Abstract
The offshore wind industry is growing rapidly meanwhile the first offshore wind projects approaches the end of their design lifetime. This currently increases the enticement to develop new innovative methods that enable the offshore wind industry to explore and realize the lifetime extension potential of ageing and even future windfarms.
In this context the present paper proposes a novel virtual sensing scheme that constitute a highly accurate and robust method for indirect measurement of the stress state in any point of a monopile supported wind turbine structure. The virtual sensing method relies on expansion of double integrated accelerations and inclinations measured in 3 locations of the tower structure, which by a linear combination with Ritz-vectors and mode shapes at low and high frequencies, enables the evaluation of stresses in the wind turbine support structure.
The validity of the proposed virtual sensing method is assessed on a 25-days dataset from an offshore wind turbine (Vattenfall Test Center), equipped with accelerometers in the tower and strain gauges as reference measurements in the foundation. It is demonstrated that the virtual sensing method provides stress range uncertainties below 3% when compared to stress ranges based on the strain gauge measurements.
