US3548602A

US3548602A - Device for self-correction of position for semi-submersible platform

Info

Publication number: US3548602A
Application number: US815582A
Authority: US
Inventors: Georges Monnereau
Original assignee: Compagnie Generale dAutomatisme SA
Current assignee: Compagnie Generale dAutomatisme SA
Priority date: 1968-04-12
Filing date: 1969-04-14
Publication date: 1970-12-22
Anticipated expiration: 1987-12-22
Also published as: NL6905190A; FR1583505A; DE1918538A1; LU58376A1; BE730936A; ES365949A1; GB1250098A

Description

Dec. 22; 1 70 G. MONNEREAU DEVICE FOR SELF-CORRECTION 0F POSITION FOR SEMI-SUBMERSIBLE PLATFORM Filed April 14, 1969 2 Sheets-Sheet 1 FIG-1 FIG. 2

Dec. 22, 1970 x 5, MONNEREAU @fiflfififi DEVICE FOR SELF-CORRECTION 0F POSITION FOR SEMI-SUBMERSIBLE PLATFORM 7 Filed April 14, 1969 2 Sheets-Sheet a United States Patent Ofi'ice 3,548,602 DEVICE FOR SELF-CORRECTION OF POSITION FOR SEMI-SUBMERSIBLE PLATFORM Georges Monnereau, Paris, France, assignor to Compagnie Generale dAutomatisme, Paris, France Filed Apr. 14, 1969, Ser. No. 815,582 Claims priority, application France, Apr. 12, 1968,

Int. Cl. E02b 17 B631) 35/44 US. Cl. 61-46 8 Claims ABSTRACT OF THE DISCLOSURE A disc-shaped element which can be inclined at will resists the disturbances due to the swell acting on submersible platforms floating or anchored to the bottom of the sea.

BACKGROUND OF THE INVENTION (1) Field of the invention It is known that such structures are used both as observation bases and as platforms for oil drilling at sea. It is also known that such platforms have to be stable to swell in order to be usable. For floating platforms in the open sea it is known from French Pat. No. 1,510,937 of 30, Nov. 1966 by the applicant Company for Improvement in Floating Platforms that a discoidal element arranged about each vertical structure and submerged to the desired depth annuls the action of the swell.

Likewise, for platforms arranged in the vicinity of the coast it is sufiicient to fix the lower end of a cylindrical structure on the bottom by a ball joint fastening in order to obtain stability of the platform mounted on the unitary cylindrical structure.

However, the swell is not the only disturbing element for such platforms, which are also subjected both to the action of the wind and to the action of sea currents.

For floating platforms, this results in a general drifting of the platform, the position of which is no longer fixed. For platforms anchored along the coast a torque is exerted on the cylindrical structure which is then rotated about its ball joint fastening and begins to oscillate on either side of a mean position inclined relative to the vertical.

SUMMARY OF THE INVENTION The object of the present invention is to eliminate respectively the drifting of floating platforms and the inclination relative to the vertical of cylindrical structures which are anchored on the sea bed by using a discoidal element having its axis of symmetry coinciding with the axis of the vertical structure and optionally inclinable.

Tests in a swell tank on a small-scale model have shown that the swell exerted on the inclined discoidal element creates a force opposing the drift due to the current. It is then sufficient, to annual the drift, to determine the value of the parameters relative to the discoidal element; its dimension, its angle of inclination and its immersion depth.

In a similar manner, after tests, a cylindrical model anchored with a ball joint to the bottom of the tank, inclined under the action of the current and oscillating 3,548,602 Patented Dec. 22, 1970 about this mean position, was returned to the vertical and oscillated with a reduced amplitude by arranging a discoidal element about it, submerged in the vicinity of the water surface level, and suitably inclined.

A device for self-correction of position according to the invention for a semi-submersible platform mounted on at least one partially submered support of hollow cylindrical form with a vertical axis and having a length substantially greater than the diameter, is characterized in that a discoidal element centered on the axis of the cylindrical support is optionally inclinable in accordance with the direction of the swell and submerged in the vicinity of the sea surface level.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in horizontal projection, an inclined disc mounted on a vertical cylindrical structure.

FIGS. 2 and 3 are partial views, in elevation, in two directions perpendicular to one another, a vertical structure with optionally inclinable disc.

FIG. 4 is a diagrammatic view, in elevation, of a platform supported by a single vertical structure with symbolic representation of an inclined disc.

lFIG. 5 shows in symbolic manner, structures anchored to the bed and inclined by a current and their reutrn to the vertical by means of a suitably inclined disc.

DESCRIPTION OF PREFERRED EMBODIMENTS The plane inclined disc 1 in FIGS. 1, 2 and 3 is mounted by universal joint means including a ring 2 on the hollow cylindrical structure 3 which has a vertical axis 9. The disc 1 is perforated with a central aperture 4 permitting its free orientation permit-ted by the universal joint type of mounting. The disc 1 is adapted to rotate relative to the ring 2 on the axis 5 common to the two studs 6 fixed to the said ring and on which it is mounted. On the other hand the ring 2 can rotate about two other studs 7 fixed to the cylindrical structure 3 and define an axis 8 perpendicular to the axis 5, the two axes intersecting on the axis of symmetry 9 of the vertical structure.

In FIG. 4 the floating platform symbolized by a working stage 10 is mounted on a single vertical cylindrical structure 11 stabilized by a hollow anti-swell disc 12 connected to the cylinder 11 by the chamber 13 serving as a machine room. Columns 14 participate in supporting the platform and columns 15 fixed below the disc 12 serve to support the counter-weight 16 intended to lower the center of gravity of the platform.

The inclined disc according to the invention is shown at 17, and mounted with a universal joint type of connection on the cylinder 11 by means of the ring 18 and is submerged in the vicinity of the average surface level 19 of the sea and subjected to the effects of the swell which has a sinusoidal profile 20 at the surface.

The inclined disc is sensitive to the swell and accepts a proportion of the energy thereof to effect either the displacement of the latter if there is no current or the annulling of its displacement in the case of drift.

When the swell is in the direction of the arrow 21 the platform is driven in the direction of the double-line arrow 22 owing to the action of the swell on the disc 17.

Similarly, in the case of a swell in the direction of the broken-line arrow 23, the disc 17, still in the same inclination, undergoes the reaction of the swell and the floating platform is urged in the direction indicated by the brokenline double arrow 24. Therefore, whatever the direction of the swell, the direction in which the platform is entrained depends on the inclination of the disc 17.

The inclined disc 17 is shown in circular form, with elliptical projection on any plane forming an angle with its own plane; but it has been found on models, that the effect of the swell can be accentuated by increasing the dimensions thereof in accordance with the inclination, that is to say the greater inclination. For example it is possible to use an elliptical-section disc, the minor axis of the ellipse remaining horizontal and the major axis being arranged in accordance with the greater inclination. Instead of the ellipse, a rectangular profile may be chosen for the disc 17, the longest side of the rectangle being arranged in accordance with the inclination. In any case the center of the profile selected, about which the universal joint connection allows the disc 17 to pivot, should be situated on the axis of symmetry 25 of the cylindrical structure 11 of the floating platform in order to prevent any asymmetrical reaction of the swell.

In FIG. 5, the cylindrical structure 26 anchored to the bed of the sea 27 by a ball joint fastening 28 remains in a vertical position as long as no disturbing phenomenon intervenes.

The same structure moved out of its vertical position by disturbances is shown in oblique positions respectively at 29 and 30.

Owing to the discoidal element according to the invention, it is possible to return the oblique structure to the vertical by the action of the swell on the suitably arranged element. When the swell is directed in accordance with arrow 31, the discoidal element is inclined as shown by the symbolic line 32 and permits returning of the structure from the oblique position 29 to the vertical position 26.

Similarly the structure in the oblique position 30 is returned to the vertical position 26 when, with the swell in the direction of the broken-line arrow 33, the discoidal element is placed in an inclined position 34 as shown in broken lines. Indeed, if it is arranged that the perpendicular to the plane of the discoidal element is directed towards the surface of the sea, the average level of which is 19, the cylindrical surface supporting it tends to be displaced in the direction of the horizontal projection of the directed perpendicular. In addition the oscillations of the structure returned to the vertical are reduced relative to oscillations in the oblique position.

What is claimed is:

1. A device for self-correction of position for semisubmersible platform mounted on at least one partly submerged support of hollow cylindrical form with a vertical axis and having a length substantially greater than the 4 diameter, said devcie comprising a discoidal element centered on the axis of the said cylindrical support and optionally inclinable in accordance with the direction of the swell and submerged in the vicinity of the surface level of the sea.

2. The self-correction device according to claim 1, wherein the inclinable discoidal element pivots about its center by means of a universal joint connection.

3. The self-correction device according to claim 2, wherein said universal joint connection includes an intermediate ring centered on the axis of the vertical cylindrical structure.

4. The self-correction device according to claim 1, wherein the inclinable discoidal element is circular and centrally apertured.

5. The self-correction device according to claim 1, wherein the inclinable discoidal element is centered on the axis of the cylindrical vertical structure and is of increased size in the direction of its greater inclination.

6. The self-correction device according to claim 1, wherein the inclinable discoidal element is elliptical and the major axis of the ellipse corresponds with its greater inclination.

7. The self-correction device according to claim 1, wherein the inclinable discoidal element is rectangular and the longest side of the rectangle is situated in the direction of the greater inclination of the said element.

8. The self-correction device according to claim 1, wherein said semi-submersible platform is anchored to the sea bed by the vertical structure to ensure that the said structure is kept vertical.

References Cited UNITED STATES PATENTS 2,897,654 8/1959 Harris 6l-46X 3,390,654 7/1968 Bromell et al 1l4.5

3,407,767 10/1968 McClintock et a1 114.5

FOREIGN PATENTS 1,510,937 12/1967 France 6 1-465 J. KARL BELL, Primary Examiner US. Cl. X.R.