ARCTIC OFFSHORE PLATFORM

• US 3,831,385 A
• Filed: 06/26/1972
• Issued: 08/27/1974
• Est. Priority Date: 06/26/1972
• Status: Expired due to Term

• Current Assignee: Gordon E. Strickland Jr, Thomas A. Hudson
• Original Assignee: Gordon E. Strickland Jr, Thomas A. Hudson
• Inventors: Hudson, Thomas A., Strickland, Gordon E. Jr.
• Primary Examiner(s): Shapiro, Jacob
• Application Number:
  US05/266,084
• Time in Patent Office: 792 Days
• Field of Search: 61/46,46.5 114/40,41,42,5D 165/47 166/.5 9/8P
• US Class Current: 405/211
• CPC Class Codes: E02B 17/0021 against ice-loads

Abstract

A method and apparatus for reducing ice forces on a marine structure erected in a body of water which becomes frozen through natural weather conditions. The structure has a wall of heat transmitting material forming its perimetrical surface in the zone where natural ice will freeze onto or impinge against the structure. Enclosed chambers are built within the structure and in heat transmitting relationship with the outer wall and heat is applied to the chambers to heat and maintain the outer wall at a temperature above the melting point of the natural ice occurring in the water around it. In a preferred embodiment the marine structure is formed with a heated wall which slopes upwardly and inwardly in the area of ice contact to provide a ramp-like surface upon which a sheet of ice will be forced with reduced friction as it moves against the structure. Thus an edge of the sheet of ice will be prevented from adhering to the structure and will be lifted above its normal position on the water surface as the ice moves against the structure, causing the sheet to be bent and fractured, reducing the force imposed by it on the structure.

Claims

1. A method for reducing ice forces on a marine structure established in a fixed condition in a body of water which becomes frozen through ambient natural conditions, comprising:

forming an enclosed chamber in said marine structure at a position on said structure at which an exterior surface of a wall portion of said chamber will be in contact with said water and in an area on said structure of potential contact with ice caused by natural freezing of said water, disposing said exterior surface of said wall portion at an angle inclined to the surface of said water to form a sloping ramplike surface to receive and elevate above its natural level an edge portion of a sheet of ice as said sheet of ice moves into contact with said surface, placing a controllable source of heat in communication with the interior of said chamber, heating the interior of said chamber an amount at least sufficient to cause the temperature of said exterior surface to be above the melting point of natural ice formed in said water adjacent said structure, and controlling the heat of said interior to maintain said temperature of said exterior surface above said melting point as said ambient conditions at the location of said structure changes, thereby preventinG said ice from freezing onto and adhering to said exterior surface thus reducing the force exerted on said fixed structure by a relative movement of said ice which is in contact with said exterior surface and assisting the ice in slipping over and upon said surface as said movement of said sheet of ice is continued.

2. The method in accordance with claim 1 wherein said interior of said chamber is heated by a heat transfer fluid at a temperature above the melting point of said ice, and wherein said heat transfer fluid is heated and circulated through the said interior of said chamber at a controlled rate sufficient to cause said temperature of said exterior wall to be maintained above the melting point of said ice.

3. The method in accordance with claim 2 wherein said heat transfer fluid is a liquid which is heated by heat generated from a source on said marine structure and is circulated through a heating means therefor and through said chamber by a circulating pump mounted on said marine structure.

4. The method in accordance with claim 2 wherein said heat transfer fluid is heated by the waste heat exhausted from an engine employed to generate power to operate the machinery and equipment associated with said marine structure.

5. The method in accordance with claim 2 wherein said heat transfer fluid is a mixture comprising water, an antifreeze component and a component to inhibit corrosion of the walls of said interior of said chamber.

6. A method for preventing ice from adhering to a selected surface of a marine structure established in a fixed condition at a location in a body of water which becomes frozen through ambient natural conditions, comprising forming an outer wall for said structure at a position which will be in contact with said water in a zone of natural freezing of said water, disposing said outer wall at an angle to the surface of said water to form a sloping wall at least throughout the region of said zone, constructing said sloping wall to receive an edge portion of a sheet of ice which moves against said wall, said wall being formed of a material which transmits heat and having an interior surface exposed within said structure and an exterior surface in contact with said water, heating said interior surface of said wall by means of a source of heat generated on said structure, and controlling said heat to maintain said exterior surface of said wall above the melting point of ice formed naturally in said water adjacent said structure as the weather conditions at the location of said structure changes to provide a film of water between said wall and said ice in contact with said wall portion, said film of water providing a means for reducing the force imposed on said structure by said ice as said ice moves upon said structure in engagement with said wall.

7. A method for reducing the force imposed on a marine structure established in a relatively fixed location by the movement against it of a sheet of ice present in the water adjacent the said structure, comprising constructing said structure with an outer surface which is sloped inwardly and upwardly of said structure in the area of potential contact with an ice sheet present in said water, heating said surface to a temperature above the melting point of said ice to prevent said ice from freezing on and adhering to said surface, maintaining said surface at a temperature above the melting point of said ice continuously during the time a sheet of ice exceeding a predetermined minimum thickness is present in the water adjacent said structure to maintain a film of water between said surface and said ice, constructing said heated surface to function as a ramp to cause a portion of a sheet of ice which moves against said structure to be lifted and bent from its normal position on said water, said film of water providing a means for reducing the force imposed on said structure by said ice as said ice moves relative to and aGainst said structure and in engagement with said surface, selecting an angle of slope of said surface of an amount to cause said portion of said sheet to be bent sufficiently to fail in bending and to fracture said ice as it moves against said structure, thereby reducing the force imposed on said structure by a sheet of ice moving relative to and in contact with said surface to an amount less than that imposed by the movement of an unfractured sheet of ice which is frozen onto said surface.

8. A marine structure constructed to be maintained in a fixed position in a body of water which becomes frozen through natural conditions, comprising a support portion of said structure, said support portion extending into a body of water and supporting a work platform above the surface of said water, a perimetrical wall of said support portion in contact with said water and extending from below the surface of said water to above said surface, said wall constructed to be disposed at an angle inclined to said surface of said water to provide a ramp-like surface to receive a sheet of ice moving relative to and in contact with said structure, at least one circumferentially disposed chamber within said support structure with said perimetrical wall forming the outer wall of said chamber, means for circulating a heat transfer fluid through said chamber, and means on said structure for heating the circulating said heat transfer fluid an amount sufficient to maintain the temperature of said perimetrical wall above the melting temperature of natural ice occurring in said body of water adjacent said wall.

9. A marine structure in accordance with claim 8, including engines on said structure for providing motive power for the operation of equipment on said structure, exhaust gases produced by the operation of said engines, heat exchanger means on said structure, means for directing said exhaust gases to said heat exchanger means, and means for circulating said heat transfer fluid through said heat exchanger means to provide said heating of said heat transfer fluid.

10. A marine structure in accordance with claim 9 wherein said heat transfer fluid is a mixture comprising water and an antifreeze component.

11. Means for reducing the effect of ice forces on a structure established and maintained in a fixed position in an open sea environment, which sea becomes frozen at the surface through natural conditions, comprising a marine structure positioned in an open sea environment in fixed relationship to the bottom of the sea, a perimetrical wall on said structure, a selected area of said wall being formed of a material which readily transmits heat, an outer surface of said selected area of wall positioned to be in contact with the ice of said sea, and disposed at an inclined angle to the surface of said water in a position to receive and support an edge portion of a sheet of ice which continuously moves into contact with said selected area and to elevate said edge portion above its natural level an amount to cause said sheet of ice to fracture continuously adjacent said structure, an inner surface of said selected area of wall, means for excluding said sea from contact with said inner surface, said selected area of wall extending upwardly from below the surface of said sea to above said surface at least throughout a zone of natural freezing of said water, a source of heat on said structure, and means for applying heat from said source to said inner surface of said selected area of wall in an amount to maintain the temperature of the said outer surface in the region of said zone above the melting point of said ice in contact with said structure to provide a film of water between said ice and said area of said wall thereby to reduce the force transmitted from the continuously moving said ice to said structure.

12. Means for reducing the effect of ice forces in accordance with claIm 11 in which the said selected area of said perimetrical wall is sloped upwardly and inwardly of said structure at an angle of approximately 45* to the horizontal to provide a ramp-like surface to receive and elevate above its natural level on said sea a portion of a sheet of ice which moves against said structure, thereby to cause said sheet of ice to bend and break adjacent said wall.

13. An offshore drilling platform for use in a body of water which becomes frozen through natural conditions, comprising a supporting base portion constructed to be installed in a relatively fixed position in a body of water, platform decks supported by said portion above the surface of said water, a circumferential wall on said base portion with at least a portion of said wall being made watertight and with a frustoconical form converging upwardly of said drilling platform and extending from a location below the surface of said water to a location above said surface, ballast compartments within said base portion and adjoining said portion of said wall in heat transmitting relationship, said base portion constructed with sufficient buoyant capacity to maintain said drilling platform in a floating condition to permit said platform to be towed through said water, means for admitting ballast into said ballast compartments to decrease said buoyant capacity an amount to cause said drilling platform to be lowered into contact with the underwater bottom, means for displacing ballast from said ballast compartments, means for circulating a heat transfer fluid through said ballast compartments, means for heating said fluid an amount sufficient to increase the temperature of said portion of said body of water adjacent said drilling platform and in contact with said portion of said wall.

14. An offshore drilling platform in accordance with claim 13 including a power generating engine on said platform, waste heat produced by said engine, and means for heating said heat transfer fluid with said waste heat.

15. An offshore work platform for use in a body of water upon which ice is formed through natural conditions, comprising, a base portion positioned in a body of water, means securing said base portion to the underwater bottom, a deck portion supported by said base portion above the surface of said water, a wall section on said base portion and extending from below said surface of said water to above said surface, said wall section formed converging upwardly and inwardly of said platform at least in the region of contact of said surface of said water with said wall section and constructed to receive and elevate above its natural level a portion of a sheet of ice which moves on said body of water into contact with said wall section, a watertight compartment enclosed within said wall section approximately in horizontal alignment with said region, heating means within said compartment and in heat transfer relationship with said wall section, and means on said platform for operating said heating means to heat said wall section in said region above the melting point of ice formed in said water and in contact with said wall section thereby to form a lubricating film of water in the area of contact between said sheet of ice and said wall section.