Blades of opportunity?

As offshore wind turbine blades get larger.

Wind Turbine Blades
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The increasing length of offshore wind turbine blades has prompted the use of advanced composite materials – with positive operational experiences so far. There is however a limited range of supporting analysis and testing methods that can be directly applied to large-scale wind turbines.
Det Norske Veritas (DNV) initiated an innovation project to develop improved integrity assessment procedures for large-scale offshore wind turbines in January 2011 and has joined the Joint Industry Project (JIP) consortium which focuses on advanced composites for wind turbines. 

The JIP utilises Instron’s experience in biaxial testing of composites with various flaws introduced, the combined finite element analysis expertise of DNV and the Energy Research Institute @ Nanyang Technological University (ERI@N) and the industry knowledge of Vestas, the project aims to provide insight into composite failure in wind turbine blades. From this, DNV will develop integrity management procedures for advanced composite wind turbine blades.

“As a natural consequence of the ambitious plans and targets set for renewable energy in many countries, we are seeing increasing projections on the amount of wind power being fed into the grid”, says managing director Bjørn Tore Markussen of DNV’s Clean Technology Centre (CTC) in an official DNV release. 

“The increased expectations for wind power generation have led to growth in wind turbine size, particularly in offshore wind. The technical and potential quality issues faced in such a rapid growth phase can be overcome by cross-industry collaboration to develop best practices, such as this project”.

Most offshore wind projects face the possibility of extreme weather conditions, which complicates key technical and operational issues such as material selection and blade manufacturing quality as well as assessment of the remaining life of blades that have sustained damage due to extreme loading. 

The integrity management procedures developed by the DNV innovation project will utilise results from the JIP to assess the integrity of advanced composite offshore wind turbine blades. The goal is to enable more accurate predictions of the remaining life of wind turbine blades, however tough the environment.

Professor Subodh Mhaisalkar, executive director of ERI@N, added: “In the first phase of this JIP, the research is addressing the development of biaxial testing methods and finite element analysis procedures that will enable development of test data for deriving and verifying models for flaw growth in the composites. This is required for remaining life predictions with regard to pre-existing manufacturing flaws or service-induced damage. 

“This project could be an important contribution to the wind industry, as the project can be extended to develop future standards, guidelines and procedures on the matter.”

Says Peter Cheng, Vestas vice president for Asia Innovation, “Vestas agrees that more work and data in this area would be valuable in helping the industry to develop better and more reliable products.” 

Markussen concludes, “We are confident that the development of a set of integrity management procedures will benefit companies that move into the evolving offshore wind industry. We therefore invite new participants from the offshore wind industry to join the next phase of the JIP.” 

Tore Høifødt

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