Current induced instability of two circular cylinders

The mean lift and drag forces on a cylinder placed in the wake of another upstream cylinder are investigated in the paper as well as the influence of these forces on the stability of the downstream cylinder. It is assumed that the two cylinders have the same diameter with the upstream cylinder always fixed. The forces are predicted based upon a free streamline model and the utilisation of some available experimental data. The stability of the downstream cylinder's equilibrium position is then analysed by finding eigenvalues of the linearised equation of motion. Numerical results of the lift and drag forces on the downstream cylinder are presented which are in a good agreement with the experimental data. It is found that under the influence of these forces the equilibrium position can become unstable through either the Hopf or stationary bifurcation depending upon the value of the mass parameter. For marine applications, the stationary bifurcation is the more likely scenario. The effect of the reduced velocity is identified in the paper.