Submerged Storage Unit

Abstract

The unit has a concrete dome fixed to a base also made of concrete. The dome has interlaced prestressed wire ropes, or cables, placing the dome in compression thereby allowing the dome to withstand the tension force resulting when the unit is stored with a fluid lighter than water. The cables are arranged preferably in a predetermined pattern to allow efficient use of material.

Description

This invention relates to a storage unit and, more particularly, to a unit submerged and placed on the ocean floor for use to store petroleum and petroleum products or other fluids lighter than sea water.

Prior art underwater storage units or compartments are made sufficiently rigid so that, when the unit is empty, hydrostatic pressure does collapse the unit. However, other prior art units, when used to store oil, are opened to the sea near the bottom so that, when the oil is withdrawn, sea water enters the unit. Therefore, the unit need not be as rigid as when the unit has to withstand hydrostatic pressure. Since oil is lighter than sea water, there is an uplift force acting on the unit which places the walls of the unit in tension. Therefore, up to now these submerged storage units have been made of steel, since steel is the most economical material that can be placed under tension. Obviously, concrete storage units are more economical, but concrete under slight tension cracks, even if it is reinforced. Reinforced concrete under tension forms hairline cracks which may not be significant under normal conditions but, in fluid storage units, the cracks are leaks.

Therefore, an object of this invention is to provide an economical submerged storage unit made of concrete.

Another object is to provide a hollow hemispherically shaped storage unit made of concrete which can be floated to a site and afterwards sunk in place.

These and other objects and features of advantages shall become more apparent in the following description of the invention when taken in conjunction with the drawings, in which:

FIG. 1 is an elevation of the novel, submerged storage unit in partial section with portions broken away to show the novel construction;

FIG. 2 is a plan view of the unit shown with portions broken away;

FIG. 3 is an enlarged section in elevation showing an upper portion of the unit;

FIG. 4 is an enlarged section in elevation showing the butt joint between the base and the hemispherical dome of the unit;

FIG. 5 is an enlarged section of a portion of the unit taken on line 5--5 in FIG. 1 showing the crossover point of three prestress cables in the unit;

FIG. 6 is a plan schematic of the hemispherical dome portion of the unit showing the crisscross pattern for the prestressing cables in solid lines and the outline of the dome in dash lines;

FIGS. 7 and 8 are elevation schematics of the hemispherical dome portion taken on axes normal to each other, also showing the crisscross pattern for the prestressing cables in solid lines and the outline of the dome in dash lines; and

FIG. 9 shows the coordinate convention used in the datum tables reproduced hereinafter.

Referring to the drawings and to FIGS. 1 and 2 in particular, the storage unit has a wide base 10 and a hemispherical dome 11 disposed on the base 10. Since the features of this invention produce advantages when used with a structural material that is weak in tension, the unit is preferably made of concrete because it is economical. At the center of the dome 11 is disposed a steel cap 12. The base 10 is preferably hexigon in shape (see FIG. 2) so that the concrete form may be readily fabricated. However, any shaped base that is consistent with structural rigidity for concrete structure may be used. The size of the unit may be, for example, 75 feet for the outer radius of the dome 11 and 225 feet from opposite points on the base 10, and a flat hexagon plate 13 in the base could be 18 inches thick. Along the periphery of the plate 13 are formed six vertical webs 14-19 each of which have an inward flange 21 as shown in FIG. 1 for web 14. The webs may be 15 feet high and 18 inches thick and the flange may be 2 to 3 feet wide and 18 inches thick. Extending from opposite corners of the plate 13 are six transverse webs 22-27 which may have a stiffening cap flange 28. Below the circumferential peripherical of the dome 12, is formed a vertically disposed circular web 29 which is capped by another flange 31, as shown in FIG. 1. The plate 13, the six peripherical webs 14-19, the six transverse webs 22-27, the flanges 21 and 28 may be reinforced with steel rods, as required, to provide structural strength and rigidity. Preferably the size of the base 10 is such that, when the unit is sealed and filled with air, the unit is floatable. The six webs 14-19 provide the required free-board. In constructing the unit, the base 10 is cast before the dome 11. When the base 10 is fully hardened, the dome 11 is formed.

The dome 11 is formed by providing a hemispherical form (not shown) over the base and, in particular, on the circular flange 31. The form may be of the type disclosed in U.S. Pat. No. 2,682,259. With the form in place on the flange 31, the cap 12 is placed on the form. Then a hemispherical sheet 41 is formed over the form preferably by applying a mixture of cement, sand, and water with pneumatic pressure through a suitable gun (generally referred to as gunite). The gunite is applied until a concrete hemispherical sheet 41 is formed to a suitable thickness of, for example, 18 inches. After the sheet 41 is formed, wire ropes, or cables, 42 of a suitable diameter are placed over the sheet in a predetermined pattern and then tensioned so that the sheet 41 is under compression. The preferred pattern and the manner for tensioning the wire ropes 42 will be described hereinafter. After the wire ropes are in place, a finish layer 43 of concrete is gunited over the wire ropes. Since the unit should be opened to the sea, suitable openings 44 are formed in cylindrical web 29. One of the openings 44 can be made sufficiently large so that a person can enter the unit to dismantle and remove the hemispherical form used to form the gunited dome 11.

Referring to FIGS. 3 and 4, there is shown the preferred structure for tying down the ends of wire ropes 42. As will be explained hereinafter, preferably only five wire ropes extend from the cap 12 to the flange 31 on web 29, each along a great circle. These wire ropes 42 have formed at their upper end a standard thimble or eyelet 44 which engages a ring 45 welded to a cylindrical wall 46 of the cap 12. The lower end of these wire ropes have each of their other end fixed to a standard socket 47 which has threads formed thereon. The sockets 47 pass through a steel sleeve 48 that was cast in place within flange 31 as shown in FIG. 4. Threaded onto the socket 47 is a nut 49. The other wire ropes, besides the five extending from the cap downwards, have sockets similar to socket 47 fixed on both ends. As will be explained hereinafter, these wire ropes extend from flange 31 over the sheet 41 back to the flange 31. After the concrete hardens and ages, the wire ropes are tightened by taking up the nuts 49 on bolts 47. The required tension load in each cable can be readily calculated by one skilled in the prestress concrete art after reading this disclosure. Since the cables have been heavily greased as is standard in the art of prestressed concrete, the cables do not adhere to concrete and can be readily tensioned.

The wire ropes 42 are draped over the concrete dome sheet 41 in a crisscross pattern so that, when the nuts and bolts are tightened, the concrete sheet 41 is placed under a prestressed compression load, i.e., when the unit is standing without performing any function, the compression pressure in the concrete is more than would be developed by dead weight alone. Since the unit is dome shape, a preferred pattern for the wire ropes has been developed so that the prestressing is uniform and a minimum amount of material is used. Referring to FIGS. 6, 7, and 8, the preferred pattern for the wire ropes is shown schematically. The various solid lines indicate the pattern that the various lengths of wire rope should have. The solid lines are located on the dome shape by first laying out the various 31 points V1 - V20, V1'- V6' and V1"- V5" according to the following tables:

SPHERICAL COORDINATES

A B Point Plan View Rotation Rotation from Positive Z __________________________________________________________________________ V1 0.degree.00'00" 20.degree.04'36" V2 72.degree.00'00" CCW 20.degree.04'36" V3 144.degree.00'00" CCW 20.degree.04'36" V4 144.degree.00'00" CW 20.degree.04'36" V5 72.degree.00'00" CW 20.degree.04'36" V6 0.degree.00'00" 43.degree.21'29" V7 72.degree.00'00" CCW 43.degree.21'29" V8 144.degree.00'00" CCW 43.degree.21'29" V9 144.degree.00'00" CW 43.degree.21'29" V10 72.degree.00'00" CW 43.degree.21'29" V11 22.degree.23'10" CCW 59.degree.00'28" V12 49.degree.36'49" CCW 59.degree.00'28" V13 94.degree.23'10" CCW 59.degree.00'28" V14 121.degree.36'49" CCW 59.degree.00'28" V15 166.degree.23'10" CCW 59.degree.00'28" V16 166.degree.23'10" CW 59.degree.00'28" V17 121.degree.36'49" CW 59.degree.00'28" V18 94.degree.23'10" CW 59.degree.00'28" V19 49.degree.36'49" CW 59.degree.00'28" V20 22.degree.23'10" CW 59.degree.00'28" V1' 0.degree.00'00" 0.degree.00'00" V2' 0.degree.00'00" 63.degree.26'05" V3' 72.degree.00'00" CCW 63.degree.26'05" V4' 144.degree.00'00" CCW 63.degree.26'05" V5' 144.degree.00'00" CW 63.degree.26'05" V6' 72.degree.00'00" CW 63.degree.26'05" V1" 36.degree.00'00" CCW 37.degree.22'38" V2" 108.degree.00'00" CCW 37.degree.22'38" V3" 108.degree.00'00" 37.degree.22'38" V4" 108.degree.00'00" CW 37.degree.22'38" V5" 36.degree.00'00" CW 37.degree.22'38" __________________________________________________________________________

RECTANGULAR COORDINATES

Point X Y Z __________________________________________________________________________ V1 0.343 0.000 0.939 V2 0.106 0.326 0.939 V3 -0.277 0.201 0.939 V4 -0.277 -0.201 0.939 V5 0.106 0.326 0.939 V6 0.686 0.000 0.727 V7 0.212 0.652 0.727 V8 -0.555 0.403 0.727 V9 -0.555 -0.403 0.727 V10 0.212 -0.652 0.727 V11 0.792 0.326 0.514 V12 0.555 0.652 0.514 V13 -0.065 0.854 0.514 V14 -0.449 0.730 0.514 V15 -0.833 0.201 0.514 V16 -0.833 -0.201 0.514 V17 -0.449 -0.730 0.514 V18 -0.065 -0.854 0.514 V19 0.555 -0.652 0.514 V20 0.792 -0.326 0.514 V1' 0.000 0.000 1.000 V2' 0.894 0.000 0.447 V3' 0.276 0.850 0.447 V4' -0.723 0.525 0.447 V5' -0.723 -0.525 0.447 V6' 0.276 -0.850 0.447 V1" 0.491 0.356 0.794 V2" -0.187 0.577 0.794 V3" -0.607 0.000 0.794 V4" -0.187 -0.577 0.794 V5" 0.491 -0.356 0.794 __________________________________________________________________________

referring to FIG. 9, the various abbreviations and notations in the tables are explained. X,Y, and Z refer to standard rectangular coordinates; "A" is the angle in the X-- Y plane and is given either clockwise (CW) or counterclockwise (CCW). "B" is the angle of rotation from the positive Z axis. Thus, five lines 51a- 51e, connecting the points as shown and mentioned above, lie on great circles extending from point V1'. Five other lines 52a- 52e, connecting the points as shown, lie substantially on great circles. Lines 52a' and 52a' substantially form circles that are disposed substantially parallel to the great circle that line 52a substantially lies on. Lines 52b' and 52b", lines 52c' and 52c", lines 52d' and 52d", and lines 52e' and 52e", like lines 52a' and 52a", substantially form circles that, in turn, are disposed substantially parallel to the respective great circles that lines 52b, 52c, 52d, and 52e, respectively, substantially lie on.

After determining where the wire ropes 42 are going to lie, holding U-clamps 61 (FIGS. 2 and 5) are inserted in the concrete before it sets at the location of each point V1-V20, V2'-V6', and V1"-V5". A U-clamp is not needed at point V1' since the wire ropes that coincide with and lie on the five lines 51a-51e are anchored to the cap 12 as shown in FIG. 3. The cap 12 is preferably made of steel wherein the cylindrical wall 46 has a flange 62 at one end so that the concrete adheres thereto. In addition, the other end of cap 12 swages down to a riser pipe 63 from which the crude oil is pumped to the surface. Inlet pipes 65 engage suitable fittings around the wall 46. Ears 66 on the cap 12 are useful in lowering the unit to the ocean floor.

When the unit is on the ocean floor, sea water enters the unit through ports 42. As crude oil or refined oil products are pumped into the unit through pipes 65, the sea water is displaced out of the unit since the oil is lighter. Since the oil is lighter, there is an upward lift on the inside of the concrete sheet 41. However, this upward lift tends to decrease the compression pressure in the concrete, but, since the wire ropes were tightened sufficiently, the concrete is always in compression. Obviously, the tension in the wire ropes 42 increases, but not sufficiently to cause the rope to yield. If more than the number of wire ropes than the amount shown are needed, because the space therebetween may be too large, additional wire ropes may be added that are disposed and run substantially parallel to two adjacent parallel wire ropes. The number of wire ropes added would be limited only by the size of the system. The spacing, between wire ropes for a given size, would depend on a number of factors; the main factor would be the thickness of the concrete sheet 41.

Claims

What is claimed is:

1. A storage unit comprising:

a base,

a hemispheric dome disposed over the base,

a cap disposed on the top of said dome,

a first plurality of wire ropes each engaging said cap by one end and extending along respective first great circles to said base, and

means for anchoring the other ends of the first plurality of wire ropes to said base and for producing a tension force within said wire ropes.

2. The unit of claim 1 wherein:

said first plurality of ropes is an odd number and said ropes are evenly disposed around said dome,

a second plurality of wire ropes equal in number to said first plurality is disposed on respective second great circles on said dome,

said second great circles are equally spaced from said cap and each one of said second great circles are disposed normal to a respective one of said first great circles,

means are provided for anchoring both ends of each of said second plurality of wire ropes to said base and for producing a tension force within said second wire ropes.

3. The unit of claim 2 wherein:

a third plurality of wire ropes are disposed on said dome,

said third plurality of wire ropes is divided into a plurality of groups that are equal in number to the wire ropes in said first plurality of wire ropes and which each of said groups contain more than one wire rope,

the wire ropes of said groups are disposed on circles that are substantially parallel to respective ones of said second great circles, and

means are provided for anchoring both ends of each wire rope in said third plurality to said base and for producing a tension force within the wire ropes in said third plurality.

4. The unit of claim 3 wherein the number of wire ropes in said first plurality is five.

5. The unit claim 3 wherein said second great circles are rotated from the vertical approximately 20.degree..

6. The unit of claim 4 wherein said second great circles are rotated from the vertical approximately 20.degree..

7. The unit of claim 6 wherein the number of wire ropes in each of said groups is two.