The determination of modal parameters from experimental data of linear and nonlinear aeroelastic systems /

The determination of the modal parameters of an airplane wing, such as damping and natural frequency, as well as the determination of the aircraft's flutter speed, is an important part of aircraft design and testing. The effect that a 'defect' can have on the system, such as a loose hinge or worn fastening, is also an important part of aircraft analysis.In this study, a two-dimensional, symmetrical airfoil was mounted as part of a linear system in a wind tunnel, subject to steady, incompressible flow. Experimental data was collected using both free and forced vibrations of the airfoil, at different increments of airspeed. This data was then analyzed using conventional modal analysis techniques, extracting the damping factor and the natural frequency of the system, thus enabling a value for the flutter speed to be calculated.A structural freeplay nonlinearity was then introduced into the system, mimicking the effects a loose hinge or worn fastening can have on the airfoil modal parameters. The same tests were performed, and the modal parameters were evaluated using special nonlinear parameter extraction techniques. The behaviour of the damping and natural frequency of the nonlinear system, obtained from all three methods of data collection, were then compared to those of the linear system