Hydroelastic excitation of cylinders.

Abstract

The transverse vibration of a bluff body in a steady fluid flow is a phenomenon that has been observed and discussed through the ages. Named after the Greek God of Wind Aeolius, the Aeolian Tones, such as are emitted by the wind in telephone or power lines, were known to the Greeks, who produced musical sounds from an Aeolian Harp by hanging it in a current of wind. The first recorded association of the transverse vibration with a periodic wake pattern was made by Leonardo Da Vinci, who observed and sketched the process of lternate periodic vortex shedding from a bluff body to form the staggered vortex trail in its wake. It is unlikely that prior to the nineteenth century many structural failures occurred due to hydrodynamic excitation. Wood, stone and brick were the main construction materials, and the elementary design methods used were very conservative ensuring that the structure had high frequency, large mass and a large damping factor. A very high flow velocity was therefore needed to initiate structural oscillations by vortex shedding and, if initiated these structural oscillations would usually be quickly damped out. During the nineteenth century the rapid advancement in the art of civil engineering design and the introduction and development of concrete and steel as a construction material led to the design of streamlined structures with more economical dimensions and consequently lower frequencies, smaller masses and smaller damping factors. Although design codes made a reasonable allowance for static loadings, dynanic loadings caused by earthquakes and hydrodynamic excitation were eirther ignored or underestimated.