Heave motion compensation

Abstract

A heave motion compensator ( 30, 40, 70, 100, 140, 300 ) for compensating heave motions comprises a cylinder ( 41 ) and a piston ( 44 ) delimiting a variable volume fluid chamber ( 49 ) in said cylinder ( 41 ), wherein said piston ( 44 ) can oscillate within said cylinder ( 41 ), said piston ( 44 ) being provided with a seal ( 48 ) frictionally engaging said cylinder. The compensator further includes a motor ( 65 ) that causes said seal ( 48 ) to revolve relative to said cylinder ( 41 ) so as to obtain a dynamic friction regime between the seal ( 48 ) and the cylinder ( 41 ). In a possible embodiment the motor ( 65 ) is arranged to rotate said piston ( 44 ), and the seal ( 48 ) is mounted on said piston ( 44 ) so as to rotate along with said piston ( 44 ).

1 . Heave motion compensator comprising a cylinder and a piston delimiting a variable volume fluid chamber in said cylinder, wherein said piston can oscillate within said cylinder, said piston being provided with a seal frictionally engaging said cylinder, 
     characterised in that said compensator further includes a motor that causes said seal to revolve relative to said cylinder. 
   
   
       2 . Compensator according to  claim 1 , wherein said motor is arranged to rotate said piston, and wherein said seal is mounted on said piston so as to rotate along with said piston. 
   
   
       3 . Compensator according to  claim 1 , wherein said motor is arranged to rotate said cylinder, and wherein said piston is adapted to be mounted non-rotatable. 
   
   
       4 . Compensator according to  claim 1 , wherein said seal is carried by a seal carrier which is mounted rotatable on said piston, and wherein said motor drives said seal carrier so as to rotate about the piston. 
   
   
       5 . Compensator according to  claim 3 , wherein the cylinder is an inner cylinder which is rotatably mounted within an outer cylinder, and wherein said outer cylinder is adapted to be mounted non-rotatable. 
   
   
       6 . Heave compensation system including a compensator according to  claim 1 . 
   
   
       7 . Heave compensation system according to  claim 6 , further including a pressurised fluid assembly interconnected to said variable volume fluid chamber and adapted to provide a controlled fluid pressure therein, possibly a constant fluid pressure independent of piston oscillation. 
   
   
       8 . Heave compensation system according to  claim 7 , wherein said pressured fluid assembly includes one or more gas reservoir storing pressurised gas therein. 
   
   
       9 . Heave compensation system according to  claim 8 , wherein said variable volume fluid chamber of said compensator is a variable volume gas chamber interconnected to said one or more gas reservoirs. 
   
   
       10 . Heave compensation system according to  claim 7 , wherein said pressurised fluid assembly includes an accumulator having a variable volume hydraulic chamber and a variable volume gas chamber and a separation there between, said variable volume fluid chamber being interconnected to said variable volume hydraulic chamber and filled with hydraulic liquid, said variable volume gas chamber being filled with pressurised gas. 
   
   
       11 . Heave compensation system including a compensator according to  claim 1 , further including a pressurised fluid assembly interconnected to said variable volume fluid chamber and adapted to provide a controlled fluid pressure therein possibly a constant fluid pressure independent of piston oscillation, wherein said pressurised fluid assembly includes an accumulator having a variable volume hydraulic chamber and a variable volume gas chamber and a separation there between, said variable volume fluid chamber being interconnected to said variable volume hydraulic chamber and filled with hydraulic liquid, said variable volume gas chamber being filled with pressurised gas, and wherein said variable volume gas chamber of the accumulator is connected to said one or more gas reservoirs. 
   
   
       12 . Heave compensation system according to  claim 6 , wherein said compensator has two variable volume fluid chambers within said cylinder and separated by said piston, a pressurised fluid assembly being provided allowing selective supply and discharge of fluid to and from said variable volume fluid chambers so as to cause controlled oscillation of said piston within said cylinder to obtain heave compensation. 
   
   
       13 . A vessel including a heave compensation system according to  claim 1 . 
   
   
       14 . A vessel load handling system including a heave compensation system according to  claim 1 . 
   
   
       15 . A floating rig drilling system including a heave compensation system according to  claim 1 . 
   
   
       16 . A floating rig drill string compensator according to  claim 1  and adapted for placement between a drill string or other drilling tubular and a drill string hoisting device. 
   
   
       17 . A wireline logging system including a wireline cable, an associated wireline winch, and one or more instruments to be conveyed into a wellbore, said system further including a heave compensation system according to  claim 1 . 
   
   
       18 . A floating drilling vessel including a heave compensated drill floor, wherein the drill floor is mobile relative to the vessel to compensate for heave motion of the vessel, wherein a heave compensation system according to  claim 1  is arranged between the vessel and the drill floor. 
   
   
       19 . Method for heave motion compensation, in particular heave motion compensated load handling on a vessel, wherein use is made of a motion compensator according to  claim 1 , and wherein said seal is made to revolve relative to the cylinder of the heave compensator such that said friction between the seal and the cylinder is in the dynamic friction regime. 
   
   
       20 . Heave motion compensator comprising a cylinder and a piston delimiting a variable volume fluid chamber in said cylinder, wherein said piston can oscillate within said cylinder, said piston being provided with a seal frictionally engaging said cylinder, characterised in that said compensator further includes a motor that imparts a relative motion between said seal and said cylinder independent from said piston oscillation. 
   
   
       21 . Heave motion compensator according to  claim 20 , wherein compensator is adapted so that a relative longitudinal oscillation of the seal with respect to the cylinder is caused by the motor independent of the longitudinal oscillation of the piston within the cylinder. 
   
   
       22 . Heave motion compensator according to  claim 21 , wherein the seal is mounted in a seal carrier, which seal carrier is mounted on the piston so as to allow for a longitudinal oscillation of the seal carrier with respect to the piston independent from the longitudinal oscillations of the piston itself. 
   
   
       23 . (canceled)