Arctic multi-angle conical structure

• US 4,245,929 A
• Filed: 04/27/1979
• Issued: 01/20/1981
• Est. Priority Date: 04/27/1979
• Status: Expired due to Term

• Current Assignee: Chevron Research Company (Chevron Corp.)
• Original Assignee: Chevron Research Company (Chevron Corp.)
• Inventors: Aagaard, Paul M., Strickland, Gordon E., Pearce, James C.
• Primary Examiner(s): Corbin, David H.
• Application Number:
  US06/034,085
• Time in Patent Office: 634 Days
• Field of Search: 405/61, 405/195, 405/211, 405/217, 405/224, 114/40, 114/41, 114/42
• US Class Current: 405/211
• CPC Class Codes: E02B 17/0021 against ice-loads

Abstract

An offshore structure which is able to withstand the ice forces imposed thereon by impinging ice sheets and other larger masses of ice wherein the structure has an upper conical portion coaxially positioned relative to a lower conical portion. The walls forming both the upper and lower portions are inclined at an angle to the horizontal to receive ice masses moving into contact with the structure. The angle of inclination from the horizontal of the upper portion is greater than the angle of inclination of the lower portion, and the cross-sectional diameter of the upper conical portion is no greater than that at the top of the lower conical portion.

Claims

1. An offshore structure for use in a body of water that contains ice masses, comprising

a lower portion having a first circumferential wall substantially in the shape of a first truncated cone so that the wall of said lower portion is inclined at an angle to the horizontal, said first circumferential wall providing a ramp-like surface means for receiving ice masses moving relative to and in contact with said structure so as to elevate said ice above its natural level to cause said ice to fail in flexure adjacent said structure;

means for affixing said lower portion to the bottom of a body of water; and

an upper portion coaxially positionable above said lower portion, said upper portion having a second circumferential wall substantially in the shape of a second truncated cone so that the wall of said upper portion is inclined at an angle to the horizontal, said second circumferential wall providing a ramp-like surface means for receiving ice masses moving relative to and in contact with said structure so as to elevate said ice above its natural level to cause said ice to fail in flexure adjacent said structure, the angle of inclination from the horizontal of the wall of said upper portion being greater than the angle of inclination from the horizontal of the wall of said lower portion and the cross-sectional diameter of the wall of said upper portion being no greater than the cross-sectional diameter at the top of the wall of said lower portion.

2. A marine structure for use in a body of water that contains ice masses, comprising

a base portion;

means for affixing said base portion to the bottom of a body of water;

a lower portion coaxially positionable on top of said base portion for joining thereto, said lower portion forming a first circumferential wall substantially in the shape of a first truncated cone so that the wall of said lower portion is inclined at an angle to the horizontal, said first circumferential wall providing a ramp-like surface means for receiving ice masses moving relative to and in contact with said structure so as to elevate said ice above its natural level to cause said ice to fail in flexure adjacent said structure; and

an upper portion coaxially positionable on top of said lower portion for joining thereto, said upper portion forming a second circumferential wall substantially in the shape of a second truncated cone so that the wall of said upper portion is inclined at an angle to the horizontal, said second circumferential wall providing a ramp-like surface means for receiving ice masses moving relative to and in contact with said structure so as to elevate said ice above its natural level to cause said ice to fail in flexure adjacent said structure, the angle of inclination from the horizontal of the wall of said upper portion being greater than the angle of inclination of the wall of said lower portion and the cross-sectional diameter of the wall of said upper portion being no greater than the cross-sectional diameter at the top of the wall of said lower portion.

3. The marine structure of claim 2 wherein the angle of inclination of the wall of said lower portion is between about 15°

and 25°

from the horizontal and wherein the angle of inclination of the wall of said upper portion is between about 26° and

70°

from the horizontal.

4. The marine structure of claim 2 wherein the angle of inclination of the wall of said lower portion is between about 19°

and 23°

from the horizontal and wherein the angle of inclination of the wall of said upper portion is between about 54° and

58°

from the horizontal.

5. The marine structure of claim 2 wherein the angle of inclination of the wall of said lower portion is about 21°

from the horizontal and wherein the angle of inclination of the wall of said upper portion is about 56°

from the horizontal.

6. The marine structure of claim 2 wherein said base portion is affixed to the bottom of said body of water.

7. The marine structure of claim 2 further including:

a cylindrical throat portion coaxially positionable on top of said upper portion for joining thereto and for extending a work platform above the surface of said body of water.

8. The marine structure of claim 7 wherein the angle of inclination of the wall of said lower portion is between about 15°

and 25°

from the horizontal and the angle of inclination of the wall of said upper portion is between about 26° and

70°

from the horizontal.

9. The marine structure of claim 7 wherein the angle of inclination of the wall of said lower portion is between about 19°

and 23°

from the horizontal and the angle of inclination of the wall of said upper portion is between about 54° and

58°

from the horizontal.

10. The marine structure of claim 7 wherein the angle of inclination of the wall of said lower portion is about 21°

from the horizontal and the angle of inclination of the wall of said upper portion is about 56°

from the horizontal.

11. The marine structure of claim 7 wherein said base portion is affixed to the bottom of said body of water.

12. An offshore structure for use in a body of water which becomes frozen through natural conditions, comprising:

a supporting base portion positioned in a body of water;

a means for securing said base portion to the underwater bottom;

a lower portion directly joined to and rigidly supported on said base portion, said lower portion forming a first peripheral wall which converges upwardly and inwardly of said base portion, said first peripheral wall providing means for receiving and supporting an edge portion of a sheet of ice or other larger mass of ice which moves in contact with said lower portion so as to elevate said ice above its natural level an amount to cause said ice to fracture continuously adjacent said offshore structure; and

an upper portion directly joined to and rigidly supported on said lower portion, said upper portion forming a second peripheral wall which converges upwardly and inwardly of said lower portion to, said second peripheral wall providing means for receiving and supporting an edge portion of a sheet of ice or other ice mass which moves into contact with said upper portion so as to elevate said ice above its natural level an amount to cause said ice to fracture continuously adjacent said offshore structure, said second peripheral wall having a base diameter no greater than that of the top diameter of said first peripheral wall and said second peripheral wall converging upwardly and inwardly at a greater slope than said first peripheral wall.

13. The offshore structure of claim 12 wherein said base portion forms a third peripheral wall which converges upwardly and inwardly of the underwater bottom and wherein the top diameter of said third peripheral wall forming said base portion is approximately equal to the base diameter of said first peripheral wall forming said lower portion.

14. The offshore structure of claim 13 further including:

a cylindrical throat portion rigidly supported on said upper portion for supporting a work platform above the surface of said body of water.

15. The offshore structure of claim 14 wherein an inverted truncated cone section is positioned between said throat portion and said work platform to deflect ice riding up the structure away from said work platform and wherein the wall of said inverted truncated cone section is inclined from the vertical at an angle of between approximately 26°

and 70°

.

16. The offshore structure of claim 14 wherein said work platform has the shape of an inverted truncated cone and wherein the walls of said inverted truncated work platform are inclined from the vertical at an angle of between approximately 26°

and 70°

.

17. The offshore structure of claim 15 or 16 wherein said first peripheral wall converges upwardly and inwardly of said base portion at an angle of between approximately 15°

and 25°

from the horizontal and wherein said second peripheral wall converges upwardly and inwardly of said lower portion at an angle of between approximately 26° and

70°

from the horizontal.

18. The offshore structure of claim 15 or 16 wherein said first peripheral wall converges upwardly and inwardly of said base portion at an angle of between approximately 19°

and 23°

from the horizontal and wherein said second peripheral wall converges upwardly and inwardly of said lower portion at an angle of between approximately 54° and

58°

from the horizontal.

19. The offshore structure of claim 15 or 16 wherein said first peripheral wall converges upwardly and inwardly of said base portion at an angle of approximately 21°

from the horizontal and wherein said second peripheral wall converges upwardly and inwardly of said lower portion at an angle of approximately 56°

from the horizontal.

20. An offshore structure for use in arctic waters comprising:

a base section constructed to be installed in a relatively fixed position in a body of water;

a lower truncated cone section in vertical abutting relationship with said base section, said lower section providing means for receiving and supporting an edge portion of an ice mass which moves into contact with said lower section so as to elevate said ice above its natural level an amount to cause said ice to fracture continuously adjacent said structure;

an upper truncated cone section of a steeper angle and of no greater cross-sectional diameter than said lower section and in vertical abutting relationship with said lower section, said upper section providing means for receiving and supporting an edge portion of an ice mass which moves into contact with said lower section so as to elevate said ice above its natural level an amount to cause said ice to fracture continuously adjacent said structure;

a cylindrical throat section in vertical abutting relationship with said upper truncated cone section;

an inverted truncated cone section in vertical abutting relationship with said throat section; and

a work platform positioned on said inverted truncated cone section.

21. An offshore structure to be located in a body of water that contains ice masses, comprising:

a base portion;

means for securing said base portion to the bottom of a body of water;

a lower portion coaxially positionable on top of said base portion, said lower portion forming a first circumferential wall substantially in the shape of a first truncated cone so that the wall of said lower portion is inclined to the bottom of the body of water at an angle of between approximately 15° and

25°

from the horizontal, said first circumferential wall providing a first ramp-like surface means for receiving ice masses moving relative to and in contact with said structure; and

an upper portion coaxially positionable on top of said lower portion, said upper portion forming a second circumferential wall substantially in the shape of a second truncated cone so that the wall of said upper portion is inclined to the bottom of the body of water at an angle of between approximately 26° and

70°

from the horizontal, said second circumferential wall providing a second ramp-like surface means for receiving ice masses moving relative to and in contact with said structure, the cross-sectional diameter of the wall of said upper portion being no greater than the cross-sectional diameter at the top of the wall of said lower portion so that the wall of said upper portion and the wall of said lower portion form a continuous ramp-like surface; and

a cylindrical throat portion supported on said upper portion.

22. The offshore structure of claim 21 wherein the wall of said upper portion is inclined to the bottom of the body of water at an angle of between approximately 54°

and 58°

from the horizontal and wherein the wall of said lower portion is inclined to the bottom of the body of water at an angle of between approximately 19° and

23°

from the horizontal.

23. The offshore structure of claim 21 wherein the wall of said upper portion is inclined to the bottom of the body of water at an angle of approximately 56°

from the horizontal and wherein the wall of said lower portion is inclined to the bottom of the body of water at an angle of approximately 21°

from the horizontal.

24. A method of reducing the ice forces imposed on an offshore structure which contains ice masses, comprising:

constructing an offshore structure with a lower portion having a first circumferential wall substantially in the shape of a first truncated cone so that the wall of said lower portion is inclined at an angle to the horizontal, said first circumferential wall providing a ramp-like surface means for receiving ice masses moving relative to and in contact with said structure; and

positioning an upper portion of said structure coaxially on top of said lower portion, said upper portion having a second circumferential wall substantially in the shape of a second truncated cone so that the wall of said upper portion is inclined at an angle to the horizontal, said second circumferential wall providing a ramp-like surface means for receiving ice masses moving relative to and in contact with said structure, the angle of inclination from the horizontal of the wall of said upper portion being greater than the angle of inclination from the horizontal of the wall of said lower portion and the cross-sectional diameter of the wall of said upper portion being no greater than the cross-sectional diameter at the top of the wall of said lower portion.

25. A method of reducing the ice forces imposed on an offshore structure which contains ice masses, comprising:

constructing an offshore structure with a base portion so that said base portion may be affixed to the bottom of a body of water;

positioning a lower portion of said structure coaxially on top of said base portion, said lower portion having a first circumferential wall substantially in the shape of a first truncated cone so that the wall of said lower portion is inclined at an angle to the horizontal, said first circumferential wall providing a ramp-like surface means for receiving ice masses moving relative to and in contact with said structure;

joining said lower portion to said base portion;

positioning an upper portion of said structure coaxially on top of said lower portion, said upper portion having a second circumferential wall substantially in the shape of a second truncated cone so that the wall of said upper portion is inclined at an angle to the horizontal, said second circumferential wall providing a ramp-like surface means for receiving ice masses moving relative to and in contact with said structure, the angle of inclination from the horizontal of the wall of said upper portion being greater than the angle of inclination from the horizontal of the wall of said lower portion and the cross-sectional diameter of the wall of said upper portion being no greater than the cross-sectional diameter at the top of the wall of said lower portion; and

joining said upper portion to said lower portion.

26. The method of claim 25 wherein the angle of inclination of the wall of said lower portion is between about 15°

and 25°

from the horizontal and the angle of inclination of the wall of said upper portion is between about 26° and

70°

from the horizontal.

27. The method of claim 25 wherein the angle of inclination of the wall of said lower portion is between about 19°

and 23°

from the horizontal and the angle of inclination of the wall of said upper portion is between about 54° and

58°

from the horizontal.

28. The method of claim 25 wherein the angle of inclination of the wall of said lower portion is about 21°

from the horizontal and the angle of inclination of the wall of said upper portion is about 56°

from the horizontal.

29. The method of claim 25 further including:

a positioning a cylindrical throat portio on top of said upper portion;

joining said throat portion to said upper portion; and

extending a work platform above the surface of said body of water.

30. The method of claim 29 wherein the angle of inclination of the wall of said lower portion is between about 15°

and 25°

from the horizontal and the angle of inclination of the wall of said upper portion is between about 26° and

70°

from the horizontal.

31. The method of claim 29 wherein the angle of inclination of the wall of said lower portion is between about 19°

and 23°

from the horizontal and the angle of inclination of the wall of said upper portion is between about 54° and

58°

from the horizontal.

32. The method of claim 29 wherein the angle of inclination of the wall of said lower portion is about 21°

from the horizontal and the angle of inclination of the wall of said upper portion is about 56°

from the horizontal.