Effect of a damper on the wind-induced oscillations of a tall mast

The wind induced oscillations in the downwind direction were studied for a tall slender mast that incorporates a unique form of damper. The damper consists of a hinged extension to the main mast, rotation of which is opposed by springs that provide stiffness and by viscous dampers. In that portion of the domain of hinge parameters (stiffness and damping) where conventional (approximate) analysis shows substantial beneficial effects of the damper, a more exact analysis shows that the benefit is not in fact realized. The exact analysis is so termed because it treats the natural modes of the linear vibration problem exactly, in contradistinction to conventional vibration analysis, which approximates complex modes by real modes. The cross vibrations associated with vortex shedding are briefly discussed.