficient Calculation Approaches},
author = {Graf, Peter and Damiani, Rick R. and Dykes, Katherine and Jonkman, Jason M.},
abstractNote = {A new adaptive stratified importance sampling (ASIS) method is proposed as an alternative approach for the calculation of the 50 year extreme load under operational conditions, as in design load case 1.1 of the the International Electrotechnical Commission design standard. ASIS combines elements of the binning and extrapolation technique, currently described by the standard, and of the importance sampling (IS) method to estimate load probability of exceedances (POEs). Whereas a Monte Carlo (MC) approach would lead to the sought level of POE with a daunting number of simulations, IS-based techniques are promising as they target the sampling of the input parameters on the parts of the distributions that are most responsible for the extreme loads, thus reducing the number of runs required. We compared the various methods on select load channels as output from FAST, an aero-hydro-servo-elastic tool for the design and analysis of wind turbines developed by the National Renewable Energy Laboratory (NREL). Our newly devised method, although still in its infancy in terms of tuning of the subparameters, is comparable to the others in terms of load estimation and its variance versus computational cost, and offers great promise going forward due to the incorporation of adaptivity into the already powerful importance sampling concept.},
doi = {10.2514/6.2017-0680},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 09 00:00:00 EST 2017},
month = {Mon Jan 09 00:00:00 EST 2017}
}

Conference:
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  • Wind turbines are designed using a set of simulations to ascertain the structural loads that the turbine could encounter. While mean hub-height wind speed is considered to vary, other wind parameters such as turbulence spectra, sheer, veer, spatial coherence, and component correlation are fixed or conditional values that, in reality, could have different characteristics at different sites and have a significant effect on the resulting loads. This paper therefore seeks to assess the sensitivity of different wind parameters on the resulting ultimate and fatigue loads on the turbine during normal operational conditions. Eighteen different wind parameters are screened using anmore » Elementary Effects approach with radial points. As expected, the results show a high sensitivity of the loads to the turbulence standard deviation in the primary wind direction, but the sensitivity to wind shear is often much greater. To a lesser extent, other wind parameters that drive loads include the coherence in the primary wind direction and veer.« less
  • No abstract prepared.
  • Wind turbines are designed using a set of simulations to ascertain the structural loads that the turbine could encounter. While mean hub-height wind speed is considered to vary, other wind parameters such as turbulence spectra, sheer, veer, spatial coherence, and component correlation are fixed or conditional values that, in reality, could have different characteristics at different sites and have a significant effect on the resulting loads. This paper therefore seeks to assess the sensitivity of different wind parameters on the resulting ultimate and fatigue loads on the turbine during normal operational conditions. Eighteen different wind parameters are screened using anmore » Elementary Effects approach with radial points. As expected, the results show a high sensitivity of the loads to the turbulence standard deviation in the primary wind direction, but the sensitivity to wind shear is often much greater. To a lesser extent, other wind parameters that drive loads include the coherence in the primary wind direction and veer.« less
  • This paper summarizes the control design work that was performed to optimize the controller of a wind turbine on the WindFloat structure. The WindFloat is a semi-submersible floating platform designed to be a support structure for a multi-megawatt power-generating wind turbine. A controller developed for a bottom-fixed wind turbine configuration was modified for use when the turbine is mounted on the WindFloat platform. This results in an efficient platform heel resonance mitigation scheme. In addition several control modules, designed with a coupled linear model, were added to the fixed-bottom baseline controller. The approach was tested in a fully coupled nonlinearmore » aero-hydroelastic simulation tool in which wind and wave disturbances were modeled. This testing yielded significant improvements in platform global performance and tower-base-bending loading.« less
  • Proper prediction of long-term extreme values for operating wind turbine loads and deflections is a critical component of wind turbine design. Direct observations or simulations of long-term extremes are not yet available; therefore, these predictions rely on some combination of large numbers of simulations and extrapolation. Extrapolation methods themselves can have significant uncertainty, and they also require that the wind turbine designer have a greater level of statistical expertise--factors that make the methods less attractive for industrial application. As an alternative to extrapolation, safety factors can be calibrated using techniques that allow designers to use smaller data sets. To calculatemore » such factors, a series of simulations was used to extrapolate 50 year extreme values for a 5 MW wind turbine. Two methods are proposed for calculating such safety factors: one based on the mean and standard deviation of extreme values, and one based on the median of extreme values. Through a process of random sampling without replacement, the safety factor based on the median of extreme values was found to be less variable and also more independent of the number of simulations. The safety factors required were as large as 1.7, or were only 1.25 if rotor thrust loads were considered the dominant design drivers.« less