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Spotting invisible cracks in wind turbines: simply

February 12, 2013 | By Anthony Capkun

February 12, 2013 – A new approach is being developed for monitoring the structural health of wind turbine components during exposure to turbulence in real time.

Physicists have developed a new method for analyzing the elastic characteristics of mechanical structures subjected to disturbances, akin to the turbulences affecting wind turbines. (These results are about to be published by Philip Rinn and his colleagues at the ForWind Center for Wind Energy Research at the University of Oldenburg, Germany.)

Turbine components weaken under turbulent air flow conditions, say researchers, making failures and eventual replacement a significant percentage of the cost of wind energy. The challenge for the team was to find a method for detecting fatigue in the wind turbines’ parts without: a) having to remove each of the components and b) while the turbine is in operation.

Researchers say that until now, standard methods have relied on “so-called spectral analysis”, which looks at differing frequency response, but these measurements are distorted by the turbulent working conditions. As a result, these detection methods often only detect really major damage, like a crack that covers more than 50% of a blade, says the team.

The authors used a simple experimental set-up of undamaged and damaged beam structures and exposed them to excitations containing an element of interfering vibrations, or noise, made by different turbulent wind conditions.

The analytical method they developed enabled them to distinguish between dynamics attributed to mechanical properties, such as stiffness of the blade, and those attributed to interfering noise, such as turbulence. The authors demonstrated that they were able to precisely detect the changing mechanical properties of the beam material based on an analysis of the mechanical vibrations. Ultimately, when the method is further refined, this could be used to identify material fatigue or untightened screws, for example, and may even be applied to more complex structures, such as automotive or airplane parts.

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