Abstract:
A bearing system including a wheel assembly transmitting load to a damping assembly, wherein the wheel assembly is configured to rotate angularly relative to the damping assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the benefit of: U.S. Prov. Ser. No. 61/813,194 filed Apr. 18, 2013, and entitled “A Bearing System”, and International Application Ser. No. PCT/US2014/034553, filed Apr. 17, 2014, and entitled “Bearing System For Turret On A Vessel,” the contents of each being incorporated herein by reference in their entireties for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to vessels such as for offshore drilling or production vessels. More particularly, the present disclosure relates to a bearing system for turrets on such vessels and a method of installing bearing systems onto such vessels. 
     BACKGROUND 
     A bearing is generally defined as a device for positioning one element relative to another in such a manner that relative movement between the elements is possible. The elements have respective bearing surfaces, which are in contact with each other. 
     Bearings are generally employed in order to absorb loads and/or support one or more elements. The element may be rotating, for example a rotating shaft, or it may be fixed, for example a bridge or the like. A bearing may also be designed to be able to absorb both axial and radial forces. The bearing type should be chosen based on its anticipated application. 
     If there are large loads in a structure, where there has to be a movement between elements therein and where external influences result in fluctuating loads in the structure and its bearings, slide bearings, for example, may be employed. 
     The use is known also of various types of devices for supporting a turret on a vessel, for example a Floating Production, Storage and Offloading Vessel (FPSO), where these may be slide bearings, roller bearings or wheel suspension. A vessel of this type can be exposed to substantial wind, current and wave influences. 
     When harsh wind and wave impact occurs on a FPSO, the turret is pressed against the radial turret bearings. This movement and the vessels hog, sag and ovality/tolerances make it necessary to have some kind of radial flexibility on the wheels of a wheel bearing system. This ensures that the distribution of the radial loads is taken on many wheels, not only overloaded onto one or two wheels. A known design is to mount and spring load wheels, such as described in U.S. Pat. No. 5,860,382. The described structure has a spring-loaded wheel in a box assembly, with a spring rod fixed horizontally and vertically to the box assembly. The outer guiding of the box assembly is done by brackets or slots in the surrounding ship structure, or with large steel sections around the rotatable turret rail. And the spring rod is fastened to a lid that has to be bolted to the surrounding structure. This type of arrangement uses a fine alignment between the box assembly and the spring rod, and also has fine tolerances in the surrounding structure. The radial loads to go through the lid bolts, even when the springs are totally compressed and extreme stemming loads occur. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. 
     An object, according to some embodiments, is to provide a bearing having relatively large internal tolerances in a preassembled system. 
     According to some embodiments, an object is also to provide a robust bearing system that can be quickly mounted to a ship interface and easily adjusted with respect to the interface. 
     According to some embodiments, another object is to provide a system that leads large radial and/or axial loads through wedges into the ship interface structure. Such systems avoid large forces and shear loads on interface bolts, which also leads to fewer interface bolts used. 
     According to some embodiments, when the spring rod of the bearing is compressed (stemmed), any additional load goes through the outer housing/wedges and not through any internal system bolts. 
     According to some embodiments, the bearing system is a wheel bearing system. Such bearing systems may be used on turrets for FPSOs. In one example, the bearing system may be used as radial bearings. In another example, the bearing system may be used as axial bearings. 
     According to some embodiments, a bearing system is described that is configured to support rotation of a turret carried by a vessel. The rotation of the turret relative to the vessel is about a substantially vertical turret axis. The bearing system includes a plurality of bearing assemblies. Each bearing assembly includes: a roller in contact with the turret bearing surface; a linkage system configured to transmit force from the bearing surface toward the roller into a supporting structure of the vessel; and a mounting system configured to securely mount the bearing assembly to the supporting structure. The mounting system includes one or more wedge-shaped members shaped so as to provide precise positioning of the bearing assembly with respect to the supporting structure and positioned so as to facilitate transmission of force from the linkage system to the supporting structure. According to some embodiments, the bearing assembly is a substantially prefabricated cartridge-type subassembly configured for easy installation and/or removal from the supporting structure. According to some embodiments, the linkage system includes a compression spring system configured to allow movement of the roller in a direction perpendicular to the bearing surface. According to some embodiments, the linkage system is configured such that when the spring system is compressed to its maximum position, further force from the bearing surface towards the roller passes directly through the linkage system to the supporting structure without increasing a load on the spring system end piece. According to some embodiments, the linkage system includes one or more linkage elements (e.g. spherical bearings) configured to allow freedom of movement of linkage elements in directions parallel to the turret bearing surface, thereby facilitating manufacture and/or assembly of the bearing assembly. 
     According to some embodiments, the bearing assemblies are axial bearing assemblies, and according to other embodiments, the bearing assemblies are radial bearing assemblies. According to some embodiments, the mounting system includes one or more slidably mating thread-free mounting elements (e.g. tongue and groove elements) configured to restrain movement of at least a front portion of the bearing assembly with respect to the supporting structure. 
     According to some embodiments each of the bearing assemblies includes: a roller in contact with the turret bearing surface; a linkage system configured to transmit force from the bearing surface toward the roller into a supporting structure of the vessel, the linkage system comprising one or more linkage elements configured to allow freedom of movement of linkage elements in directions parallel to the turret bearing surface in a location contacted by the roller, the freedom of movement facilitating manufacture and/or assembly of the bearing assembly; and a mounting system configured to securely mount the bearing assembly to the supporting structure. 
     According to some embodiments, a method is described for installing a bearing system configured to support rotating of a turret carried by a vessel. The method includes: placing a prefabricated bearing assembly onto a supporting structure of the vessel; sliding the placed bearing assembly towards the bearing surface; inserting one or more wedge-shaped members into one more openings in the supporting structure; and adjusting the position of the bearing assembly with respect to the supporting structure and to the bearing surface by modifying the vertical position of the one or more wedge-shaped members. The wedge-shaped members are also positioned and configured to facilitate transmission of force from the linkage system to the supporting structure. According to some embodiments, after the adjusting of the position of the bearing assembly, the bearing assembly is fastened to the supporting structure using a plurality of bolt fasteners. According to some embodiments, the method also includes installing one or more shim pieces in proximity to the wedge-shaped members so as to aid in the adjusting the position of the bearing assembly. 
     According to some embodiments, a bearing system is described that includes a wheel assembly configured to transmit loads to a damping assembly via connecting means, wherein the connecting means enable angular rotation between the wheel assembly and the damping assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the subject disclosure, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
         FIG. 1  is a diagram illustrating a vessel supporting a turret using a bearing system, according to some embodiments; 
         FIG. 2  is a perspective view showing a bearing system for a rotatable turret, according to some embodiments; 
         FIG. 3  is a cross-section view of a bearing cartridge used for supporting a rotatable turret on a vessel, according to some embodiments; 
         FIGS. 4-1 and 4-2  are cross sectional views illustrating aspects of a bearing cartridge used for supporting a rotatable turret on a vessel, according to some embodiments; 
         FIG. 5  is a perspective view showing further aspects of a bearing cartridge used for supporting a rotatable turret on a vessel, according to some embodiments; 
         FIG. 6  is a perspective view of a bearing cartridge installed on a cartridge support structure in a vessel, according to some embodiments; 
         FIG. 7  is a perspective view of several bearing cartridges installed on a vessel, according to some embodiments; 
         FIG. 8  is a perspective view showing further aspects of a bearing cartridge used for supporting a rotatable turret on a vessel, according to some embodiments; 
         FIGS. 9-1, 9-2, 9-3 and 9-4  are perspective views showing further aspects of a cartridge support structure and vessel structure onto which a bearing cartridge can be mounted, according to some embodiments; and 
         FIGS. 10-1, 10-2, 10-3 and 10-4  are perspective views showing further aspects of mounting a bearing cartridge to a support structure in a vessel, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the subject disclosure only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the subject disclosure. In this regard, no attempt is made to show structural details of the subject disclosure in more detail than is necessary for the fundamental understanding of the subject disclosure, the description taken with the drawings making apparent to those skilled in the art how the several forms of the subject disclosure may be embodied in practice. Further, like reference numbers and designations in the various drawings indicate like elements. 
       FIG. 1  is a diagram illustrating a vessel supporting a turret using a bearing system, according to some embodiments. Vessel  112  is shown on the surface of seawater  102 . According to some examples, vessel  112  is a Floating Production, Storage and Offloading Vessel (FPSO) configured to receive hydrocarbons produced from subsea subterranean reservoirs, to processing and/or store the received hydrocarbons. Vessel  112  includes turret  110  and is supported by a surrounding vessel structure  116 . The bearing system  120  can include slide bearings, roller bearings and/or wheel suspensions. 
     Vessel  112  can be exposed to substantial wind, current and wave influences. When harsh wind and wave impact occurs on vessel  112 , the turret  110  is pressed against the radial turret bearings, which form part of the bearing system  120 . In many designs a certain amount of radial flexibility on the bearing system  120  is highly beneficial to accommodate such movements along with the vessel&#39;s hog, sag and ovality/tolerances. Such radial flexibility ensures that the distribution of the radial loads is taken on many wheels, rather than overloaded on any one or two wheels. 
     According to some embodiments, bearing system  120  includes a plurality of wheel bearing cartridges to support rotatable turret  110  on FPSO  112  that allow the FPSO  112  to weathervane 360° around vertical turret axis  114 , as shown by the dotted arrows. Risers  130  and the anchor chains  132  are locked to the lower part of turret  110 . According to some embodiments, rotating turret  110  is also used to supply umbilical  136  to subsea system  134  which can be, for example, a subsea pump and/or compressor. 
       FIG. 2  is a perspective view showing a bearing system for a rotatable turret, according to some embodiments. In the example shown, bearing system  120  includes a total of 24 bearing cartridges, such as bearing cartridges  210 ,  212 ,  214  and  216 , which are placed around a rotatable turret  110  (a portion of which is shown). Although  24  bearing cartridges are shown in this example, the number of cartridges will vary from ship to ship. According to some alternative embodiments, groups of cartridges can be radially spread out instead of evenly spaced, as shown. For purposes of clarity, portions of the rotatable turret  110  are not shown, and the structural ship walls between the cartridges are not shown in full height. 
       FIG. 3  is a cross-section view of a bearing cartridge (e.g., bearing cartridge  210 ) used for supporting a rotatable turret on a vessel, according to some embodiments. In the example shown, bearing cartridge cartridge  210  includes a fixed (to ship or receiving structure) outer housing with an inner moving wheel assembly box and a disc spring or damping system. When used in an FPSO, the horizontal turret movement/loads/ovality can push the inner wheel/box assembly radially away from turret center so as to compress the damping assembly. 
     As shown in  FIG. 3 , a wheel  301  with a radial plain bearing  302  is on a wheel shaft  303 . The wheel shaft  303  and radial plain bearing  302  are fixed inside inner box  304  by axial plain bearings  305  on the top of and under the wheel  301 . According to some alternative embodiments, roller bearing can be used instead of one or more of the plain bearings shown. The inner box  304  is open to the front side (the side facing the turret center, when installed) and to the back side (the side away from the turret center, when installed). 
     A spring shaft  306  is placed behind the wheel and is also fixed on the top and bottom to the box  304 . A first spherical bearing  307  and a rod end  308  are placed on the spring shaft  306 . The first spherical bearing  307  is fixed vertically in the inner box  304  by two thin pipes  309 . In this example, one of the pipes  309  is placed over the first spherical bearing  307  and the other is placed below bearing  307 . 
     According to some embodiments, the rod end  308  is fastened and/or threaded to a damping assembly via a spring rod  310 . A second spherical bearing  311  is placed on the back end of the spring rod  310 . The second spherical bearing  311  is fixed in a spring housing lid  312  and a cover  313 . The cover  313  can be fastened to the spring housing lid  312 , for example, by bolts  314 . The spring housing lid  312  can be fastened to a spring housing  315  by bolts  316 . According to some embodiments, the damping assembly  330  includes a number of disc springs  317  that are placed on the spring rod  310 . The disc springs  317  can be arranged in any of a number of different ways on the spring rod  310  depending on the purpose as will be known by one skilled in the art. Alternatively, different disc types (e.g. differing in thickness, shape and/or material) can also be combined on the same rod assembly  310 . The disc springs  317  and spring rod  310  can be designed to be preloaded or not, depending on the particular application. According to some alternative embodiments to disk springs  317 , conventional compression springs, elastomers or different combinations of these three types can be used. According to some alternative embodiments, the damping system  330  might comprise a piston rod (instead of the spring rod  310 ) and use hydraulics to obtain and/or apply loads so to exert damping effect. The spring housing  315  is fastened to an outer housing  318  by, for example, bolts  319 . 
     In the example shown in  FIG. 3 , the spring rod assembly is thus freely hinged (using spherical bearings  307  and  311 ) both within box  304  and within spring housing  315 . It has been found that providing such freedom of movement enables parts of the bearing cartridge  210  to have substantially rougher tolerances. For example, the various parts do not have to be perfectly aligned when assembled. This enables low production and assembling costs. According to some embodiments, conventional compression springs and/or elastomers are used rather than disc springs for the damping assembly  330 . Another alternative is to replace the spring system with a piston rod and use hydraulic fluid to obtain/apply loads. 
     According to some embodiments, the outer housing  318  has in front a tongue and groove interface to the ship structure to take vertical and side forces of the turret, as will be described in further detail, infra. 
       FIGS. 4-1 and 4-2  are cross sectional views illustrating aspects of a bearing cartridge used for supporting a rotatable turret on a vessel, according to some embodiments. Referring to  FIG. 4-1 , radial turret forces (e.g. due to movement, tolerances, and/or ovality) press radial turret rail  410  away from the central axis of turret  110 , as shown by dotted arrow  400 . Wheel  301  and inner box  304  slide backwards, and the disc springs  317  are compressed. The load is then transferred through the disc springs  317 , via the spring housing lid  312 , through spring housing  315  and into the outer housing  318 . The force is passed through wedge supports  422  and main wedges  420  into the vessel structure  116 , as shown by the dotted arrows. Note that the maximum compression distance of the damping system  330  is the gap s between the flange of rod end  308  and front of the spring housing  315 . 
     Referring to  FIG. 4-2 , when the maximum compression for damping system  330  is reached (i.e. s=0), any additional increasing load goes from flange of rod end  308  through the front of spring housing  315  and into the outer housing  318 , wedge supports  422  and main wedges  420 . This configuration prevents overloading on the spring housing bolts  316  and spring housing lid  312 . 
     In the described embodiments, the horizontal load from the wheel/spring system is going via the outer housing  318  and then through a pair of wedge assemblies ( 422  and  420 ) into the cartridge support structure  116 . This reduces the need for vertical fastening bolts. Furthermore, the few vertical fastening bolts that are used are not exposed to any large shear forces. The main wedges  420  have sloped interfaces  424  to the cartridge support structure  116 , making it easy to make fine adjustments in the horizontal position of cartridge system  210 , by moving the wedges  420  up or down. 
       FIG. 5  is a perspective view showing further aspects of a bearing cartridge (e.g., bearing cartridge  210 ) used for supporting a rotatable turret on a vessel, according to some embodiments. Visible in  FIG. 5  on bearing cartridge  210  are a number of plain linear bearing plates are fastened by bolts close to the inner corners of the outer housing  318 , such as plain bearing  321  fastened by bolts  320 . In the embodiment shown in  FIG. 5 , a plurality of first linear bearing plates (such as bearing plate  321 ) are placed in front, and a plurality of second linear bearing plates in the back (such as bearing plate  322 ). The plates fix the inner box  304  in vertical and lateral directions. According to some embodiments, the bearing plates can be made of a softer material (for example bronze, brass alloys etc.). According to some alternative embodiments, matching hard metal plates (stainless steel etc.) are fastened to the inner box  304 . According to some other alternate embodiments, the soft material plates are fastened to the inner box  304  and the hard plates (if used) are fastened to the outer housing  318 . According to some embodiments, in front of the outer housing  318  there are a plurality of fine machined surfaces for ship interface mounting: namely horizontal bearing surfaces  523  and vertical bearing surfaces  524 . 
       FIG. 6  is a perspective view of a bearing cartridge installed inside a cartridge support structure in a vessel, according to some embodiments. Bearing cartridge  210  is shown mounted in a cell  610  that forms part of surrounding vessel structure  116 . More particularly, in this example, cell  610  is formed on the deck of the vessel and has four walls. The sidewalls are solid, the rear wall has a large access window  612  and the front wall as a smaller wheel window  614 . When bearing cartridge  210  is installed on cartridge support structure  620  within cell  610 , the wheel  301  protrudes through window  614  and contacts outer annular rail  410  of the turret  110 . Also visible in  FIG. 6  are rear fastening bolts  630  used to secure bearing cartridge  210  to cartridge support structure  620 . Note, as will be described in further detail infra, no fastening bolts are used to secure the front end of bearing cartridge  210  to support structure  620 . 
       FIG. 7  is a perspective view of several bearing cartridges installed on a vessel, according to some embodiments. As can be seen, bearing cartridges  210 ,  212 ,  214  and  216  are installed on support structures  620 ,  722 ,  724  and  726  respectively, which are positioned in cells  610 ,  712 ,  714  and  716  respectively. 
       FIG. 8  is a perspective view showing further aspects of a bearing cartridge used for supporting a rotatable turret on a vessel, according to some embodiments. Visible on the underside of bearing cartridge  210  are four ribs  831  that are positioned to fit just outside of the cartridge support structure rails (not shown) to provide for easy mounting and guiding of the bearing cartridge  210 . Also visible on the underside of cartridge  210  are two large windows  850  into which wedge supports  422  and main wedges  420  protrude when cartridge  210  is mounted. Two sets of three slotted holes  830  are also visible through which rear fastening bolts  630  (not shown) can pass. 
       FIGS. 9-1, 9-2, 9-3 and 9-4  are perspective views showing further aspects of a cartridge support structure and vessel structure onto which a bearing cartridge can be mounted, according to some embodiments.  FIG. 9-1  shows a support structure  620  which will be mounted (e.g. by welding) to a ship deck (not shown), before mounting the bearing system. In the front of the support structure  620  is a plurality of fine-machined surfaces within slots  962  and on the two inner side surfaces, as will be described in further detail, infra. The machined surfaces associated with slots  962  will fix the bearing cartridge vertically and laterally when mounted. According to some embodiments, in the middle of the support structure  620  a fine-machined surface  930  is formed where the rear bottom of the bearing cartridge will rest and be fastened by bolts and wedges. The structure  620  also has two large holes  950  to accommodate the wedge supports  422  and main wedges  420  when the bearing cartridge is mounted. Also visible are bolt holes  960  through which rear fastening bolts can pass. Note that the spacing of the outer edges of the rails  931  are dimensioned to match the small ribs  831  on the under side of the bearing cartridge (as shown in  FIG. 8 ). The use of the ribs  831  and rails  931  further ease the mounting and guiding of the bearing cartridge to the support structure  620 .  FIG. 9-2  shows a portion of the cell  610  (with walls shortened for clarity) into which the support structure  620  is welded. Note that according to some embodiments, the floor of the cell  610  is ship deck  926  which forms part of surrounding vessel structure  116 .  FIG. 9-3  shows the support structure  620  mounted (e.g. by welding) into cell  610  prior to mounting the bearing cartridge.  FIG. 9-4  shows further details of slots  962 . In the example shown, there are four horizontal fine-machined surfaces  928  (upper and lower for each slot) and two vertical fine-machined surfaces  929  (on the inner sides slot-arm). Surfaces  928  and  929  will contact surfaces  523  and  524 , respectively (which are visible in  FIGS. 5 and 8 ). 
       FIGS. 10-1, 10-2, 10-3 and 10-4  are perspective views showing further aspects of mounting a bearing cartridge to a support structure in a vessel, according to some embodiments.  FIG. 10-1  shows the bearing cartridge  210  being positioned on the support structure  620  after which it is slid forward as indicated by the dotted arrow. Note that the downward protruding ribs  831  fit just outside the outside edges of rails  931 , so as to aid in the positioning of bearing cartridge  210 .  FIG. 10-2  shows a desired position for the wheel  301  in relation to contacting the outer annular rail  410  of the turret  110 . Note that the exact desired position depends on the application and design of the system. For example, the desired position might be preloaded, where the wheel  301  touches the rail  410 , and the outer housing  318  is moved even closer to turret center so as to compress the damping system a predetermined amount. According to some embodiments, the desired position may be the wheel  301  just touching rail  410  (which is shown in  FIG. 10-2 ). According to some other embodiments, the desired position may be where the wheel  301  is spaced a predetermined distance (e.g. a few millimeters) from rail  410 . This positioning may be desirable, for example, due to tolerances and/or ovality. Note that slotted bolt holes  830  (visible in  FIG. 10-1 ) in the outer housing  318  can be used for adjustment purposes. Visible in  FIG. 10-3  is bolt bracket  1033  placed over the holes  830  and then fastened by bolts  630  and nuts  1035 . The bolts  630  keep the rear end of the cartridge  210  fixed vertically and laterally, but do not have to be designed to take large radial forces due to the wedge supports  422  and main wedges  420  as shown in  FIG. 10-4 .  FIG. 10-4  is a cross-section view through wedge support  422 , shim  1037  and main wedge  420  on the near side (or left side) of the cartridge. The tapered or wedge-shape of main wedge  420  is apparent in  FIG. 10-4 , as is a matching shape on the sidewall  1050  of hole  950  in support structure  620  that is engaged by main wedge  420 . 
     After the rough position of bearing cartridge  210  on support structure  620  is made, the wedge assemblies are installed, according to some embodiments. According to some embodiments, the wedge assembly includes a wedge support  422 , one or more shim plates  1037  (for larger adjustments), a main wedge  420 , a bolt plate  1039 , bolts  1040  and nuts  1041 . The main wedges  420  have slotted (or oblong) boltholes and a slope interface surface which engages the rear edge of holes  950  of support structure  620 . The radial placement of the cartridge  210  can be finely adjusted by moving the main wedges  420  up or down before the final tightening of all the fastening parts. Heavy radial (and lateral) loads onto the bearing cartridge  210  from the turret  110  in operation will mainly pass through the outer housing  318 , then into the lower part of the wedge assemblies and then into the support structure  620  and deck/ship walls in surrounding vessel structure  116 . In this way, the vertical bolts  630  do not take any large sheer forces. 
     According to some embodiments, the described bearing system allows relatively rough internal tolerances and alignment features for the inner parts of the bearing cartridge. The cartridge can be pre-mounted and/or the spring system preloaded. The cartridge-type mounting in the vessel allows for quick and easy mounting and/or dismounting in the vessel. The design also allows for easy fine-tuning of the radial position of the bearings in the vessel. The radial forces are transferred from bearing cartridge to vessel via wedges, with no large shear forces placed on interface bolts. The tongue-and-groove-type interface between the ship structure and the front end of the bearing cartridge are configured to take vertical forces and lateral forces while using very few interface bolts. The system described is thus also configured for easy inspection and/or lubrication of the wheels and turret rail. 
     While the subject disclosure is described through the above embodiments, it will be understood by those of ordinary skill in the art that modification to and variation of the illustrated embodiments may be made without departing from the inventive concepts herein disclosed. Moreover, while the preferred embodiments are described in connection with various illustrative structures, one skilled in the art will recognize that the system may be embodied using a variety of specific structures. Accordingly, the subject disclosure should not be viewed as limited except by the scope and spirit of the appended claims.