Abstract:
An ocean riser assembly for conveying fluids between the seabed and the surface of the sea includes a fluid conveying pipe formed into a helical configuration or into a planar cyclically undulating configuration, such as a sinusoid, that extends longitudinally from the bottom of the sea to the surface. One or more flexible and preferably elastic tension members extend in the longitudinal direction of the riser assembly and are secured to the pipe at spaced intervals, so that they absorb tension forces applied between the ends of the riser assembly. The helical or undulating configuration of the riser pipe decouples axial stresses in the pipe caused by internal fluid pressure from stresses caused by external tension forces acting on the riser assembly, the external tension forces being converted to torque and bending moments acting on the pipe itself. This arrangement permits substitution of carbon steel pipe for flexible pipe, at substantial cost savings. The riser assembly can be used in very deep water, but it also is useful in shallow water, particularly in the planar undulating configuration of the fluid conveying pipe.
Abstract:
A vessel with a mooring recess on the bottom of the hull moors to a submerged buoyant mooring element anchored to the ocean bottom by hoisting the mooring element from a stowed position at a depth of net neutral buoyancy of the mooring element and its anchoring system into contact with the mooring recess. The mooring operation is completed safely, quickly, and positively by rapidly withdrawing seawater into the hull through an opening in the mooring recess so as to reduce the hydrostatic pressure acting on the top of the mooring element as the element comes into contact with the hull of the vessel. The pressure reduction is sufficient to shift the mooring element and its anchoring system from a net negative to a net positive buoyancy condition at the keel depth of the vessel. The seawater may be withdrawn by a high capacity pump that is either specifically installed for this purpose or is part of a bow thruster system of a type commonly found on large vessels. Alternative, or additional, seawater suction apparatus includes an evacuated hermetic chamber having a valve opening into the mooring recess. The mooring recess may be coaxial with a vertical well in the hull, in which case water in the well may be drained into an empty hold through a valve opening into the well near the bottom of the hull. The mooring element has an upper part that makes sealing contact with the hull of the vessel and a lower part that is connected to the anchor lines. At least one bearing mounted between the parts permit the upper part to rotate relative to the lower part, so that the vessel may weathervane in response to wind, wave, and current forces.
Abstract:
A vessel with a downward-facing mooring part moors to a submerged buoyant mooring element anchored to the ocean bottom by hoisting the mooring element from a stowed position, at a depth of net neutral buoyancy of the mooring element and its anchoring system, until a mating upper part of the mooring element comes into contact with the mooring part. The mooring operation is completed safely, quickly, and positively by securing the mooring element to the vessel with a multiplicity of hooks that are lowered by actuators mounted in the vessel to engage a mooring ring on the upper part of the mooring element and are then raised to exert a predetermined compression force on a resilient compression member. The mooring part may include a turret rotatably mounted in the vessel, or the mooring element may have an upper part that makes sealing contact with the hull of the vessel and a lower part that is rotatable with respect to the upper part and is connected to the anchor lines, so that the vessel may weather vane in response to wind, wave, and current forces.
Abstract:
A vessel with a mooring recess on the bottom of the hull moors to a submerged buoyant mooring element anchored to the ocean bottom by hoisting the mooring element from a stowed position at a depth of net neutral buoyancy of the mooring element and its anchoring system into contact with the mooring recess. The mooring operation is completed safely, quickly, and positively by rapidly withdrawing seawater into the hull through an opening in the mooring recess so as to reduce the hydrostatic pressure acting on the top of the mooring element as the element comes into contact with the hull of the vessel. The pressure reduction is sufficient to shift the mooring element and its anchoring system from a net negative to a net positive buoyancy condition at the keel depth of the vessel. The seawater may be withdrawn by a high capacity pump that is either specifically installed for this purpose or is part of a bow thruster system of a type commonly found on large vessels. Alternative, or additional, seawater suction apparatus includes an evacuated hermetic chamber having a valve opening into the mooring recess. The mooring recess may be coaxial with a vertical well in the hull, in which case water in the well may be drained into an empty hold through a valve opening into the well near the bottom of the hull. The mooring element has an upper part that makes sealing contact with the hull of the vessel and a lower part that is connected to the anchor lines. At least one bearing mounted between the parts permit the upper part to rotate relative to the lower part, so that the vessel may weathervane in response to wind, wave, and current forces.
Abstract:
An end fitting for a cylindrical high pressure vessel made from components all having thin walls, thereby tripling the practical diameter of such pressure vessels. The end fitting includes a toroidal shell defining a hole; centrally disposed piece for closing the hole comprising a pipe and a center end fitting and structural members. In a first embodiment, the structural members comprise slices of an end of the pipe welded to the outer cylindrical wall of the vessel. In a second embodiment, the structural members are plates connecting the pipe to the outer cylindrical walls. In the third embodiment, the plates connect an extension of the outer cylindrical wall beyond the toroidal shell to an extension of the outer cylindrical wall of the pressure vessel. The center end fitting may be hemispheric or ellipsoidal.
Abstract:
An end fitting for a cylindrical high pressure vessel made from components all having thin walls, thereby tripling the practical diameter of such pressure vessels. The end fitting includes a toroidal shell defining a hole; centrally disposed piece for closing the hole comprising a pipe and a center end fitting and structural members. In a first embodiment, the structural members comprise slices of an end of the pipe welded to the outer cylindrical wall of the vessel. In a second embodiment, the structural members are plates connecting the pipe to the outer cylindrical walls. In the third embodiment, the plates connect an extension of the outer cylindrical wall beyond the toroidal shell to an extension of the outer cylindrical wall of the pressure vessel. The center end fitting may be hemispheric or ellipsoidal.
Abstract:
A method and arrangement for transferring liquified natural gas from a seagoing tanker to an on-shore facility including boosting the pressure of the liquefied natural gas to above the critical pressure and passing the liquefied natural gas through a heat exchanger immersed into the sea thereby heating the gas to near ambient temperature.
Abstract:
In hydrate-based desalination or other water purification conducted using naturally buoyant or trapped-gas-assisted buoyancy hydrate in a hydrate fractionation column, a portion of fresh or purified product water is extracted from an upper, hydrate dissociation region of the fractionation column and reintroduced into a lower portion of the fractionation column at a point above but generally near a product water/saline water interface. The difference in density between the reintroduced product water and the fluid in the hydrate fractionation column above the point of reintroduction (water, hydrate, and gas) drives a natural circulation system which enhances the rate at which hydrate rises into the hydrate dissociation region.
Abstract:
A mooring system for a vessel including a mooring area on a bottom surface thereof, includes a mooring element coupled to the sea floor by a plurality of mooring tethers which resides, when not in use, in a storage position a preselected depth below the surface. An upper surface of the mooring element includes a sealing surface surrounding a target area to be coupled within the mooring area. The system includes apparatus for raising the mooring element from the storage position into a mooring position in which the sealing surface is in contact with the bottom surface of the vessel so that mooring area is sealed between the bottom surface of the vessel and the target area and a pump for lowering the pressure between the bottom surface of the vessel and the target area of the upper surface of the mooring element to a first level for immobilizing the mooring element with respect to the bottom surface of the vessel and a second level so that the mooring element is maintained in sliding contact with the bottom surface of the vessel. The system also includes a device for detecting a displacement of the mooring element from a desired position of the mooring element within the mooring area.