Stationary and Hopf Bifurcations of Equilibrium Positions of a Cylinder Situated in Near and Far Wake Fields of an Upstream Cylinder

摘要

For a deepwater vertical riser cluster, interference between the individual risers in strong ocean currents is a key design concern. The riser lateral deflections are likely to be large and the risers are prone to wake-induced clashing with possible detrimental effects. In this paper, a stability analysis methodology is developed to address the wake-induced instability of a pair of vertical risers with one located in the wake of another. A comprehensive parametric investigation is carried out to examine the effects of various parameters varying in wide ranges. In particular, effort is made to investigate the different instability mechanisms of a marine riser situated in the near or far wake field of the upstream riser. It is found that the fluid-elastic instability of the downstream riser can be caused by either a Hopf or a stationary bifurcation depending upon its relative position to the upstream riser.