Efficient models for wind turbine extreme loads using inverse reliability

Abstract

The reliability of wind turbines against extreme loads is the focus of this study. A procedure to establish nominal loads for use in a conventional load-and-resistance-factor-design (LRFD) format is presented. The procedure, based on an inverse reliability approach, permits inclusion of randomness in the gross wind environment as well as in the extreme response given wind conditions. A detailed example is presented where three alternative nominal load definitions are used to estimate extreme bending loads for a 600kW three-bladed horizontal-axis wind turbine. Only operating loads -here, flapwise (out-of-plane) bending moments -at a blade root are considered but the procedure described may be applied to estimate other loads and response measures of interest in wind turbine design. Results suggest that a full random characterization of both wind conditions and short-term maximum response (given wind conditions) will yield extreme design loads that might be approximated reasonably well by simpler models that include only the randomness in the wind environment but that account for response variability by employing appropriately derived "higher-than-median" fractiles of the extreme bending load conditional on inflow parameter values.

Design Loads for Wind Turbines Using the Environmental Contour Method

“…Details related to the theoretical framework for the application of the method can be found elsewhere. 11,13,17 Since the method is derived from the classical First-Order Reliability Method (FORM), it assumes that in the space of the random variables affecting performance of the structure under consideration, the safe and unsafe regions are separated by a linear limit state hyperplane. Also, the EC method only considers the environmental variables as random; a contour associated with the desired probability of failure, p f , is constructed, and the largest "median" extreme load with different environmental variables on the p f contour is sought.…”

“…The method is approximate for two reasons: (i) it ignores response variability as already pointed out; and (ii) it assumes linear limit state surfaces that separate the "safe" domain from the "unsafe' domain of random variables in the problem. Recently, Peeringa, 9 Fitzwater et al, 12 and Saranyasoontorn and Manuel 13 demonstrated how the EC method could be applied to establish ultimate wind turbine blade bending design loads for various wind turbines.…”

HLRF‐BFGS‐Based Algorithm for Inverse Reliability Analysis

“…As an extension of this method to general limit states, Der Kiureghian et al [11] developed an algorithm, inverse-FORM, which was based on the Hasofer Lind Rackwitz Fiessler (HLRF) algorithm [12][13][14]. This inverse reliability method was used by other researchers for various applications including extreme and nominal loads on wind turbines [15,16] and critical earthquake loads [17]. This HLRF-based method was found to have a fast convergence as demonstrated by the numerical examples considered by Der Kiureghian et al [11].…”

“…In the calculation of d 2 in (13), the values of d 2 , and 2 are calculated using the following formulae instead of (16) and (17):…”

Investigation of Site-Specific Wind Field Parameters and Their Effect on Loads of Offshore Wind Turbines

“…These methods transform the physical environmental variables (e.g., wind speed, turbulence intensity, wave hight) into random variables in the standard normal space. The inverse first-order reliability method, which is based on the Environmental Contours (EC) method, is presented in [6,14]. For example, the EC method has been used by [15,16].…”