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FP5

RECOFF Résumé de rapport

Project ID: ENK5-CT-2000-00322
Financé au titre de: FP5-EESD
Pays: Denmark

Probabilistic methods

Scientific aspects of the result:
The focus has been on determining partial safety factors and characteristic values for combined extreme wind and wave load effects in the storm situation. However fatigue loads have also been examined.

Social and commercial aspects of the result:
There has been an immediate need for the project. Currently and over the next few years, the expansion in offshore wind energy, especially in Europe, accelerates and at project start there were no thorough and coherent guidelines for the design of offshore wind power plants. The existing offshore standards are not suitable to cover the offshore wind energy technology.

A combination of these offshore standards and the existing onshore wind energy standards is a very complex process and significant technology gaps exist. One of the major tasks of the project has been the attempt to combine the practices of wind turbines engineering and offshore engineering. According to the main results stated in the executive summary the project has succeeded in this, and thus it is the view of the project partners that the project outcome has aided a development with the potential of preventing erroneous decision-making on large investments in Europe on a technical weak basis.

Potential applications for and End-users of the result:
End-users are designers of offshore wind turbines i.e. manufactures, certifying bodies, writers of standards and regulations, and possibly owners and operators of offshore wind farms.

Innovative features:
As in many other aspects of this project the challenge has been to find a way to combine the tradition of offshore engineering and wind turbine engineering. This has involved a discussion of the level of structural reliability of onshore wind turbines on the one side and the reliability of offshore structures on the other. The outcome of a case study based on the background study for the latest revision of the ISO standard for fixed offshore steel structures and a background study for the latest revision of the IEC 61400-1 Ed. 3 has shown that it is possible to merge the traditions of using 3h reference periods for wave loads and 10 minute reference periods for wind loads as long as the same load partial safety factor, e.g. 1.35, and the same return period are used. Comparison of safety levels suggests, in accordance with the practise regarding exposure levels proposed in the ISO standard, using a return period of 50 years instead of the usual 100 years for offshore structures is allowed. This implies a reduction of costs mainly for the support structure.

Contact

Niels Jacob TARP-JOHANSEN, (Senior Scientist)
Tél.: +45-4677-5078
Fax: +45-4677-5960
E-mail