WO2010141436A2

WO2010141436A2 - Vortex induced vibration suppression systems and methods

Info

Publication number: WO2010141436A2
Application number: PCT/US2010/036856
Authority: WO
Inventors: Stephen Paul Armstrong
Original assignee: Shell Internationale Research Maatschappij BV; Shell Oil Co
Current assignee: Shell Internationale Research Maatschappij BV; Shell USA Inc
Priority date: 2009-06-03
Filing date: 2010-06-01
Publication date: 2010-12-09
Anticipated expiration: 2011-12-03
Also published as: WO2010141436A3

Abstract

An apparatus for controlling vortex-induced vibration, comprising a body suitable for abutting against a cylindrical marine element; a connector supported by the faring body, the connector comprising a pin; a strap comprising an opening adapted to receive the pin to form a connection.

Description

VORTEX INDUCED VIBRATION SUPPRESSION SYSTEMS AND METHODS

Field of the Invention

This invention is related to vortex induced vibration suppression devices that can be attached to offshore structures to reduce drag and/or vortex induced vibration (VIV). Background of the Invention

Whenever a bluff body in a fluid environment, such as a cylinder, is subjected to a current in the fluid, it is possible for the body to experience vortex-induced vibrations (VIV). These vibrations may be caused by oscillating hydrodynamic 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 may include 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 minispar or spar floating production system (a "spar").

Risers as used herein are defined to be a non-exclusive example of a marine element subject to VIV. Generally a riser system is used for establishing fluid communication between the surface and the bottom of a water body. The principal purpose of the riser is to provide a fluid flow path between a drilling vessel and a well bore and to guide a drill string to the well bore.

A typical riser system may include one or more fluid-conducting conduits that extend from the surface to a structure (e.g., wellhead) on the bottom of a water body. For example, in the drilling of a submerged well, a drilling riser usually consists of a main conduit through which the drill string is lowered and through which the drilling mud is circulated from the lower end of the drill string back to the surface. In addition to the main conduit, there may be provided auxiliary conduits such as, for example, choke and kill lines, pressurized fluid lines, hard pipes, and electrical lines, which extend relatively parallel to the main conduit. These auxiliary conduits and lines are commonly referred to as umbilical elements and/or umbilicals. There are generally two kinds of water current induced stresses to which elements of a riser system may be exposed. The first kind of stress as mentioned above is caused by vortex- induced alternating forces that vibrate the underwater structure in a direction perpendicular to the direction of the current. These are referred to as vortex-induced vibrations (VIV). When water flows past the structure, vortices are alternately shed from each side of the structure. This produces a fluctuating force on the structure transverse to the current. 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 have been known to cause structures such as risers to break apart and fall to the ocean floor. The second type of stress is 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 vibrations of the structure. For instance, a riser pipe that is vibrating due to vortex shedding will disrupt the flow of water around it more so than a stationary riser. This results in greater energy transfer from the current to the riser, and hence more drag.

Many methods have been developed to reduce vibrations of sub sea structures. Some of these methods to reduce vibrations caused by vortex shedding from subsea structures operate by stabilization of the wake. These methods include streamlined fairings, wake splitters and flags. Streamlined or teardrop shaped, fairings that swivel around a structure have been developed that almost eliminate the shedding or vortexes. Other conventional methods to reduce vibrations caused by vortex shedding from sub sea structures 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 methods include the use of helical strakes around a structure, or axial rod shrouds and perforated shrouds.

U.S. Patent 6,401,646 discloses a fairing system for the reduction of vortex-induced vibration and minimization of drag about a substantially cylindrical element immersed in a fluid medium. The fairing system includes a plurality of cylindrical shells rotatably mounted about a cylindrical element immersed in a fluid medium. Each cylindrical shell has opposing edges defining a longitudinal gap configured to allow the shells to snap around the cylindrical element. The longitudinal gap has a circumference of about 120° relative to the circumference of each shell. Alternatively the longitudinal gap can have a circumference of about 60° relative to the circumference of each shell. The shells also include a fin positioned along the each opposing edge of the longitudinal gap, in which each fin extends outwardly from each shell. The fins are positioned on each shell so as to reduce vortex-induced vibration and minimize drag on the cylindrical element. U.S. Patent 6,401,646 is herein incorporated by reference in its entirety. U.S. Patent 5,738,034 discloses an apparatus and method for minimizing vortex induced vibrations and hydrodynamic drag of a drilling riser. Vortex induced vibrations and hydrodynamic drag are minimized by installing on a drilling riser streamlined faring sections. The fairing sections are installed on and removed from a riser through the use of one or more door panels on a rounded front portion that have a latch mechanism which can be easily opened and closed. The fairing sections are configured so they can nest one inside the other for easy storage. A tapered back or tail section of each fairing section has an attachment receptacle for engagement by a handling mechanism with a telescoping arm for grasping the fairing section. The handling mechanism is designed to move the fairing sections between a rack, where they are stored, and a position adjacent to the riser. U.S. Patent 5,738,034 is herein incorporated by reference in its entirety.

Co-pending patent application PCT/US2009/031446, having attorney docket number TH3351, discloses a system comprising a vortex induced vibration suppression device comprising a base section comprising at least two connected portions; and a tail section connected to the base section. Co-pending patent application PCT/US2009/031446 is herein incorporated by reference in its entirety.

Co-pending U.S. patent application publication 2006/0021560, having attorney docket number TH1433, discloses tail fairings designed with features for fast installation and/or for suppression of vortices addition between fairings, apparatus incorporating such fairings, methods of making and using such fairings and apparatus, and methods of installing such fairings. Co-pending patent application 2006/0021560 is herein incorporated by reference in its entirety.

VIV suppression devices such as fairings are often installed from floating structures such as boats or ships, which are rented by the day, at high day rates. As such, the time to install the VIV suppression devices is limited.

There is a need in the art for improved apparatus and methods for suppressing VIV.

There is a need in the art for apparatus and methods for suppressing VIV that do not suffer from the disadvantages of the prior art.

There is a need in the art for apparatus and methods for providing VIV suppression to a subsea structure with a fast installation feature.

There is a need for systems and methods of installing VIV suppression devices with easier installation. These and other needs will become apparent to those of skill in the art upon review of this specification, including its drawings and claims. Summary of the Invention

Aspects of the invention provide for an apparatus, systems and methods for suppressing VIV and reducing drag of a marine element.

Other aspects of the invention provide for an apparatus, systems and methods for suppressing VIV and reducing drag of a marine element, which are easier and/or quicker to install.

According to one embodiment of the present invention, there is provided an apparatus for controlling vortex-induced vibration, comprising a body suitable for abutting against a cylindrical marine element; a connector supported by the faring body, the connector comprising a pin; a strap comprising an opening adapted to receive the pin to form a connection.

According to another embodiment of the present invention, there is provided a system for controlling drag and vortex-induced vibration, comprising a substantially cylindrical marine element; a fairing body abutted against the marine element, and comprising a connector supported by the faring body, the connector comprising a pin; a strap comprising an opening adapted to receive the pin to form a connection, and wherein the strap and the fairing are installed about the marine element. 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 subsea structure system.

Figure 2 illustrates a perspective view of a VIV suppression device. Figure 3 illustrates an exploded view of the connector assembly of Figure 2.

Figure 4 illustrates a cross sectional view of the connector assembly of Figure 3 in a retracted configuration.

Figure 5 illustrates a cross sectional view of the connector assembly of Figure 4 in an extended configuration. Detailed Description

Figure 1:

Referring now to Figure 1 there is illustrated offshore system 100. System 100 includes surface structure 102 near a water surface. Surface structure 102 is connected to subsurface structure 103 adjacent to seafloor 108 by a tubular structure 104. In some embodiments, tubular structure 104 may be a riser. Exterior to riser 104 is buoyancy material 106, such as a foam, which may serve to insulate and/or provide buoyancy to riser 104. The water has current 110, which may cause vortex-induced vibration (VIV) of riser 104 and buoyancy material 106. To counter VIV, VIV suppression devices 114 may be installed along the length of riser 104. In this embodiment, VIV suppression devices 114 are tail-fin fairings.

Collars 112 are further installed about riser 104 and between VIV suppression devices 114 to keep VIV suppression devices 114 from moving along the length of riser 104. Representatively, collars 112 may be hinged, load-bearing collars installed when riser 104 is being initially deployed from a floating drilling unit.

Figure 2:

Figure 2 illustrates a perspective view of a VIV suppression device. In this embodiment VIV suppression device 114 is a tail-fin fairing. Tail-fin fairing 114 includes tail-fin 216 and straps 218a and 218b. Straps 218a and 218b are dimensioned to wrap around the underlying tubular and attach at opposite ends to opposite sides of tail-fin 216. Tail-fin 216 and straps 218a and 218b may be made of any one of numerous materials including, but not limited to, thermoplastics, fiber-reinforced polymer (e.g., fiberglass) and metals.

Although two straps 218a and 218b are illustrated, there may be from two to six straps, for example from two to four straps provided per tail-fin 216. In some embodiments, straps 218a and 218b may have a height from about 2% to about 20%, for example from about 5% to about 10% of the height of tail-fin 216.

Receptacles 220a and 220b are positioned on sides of tail-fin 216 to receive ends of straps 218a and 218b. In this aspect, receptacles 220a and 220b may be square or rectangularly shaped and have an opening at one end to allow ends of straps 218a and 218b to be inserted therein. Receptacles 220a and 220b may be made of any one of numerous materials, including, but not limited to thermoplastics, fiber-reinforced polymer (e.g., fiberglass) and metals. Receptacles 220a and 220b may be attached to sides of tail-fin 216 by, for example, welding, molding, bolts or other similarly suitable connecting means.

Receptacles 220a and 220b include connector assembly 222a and connector assembly 222b. Connector assembly 222a and connector assembly 222b may be self-latching mechanisms which serve to lock straps 218a and 218b within receptacles 220a and 220b and release straps 218a and 218b when desired with or without the use of additional tooling. Connector assemblies 222a and 222b will be discussed in further detail below in regard to Figures 3-5.

During installation, tail-fin 216 is positioned against the underlying tubular by, for example, resting the lower end of tail-fin 216 on a load bearing collar (not shown). Strap 218b may then be positioned around the tubular and opposite ends of strap 218b may be inserted within receptacle 220b and a second receptacle (not shown) positioned along the other side of tail-fin 216. Strap 218a may further be positioned around the tubular and its ends inserted in receptacle 220a and a second receptacle (not shown) positioned along the other side of tail-fin 216.

Figures 3-5:

Figure 3 illustrates an exploded view of an embodiment of a connector assembly of Figure 2. Although connector assembly 222a is referenced in the foregoing description, it is to be understood that each of the connector assemblies illustrated in Figure 2 may be substantially the same. Therefore the description provided herein may also be applicable to connector assembly 222b as well as possibly others that are not shown. Connector assembly 222a includes housing 324 attached to receptacle 220a.

Housing 324 is a cylindrical member having a hollow chamber therein to accommodate components of connector assembly 222a. As will be shown in detail in reference to Figures 4 and 5, components of connector assembly 222a may include biasing mechanism 432 such as a spring, gas or hydraulic piston or other suitable biasing mechanisms, pin 434 attached to shaft 328 extending from handle 326, cross pin 438 and cross bar 440 attached to shaft 328. Housing 324 includes openings at each end to allow for passage of some of these components. The end of housing 324 adjacent receptacle 220a includes a first opening 436 (see Figures 4 and 5) dimensioned to allow for passage of pin 434. Manipulation of handle 326 (e.g. raising, lowering and/or turning) causes pin 434 to be retracted within or extend out the end of housing 324 and through opening 330 of strap 218a formed within receptacle 220a. Positioning of pin 434 through opening 330 of strap 218a locks strap 218a to the tail-fin. To release strap 218a, handle 326 is pulled in a direction away from receptacle 220a which in turn lifts pin 434 out of opening 330 and into housing 324. It is further contemplated that during the initial insertion of the ends of straps 218a and

218b in receptacles 220a and 220b, pin 434 may extend from housing 324 and into the cavity of receptacles 220a and 220b. The end of pin 434 may be angled (e.g. wedge shaped) such that insertion of straps 218a and 218b within receptacles 220a and 220b pushes pin 434 in an upward direction (i.e. toward housing 324) so that straps 218a and 218b can slide within receptacles 220a and 220b under pin 434. Once pin 434 reaches opening 330, spring 432 drives pin 434 through opening 330 without any user intervention.

In another embodiment (not shown) during the initial insertion of the ends of straps 218a and 218b in receptacles 220a and 220b, pin 434 may be held within housing 324 by a release mechanism (not shown). As straps 218a and 218b are inserted within receptacles 220a and 220b, release mechanism is engaged to release pin 434 in a downward direction due to the force of biasing mechanism 432 so that straps 218a and 218b can slide within receptacles 220a and 220b then be locked in place by pin 434. Once pin 434 reaches opening 330, biasing mechanism 432 drives pin 434 through opening 330 without any user intervention. The end of housing 324 opposite receptacle 220a includes a second opening 332 (see Fig. 3) to facilitate locking of pin 434 in the retracted position. A center portion of second opening 332 is dimensioned to allow for passage of shaft 328. Second opening 332 further includes narrower portions extending from the center portion. The narrower portions act as slots which allow for passage of cross pin 438 (see Figures 4 and 5) extending from shaft 328 when it is aligned with the narrower portions. The narrower portions further act to prevent passage of cross pin 438 when it is not aligned with the opening. In this aspect, pin 434 can be locked in the retracted position by first aligning cross pin 438 with the narrower portions and pulling on handle 326 until cross pin 438 is above housing 324. Handle 326 is then turned approximately 90 degrees such that cross pin 438 is no longer aligned with the narrower portions and instead catches on the top surface of housing 324 and shaft 328 thereby preventing shaft 328 from springing back down toward strap 218a.

Figure 4 illustrates a cross sectional view of the connector assembly of Figure 3 in a retracted configuration. As can be seen from Figure 4, connector assembly 222a includes handle 326 attached to shaft 328. Shaft 328 is positioned through housing 324 and connected at an end opposite that of handle 326 to pin 434. Pin 434 may be screwed onto the end of shaft 328 or integrally formed with shaft 328. Shaft 328 includes cross pin 438 and cross bar 440. Spring 432 is positioned around shaft 328 between cross pin 438 and cross bar 440. In the retracted position as shown in Figure 4, spring 432 is compressed between a top lip of housing 324 and cross bar 440. Spring 432, pin 434, shaft 328, handle 326, cross pin 438 and cross bar 440 may be made of the same or different materials including, but not limited to, thermoplastics, fiber-reinforced polymer (e.g., fiberglass) and metals.

Figure 5 illustrates a cross sectional view of the connector assembly of Figure 4 in an extended configuration. In this embodiment, cross pin 438 is aligned with opening 332 of housing 324 by turning handle 326 approximately 90 degrees from that which is shown in Figure 4. Cross pin 438 passes through opening 332 and spring 432 is allowed to expand over cross pin 438 such that it presses against the top lip of housing 324 and drives pin 434 through opening 436 of housing 324 and into opening 330 of strap 218a. The force of expanded spring 432 then holds pin 434 within opening 330 of strap 218a. A further locking mechanism (not shown) may also be provided to hold pin 434 within opening 330 of strap 218a, such as a bar or opening within housing to engage cross pin 438.

To remove pin 434 from opening 330 of strap 218a back to the retracted position, handle 326 is rotated approximately 90 degrees from that which is shown in Figure 5 so that cross pin 438 aligns with opening 332 of housing 324. Handle 326 is then pulled in a direction away from receptacle 220a such that cross pin 438 passes through opening 332 allowing pin 434 to be raised out of opening 330. To lock pin 434 in this position and prevent pin 434 from being forced back into opening 330 by spring 432, handle 326 is rotated approximately 90 degrees. Rotation of handle 326 causes a misalignment between cross pin 438 and opening 332 of housing 324 such that cross pin 438 catches on the top portion of housing 324 as previously discussed. This prevents shaft 328 from springing toward strap 218a and in turn pin 434 from being positioned within opening 330.

It is noted that although it is described herein that the dimensions of cross pin 438 and second opening 332 are used to facilitate locking of pin 434 in a desired position, it is contemplated that other structural features may be modified to allow for locking of pin 434. Representatively, the dimensions of pin 434 and opening 436 of housing 324 may be modified such that pin 434 can be aligned or misaligned with opening 436. For example, pin 434 may have a wedge shape similar to that of a door latch and opening 436 may be elongated such that the wedge shaped pin 434 can pass through opening 436 in one orientation but is blocked when rotated out of alignment with opening 436.

Alternative Embodiments:

In the preceding detailed description, reference is made to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Fairings may be replaced with strakes, shrouds, wake splitters, tail fairings, buoyancy modules, or other devices as are known in the art. 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 TH1433; 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 TH3112; 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 fairings, 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 11/596,437, having attorney docket number TH2900; U.S. Patent Application Number 11/468,690, 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. The fairings may be installed on the tubular member (e.g. buoyancy material and riser) before or after the tubular member is placed in a body of water.

The fairings and/or other devices exterior to the structure may have a clamshell configuration, and may be hinged with a closing mechanism opposite the hinge, for example a mechanism that can be operated with an ROV. Fairings may be provided with copper plates on their ends to allow them to weathervane with adjacent fairings or collars.

Fairings may be partially manufactured from copper, or have copper strips installed on an inner surface to retard marine growth, and/or be coated with an anti-fouling paint or other coating.

Illustrative Embodiments:

In one embodiment, there is disclosed an apparatus for controlling vortex-induced vibration, comprising a body suitable for abutting against a cylindrical marine element; a connector supported by the faring body, the connector comprising a pin; a strap comprising an opening adapted to receive the pin to form a connection. In some embodiments, the connector further comprises a handle connected to the pin. In some embodiments, the connector further comprises a biasing device connected to the pin, the biasing device adapted to force the pin into the opening. In some embodiments, the apparatus also includes a second strap for forming a second connection to secure the body about the cylindrical marine element. In some embodiments, the body comprises a fairing body. In some embodiments, the apparatus also includes a second connector supported by the faring body, the second connector comprising a second pin; the strap comprising a second opening adapted to receive the second pin to form a second connection. In some embodiments, the strap comprises the opening at a first end and the second opening at a second end. In some embodiments, the fairing body comprises a tail having at least one of holes and/or ribs. In some embodiments, the strap comprises the opening at a first end and is permanently connected to the body at a second end. In one embodiment, there is disclosed a system for controlling drag and vortex- induced vibration, comprising a substantially cylindrical marine element; a fairing body abutted against the marine element, and comprising a connector supported by the faring body, the connector comprising a pin; a strap comprising an opening adapted to receive the pin to form a connection, and wherein the strap and the fairing are installed about the marine element. In some embodiments, the connector comprises a spring adapted to bias the pin into the opening. In some embodiments, the connector comprises a release adapted to hold the pin in a retracted position until the opening of the strap is located beneath the pin, when the release is engaged and the spring forces the pin into the opening. In some embodiments, the system also includes a second strap for securing the fairing body about the marine element. In some embodiments, the fairing body comprises thermoplastic polymer, a thermoset polymer, high-density polyethylene, or polyacrylonitrile butadiene styrene. In some embodiments, the fairing body comprises a tail having at least one of holes and/or ribs.

Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments, configurations, materials and methods without departing from their spirit and scope. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described and illustrated herein, as these are merely exemplary in nature.

Claims

C L A I M S

1. An apparatus for controlling vortex-induced vibration, comprising: a body suitable for abutting against a cylindrical marine element; a connector supported by the faring body, the connector comprising a pin; a strap comprising an opening adapted to receive the pin to form a connection.

2. The apparatus of claim 1, wherein the connector further comprises a handle connected to the pin.

3. The apparatus of one or more of claims 1 or 2, wherein the connector further comprises a biasing device connected to the pin, the biasing device adapted to force the pin into the opening.

4. The apparatus of one or more of claims 1-3, further comprising a second strap for forming a second connection to secure the body about the cylindrical marine element.

5. The apparatus of one or more of claims 1-4, wherein the body comprises a fairing body.

6. The apparatus of one or more of claims 1-5, further comprising a second connector supported by the faring body, the second connector comprising a second pin; the strap comprising a second opening adapted to receive the second pin to form a second connection.

7. The apparatus of claim 6, wherein the strap comprises the opening at a first end and the second opening at a second end.

8. The apparatus of one or more of claims 1-7, wherein the fairing body comprises a tail having at least one of holes and/or ribs.

9. The apparatus of one or more of claims 1-8, wherein the strap comprises the opening at a first end and is permanently connected to the body at a second end.

10. A system for controlling drag and vortex-induced vibration, comprising: a substantially cylindrical marine element; a fairing body abutted against the marine element, and comprising a connector supported by the faring body, the connector comprising a pin; a strap comprising an opening adapted to receive the pin to form a connection, and wherein the strap and the fairing are installed about the marine element.

11. The system of claim 10, wherein the connector comprises a spring adapted to bias the pin into the opening.

12. The system of one or more of claim 11, wherein the connector comprises a release adapted to hold the pin in a retracted position until the opening of the strap is located beneath the pin, when the release is engaged and the spring forces the pin into the opening.

13. The system of one or more of claims 10-12, further comprising a second strap for securing the fairing body about the marine element.

14. The system of one or more of claims 10-13, wherein the fairing body comprises thermoplastic polymer, a thermoset polymer, high-density polyethylene, or polyacrylonitrile butadiene styrene.

15. The system of one or more of claims 10-14, wherein the fairing body comprises a tail having at least one of holes and/or ribs.