Explain vortex shedding and the Strouhal number. How do you prevent flow-induced vibrations?

Vortex shedding occurs when flow separates alternately from sides of a bluff body, creating periodic pressure fluctuations. Strouhal number St = fD/V relates shedding frequency (f) to flow velocity (V) and characteristic dimension (D). For circular cylinders, St ≈ 0.2 over wide Re range (300-10⁵). When shedding frequency approaches structure's natural frequency, resonance causes large-amplitude vortex-induced vibrations (VIV). Prevention strategies: helical strakes disrupt vortex correlation along span, shrouds reduce approaching velocity, fairings streamline body to prevent separation, mass dampers absorb energy, stiffening raises natural frequency above shedding range, galloping analysis for non-circular sections. Critical for offshore risers, heat exchanger tubes, chimneys, and bridge cables.