A countermeasure based on structural mechanics that is effective in decreasing the amplitude of vortex-induced oscillations observed during tower construction is known as what?

• A. Stiffening
• B. Aerodynamic Smoothing
• C. Damping
• D. Mass Redistribution

Answer: (C)

Damping reduces the amplitude of vortex-induced oscillations by dissipating energy in the structure. VIV occurs when wind energy is transferred into the tower through fluctuating lift forces from shed vortices. The resulting vibration level depends on the balance between energy input from the wind and energy that's dissipated by the structure each cycle. Increasing damping makes the structure convert more of that vibrational energy into heat or other non-recoverable forms, lowering the resonant peak and suppressing both transient and steady-state motions. This is a direct structural-mechanics approach to control vibration, and it can be implemented with dampers or materials that absorb energy.

Stiffening would shift the natural frequency and mode shapes, which can help only under specific wind conditions and doesn’t address energy dissipation as directly. Aerodynamic smoothing targets the flow around the tower rather than the structural response, and mass redistribution alters inertia but is less practical or reliable for reducing VIV amplitude during construction.