Vibration problems encountered by bluff bodies in ocean environment present considerable similarity to vortex resonance and galloping type of instabilities, extensively studied by industrial aerodynamicists. The paper briefly reviews control of this class of vibration problems using both passive as well as active procedures involving nutation dampers and the Moving Surface Boundary-layer Control (MSBC), respectively. It is suggested that both the procedures present considerable promise in resolving vibration problems of bluff offshore structures caused by ocean waves and currents.
Vibration of mechanical systems is a universal phenomenon extending to outer space, continuum atmosphere, earth and ocean based structures. Suppression of mechanical oscillations, forced or self-excited, or at least their minimization to an acceptable level, is a challenge faced by engineers in all disciplines. Perhaps the earliest vibration problems caused by fluid flow, to receive significant as well as sustained attention, pertain to flutter and divergence of aerodynamic surfaces. Advent of the space age brought to light vibration problems of highly flexible large space structures [Modi, 1996], such as the proposed International Space Station Alpha, operating in the free molecular and microgravity environment. However, here the attention is focused on the earth and ocean based structures, usually bluff in geometry, subjected to wind, waves and currents. The spectacular collapse of the Tacoma Narrows Bridge in 1940 provided considerable impetus to the understanding of wind effects on civil engineering structures. Ever since, a vast body of literature aimed at fluid dynamics and dynamics of bluff bodies has evolved which has been reviewed quite effectively by Cermak (1975), Welt (1988), Modi et al. (1995), Seto (1996), Munshi (1996) and others. The fluidstructure interaction induced instabilities of concern have been the vortex resonance and self-excited oscillations of the galloping type.