Fatigue design load calculations of the offshore NREL 5 MW benchmark turbine using quadrature rule techniques

Laurent Van Den Bos,Wim Bierbooms,Armando Alexandre,Benjamin Sanderse,Gerard Van Bussel

doi:10.1002/we.2470

Laurent Van Den Bos, Wim Bierbooms + Show 3 more

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https://doi.org/10.1002/we.2470

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Abstract

AbstractA novel approach is proposed to reduce, compared with the conventional binning approach, the large number of aeroelastic code evaluations that are necessary to obtain equivalent loads acting on wind turbines. These loads describe the effect of long‐term environmental variability on the fatigue loads of a horizontal‐axis wind turbine. In particular, Design Load Case 1.2, as standardized by IEC, is considered. The approach is based on numerical integration techniques and, more specifically, quadrature rules. The quadrature rule used in this work is a recently proposed “implicit” quadrature rule, which has the main advantage that it can be constructed directly using measurements of the environment. It is demonstrated that the proposed approach yields accurate estimations of the equivalent loads using a significantly reduced number of aeroelastic model evaluations (compared with binning). Moreover, the error introduced by the seeds (introduced by averaging over random wind fields and sea states) is incorporated in the quadrature framework, yielding an even further reduction in the number of aeroelastic code evaluations. The reduction in computational time is demonstrated by assessing the fatigue loads on the NREL 5 MW reference offshore wind turbine in conjunction with measurement data obtained at the North Sea, for both a simplified and a full load case.

Highlights

For the certification of the design of a wind turbine, various load cases have been formulated in the IEC 61400 standard for both onshore [19] and offshore [20] wind turbines
In this work arguably one of the most costly load cases is considered: Design Load Case (DLC) 1.2, describing fatigue loading for a power producing offshore wind turbine under regular environmental conditions
As the time span of this load case is the full lifetime of the turbine, a large number of model runs is necessary to assess the statistics of the fatigue loading

Summary

Introduction

For the certification of the design of a wind turbine, various load cases have been formulated in the IEC 61400 standard for both onshore [19] and offshore [20] wind turbines. The conventional approach to assess the effect of environmental variability on the turbine lifetime is to firstly split the domain of the variables describing the environmental conditions in bins, secondly run the aeroelastic model several times in each bin (the so-called seeds), and determine the quantity of interest (e.g. the weighted equivalent load) incorporating the probability of occurrence of each bin. This approach is suggested in the aforementioned standard [19, 20] and has been successfully applied in previous research [1, 14, 31]

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