Tension Leg Platform With Improved Hydrodynamic Performance

Abstract

A tension leg platform that is stable with a quayside-integrated deck without the use of temporary stability modules or specialized installation techniques. The hull preferably consists of four radially-oriented vertical corner columns connected with four central ring pontoon segments. The vertical columns are fixed to the outer periphery of the central pontoon. The columns are characterized by a major radial axis and a minor transverse axis. The mooring system includes tendons supported at tendon porches directly at the four column outboard lower corners, without additional radially-extending tendon support structures.

1 . A tension leg platform ( 10 ) comprising:
 a hull ( 11 ,  11   a ,  11   b ) including a plurality of vertical columns ( 12 ,  112 ), a pontoon structure ( 14 ,  114 ) disposed inboard of said columns and adjoined to said columns at lower ends ( 12   a ,  112   a ) thereof, each of said columns having a horizontal cross-sectional shape that defines a major axis A 1 ) that is oriented radially outward from a center point (C) of said hull;   a deck ( 13 ) supported at upper ends ( 12   b ,  112   b ) of said columns; and   a plurality of tendons ( 17 ) connected under tension between said columns and the seabed for maintaining said tension leg platform above a desired subsea location and substantially restraining said tension leg platform from vertical heave motions.   
     
     
         2 . The tension leg platform ( 10 ) according to  claim 1  wherein:
 said columns ( 12 ,  112 ) and said pontoon structure ( 14 ,  114 ) are constructed substantially of flat plate. 
 
     
     
         3 . The tension leg platform ( 10 ) according to  claim 1  wherein:
 each of said plurality of columns ( 12 ,  112 ) has a polygonal transverse cross-section. 
 
     
     
         4 . The tension leg platform ( 10 ) according to  claim 1  wherein:
 each of said plurality of columns ( 12 ,  112 ) has a quadrilateral transverse cross-section. 
 
     
     
         5 . The tension leg platform according to  claim 4  wherein:
 each of said plurality of columns ( 112 ) has a generally trapezoidal transverse cross-section defined by an inboard side wall ( 112   d ) and an outboard side wall ( 112   e ) interconnected in parallel spaced relation by two nonparallel laterally spaced side walls ( 112   c ), said outboard side wall ( 112   e ) being wider than said inboard side wall ( 112   d ), whereby said major axis (A 1 ) extends between said inboard and outboard side walls. 
 
     
     
         6 . The tension leg platform ( 10 ) according to  claim 4  wherein:
 each of said plurality of columns ( 12 ) has a generally rectangular horizontal cross-section defined by an inboard side wall ( 12   d ) and an outboard side wall ( 12   e ) of substantially equal width interconnected in parallel spaced relation by two parallel laterally spaced side walls ( 12   c ) of greater width than said inboard and outboard side walls ( 12   d ,  12   e ), whereby said major axis (A 1 ) extends between said inboard and outboard side walls. 
 
     
     
         7 . The tension leg platform ( 10 ) according to  claim 1  wherein:
 said pontoon structure ( 14 ,  114 ) is octagonal-shaped. 
 
     
     
         8 . The tension leg platform ( 10 ) according to  claim 7  wherein:
 each of said columns ( 12 ,  112 ) is adjoined to a corner portion ( 14   b ,  114   b  of said pontoon structure ( 14 ,  114 ) by an extension member ( 15 ). 
 
     
     
         9 . The tension leg platform ( 10 ) according to  claim 1  wherein:
 said pontoon structure ( 14 ) includes a central moonpool opening ( 14   c ) formed vertically therethrough. 
 
     
     
         10 . The tension leg platform ( 10 ) according to  claim 9  wherein:
 said pontoon structure ( 14 ) includes four orthogonally-oriented side segments ( 14   a ) interconnected with four diagonally-oriented corner segments ( 14   b ); and 
 each of said side segments and corner segments ( 14   a ,  14   b ) are generally rectangular in transverse cross section and define horizontal axes (HC). 
 
     
     
         11 . The tension leg platform ( 10 ) according to  claim 9  wherein:
 each of said columns ( 12 ,  112 ) is adjoined to one of said corner segments ( 14   b ) of said pontoon structure ( 14 ) by an extension member ( 15 ). 
 
     
     
         12 . A tension leg platform ( 10 ) comprising:
 a hull ( 11 ,  11   a ,  11   b ) including a pontoon structure ( 14 ,  114 ) having an outer periphery surrounding a central vertical axis (C), vertical columns ( 12 ,  112 ) each adjoined at a lower end ( 12   a ,  112   a ) to said pontoon structure outer periphery, said pontoon structure disposed inboard of said columns, each of said columns defining a vertical column axis (VC) located radially outward from said central vertical axis (C) a first non-zero distance (D 1 ) from said outer periphery of said pontoon structure;   a deck ( 13 ) supported by upper ends ( 12   b ,  112   b ) of said columns; and   tendons ( 17 ) under tension connected at upper ends to said columns by tendon porches ( 18 ) mounted directly to said columns ( 12 ,  112 ) and at lower ends to the seabed for maintaining said tension leg platform above a desired subsea location and substantially restraining said tension leg platform from vertical heave motions.   
     
     
         13 . The tension leg platform ( 10 ) according to  claim 12  wherein:
 each of said columns ( 12 ,  112 ) has a transverse cross-sectional shape with a horizontal major axis (A 1 ) oriented radially outward from said central vertical axis (C). 
 
     
     
         14 . The tension leg platform ( 10 ) according to  claim 13  wherein:
 said pontoon structure ( 14 ) includes a vertical central opening ( 14   c ) formed therethrough; 
 said pontoon structure ( 14 ) includes four orthogonally-oriented side segments ( 14   a ) intervaled with four diagonally-oriented corner segments ( 14   b ); 
 each of said side segments and corner segments ( 14   a ,  14   b ) have a polygonal vertical cross-section and define horizontal longitudinal axes (HC) therethrough; and 
 each vertical column axis (VC) of each column ( 12 ,  112 ) is located a second non-zero distance (D 2 ) radially outward from the horizontal longitudinal axis (HC) of an adjacent corner segment ( 14   b ) of said pontoon structure ( 14 ). 
 
     
     
         15 . The tension leg platform ( 10 ) according to  claim 13  wherein:
 each of said columns ( 12 ,  112 ) has a polygonal transverse cross section. 
 
     
     
         16 . The tension leg platform ( 10 ) according to  claim 15  wherein:
 each of said columns ( 112 ) has a generally trapezoidal transverse cross section formed of D an inboard side wall ( 112   d ) and a outboard side wall ( 112   c ) that is narrower than said inboard side wall, which are interconnected in parallel spaced relation by two nonparallel laterally spaced side walls ( 112   c ). 
 
     
     
         17 . The tension leg platform ( 10 ) according to  claim 15  wherein:
 each of said columns ( 12 ) has a generally rectangular transverse cross section formed of an inboard side wall ( 12   d ) and an outboard side wall ( 12   e ) of substantially equal width interconnected in parallel spaced relation by two parallel laterally spaced side walls ( 12   c ) of greater width than said inboard and outboard side walls. 
 
     
     
         18 . The tension leg platform ( 10 ) according to  claim 12  wherein:
 an imaginary line (S) extending between the vertical column axes (VC) of two adjacent columns ( 12 ,  112 ) lies outboard of said pontoon structure outer periphery. 
 
     
     
         19 . The tension leg platform ( 10 ) according to  claim 14  wherein:
 an imaginary line (S) extending between the vertical column axes (VC) of two adjacent columns ( 12 ,  112 ) lies outboard of the horizontal longitudinal axis (HC) of the side segment ( 14   a ) located generally between said two adjacent columns. 
 
     
     
         20 . A tension leg platform ( 10 ) comprising:
 a ring pontoon structure ( 14 ) surrounding a central opening ( 14   c ) and formed by a plurality of segments ( 14   a ,  14   b ) which in transverse cross section define a horizontal center line (HC);   vertical columns ( 12 ,  112 ) each adjoined at a lower end ( 12   a ,  112   a ) to an outboard side of said pontoon structure ( 14 ) so that said pontoon structure is disposed inboard of said columns, each of said columns defining a central vertical longitudinal axis (VC) disposed radially outward from a platform center (C) a distance (D 2 ) from said horizontal axial center line (HC) so as not to intersect therewith; and   vertical mooring tendons ( 17 ) connected between said columns and the seabed.