This thesis deals with the design of a sensing system for the early detection of aeroelastic instability known as flutter. The proposed system uses two piezoelectric sensors attached with different directional orientations. Due to this configuration, the sensors exhibit different sensitivity to bending and torsional vibration of a flexible structure.
The response of the sensing system was first investigated on a designed experimental structure. The main requirement for the structural design was to enable simple excitation of bending and torsional mode shapes at low frequencies. The experimental part also included measurements of the piezoelectric sensor response during shaker excitation. The obtained results were compared with numerical response modelling in Ansys.
Based on the experimental and numerical results, an analytical computational procedure was developed to transform the mechanical response of the structure into the electrical voltage of the piezoelectric sensors. The model is based on a simplified description of the structure using two generalized coordinates corresponding to bending-torsional vibration, represented by vertical displacement and rotation angle. These quantities were used to determine strains at the sensor locations, and the electrical response was then calculated using the constitutive relations of piezoelectric materials.
An aeroelastic model of the structure with aerodynamic excitation and feedback was then created. A nonlinear dependence of the lift coefficient on the wing angle of attack was considered for the selected profile. The stability of the system was evaluated using time responses, bifurcation diagrams and eigenvalue analysis.
Finally, a virtual piezoelectric sensing system was incorporated into the model. Changes in amplitude, frequency, period and relative phase between the two piezoelectric sensors were evaluated. The results show that differently oriented piezoelectric sensors can provide information about changes in the character of the structural response.