Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B21/00—Tying-up; Shifting, towing, or pushing equipment; Anchoring
  • B63B21/24—Anchors
  • B63B21/26—Anchors securing to bed

Definitions

• the invention relates to an anchor device for offshore or onshore use.
• the anchor device is primarily intended for anchoring offshore constructions such as floating rigs or vessels for similar purposes the anchorages of which should be relatively easy to establish and flexible.
• the anchor device of the invention can be used e.g. for tension leg platforms, mooring or loading buoys, plants for recovering wind, wave or heat energy, different types of seabed-connected, rigid or articu ⁇ lated constructions such as drilling steel jackets and loading columns.
• the anchor device can also be used onshore for staying several constructions such as towers, masts, or scaffolds.
• anchors 8 to 12
• the anchors which are put out from the rig by means of special anchor handling ships, then are hauled towards the rig until they engage the bottom.
• the anchor is of the type which is similar to the conven-t tional ship anchor and can be loaded substantially by . horizontal forces only.
• the anchor line therefore must have such a length that a curved shape will be imparted to it by gravity, the line being tangent to a horizontal line at the engagement location.
• the length of the line can be slightly reduced if the line adjacent the anchor is held down by means of weights.
• the anchor is affected by deviations in the direction of
• FR 2,383,825 describes a prior art anchor device comprising a plate and a pole extending through said plate, for connecting an anchor chain.
• the pole extends centrally through the plate, it is possible to arrange the line of action of the anchoring force through the centre of pressure (C.P.) of the pole only if the pole has a large diameter in relation to the Tength ' thereof, which means that it will be difficult to ram the pole into the bottom or the ground.
• C.P. centre of pressure
• the anchor device of the invention comprises a plate to bear on the bottom or ground surface, and cylindrical elements extending through the plate into the bottom or ground layers.
• the anchor device has obtained the characterizing features of claim 1.
• This anchor device can be engaged and disengaged in a relatively easy manner by simple operations and low power hich can be exercised at large depths. Thus, substantial parts of the anchor device can be re-used. Since the anchor device can be loaded by vertical component forces, shorter anchor lines can be used. Because the anchor device can be dimensioned with due consideration of the geological conditions at the pre- determined locations, each anchor unit will be more reliable and thus fewer anchor units will be required. Shorter lines and fewer units provide an anchor system of a correspondingly lower weight.
• FIG. 1 is a diagrammatic perspective view of a rig wh.ich is anchored by means of four anchor devices of the invention
• FIG. 2 is a perspective view of the anchor device
• FIG. 3 is a cross-sectional view along line a - a in FIG. 2
• FIG. 4 is a fragmentary perspective view, partly a cross-sectional view, of an attachment on the anchor device
• FIG. 5 is a diagrammatic perspective view of a rig which is anchored by means of four groups each having three anchor devices of the invention
• FIG. 6 illustrates the geometry of a group of three anchor devices as shown in FIG. 5
• FIG. 7 is a plan view of branch lines and anchor devices when six branch lines are arranged
• FIG. 8 is a plan view similar to that of FIG. 7, the anchor devices being interconnected with the branch lines forming a net structure
• FIG. 9 is a plan view similar to that of FIG. 7, when five branch lines are arranged.
• a rig 10 floating on the water is anchored by means of four identical anchor devices 14 of the invention each provided with an anchor line 11.
• the anchor device 14 is shown in more detail in FIG.
• FIG. 2 and comprises a bottom plate 15 bearing on the bottom, said plate preferably being circular, and a plurality of cylindrical elements 16 which are rammed through the bottom plate into the bottom material to form a tubular, in this case cylindrical envelope as indicated by dot-and-dash lines in FIG. 2 wherein only a few elements are shown.
• the bottom plate 15 forms a flange at the upper end of the tube formed by the elements 16.
• the elements are supported by the bottom plate which pro ⁇ vides a rigid connection, the bundle of elements in its entirety being kept together by the rigid bottom plate. Due to the fact that the anchor device 14 is constructed as described it is achieved that power resources which are small in relation to the holding capacity, are required in order to engage the device in a predetermined position and in 'order to disengage the device from said position, respectively.
• the dimensions of the bottom plate 15, the number of elements 16, and the dimensions of said elements should be adapted to the geological conditions such that the ram force required will be optimized in relation to the load capacity of the anchor device obtained.
• the cylindrical elements In order to increase the lateral resistance of the bundle of elements the cylindrical elements can be arranged in a so-called zigzag formation as shown in FIG. 3.
• a mixture of cement and water can be injected into the bottom material around the elements in order to strengthen the bottom material .
• the line of action of the anchoring force passes through the centre of pressure and that the lateral and axial resistances of the device at the same time are sufficient in order to withstand the component forces in the corresponding directions .
• the position of the centre of pressure is defined not only by the dimensions and arrangement of the element bundle but also by the area of the bottom plate and the nature of the bottom layers.
• the load capacity will be the same in all directions of orientation. If the attachment is made displaceable such that it can move freely along the circumferential circular edge of the plate, it is achieved that the anchor device will never be exposed to a torsional moment when the line of action of the anchoring force intercepts a normal through the centre of the bottom plate (symmetry axis) notwithstanding the direction of the anchor line.
• a line attachment 17 for the anchor line 13 connected to the anchor device which is mounted at the edge of the bottom plate and can be displaced freely along said edge.
• the line attachment is shown in FIG. 4 and embraces at a recess 21 two guide rails 19 and 20 connected by welding to the plate, the rail 19 being annular and extending along the outer edge of the bottom plate 15, and the rail 20 extending along the upper portion of the cylindrical surface of the plate.
• the attach ⁇ ment is displaceably guided by the rails.
• FIG. 5 there is shown one manner in which the anchor devices 14 preferably are used for anchoring a rig 10 floating on the water.
• Four identical groups each having three anchor devices 14 of the invention, are arranged and each group thereof comprises an anchor line or a main line 14 connected to the rig at one end thereof and connected to a block 12 at the other end thereof.
• Three branch lines 13 extend from the block 12, each of which is connected to one anchor device 14 engaged with the sea bottom.
• the term line relates not only to steel* wire ropes but also to ropes of synthetic fibres and chains as well as combinations thereof.
• the anchor. devices are distributed around the block 12, and it is necessary to have at least two devices for proper functioning of the arrangement. However, it is preferred to use at least three anchor devices for symmetry reasons. The number can also be larger than three. However, in that case special arrangements are required in order to obtain a statically defined load distribution, as will be described below.
• the anchoring method principally is based on a conversion of size and direction of the forces, force transformation, by the forces being split-up into vectors such that the force in the main line 11 having a large elevation angle ⁇ , will be converted into forces in the branch lines, hav ⁇ ing defined smaller elevation angles ⁇ -, , 2J and ⁇ ,, and conversely larger forces which are reduced, however, by the total anchoring force in the main line being split-up into several anchor forces in the branch lines.
• the elevation angle generally is defined as the inclina ⁇ tion angle of the line and the force, respect vely, to the horizontal plane at the attachment point as measured in a plane through the vertical line at the attachment point and the line/force.
• the force geometry i.e. the vector geometry
• FIG. 7 one embodiment of this kind is dis ⁇ closed wherein the forces from the anchor devices are reduced by the devices being interconnected in a bifurcated arrangement comprising six anchor devices 14.
• the number of branch lines 13 connected to the block 12 is reduced to three lines. It is achieved that all lines always are stretched and that the forces are statically defined, the arrangement at the same time including no moving parts.
• the configuration can be successively extended to comprise an indefinite number of anchor devices .
• the inter ⁇ connection of the branch lines i .e. the net structure
• the dash lines indicate lines which may be excluded. If these lines are included in the net structure, they are located in a plane below " the block and they are inter ⁇ connected independently of the block.

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20353095

Family Applications (1)

Country Status (14)

Cited By (1)

Citations (6)

Family Cites Families (1)

• 1983
  • 1983-10-28 SE SE8305933A patent/SE8305933D0/xx unknown
• 1984
  • 1984-10-26 IT IT23329/84A patent/IT1177049B/it active
  • 1984-10-26 ES ES1984293271U patent/ES293271Y/es not_active Expired
  • 1984-10-29 JP JP59504087A patent/JPS61500218A/ja active Pending
  • 1984-10-29 BR BR8407355A patent/BR8407355A/pt unknown
  • 1984-10-29 WO PCT/SE1984/000360 patent/WO1985001925A1/en active IP Right Grant
  • 1984-10-29 DE DE8484904193T patent/DE3469288D1/de not_active Expired
  • 1984-10-29 EP EP84904193A patent/EP0191765B1/en not_active Expired
  • 1984-10-29 AU AU35557/84A patent/AU591053B2/en not_active Expired - Fee Related
  • 1984-10-29 KR KR1019850700102A patent/KR850700024A/ko not_active Application Discontinuation
  • 1984-10-30 IE IE2784/84A patent/IE55888B1/xx unknown
• 1985
  • 1985-06-24 NO NO852530A patent/NO852530L/no unknown
  • 1985-06-25 DK DK286585A patent/DK286585D0/da not_active Application Discontinuation
• 1986
  • 1986-04-25 FI FI861754A patent/FI861754A0/fi not_active Application Discontinuation

Patent Citations (6)

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