Patent ID: 7108457
Filing Date: 2006-09-19
Classification: B63B,E21B,F15D,Y02T

Abstract:
1. A marine riser, comprising: (a) a riser pipe having an outer riser pipe surface; (b) an annular sheath surrounding the riser pipe and forming a conduit between the outer riser pipe surface and an inner surface of the annular sheath, the annular sheath having an outer surface; (c) at least one pair of nozzles for discharging water carried by the conduit out of the annular sheath in a direction substantially tangential to the outer surface of the annular sheath; (d) when the marine riser is beset by a current, the discharge of water by the at least one pair of nozzles substantially preventing flow separation of the current on a down-current side of the marine riser and thereby substantially preventing hydrodynamic drug and vortex induced vibration (VIV) that the marine riser would experience in the absence of the discharge of water by the at least one pair of nozzles; and a system for pumping water through the conduit to at least one of the pair of nozzles, a system for rotating the annular sheath including a gear for rotating the annular sheath and the at least one pair of nozzles relative to the riser pipe and a gear motor for driving the gear, wherein the system for rotating the annular sheath further includes a ring gear supported by a bulkhead surrounding the riser pipe and at least one pinion gear for engaging the ring gear, wherein the annular sheath includes an inner tube surrounding the riser pipe and an outer tube surrounding the inner tube, wherein a region is formed between the riser pipe and the inner tube, the region containing buoyancy material, and wherein the system for rotating the annular sheath is for rotating the outer tube, the inner tube, and the at least one pair of nozzles relative to the riser pipe.