Vortex Induced Vibrations of a Double Pendulum*

We present the dynamics of a double pendulum with a constant cross section undergoing vortex induced vibration (VIV). Angular displacements and forces generated at the pendulum base are reported for a range of flow velocities, and the vortex shedding patterns are analyzed for multiple points of interest throughout the pendulum response.

Unlike the classic experimental demonstration of VIV wherein a flexibly mounted rigid cylinder is exposed to fluid flow, the amplitude of oscillation along the length of the double pendulum is not uniform and wake produced is therefore more complex. This, combined with the increase in the number of structural natural frequencies to two, gives rise to unique oscillatory behavior.

These experiments serve to fill the gap in VIV research between flexibly mounted rigid and fully flexible structures, while providing insight on behavioral trends that can be directly applied to a range of fields involving structures that can be modeled as a double pendulum, including human and robotic limbs operating in fluid environments and emerging energy harvesting technologies.