GB2212452A

GB2212452A - A method and apparatus for locally breaking a sheet of ice in a cold sea

Info

Publication number: GB2212452A
Application number: GB8803530A
Authority: GB
Inventors: Francois Gabriel Sedillot; Gerard Alexis Andre Barbaras
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-11-17
Filing date: 1988-02-16
Publication date: 1989-07-26
Anticipated expiration: 2008-02-16
Also published as: FR2623220A1; GB2212452B; GB8803530D0; FR2623220B1

Abstract

A method and apparatus for locally breaking a sheet of ice in cold waters, from a structure held in the ice or submerged under the ice; from this structure the ice sheet is subjected to a substantially perpendicular thrust in such away as to bend the sheet, the thrust and the bending being increased to the point of cracking and rupture. For that purpose a submerged vessel 1 is provided with a projection (3) which may be telescopic adapted to apply on the ice and to transmit thereto an upwardly vertical thrust through a contact head, or the projection may be mounted to a ballastable chamber to produce upward thrust on the ice from an offshore platform (Fig 11). Alternatively downward thrust on the ice surface may be made by projections on fixed or floating offshore platforms (Figs 14 and 15). <IMAGE>

Description

A Method and Apparatus for locally Breaking a Sheet of Ice in a Cold Sea This invention concerns a method and an apparatus for locally breaking a sheet of ice in cold waters.

The problem which the Applicant has encountered is specifically that of a submersible vessel which, being immersed under sheet of ice, the thickness of which may reach a value of the order of one metre, must be able to break the ice above it in order to surface. The problem also arises, albeit under different conditions, in respect of such installations as off-shore exploitation platforms, or bridge piers that have a submerged portion which is therefore under the ice at certain times of the year, so that the ice should be broken locally, for example in order to protect the structure or to be able to reach the foundations.

The method which forms the subject of the invention is characterised in that, in the zone in which it is desired to cause the rupture, the ice is subjected to a substantially perpendicular thrust, in such a way as to bend the sheet of ice; and in that the thrust and bending are increased until rupture occurs.

In the case of a submarine, or an instailtion having a submerged floating portion, the thrust, directed upwardly, is produced by the hydrostatic force resulting from ballast being suitably discharged.

The invention alsú embraces the apparatus for putting the method into practice, the apparatus being characterised by a projection which may take the form of a mast, the upper end of which will be applied to engage on the underside of the ice sheet.

This projection or mast may be retractable or fixed.

In the case of a submarine, the mast will usually be retractable, consisting of a telescopic system in such a manner that, when the mast is out of action, it is completely concealed within the hull without leaving any projection which could be prejudicial to good hydrodynamic perfornance of the submarine.

Tne description that follows, with reference to the annexed drawings, given as a matter of example, will allow to understand how the invention may be put into practice.

Figures 1 to 6 are schematic views reliresenting tl:e various operation phases of the invention, in the case of a submarine navigating under an ice sheet.

Figure 7 snows in section, on a larger scale, one embodiment of a telescopic mast, in a retracted position.

Figure 8 shows the same mast extended.

Figure 9 is a graph showing the variation of the force exerted by the mast in order to break the ice, as a function of the thickness of the latter, for different mast diameters.

Figure 10 is a transverse section of the submarine with one particular embodiment of a secondary mast.

Figure 11 shows the application of the invention in the case of a platform, the foundation of which rests on the sea bed.

Figures 12 and 13 show a floating platform case.

Figures 14 and 15 show two variants in applying the invention to marine platforms, in which variants the force exerted by the mast to break the ice is directed downwardly.

In Figure 1, there is seen at 1 a submarine or submersible vessel, civil or military, whether tanned or not, which navigates under an ice sheet 2.

In Figure 2, this vessel begins an upwards movement by discharging ballast so as to come into contact with the ice to be broken.

A first mast 3, which is actually the rupturing mast and will be referred to as the main mast, is deployed on the conning tower or superstructure 4 of the vessel, and a second mast 5, which will be referred to as the secondary mast, is similarly deployed, towards the stern of the vessel, so as to engage the ice and to protect the working parts at the stern, which are fragile. The ballast is deployed in such a fashion that the rising buoyancy force has its resultant acting close to the main mast, but slightly offset towards the secondary mast. This arrangement permits, on the one hand, maximum available rupturing force at the main mast, and on the other hand the achievement of longitudinal stability of the vessel.

In Figure 3, the vessel approaches the ice while ascending under the effect of upward force created by deballasting.

In Figure 4, contact has been made by the secondary mast as well as by the main mast 3, and the force exerted by the main mast on the ice sheet puts it in a bending mode progressively.

In Figures 5 and 6, the ice is broken and the superstructure is emerging the surface, this being the desired result. Surfacing can also be carried out up to the level of normal buoyancy, according to the quantity of ballast released.

In the embodiment shown in Figures 7 and 8, both the main mast and the secondary mast are constituted by a telescopic system.

In the example shown, this system has two elements, namely a fixed cylinder 6 and a piston 7 movable in the cylinder and constituting with it a hydraulic jack, the power of which is large enough to balance the buoyancy force exerted by the submarine, the stroke of the jack being large enough to take account of irregularities in the underside of the ice sheet. This jack is preferably double acting, so as to ensure return to the concealed position within the conning tower of the submarine. The cylinder 6 is provided at its ends with pipes 8 and 9 equipped with three-position gate valves 10 and 11 so as to connect the pipes for supply of liquid under pressure or for exhaust purposes.

At the upper end of the piston rod, there is a contact head 12 for engaging under the ice sheet, and which may be simply of circular shape. Fixed below the head 12 is a sleeve 13, which slides into a fixed casing 14 provided with bearing rings 15, 16 for easy guiding of the sleeve 13.

The tubular casing 14 is fixed partly to the outer hull 17 of the submarine, and partly, by means of a flange 18, to the bulkhead or the inner hull 19. The whole system is arranged in such a manner that in the retracted condition, the outer face of the head 12 is exactly flush with the outer hull with substantially no projection.

The sleeve 13 protects the piston rod against damage by the ice. Moreover, the assembly of the sleeve 13 and the casing 14, maintained by the bearing rings 15 and 16, ensures better resistance of the system to lateral forces. These lateral forces can be caused by inclination of the underside of the ice, or by a non-vertical orientation of the main mast due to the trim of the vessel.

The method of operation of the apparatus can easily be understood.

Starting with the retracted condition shown in Figure 7, in order to deploy the mast, the valve 10 is set so as to provide pressurised liquid below the piston 7, and the valve 11 is set so as to allow the exhaust of the liquid above the opposite face of the said piston. The mast is then deployed as shown in Figure 8.

The mast is locked in its deployed position by simple closing of the valves 10 and 11, which, so long as ballast is being discharged, will allow the value of the forces applied to the underside of the ice by the main mast (and also by the secondary mast) to be continuously monitored by simple reading of the hydraulic pressure inside of the cylinder 6.

This principal locking system is supplemented by a locking system of a mechanical type, which will be operated after the deployment of the mast, but which should only be effective in the event of failure of the hydraulic pressure, for example due to leakage.

Such a system is represented as 21. It may comprise bolts 22, movable transversely so as to come into engagement with holes provided in the sleeve 13, thus securing the latter.

In order to retract the mast, the valve 1u is turned into the exhaust position, and the valve 11 into the supply position, after releasing the mechanical bolts 22.

The curves in Figure 9 were traced for different diameters of the contact head 12, these diameters being respectively equal to 0.5 m, 1 m and 2 m. Tfle thickness of the ice sheet in metres has been represented in the abscisse, while the forces required to crack the ice sheet has been represented in meganewtons along the ordinate.

These curves show that it is advantageous to reduce surface of applied force, that is to say the surface of the contact head 12, in order to crack a given thickness of the ice sheet while developing a force as limited as possible; or of course, as a corollary, to crack a thickness of ice as great as possible while developing a given force.

Figure 10 shows one particular embodiment of te secondary mast, which, instead of consisting of a single mast, comprises two masts 5a, 5b disposed in a common transverse plane and divergent from each other. This has the advantage of providing, with the main mast, a tripod system which improves the transverse stability of the vessel when in contact with the ice.

Figure 11 illustrates another application of the invention. It shows a platform 25 which rests on the sea bed through a base 26, the submerged part of which lies below the ice sheet 2.

In order to break the ice and to limit or eliminate the forces exerted by the ice on the structure, or to enable access to the base, breaking ice masts 3 may be disposed on the base. In this application, it is unnecessary for the masts to be telescopic. They may be permanently deployed as in the embodiment shown in Figure 11, in which each mast 3 is supported by a buoyant chamber 27 movable in a fixed cylinder 28. In this case, the assembly comprising the masts and the movable buoyant chambers will be actuated by a simple Archimedean effect, resulting from the deballasting of water held in the chambers 27, a fluid-tight seal between the chambers 27 and the cylinders 28 being in this case unnecessary.The deballasting of the chambers and their further ballasting to ensure their return to the initial position, is effected with the aid of a system of pipework 30 comprising flexible portions 29, and connected to pumps, not shown, installed on the platform.

Alternatively, in an embodiment which is not shown, the movable chambers 27 may be raised by a piston force, with the aid of the water fed under pressure into the part of the cylinders 28 immediately below them. In this case it is necessary to ensure fluid-tightness between the movable chambers 27 and the cylinders 28.

The right-hand part of Figure 11 shows the rest position, and the left-hand part shows the position for breaking the ice.

Figures 12 and 13 represent the case of a floating platform 25 attached by moorings 31 which are anchored to the sea bed. A platform of this kind contains ballasts, the intake and discharge of which allows to vary the draught of the submerged part. Masts 3 can be arranged on the submerged part, and may be fixed, or deployable by reams of a telescopic system similar to that which has been described with reference to Figures 7 and 8.

Figure 12 shows the platform 25 with a base submerged below the sheet of ice which has formed on the surface of the water. When the ice sheet has to be broken, ballast is discharged, after the masts 3 have been deployed if they are telescopic. Deballasting produces an upwardly directed force, so that the masts exert pressure on the ice and break it as explained above.

Alternatively, the floating platform 25 can be equipped with ballast chambers which can be emptied individually, as in the case of the fixed platform shown in Figure 11.

A further arrangement, in which the ice is broken with a downwardly directed force, is shown in Figures 14 and 15.

Figure 14 shows a fixed platform 25 resting on the sea bed through a base 26, the submerged part of the platform being under the sheet of ice 2. In order to break this sheet, masts 3 are deployed, these being fixed in the emergent part 40 of the platform. The masts 3 function in a similar way to the telescopic jacks applying upwardly vertical forces, so as to break the ice locally and thus protect the platform from ice forces.

Figure 15 shows a floating platform 25, attached by moorings 31 anchored to the sea bed. The masts 3, fixed in the emergent part 40 of the platform, apply downwardly vertical forces on the ice sheet, the forces being created by ballasting and controlled immersion of the structure. The masts 3 may be fixed or extensible by virtue of a telescopic system similar to that which has been described with reference to Figures 7 and 8.

It goes without saying that the embodiments described have only been given by way of example, and that they could be modified, especially by substituting equivalent techniques, without departing from. the spirit of the invention.

For example, the hydraulic jacks described could be replaced by jacks of different types, especially mecnanical jacks.

Furtherore, to assist in breaking the ice, additional means can be employed in order to locally reduce cohesion and mechanical resistance of the ice sheet. Such means may for example be adapted for heating the ice in the zone of contact of the each or all projections or masts.

These would, for instance, consist of steam ejectors. The additional means can also operate b physico-cheicsl action, for example by depressing the freezing point, vr again by purely mechanical action, for instance b vibrators or percussion devices of the rock hammer type, driven by compressed air.

Claims

C Ii A I 1 S

1. A method for locally breaking a sheet of ice in cold waters, from a structure field in the ice or submerged below the ice, characterised in that, the sheet of ice is 'subjected to a substantially perpendicular thrust originated from the said structure in such a way as to bend the sheet of ice, and in that the thrust and bending are increased to the point of cracking and rupture.

2. A method according to Claim 1, applicable to a submarine or to a partly-submerged installation, characterised in that the thrust is directed upwardly on to the underside of the ice sheet and is produced by a hydrostatic force resulting from discharge of ballast.

3. A method according to Claim 1, characterised in that the thrust is exerted downwardly on to the surface of the ice sheet from an emergent part.

4. A method according to one of Claims 1 to 3, characterised bg the use of additional thermal, physico- chemical or mechanical means, in order to reduce the cohesion and mechanical resistance of the ice.

5. Apparatus for performing the method according to one of the preceding Claims, characterised in that the submerged vessel, or the submerged or emergent part of a structure, is provided with a projection (3) adapted to apply on the ice sheet and to transit thereto a vertical thrust through a cal-ibrated contact face (12).

6. Apparatus according tc Claim 5, characterised in that the projection is in the form of a mast.

7. Apparatus according to Claim 5 or Claim 6, characterised in that the projection is coupled with a jack (6, 7), for moving it towards the ice sheet so as to bring it into contact with the latter.

8. Apparatus according to one of Claims 5 to 7, characterised in tat the protection or mast comprises a telescopic system such that it can either be concealed completely below the surface of the vessel, or be deployed from it.

9. Apparatus according to Claim 7 or Claim 8, characterised in that the jack is of hydraulic type, and is provided with gate valves (10, 11) for isolating, supplying and exhausting it so as to secure it in its working position.

10. Apparatus according to Claim 9, characterised by a device for indicating the hydraulic pressure existing in the jack, and therefore the force applied to the ice sheet.

11. Apparatus according to one of Claims 7 to IC, characterised in that the jack is provided with a sleeve (13), a casing (14), and bearing rings (15, 16) in such a manner as to ensure protection of the jack and increased rigidity of the mast against lateral forces.

12. Apparatus according to Claim 5 or Claim 6, characterised in that the projection is coupled with a movable, de-ballastable chamber (27) buoyancy of which produces the thrust on the ice sheet.

13. Apparatus according to one of Claims 5 to 10, applied to a submarine, characterised in that the main projection (3), mounted on the superstructure of the vessel, is associated with a second projection (5), disposed near the stern su as to improve stability of the submarine.

14. Apparatus according to Claim 13, characterised in that the additional projection comprises two divergent masts (5a, 5b), disposed in a plane substantially perpendicular to the axis of the submarine.