초록 ▼

A device and method for the reduction of vortex-induced vibration of a deepwater riser. A device for attachment to a structure, which is subject to movement relative to a fluid surrounding the structure, for reducing vortex-induced vibration effects on the structure, the device comprising: a flexibl

A device and method for the reduction of vortex-induced vibration of a deepwater riser. A device for attachment to a structure, which is subject to movement relative to a fluid surrounding the structure, for reducing vortex-induced vibration effects on the structure, the device comprising: a flexible netting (4) interconnecting a plurality of relatively inflexible members comprising a plurality of elongate members (3) and a plurality of spacer members (6), wherein each elongate member has a first cuter boundary and each spacer member has a second outer boundary wherein the second boundary extends radially outward of the first outer boundary relative to the netting, over at least: a substantial portion of the boundary.

대표청구항 ▼

1. A device for attachment to a structure which is subject to movement relative to a fluid surrounding the structure, the device being adapted for reducing vortex-induced vibration effects on the structure, the device comprising: a flexible netting interconnecting a plurality of relatively inflexibl

1. A device for attachment to a structure which is subject to movement relative to a fluid surrounding the structure, the device being adapted for reducing vortex-induced vibration effects on the structure, the device comprising: a flexible netting interconnecting a plurality of relatively inflexible members comprising a plurality of elongate members and a plurality of spacer members,wherein each elongate member has a first outer boundary and each spacer member has a second outer boundary wherein the second boundary extends radially outward of the first outer boundary relative to the netting, over at least a substantial portion of the boundary. 2. A device according to claim 1, wherein each elongate member comprises an integral spacing member. 3. A device according to claim 1, wherein each elongate member is mounted on the netting separate to the spacer members. 4. A device according to claim 2, wherein the spacer member is located spaced from both ends of the elongate member. 5. A device according to claim 4 wherein the spacer member is approximately at the centre of the length of the elongate member. 6. A device according to claim 1, wherein each elongate member comprises two spacer members spaced from each other along the length of said elongate member. 7. A device according to claim 1, wherein each elongate member comprises an elongate cylinder having a first diameter and a first length, and each spacer member comprises a disc having a second diameter which is larger than said first diameter, and a second length which is shorter than said first length. 8. A device according to claim 7, wherein said first length is between two and six times said first diameter. 9. A device according to claim 8, wherein said first length is between three and five times said first diameter. 10. A device according to claim 7, wherein said second diameter is approximately three times said first diameter. 11. A device according to claim 7, wherein said second length is approximately between one-half and one and one-half times said first diameter. 12. A device according to claim 11, wherein said second length is approximately equal to said first diameter. 13. A device according to claim 7, wherein said first diameter is approximately between one-eighth and one-twelfth the diameter of the structure. 14. A device according to claim 13, wherein said first diameter is approximately one-tenth of the diameter of the structure. 15. A device according to claim 7 wherein said first diameter is approximately between one-twelfth and one-twentieth the diameter of the structure. 16. A device according to claim 1, wherein each elongate member is hollow. 17. A device according to claim 1, wherein said spacer members are arranged to abut the surface of said structure to locate the elongate members at a predefined distance from the surface of the structure. 18. A device according to claim 1, wherein said flexible netting comprises a plurality of flexible cords for joining the plurality of elongate members and spacer members. 19. A device according to claim 18, wherein said flexible cords comprise a first, longitudinal, set of cords arranged to join respective sets of elongate members and spacer members in a plurality of generally parallel and spaced lines, with the elongate members being separated one from each other. 20. A device according to claim 19, wherein said flexible cords comprise a second, transverse, set of cords arranged to join the first set of cords to form said flexible net. 21. A device according to claim 1, wherein said device is formed as a flexible tube arranged to surround the structure. 22. A device according to claim 21, wherein the flexible tube has a circumference approximately four times larger than the diameter of the structure. 23. A device according to claim 1, wherein the flexible netting comprises polypropylene. 24. A device according to claim 1, wherein the inflexible members are made from polypropylene. 25. A method of reducing vibrations on a structure which is subject to relative movement compared to a fluid surrounding the structure, the method comprising surrounding the structure with a device according to claim 1. 26. A method of reducing vibrations on a structure which is subject to relative movement compared to a fluid surrounding the structure, the method comprising: surrounding the structure with a flexible tubular net having a two dimensional arrangement of flexible cords interconnecting a plurality of relatively inflexible members, wherein the inflexible members comprise a plurality of elongate members and a plurality of spacing members arranged to locate the elongate members at positions spaced from the structure. 27. A method according to claim 26, wherein the flexible net is arranged to surround the structure with clearance around at least part of the surface of the structure. 28. A method according to claim 26, wherein the structure comprises an underwater pipe. 29. A method according to claim 27 wherein each elongate member has a diameter and the structure has a diameter, and the elongate member diameter is approximately between one-tenth and one-twentieth the structure diameter.