Aerodynamic Self Excitation of a Taut Elastic Ribbon

The investigators analyzed, both theoretically and experimentally, the motion of a taut ribbon of elastic material in an air stream to show that the resulting standing-wave motion is a manifestation of self excitation. Self excitation is a phenomenon in which the oscillatory motion of the object extracts energy from a steady energy source. Such a ribbon simulates the motion of the human vocal folds as well as that of unstable bridge ``galloping,'' such as is famously exemplified in the Tacoma Narrows bridge collapse. The phenomenon discussed in this talk is also relevant to aerodynamic flutter and the ``quaking'' of leaves of trees in the breeze. Chief among the findings of this work is the origin of inharmonic modes of oscillation of a self excited ribbon.