Abstract

Oscillations can arise spontaneously due to the interaction of a steady background flow and an elastic structure. Examples include flutter of aircraft wings, swaying of bridges, speech generation in vocal cords and seismic oscillation excited by underground magma flows.

In the first part of the talk, I describe a mechanism for the excitation of the elastic modes of oscillation through a linear instability. These mode are by definition decoupled from each other in vacuo, but may interact with each other owing to the surrounding fluid. The mechanism I will describe involves this interaction as the essential destabilizing agency.

In the second part of the talk, I consider the modes of an acoustic cavity instead of an elastic body. An example of such a phenomena is the sound generated by blowing across a bottle, which I will analyze from the perspective of a linear instability. The role of elasticity may be considered to be played by compressibility of air in the acoustic cavity. However, the essential mechanism in this case involves the interaction between the blown jet and acoustic perturbations in the cavity.