Multiple Static Solutions And Stability Of A Vertical Riser In The Wake Of An Upstream Vertical Riser

摘要

The static solution and its associated dynamic stability of arnvertical riser situated in the wake of an upstream riser isrninvestigated in this paper. Both the upstream and downstreamrnrisers are top tensioned and pinned at the bottom ends on thernseabed. Due to the wake effect, the downstream riser is subjectrnto lift force as well as drag along its length. It is shown thatrnunder certain current conditions there exist multiple stable andrnunstable static solutions of the downstream riser. There alsornexists a critical current velocity and once this velocity isrnexceeded no static solutions of the downstream riser can bernfound. The disappearance of static solutions is closely related tornthe loss of stability which is likely to cause clashing between therntwo risers. The critical current velocity is best described by arnnon-dimensional parameter involving both the mass parameterrnand the reduced velocity.