State Observation in Beam-Like Structures Under Unknown Excitation

Measuring and logging of fatigue loads is essential for individual life time estimations of dynamically loaded mechanical structures like operating wind turbines. A fundamental intermediate step is the accurate derivation of structural displacement fields at all critical spots, for which, in practical applications usually only a limited number of sensor information is available. Another challenge is the generally unknown system excitation, e.g. by wind loads. This contribution investigates fundamental requirements for the implementation of Unknown Input Observers (UIO) on flexible mechanical systems. To also account for large nonlinear motions, we propose a substructuring approach, which is demonstrated and validated by two numerical examples: (1) A finite element model of a comparatively simple cantilever beam structure, (2) A detailed flexible multibody model of a small-scale wind turbine test stand.