Journal cover Journal topic
Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
https://doi.org/10.5194/wes-2018-43
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research articles
13 Jun 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Wind Energy Science (WES).
Reducing the number of load cases for fatigue damage assessment of offshore wind turbine support structures by a simple severity-based sampling method
Lars Einar S. Stieng and Michael Muskulus Department of Civil and Environmental Engineering, Norwegian University of Science and Technology NTNU, Trondheim, Norway
Abstract. The large amount of computational effort required for a full fatigue assessment of offshore wind turbine support structures under operational conditions can make these analyses prohibitive. Especially for applications like design optimization, where the analysis would have to be repeated for each iteration of the process. To combat this issue, we present a simple procedure for reducing the number of load cases required for an accurate fatigue assessment. After training on one full fatigue analysis of a base design, the method can be applied to establish a deterministic, reduced sampling set to be used for a family of related designs. The method is based on sorting the load cases by their severity, measured as the product of fatigue damage and probability of occurrence, and then calculating the relative error resulting from using only the most severe load cases to estimate the total fatigue damage. By assuming this error to be approximately constant, one can then estimate the fatigue damage of other designs using just these load cases. The method yields a maximum error of about 6 % when using around 30 load cases (out of 3647) and, for most cases, errors of less than 1–2 % can be expected for sample sizes in the range 15–60. One of the main points in favor of the method is its simplicity when compared to more advanced sampling-based approaches. The method as is can be used without further modifications and is especially useful for design optimization and preliminary design. We end the paper by noting a few possibilities for future work that extend or improve upon the method.
Citation: Stieng, L. E. S. and Muskulus, M.: Reducing the number of load cases for fatigue damage assessment of offshore wind turbine support structures by a simple severity-based sampling method, Wind Energ. Sci. Discuss., https://doi.org/10.5194/wes-2018-43, in review, 2018.
Lars Einar S. Stieng and Michael Muskulus
Lars Einar S. Stieng and Michael Muskulus
Lars Einar S. Stieng and Michael Muskulus

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Short summary
This study was done in order to simplify the analysis needed for the assessment of safety criteria that offshore wind turbine support structures must satisfy. The work was done via simulations of the system and computations and analyses of the resulting data. The results show that the proposed methodology has great potential for simplifying the assessment procedure while retaining acceptable accuracy compared to the full analysis. There are several applications within both research and industry.
This study was done in order to simplify the analysis needed for the assessment of safety...
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