State estimation in elastic mechanical structures under unknown excitation on the example of wind turbines

The present dissertation introduces a thorough and consistent framework for model-based estimation of elastic deformations in wind turbine support structures which solely relies on inertial sensor provided by so-called Inertial Measurement Units (IMU). An IMU is essentially a combination of accelerometers and gyroscopes that convinces through its vibrational robustness and comparably low cost. The analyses presented are in fact driven by but not restricted to wind turbine systems, since fundamental aspects similarly apply to general elastic mechanical structures. In contrast to traditional strain-based fatigue estimation schemes, the IMU-based sensor concept requires thorough and carefulf signal processing to extract information on the structural deformation fields. As a central idea of the developed framework, the wind turbine support structure is divided into individual mechanical substructures for the tower and the rotor blades. Recovery of deformation fields is then performed for each subsystem independently by means of a classical state observer scheme which requires a suitable mathematical model of the substructure under consideration. A model representation is regarded suitable in this context if it is able to represent the structural dynamics of the relevant wind turbine components and provide consistent stress and strain recovery. Therefore, the promising Nodal-based Floating Frame of Reference (NFFR) formulation is pursued and analyzed in detail within this thesis, as it allows to derive the corresponding Equations Of Motion (EOM) for each substructure based on standard data provided by every commercial finite element software environment. The preformance of the proposed state estimation framework is demonstrated by application to different simulation models with gradually increasing complecity as well as by practical test scenarios using a small-scale wind turbine.