Modeling Vortex Induced Motion in Sheared Currents

In this paper we examine the vortex induced motions (VIM) of a spar platform in a sheared current. This study is motivated in part by the problem of using flume tanks for the simulation of platform VIM in sheared currents. To date, such experiments have not tried to reproduce the density gradients seen in the ocean in the presence of a stable sheared current. Instead, the flume tanks are kept short so that a velocity gradient introduced at one end is preserved long enough so that a sheared current exists at the model. In this paper we use computational fluid mechanics to simulate both problems. It is shown that buoyancy effects can be significant and need to be considered in the interpretation of flume tank experiments.