FLUTTER PREDICTION USING AN EIGENVECTOR ORIENTATION APPROACH

A method for predicting the onset of coupled-mode flutter is presented . A distinguishing characteristic of this method is that it emphasizes eigenvectors rather than eigenvalues. In the popular methods based on eigenvalues, flutter is predicted as instability begins to occur, as evidenced by the movement of one or more eigenvalues from the left-han d to the right-hand side of the s-plane, or the coalescence of eigenva lues. Alternatively, the method of eigenvector orientation being prese nted has the potential to predict the occurence of instability. Althou gh the eigenvectors of vibrating systems generally satisfy the orthogo nality condition, there are certain cases In aeroelasticity in which t hey are not orthogonal. In a typical case of coupled-mode flutter, the eigenvectors initially may be oriented orthogonally but gradually los e orthogonality as airspeed is varied. The consequence of such a progr essive loss of eigenvector orthogonality on structural dynamics is a p henomenon that seems to warrant further investigation. This investigat ion has applications in areas such as helicopter dynamics, aeroelastic analysis of plate and shell structures, analysis of slightly mistuned bladed disk assemblies, and rotordynamics.