Abstract: A marine riser that includes active boundary-layer control (“BLC”) for reducing hydrodynamic drag and vortex-induced-vibration (“VIV”) caused by currents. The marine riser includes at least one riser pipe surrounded by a BLC sheath. Extending through the sheath is at least one nozzle, preferably at least one pair of slot-nozzles, for discharging water into the sea in which the marine riser is deployed. The BLC sheath may be rotate-able to align a pair of slit-nozzles with the current direction, or in a fixed BLC sheath, pairs of slot-nozzles may be selectively activated based on the current direction. The BLC sheath may also include a tail-jet or retractable tail-fin. The BLC sheath may be formed from telescoping sections that decrease in diameter toward the bottom of the riser and that are nested when the telescoping sheath is retracted. Finally, a BLC system may also be implemented in a production riser system.

Abstract: A system for reducing hydrodynamic drag and vortex-induced-vibration (“VIV”) in a bluff hull. In a bluff hull that is designed to be at least partially submerged in a fluid, such as water, the hull has an internal area for holding or transferring fluid. When the hull is beset by a current present in the water, the surface of the bluff hull has an up-current side and a down-current side. The hull surface has at least one opening, preferably a slot-nozzle, for discharging the fluid from the internal fluid area of the bluff hull out of the hull surface and into the surrounding water at a velocity greater than the current velocity, so as to reduce flow separation of the current on the down-current side of the hull surface. Also, preferably, the fluid is discharged out of the opening at an angle substantially tangential to the hull surface at the location of the opening and substantially in the direction of the current.

Abstract: A system for reducing hydrodynamic drag and vortex-induced-vibration ("VIV") in a bluff hull. In a bluff hull that is designed to be at least partially submerged in a fluid, such as water, the hull has an internal area for holding or transferring fluid. When the hull is beset by a current present in the water, the surface of the bluff hull has an up-current side and a down-current side. The hull surface has at least one opening, preferably a slot-nozzle, for blowing the fluid from the internal fluid area of the bluff hull out of the hull surface and into the surrounding water at a velocity greater than the current velocity, so as to reduce flow separation of the current on the down-current side of the hull surface. Also, preferably, the fluid is blown out of the opening at an angle substantially tangential to the hull surface at the location of the opening and substantially in the direction of the current.