WO2010048080A1

WO2010048080A1 - Systems and methods for reducing vortex induced vibrations

Info

Publication number: WO2010048080A1
Application number: PCT/US2009/061156
Authority: WO
Inventors: Donald Wayne Allen; Stephen Paul Armstrong; Julie Ann Dehne; Dean Leroy Henning; Damon Michael Mcmillan; Christopher Steven West; Mcmillan (Deceased), David Wayne
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2008-10-23
Filing date: 2009-10-19
Publication date: 2010-04-29

Abstract

A system for reducing drag and/or vortex induced vibration of a structure, the system comprising a multiple sided device comprising from 4 to 6 sides, the multiple sided device comprising a first portion and a second portion, the first portion and the second portion adapted to attach to each other about the structure.

Description

SYSTEMS AND METHODS FOR REDUCING VORTEX INDUCED VIBRATIONS

Field of the Invention

The present invention relates to systems and methods for reducing drag and/or vortex-induced vibration ("VIV").

Background of the Invention

Whenever a bluff body, such as a cylinder, experiences a current in a flowing fluid environment, it is possible for the body to experience vortex-induced vibration (VIV). These vibrations may be caused by oscillating dynamic forces on the surface, which can cause substantial vibrations of the structure, especially if the forcing frequency is at or near a structural natural frequency.

Drilling for and/or producing hydrocarbons or the like from subterranean deposits which exist under a body of water exposes underwater drilling and production equipment to water currents and the possibility of VIV. Equipment exposed to VIV includes structures ranging from the smaller tubes of a riser system, anchoring tendons, or lateral pipelines to the larger underwater cylinders of the hull of a mini spar or spar floating production system (hereinafter "spar").

The magnitude of the stresses on the riser pipe, tendons or spars may be generally a function of and increases with the velocity of the water current passing these structures.

It is noted that even moderate velocity currents in flowing fluid environments acting on linear structures can cause stresses. Such moderate or higher currents may be readily encountered when drilling for offshore oil and gas at greater depths in the ocean or in an ocean inlet or near a river mouth. There are generally two kinds of current-induced stresses in flowing fluid environments. The first kind of stress may be caused by vortex-induced alternating forces that vibrate the structure ("vortex-induced vibrations") mainly in a direction perpendicular to the direction of the current. When fluid flows past the structure, vortices may be alternately shed from each side of the structure. This produces a fluctuating force on the structure transverse to the current. If the frequency of this harmonic load is near the resonant frequency of the structure, large vibrations transverse to the current can occur. These vibrations can, depending on the stiffness and the strength of the structure and any welds, lead to unacceptably short fatigue lives. In fact, stresses caused by high current conditions in marine environments have been known to cause structures such as risers to break apart and fall to the ocean floor. The second type of stress may be caused by drag forces, which push the structure in the direction of the current due to the structure's resistance to fluid flow. The drag forces may be amplified by vortex-induced vibration of the structure. For instance, a riser pipe that is vibrating due to vortex shedding will generally disrupt the flow of water around it more than a stationary riser. This may result in more energy transfer from the current to the riser, and hence more drag.

Many types of devices have been developed to reduce vibrations of sub sea structures. Some of these devices used to reduce vibrations caused by vortex shedding from sub-sea structures operate by stabilization of the wake. These methods include use of streamlined fairings, wake splitters and flags. Devices used to reduce vibrations caused by vortex shedding from sub-sea structures may operate by modifying the boundary layer of the flow around the structure to prevent the correlation of vortex shedding along the length of the structure. Examples of such devices include sleeve-like devices such as helical strakes, shrouds, fairings and substantially cylindrical sleeves. Elongated structures in wind in the atmosphere can also encounter VIV and/or drag, comparable to that encountered in aquatic environments. Likewise, elongated structures with excessive VIV and/or drag forces that extend far above the ground can be difficult, expensive and dangerous to reach by human workers to install VIV and/or drag reduction devices. Fairings may be used to suppress VIV and reduce drag acting on a structure in a flowing fluid environment. Fairings may be defined by a chord to thickness ratio, where longer fairings have a higher ratio than shorter fairings. Long fairings are more effective than short fairings at resisting drag, but may be subject to instabilities. Short fairings are less subject to instabilities, but may have higher drag in a flowing fluid environment.

Co-pending PCT Patent Application PCT/US2008/072771 , filed August 11 , 2008, discloses a system for reducing drag and/or vortex induced vibration of a structure, the system comprising a multiple sided device comprising from 4 to 6 sides. Co-pending PCT Patent Application PCT/US2008/072771 is herein incorporated by reference in its entirety.

Co-pending PCT Patent Application PCT/US2008/078541, filed October 2, 2008, discloses a system for reducing drag and/or vortex induced vibration of a structure, the system comprising a multiple finned device comprising from 4 to 6 fins substantially aligned along a longitudinal axis of the structure. Co-pending PCT Patent Application PCT/US2008/078541 is herein incorporated by reference in its entirety.

There are needs in the art for one or more of the following: apparatus and methods for reducing VIV on structures in flowing fluid environments, which do not suffer from certain disadvantages of the prior art apparatus and methods; improved

VIV suppression devices; high stability devices; devices which delay the separation of the boundary layer, and/or devices which provide decreased VIV and/or devices which provide reduced drag; devices suitable for use at a variety of fluid flow velocities; devices that can achieve a high degree of VIV suppression with a low coverage density; and/or devices that have a high stability.

These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

Summary of the Invention

One aspect of invention provides a system for reducing drag and/or vortex induced vibration of a structure, the system comprising a multiple sided device comprising from 4 to 6 sides, with a first portion and a second portion, the first portion and the second portion adapted to attach to each other about the structure. Another aspect of invention provides a method for modifying a structure subject to drag and/or vortex induced vibration, said method comprising positioning at least one multiple sided device around the structure, the multiple sided device comprising from 4 to 6 sides, with a first portion and a second portion, the first portion and the second portion adapted to attach to each other about the structure. Advantages of the invention may include one or more of the following: improved VIV reduction; improved device stability; delaying the separation of the boundary layer over the device body; lower cost devices; devices that are easier to install; and/or lighter weight devices. These and other aspects of the invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.

Brief Description of the Figures Figure 1 illustrates a side view of plurality of VIV suppression devices installed along the length of a structure.

Figure 2a illustrates a top view of a multiple sided VIV suppression device in a closed position.

Figure 2b illustrates a top view of the multiple sided VIV suppression device of Figure 2a in an open position.

Figure 2c illustrates a top view of a multiple sided VIV suppression device. Figure 2d illustrates a top view of a multiple sided VIV suppression device. Figure 3 illustrates a top view of a VIV suppression device. Figure 4a illustrates a top view of a multiple sided VIV suppression device. Figure 4b illustrates a top view of the multiple sided VIV suppression device of

Figure 4a in an open position.

Figure 5a illustrates a top view of a multiple sided VIV suppression device and mechanism for positioning the device around a structure.

Figure 5b illustrates a top view of the mechanism for positioning a multiple sided VIV suppression device around the structure of Figure 5a in a closed position. Figure 6 illustrates a top view of a mechanism for positioning a multiple sided VIV suppression device around a structure.

Figure 7 illustrates a perspective view of a multiple sided VIV suppression device and mechanism for positioning the device around a structure. Figure 8 illustrates a perspective view of a multiple sided VIV suppression device and tool for positioning the device around a structure.

Detailed Description

Conventional VIV suppression devices may include, for example, long and short fairings. Fairings may be defined by a chord to thickness ratio, where long fairings have a higher ratio than short fairings. Long fairings are more effective than short fairings at resisting drag, but may be subject to instabilities. Short fairings are less subject to instabilities, but may have higher drag in a flowing fluid environment. Regardless of their size, VIV suppression devices such as fairings have a high coverage density meaning they must cover a substantial portion of the length of an underlying structure to suppress VIV. Thus, retrofitting of fairings to pre-installed structures such as tubulars can be expensive. In this aspect, retrofit installation costs can be reduced by installing VIV suppression devices which perform well at lower coverage densities. Such devices which perform well at lower coverage densities than fairings and mechanisms for retrofit installation of these devices are disclosed herein.

Figure 1 : Referring now to Figure 1 there is illustrated a structure having a plurality of vortex induced vibration (VIV) suppression devices installed along its length identified by height 108 that may be a full length of a structure such as a tube or riser or portion of less than a full length. Structure 102 is subjected to fluid flow in a direction 110. In this embodiment, VIV suppression devices 104a, 104b, 104c and 104d are installed about structure 102 to suppress vortex induced vibration of structure 102 (e.g. tube or riser). In some embodiments, collars may be provided between adjacent VIV suppression devices or placed between every few devices to prevent them from sliding along a length of structure 102 and/or to provide a bearing surface for the device to rotate. Device 104a has a height 124a and distance 126 between adjacent devices

104a and 104b. Devices 104b, 104c and 104d have heights 124b, 124c and 124d, respectively. Devices 104a, 104b, 104c and 104d each have a length 106. Devices 104a-104d may have the same or different heights and lengths.

Devices 104a-104d may cover from about 10% to about 100% of height 108, for example from about 10% to about 80%, or from about 30% to about 50%.

Length 106 may be from about 1.25 times the diameter of structure 102 to about 3 times. For example, the length may range from 1.1 times the diameter to 3.5 times the diameter. In another example, the length may range from about 1.5 times to about 2 times the diameter. Heights 124a, 124b, 124c and 124d may be less than the diameter of structure 102 or from about 1 times the diameter of structure 102 to about 10 times. For example, the height may range from 1.1 to 6 times the diameter of structure 102. In another embodiment, the height may range from 1.25 to 3 times the diameter or from 1.5 times to 2 times the diameter. Distance 126 may be the same or different between devices 104a-104d. Distance 126 may be from about 0.5 times the diameter of structure 102 to about 12 times. For example, distance 126 may range from 1 times the diameter to 10 times the diameter of structure 102, from 1.5 times to 6 times the diameter of structure 102 or from 2 times to 4 times the diameter.

Figure 2a:

Referring now to Figure 2a, a multiple sided VIV suppression device is illustrated. Device 204 is shown installed about structure 202. Structure 202 may be in a flowing fluid environment with flow 210, where structure 202 may be subject to vortex induced vibration. Structure 202 is, for example, a pipe or other tubular structure. Device 204 may be used to suppress the vortex induced vibration of structure 202.

Device 204 has chord 206 and thickness 208, which may vary if device 204 rotates relative to structure 202. Chord 206 is measured parallel to flow 210 and thickness 208 is measured perpendicular to flow 210. Chord to thickness ratio of device 204 shown in Figure 2a may be less than about 1.5, or less than about 1.25, or less than about 1.1 , for example 1. Chord to thickness ratio of device 204 shown in Figure 2a may be greater than about 0.6, or greater than about 0.75, or greater than about 0.9, for example 1.

Device 204 includes four sides and brace members 222 connected to the sides. Brace members 222 may extend from the sides of device 204 to structure 202. Brace members 222 may be positioned at any angle with respect to the axis of structure 202. All of the sides may have the same length, three of the sides may have the same length, two of the sides may have the same length or each side may have a different length. The sides may be substantially straight, or may have a slight convex or concave curvature. Each of the sides may have a length from about 0.75 to about 4 times a diameter of structure 202, for example from 0.9 to 2 times, or from 1 to 1.5 times, or about 1.25 times. The sides may make an angle from about 30 to about 150 degrees with each other, for example from 60 to 120 degrees, or from 75 to 105 degrees, or 90 degrees.

Device 204 may be able to rotate about structure 202 or it may be in a fixed angular orientation. Device 204 may have a collar mounted above and/or below device 204 to secure device 204 at a fixed location along the length of structure 202 and/or to provide a bearing surface for device 204 to rotate.

Device 204 may have two sides aligned substantially parallel with flow 210. Device 204 may be molded, welded, bent, cast, glued, or otherwise formed with manufacturing techniques as are known in the art. Device 204 may be made of metals such as steel or aluminum, polymers such as polyethylene or polypropylene, or composite materials such as fiberglass or carbon fiber composites, or other conventional materials.

Device 204 may be a square, a rectangle, a triangle, a parallelogram, a trapezoid or a diamond shape. Space may be provided in corners of device 204 to accommodate additional components. Representatively, marine growth protection components such as copper may be positioned within the corners. In still further embodiments, buoyancy material (e.g. foam) may be attached to corners or other spaces provided in device 204 to provide additional insulation or buoyancy to structure 202.

In the embodiment illustrated in Figure 2a, device 204 includes first portion 228 and second portion 230 each having a generally triangular cross-section. Device 204 may include hinge 224 to open and close device 204. Device 204 may further include attachment mechanism 226 to secure first portion 228 to second portion 230 in the closed position. In some embodiments, attachment mechanism 226 may be a clamp, clasp, bolt, serrated latch pin or any other type of attachment mechanism suitable for securing first portion 228 and second portion 230 in a closed position. Hinge 224 and attachment mechanism 226 may be attached to device 204 such that hinge 224 and attachment mechanism 226 are positioned within the space provided in a corner of device 204 when device 204 is in a closed position. In still further embodiments, hinge 224 and attachment mechanism 226 may be exterior to a surface of device 204. Hinge 224 may be positioned at one corner of device 204 and attachment mechanism 226 may be positioned at an opposite corner of device 204. In still further embodiments, hinge 224 may be positioned at one corner of device 204 and attachment mechanism 226 positioned at an adjacent corner of device 204.

Hinge 224 allows first portion 228 and second portion 230 of device 204 to pivot about hinge 224 from a closed position to an open position and from an open position to a closed position. In some embodiments, first portion 228 or second portion 230 of device 204 may pivot 270 degrees or less about hinge 224 to the open or closed position. In other embodiments, first portion 228 or second portion 230 may pivot 270 degrees or more about hinge 224. Device 204 is shown in the closed position in Figure 2a.

Figure 2b:

Referring to Figure 2b, device 204 is shown in an open position. To open device 204 from the closed position of Figure 2a, second portion 230 is pivoted about hinge 224 in the direction of arrow 234. Alternatively, first portion 228 may be pivoted about hinge 224 to open device 204. In embodiments where attachment mechanism 226 is a latch type mechanism, latch pin 232 may extend from a corner of second portion 230 of device 204. When device 204 is closed, latch pin 232 is inserted into a receptacle of attachment mechanism 226 at a corner of first portion 228 to secure device 204 around structure 202. Alternatively, latch pin 232 may extend from a corner of first portion 228 and the receptacle of attachment mechanism 226 may extend from a corner of second portion 230. Although a latch type attachment mechanism 226 is disclosed, it is contemplated that any other suitable type of attachment mechanism may be used to secure first portion 228 to second portion 230. In some embodiments, attachment mechanism 226 and hinge 224 may be exterior to the surface of device 204. In other embodiments, attachment mechanism 226 and hinge 224 may be positioned along an inner surface of device 204, for example, in the space provided at the corners of device 204.

Device 204 may be attached to structure 202 by retrofitting with a diver or a remotely operated vehicle (ROV). In this aspect, to attach device 204 to structure 202, a diver or ROV rotates first portion 228 and/or second portion 230 to the open position. The opened surface of device 204 is positioned adjacent structure 202. Once in position, first portion 228 and second portion 230 are pushed together around structure 202. The diver or ROV may then secure first portion 228 and second portion 230 together with attachment mechanism 226.

In still further embodiments, it is contemplated that a collar attached to structure 202 may be used to facilitate attachment of device 204 to structure 202. Representatively, first portion 228 or second portion 230 of device 204 may be attached to the collar prior to or after installation of the collar about structure 202. First portion 228 or second portion 230 of device 204 may be attached to the collar using any suitable attachment device such as, for example, a clamp, clasp, bolt, pin or serrated latch pin. Once the collar and device 204 are at the desired position along structure 202, the portion of device 204 not attached to the collar (e.g. second portion 230) may be closed around structure 202 and attached to the other portion (e.g. first portion 228) with attachment mechanism 226 as previously discussed. Once first portion 228 and second portion 230 are connected together, the portion of the device attached to the collar may be released from the collar.

Figure 2c:

Referring to Figure 2c, device 204 of Figure 2a is illustrated having two separable portions. In this embodiment, hinge 224 is omitted such that first portion 228 and second portion 230 may be assembled around structure 202 as two separate pieces. To facilitate connecting first portion 228 to second portion 230, a second attachment mechanism may be connected at an end of device 204 opposite that of attachment mechanism 226. Representatively, the attachment mechanism may have a receptacle portion 240 and latch pin 242 similar to attachment mechanism 226.

Device 204 shown in Figures 2b and 2c includes first portion 228 and second portion 230 having substantially triangular profiles. It is contemplated, however, that first portion 228 and second portion 230 of device 204 may have different shapes depending upon the overall shape of device 204 and the line along which device 204 is bisected to form first portion 228 and second portion 230.

Figure 2d:

Figure 2d illustrates another embodiment of a multiple sided VIV suppression device. Device 2004 is substantially similar to device 204 except that device 2004 includes first portion 2028 and second portion 2030 having substantially rectangular profiles. In this aspect, device 2004 includes brace members 2022 connected to the sides. Brace members 2022 may extend from the sides of device 2004 to an underlying structure. Brace members 2022 may be positioned at any angle with respect to the axis of the structure as previously discussed.

To facilitate connecting first portion 2028 to second portion 2030, attachment mechanisms 2040 and 2026 may be connected at free ends of the sides of first portion 2028 and second portion 2030 of device 2004. The attachment mechanisms may have receptacle portions 2026, 2040 and complimentary latch pins 2032, 2042 for inserting into receptacle portions 2026, 2040, respectively.

Device 204 may be molded, welded, bent, cast, glued, or otherwise formed with manufacturing techniques as are known in the art. Device 204 may be made of metals such as steel or aluminum, polymers such as polyethylene or polypropylene, or composite materials such as fiberglass or carbon fiber composites, or other conventional materials.

In the closed position, device 2004 may be a square, a rectangle, a triangle, a parallelogram, a trapezoid or a diamond shape.

Figure 3:

Referring now to Figure 3, a VIV suppression device having blades is illustrated. Device 304 is shown installed about structure 302. Structure 302 may be in a flowing fluid environment where structure 302 may be subject to vortex induced vibration. Device 304 may be used to suppress the vortex induced vibration of structure 302.

Body 306 of device 304 is substantially cylindrical. Blades 310 are positioned parallel or substantially aligned to a length dimension of body 306 and extend outward from body 306. Although four blades 310 are illustrated in Figure 3, it is contemplated that any number of blades suitable for suppressing VIV of structure 302 may be used. All of blades 310 may extend the same distance from body 306, some may extend the same distance or they may extend different distances from body 306. Blades 310 may be substantially straight. Each of blades may extend a distance from body 306 of, for example, from 5 to 50%, for example from 10 to 30% of the outside diameter of the tubular the device is applied to.

In some embodiments, blades 310 are integrally formed with body 306. In other embodiments, body 306 may be installed about body 306 by inserting them into rings positioned adjacent body 306 that have receptacles for receiving blades 310. The rings may or may not be temporarily locked to structure 302 or adjacent collars during installation.

Device 304 may be able to rotate about structure 302 or it may be in a fixed angular orientation. Device 304 may have a collar mounted above and/or below device 304 to secure device 304 at a fixed location along the length of structure 302 and/or to provide a bearing surface for device 304 to rotate.

Device 304 may be molded, welded, bent, cast, glued, or otherwise formed with manufacturing techniques as are known in the art. Device 304 may be made of metals such as steel or aluminum, polymers such as polyethylene or polypropylene, or composite materials such as fiberglass or carbon fiber composites, or other conventional materials.

Device 304 may include hinge 312 to open and close device 304. Device 304 may further include attachment mechanism 314 to secure first portion 316 to second portion 318 in the closed position. In some embodiments, attachment mechanism 314 may be a clamp, clasp, bolt, serrated latch pin or any other type of attachment mechanism suitable for securing first portion 316 and second portion 318 in a closed position. Hinge 312 and attachment mechanism 314 may be attached to device 304 such that hinge 312 and attachment mechanism 314 are positioned substantially between device 304 and structure 302 in a closed position. Alternatively, hinge 312 and attachment mechanism 314 may be positioned exterior to a surface of device 304. Device 304 is shown in the closed position in Figure 3.

Although device 304 is illustrated having hinge 312, it is further contemplated that hinge 312 may be omitted and device 304 may include two separable portions 316 and 318. In this aspect, an additional attachment mechanism may be provided to facilitate attachment of first portion 316 to second portion 318.

In addition, although braces extending from device 304 to structure 302 are not illustrated in Figure 3, it is contemplated that braces similar to those previously discussed in reference to Figure 2a may be included to help support device 304 about structure 302.

Blades 310 may make an angle of less than 15 degrees with a longitudinal axis of body 306, for example less than about 10, or less than about 5 degrees.

Blades 310 may be free to weathervane about structure 302 in response to a changing current.

Figure 4a:

Figure 4a illustrates a multiple sided vibration induced suppression device. Device 404 is shown installed about structure 402. Structure 402 may be in a flowing fluid environment where structure 402 may be subject to vortex induced vibration. Device 404 may be used to suppress the vortex induced vibration of structure 402.

Device 404 may have a chord to thickness ratio similar to that discussed in reference to Figure 2a. Device 404 includes three sides 406 and a fourth side 408 which serves to close opening 414. In this aspect, fourth side 408 may be rotatably attached at one end to a free end of one of three sides 406. Representatively, fourth side 408 and one of three sides 406 may be connected by a hinge or other mechanism which allows side 408 to rotate between an open and closed position. All of the sides may have the same length, three of the sides may have the same length, two of the sides may have the same length or each side may have a different length. The sides may be substantially straight, or may have a slight convex or concave curvature. Each of the sides may have a length from about 0.75 to about 4 times a diameter of structure 702, for example from about 0.9 to about 2 times, or from about 1 to about 1.5 times, or about 1.25 times. The sides may make an angle from about 30 to about 150 degrees with each other, for example from about 60 to about 120 degrees, or from about 75 to about 105 degrees, or about 90 degrees.

Device 404 may be able to rotate about structure 402 or it may be in a fixed angular orientation. Device 404 may have a collar mounted above and/or below device 404 to secure device 404 at a fixed location along the length of structure 402 and/or to provide a bearing surface for device 404 to rotate.

Device 404 may have two sides aligned substantially parallel with a fluid flow.

Device 404 may be molded, welded, bent, cast, glued, or otherwise formed with manufacturing techniques as are known in the art. Device 404 may be made of metals such as steel or aluminum, polymers such as polyethylene or polypropylene, or composite materials such as fiberglass or carbon fiber composites, or other conventional materials.

Device 404 may be a square, a rectangle, a parallelogram, a trapezoid, or a diamond shape. Space may be provided in corners of device 404 to accommodate additional components. Representatively, marine growth protection components such as copper may be positioned within the corners.

Device 404 may further include attachment mechanism 416 to attach a free end of side 408 to one of sides 406 in the closed position. In some embodiments, attachment mechanism 416 may be a clamp, clasp, bolt, serrated latch pin or any other type of attachment mechanism suitable for securing side 408 to side 406 in a closed position. Representatively, attachment mechanism 416 may include pin 418 connected to side 408 and receptacle 420 for receiving pin 418 connected to side 406. Although side 408 is described as being hinged to side 406, it is further contemplated that side 408 may be a structure separate from side 406. In this aspect, once device 404 is properly positioned around structure 402, side 408 is positioned over opening 414 and connected to side 406 at each end. In some embodiments, side 408 is connected using, for example, a clamp, clasp, bolt, serrated latch pin or any other type of attachment mechanism. In other embodiments, ends of side 406 adjacent opening 414 may include receptacles which receive and attach side 408 to side 406.

Retaining mechanisms 410 and 412 for retaining structure 402 within device 404 may further be provided. Retaining mechanisms 410 and 412 may extend from end portions of side 406 and into opening 414. Retaining mechanisms 410 and 412 may be any type of device which allows structure 402 to pass through opening 414 and into device 404 while preventing structure 402 from exiting device 404. Representatively, in one embodiment, retaining mechanisms 410 and 412 may be spring loaded clamps. Clamps 410 and 412 are designed to retract toward sides 406 of device 402 when pressure is applied by, for example, structure 402 passing through opening 414 as illustrated in Figure 4b. Once the pressure is removed, for example structure 402 is positioned entirely within device 404, clamps 410 and 412 spring back to their natural position as illustrated in Figure 4a due to the action of an internal spring. Clamps 410 and 412 do not move away from side 406 beyond their natural positions as shown. Thus, once structure 402 is positioned within device 404, movement or force from structure 402 against clamps 410 and 412 does not compress the springs or otherwise allow for removal of structure 402 from device 404.

Figure 4b:

Figure 4b illustrates the VIV suppression device of Figure 4a in an open position. In this embodiment, side 408 is in an open position so that structure 402 may be inserted through opening 414. Although side 408 is shown attached to side 406, it is further contemplated that as previously discussed, in some embodiments, side 408 is separable and therefore may be completely removed to allow for insertion of structure 402 within device 404. As can be seen from Figure 4b, clamps 410 and 412 are pushed toward side 406 by structure 402 being inserted through opening 414. Once structure is all the way through opening 414 and properly positioned within device 404, clamps 410 and 412 will spring back to their natural position as illustrated in Figure 4a.

It is contemplated that device 404 may be installed about structure 402 using an ROV, diver and/or one of the tools which will be discussed in more detail below in reference to Figure 5 to Figure 8.

Figure 5a:

Referring to Figure 5a, a tool for attaching a VIV suppression device to a structure is illustrated. In this embodiment, tool 500 is shown attaching device 204 of Figure 2a to structure 202. Although tool 500 is shown attaching device 204, it is contemplated that tool 500 may be used to attach any of the previously discussed devices to a structure.

Tool 500 may have arms 502 and 504 which are connected at adjacent ends to hinge 516 to allow arms 502 and 504 that rotate with respect to one another. Handle 506 may be attached to and extend from hinge 516 to facilitate positioning of tool 500 and device 204 attached thereto about structure 202. Actuator 508 to facilitate opening and closing of arms 502 and 504 is further attached to arms 502 and 504.

Arms 502 and 504 are dimensioned to extend around a portion of device 204 and attach to each of first portion 228 and second portion 230. In this aspect, arms 502 and 504 may have a curved configuration such that they fit around device 204 in the closed position as illustrated in Figure 5b, and/or arms 502 and 504 may have an elastic configuration adapted to bend as first portion 228 and second portion 230 are closed about structure 202. It is further contemplated that arms 502 and 504 may have two or more angled straight segments which conform to the angular outer dimensions of device 204, which may optionally be hinged between the straight segments. Representatively, arms 502 and 504 may each take the form of a half of a square or rectangle such that in the closed position they form a square or rectangle. Arms 502 and 504 may be molded, welded, bent, cast, glued, or otherwise formed with manufacturing techniques as are known in the art. Arms 502 and 504 may be made of metals such as steel or aluminum, polymers such as polyethylene or polypropylene, or composite materials such as fiberglass or carbon fiber composites, or other conventional materials.

Arms 502 and 504 may be attached to first portion 228 and second portion 230 by connectors 510 and 512 positioned at the ends of arms 502 and 504, respectively. Connectors 510 and 512 may be connectors which allow arms 502 and 504 to be removably attached to device 204. Representatively, connectors 510 and 512 may be clamps or clips attached to ends of arms 502 and 504. In this aspect, once device 204 is positioned around structure 202 using tool 500, the tool can be removed.

Opening and closing of arms 502 and 504 may be controlled using actuator 508. In some embodiments, actuator 508 is a hydraulic control mechanism. In this aspect, actuator 508 includes hydraulic cylinders 508a and 508b. Hydraulic cylinders 508a and 508b are attached at one end to handle 506 and at opposite ends to each of arms 502 and 504, respectively. When arms 502 and 504 are in the open position as illustrated in Figure 5a, piston rods 514a and 514b are retracted within the cylinder barrel of hydraulic cylinders 508a and 508b, respectively. To close arms 502 and 504 as illustrated in Figure 5b, piston rods 514a and 514b come out of the cylinders thereby pushing arms 502 and 504, respectively, toward one another. This in turn pushes first portion 228 and second portion 230 of device 204 toward each other and around structure 202. Hydraulic fluid may be supplied to hydraulic cylinders 508a and 508b by a hydraulic pump attached directly to tool 500. Alternatively, the hydraulic pump may be attached to a structure above the water surface and fluid may be pumped to hydraulic cylinders 508a and 508b through umbilicals.

Although actuator 508 is described as hydraulic cylinders 508a and 508b it is further contemplated that any other type of actuating mechanism suitable for facilitating opening and closing of tool 500 may be used. Representatively, a spring type mechanism which biases arms 502 and 504 in a closed position may be used. In this aspect, arms 502 and 504 may be pulled apart and held in an open position. Representatively, arms 502 and 504 may be held in the open position by, for example, a latch or clamp which prevents them from closing. Free ends of arms 502 and 504 may then be attached to first portion 228 and second portion 230. Once first portion 228 and second portion 230 are aligned with structure as desired, the latch or pin holding arms 502 and 504 apart may be released allowing arms 502 and 504 to spring toward each other into the closed position. This in turn closes first portion 228 and second portion 230 around structure 202.

It is contemplated that a diver or ROV may be used to position device 204 about structure 204 and operate tool 500.

Figure 5b:

Referring to Figure 5b, the tool of Figure 5a is illustrated closing the device around the structure. In this aspect, arms 502 and 504 of tool 500 attached to first portion 228 and second portion 230 of device 204 are used to push first portion 228 and second portion 230 together around structure 202. Once device 204 is secured around structure 202, arms 502 and 504 are released from edges of device 204 and tool 500 is removed from device 204.

Suitable systems for closing mechanism 226 and connectors 510, 512 are disclosed in the referenced patents and applications discussed below.

Figure 6:

Referring to Figure 6, a multiple sided VIV suppression device and tool for positioning the device around a structure is illustrated. Device 604 may be similar to device 204 illustrated in Figure 2c.

Device 604 includes four sides and brace members 622 connected to the sides. The brace members 622 may have a semicircular shaped ring (not shown) with a diameter slightly larger than the diameter of structure 602 attached to their ends, where the ring is adapted to receive structure 602. All of the sides may have the same length, three of the sides may have the same length, two of the sides may have the same length or each side may have a different length. The sides may be substantially straight, or may have a slight convex or concave curvature. Each of the sides may have a length from about 0.75 to about 4 times a diameter of structure 602, for example from about 0.9 to about 2 times, or from about 1 to about 1.5 times, or about 1.25 times.

The sides may make an angle from about 30 to about 150 degrees with each other, for example from about 60 to about 120 degrees, or from about 75 to about 105 degrees, or about 90 degrees. Device 604 may be able to rotate about structure 602 or it may be in a fixed angular orientation. Device 604 may have a collar mounted above and/or below device 604 to secure device 604 at a fixed location along the length of structure 602 and/or to provide a bearing surface for device 604 to rotate. Device 604 may be molded, welded, bent, cast, glued, or otherwise formed with manufacturing techniques as are known in the art. Device 604 may be made of metals such as steel or aluminum, polymers such as polyethylene or polypropylene, or composite materials such as fiberglass or carbon fiber composites, or other conventional materials. Latch 606a having a receptacle therein for receiving latch pin 608b may be attached to an edge of second portion 630. Latch 606b having a receptacle therein for receiving latch pin 608a may be attached to an edge of first portion 628. Latches 606a, 606b and latch pins 608a, 608b may be positioned along edges of first portion 628 and second portion 630 such that when first portion 628 and second portion 630 are pushed together around structure 602, latch pin 608b is received by the receptacle of latch 606a and latch pin 608a is received by the receptacle of latch 606b to hold device 604 around structure 602.

Tool 610 may be used to position device 604 around structure 610. Tool 610 includes arms 632 and 638. Arms 632 and 638 may be made of a similar material to the arms discussed in regard to tool 500 of Figures 5a and 5b. In tool 610, arms 632 and 638 are shown having three straight segments at angles to each other such that an overall shape of arms 632 and 638 is that of half of a square. In this aspect, arms 632 and 638 may fit around first portion 628 and second portion 630 of device 604, respectively. The free ends of arms 632 and 638 may include holding members 636a, 636b, 636c and 636d for holding first portion 628 and second portion 630 within arms 632 and 638, respectively, during installation. Representatively, holding members 636a, 636b, 636c and 636d may be, for example, clamps, clasps, latches or clips which extend from an inner surface of arms 632 and 638 and grasp edges of first portion 628 and second portion 630 to attach them to arms 632 and 638 while device 604 is being positioned around structure 602. Once first portion 628 and second portion 630 are properly positioned and attached around structure 602, holding members 636a, 636b, 636c and 636d are released from device 604 and tool 610 is removed. Although holding members 636a, 636b, 636c and 636d are shown attached to corners of first portion 628 and second portion 630, holding members 636a, 636b, 636c and 636d may be attached to any portion of device 604 suitable for attaching first portion 628 and second portion 630 to tool 610 during installation.

Arm 632 may be provided with a male pin, and arm 638 may be provided with a female funnel shaped receptacle to ease the alignment of arms 632 and 638. It is noted that although first portion 628 and second portion 630 of device 604 are shown having a substantially triangular shape, it is further contemplated that in some embodiments, device 604 may be bisected along an axis perpendicular to a side of device 604 such that first portion 628 and second portion 630 have a rectangular profile as illustrated in Figure 2d. In this aspect, the longest side of each portion may be positioned adjacent the long side of arms 632 and 638 adjacent handles 634 and 640, respectively.

Once positioned around each portion of device 604, a diver or ROV may position first portion 628 and second portion 630 around structure 602. Arms 632 and 638 are then pressed together using handles 634 and 640, respectively, to attach first portion 628 to second portion 630. Once first portion 628 and second portion 630 are attached together via pins 608a and 608b and latches 606a and 606b, respectively, tool 610 is removed.

Although VIV suppression device 604 illustrated in Figure 6 is a four sided device, devices having more or less sides may be suitable for use with tool 610. Representatively, the device may have any number of sides so long as arms 632 and 638 can fit around and be attached to each portion of the device.

Figure 7:

Figure 7 illustrates a mechanism for positioning a multiple sided vibration induced suppression device around a structure. Tool 700 may be used to position VIV suppression devices such as those described in reference to Figures 2d and 6 which include separable halves.

Tool 700 may be an assembly which stores and feeds VIV suppression devices to a desired region of structure 702. Once the desired region is reached, tool 700 may be used to position the VIV suppression devices around structure 702. In this aspect, tool includes body 706a and 706b for storing and feeding first portion 722 and second portion 724, respectively, of VIV suppression device 704 to a desired region of structure 702. Body 706a and 706b are positioned along opposite sides of structure 702. Once the desired region is reached, first portion 722 and second portion 724 of VIV suppression device 704 may be ejected from body 706a and 706b to position them around structure 702. It is noted that body 706a and 706b are substantially the same structure therefore the same features described in reference to body 706a are found in 706b. As illustrated in Figure 7, body 706a and 706b are dimensioned to receive and feed a plurality of VIV suppression device portions 722, 724 to structure 702. In this aspect, multiple VIV suppression devices may be transported down to a desired region of structure 702 at once. To accommodate the plurality of VIV suppression device portions 722, 724, body 706a and 706b may have an elongated structures within which a desired number of device portions 722, 724 may be loaded. In some embodiments, body 706a and 706b may have a length suitable for accommodating five device portions, ten device portions and in some embodiments, up to about fifteen device portions. In some embodiments, body 706a and 706b may have a substantially "L" or "J" shaped structure. In other embodiments, body 706a and 706b may be in the shape of a column. An opening 708 may be provided at an end of body 706a and 706b to allow for ejection of device portions 722, 724 loaded therein. The device portions may be loaded into body 706a (and similarly body 706b) through end 728. Device portions are loaded into body 706a such that when the device portions are ejected from opening 708 of tool 700, the regions of the device portions which are to encircle structure 702 are facing structure 702. In some embodiments, the device portions may be loaded into body 706a prior to lowering of tool 700 to the desired region of structure 702. Once loaded, end 728 may be closed with, for example, cap 710. Umbilical 726 may be attached to cap 710 (e.g. bolted) to facilitate raising and lowering of tool 700 to the desired region of structure 702. In this aspect, umbilical 726 may be a cable suitable for supporting tool 700 and VIV suppression device portions therein.

In some embodiments, device portions 722, 724 are pressure fed from one end of body 706a and 706b to an opposite end adjacent structure 702. Representatively, tool 700 may include a spring mechanism 714 which is positioned between end cap 710 of body 706a and a VIV suppression device portion closest to cap 710. Spring mechanism 714 applies a constant pressure to the VIV suppression device portions within body 706a pushing them down toward an opposite open end 708 of body 700. Thus, a VIV suppression device portion which is ejected from body 706a is replaced by the next VIV suppression device portion adjacent to the ejected portion. Although a spring mechanism 714 is illustrated in Figure 7, it is further contemplated that other mechanisms may be used to advance each of the VIV suppression device portions through body 706a. Representatively, a ratcheting mechanism or belt feeding mechanism may be incorporated into body 706a to advance the VIV suppression device portions through body 706a.

Once a VIV suppression device portion reaches open end 708, an ejection mechanism 716 may be provided to facilitate ejection of VIV suppression device portions from body 706a. In some embodiments, ejection mechanism 716 may be a hydraulic cylinder having hydraulic barrel 718 and piston rod 720. Hydraulic barrel 718 may be attached (e.g. bolted) to a portion of body 706a such that piston rod 720 moves in a direction of opening 708 to facilitate ejection of VIV suppression device portions from body 706a.

In some embodiments, receiving member 712 for receiving VIV suppression device portions to be ejected is attached to an end of piston rod 720. Once a VIV suppression device portion is positioned within receiving member 712, piston rod 720 may be extended out of hydraulic cylinder 718 to advance the VIV suppression device portion toward structure 702. Once the VIV suppression device portion is securely attached around structure 702 to its opposite half, the VIV suppression device portion may be released from receiving member 712 by retracting piston rod 720 back into hydraulic cylinder 718. In this aspect, receiving member 712 may be dimensioned to removably receive the VIV suppression device portion. Representatively, in the case of square shaped VIV suppression devices, receiving member 712 may be a rectangularly shaped structure having an open center dimensioned to receive and retain the VIV suppression device portion therein. It is contemplated that the receiving member 712 should fit around a region of the VIV suppression device portion furthest from structure 702 so as not to interfere with positioning of the device portions around structure 702 and attachment of the free ends of the device portions to each other. Although a rectangularly shaped receiving member 712 is described, it is contemplated that the size, shape and dimensions of receiving member 712 may vary depending upon the size, shape and dimensions of the VIV suppression device portions received therein.

Body 706a and 706b may be made of any suitable material for storing and feeding device 704 there from. Representatively, body 706a and 706b may be made of metals such as steel or aluminum, polymers such as polyethylene or polypropylene, or composite materials such as fiberglass or carbon fiber composites, or other conventional materials. Body 706a and 706b may be molded, welded, bent, cast, glued, or otherwise formed with manufacturing techniques as are known in the art. In another embodiment, a single feeding mechanism may be used to eject both portions of the device 722, 724, which could be attached to each other at one side, and open at the other side to receive structure 702.

In another embodiment, a feeding mechanism could be used which does not eject the portions 722, 724, but provides them for an ROV to come pick them up.

Figure 8:

Figure 8 illustrates a mechanism for positioning a multiple sided vibration induced suppression device around a structure. Tool 800 may be used to position VIV suppression devices such as those described in reference to, for example, Figure 6 which includes separable halves. Tool 800 is substantially similar to tool 700 described in reference to Figure 7 except that instead of using ejection mechanism 716 to advance each VIV suppression portion individually, a similar mechanism is used to move each of body 706a and 706b toward structure 702. In this aspect, brace members 802a and 802b extend from body 706a toward structure 702. Similarly brace members 804a and 804b extend from body 706b toward structure 702. Hydraulic cylinder 806 having hydraulic barrel 808 and piston rod 810 is attached to ends of brace members 802a and 804a. Although not shown, a second hydraulic cylinder is attached to ends of brace members 802b and 804b. In this aspect, movement of piston rod 810 into hydraulic barrel 808 pulls body 706a and 706b toward each other. This in turn pulls VIV suppression device portions 722 and 724 toward each other and around structure 702. Once ends of portions 722 and 724 meet they may be attached together to hold them around structure 702. Movement of piston rod out of hydraulic barrel 808 pushes body 706a and 706b away from each other thereby releasing the VIV suppression device portions from receiving member 712.

Alternative Embodiments:

Although tools for installing the VIV suppression devices disclosed herein about an underlying structure are described, it is further contemplated that the devices may be installed about the structure by hand at the surface and then dropped or lowered down to the target depth. In this aspect, cables, ropes or other guides may be used to keep the devices from impacting the water too hard or from traveling too fast down the structure due to gravity. It is further contemplated that water breaks may also be used to slow free fall off the device through the water.

When the devices disclosed herein are to be installed around an umbilical or a structure with sensitive coating, one or more inner rings or friction pads may be installed between the device and the structure to prevent damage to the sensitive coating. Suitable sleeves, suitable collars, and suitable devices to install exterior to structures, and methods of their installation are disclosed in U.S. Patent Application Number 10/839,781 , having attorney docket number TH 1433; U.S. Patent Application Number 11/400,365, having attorney docket number TH0541 ; U.S. Patent Application Number 11/419,964, having attorney docket number TH2508; U.S. Patent Application Number 11/420,838, having attorney docket number

TH2876; U.S. Patent Application Number 60/781 ,846 having attorney docket number TH2969; U.S. Patent Application Number 60/805,136, having attorney docket number TH1500; U.S. Patent Application Number 60/866,968, having attorney docket number TH31 12; U.S. Patent Application Number 60/866,972, having attorney docket number TH3190; U.S. Patent Number 5,410,979; U.S. Patent

Number 5,410,979; U.S. Patent Number 5,421 ,413; U.S. Patent Number 6,179,524; U.S. Patent Number 6,223,672; U.S. Patent Number 6,561 ,734; U.S. Patent Number 6,565,287; U.S. Patent Number 6,571 ,878; U.S. Patent Number 6,685,394; U.S. Patent Number 6,702,026; U.S. Patent Number 7,017,666; and U.S. Patent Number 7,070,361 , which are herein incorporated by reference in their entirety.

Suitable methods for installing collars, and other devices to install exterior to structures, are disclosed in U.S. Patent Application Number 10/784,536, having attorney docket number TH1853.04; U.S. Patent Application Number 10/848,547, having attorney docket number TH2463; U.S. Patent Application Number 1 1/596,437, having attorney docket number TH2900; U.S. Patent Application Number 1 1/468,690, having attorney docket number TH2926; U.S. Patent Application Number 11/612,203, having attorney docket number TH2875; U.S. Patent Application Number 60/806,882, having attorney docket number TH2879; U.S. Patent Application Number 60/826,553, having attorney docket number TH2842; U.S. Patent Number 6,695,539; U.S. Patent Number 6,928,709; and U.S. Patent Number 6,994,492; which are herein incorporated by reference in their entirety.

Illustrative Embodiments:

In one embodiment, there is disclosed a system for reducing drag and/or vortex induced vibration of a structure, the system comprising a multiple sided device comprising from 4 to 6 sides, the multiple sided device comprising a first portion and a second portion, the first portion and the second portion adapted to attach to each other about the structure. In some embodiments, the device comprises a chord to thickness ratio of less than 1.5. In some embodiments, the device comprises a chord to thickness ratio of less than 1.25. In some embodiments, the device comprises a hinge between the first portion and the second portion. In some embodiments, the device comprises a height from 0.5 to 10 times a diameter of the structure. In some embodiments, the device comprises 4 sides. In some embodiments, the device comprises 2 sides aligned substantially parallel with a fluid flow encountering the structure. In some embodiments, the device comprises an even number of sides. In some embodiments, the device comprises a square shape. In some embodiments, the system also includes a plurality of multiple sided devices along a length of the structure. In some embodiments, the system also includes at least 3 corners, each corner having a radius of curvature less than a radius of the structure. In some embodiments, the device comprises an attachment mechanism between the first portion and the second portion. In some embodiments, the device comprises a plurality of brace members. In some embodiments, the device comprises at least one retaining mechanism adapted to move from a first open configuration that allows the structure to move in and out of the device, and a second closed configuration that locks the structure within the device. In some embodiments, the system also includes a tool comprising a first arm adapted to releasably connect to the first portion and a second arm adapted to releasably connect to the second portion. In some embodiments, the system also includes a tool comprising an actuator, the actuator adapted to move the tool from a first open configuration that allows the structure to move in and out of the device, and a second closed configuration that surrounds the structure within the device. In some embodiments, the tool comprises a storage compartment adapted to store a plurality of first portions and a plurality of second portions.

In one embodiment, there is disclosed a method for modifying a structure subject to drag and/or vortex induced vibration, said method comprising positioning a first portion and a second portion of at least one multiple sided device around the structure, the multiple sided device comprising from 4 to 6 sides; and connecting the first portion to the second portion. In some embodiments, the positioning comprises positioning at least two multiple sided devices about the structure. In some embodiments, the method also includes positioning a collar, a buoyancy module, and/or a clamp around the structure. In some embodiments, the device comprises a four sided shape, wherein the first portion and the second portion comprise a triangle or a rectangle shape. In some embodiments, the method also includes locking the device at a preferred angular orientation based on ambient expected currents acting on the structure. In one embodiment, there is disclosed a system for reducing drag and/or vortex induced vibration of a structure, the system comprising a multiple sided device comprising from 4 to 10 sides, the device free to rotate about the structure, the multiple sided device comprising a first portion and a second portion adapted to connect to each other about the structure. In some embodiments, the system also includes one or more thrust collars located about the structure, above and/or below the device.

While the devices have been described as being used in aquatic environments, they may also be used for VIV and/or drag reduction on elongated structures in atmospheric environments. While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the invention, including all features which would be treated as equivalents thereof by those skilled in the art to which this invention pertains.

Claims

C L AIM S

1. A system for reducing drag and/or vortex induced vibration of a structure, the system comprising: a multiple sided device comprising from 4 to 6 sides, the multiple sided device comprising a first portion and a second portion, the first portion and the second portion adapted to attach to each other about the structure.

2. The system of claim 1 , wherein the device comprises a chord to thickness ratio of less than 1.5.

3. The system of one or more of claims 1-2, wherein the device comprises a chord to thickness ratio of less than 1.25.

4. The system of one or more of claims 1-3, wherein the device comprises a hinge between the first portion and the second portion.

5. The system of one or more of claims 1-4, wherein the device comprises a height from 0.5 to 10 times a diameter of the structure.

6. The system of one or more of claims 1-5, wherein the device comprises 4 sides.

7. The system of one or more of claims 1-6, wherein the device comprises 2 sides aligned substantially parallel with a fluid flow encountering the structure.

8. The system of one or more of claims 1-7, wherein the device comprises an even number of sides.

9. The system of one or more of claims 1-8, wherein the device comprises a square shape.

10. The system of one or more of claims 1-9, further comprising a plurality of multiple sided devices along a length of the structure.

1 1. The system of one or more of claims 1-10, further comprising at least 3 corners, each corner having a radius of curvature less than a radius of the structure.

12. The system of one or more of claims 1-1 1 , wherein the device comprises an attachment mechanism between the first portion and the second portion.

13. The system of one or more of claims 1-12, wherein the device comprises a plurality of brace members.

14. The system of one or more of claims 1-13, wherein the device comprises at least one retaining mechanism adapted to move from a first open configuration that allows the structure to move in and out of the device, and a second closed configuration that locks the structure within the device.

15. The system of one or more of claims 1-14, further comprising a tool comprising a first arm adapted to releasably connect to the first portion and a second arm adapted to releasably connect to the second portion.

16. The system of claim 15, the tool comprising an actuator, the actuator adapted to move the tool from a first open configuration that allows the structure to move in and out of the device, and a second closed configuration that surrounds the structure within the device.

17. The system of one or more of claims 15-16, wherein the tool comprises a storage compartment adapted to store a plurality of first portions and a plurality of second portions.

18. A method for modifying a structure subject to drag and/or vortex induced vibration, said method comprising: positioning a first portion and a second portion of at least one multiple sided device around the structure, the multiple sided device comprising from 4 to 6 sides; and connecting the first portion to the second portion.

19. The method of claim 18, wherein the positioning comprises positioning at least two multiple sided devices about the structure.

20. The method of one or more of claims 18-19, further comprising: positioning a collar, a buoyancy module, and/or a clamp around the structure.

21. The method of one or more of claims 18-20, wherein the device comprises a four sided shape, wherein the first portion and the second portion comprise a triangle or a rectangle shape.

22. The method of one or more of claims 18-21 , further comprising: locking the device at a preferred angular orientation based on ambient expected currents acting on the structure.

23. A system for reducing drag and/or vortex induced vibration of a structure, the system comprising: a multiple sided device comprising from 4 to 10 sides, the device free to rotate about the structure, the multiple sided device comprising a first portion and a second portion adapted to connect to each other about the structure.

24. The system of claim 23, further comprising one or more thrust collars located about the structure, above and/or below the device.