Induced vibrations of an hydrodynamic pendulum

We numerically study the movements of a cylinder subjected to the actions of a hydrodynamic flow. The system mechanism simple by the low number of parameters which characterize it, has only one degree of freedom. It can be analysed like an oscillator undergoing a return force related to the vortex shedding. The dominant frequency of oscillation of the pendulum is close to the frequency of emission, of the Von Karman street in the case of the motionless cylinder The pendulum's oscillation amplitude, whatever the length l(b), is always close to the radius of the cylinder (A/D approximate to 0.5 for 3 < l(b) = 7). However; the vortex shedding patterns observed in the wake are very frequently different and related to the length l(b) for the Reynolds number of 2000 imposed here. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.