CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. provisional patent application Serial No. 62/676,086 filed May 24, 2018, and entitled “Offshore Spar Structure with Hydrodynamic Dampers and Methods for Deploying and Installing Same,” which is hereby incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND

[0003] The disclosure relates generally to offshore structures. More particularly, the disclosure relates to floating offshore platforms for offshore drilling and/or production operations. Still more particularly, the disclosure relates to deploying, installing, and stabilizing floating offshore platforms such as offshore spar platforms.

There are several types of offshore structures that may be employed to drill and/or produce subsea oil and gas wells. Some offshore platforms such as jacket rigs are directly anchored to the sea floor, whereas other offshore platforms (e.g., as semi-submersibles platforms, spar platforms, and tension leg platforms) float on the sea surface. Often, the type of offshore platform used for offshore operations will depend on the depth of water at the well location. For instance, jack-up platforms are commonly employed as drilling structures in water depths less than about 400 feet; fixed platforms and gravity based structures are commonly employed as production structures in water depths between about 300 and 800 feet; and floating systems such as semi- submersible platforms and spar platforms are commonly employed as production structures in water depths greater than about 800 feet. [0004] During offshore operations, platforms continuously move in response to winds, waves, and currents. Floating platforms typically rely on mooring systems to resist the lateral environmental loads caused by winds, waves, and currents.

BRIEF SUMMARY OF THE DISCLOSURE

[0005] In an embodiment, a floating offshore structure comprises an adjustably buoyant hull having a central axis, a first end, and a second end opposite the first end; a plurality of circumferentially-spaced hydrodynamic dampers disposed about the hull and axially positioned between the first end and the second end of the hull, wherein the hydrodynamic dampers are radially spaced from the hull.

[0006] In an embodiment, a floating offshore structure comprises an adjustably buoyant hull having a central axis, a first end, and a second end opposite the first end; a plurality of circumferentially-spaced hydrodynamic dampers disposed about the hull and axially positioned between the first end and the second end of the hull, wherein the hydrodynamic dampers are pivotally coupled to the hull; wherein each hydrodynamic damper has a retracted position radially adjacent the hull and an extended position radially spaced from the hull.

[0007] In an embodiment, an offshore structure comprises an adjustably buoyant hull having a central axis, a first end, and a second end opposite the first end; an annular hydrodynamic damper extending circumferentially about the hull and radially spaced from the hull, wherein the annular hydrodynamic damper is axially aligned with a center of rotation of the hull.

[0008] In an embodiment, a method for deploying an offshore structure comprises (a) positioning an elongate adjustably buoyant hull in a horizontal orientation, wherein the hull has a central axis, a first end, and a second end;

(b) coupling a hydrodynamic damper to the hull with the hull in the horizontal orientation, wherein the hydrodynamic damper is coupled to the hull between the first end and the second end; (c) transporting the hull to an offshore installation site after (b) with the hull in the horizontal orientation; (d) transitioning the hull from the horizontal orientation to a vertical orientation at the installation site after (c).

[0009] Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a detailed description of the disclosed exemplary embodiments, reference will now be made to the accompanying drawings, wherein:

[0011] Figure 1 is a perspective schematic view of an embodiment of an adjustably buoyant floating offshore structure in accordance with the principles disclosed herein;

[0012] Figure 2 is a side view of the offshore structure of Figure 1 ;

[0013] Figure 3 is a front view of the offshore structure of Figure 1 responding to a downward heave motion;

[0014] Figure 4 is a front view of the offshore structure of Figure 1 responding to an upward heave motion;

[0015] Figure 5 is a front view of the offshore structure of Figure 1 responding to a clockwise left to right lateral pitch/roll motion;

[0016] Figure 6 is a front view of the offshore structure of Figure 1 responding to a counterclockwise right to left lateral pitch/roll motion; [0017] Figures 7-10 are perspective schematic views of embodiments of an adjustably buoyant floating offshore structure in accordance with the principles disclosed herein;

[0018] Figure 1 1 is a side view of the offshore structure of Figure 1 illustrating the attachment of the dampers with a crane;

[0019] Figure 12 is a side view of the offshore structure of Figure 5C illustrating the attachment of the damper with a crane;

[0020] Figure 13 is a side schematic view of an embodiment of an adjustably buoyant floating offshore structure in accordance with the principles disclosed herein illustrating the attachment of an extendable damper;

[0021] Figure 14 is a side view of the offshore structure of Figure 7A with multiple extendable dampers attached thereto;

[0022] Figure 15 is a side view of the offshore structure of Figure 7B in a vertical orientation and with an exemplary extendable damper in a retracted position;

[0023] Figure 16 is a side view of the offshore structure of Figure 7B in a vertical orientation and with the exemplary extendable damper in an extended position;

[0024] Figure 17 is a graph of Fleave RAO versus Time for adjustably buoyant floating offshore structures with and without dampers; and

[0025] Figure 18 is a graph of Pitch RAO versus Time for adjustably buoyant floating offshore structures with and without dampers.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] The following description is exemplary of certain embodiments of the disclosure. One of ordinary skill in the art will understand that the following description has broad application, and the discussion of any embodiment is meant to be exemplary of that embodiment, and is not intended to suggest in any way that the scope of the disclosure, including the claims, is limited to that embodiment.

[0027] The figures are not necessarily drawn to-scale. Certain features and components disclosed herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. In some of the figures, in order to improve clarity and conciseness, one or more components or aspects of a component may be omitted or may not have reference numerals identifying the features or components. In addition, within the specification, including the drawings, like or identical reference numerals may be used to identify common or similar elements.

[0028] As used herein, including in the claims, the terms “including” and “comprising,” as well as derivations of these, are used in an open-ended fashion, and thus are to be interpreted to mean“including, but not limited to...

As used herein, the phrases“consisting of” and“consists of” are used to refer to exclusive components of a structure or apparatus, meaning only those expressly recited components are included in the structure or apparatus. Also, the term“couple” or“couples” means either an indirect or direct connection. Thus, if a first component couples or is coupled to a second component, the connection between the components may be through a direct engagement of the two components, or through an indirect connection that is accomplished via other intermediate components, devices and/or connections. The recitation“based on” means“based at least in part on.” Therefore, if X is based on Y, then X may be based on Y and on any number of other factors. The word“or” is used in an inclusive manner. For example,“A or B” means any of the following:“A” alone,“B” alone, or both“A” and“B.” In addition, the terms “axial” and“axially” generally mean along a given axis, while the terms“radial” and“radially” generally mean perpendicular to the axis. For instance, an axial distance refers to a distance measured along or parallel to a given axis, and a radial distance means a distance measured perpendicular to the axis. As understood in the art, the use of the terms“parallel” and“perpendicular” may refer to precise or idealized conditions as well as to conditions in which the members may be generally parallel or generally perpendicular, respectively. As used herein, the terms“approximately,”“about,”“substantially,” and the like mean within 10% (i.e. , plus or minus 10%) of the recited value. Thus, for example, a recited angle of“about 80 degrees” refers to an angle ranging from 72 degrees to 88 degrees.

[0029] As previously described, floating offshore platforms such as semi- submersible platforms and spar platforms typically rely on mooring systems to maintain position at the installation site. Such floating platforms are relatively large and heavy structures that must withstand intense loads/forces from the environment. For example, floating platforms must withstand dynamic loads induced by waves, winds, and currents to provide a stable structure for performing various types of offshore operations (e.g., drilling and/or production operations). The large size and mass of these structures results in a relatively high inertia that resists such dynamic loads. In contrast, permanently moored, relatively small and lightweight floating offshore platforms often have relatively low inertia, and thus, have a reduced ability to resist dynamic loads. As a result, smaller lightweight floating offshore structures may move excessively in response to dynamic loads induced by waves, winds, and currents.

[0030] Embodiments described herein are directed to floating offshore platforms, and in particular, spar-type platforms that include hydrodynamic dampers (“dampers”) designed to resist and/or prevent large motions in response to dynamic loads even in cases when the platform has a relatively small weight and low inertia. The dampers offer the potential to reduce vertical heave motions and rotational pitch and roll motions. This enhances the ability of the floating offshore platform to maintain the desired orientation, position, and depth. Such embodiments may be particularly suitable for small installations in relation to standard offshore production platforms (e.g., as floating offshore communication hub systems, emergency landing decks, offshore fluid offloading systems, wind turbines etc.).

[0031] Referring now to Figures 1 and 2, an embodiment of a floating offshore structure 100 is shown. Structure 100 is deployed in a body of water 102 at an offshore site and generally floats at the surface 108 of water 102. As will be described in more detail below, structure 100 relies on one or more dampers and a mooring system (not shown) to maintain its position at the installation site. In general, structure 100 may be deployed offshore to drill a subsea wellbore and/or produce hydrocarbons from a subsea wellbore. In this embodiment, structure 100 is a spar type platform including an adjustably buoyant hull 104 and a topside or deck 106 mounted to hull 104 above the sea surface 108. In general, communication hub systems, emergency landing decks (helideck), offshore fluid offloading systems and the like, can be disposed on and supported by topside 106. Hull 104 has a central axis 1 10, a first or upper end 104a, and a second or lower end 104b.

[0032] As described above, in this embodiment, structure 100 is a spar-type platform, and thus, hull 104 comprises a single, elongate column 105 extending axially between ends 104a, 104b. Column 105 includes a plurality of axially stacked chambers or tanks defined by a plurality of axially spaced bulkheads. When column 105 is vertically oriented as shown in Figure 1 , the chambers are vertically stacked and the bulkheads defining the chambers are vertically spaced. In this embodiment, the chambers in column 105 include one or more buoyancy chambers 1 13 provided in an upper section 1 12 of column 105, one or more adjustable and variable ballast chambers 1 16 provided in an intermediate section 1 14 of column 105, and one or more fixed ballast chambers 120 provided in a lower section 1 18 of column 105. As shown in Figures 1 and 2, upper section 1 12 of column 105 extends from upper end 104a to intermediate section 1 14, and lower section 1 18 of column 105 extends from lower end 104b to intermediate section 1 14. Thus, intermediate section 1 14 is axially positioned between sections 1 12, 1 18.

[0033] Buoyancy chambers 1 13 are filled with air and sealed, thereby providing buoyancy to column 105 and hull 104. Variable ballast chambers 1 16 can be selectively and controllably filled with ballast water and/or air (e.g., compressed air) to adjust the weight of hull 104 and the buoyancy force applied to hull 104. Fixed ballast chambers 120 are at least partially filled with relatively heavy permanent ballast, such as magnetite, to provide hull 104 and column 105 with a relatively low center of gravity.

[0034] Referring still to Figures 1 and 2, hull 104 has an axial length measured axially (parallel to axis 1 10) between ends 104a, 104b that defines the vertical height H104 of hull 104 when it is vertically oriented. In addition, hull 104 has a diameter or maximum width W104 measured radially (perpendicular to axis 1 10). Since hull 104 is formed by a single column 105, the width W104 is also the diameter and maximum width of column 105. For most offshore installations, embodiments described herein have a vertical height H104 ranging from about 100 m to about 200 m, and preferably between 100 m and 170 m, and a width W104 ranging from about 5.0 m to about 15.0 m. Water depths in which structure 100 is deployed may range from 300 m to 3,000 m. Structure 100 may also be deployed in deeper water depths (e.g., greater than 3,000 m) provided the weight of the mooring lines of the mooring system do not compromise the buoyancy capacity of the hull (e.g., hull 104).

[0035] In this embodiment, structure 100 also includes a plurality of uniformly circumferentially-spaced hydrodynamic dampers 126 disposed about hull 104, and in particular, disposed about a center of rotation 128 of hull 104. As will be described in more detail below, dampers 126 resist vertical movement of hull 104 relative to water 102 and resist rotation of hull 104 about horizontal axes relative to water 102. In this embodiment, each damper 126 is a plate having a planar top side or surface“A” and a planar bottom side or surface“B” oriented parallel to top side A. In addition, dampers 126 generally lie in a common reference plane oriented perpendicular to axis 1 10 of hull 104. More particularly, top sides A are parallel and lie in a common plane oriented perpendicular to axis 1 10, and bottom sides B are parallel and lie in a common plane oriented perpendicular to axis 1 10. The planar sides A, B of dampers 126 and the orientation of dampers 126 (generally disposed in a plane oriented perpendicular to axis 1 10) creates drag in water 102, which resists and dampens vertical motion of structure 100 relative to water 102 and rotational motion of structure 100 about horizontal axes relative to water 102.

[0036] Dampers 126 are radially spaced from hull 104 but fixably coupled to hull 104 with a rigid attachment frame 130 that extends radially outward from column 105 to each damper 126, and extends circumferentially between circumferentially-adjacent dampers 126. In general, attachment frame 130 may be formed from pipes, rods, beams, bars, steel wire cables or combinations thereof. In this embodiment, attachment frame 130 includes a plurality of circumferentially-spaced rigid support beams 131 extending from column 105 and dampers 126 and a plurality of rigid support beams 132 extending circumferentially between each pair of circumferentially adjacent dampers 126. More specifically, one support beam 131 extends axially away from upper end 104a and radially outward from column 105 to upper surface A of each damper 126, one support beam 131 extends axially away from lower end 104b and radially outward from column 105 to lower surface B of each damper 126, and one support beam 132 extends circumferentially between each pair of circumferentially-adjacent dampers 126. Thus, for each damper 126, a pair of support beams 131 and column 105 generally form a triangular configuration with the damper 126 positioned at the vertex. As best shown in Figure 1 1 , each support beam 131 is oriented at an acute angle a relative to axis 1 10. In embodiment described herein, acute angle a ranges from 20° to 45°. Support beams 132 lie in the same common reference plane as dampers 126.

[0037] As shown in Figure 2, each damper 126 is disposed at radial distance R126 measured radially from column 105 to the radially innermost edge or point of the damper 126. In this embodiment, the radial distance R126 between column 105 and each damper 126 is the same. For most offshore installations, the radial distance R126 ranges from 1 .0 to 3.0 times the width W104 of hull 104. The circumferential spacing of dampers 126 will depend on the size of dampers 126 and the number of dampers 126. Although illustrated with six dampers, hull 104 can include three to ten dampers (e.g., dampers 126).

[0038] In Figures 1 and 2, six dampers 126 are provided and each damper 126 is the same (e.g., each damper 126 has the same rectangular geometry). For most offshore applications, each damper 126 is a rectangular plate with a face area ranging from 0.25 to 1 .0 times the cross-sectional area of hull 104 in a plane oriented perpendicular to axis 1 10 (e.g., water plane area of column 105). As used herein, the term“face area” is used to refer to the surface area of one side of a plate or damper (e.g., the surface area of side A or side B of damper 126). The length and width of each damper 126 may be the same (i.e. , each damper 126 may be a square plate). Flowever, as will be described in more detail below with respect to Figures 7-10, in other embodiments, the number and geometry of the damper(s) may be different.

[0039] Referring again to Figures 1 and 2, as previously described, dampers 126 are disposed about center of rotation 128, which is below the surface 108 of water 102. Thus, center of rotation 128 and dampers 126 are disposed at the same axial position along hull 104 and column 105 below the surface 108. In general, the center of rotation of a floating object (e.g., center of rotation 128) is the metacenter, which is above the center of buoyancy, and is determined using techniques known in the art.

[0040] Referring now to Figures 3 and 4, axially oriented heave motions of hull 104 are resisted by dampers 126 - downward heave motion represented by arrow 134 in Figure 3 and upward heave motion represented by arrow 138 in Figure 4)- are resisted by dampers 126. In particular, due to the planar geometry of sides A, B of dampers 126 and the orientation of dampers 126 in the reference plane oriented perpendicular to central axis 1 10, movement of hull 104 and dampers 126 fixably coupled to hull 104 parallel to axis 1 10 results in drag and inertial forces (due to added mass). As a result, downward heave motion 134 of hull 104 and dampers 126 relative to water 102 results in upward forces represented by arrows 136 (Figure 3) applied to dampers 126, which is transferred to hull 104 via attachment frame 130; and upward heave motion represented by arrows 138 (Figure 4) of hull 104 and dampers 126 relative to water 102 results in downward forces 140 applied to dampers 126, which is transferred to hull 104 via attachment frame 130. In other words, dampers 126 dampen and resist axial movement (up and down) of hull 104, thereby reducing the amplitudes of heave motions 134, 138 of hull 104 and enhancing its stability.

[0041] Referring now to Figures 5 and 6, pitch and roll motions of hull 104 about axes oriented perpendicular to axis 1 10 (e.g., axes intersecting center of rotation 128 and oriented perpendicular to axis 1 10) are resisted by dampers 126 - clockwise pitch and roll motion represented by arrow 142 in Figure 5 and counter clockwise pitch and roll motion represented by arrow 144 in Figure 6 - are resisted by dampers 126. In particular, due to the planar geometry of sides A, B of dampers 126, the orientation of dampers 126 perpendicular to central axis 1 10, and the distance of dampers 126 from hull 104, rotation of hull 104 and dampers 126 fixably coupled to hull 104 about axes perpendicular to axis 1 10 results in drag and inertial forces. As a result, clockwise pitch and roll motion 142 of hull 104 and dampers 126 relative to water 102 results in counterclockwise torque represented by arrow 144 applied to dampers 126 (Figure 5), which is transferred to hull 104 via attachment frame 130; and counterclockwise pitch and roll motion 144 of hull 104 and dampers 126 relative to water 102 results in clockwise torque represented by arrow 142 applied to dampers 126 (Figure 6), which is transferred to hull 104 via attachment frame 130. In other words, dampers 126 dampen and resist pitch and roll movement (clockwise and counterclockwise) of hull 104, thereby reducing the amplitudes of pitch and roll motions 142, 144 of hull 104 and enhancing its stability.

[0042] The embodiment of offshore structure 100 previously described and shown in Figures 1 and 2 includes six uniformly circumferentially-spaced rectangular shaped dampers 126. Flowever, in other embodiments, the number and geometry of the dampers may be different. Referring now to Figures 7-10, embodiments of adjustably buoyant floating offshore structures 100b, 100c, 100d, 100e including alternative geometries of dampers are shown. Each structure 100b, 100c, 100d, 100e includes a hull 104 as previously described and one or more dampers 150, 151 , 152, 153, 154, 155, respectively, fixably coupled to hull 104 with an attachment frame 130 as previously described. In these embodiments, dampers 150, 151 , 152, 153, 154, 155 are disposed about center of rotation 128 of the corresponding hull 104 and positioned at the same axial position relative to axis 1 10 as center of rotation 128. In addition, each damper 150, 151 , 152, 153, 154, 155 has planar upper side or surface A disposed in a plane oriented perpendicular to axis 1 10 and a planar lower side or surface B disposed in a plane oriented perpendicular to axis 1 10.

[0043] In Figure 7, a plurality of uniformly circumferentially-spaced dampers 150 are disposed about hull 104. In this embodiment, each damper 150 is a circular or disc-shaped plate. In addition, each damper 150 is disposed in a common reference plane oriented perpendicular to axis 1 10 (e.g., upper sides A are disposed in the same plane oriented perpendicular to axis 1 10 and lower sides B are disposed in the same plane oriented perpendicular to axis 1 10). Each damper 150 has the same size and geometry, and further, is disposed at the same radial distance from hull 104 (measured radially from hull 104 to the radially innermost edge or point of each damper 150). For most offshore applications, each damper 150 has a diameter ranging from 0.25 to 1 .0 times the width W104 of the hull 104, and each damper 150 is disposed at the same radial distance from hull 104 ranging from 1 .0 to 3.0 times the width W104 of the hull 104. Although dampers 150 are circular in this embodiment, in other embodiments, the circumferentially-spaced dampers may have other geometries such as square, rectangular, hexagonal, or another similar geometry that produces a flat area to work as a hydrodynamic damper in the vertical direction. The dimensions, area, configuration, and spacing of each of these dampers may be the same as described above (e.g., damper 126).

[0044] In Figure 8, one damper 153 extends continuously and circumferentially about hull 104. In particular, damper 153 is an annular or ring-shaped plate disposed about hull 104. In addition, damper 153 is disposed in a reference plane oriented perpendicular to axis 1 10 (e.g., upper side A is disposed in the same plane oriented perpendicular to axis 1 10 and lower side B is disposed in the same plane oriented perpendicular to axis 1 10). Damper 153 is coaxially aligned with hull 104. For most offshore applications, damper 153 has a radial width (measured radially from the radially innermost edge of damper 153 to the radially outermost edge of damper 153) ranging from 0.20 to 0.50 of the width Wi 04 of the hull 104, and damper 153 is disposed at a radial distance from hull 104 (measured radially from hull 104 to the radially innermost edge of damper 153) ranging from 0.50 to 3.0 times the width W104 of the hull 104.

[0045] In Figure 9, one damper 154 extends continuously and circumferentially about hull 104. Damper 154 is the same as damper 153 previously described with the exception that damper 154 is disposed at a greater radial distance from hull 104 as compared to damper 153. [0046] In Figure 10, one damper 155 extends continuously and circumferentially about hull 104. Damper 155 is the same as damper 153 previously described with the exception that damper 155 is disposed at a greater radial distance from hull 104 as compared to damper 153, and further damper 155 has a radial width that is greater than the radial width of damper 153. In general, an increase in the radial width of annular damper 153, 155 results in an increase in the total face area of damper 153, 155 respectively (assuming the radial width of damper 153, 155 remains the same), and an increase in the radial distance from hull 104 to damper 153, 155 results in an increase in the total face area of damper 153, 155, respectively (assuming the radial width of damper 153, 155 remains the same).

[0047] Without being limited by this or any particular theory, the total face area of all the damper(s) coupled to a platform, the greater the total damping force generated by the damper(s) to resist vertical heave and pitch/roll motions. Referring now to Figures 17 and 18, the impact of the total face area of all the dampers on the platform Response Amplitude Operators (RAOs) is shown. RAO is parameter known in the art to quantify the motion response of a floating structure under the action of ocean waves. RAOs can be determined using computer software to solve the wave diffraction and radiation phenomena by potential theory equations, also known as a panel method. In this method, a floating structure’s displacement and rotation responses per unit of incident wave height are calculated for each degree of freedom, i.e., heave, surge, and sway translations, and roll, pitch, and yaw rotations about the x, y, and z axes of a coordinate system. Fleave and pitch RAOs were calculated for exemplary embodiments disclosed herein and compared to results of both conventional and deep-draft semi-submersible platforms. In particular, small spar structures were modeled for a topside payload of 1 ,500 tons and the semi-submersibles for a payload of about 25,000 tons. Results of the heave and pitch RAOs shown in Figures 17 and 18, respectively, are for a predominant wave period of between 6 and 20 seconds. As shown, the heave and pitch RAOs decrease as the total face area of the damper(s) for both the ring and the square damper types increase. As shown, the utilization of dampers in light structures (e.g., small spar structures) offers the potential to substantially improve the motion response to levels close to or better than much heavier conventional and deep- draft semi-submersible platforms. The increase in the total face area of the damper(s) also delayed the natural period of motion, which is beneficial to avoid resonance with ocean wave periods.

[0048] Referring now to Figure 1 1 , the coupling of one damper 126 and attachment frame 130 to hull 104 is shown, it being understood that each damper 126 is fixably coupled to hull 104 in the same manner to form offshore structure 100 previously described and shown in Figures 1 and 2. In Figure 1 1 , deck 106 is coupled to upper end 104a of hull 104 prior to installation of dampers 126, however, in other embodiments, deck 106 can be coupled to upper end 104a after installation of dampers 126. Although one damper 126 is shown being coupled to hull 104 in Figure 1 1 , in general, the same approach can be used to fixably couple the dampers of other embodiments disclosed herein to hull 104 (e.g., dampers 150, 151 , 152, 153, 154, 155). In general, coupling of dampers 126 can be performed at the shipyard dry dock, quayside, near shore, or at the desired installation site for structure 100.

[0049] As shown in Figure 1 1 , one or more variable ballast chambers 1 16 are selectively ballasted and/or deballasted to orient hull 104 in a horizontal orientation while ensuring hull 104 floats at the surface 108. In this embodiment, each damper 126 and corresponding support beams 131 are pre-assembled and then coupled to hull 104 one at a time. In particular, with hull 104 in the horizontal orientation at the surface 108, a crane is employed to manipulate a crane sling 158 suspending damper 126 and support beams 131 extending therefrom directly above hull 104 at the desired axial positon along hull 104 (e.g., at the center of rotation 128 of hull 104). Next, the crane lowers crane sling 158 and damper 126 downward toward hull 104 to position the lower ends of support beams 131 into engagement with hull 104, and crane holds damper 126 and beams 131 in position as the lower ends of beams 131 are fixably attached to hull 104 (e.g., via welding). With damper 126 fixably coupled to hull 104 with beams 131 , hull 104 is rotated about axis 1 10 at the surface 108 to install a circumferentially adjacent damper 126 in the same manner as previously described. This process is repeated to install all of the dampers 126. Support beams 132 may be fixably attached to each pair of circumferentially-adjacent dampers 126 as each damper 126 is coupled to hull 104 or after any number of dampers 126 (e.g., all of dampers 126) are coupled to hull 104.

[0050] As previously described, the coupling of dampers 126 to hull 104 to form offshore structure 100 can be performed at the shipyard dry dock, quayside, near shore, or at the desired installation site for structure 100. If dampers 126 are fixably attached to hull 104 at a location remote from the installation site (e.g., dry dock, quayside, or near shore), offshore structure 100 can be transported and deployed to the offshore installation site in the horizontal orientation on a barge or floated out to the installation site in the horizontal orientation. If offshore structure 100 is transported to the installation site on a barge, it can be lifted off the barge with a crane and placed into the water 102 in the horizontal orientation or floated off the barge in the horizontal orientation.

[0051] After all the dampers 126 and beams 131 , 132 are installed on hull 104, one or more variable ballast chambers 1 16 are ballasted and/or deballasted to transition hull 104 from the horizontal orientation to the vertical orientation with upper end 104a disposed above the surface 108 and lower end 104b disposed below the surface 108. Next, one or more variable ballast chambers 1 16 are ballasted and/or deballasted to position offshore structure 100 at the desired draft in water 102. With offshore structure 100 in the vertical orientation at the desired position and desired draft in water 102, a mooring system (not shown) may be installed to couple structure 100 to the sea floor. If topsides 106 is not installed prior to the installation of dampers 126, it can be installed atop hull 104 via a floating crane or float-over method after hull 104 is vertically oriented. In general, embodiments of offshore structures including a plurality of circumferentially-spaced dampers such as offshore structure 100b shown in Figure 7 can be assembled, deployed, and installed at an offshore installation site in the same manner as offshore structure 100 previously described.

[0052] Embodiments of offshore structures including annular or ring-shaped dampers such as offshore structures 100c, 100d, 100e can be assembled in a similar manner as offshore structure 100 previously described. In particular, as shown in Figure 12, one or more variable ballast chambers 1 16 are selectively ballasted and/or deballasted to orient hull 104 in a horizontal orientation while ensuring hull 104 floats at the surface 108. In this embodiment, annular damper 153 is fixably coupled to hull 104 with attachment frame 130 to form offshore structure 100c by installing damper 153 in a plurality of circumferential segments. Namely, each segment of damper 153 and corresponding support beams 131 is pre-assembled and then coupled to hull 104 one at a time - with hull 104 in the horizontal orientation at the surface 108, a crane is employed to manipulate a crane sling 158 suspending the segment of damper 153 and support beams 131 extending therefrom directly above hull 104 at the desired axial positon along hull 104 (e.g., at the center of rotation 128 of hull 104). Next, the crane lowers crane sling 158 and the segment of damper 153 to position the lower ends of support beams 131 into engagement with hull 104, and crane holds the segment of damper 126 and beams 131 in position as the lower ends of beams 131 are fixably attached to hull 104 (e.g., via welding). With the segment of damper 153 fixably coupled to hull 104 with beams 131 , and hull 104 in the horizontal orientation, hull 104 is rotated about axis 1 10 at the surface 108 to install a circumferentially adjacent segment of damper 153 in the same manner as previously described. This process is repeated to install all of the segments of damper 153.

[0053] The ends of each circumferential segment of damper 153 are fixably coupled to the ends of the circumferentially-adjacent segments of damper 153 (e.g., via welding) to form the continuous annular damper 153 and complete the assembly of offshore structure 100c. In general, the ends of each segment of damper 153 can be coupled to the ends of the circumferentially-adjacent segments of damper 153 as each segment is coupled to hull 104 or after any number of the segments (e.g., all of segments of damper 153) are coupled to hull 104. Once assembled, offshore structure 100c is deployed and installed at an offshore location site in the same manner as offshore structure 100 previously described. In general, embodiments of offshore structures including annular dampers such as offshore structures 100d, 100e shown in Figures 9 and 10, respectively, can be assembled, deployed, and installed at an offshore installation site in the same manner as offshore structure 100c previously described.

[0054] Referring now to Figures 13 and 14, an embodiment of a method for coupling dampers 126 to hull 104 to form an adjustably buoyant floating offshore structure 10Oj is shown. In this embodiment, dampers 126 and hull 104 are each as previously described. However, unlike offshore structure 100 previously described, in this embodiment, dampers 126 are not fixably coupled to hull 104 with attachment frame 130. Rather, in this embodiment, each damper 126 is pivotally coupled to hull 104. More specifically, a rigid arm 164 extends radially from each damper 126 to a fulcrum 160 fixably secured to hull 104 at the same axial position along hull 104 as center of rotation 128. Each fulcrum 160 includes pivot point 162 (e.g., a hole) and the radially inner end of each arm 164 is pivotally coupled to the corresponding pivot point 162 with a pin 165, thereby allowing each arm 164 and associated damper 126 to pivot about pivot point 162 relative to hull 104. Thus, arm 164 and the corresponding damper 126 may be described as having a retracted position (Figures 13-15) with arm 164 and damper 126 rotated to positions radially adjacent hull 104 and an extended position (Figure 16) with arm 164 and damper 126 rotated into a position extending radially from hull 104. A stopping/locking mechanism may be provided to limit the rotation of each arm 164 to 90° downward from vertical (Figure 16). To maintain arms 164 and dampers 126 in the extended positions (extending radially from hull 104 in a generally horizontal orientation), a pair of wires or cables 166a, 166b are attached to each damper 126 and hull 104 at attachment points 168, 170, respectively. Attachment points 168, 170 are positioned along hull 104 on opposite sides of the corresponding fulcrum 160. In this embodiment, attachment points 168, 170 comprise pulleys. Tension applied and maintained on wires 166a, 166b with dampers 126 in the extended positions to ensure dampers 126 remain in the extended positions.

[0055] The assembly, deployment, and installation of offshore structure 10Oj is shown in Figures 13-16. In Figure 13, the installation of dampers 126 onto hull 104 is shown, in Figure 14, the deployment of structure 10Oj to the installation site is shown, and in Figures 15 and 16, the installation of structure 10Oj at the installation site is shown.

[0056] Referring now to Figure 13, the coupling of one damper 126 and arm 164 to hull 104 is shown, it being understood that each damper 126 is pivotally coupled to hull 104 in the same manner to form offshore structure 10Oj. In Figure 13, deck 106 is not coupled to upper end 104a of hull 104 prior to installation of dampers 126, however, in other embodiments, deck 106 can be coupled to upper end 104a prior to installation of dampers 126. Although one damper 126 is shown being pivotally coupled to hull 104 in Figure 13, in general, the same approach can be used to pivotally couple other embodiments of dampers disclosed herein to hull 104 (e.g., dampers 150, 151 , 152). In general, coupling of dampers 126 to hull 104 can be performed at the shipyard dry dock, quayside, near shore, or at the desired installation site for structure 10Oj.

[0057] As shown in Figure 13, one or more variable ballast chambers 1 16 are selectively ballasted and/or deballasted to oriented hull 104 in a horizontal orientation while ensuring hull 104 floats at the surface 108. In this embodiment, each damper 126 and corresponding arm 164 is pre-assembled and then coupled to hull 104 one at a time. In particular, with hull 104 in the horizontal orientation at the surface 108, a crane is employed to manipulate a crane sling 158 suspending damper 126 and arm 164 extending therefrom directly above hull 104 at the desired axial positon along hull 104 (e.g., with the end of arm distal damper 126 positioned at the center of rotation 128 of hull 104). Next, the crane lowers crane sling 158, damper 126, and arm 164 to pivotally couple the end of arm 164 distal damper 126 to fulcrum 160 with pin 165. Sling 158 holds damper 126 and arm 164 in position as pin 165 is advanced through aligned holes in fulcrum 160 and the end of arm 164. With damper 126 pivotally coupled to hull 104 with fulcrum 160 and pin 165, and hull 104 in the horizontal orientation, hull 104 is rotated about axis 1 10 at the surface 108 to install a circumferentially adjacent damper 126 in the same manner as previously described. This process is repeated to install all of the dampers 126. [0058] The installed dampers 126 are disposed in the retracted positions with dampers 126 rotated toward upper end 104a and radially adjacent hull 104. With dampers 126 in the retracted positions, wires 166a are installed by passing each through a corresponding pulley 170 and coupling an end to the corresponding damper 126. Wires 166a have sufficient lengths to allow dampers 126 to rotate generally downward and away from hull 104 to the extended positions.

[0059] As previously described, the coupling of dampers 126 to hull 104 can be performed at the shipyard dry dock, quayside, near shore, or at the desired installation site for structure 10Oj. If dampers 126 are pivotally coupled to hull 104 at a location remote the installation site (e.g., dry dock, quayside, or near shore), hull 104 and dampers 126 pivotally coupled thereto can be transported and deployed to the offshore installation site in the horizontal orientation on a barge or floated out to the installation site in the horizontal orientation. In both cases, dampers 126 are preferably in the retracted positions to minimize interference with dampers 126 and any associated drag. If hull 104 and dampers 126 pivotally coupled thereto are transported to the installation site on a barge, the assembly can be lifted off the barge with a crane and placed into the water 102 in the horizontal orientation or floated off the barge in the horizontal orientation.

[0060] With dampers 126 installed and hull 104 in the horizontal orientation at the installation site, one or more variable ballast chambers 1 16 are ballasted and/or deballasted to transition hull 104 from the horizontal orientation to the vertical orientation with end 104a above the surface 108 and end 104b below the surface 108 as shown in FIG. 15, and then one or more variable ballast chambers 1 16 are ballasted and/or deballasted to position hull 104 at the desired draft in water 102. Next, as shown in Figure 16, dampers 126 are transitioned from the retracted positions to the extended positions. In this embodiment, wires 166b are installed following the rotation of dampers 126 to the extended positions. In particular, wires 166b are installed by passing each through a corresponding pulley 168 and coupling an end to the corresponding damper 126. In other embodiments, wires 166b are installed prior to rotating dampers 126 to the extended positions, and are employed to aid in rotating dampers 126 downward to the extended positions. In either case, once dampers 126 are in the extended positions, tension is applied to wires 166a, 166b to ensure dampers 126 remain in the extended positions.

[0061] With dampers 126 disposed in the extended position, wires 166a, 166b installed, and hull 104 in the vertical orientation at the desired position and draft in water 102, a mooring system may be installed to couple structure 100 to the sea floor. In general, deck 106 can be installed onto end 104a of hull 104 at any point (before, during or after installation of dampers 126).

[0062] While exemplary embodiments have been shown and described, modifications thereof can be made by one of ordinary skill in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations, combinations, and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. The inclusion of any particular method step or operation within the written description or a figure does not necessarily mean that the particular step or operation is necessary to the method. The steps or operations of a method listed in the specification or the claims may be performed in any feasible order, except for those particular steps or operations, if any, for which a sequence is expressly stated. In some implementations two or more of the method steps or operations may be performed in parallel, rather than serially. The recitation of identifiers such as (a), (b), (c) or (1 ), (2), (3) before operations in a method claim are not intended to and do not specify a particular order to the operations, but rather are used to simplify subsequent reference to such operations.