Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
  • B63B35/44—Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices
  • B63B35/4413—Floating drilling platforms, e.g. carrying water-oil separating devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B2211/00—Applications
  • B63B2211/06—Operation in ice-infested waters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B2241/00—Design characteristics
  • B63B2241/02—Design characterised by particular shapes
  • B63B2241/04—Design characterised by particular shapes by particular cross sections
  • B63B2241/06—Design characterised by particular shapes by particular cross sections circular

Definitions

• the present invention relates to floating platforms and particularly floating platforms applicable for operation in exposed waters.
• Such a construction has shown to have advantageous large capacity both for storage of oil and load capacity on deck. Further the cost of the construction is low, the assembly period short and it is achieved large flexibility for different applications.
• Such a platform may be positioned by scattered anchoring and neither a turret nor a swivel are needed to handle risers/hoses and anchoring lines.
• the round or mainly rounded cross section is beneficial due to that rotation according to weather is not necessary and it has been shown that the movement and stresses on the platform is surprisingly low compared with other types of floating installations. Thus the level of stretch and tension are limited.
• the form of the hull provides a compact construction which contribute to the wave loads only having a limited degree of influence on tension and stretch forces.
• the present invention providing a floating platform for drilling, production, storage or other applications, particularly in icy waters, the platform comprising a hull with outer sidewalls mainly positioned rotation symmetrically around a vertical centre axis in the platform and in a lower part closed by a bottom, a deck in the upper end of the hull equipped suitably according to the intended application, the platforms draught being considerably less than the diameter of the platform and the buoyancy centre of the platform for the submerged part is positioned lower than the centre of gravity of the platform.
• the platform according to the invention is characterized by its mainly symmetrically outer side of the hull includes at least three sections counted from the upper end of the hull: a waterline section with diminishing diameter in the direction downwards along the centre axis, in which water level section the water level of the sea is to be located during operation in icy waters, an intermediate section with cylinder form and an under section with increasing diameter in the direction downwards along the centre axis.
• hull is mainly symmetrical around a vertical centre axis of the platform, implies that the hull is round or nearly round in the form defined by the outer sidewall.
• the ratio between the platforms draughts and diameter at water level is preferably 0.2-0.3 during operation in non-icy waters, were the water level can be added to the intermediate section of the hull.
• the ratio between the draughts of the platform and diameter at the water level is preferably approximately 0.3-0.4.
• a generally preferred ratio is about 0.3.
• the water level section has preferably an inclination inward in downward direction of about 45°, which is considered preferable with regard to icebreaking and the prevailing forces.
• the inclination in the under section is preferably approximately 45° outwardly, as seen in the direction downwards, which is considered to be preferable with regard to the handling and transport of ice radial away from the platform.
• the under section contribute to give the ice a movement preventing it to be led under the hull. Other inclinations may, however, also be applicable.
• the transition between the sections can be sharp or gliding, so that the form can resemble an hourglass or an inner part of a laying U.
• Typical dimensions of the sections is a water level section with height of 10-15 m, an intermediate section with height 5-15 m and an under section with height 2-4 m.
• the dimensions of the sections can be beyond the above and depend on the ice thickness and other expected ice conditions in the scheduled operational area as well as the size and draught of the platform.
• the platform comprises preferably a removable, downward extending body (connecting member), coaxially located with the platforms vertical centre axis, withdrawn from the lower edge of the outer sidewall for attachment and/or through-guiding of anchoring lines, chains, risers, and/or cables and with inherit buoyancy.
• a removable member For icy waters such a removable member is preferred, because risers, houses, cables, anchoring lines and chains are pulled away from the pherimeter and thus protected from the ice and exposed connecting area is pulled down a distance under the bottom of the platform. Any ice entering under the platform must be moved a fair distance inward towards the centre of the platform for the area of attachment is reached so that the ice probably must be raised to the bottom of the platform and not hitting any risers, anchoring lines etc. Should a large iceberg arrive, the connecting member can be detached; whereupon it will sink down to the safe depth determined by the balance between the buoyancy of the connecting member and the weight of attached devices.
• the removable connecting member is extending at least 10 m below the bottom of the platform before the area for attachment/through-guiding of the risers is met.
• Dynamic positioning may be used for positioning of the floating platform for some applications, for instance during drilling at deep waters.
• a method for operation in icy waters with a floating platform according to the present invention, characterized by the platform is ballasted so that the water level is situated in the water level section during the operation of integrated devices for ballasting.
• Fig. 1 shows a view of a floating platform according to the invention
• figures 2, 3 and 4 show comparable data between the round, vertically standing Sevan-platforms of which the present platform is one type, a semi-submersible platform and a vessel, respectively, in that fig. 2 illustrates data for heave movement, fig. 3 illustrates data for pitch movements and fig. 4. illustrates data for rolling movements.
• fig. 2 illustrates data for heave movement
• fig. 3 illustrates data for pitch movements
• fig. 4. illustrates data for rolling movements.
• FIG. 1 in a side view illustrates a floating platform according to the present invention. Further is illustrated a floating platform 1, comprising a hull 2 which is mainly symmetrical around a vertical centre axis in the platform and in a lower end closed by a bottom 3. A deck 4 is illustrated in an upper end of the hull equipped suitably according to the intended use. It would clearly appear from the figure that the draught of the platform is considerably less than the diameter of the platform. What is not so obvious is that the centre of buoyancy for the submerged part of the platform is lower than the centre of gravity of the platform.
• the rotation symmetrical outer side of the hull 2 includes at least three sections counted from the upper end of the hull, namely: a water level section 5 with diminishing diameter in the direction downwards along the centre axis, in which water level section, the water level of the sea is situated during operation in icy waters, a intermediate section 6 with a cylinder form, and an under section 7 with increasing diameter in the direction downwards along the centre axis.
• the water level section In the direction downward the water level section inclines inwardly towards the centre axis approximately 45°, while the under section inclines outwardly about 45°.
• the ratio between draught and diameter of the platform at the water level is approximately 0.3.
• a removable, downwardly extending member (connecting member) 8 coaxially located with the platforms vertical centre axis and withdrawn such that it is positioned far from the outer side walls lower edge of the hull.
• the connecting member 8 is for connecting risers, anchoring lines/chains, hoses, cables and similar, as needed.
• the connecting area for risers is at least 10 m lower than the bottom of the platform, which is beneficial in icy waters.
• the platform is ballasted so that the water level is at the water level section. Further, it is considered beneficial to position the water level so that an upper edge of the level is meeting in the upper part of the water level section.
• the ballasting can be such that the water level is in the intermediate section 6 having a cylinder form, in that a cylinder form with vertical sides at the water level gives less movements for the platform.
• the floating platform can have many applications and is equipped conveniently according to the intended application both on deck and inside. Further, the platform can be used as an FPSO (Floating Production Storage Offloading), a FPU (Floating Production Unit), a MODU (Mobile Offshore Drilling Unit), a MSV (Multipurpose Support Vessel), a FLNG (Floating Liquified Natural Gas Production), a GTW (Gas Through Wire, that is an offshore power plant), a FDPSO (Floating Drilling Production Storage Offloading), a FAU (Floating Accommodation Unit, that is a residential quarter), or other applications.
• FPSO Floating Production Storage Offloading
• FPU Floating Production Unit
• MODU Mobile Offshore Drilling Unit
• MSV Multipurpose Support Vessel
• FLNG Floating Liquified Natural Gas Production
• GTW Gas Through Wire
• FDPSO Floating Drilling Production Storage Offloading
• FAU Floating Accommodation Unit, that is a residential quarter
• FIG 2 is viewed curves of heaveheave-movements for standing rotational symmetrical platforms (Sevan) and semi-submersible platforms and vessel with waves coming in from the front from the side of the vessel, respectively.
• figure 3 is illustrated pitch under similar conditions for a Sevan platform, a semi-submersible platform with sea coming in from the front and a vessel with sea coming in from the front and clearly that the general Sevan construction is beneficial under many operating conditions.
• figure 4 is viewed rolling of similar, floating installations at corresponding conditions and it is clearly seen that the Sevan construction has very beneficial properties closely followed by the semi-submersible installation while a vessel has considerably more rolling, comparably. Due to very limited storage and load capacity, as well as little applicability in icy waters, semi-submersible platforms cannot be compared with the present, floating platform, because the functionality is insufficient.
• the platform is thus rocking or pitching around a horizontal axis, but the construction of the platform entails that by rocking the platform the moment due to buoyancy is increasing considerably faster than the moment applied by the ice, which entails very moderate movement and this effect is considered to be particularly pronounced with the water level in the water level section.
• a certain amount of ice is accumulated towards the side of the water level sections, a power balance will be achieved but the inherent ability of the platform to correct the moment due to buoyancy will be changed considerably by the centre of buoyancy being moved considerably to the side (the distance between the centre of gravity and buoyancy centre is increasing), which entails that the platform is rocking/rotating back to the starting position while the ice is broken up and diverged in the direction downwards.
• the movement of the water current and the platform motion guide the ice downwards along the intermediate section whereupon the ice by the water current is lead further down along the under section and diverged in the direction away from the centre axis, along the outer surface of the under section.
• the ice is bent/broken down, is guided down and guided in the direction back against the direction of the driving ice whereupon the ice is floating up again as smaller fragments and lead around the platform by means of the increased velocity of the water current near the platform wall.
• the ice is broken very efficiently and moved efficiently around the platform without doing any damage.
• the moderate rocking movements of the platform contribute to a reduced friction between the ice fragments and the platform in that a radially outward directed water current is created when the platform swings back again.
• the swinging movement or the heave movement seems to adapt a natural frequency.
• the velocity of the water current is higher around the platform than the surrounding water because the water will have to follow the way around the platform. This contributes to the ice fragments being transported on a "water cushion" around the platform.
• the water currents hitting the platform can also be split in a current passing under the platform, particularly for a large platform, because it means a shorter or easier path for the current then all the way around the platform. This may lead to ice fragments under the platform, which is undesirable, but the shape of the under section has proved to be efficient to prevent ice under the platform as mentioned above, in addition to contribute to an improved "water cushion" effect.
• the platform is preferably equipped with propulsion for operating on assembling, which propulsion preferably also is adapted for utilization for propeller washing in the area around the under section with effect towards the surface at the wind board side and outwards towards the sides.

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• Engineering & Computer Science (AREA)
• Architecture (AREA)
• Civil Engineering (AREA)
• Structural Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• Ocean & Marine Engineering (AREA)
• Earth Drilling (AREA)
• Testing Or Calibration Of Command Recording Devices (AREA)
• Other Liquid Machine Or Engine Such As Wave Power Use (AREA)
• Piles And Underground Anchors (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

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Cited By (10)

Families Citing this family (6)

Citations (6)

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• 2008
  • 2008-05-09 NO NO20082189A patent/NO336984B1/no unknown
• 2009
  • 2009-05-08 CA CA2723410A patent/CA2723410C/en active Active
  • 2009-05-08 RU RU2010150346/11A patent/RU2502629C2/ru active
  • 2009-05-08 WO PCT/NO2009/000177 patent/WO2009136799A1/en active Application Filing
  • 2009-05-08 CN CN200980115983.0A patent/CN102015436B/zh active Active
• 2010
  • 2010-01-11 DK DKPA201070011A patent/DK179027B1/da active

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