Lateral support members for a tension leg platform
AssigneeUnion Oil Company of California
InventorsDonald D. Engle, Jr., Michael E. Utt
Life of this patent
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Abstract
Apparatus and method for mooring a tension leg platform at an offshore location wherein the tensioned cables of the platform legs are laterally supported by a plurality of rigid, fixed-dimensioned support members which interconnect the legs and are vertically spaced at predetermined positions along the cables to reduce the unsupported length thereof and to thereby increase the fundamental frequency of the cables to a value higher than the flutter frequencies likely to be encountered. Resonant fluttering of the cables due to vortex shedding is thereby prohibited and the useful life of the cables is extended. The support members can be variably buoyant and/or can be adapted to provide storage for fluids produced at the offshore location.
Claims13
A platform for operations in a body of water at an offshore location, which comprises:
- a working deck;
- a buoyant structure for supporting said working deck above the body of water;
- a plurality of anchors on the floor of the body of water;
- a plurality of tension legs, each of said legs being comprised of one or more cables and being attached at one end to one of said anchors and at the other end to said buoyant structure;
- tensioning means for applying tension to said cables and thereby drawing down said buoyant structure to a working position in the body of water;
- and
- one or more rigid, fixed-dimensioned support members interconnecting said legs and each of said cables, each of said support members being vertically positioned along the length of said cables between the buoyant structure and the anchors to reduce the unsupported length thereof such that the fundamental frequency of the unsupported sections of said cables is higher than the highest flutter frequencies likely to be encountered.
A tension leg platform for operations in a body of water at an offshore location, which comprises:
- a working deck;
- a buoyant structure for supporting said working deck above the body of water;
- a plurality of deadweight anchors on the floor of the body of water;
- a plurality of substantially parallel tension legs each comprised of one or more cables, each of said legs being attached at one end to one of said anchors and at the other end to one of a plurality of points spaced about the perimeter of said buoyant structure;
- tensioning means at said points for applying tension to said cables and thereby drawing down said buoyant structure to a working position in the body of water;
- and
- one or more rigid, fixed-dimensioned support members interconnecting said legs and each of said cables at vertical positions along the length of said cables between the buoyant structure and the anchors such that the unsupported length L(x) of said cables at all depths x in the body of water is defined as follows:
- L(x) <
- 2D/[V(x)].sqroot.(T.multidot.G)/W
- wherein:
- D = the diameter of said cables,
- V(x) = the maximum anticipated relative velocity of the water flowing past said cables at the water depth x,
- T = the tension on the cables,
- G = the acceleration of gravity,
- W = the weight per unit length of said cables.
In the method for mooring a buoyant structure at an offshore location in a body of water wherein the buoyant structure is drawn down to a working position by applying tension to a plurality of spaced platform legs each comprised of one or more cables, each of which legs connect the buoyant structure to one of a plurality of anchors positioned at the bottom of the body of water, the improvement which comprises:
- interconnecting said platform legs and each of said cables with one or more rigid, fixed-dimensioned support members;
- and
- vertically-positioning said support members at selected positions along the length of said legs between the buoyant structure and the anchors to reduce the unsupported length of said legs and thereby increase the fundamental frequency of the unsupported sections of said legs to a value higher than the flutter frequencies likely to be encountered,
- whereby the condition of resonant flutter is avoided and the useful life of said legs is prolonged.
Dependencies are inferred from the claim text.