Virtual assessment of structural health monitoring techniques for wind turbines using vibration data

Operational Modal Analysis (OMA), also known as output-only modal analysis, allows identifying modal parameters only by using the response measurements of the structure in operational conditions when the input forces cannot be measured. This information can then be used to improve numerical models in order to monitor the operating and structural conditions of the system. This is a critical aspect both for condition monitoring and maintenance of large wind turbines, particularly in the off-shore sector where operation and maintenance represent a high percentage of total costs. The availability of commercial numerical aeroelastic simulation codes simulating the response of wind turbines in operation can be used as a virtual design and verification tool. Effects of design modifications and variations in the environmental and structural conditions can all be simulated using these tools. However, experimental test campaigns should be able to provide accurate and reliable data with which the model can be updated and be more representative of the real response. Thus, the improvement of these simulation models is strongly related to the improvement of the current Operational Modal Analysis (OMA) modal parameter estimation techniques. The main issue for these methods is that, due to blade rotation, force periodicity and the presence of control surfaces which modify continuously the system configuration, most of the applicability assumptions of OMA are violated. In this paper, some preliminary assessments on how to combine numerical and experimental techniques for Structural Health Monitoring (SHM) of wind turbines are investigated.