Vertically moored platform

Abstract

This invention relates to a structure floating on a body of water. Three or more spar buoy-type floats support the structure above the water. The structure is connected to anchors in the floor of the body of water by .[.elongated members such as.]. large diameter pipe .Iadd.for example.Iaddend.. There are no other anchoring connections in the system. Each spar buoy has a unique structure so that vertical forces and overturning moments on the floating structure are minimized. .[.The spar buoys have a buoyancy means having a volume of two parts..]. g The buoy of each spar buoy has a volume of two parts. The first part can be defined as resulting from a straight, vertical, prismatic shape which runs the entire vertical length of the .[.buoyancy means..]. .Iadd.buoy.Iaddend.. The volume of this prismatic portion comprises between about 40 and 80 percent of the total displacement. The .[.buoyancy means have a second or.]. .Iadd.second part has an .Iaddend.auxiliary volume of displacement which runs considerably less than the vertical length of the prismatic portion. This critical arrangement of buoyancy between these two parts as taught in this invention minimizes mooring forces imposed on the vertical elongated members, such as occur to react forces on the structure due to passing waves.

I claim: 
     
       1. A floating structure having limited lateral movement for use in a body of water which comprises: a working deck;   buoyancy means for supporting said working deck, said buoyancy means including a plurality of slender vertical float members;   anchor means in the floor of the body of water;   horizontally spaced-apart, parallel, elongated members interconnecting the said buoyancy means and said anchor means whereby said deck is maintained parallel to and at a substantially constant angle with reference to the horizontal;   each said vertical float member of said buoyancy means having prismatic volume resulting from a straight, vertical, prismatic shape which runs the entire vertical length of the buoyance means, the volume of the prismatic portion comprising between about 40 and80 percent of the total displacement of the buoyancy means, and the structure having an auxiliary buoyancy portion having a volume of displacement between about 20 and about 60 percent of the total displacement of the buoyancy means, said auxiliary volume being placed below the trough of an expected maximum wave;   said platform and buoyancy means being free of any anchoring connection with the water bottom other than said parallel elongated members.   
     
     
       2. A structure as defined in claim 1 in which the volume of the prismatic portion comprises between about 40 and about 60 percent of the total displacement of the buoyancy means. 
     
     
       3. A structure as defined in claim 1 in which the ratio h max  /H is about 0.8 in which h max  is the height of an expected maximum wave and H is the still water draft. 
     
     
       4. A structure as defined as claim 3 in which the still water draft is between about 75 feet and about 150 feet. 
     
     
       5. A structure as defined in claim 1 in which the structure is so designed so as to have a still water draft between about 75 feet and about 150 feet. 
     
     
       6. An apparatus as defined in claim 1 including pivotal means connecting the lower ends of said elongated members with said anchor means and additional pivotal means connecting the upper ends of said elongated members with said buoyance means. 
     
     
       7. An apparatus as defined in claim 1 including horizontal fins attached to the lower portion of said buoyancy means. 
     
     
       8. An apparatus as defined in claim 7 including means to move said horizontal fins about a horizontal axis. 
     
     
       9. An apparatus as defined in claim 1 in which said elongated members are tubular members. 
     
     
       10. An apparatus as defined in claim 1 including cross bracing between the vertical float means, said cross bracing being restricted to the areas below the still water line. 
     
     
       11. A floating structure for use in the body of water having an expected maximum wave which comprises: a deck;   buoyancy means rigidly supporting said deck, said buoyancy means including at least three slender, vertical float members, each such float member having two parts, the first part resulting from a straight, vertical, prismatic shape which runs the entire vertical length of the vertical float member, the volume of the prismatic portion comprising between about 40 and about 80 percent of the total displacement of the vertical float member, and an auxiliary portion exterior said prismatic portion and, comprising between about 20 and about 60 percent of the total displacement of the buoyancy means below still water, said auxiliary portion being placed below the trough of the expected maximum wave;   anchor means at the bottom of said body of water;   an elongated member connecting each said vertical float member and said anchor means, said elongated members being parallel;   said structure being free of any anchoring connection with the water bottom other than said parallel elongated members.   
     
     
       12. A structure as defined in claim 11 in which the volume of the prismatic portion of the vertical float member is between about 45 and 65 percent of the total displacement of the vertical float member and the auxiliary portion exterior of said prismatic portion comprises between about 55 and about 35 percent of the total displacement of the buoyancy means below still water. 
     
     
       13. An apparatus as defined in claim 11 including pivotal means connecting the lower ends of said elongated members with said anchor means and additional pivotal means connecting the upper ends of said elongated members with said buoyancy means. 
     
     
       14. An apparatus as defined in claim 11 in which said elongated members are tubular members. 
     
     
       15. A structure as defined in claim 11 in which the ratio h max  /H is about 0.8 in which h max  is the expected maximum wave height and H is the still water draft. 
     
     
       16. A structure as defined in claim 11 with a ratio h max  /H that is between about 0.65 and about 1.00 where h max  is the expected maximum wave height and H is the still water draft. 
     
     
       17. A floating structure for use in a body of water having an expected maximum wave height h max  which comprises: a deck;   buoyancy means rigidly supporting said deck, said buoyancy means providing a total still water displacement B and including at least one slender vertical float member having a still water draft H, comprising two parts, the first part resulting from a straight prismatic shape which runs the entire vertical length of the vertical float member and an auxiliary portion exterior to said prismatic portion having an overall vertical length L, said auxiliary portion being placed below the trough of the expected maximum wave, for which the shape of the slender, vertical float member is defined by a value of r, said parameter r being the ratio of the maximum radius of the auxiliary portion to the radius of the prismatic portion, which value r is Equations (32) through (34);   anchor means at the bottom of said body of water;   elongated member interconnecting each said slender vertical float member and said anchor means, if there is more than one vertical float member, the said elongated members associated therewith are parallel;   said structure being free of any anchoring connection with the water bottom other than said elongated member.   
     
     
       18. A structure as defined in claim 17 in which the ratio (h max  /H) is about 0.8. 
     
     
       19. A structure as defined in claim 17 in which the ratio h max  /H is between about 0.65 and about 1.00. 
     
     
       20. A structure as defined in claim 17 in which said elongated members are tubular members. 
     
     
       21. A structure as defined in claim 17 in which there are at least three slender vertical float members and an elongated member connecting each said slender vertical float member and said anchor means, said elongated members being parallel; said structure being free of any anchoring connecting with the water bottom other than said elongated members. 
     
     
       22. A structure as defined in claim 21 in which the ratio h max  /H is between about 0.65 and about 1.00. 
     
     
       23. A structure as defined in claim 22 in which the ratio h max  /H is about 0.8. 
     
     
       24. A structure as defined in claim 17 in which r is between about r 3  and r 4 . 
     
     
       25. A floating structure for use in a body of water and having an expected maximum wave height h max  which comprises: a deck;   buoyancy means rigidly supporting said deck, said buoyancy means providing a total still water displacement B and including at least one slender vertical float member, said vertical float member having a still water draft H, comprising two parts, the first part resulting from a straight prismatic shape which runs the entire vertical length of the vertical float member and an auxiliary portion exterior to said prismatic portion having an overall vertical length L, said auxiliary portion being placed below the trough of the expected maximum wave, for which the shape of the slender, vertical float member is defined by a value of r, said parameter r being the ratio of the maximum radius of the auxiliary portion to the radius of the prismatic portion, which value r is between about [r 1  -(0.3341 kips/ft. 2 )(H 2  /B)] and about [r 2  +(34.41 kips/ft.)(H/B)] where r 1  is determined from equations (20) through (22) and r 2  is determined from equations (23) through (25);   anchor means at the bottom of said body of water;   an elongated member interconnecting each said vertical float member and said anchor means, if there is more than one vertical float member, the said elongated members associated therewith are parallel;   said structure being free of any anchoring connection with the water bottom other than said parallel elongated members.   
     
     
       26. An apparatus as defined in claim 25 including pivotal means connecting the lower ends of said elongated members with said anchor means and additional pivotal means connecting the upper ends of said elongated members with said buoyancy means. 
     
     
       27. An apparatus as defined in claim 25 in which said elongated members are tubular members. 
     
     
       28. A structure as defined in claim 25 in which there are at least three slender vertical float members and an elongated member connecting each said slender vertical float members and said anchor means, the said elongated members associated therewith being parallel; said structure being free of any anchoring connected to the water bottom other than said elongated members.   
     
     
       29. A structure as defined in claim 28 in which the ratio h max  /H is between about 0.65 and about 1.00. 
     
     
       30. A structure as defined in claim 29 in which the ratio h max  /H is about 0.8. 
     
     
       31. A structure as defined in claim 25 in which the value of r is between about r 1  and r 2 . 
     
     
       32. A floating structure as defined in claim 25 in which the ratio h max  /H is between about 0.75 and about 0.85. 
     
     
       33. A structure as defined in claim 32 in which the ratio h max  /H is about 0.8. 
     
     
       34. A floating structure for use in a body of water having an expected maximum wave height h max  which comprises: a deck;   buoyancy means rigidly supporting said deck, said buoyancy means providing a total still water displacement B and including at least one slender vertical float member having a still water draft H, each said vertical float member comprising two parts, the first part resulting from a straight prismatic shape which runs the entire vertical length of the vertical float member and an auxiliary portion exterior to said prismatic portion having an overall vertical length L, said auxiliary portion being placed below the trough of the expected maximum design wave, for which the shape of the slender, vertical float member is defined by a value of r, said parameter r being the ratio of the maximum radius of the auxiliary portion of the radius of the prismatic portion, which value r is between about [r bt  -(0.3441 kips/ft. 2  )(H 2  /B)] and about [r bt  +(34.41 kips/ft.)(H/B)] where r bt  is determined from Equations (10), (16) and (17);   anchor means at the bottom of said body of water;   an elongated member connecting each said vertical float member and said anchor means, said elongated members associated therewith being parallel;   said structure being free of any anchoring connection with the water bottom other that said parallel elongated members.   
     
     
       35. An apparatus as defined in claim 34 including pivotal means connecting the lower ends of said elongated members with said anchor means and additional pivotal means connecting the upper ends of said elongated members with said buoyancy means. 
     
     
       36. A structure as defined in claim 34 in which there are at least three slender vertical float members and an elongated member connecting each said slender vertical float members and said anchor means, the said elongated members associated therewith being parallel; said structure being free of any anchoring connection to the water bottom other than said elongated members.   
     
     
       37. An apparatus as defined in claim 34 in which said elongated members are tubular members. 
     
     
       38. A structure as defined in claim 34 in which the value of r is equal to r bt . 
     
     
       39. A structure as defined in claim 34 wherein said ratio h max  /H is about 0.8. 
     
     
       40. A structure as defined in claim 36 in which the ratio h max  H is about 0.8. 
     
     
       41. A floating structure for use in a body of water which comprises: a deck;   buoyancy means rigidly supporting said deck, said buoyancy means providing a total still water displacement between about 15,000,000 pounds and about 60,000,000 pounds and including at least three slender, vertical float members, each such vertical float member having a still water draft between about 75 and about 150 feet and comprising two parts, the first part resulting from a straight, vertical prismatic shape which runs the entire vertical length of the vertical float member and an auxiliary portion exterior to said prismatic portion, said auxiliary portion being placed below the trough of the maximum design wave, for which the shape of the slender, vertical float member is defined by either (a) values of p and r which when plotted as a point falls into the shaded regions of either FIGS. 15B through 23B or falls into shaded regions obtained by a linear interpolation between the shaded regions of these figures, said interpolation being made on the basis of still water displacement and still water draft, or (b) values of (L/H) and r which when plotted as a point falls into the shaded regions of either FIGS. 15A through 23A, or falls into shaded regions obtained by a linear interpolation between the shaded regions of these figures, said interpolation being made on the basis of still waster displaceent and still water draft; anchor means at the bottom of said body of water;   an elongated member interconnecting each said buoyancy means and said anchor means, said elongated members associated therewith being parallel;   said structure being free of any anchoring connection with the water bottom other than said parallel elongated members.   
     
     
       42. An apparatus as defined in claim 41 in which said elongated members are tubular members. .Iadd. 
     
     
       43.  A structure as defined in claim 9 including means for conducting drilling operations through said tubular members to underground formations. .Iaddend. .Iadd. 
     
     
       44.  A structure as defined in claim 9 wherein said anchor means includes piles extending into the floor of said body of water whereby holes can be drilled in said floor through said tubular members. .Iaddend. .Iadd. 
     
     
       45.  A structure as defined in claim 9 including wellhead equipment located at the surface of the body of water. .Iaddend. .Iadd. 
     
     
       46.  A structure as defined in claim 9 wherein said structure is used as a production gathering facility. .Iaddend. .Iadd. 
     
     
       47.  A structure as defined in claim 14 including means for conducting drilling operations through said tubular members to underground formations. .Iaddend. .Iadd. 
     
     
       48.  A structure as defined in claim 14 wherein said anchor means includes piles extending into the floor or said body of water whereby holes can be drilled in said floor through said tubular members. .Iaddend. .Iadd. 
     
     
       49.  A structure as defined in claim 14 including wellhead equipment located at the surface of the body of water. .Iaddend. .Iadd. 
     
     
       50.  A structure as defined in claim 14 wherein said structure is used as a production gathering facility. .Iaddend. .Iadd. 
     
     
       51.  A structure as defined in claim 20 including means for conducting drilling operations through said tubular members to underground formations. .Iaddend. .Iadd. 
     
     
       52.  A structure as defined in claim 20 including wellhead equipment located at the surface of the body of water. .Iaddend. .Iadd. 
     
     
       53.  A structure as defined in claim 20 wherein said structure is used as a production gathering facility. .Iaddend. .Iadd. 
     
     
       54.  A structure as defined in claim 27 including means for conducting drilling operations through said tubular members to underground formations. .Iaddend. .Iadd. 
     
     
       55.  A structure as defined in claim 27 including wellhead equipment located at the surface of the body of water. .Iaddend. .Iadd. 
     
     
       56.  A structure as defined in claim 27 wherein said structure is used as a production gathering facility. .Iaddend. .Iadd. 
     
     
       57.  A structure as defined in claim 37 including means for conducting drilling operations through said tubular members to underground formations. .Iaddend. .Iadd. 
     
     
       58.  A structure as defined in claim 37 including wellhead equipment at the surface of the body of water. .Iaddend. .Iadd. 
     
     
       59.  A structure as defined in claim 37 wherein said structure is used as a production gathering facility. .Iaddend. .Iadd. 
     
     
       60.  A structure as defined in claim 42 including means for conducting drilling operations through said tubular members to underground formations. .Iaddend. .Iadd. 
     
     
       61.  A structure as defined in claim 42 including wellhead equipment located at the surface of the body of water. .Iaddend. .Iadd. 
     
     
       62.  A structure as defined in claim 42 wherein said structure is used as a production gathering facility. .Iaddend.