Vortex Induced Vibration

For the last few days I’ve tried to simulate flow over a circular cylinder at Re=22k using OpenFOAM. The cylinder is attached to a mass-damping system in one degree of freedom (cross-stream). The simulation only success when the natural frequency of the system is high, omega_o >= 2 x vortex shedding frequency. I believe that I need to work out on the resonant response of the system.