Vortex-induced vibrations – the Scruton number revisited

Abstract

The paper focuses on vortex-induced vibrations of structures with rectangular cross-sections, some of them having similar in-wind and cross-wind dimensions and others having in-wind dimensions much larger or much smaller than the cross-wind dimension. Traditionally, the Scruton number has been used to determine the effects of motion-induced wind loads acting on structures; however, because it depends on the cross-wind dimension only and not on the in-wind dimension, the Scruton number does not contain any information on the wind load exposed length. This paper proposes a general non-dimensional mass-damping parameter that includes the wind load exposed length and describes effects of motion-induced wind load consistently for the structures considered. This general non-dimensional mass-damping parameter is derived by considering the relative wind velocities approaching the structure vibrating due to vortex shedding and by assuming that the motion-induced wind load is proportional to the wind load exposed length being equal to the in-wind dimension. Wind tunnel tests carried out confirm that it describes the effects of motion-induced wind load more consistently than the Scruton number normally applied. The general non-dimensional mass-damping parameter is equal to the Scruton number when the cross-wind dimension is equal to the in-wind dimension.