WO2011031656A1

WO2011031656A1 - Riser arrays or groups having vortex-induced vibration (viv) suppression devices connected with spacers

Info

Publication number: WO2011031656A1
Application number: PCT/US2010/047942
Authority: WO
Inventors: Donald Wayne Allen; Dean Leroy Henning; Li Lee
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2009-09-10
Filing date: 2010-09-07
Publication date: 2011-03-17

Abstract

A system comprising a support structure in a flowing fluid environment; a spacer plate connected to the support structure, the spacer plate comprising at least one opening therethrough; at least one vortex induced vibration suppression device connected to the spacer plate, the vortex induced vibration suppression device comprising an opening therethrough; wherein the spacer plate and the vortex induced vibration suppression device are adapted to receive a structure through the openings of the spacer plate and the vortex induced vibration suppression device.

Description

RISER ARRAYS OR GROUPS HAVING VORTEX-INDUCED VIBRATION (VIV) SUPPRESSION DEVICES CONNECTED WITH SPACERS

Field of the Invention

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

Background of the Information

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.

Floating vessels may be used to liquify and gasify natural gas. Sea water may be used to cool or heat the natural gas. It may be desired to separate the water inlet from the water outlet due to the temperature differences. A plurality of risers may be used to collect or deposit water at a depth from the floating vessel. These risers may be exposed to VIV.

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 and the length of the structure.

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") in a direction mainly 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 one of the natural frequencies 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 and/or drag 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 or other flowing fluids 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 length 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.

U.S. Patent Number 6,223,672 discloses an ultrashort fairing for suppressing vortex-induced vibration in substantially cylindrical marine elements. The ultrashort falling has a leading edge substantially defined by the circular profile of the marine element for a distance following at least about 270 degrees thereabout and a pair of shaped sides departing from the circular profile of the marine riser and converging at a trailing edge. The ultrashort fairing has dimensions of thickness and chord length such that the chord to thickness ratio is between about 1 .20 and 1 .10. U.S. Patent Number 6,223,672 is herein incorporated by reference in its entirety.

U.S. Patent Number 3,978,804 discloses a structure floating on a body of water, and particularly a structure for drilling or producing wells from below the water. Buoyant members support at least a part of the structure above the surface of the water. The structure is connected to anchors in the floor of the body of water by a series of parallel leg members. Each leg member is composed of a plurality of elongated members, such as large diameter pipe usually called risers. These risers are parallel. Vertically spaced spacers are provided along the risers of each leg to (1 ) maintain the risers a fixed distance apart and (2) change the natural or resonant frequency of the individual riser pipes to be greater than the flutter frequency caused by the motion of the water past the risers. U.S. Patent Number 3,978,804 is herein incorporated by reference in its entirety. U.S. Patent Number 6,089,022 discloses a system and a method for regasifing LNG aboard a carrier vessel before the re-vaporized natural gas is transferred to shore. The pressure of the LNG is boosted substantially while the LNG is in its liquid phase and before it is flowed through a vaporizer(s) which, in turn, is positioned aboard the vessel. Seawater taken from the body of water surrounding said vessel is flowed through the vaporizer to heat and vaporize the LNG back into natural gas before the natural gas is off-loaded to onshore facilities. U.S. Patent Number 6,089,022 is herein incorporated by reference in its entirety.

U.S. Patent Number 6,832,875 discloses a floating plant for liquefying natural gas having a barge provided with a liquefaction plant, member for receiving natural gas and with member for storing and discharging liquefied natural gas. The liquefaction plant involves a heat exchange in which heat is removed when liquefying natural gas is transferred to water. The barge is further provided with a receptacle; an open-ended water intake conduit having an inlet; a connecting conduit extending from the outlet of the water intake conduit to the receptacle; a pump for transporting water from the receptacle to the heat exchanger and a water discharge system for discharging water removed from the heat exchanger. The connecting conduit has the shape of an inverted "U" of which the top is located above the receptacle. U.S. Patent Number 6,832,875 is herein incorporated by reference in its entirety.

Co-pending PCT patent application PCT/US2009/068513 having attorney docket number TH3629 discloses an array of structures in a flowing fluid environment, the array comprising at least 3 structures; and vortex induced vibration suppression devices on at least 2 of the structures. PCT patent application PCT/US2009/068513 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 and/or drag on structures in flowing fluid environments, which do not suffer from certain disadvantages of the prior art apparatus and methods; apparatus and methods for reducing VIV and/or drag on multiple structures in flowing fluid environments; apparatus and methods for reducing VIV and/or drag on a riser array or bundle; apparatus and methods for reducing VIV and/or drag on a riser array or bundle which allows the riser array or bundle to be easily installed, removed and/or serviced.

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 the invention provides a method of suppressing the vortex induced vibration of a subsea structure comprising providing a floating structure at a surface of a body of water; connecting a support structure to the floating structure, the support structure having a first end at the surface and a second end at first depth in the body of water; connecting a spacer plate to the support structure at a second depth between the surface and the first depth, the spacer plate comprising at least one opening therethrough; connecting a vortex induced vibration suppression device to the spacer plate, the vortex induced vibration suppression device comprising an opening therethrough aligned with the opening of the spacer plate; and feeding the subsea structure through the opening of the spacer plate and through the opening of the vortex induced vibration suppression device.

Another aspect of the invention provides a system comprising a support structure in a flowing fluid environment; a spacer plate connected to the support structure, the spacer plate comprising at least one opening therethrough; at least one vortex induced vibration suppression device connected to the spacer plate, the vortex induced vibration suppression device comprising an opening therethrough; wherein the spacer plate and the vortex induced vibration suppression device are adapted to receive a structure through the openings of the spacer plate and the vortex induced vibration suppression device.

Advantages of the invention may include one or more of the following: improved VIV reduction of a plurality of structures; improved drag reduction of a plurality of structures; lower cost VIV reduction; and/or VIV reduction of a plurality of structures with fewer VIV suppression 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 Several Views of the Drawings

The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention. In the drawings:

Figure 1 illustrates an example marine system in which embodiments may be implemented.

Figure 2 is a side view illustrating introducing a tubular structure having a connected vortex-induced vibration (VIV) suppression device through an internal opening in a spacer.

Figure 3 is a side view illustrating a VIV suppression device fixedly connected with a spacer, according to one or more embodiments.

Figure 4 is a top planar view of a spacer taken along section line 4- -4 in Figure 3, according to one or more embodiments.

Figure 5 is a cross-sectional top view illustrating a first suitable VIV suppression device, according to one or more embodiments.

Figure 6 is a cross-sectional top view illustrating a second suitable VIV suppression device, according to one or more embodiments.

Figure 7 is a block flow diagram of a method of introducing a tubular structure through an opening in a VIV suppression device that is connected with a spacer, according to one or more embodiments.

Figures 8A-8B illustrate introducing a tubular structure through an opening in a VIV suppression device that is connected with a spacer, according to one or more embodiments.

Figure 9 is a block flow diagram of a method of withdrawing a tubular structure from a VIV suppression device, and subsequently introducing a tubular structure through the VIV suppression device, according to one or more embodiments.

Figure 10 is a side view of two or more VIV suppression devices strung together or otherwise connected in series, and connected with one or more spacers, according to one or more embodiments.

Figure 11 is a side view of a VIV suppression device that is operable to accommodate insertion of a plurality of tubular structures, according to one or more embodiments.

Detailed Description

In the following description, numerous specific details are set forth. However, it is understood that embodiments may be practiced without these specific details. In other instances, well-known structures and techniques have not been shown in detail in order not to obscure the understanding of this description.

Figure 1 :

Figure 1 illustrates an example marine system 100 in which embodiments may be implemented. Marine system 100 includes surface structure 102 near water surface 104, such as a surface of the ocean. By way of example, the surface structure may include a ship, a barge, a vessel, an offshore rig, an offshore platform, a floating plant, a floating liquefied natural gas plant, or other floating or surface structures known in the art.

Two or more tubular structures 106 are connected with surface structure 102. By way of example, the tubular structures may be connected with the surface structure through a marine riser tensioner, a swivel joint, a ball joint, or the like.

Examples of suitable tubular structures 106 include, but are not limited to, risers, marine risers, riser pipes, marine pipes, pipes, tubes, tendons, umbilicals, or the like, or combinations thereof. In one or more embodiments, the tubular structures may have outer diameters of at least six inches, often at least one foot, and may have lengths of at least 50 feet, often at least 100 feet, or more. The tubular structures may extend all the way to seafloor 108, or only part way to the seafloor. In some cases, mud, crude, natural gas, water, cold water from depth, and/or other fluids may be conveyed through the tubular structures. Alternatively, tubular structures 106 may be tendons, cables, anchor lines, or other structural members.

In one embodiment, tubular structures 106 may have circular or oval cross-sections. In another embodiment, the cross-sections of the tubular structures need not be circular or oval, but may have other shapes such as, but not limited to, square, rectangular, etc. For clarity, the term "tubular" is intended to encompass either circular or non-circular cross-sections.

In the illustration, two tubular structures 106A-106B are visible. However, in alternate embodiments, more tubular structures may optionally be included (e.g., at least three, at least four, at least six, at least nine, or more tubular structures, for example up to about 50 or 100). One of the tubular structures may serve as a structural support tubular structure, as will be discussed more fully below.

Marine system 100 also includes one or more guide sleeves or other spacers 1 1 OA, 1 10B. The spacers may physically connect the tubular structures together, or hold the tubular structures in position relative to one another, or otherwise associate the tubular structures with one another, as a group, bundle, array, other ordered arrangement, or other associated plurality of tubular structures. By way of example, the spacers may include solid sheets or plates having internal openings through which the tubular structures are inserted. The spacers may help to keep the tubular structures relatively close together, but separated so that the tubular structures do not significantly strike into or other interfere with one another, which may tend to cause damage. In the illustration, two spacers 1 10A, 1 10B are shown, but more may optionally be included. In one aspect, several spacers located at various depths, and intermittently spaced apart along the length of the tubular structures, may be used to restrain the tubular structures, and help prevent the tubular structures from contacting one another.

Referring again to Figure 1 , it is not uncommon that tubular structures 106 will be disposed in water having current 1 12. The current may tend to cause hydrodynamic drag and/or vortex-induced vibration (VIV) of the tubular structures. Further, in a group of tubular structures connected or positioned together with a spacer (e.g., spacer 1 10A), VIV directly induced by the current on one tubular structure of the group may be imparted to other tubular structures of the group. Such VIV is generally undesirable, and if not suppressed, may tend to result in damage, fatigue, high drag, or even premature failure of the tubular structures. Accordingly, it is generally desirable to reduce the VIV of the tubular structures.

One or more VIV suppression devices (not shown) may be included in marine system 100 to help suppress VIV. One way to include one or more VIV suppression devices in the marine system would be to physically connect or attach the VIV suppression devices to or with one of tubular structures 106. However, one challenge with this approach is that assembly or installation of an array or other group of tubular structures tends to be difficult, and/or time consuming, and/or expensive when the one or more VIV suppression devices or structures are attached or connected to or with a tubular structure.

A representative method of assembling a group of tubular structures may include initially threading or otherwise introducing a structural support tubular structure through an internal opening of the spacer. When in place, the spacer may be fixedly connected with the structural support tubular structure, such as, for example, by welding, bolts, rivets, or the like. Similarly, several other spacers may be connected at different locations along the length of the structural support tubular structure. Then, the structural support tubular structure having the spacers may be submerged in the ocean to the appropriate depth. The assembly of the remaining tubular structures may be performed underwater. Each of the other tubular structures may be threaded or otherwise introduced through an internal opening in each of the spacers. Difficulties or challenges may be encountered when threading or introducing tubular structures having VIV suppression devices connected thereto through the openings in the spacers.

Figure 2:

Figure 2 is a side view illustrating introducing tubular structure 206 having VIV suppression device 214 connected therewith through internal opening 218 in spacer 210. Conventional collars (not shown) may be used to keep the VIV suppression devices from moving along the length of the tubular structure. The spacer has already been connected to structural support tubular structure 216. The tubular structure having the connected VIV suppression device is moved downward in the direction of arrow 220 until the tubular structure and the VIV suppression device pass into and through the opening in the spacer. As previously mentioned, in one aspect, this may be performed underwater.

One challenge is that the VIV suppression device tends to make the tubular structure more bulky, difficult to handle, difficult to maneuver and/or difficult to align and introduce through the opening in the spacer. In the case of a fairing as a VIV suppression device, for example, the fairing may tend to rotate or otherwise move, for example, due to waves and/or ocean currents. Likewise, certain other VIV suppression devices may also tend to move during installation.

In some cases, it may be desirable to retrieve a tubular structure from the array and subsequently re-introduce a tubular structure back into the array, such as, for example, for cleaning, inspection, repair, replacement, or the like. Connecting the VIV suppression devices with the tubular structures may also tend to make retrieval and re-introduction of a tubular structure more difficult, and/or more time consuming, and/or more expensive.

Additionally, in order for the tubular structure having the VIV suppression device to be introduced through the internal opening in the spacer, the internal opening in the spacer needs to be large enough to accommodate the outer dimensions of the VIV suppression device. Typically, the VIV suppression device is larger in at least one dimension than the tubular structure. As shown, the internal opening in the spacer would need to have a diameter or other cross- sectional dimension (d3) that is not only greater than an outer diameter or other cross-sectional dimension of the tubular structure (d1 ), but also greater than a larger outer diameter or other cross-sectional dimension of the VIV suppression device (d2). By way of example, the internal opening in the spacer would need to be large enough to accommodate helical strakes protruding from a tubular structure, or the distance from head to tail of a fairing installed around a tubular structure. As a result, the cross-sectional dimension of the openings in the spacer (d3) may be larger than desirable. During use, this may tend to give the tubular structure more freedom to move as a result of current, waves, or vibration, which may tend to lead to mechanical damage.

One way to avoid some of these difficulties is to omit VIV suppression devices from one or more of the tubular structures of the array or other group of tubular structures. VIV of an array or other group of tubular structures may be sufficiently suppressed if only a subset of the tubular structures have VIV suppression devices. This may also help to reduce equipment cost. However, it is typically desirable for at least some VIV suppression devices to be included in the marine system in order to help suppress vibrations.

Accordingly, other approaches for including one or more VIV suppression devices in a marine system and/or in a bundle, array, or other group of tubular structures that avoid, or at least reduce, one or more of these aforementioned challenges or difficulties, would offer certain advantages.

In one or more embodiments, instead of connecting a VIV suppression device with a tubular structure, the VIV suppression device may be connected with a spacer or other structure connected with or secured to a structural support tubular structure. Advantageously, this may help to reduce some of the difficulties associated with moving a tubular structure having a VIV suppression device connected therewith and/or help to reduce some of the difficulties or problems associated with having to introduce the VIV suppression device through an opening in the spacer.

Figure 3:

Figure 3 is a side view of vortex-induced vibration (VIV) suppression device 314 fixedly connected with spacer 310, according to one or more embodiments. The spacer is fixedly connected with structural support tubular structure 316.

The structural support tubular structure is inserted or introduced through a first opening 322 in the spacer and fixedly connected with the spacer. Examples of suitable connections include, but are not limited to, welding, rivets, bolts, screws, joints, clamps, adhesives, other fasteners, combinations thereof, and other like conventional connections known in the arts.

VIV suppression device 314 is fixedly or removably connected to spacer 310. The term "connected," along with its derivatives, are used herein. As used herein, "connected" may mean that two or more elements or components are in direct physical contact. However, "connected" may also mean that two or more elements or components are not in direct physical contact, but yet still co-operate or interact with each other. For example, the elements or components may be connected through one or more intervening components.

In this particular embodiment, connector 324 is used to connect VIV suppression device 314 with spacer 310. The term connector is to be interpreted broadly herein, since a wide variety of connectors will be suitable for various embodiments. Examples of suitable connectors include, but are not limited to, mechanical connectors, connecting structures, connecting elements, connecting devices, joints, joining structures, joining elements, joining devices, fasteners, fastening structures, fastening elements, fastening devices, and the like. Specific examples of suitable connectors include, but are not limited to, cables, chains, chain links, bolts, flanges, hinges, hinge joints, rods, pins, hooks, and the like, and combinations thereof.

In one or more embodiments, VIV suppression device 314 may be intended to weathervane or otherwise rotate relative to spacer 310. For example, fairings, Henning devices, and certain other VIV suppression devices may be intended to weathervane or rotate during operation in order to suppress vibrations. Accordingly, in one or more embodiments, connector 324 may include a rotation connector. Examples of suitable rotation connectors include, but are not limited to, rotation joints, swivels, swivel joints, swivel ring systems, ball joints, ball-and-socket joints, pivots, ring and bearing systems, interlocked rings, and the like, and combinations thereof.

Opening 317 through VIV suppression device 314 is aligned with opening 318 through spacer 310. In the illustration, the VIV suppression device is below the spacer, VIV suppression device 314 may be installed below spacer 310 and above a second spacer (not shown) further down structure 316. Alternatively, the VIV suppression device may be above the spacer 310. If desired, one VIV suppression device may be fixedly connected above the spacer and another VIV suppression device may be fixedly connected below the spacer. The one or more VIV suppression devices such as VIV suppression device 314 may be connected to spacer 310 prior to submerging the spacer in water or after it is submerged.

Spacer 310 holds VIV suppression device 314 in place. Since the VIV suppression device is connected with the spacer, and since the spacer is connected with the structural support tubular structure, the VIV suppression device is mounted or held in place even when a tubular structure is not inside of the VIV suppression device. This is different than the typical approach of fixedly connecting a VIV suppression device with a tubular structure.

Figure 4:

Figure 4 is a top planar view of spacer 410. Spacer 410 is one possible design for a spacer and, relative to Figure 3, the planar view is representative view taken along section line 4-4 in Figure 3, according to one or more embodiments. Spacer 410 has body 430. As shown, body 430 may have a shape of a rectangle. Alternatively, the body may have the shape of a square, circle, oval, triangle, or star, to name just a few examples.

In this embodiment, body 430 includes a solid sheet or plate of a material that has a sufficient strength and/or thickness. Examples of suitable materials include, but are not limited to, metals (e.g., stainless steel, coated steel, copper, alloys, etc.), fiber reinforced plastics (e.g., fiberglass), carbon fiber materials, composite materials, and the like, and combinations thereof. It will be appreciated by those skilled in the art, that the thickness and/or strength requirements may depend on a number of factors, such as, for example, the number of spacers, the amount of separation between the spacers, the amount of current or vibration expected, the length of the tubular structures, etc. Representatively, for stainless steel, a thickness ranging from about one quarter of an inch to one inch will often be suitable.

Multiple internal openings 432, 434 are defined within body 430. In the illustration, two openings 432, 434 are shown, although in alternate embodiments fewer or more openings may be included. Each of the internal openings may accommodate a different tubular structure. A first opening 432 accommodates structural support tubular structure 416. A second opening 434 is to accommodate another tubular structure (not shown). As shown, the openings may have generally circular shapes to accommodate cylindrical tubular structures. Alternatively, the openings may have oval, rectangular, triangular, or other shapes, to accommodate correspondingly shaped tubular structures. A dashed circle 414 is used to show a position where VIV suppression device 314 may be connected with the bottom of the spacer.

Referring again to Figure 3, other designs for spacer 310 are also suitable. For example, instead of a solid sheet or plate, the body of a spacer may have an open structure. By way of example, the open structure may include a frame having sides around a perimeter (e.g., of a polygon) and braces across the frame connecting the sides and/or corners. Openings may be defined between the sides and the braces. One or more guide sleeves or openings may be included in the frame and/or in the braces to accommodate tubular structures. The open structure may be integrally formed, or may be separate components connected together, for example, by bolts, rivets, welding, or the like. By way of example, the open structure may be made of rectangular strips, pipes, rods, or other tubular structures. Still other spacer designs will be apparent to those skilled in the art and having the benefit of the present disclosure.

Still referring to Figure 3, various different types of VIV suppression devices are suitable for VIV suppression device 314. Examples of suitable VIV suppression devices or structures include, but are not limited to, strakes, fairings, Henning devices, shrouds, wake splitters, and other types of VIV suppression devices or structures known in the arts. To further illustrate certain concepts, several different types of VIV suppression devices or structures suitable for one or more embodiments will be shown and described briefly.

Suitable VIV suppression devices are disclosed in U.S. Patent Publication Number 2006-0021560 A1 , having attorney docket number TH1433; U.S. Patent Number 7,406,923, having attorney docket number TH0541 ; U.S. Patent Publication Number 2006-0280559 A1 , having attorney docket number TH2508; U.S. Patent Publication Number 2007-0003372 A1 , having attorney docket number TH2876; U.S. Patent Publication Number 2007-0003372 A1 having attorney docket number TH2969; WIPO Publication Number 2007/149770, having attorney docket number TH1500; WIPO Publication Number 2008/064104, having attorney docket number TH31 12; WIPO Publication Number 2008/064102, 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 VIV suppression devices are disclosed in U.S. Patent Number 7,578,038, having attorney docket number TH1853.04; U.S. Patent Publication Number 2005-0254903 A1 , having attorney docket number TH2463; U.S. Patent Publication Number 2008-0056828 A1 , having attorney docket number TH2900; U.S. Patent Publication Number 2007- 0125546 A1 , having attorney docket number TH2926; U.S. Patent Publication Number 2007-0140797 A1 , having attorney docket number TH2875; WIPO Publication Number 2008/008728, having attorney docket number TH2879; WIPO Publication Number 2008/070245, 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.

Suitable Henning devices are disclosed in WO Patent Publication Number 2009/023624, having attorney docket number TH3245; and WO Patent Publication Number 2009/046166, having attorney docket number TH3350, which are herein incorporated by reference in their entirety.

Figure 5:

Figure 5 is a cross-sectional top view illustrating a first suitable VIV suppression device 514 having body 536 and strakes 538 connected with the body, according to one or more embodiments. The strakes may be helical strakes, which are helically wrapped or coiled around the body. A dashed circle 506 is used to show a position where a tubular structure may be introduced into the VIV suppression device. Note that the strakes are connected with the body of the VIV suppression device, not to the tubular structure. The body may represent a sleeve through which the tubular structure is inserted or otherwise introduced. There may not necessarily be contact or connection between the VIV suppression device and the tubular structure.

In another embodiment, strakes 538 may be attached to a first plate above the strakes (such as plate 430) and to a second plate below the strakes without the need for body 536. A tubular structure may be introduced into an opening in first plate, through the strakes, and then through an opening in second plate.

Figure 6:

Figure 6 is a cross-sectional top view illustrating a second suitable VIV suppression device 614, according to one or more embodiments. In this embodiment, the VIV suppression device is fairing 640. The fairing has nose 642 and tail 644. A dashed circle 606 is used to show a position where a tubular structure may be introduced into the VIV suppression device. The body may represent a sleeve through which the tubular structure is inserted or otherwise introduced. There may not necessarily be contact or connection between the VIV suppression device and the tubular structure. The fairing may swivel around the tubular structure, for example based on the ocean current, as shown by arrow 646, or may be in a fixed orientation.

In another embodiment, fairing tail 644 may be attached to a first plate above the strakes (such as plate 430) and to a second plate below the strakes without the need for nose 642. A tubular structure may be introduced into an opening in first plate, adjacent the tail, and then through an opening in second plate.

Other VIV suppression devices are suitable. Representatively, a Henning device (not shown) may include a cylinder or other tubular structure having a number, such as four to ten, blades or other appurtenances projecting from the tubular structure and operable to rotate, or may be in the form of a polygonal structure.

Figure 7:

Other embodiments of the invention pertain to methods of assembly or installation of subsea assemblies. Figure 7 is a block flow diagram of a method 750 of introducing a tubular structure through an opening in a VIV suppression device connected with a spacer, according to one or more embodiments. The method includes providing a structural support tubular structure, a spacer fixedly connected with the structural support tubular structure, and a VIV suppression device connected with the spacer, at block 751 . In one or more embodiments, this may include providing an assembly similar to, or the same as, that shown in Figure 3. In one or more embodiments, the assembly may be submerged in a body of water, such as the ocean, and subjected to water currents.

As used herein, "providing" an assembly is to be interpreted broadly to mean that the assembly becomes available by some means. Providing may include, but does not necessarily include, either making or assembling. Another entity may do part or all of the making and/or assembly. Providing is to encompass, at least, making the components and then assembling the components, purchasing or otherwise obtaining the components from another entity and then assembling the components, making the components and then having another entity partly or fully assemble the components, purchasing or otherwise obtaining the components from another entity and then having another entity (either the same or different entity) partly or fully assemble the components, or the like.

In one or more embodiments, providing may include fixedly connecting a spacer (whether made or otherwise acquired) to a structural support tubular structure (whether made or otherwise acquired), and connecting a VIV suppression device (whether made or otherwise acquired) to the spacer. These components may be connected in any order.

Referring again to Figure 7, a tubular structure may be threaded, inserted, or otherwise introduced through an opening in the VIV suppression device connected with the spacer, at block 752. The VIV suppression device may be held or fixed in place by the spacer, while the tubular structure is introduced through the opening in the VIV suppression device. As a result, the VIV suppression device may be substantially stationary (except for rotation or other movement associated with VIV suppression or other minor movement due to waves, ocean current, etc.), while the tubular structure is introduced through the opening in the VIV suppression device.

Figures 8A-8B:

Figures 8A-8B illustrate introducing tubular structure 806 through opening 817 in VIV suppression device 814 connected with spacer 810, according to one or more embodiments. As previously mentioned, this may be performed when VIV suppression device 814 and spacer 810 are submerged (e.g., underwater in the ocean).

Figure 8A is a side view illustrating structural support tubular structure 816, spacer 810 fixedly connected with the structural support tubular structure through connector 824, and VIV suppression device 814 fixedly connected with the spacer. Tubular structure 806 is positioned above the spacer.

Spacer 810 has first opening 822 having structural support tubular structure 816 inserted therein, and second opening 818 to receive tubular structure 806. VIV suppression device 814 has opening 817. As shown, opening 817 in the VIV suppression device may be substantially vertically aligned with second opening 818 in the spacer.

During installation or assembly, tubular structure 806 may be introduced into and through the opening in the spacer and into the opening in the VIV suppression device. For example, the tubular structure may be moved downward in the direction of arrow 820 until the tubular structure passes into and through the opening in the spacer and into the opening in the VIV suppression device.

While tubular structure 806 is introduced into opening 817 in VIV suppression device 814, the VIV suppression device may be held fixed in place, and substantially stationary, by spacer 810. It is to be appreciated that fairings and certain other VIV suppression devices may rotate or otherwise move in conjunction with suppressing VIV, and that there may be minor amounts of movement or jostling due to waves, ocean current, or the like. However, since the VIV suppression device is not connected with, the tubular structure, the VIV suppression device does not move with the tubular structure and the VIV suppression device does not need to be introduced through the opening in the spacer. Advantageously, this may help to avoid, or at least reduce, some of the aforementioned difficulties and/or problems associated with introducing and/or withdrawing a tubular structure having a connected VIV suppression device through the opening in the spacer.

Referring again to Figure 8A, it is not required that the opening in the spacer have a diameter or other cross-sectional dimension (d3) that is greater than an outer diameter or other cross-sectional dimension (d2) of the VIV suppression device. As shown, in one or more embodiments, dimension (d3) may optionally be less than dimension (d2), as long as dimension (d3) is greater than an outer diameter or other cross-sectional dimension (d1 ) of tubular structure, plus any desired clearance or tolerance. Advantageously, reducing the size of the opening in the spacer may help to restrict or restrain the movement of the tubular structure, which may help to reduce mechanical damage. Alternatively, dimension (d3) may be greater than dimension (d2), if desired.

In one embodiment, a funnel (not shown) may be provided above spacer with a large diameter opening, for example from about 125% to about 300% d1 or 150% to about 200% d1 that then tapers down to a smaller opening with a diameter d3 aligned with opening 818. Funnel provides an easier method of feeding tubular 806 into opening 818. Other funnels may be provided for each of the openings on each of the spacers.

Figure 8B is a side view after introducing tubular structure 806 through second opening 818 in spacer 810 and opening 817 in VIV suppression device, according to one or more embodiments.

VIV suppression device 814 is disposed around tubular structure 806. The VIV suppression device may represent a sleeve or tubular part fitting around the tubular structure. As shown, in one or more embodiments, there may not be appreciable or consistent contact or connection between the tubular structure and the VIV suppression device. In one aspect, the tubular structure may be disposed within the opening and yet entirely separate and/or unconnected from the VIV suppression device. Alternatively, there may be some contact or connection. However, in one or more embodiments, the amount of contact or the nature of connection between the tubular structure and the VIV suppression device may be small enough or such that the tubular structure may be readily retrieved from, pulled out of, removed from, or withdrawn from, the opening in the VIV suppression device, if desired. For example, it may be desirable to clean, unclog, repair, coat, treat, inspect, examine, replace a tubular structure, etc.

Figure 9:

Figure 9 is a block flow diagram of a method 956 of withdrawing a tubular structure from a VIV suppression device, and subsequently introducing a tubular structure into the VIV suppression device, according to one or more embodiments.

A tubular structure may be retrieved from, pulled out of, removed from, or withdrawn from, an opening in a VIV suppression device, at block 957. As previously described, the VIV suppression device may be connected with a spacer, and the spacer may be fixedly connected with a structural support tubular structure. If desired, the withdrawn tubular structure may be cleaned, repaired, inspected, discarded, etc.

After withdrawing the tubular structure, a tubular structure may be introduced into the opening in the VIV suppression device that is connected with the spacer, at block 958. Either the same tubular structure or a different tubular structure may be introduced.

Advantageously, since the VIV suppression device is connected with the spacer, instead of with the tubular structure, the tubular structure may be withdrawn from and introduced into the opening in the spacer much easier than would be the case if the tubular structure(s) had VIV suppression devices connected thereto. In particular, the tubular structures without the VIV suppression devices connected thereto may, in some cases, be generally cylindrical structures, that are readily threaded or otherwise introduced through the openings in the spacers. There may be an initial investment of time and/or cost to connect the VIV suppression devices with the spacers, but then withdrawing and introducing tubular structures may be easier, faster, and/or less expensive.

For ease of illustration, a single VIV suppression device connected with a spacer has been shown in each of Figures 3, 8A, and 8B. However, commonly more than one VIV suppression device may be utilized for a given tubular structure, for example, in order to provide more VIV suppression.

Figure 10:

Figure 10 is a side view of two or more VIV suppression devices 1014A, 1014B strung together or otherwise connected in series, and connected with one or more spacers 101 OA, 1010B, according to one or more embodiments.

Upper spacer 101 OA and lower spacer 1010B are both fixedly connected with structural support tubular structure 1016. Two VIV suppression devices 1014A, 1014B are connected between the upper and the lower spacers. In addition, the two VIV suppression devices are "strung" together, or otherwise connected in series.

In particular, a top end or portion of upper VIV suppression device 1014A is connected with upper spacer 101 OA through first connector 1024A. A bottom end or portion of upper VIV suppression device 1014A is connected with a top end or portion of lower VIV suppression device 1014B through second connector 1024B. A bottom end or portion of lower VIV suppression device 1014B is connected with lower spacer 1010B through third connector 1024C.

Connecting the VIV suppression devices in series generally allows for a given tubular structure to be threaded or otherwise introduced through openings in the VIV suppression devices. For example, the openings in the series of VIV suppression devices may be generally aligned with one another to receive a tubular structure. As shown, upper opening 1017A in upper VIV suppression device 1014A is generally aligned with lower opening 1017B in lower VIV suppression device 1014B. Moreover, upper and lower openings 1017A, 1017B are generally aligned with upper opening 1018A in upper spacer 101 OA and with lower opening 1018B in lower spacer 101 OB. A tubular structure (not shown) may be threaded or otherwise introduced through all four of these aligned openings, as previously described.

Since spacers 101 OA, 1010B are fixedly connected with structural support tubular structure 1016, and since VIV suppression devices 1014A, 1014B are fixedly connected with the spacers, the VIV suppression devices are fixedly mounted or held in place prior to and during insertion of a tubular structure through the openings in the spacers and the openings in the VIV suppression devices. The VIV suppression devices are not connected with, or held in place by, the tubular structure inserted through them.

As shown, in one or more embodiments, the distance between adjacent spacers 101 OA, 1010B may be greater than the lengths of VIV suppression device 1014A, 1014B. In the illustrated embodiment, the distance between the spacers is enough for the two VIV suppression devices to be connected together in series between the spacers. In alternate embodiments, the distance between adjacent spacers may be more, or less. For example, at least three or more VIV suppression devices may be connected together in series between adjacent spacers.

As shown, in one or more embodiments, two or more VIV suppression devices may be connected together, such as, for example, by intervening second connector 1024B. However, this is not required. In one or more alternate embodiments, there may potentially be gaps or spaces between adjacent VIV suppression devices. For example, lower VIV suppression device 1014B may be omitted, and another VIV suppression device (not shown) may be provided at a bottom of lower spacer 101 OB, such that a gap may exist between adjacent VIV suppression devices in a series at the location of lower VIV suppression device 1014B.

In this particular illustration, two VIV suppression devices 1014A, 1014B and two spacers 101 OA, 101 OB are shown, although more VIV suppression devices may optionally be included, if desired, and as few as one spacer may be connected with the VIV suppression devices. In one aspect, at least three, at least four, at least six, at least eight, at least ten, or more than ten VIV suppression devices may be "strung" together, or otherwise connected in series along the length of a given tubular structure. This string or series of VIV suppression devices may be connected with one or more, or most spacers along its length, or all spacers along its length.

It is not required that VIV suppression devices be provided along an entire length of a tubular structure. Intervals or gaps along the length of the tubular structure may omit VIV suppression devices. For example, VIV suppression devices may be included between some pairs of adjacent spacers, but not between other pairs of adjacent spacers. In some cases, continuous cables, chains, or other continuous connectors may be used to string together or otherwise connect VIV suppression devices. Gaps may potentially exist along the length of the cables, chains, or other continuous connectors where VIV suppression devices are omitted.

It is not required that a VIV suppression device accommodate insertion of only one tubular structure. In one or more embodiments, a VIV suppression device may accommodate insertion of a plurality of tubular structures, or an entire bundle, array, or other group of tubular structures.

Figure 1 1 :

Figure 11 is a side view of VIV suppression device 1 1 14 that is operable to accommodate insertion of a plurality of tubular structures 1 106A, 1 106B, according to one or more embodiments. The VIV suppression device is fixedly connected with spacer 1 1 10 through connector 1 124. The previously described connectors and rotation connectors are suitable. The spacer is fixedly connected with structural support tubular structure 1 1 16. In another embodiment, there may be multiple support structures 1 1 16 in parallel all connected to spacer 1 1 10.

Aside from the aspect that VI V suppression device 1 1 14 is to accommodate insertion of a plurality of tubular structures (instead of a single tubular structure), and may potentially have a bigger size, VIV suppression device 1 1 14 may be similar to the previously described VIV suppression devices (e.g., VIV suppression device 314 in Figure 3). The previously described types of VIV suppression devices are suitable. By way of example, VIV suppression device 1 1 14 may represent a large fairing, straked tubular, or Henning device, around an entire bungle, array, or other group of tubular structures. VIV suppression device 1 1 14 may represent a cylinder, tubular structure, or other sleeve around the plurality or group of tubular structures.

For ease of illustration, VIV suppression device 1 1 14 is shown to be operable to accommodate insertion of two tubular structures 1 106A, 1 106B. However, it is to be appreciated that in alternate embodiments, a VIV suppression device may be operable to accommodate insertion of more than two tubular structures, up to an entire bundle, array, or other group of tubular structures.

In the illustration, VIV suppression device 1 1 14 is below spacer 1 1 10. Alternatively, the VIV suppression device may be above the spacer.

If desired, VIV suppression device 1 1 14 may be "strung" together, or otherwise connected together in series with one or more other VIV suppression devices each also operable to accommodate insertion of a plurality of tubular structures. This may be done substantially as previously described.

In one particular embodiment, VIV suppression device may include a Henning device. A large cylinder or tubular structure of the device may be disposed around an entire bundle, array, or other group of tubular structures. Representatively, the Henning device may have a height ranging from about 10 to 30 feet. A rotation connector may connect the Henning device with the spacer. The Henning device may be above or below a spacer. The Henning device may weathervane or otherwise rotate due to current. One potential advantage of Henning devices is that they tend to work well at suppressing VIV even at low coverage densities. Typically less than 50%, often less than 30%, sometimes less than 20%, often more than about 5% of the length of the bundle, array, or other group of tubular structures need to be covered with Henning devices in order to adequately suppress VIV. Accordingly, in some cases, Henning devices be strung together or connected in series rather sparsely along the length of the bundle, array, or other group of tubular structures. In one example, Henning devices may be provided only on top, or on bottom, or both on top and on bottom, of some or all of the spacers, with coverage densities often less than 50% of the length of the bundle. It is to be appreciated that this is just one illustrative example, and the scope of the invention is not limited to this particular example.

Alternative Embodiments:

The bundles, arrays, or other groups of risers or other tubular structures disclosed herein may be used for various purposes.

In one or more embodiments, a group of tubular structures as described herein may be used by a Floating Liquefied Natural Gas (FLNG) plant located on/in a surface of the ocean. The tubular structures may be connected with the FLNG plant and project from the FLNG plant generally downward into the ocean, but not necessarily to the seafloor. In one particular example, the tubular structures may project to depths of around 150 to 600 feet, for example from about 400 to about 500 feet. Due to the ocean current, the tubular structures may deflect from vertical. To accommodate for such deflection, the tubular structures may be connected with the FLNG plant through a swivel joint, a ball joint, a riser hanger, or other pivotable connector.

Some or all of the tubular structures may serve as water intake risers for the FLNG plant. The water intake risers may take in cooling water at depth, and convey the cooling water upward to the FLNG plant. The cooling water may be input to heat exchangers of the FLNG plant in order to cool natural gas in conjunction with liquefying the natural gas. The heated ocean water from the outlet of the heat exchangers may be discharged back into the ocean at the surface.

Alternatively, warm water may be taken from the surface for a gasifying liquefied natural gas, and then the cold water may be released at depth through the water output risers.

In one particular embodiment, nine risers or tubular structures may be arranged in a three-by-three rectangular array, although the scope of the invention is not so limited. Eight tubular structures may be located around a periphery of the array, and one tubular structure may be located at a center of the array. The eight tubular structures around the periphery may be capable of serving as water intake risers. It is not necessary that all of the tubular structures operate at any one time to provide cooling water to the FLNG plant. For example, one or more of the tubular structures may be surplus or reserve water intake risers. The tubular structure at the center may serve as a structural support riser or tubular structure for the spacers. The structural support tubular structure may, or may not, serve as a water intake riser. In one particular embodiment, the eight tubular structures along the periphery may each have an outer diameter of about 42 inches and a wall thickness of about 1 inch, while the structural support tubular structure may have an outer diameter of about 24 inches and a thickness of about 0.75 inches. The eight tubular structures along the periphery may be equally spaced apart by a distance of about one outer diameter or about 42 inches. In alternate embodiments, various other numbers of tubular structures may be included and/or may be arranged in various other configurations (e.g., circular, star, triangular, etc.) and/or have larger or smaller tubular and/or spacing dimensions.

If desired, a filter may optionally be connected with the bottom of each of the tubular structures that is to serve as a water intake riser. The filters may help to prevent soil, marine life (e.g., seaweed, algae, fish, etc.), and the like, from entering the tubular structures. Over time, the filters may tend to become clogged or dirty, and it may be desirable to remove the tubular structures and clean the filters.

The tubular structures may tend to experience VIV and in one or more embodiments, VIV suppression devices may be connected with spacers or otherwise connected with a structural support tubular structure as described elsewhere herein. Any of the various VIV suppression device configurations described herein may optionally be utilized. Advantageously, it is believed that the approaches described herein may help to reduce the cost, labor, and/or time associated with removing tubular structures from the array, such as, for example to clean filters, to clean the tubular structures, for inspection, repair, to apply a protective coating, or the like, and also to subsequently reinsert the tubular structures. In one or more embodiments, VIV suppression devices are applied to only a subset of tubular structures, although this is not required.

Alternatively, the bundles, arrays, or other groups of risers or other tubular structures disclosed herein may be used for other purposes besides for FLNG plants. For example, the tubular structures may be used as drilling riser arrays, production riser arrays, TLP tendons, for other plants or offshore structures, etc.

The VIV suppression devices disclosed herein may be made of conventional materials and/or other materials suitable for their intended uses in an underwater, in some cases high-pressure environments, and as long as they are sufficiently strong to handle the vibrations and mechanical forces involved. A few examples of suitable materials include, but are not limited to, certain metals (e.g., stainless steel, coated steel, copper, etc.), certain sufficiently strong and/or sufficiently thick plastics, fiber reinforced plastics (e.g., fiberglass), composites, carbon fiber materials, rubbers, and combinations thereof, to name just a few illustrative examples. Many of the materials for the VIV suppression devices are also suitable for the spacers and/or the connectors that connect the VIV suppression devices with the spacers and/or with the structural support tubular structure assembly. Commonly, the VIV suppression devices, the spacers, and the connectors may be made of metal. If desired, the materials may optionally have anti-fouling materials or coatings, for example copper or copper based materials. If desired, protective materials or structures, such as, for example, covers, caps, bumpers, or the like, may optionally be included on the VIV suppression devices, the spacers, and/or the connectors to help prevent damage. The protective structures may comprise pliable materials, such as, for example, rubber, pliable plastics, etc.

Illustrative Embodiments:

In one embodiment, there is disclosed a system comprising a support structure in a flowing fluid environment; a spacer plate connected to the support structure, the spacer plate comprising at least one opening therethrough; at least one vortex induced vibration suppression device connected to the spacer plate, the vortex induced vibration suppression device comprising an opening therethrough; wherein the spacer plate and the vortex induced vibration suppression device are adapted to receive a structure through the openings of the spacer plate and the vortex induced vibration suppression device. In some embodiments, the spacer plate and the vortex induced vibration suppression device are within a body of water. In some embodiments, at least one end of the support structure is connected to a floating vessel. In some embodiments, the system also includes a plurality of openings in the spacer plate and a plurality of vortex induced vibration suppression devices connected to the spacer plate. In some embodiments, the system also includes a plurality of tubular structures, wherein each tubular structure is fed through one of the openings in the spacer plate and through one of the vortex induced vibration suppression devices. In some embodiments, the system also includes a plurality of spacer plates at a plurality of locations along a length of the support structure. In some embodiments, the support structure comprises an internal structure, further comprising a plurality of external structures that form a periphery about the internal structure, further comprising vortex induced vibration suppression devices about from 30% to 80% of the external structures. In some embodiments, the system also includes a plurality of tubular structures, wherein at least two of the tubular structures are fed through the opening in the spacer plate and through the opening of the vortex induced vibration suppression device. In some embodiments, the vortex induced vibration suppression device is selected from henning devices, smooth sleeves, strakes, and fairings. In some embodiments, the vortex induced vibration suppression device comprise at least two different types of devices. In some embodiments, the system also includes at least one tubular, each tubular comprising an opening therethrough for transportation of a fluid.

In one embodiment, there is disclosed a method of suppressing the vortex induced vibration of a subsea structure comprising providing a floating structure at a surface of a body of water; connecting a support structure to the floating structure, the support structure having a first end at the surface and a second end at first depth in the body of water; connecting a spacer plate to the support structure at a second depth between the surface and the first depth, the spacer plate comprising at least one opening therethrough; connecting a vortex induced vibration suppression device to the spacer plate, the vortex induced vibration suppression device comprising an opening therethrough aligned with the opening of the spacer plate; and feeding the subsea structure through the opening of the spacer plate and through the opening of the vortex induced vibration suppression device. In some embodiments, the method also includes connecting a plurality of spacer plates to the support structure, each spacer plate at a different depth. In some embodiments, the method also includes providing a plurality of openings in the spacer plate and a plurality of vortex induced vibration suppression devices connected to the spacer plate. In some embodiments, the method also includes feeding at least one subsea structure through each of the openings in the spacer plate and through each of the vortex induced vibration suppression devices. In some embodiments, the method also includes connecting a plurality of spacer plates to the support structure, each spacer plate at a different depth, and then connecting a string of at least two vortex induced vibration suppression devices to each other, the string comprising a first end connected to a first spacer plate and a second end connected to a second spacer plate.

In the description above, for the purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the embodiments. It will be apparent however, to one skilled in the art, that one or more other embodiments may be practiced without some of these specific details. The particular embodiments described are not provided to limit the invention but to illustrate it. The scope of the invention is not to be determined by the specific examples provided above but only by the claims below. In other instances, well-known structures, devices, and operations have been shown in block diagram form or without detail in order to avoid obscuring the understanding of the description. Where considered appropriate, reference numerals or terminal portions of reference numerals have been repeated among the figures to indicate corresponding or analogous elements, which may optionally have similar characteristics.

It should also be appreciated that reference throughout this specification to "one embodiment", "an embodiment", or "one or more embodiments", for example, means that a particular feature may be included in the practice of the invention. Similarly, it should be appreciated that in the description various features are sometimes grouped together in a single embodiment, Figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of a single disclosed embodiment. For example, unless specified or claimed otherwise, the floating structure or floating liquefied gas plant shown in a Figure is not intended to be a part of the invention. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of the invention.

Claims

C L A I M S

1 . A system comprising:

a support structure in a flowing fluid environment;

a spacer plate connected to the support structure, the spacer plate comprising at least one opening therethrough;

at least one vortex induced vibration suppression device connected to the spacer plate, the vortex induced vibration suppression device comprising an opening therethrough;

wherein the spacer plate and the vortex induced vibration suppression device are adapted to receive a structure through the openings of the spacer plate and the vortex induced vibration suppression device.

2. The system of claim 1 , wherein the spacer plate and the vortex induced vibration suppression device are within a body of water.

3. The system of one or more of claims 1 -2, wherein at least one end of the support structure is connected to a floating vessel.

4. The system of one or more of claims 1 -3, further comprising a plurality of openings in the spacer plate and a plurality of vortex induced vibration suppression devices connected to the spacer plate.

5. The system of claim 4, further comprising a plurality of tubular structures, wherein each tubular structure is fed through one of the openings in the spacer plate and through one of the vortex induced vibration suppression devices.

6. The system of one or more of claims 1 -5, further comprising a plurality of spacer plates at a plurality of locations along a length of the support structure.

7. The system of one or more of claims 1 -6, wherein the support structure comprises an internal structure, further comprising a plurality of external structures that form a periphery about the internal structure, further comprising vortex induced vibration suppression devices about from 30% to 80% of the external structures.

8. The system of one or more of claims 1 -7, further comprising a plurality of tubular structures, wherein at least two of the tubular structures are fed through the opening in the spacer plate and through the opening of the vortex induced vibration suppression device.

9. The system of one or more of claims 1 -8, wherein the vortex induced vibration suppression device is selected from henning devices, smooth sleeves, strakes, and fairings.

10. The system of one or more of claims 1 -9, wherein the vortex induced vibration suppression device comprise at least two different types of devices.

1 1. The system of one or more of claims 1 -10, further comprising at least one tubular, each tubular comprising an opening therethrough for transportation of a fluid.

12. A method of suppressing the vortex induced vibration of a subsea structure comprising:

providing a floating structure at a surface of a body of water;

connecting a support structure to the floating structure, the support structure having a first end at the surface and a second end at first depth in the body of water;

connecting a spacer plate to the support structure at a second depth between the surface and the first depth, the spacer plate comprising at least one opening therethrough;

connecting a vortex induced vibration suppression device to the spacer plate, the vortex induced vibration suppression device comprising an opening therethrough aligned with the opening of the spacer plate; and

feeding the subsea structure through the opening of the spacer plate and through the opening of the vortex induced vibration suppression device.

13. The method of claim 12, further comprising connecting a plurality of spacer plates to the support structure, each spacer plate at a different depth.

14. The method of one or more of claims 12-13, further comprising providing a plurality of openings in the spacer plate and a plurality of vortex induced vibration suppression devices connected to the spacer plate.

15. The method of claim 14, further comprising feeding at least one subsea structure through each of the openings in the spacer plate and through each of the vortex induced vibration suppression devices.

16. The method of one or more of claims 12-15, further comprising connecting a plurality of spacer plates to the support structure, each spacer plate at a different depth, and then connecting a string of at least two vortex induced vibration suppression devices to each other, the string comprising a first end connected to a first spacer plate and a second end connected to a second spacer plate.