Catenary Line Dynamic Motion Suppression

Abstract

Dynamic motion decoupling is effected with the use of mass, added mass, buoyancy, submerged weight and drag in areas of relatively low tension. High curvatures of lines on some configurations, together with their low slope may be utilized. The original line configuration may or may not be modified. Known motion suppressing device designs can be used. Because of the low slope on some configurations, said motion suppressing devices can be installed on arbitrarily long line segments to achieve objections required. Novel, drag and added mass enhancing devices effective in all directions can be used to increase the suppression effectiveness and/or in order to reduce the number of devices used. This invention is suitable for use on new designs and it is also suitable for retrofitting on existing, already installed lines.

1 . Dynamics decoupling, damping and added mass enhancing arrangement including a single device and also including a system of multiple devices and also including any plurality of systems of such devices, which affect catenary line dynamic motion in marine engineering; whereas said catenary line is provided with said decoupling, damping and added mass enhancing devices fitted on said catenary line along a said line segment located in the vicinity of the seabed, so that a segment of the said catenary line in the said vicinity of the seabed has any plurality of segments, including a single segment, of a non-negative buoyancy, which includes any combination of approximately neutral and positive buoyancies. 
   
   
       2 . Dynamic motion suppressing arrangement according to  claim 1  utilizing said devices arranged on said catenary lines essentially continuously, including arrangements in groups and including distinctly located devices along said segment. 
   
   
       3 . Dynamic motion suppressing arrangement according to  claim 1  that is used on any new built line of known configuration. 
   
   
       4 . Dynamic motion suppressing arrangement according to  claim 1  that utilizes any decoupling, damping and added mass enhancing device, including any plurality of such devices of known design. 
   
   
       5 . Dynamic motion suppressing arrangement according to  claim 1  that utilizes any decoupling, damping and added mass enhancing device, including any plurality of such devices of novel design. 
   
   
       6 . Line configuration involving any multitude of said devices, including continuously distributed said devices, as described in  claim 1  installed on said line so that most of said distributed length lies in the lower ⅜ of the line suspended length. 
   
   
       7 . Line configuration involving any multitude of positively buoyant devices, including continuously distributed said devices, as described in  claim 1  installed on said line so that at least a part of said distributed length with said devices installed stretches on both side of the design touch down point in any design line configuration. 
   
   
       8 . Line configuration involving any multitude of approximately neutrally buoyant devices, including continuously distributed said devices, as described in  claim 1  installed on said line so that most of distributed length lies in the lower ⅜ of the line suspended length. 
   
   
       9 . Line configuration involving any multitude of negatively buoyant continuously distributed devices, as described in  claim 1  installed on said line so that most of said distributed length lies in the lower ⅜ of the line suspended length. 
   
   
       10 . Line configuration involving any multitude of added mass and drag enhancing devices, including continuously distributed said devices, as described in  claim 1  installed on said line so that most of said distributed length lies in the lower ⅜ of the line suspended length. 
   
   
       11 . Any multitude of added mass and drag enhancing devices as claimed in  claim 1  using arbitrary geometrical shapes according to this invention intersect at wide range of angles including acute angles and right angles. 
   
   
       12 . Dynamic motion suppressing arrangement according to  claim 1  that is retrofitted to suppress motions on any existing, already installed line. 
   
   
       13 . The design optimization process as described in  claim 1  that is used in the motion suppression optimization design. 
   
   
       14 . Any field development and any field redevelopment project that uses arrangements, devices and design processes described in  claim 1 . 
   
   
       15 . An apparatus for adjusting the local buoyancy of a subsea line selected from the group consisting of risers, flow lines, control lines and umbilical lines said subsea line having a first end attached to a device on the seafloor and a second end proximate the sea surface comprising: at least one buoyancy control module located so as to configure said subsea line in a double-catenary configuration said buoyancy control module located such that, in use, it is at a depth that is at least about 60 percent of the local water depth, said subsea line being free to move in response to movement of the second end thereof. 
   
   
       16 . An apparatus as recited in  claim 15  wherein the buoyancy control module is located, in use, at a depth that is less than about 90 percent of the water depth. 
   
   
       17 . An apparatus as recited in  claim 15  wherein the buoyancy control module is located, in use, at a depth that is at least about 80 percent of the local water depth. 
   
   
       18 . A method of stabilizing the touchdown point of subsea line selected from the group consisting of risers, flow lines, control lines and umbilical lines, said subsea line having a first end attached to a device on the seafloor and a second end proximate the surface of the sea comprising: providing at least one buoyancy module on the subsea line located so as to configure said subsea line in a double-catenary configuration wherein the at least one buoyancy module is located such that, in use, it floats at a depth which is greater than about 60 percent of the water depth. 
   
   
       19 . A method as recited in  claim 18  wherein the buoyancy module is located at a depth which is less than about 95 percent of the water depth. 
   
   
       20 . A method as recited in  claim 18  wherein the buoyancy module, in use, floats at a depth which is greater than about 80 percent of the water depth. 
   
   
       21 . A method as recited in  claim 18  wherein the buoyancy module, in use, floats at a depth which is greater than about 90 percent of the water depth.