Galloping Oscillations of Prismatic Structures

Abstract

Galloping oscillations can arise above a certain onset wind velocity with lateral force coefficient A1 > 0 (unstable cross sections) and also at A1 ≤ 0 (stable cross sections). In the latter case, an initial disturbance is also necessary to trigger the vibrations. This triggering disturbance must be larger than the unstable amplitude, proportional to structural damping, and in some cases must be able to decrease with increasing wind velocity. The onset velocities are higher with A1 ≤ 0 and are directly proportional to structural damping in all cases. Turbulence can drastically change the aeroelastic stability of prismatic bodies. With rectangular cross sections of 2/1 the tendency to galloping instability from zero position decreases with increasing turbulence intensity and can vanish at intensities of 8% or so. On the contrary, prisms of 1/2, stable in the smooth flow, can become unstable in the turbulent flow and their tendency to galloping oscillations increases with turbulence intensity.