Methods and systems for VIV suppression utilizing retractable fins

Embodiments disclosed herein describe cylindrical structures with indents configured to reduce vortex induced vibrations (VIV). For example, the cylindrical structures may be configured to reduce VIV for risers subject to ocean currents.

BACKGROUND INFORMATION

Field of the Disclosure

Examples of the present disclosure relate to retractable fins positioned within indents on a drilling riser buoyancy module or a submerged cylinder. More specifically, embodiments relate to fins that are configured to reduce vortex induced vibrations for submerged cylinders.

Background

Offshore drilling is a process where a wellbore is drilled below a seabed. When offshore drilling, a riser is utilized as an interface between the seabed and a surface vessel. Offshore drilling, production, and mining is more challenging than land-based due to remote and harsher environments, wherein components for offshore operation, the risers, are required to be submerged in water.

In conventional offshore platforms, risers are submerged in fluid. Some Risers are partially supported via buoyancy modules that reduce the load on the offshore platforms or surface vessels. As fluid currents pass by the outer surface of the buoyancy modules, vortices shed alternately from the sides of the riser buoyancy modules and travel downstream. This phenomenon is known as “Karman vortex street.”

The frequency and magnitude of the vortex shedding is determined by the current's speed and the cross-sectional profile of the buoyancy modules. As a result of the vortex shedding, oscillating lift forces are produced. These lift forces are generally normal to the axis of the buoyancy modules and predominately in a cross-flow direction. This causes forced oscillations of the risers with buoyancy modules installed, known as vortex induced vibrations (VIV).

Conventional buoyancy modules include circular cross sections that are identical across a longitudinal axis of the cylindrical structures. Due to the identical cross sections, a spanwise correlation/coherence of vortex shedding is established. This produces in phase net lift forces having substantially large magnitudes. When vortex shedding frequency is close to a natural frequency of the riser, a resonant-vibration phenomenon known as “lock-in” occurs, which increases the amplitude of the vibrations.

Furthermore, conventional riser buoyancy modules have not adopted any VIV suppression devices, while other submerged cylindrical members such as risers use fairings, strakes, or fins to break the correlation of vortex shedding along the span of the structure, which diminishes the net lift force and VIV. The fairings, strakes, or fins protrude from the surface of the buoyancy modules. Thus the fairings, strakes, or fins cause larger drag forces from the flowing fluid on the submerged buoyancy modules. In addition these embodiments pose difficulties in operation, transporting, handling, and installing the structural system.

Accordingly, needs exist for effective systems and methods for buoyancy modules with retractable fins configured to reduce VIV.

SUMMARY

Embodiments disclosed herein describe cylindrical structures or buoyancy modules (referred to hereinafter collectively and individually as “cylindrical structures”) with movable or retractable fins (referred to hereinafter individually and collectively as “retractable fins”) positioned within indents, wherein the retractable fins are configured to reduce VIV. For example, the cylindrical structures may be configured to reduce VIV for risers subject to ocean currents.

Embodiments may include indents and retractable fins. In embodiments, the indents may be grooves within an outer surface of the cylindrical structures, wherein the indents include pairs of indents, alternating pairs notches positioned along an axis, and/or staggered indents. The paired indents may be symmetrical or asymmetrical, which may be continuous or staggered.

The retractable fins may be positioned within the indents. In embodiments, the retractable fins may be positioned within the indents, and have an axis of rotation that is aligned with the axis of the notches. In a first mode, the movable fins may be configured to be positioned within the indents such that an inner sidewall of the retractable fins is positioned adjacent to a sidewall of the notches. In a second mode, the retractable fins may rotate approximately ninety degrees and projection away from the indents. Based on the positioning of the retractable fins, the retractable fins may interact with changing ocean currents to reduce VIV applied to the cylindrical structures. In embodiments, the retractable fins may be configured to move between the first mode and the second mode based on a direction and force of the ocean currents.

In other embodiments, the retractable fins may be configured to be positioned within a tubing and in the first mode while being submerged in fluid. The tubing may be configured to secure the retractable fins in the first, retracted position by applying forces towards a central axis of the cylindrical structures. Responsive to removing the tubing and the corresponding forces towards the central axis of the cylindrical structures, the retractable fins may automatically move from the first mode to the second mode.

DETAILED DESCRIPTION

Embodiments disclosed herein describe cylindrical structures with indents with retractable flaps configured to reduce VIV. In embodiments, the indents may be positioned within an outer surface of the cylindrical structures.

Turning now toFIG. 1,FIG. 1depicts a cylindrical structure100configured to be a riser buoyancy module, according to an embodiment. A riser may be a conduit that is configured to provide a temporary extension of a subsea equipment to a surface facility. When used in water with a substantial depth, a riser should be tensioned to maintain stability. The level of tension required is related to the weight of the riser equipment, the buoyancy of the riser, the forces from waves and current, the weight of internal fluids, etc. To reduce the top hookload of the equipment on the surface, buoyancy modules are used to help maintain the required tension along the riser.

Cylindrical structure100may be a riser buoyancy module comprised of two halves110(a)110(b), pipe orifices115, and indents120,130. Cylindrical structure100may be configured to be submerged in fluid, and minimize downtime caused by loop current VIV, which may increase operability of the surface facility.

The two halves110(a) and110(b) may be configured to encompass a riser pipe, wherein the riser pipe may be configured to be inserted into pipe orifices115. The drilling riser pipe may be positioned within the cylindrical structure100. The circumferences of two halves110(a) and110(b) may form a cylindrical outer surface. In embodiments, two halves110(a) and110(b) may be coupled together.

Cylindrical structure100may include a plurality of alternating V-shaped notches120,130positioned on opposite sides of an axis150, wherein the axis150extends from a first end of cylindrical structure100to a second end of cylindrical structure100, which may cross both halves110(a),110(b). In embodiments, as shown in the cross sections, notches120,130may be configured to reduce VIV considering the directional flow of the current and the positioning of notches120,130. In embodiments, the V-shaped notches120,130may be offset such notches120,130are positioned cattycorner from each other across axis130, such that a first leg of notch120is positioned on a first side of axis130, and a first leg of notch130is positioned on a second side of axis130. Thus, the first legs of notches120,130may create alternating continuous grooves from a first end of cylindrical structure100to a second end of cylindrical structure100, wherein the grooves are not continuous on each side of axis150due to spacers140.

In embodiments, a plurality of cylindrical structures100may be coupled together, wherein notches and axis on a first end of a first cylindrical structure100may be aligned with notches and axis on a second end of a second cylindrical structure100. Accordingly, a drilling riser may include continuous, bidirectional, helical notches and axis extending from the first end of a riser to the second end of the riser.

Axis150may be a helical axis with a curve between the first and second ends of cylindrical structure100. Each of the V-shaped notches120,130may have a first leg and a second leg, wherein the V-shaped notches120,130form square cutouts embedded within cylindrical structure100. The first leg of the V-shaped notch may be a straight leg, and the second leg of the V-shaped notched may be curved, wherein the curvature of the second leg curves inward towards the longitudinal axis of cylindrical structure100. Alternatively, the second leg of the V-shaped notches may be a straight leg.

FIG. 2depicts a cylindrical structure100with embedded retractable fins210, according to an embodiment. Elements depicted inFIG. 2may be substantially the same as those discussed above. For the sake of brevity, a further description of these elements is omitted.

As depicted inFIG. 2, a movable fin210may be positioned within a notch110,120. Movable fin210may include an inner surface212, outer surface214, and hinge220. Movable fin210may be configured to rotate between an open position and a closed position. In embodiments, the closed position may be a first mode, and the open position may be a second mode.

Inner surface212of retractable fin210may be configured to be positioned adjacent and flush against a second leg230of the notch in the first mode. In the second mode, inner surface212may be configured to be positioned away from second leg230of the notch.

Outer surface214of retractable fin210may be configured to be positioned adjacent and flush against a first leg240of the notch in the second mode. In the first mode, outer surface214may be configured to be positioned away from first leg240. Furthermore, first leg240of the notch may limit the angle of rotation of movable fin210, wherein first leg240may limit the angle to ninety degrees. In embodiments, first leg240may be configured to be positioned perpendicular to second leg230.

Hinge220may be a mechanical bearing that is configured to couple retractable fin210within a notch of a cylindrical structure100. Hinge220may be configured to allow retractable fin210to rotate between the first position and the second position. In embodiments, hinge220may be spring loaded such that hinge220applied force against retractable fin210to maintain retractable fin210in the opened position if outside forces are not applied to retractable fin210.

When retractable fin210is in the first mode a body of retractable fin210may be positioned within the notch and a distal end of retractable fin210may not project past second leg230. When retractable fin210is in the second mode, a proximal end of retractable fin210may be positioned within the notch and a distal end of retractable fin210may project away from the first leg240of notch. When retractable fin210projects away from first leg240the diameter of cylindrical body100may increase This may be due to the body of retractable fin210having a length that is shorter than a length of second leg230and longer than that of first leg240, wherein the length of second leg230may be greater than first leg240.

In embodiments, retractable fin210may be positioned in the first mode while retractable fin210is in a housing, such as a tube, and the housing limits the expansion of retractable fin210. Responsive to removing the retractable fin210from the housing, the retractable fin210may automatically move from the first mode to the second mode due to the housing no longer limiting the expansion of retractable fin210. Retractable fin210may remain in the second mode unless outside forces are applied against retractable fin210to move to back to the first mode.

FIG. 3depicts a cylindrical structure100with a plurality of retractable fins210,310,320. Elements depicted inFIG. 3may be described above, and for the sake of brevity a further description of these elements is omitted.

As depicted inFIG. 3, different retractable fins210,310,320may be positioned on the alternating notches on the different sides of axis130. In embodiments, moveable fins210,320on the same side of axis130may be configured to rotate in a first direction towards axis130, and retractable fin310positioned on a different side of axis130may be configured to rotate in a second direction towards axis130. By positioning movable fins210,310,320on different sides of axis130and at different positioning from a top to bottom of cylindrical structure100different fluid forces surrounding cylindrical structure100may impact each retractable fin210,310,320differently at different times. This may allow for greater reductions in vibrations.

FIG. 4depicts a cross section of cylindrical structure100with a plurality of retractable fins405,410,420. Elements depicted inFIG. 4may be described above, and for the sake of brevity a further description of these elements is omitted.

As depicted inFIG. 4, a cross section of cylindrical structure100may have multiple retractable fins405,410,420. Each of the retractable fins405,410,420may be vertically aligned with each other, such that each of the movable fins405,410,420corresponds with a different axis and/or pairs of notches.

As further depicted inFIG. 4, the notches430may be “V-Shaped” notches, which a convex curved leg or legs. Inner surfaces of retractable fins405,410,420may be similarly curved. The curvature of the notches430of movable fins405,410,420may allow flowing fluid to interact the fins and notches430more effectively. More specifically, as fluid is flowing around the cylindrical structure in an eddy, the curvature of the eddy may correspond more to the curvature of notches430than notches with a planar bottom surface, while increasing the amount of surface area that the flowing fluid impacts.

FIGS. 5-8depict different variations of retractable fins, according to embodiments. Elements depicted inFIGS. 5-8may be described above, and for the sake of brevity a further description of these elements is omitted.

As depicted inFIG. 5, retractable fin500may include a stop510positioned on the outer surface502of retractable fin500. Stop510may be comprised of a different material than moveable fin500. For example, stop510may be comprised of a compressive rubber. Responsive to retractable fin500being in the second mode, stop510may be positioned adjacent to the first leg of a notch. This may be utilized to limit the erosion of retractable fin500, and/or the legs of the cylindrical structures.

As depicted inFIG. 6, retractable fin600may be embedded within a notch that is substantially square shape610. The square shape notches610may have two sidewalls612,614that are configured to be encompassing the ends of retractable fin600. The square shape notches610may have open ends616,618that is not configured to obstruct the rotation of retractable fin600, wherein a planar surface is positioned between the sidewalls612,614and open ends616,618.

Further, when embedded within square shape notches610, retractable fin610may be coupled to sidewalls612,614, via a hinge630that is positioned at a midway point within notch610. Accordingly, in a first mode a distal end of602of retractable fin600may be positioned proximate to open end616, in a second mode distal end602may be positioned proximate to open end618, and in a third mode extend away from body610such that retractable fin600is positioned in a direction perpendicular to a central axis of the cylindrical structure and be positioned beyond the ends of sidewalls612,614. In embodiments, a distance between the midway point of notch610and the open ends616,618may be less than a distance from a proximal end to distal end602of retractable fin600, while the distance from the proximal end to the distal end602of retractable fin600may be greater than the height of sidewalls612,614.

As depicted inFIG. 7, hinge710may be positioned along a sidewall of a leg of a notch720, and not at an apex where the two legs of the notch720intersect. This may enable fin705to rotate ninety degrees even when notch720is a deep v-shaped with a curved leg.

As depicted inFIG. 8, a curved fin810may be positioned within a deep-v notch820, wherein at least one leg of notch820is curved. The curvature of fin810may allow fin810to be positioned adjacent to the curved leg820of notch820when fluid is not interacting with fin810.

FIG. 9depicts different variations of retractable fins, according to an embodiment. Elements depicted inFIG. 9may be described above, and for the sake of brevity a further description of these elements is omitted.

As depicted inFIG. 9, cylindrical structure902may include a substantially rectangular notch920that extends towards the central axis of cylindrical structure902. A spring905and retractable fin910may be configured to be housed within notch920when a force is applied against a distal end of retractable fin910, such as when cylindrical structure is being inserted through tubing. The force applied against the distal end of fin910may be translated to spring905to compress spring905.

Responsive to the tubing no longer applying pressure against the distal end of fin910, spring905may elongate. This elongation of spring905may move distal end of fin910from a position flush with the outer surface of cylindrical structure902to a position away from the outer surface of cylindrical structure902.

FIG. 10depicts different variations of movable fins, according to an embodiment. Elements depicted inFIG. 10may be described above, and for the sake of brevity a further description of these elements is omitted.

As depicted inFIG. 10, a housing1030may be positioned within a deep-v notch1020with a curved leg. The housing1030may be positioned adjacent to a planar leg of notch1020, and may extend from an apex of notch1020to the circumference of cylindrical structure1002. Housing1030may be configured to store spring1005and moveable fin1010. Spring1005and moveable fin1010may be configured to be positioned within housing1030when a force is applied against a distal end of movable fin1010, such as when cylindrical structure1002is being inserted through tubing. The force applied against the distal end of fin1010may be translated to spring1005to compress spring1005.

Responsive to the tubing no longer applying pressure against the distal end of fin1010, spring1005may elongate. This elongation of spring1005may move distal end of fin1010from a position flush with the outer surface of cylindrical structure1002and housing1030to a position away from the outer surface of cylindrical structure1030.

FIG. 11depicts different variations of a cylindrical structure1100, according to an embodiment. Elements depicted inFIG. 11may be described above, and for the sake of brevity a further description of these elements is omitted.

As depicted inFIG. 11, cylindrical structure1100may include overlapping notches1110and1120, wherein each of the notches is different sized and shaped. More specifically, notches positioned closer to a first end1140of cylindrical structure1100may be shorter and have a smaller width than notches positioned closer to a second end1140of cylindrical structure1100.

The notches on cylindrical structure1100may overlap, such that the ends of a first notch positioned on a first side of axis1160are aligned with two different notches on a second side of axis1160. Furthermore, due to the varying sizes of the notches on cylindrical structure1100there may be a varying distance between notches on the same side of axis1160. Additionally, there may be a varying distance between notches on a first side of axis1160and notches on a second side of axis1160. The varying distances in multiple dimensions may allow fluid flowing around cylindrical structure1100to each impact each notch different. This may allow for more efficient and effective reducing of vibrations. Furthermore, embodiments may include retractable fins that have different lengths and widths that are configured to correspond to the varying sizes of the notches with different sizes. This may enable each of the retractable fins to impact the VIV dampening differently.

FIGS. 12-13depict different variations of a cylindrical structure1200, according to embodiments. Elements depicted inFIGS. 12-13may be described above, and for the sake of brevity a further description of these elements is omitted.

As depicted inFIG. 12, notches1210,1220,1230may overlap adjacent notches. Accordingly, ends of the notches positioned on a first side of axis1250may be aligned with different notches positioned on the second side of axis1250. In embodiments, the ends of the notches on a first side of axis1250may be configured to overlap with different notches positioned on the second side of axis1250. This may create series of overlapping notches. Furthermore, the notches may be directly adjacent to axis1250, such that the notches positioned on different sides of axis1250are adjacent to each other.

The notches may vary in size and spacing from the first end of cylindrical structure1200to a second end of cylindrical structure1200. This may cause spaces1240between adjacent notches on the same side of axis1250to be different.

As depicted inFIG. 13, notches1210,1220positioned on the same side of axis1250may have spacer1240positioned between them, wherein spacer1240has a curved sidewall.

The sidewalls of spacer1240may be aligned the ends of notches1210,1220positioned on the same side of axis1250. Further, spacer1240may have a sidewall that is aligned with a sidewall of notch1310positioned on a second side of axis1250. A similar spacer may be positioned between notches on the other side of axis1250of notch1230.

Furthermore, as notches1210and1310and1220overlap, there may be a passageway, void, etc. positioned between the two that extend across axis1250. This passageway may allow for communication of fluid between the notches on different sides of axis1250.

FIGS. 14Aand B depict different variations of a gap bracket14001402, according to embodiments. Elements depicted inFIGS. 14A and 14Bmay be described above, and for the sake of brevity a further description of these elements is omitted.

Gap bracket1400may be configured to be inserted into a notch1210,1220,1230and across a passageway between the notches to limit the exposed cutouts of notches1210,1220,1230. Gap bracket1400,1402may be a replaceable device that is configured to divert the fluid flowing around cylinder1200. The gap brackets1400,1402may be utilized to vary the impact and vibrations caused by fluid flowing around cylinder1200. As such, each cylinder1200may have a different layout. Further, due to gap bracket1400,1402being replaceable, if gap bracket1400,1402is eroded, a new gap bracket1400,1402may be inserted.