Abstract:
A method of fabricating a composite rope structure comprising the following steps. Impregnated yarns comprising fibers within a resin matrix are fabricated at a first location. The impregnated yarns are transported from the first location to a second location. The impregnated yarns are dispensed at the second location. The resin matrix of the dispensed impregnated yarns is cured at the second location to obtain the composite rope structure.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. Provisional Patent Application Ser. No. 60/931,088 filed May 19, 2007, the contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to composite rope structures and, in particular, to systems and methods for fabricating cured composite rope structures. 
       BACKGROUND 
       [0003]    The need often exists for a rope structure to be arranged in tension between two objects. The characteristics of a given type of rope structure determine whether that type of rope structure is suitable for a specific intended use. Characteristics of rope structures include breaking strength, elongation, flexibility, weight, and surface characteristics such as abrasion resistance and coefficient of friction. Additionally, environmental factors such as heat, cold, moisture, UV light, bending, abrasion, and the like may affect the characteristics of a rope structure. 
         [0004]    The intended use of a rope thus typically determines the acceptable range for each characteristic of the rope. The term “failure” as applied to rope will be used herein to refer to a rope being subjected to conditions beyond the acceptable range associated with at least one rope characteristic. 
         [0005]    Composite rope structures have been proposed for certain environments. Composite rope structures comprise fibers arranged within a resin matrix. The resin may be cured or uncured: when uncured, the resin is plastic or malleable; when cured, the resin is no longer flexible, and a cured composite rope structure is relatively rigid. 
         [0006]    One environment in which the characteristics of a composite rope structure may be desirable is a deepwater drilling system. The present invention will be described below in the context of a mooring system for a deepwater drilling system, but the principles of the present invention may be employed in other environments in which the characteristics of composite rope structures may be desirable. 
         [0007]    The need thus exists for improved composite rope structures and in particular for systems and methods for producing and deploying composite rope structures. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention may be embodied as a method of fabricating a composite rope structure comprising the following steps. Impregnated yarns comprising fibers within a resin matrix are fabricated at a first location. The impregnated yarns are transported from the first location to a second location. The impregnated yarns are dispensed at the second location. The resin matrix of the dispensed impregnated yarns is cured at the second location to obtain the composite rope structure. 
         [0009]    The present invention may also be embodied as a method of fabricating a composite rope structure comprising the following steps. Impregnated yarns comprising fibers within a resin matrix are fabricated at a first location. The impregnated yarns are collected on a plurality of yarn bobbins. The impregnated yarns on the plurality of yarn bobbins are combined at the first location to obtain uncured strands. The uncured strands are collected on a plurality of strand bobbins. The uncured strands on the plurality of strand bobbins are combined at the first location to obtain an uncured rope structure. The uncured rope structure is collected on a rope bobbin. The uncured rope structure collected on the rope bobbin is transported from the first location to a second location. The uncured rope structure is dispensed at the second location by removing the uncured rope structure from the rope bobbin. The resin matrix is cured at the second location to obtain the composite rope structure. 
         [0010]    The present invention may also be embodied as a system for fabricating a composite rope structure comprising a twisting system, a first release agent stage, a first combining system, a second release agent stage, and a second combining system. The twisting system twists fibers within a resin matrix to obtain impregnated and twisted yarns. The first release agent stage applies release agent to the impregnated and twisted yarns. The first combining system combines the impregnated and twisted yarns to obtain uncured strands. The second release agent stage applies release agent to the uncured strands. A second combining system combines the uncured strands to obtain the composite rope structure 
         [0011]    The present invention may also be embodied as a system for deploying a composite rope structure comprising a rope bobbin, a heating element, and a shaping die. The rope bobbin supports an uncured rope structure comprising fibers and a resin matrix. The heating element heats the uncured rope structure such that the uncured resin matrix cures. The shaping die engages the uncured rope structure to maintain the uncured rope structure in a desired geometry as the resin matrix cures. 
         [0012]    The present invention may also be embodied as a system for fabricating and deploying a composite rope structure comprising a fabricating system at a first location and a deploying system at a second location. The fabricating system comprises a twisting system and first and second combining systems. The twisting system twists fibers within a resin matrix to obtain impregnated yarns. The first combining system combines uncured yarns to obtain uncured strands. The second combining system combines the uncured strands to obtain the uncured rope structure. The deploying system comprises a rope bobbin, a heating element, and a shaping die. The rope bobbin supports an uncured rope structure comprising fibers and a resin matrix. The heating element heats the uncured rope structure such that the uncured resin matrix cures. The shaping die engages the uncured rope structure to maintain the uncured rope structure in a desired geometry as the resin matrix cures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a somewhat schematic view of a deepwater drilling system employing a cured composite rope structure of the present invention; 
           [0014]      FIG. 2  is a somewhat schematic view of a portion of the deepwater drilling system of  FIG. 1  further depicting an onsite curing system used to cure the uncured composite rope structure according to the principles of the present invention; 
           [0015]      FIG. 3  is a highly schematic view of an example twisting system used as part of the process of fabricating the cured composite rope structure depicted in  FIGS. 1 and 2 ; 
           [0016]      FIG. 4  is a highly schematic view of a first combination system that may be used as part of the process of fabricating the cured composite rope structure depicted in  FIGS. 1 and 2 ; 
           [0017]      FIG. 5  is a highly schematic view of a second combination system that may be used as part of the process of fabricating the cured composite rope structure depicted in  FIGS. 1 and 2 ; and 
           [0018]      FIG. 6  is a highly schematic view of the onsite curing system depicted in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring initially to  FIG. 1  of the drawing, depicted therein is a deepwater drilling system  20  employing one or more cured composite rope structures  22  fabricated according to the principles of the present invention. The deepwater drilling system  20  is not per se part of the present invention and will be described herein only to the extent necessary for a complete understanding of the present invention. 
         [0020]    The deepwater drilling system  20  comprises a platform  30  secured at a desired location  32  on the ocean surface  34  by a mooring system  36  connected to the ocean floor  38 . The mooring system  36  comprises a plurality of mooring lines  40  that extend in a radial pattern from the platform  30 . The mooring lines  40  are secured to pilings  42  driven into the ocean floor  38 . Each mooring line  40  is taut but has some flexibility and thus forms a catenary between the platform  30  and the ocean floor  38 . While only two mooring lines  40  are depicted in  FIG. 1 , typically twelve anchor lines  40  are provided. 
         [0021]    Each anchor line comprises a top section  50 , a bottom section  52 , and an intermediate section  54 . The top sections  50  are coupled to the intermediate sections  54  by upper coupler assemblies  56 , while the bottom sections  52  are coupled to the intermediate sections  54  by lower coupler assemblies  58 . In the example mooring system  36 , the intermediate sections  54  are formed by the cured composite rope structure  22  of the present invention. 
         [0022]    Referring now to  FIG. 2  of the drawing, depicted therein is an onsite curing system  60  that is supported by the platform  30 . The onsite curing system  60  comprises a rope bobbin  62  and a curing assembly  64 . The rope bobbin  62  stores an uncured (or partly cured) composite rope structure  22   a . The uncured composite rope structure  22   a  is unwound from the rope bobbin  62  and passed through the curing assembly  64  to form the cured composite rope structure  22 . 
         [0023]    In both the cured state  22  and uncured state  22   a , the composite rope structure of the present invention comprises a plurality of fibers embedded within a matrix of resin, as will be described in further detail below. Examples of composite rope members in connection with which the present invention may be used are described in the Applicant&#39;s copending U.S. Patent Application Ser. Nos. 60/930,853 (Attorney Matter No. P215308) and 60/931,089 (Attorney Matter No. P215422). 
         [0024]    In the uncured state  22   a , the resin matrix is uncured and is thus malleable or plastic. The uncured composite rope structure  22   a  is flexible, allowing it to be wound onto and unwound from the rope bobbin  62 . In the cured state  22 , the resin is cured and no longer malleable or plastic. Accordingly, the cured composite rope structure  22  is sufficiently rigid that it cannot be wound onto the rope bobbin  62 . 
         [0025]    By supporting the curing system  60  on the platform  30 , the uncured composite rope structure  22   a  may be stored and transported in rolled form on one or more rope bobbins  62 . The rope bobbins  62  can hold thousands of feet of the uncured composite rope structure  22   a  in easily manageable packages. Then, immediately prior to deployment, the uncured composite rope structure  22   a  is passed through the curing assembly  64  and cured into the relatively rigid cured composite rope structure as depicted in  FIGS. 1 and 2 . The cured composite rope structure  22  thus may be engineered to function as one or more of the intermediate sections  54  of the anchor lines  40 . 
         [0026]    Referring now to  FIGS. 3-6  of the drawing, one example of the process of fabricating an example uncured composite rope structure  22   a  and then curing the uncured composite rope structure  22   a  to form the example cured composite rope structure  22  will now be described in detail. The process of manufacturing the example cured composite rope structure  22  comprises a twisting step depicted in  FIG. 3 , a first combination step depicted in  FIG. 4 , a second combination step depicted in  FIG. 5 , and a curing step depicted in  FIG. 6 . The twisting step, first combination step, and second combination step will be performed at a dedicated manufacturing facility, while the curing step will be performed onsite as depicted, for example, in  FIG. 2 . 
         [0027]    Referring first to  FIG. 3 , depicted therein is a twisting system  120  for twisting impregnated yarns  122 ; the impregnated yarns  122  are identified in their untwisted state by reference character  122   a  and in their twisted state by reference character  122   b . The use of broken lines in  FIGS. 2-6  indicates that the resin matrix is uncured, while the use of solid lines indicates that the resin matrix is cured. 
         [0028]    The impregnated yarns  122  are composite structures comprising fibers and resin. The fibers are primarily responsible for the strength properties of the yarns  122  under tension loads. The resin forms a matrix of material that surrounds the fibers and transfers loads between the fibers. The resin matrix further protects the fibers from the surrounding environment. As examples, the resin matrix can be formulated to protect the fibers from heat, abrasion, UV, and other external environmental factors. 
         [0029]    The example resin portion of the impregnated yarns  122  exists in an uncured state and a cured state. In the uncured state, the resin material is flexible, and the matrix allows the impregnated yarns  122  to be bent, twisted, and the like. In general, the resin matrix becomes more plastic or malleable when heated, up to a cure temperature. Above the cure temperature, the resin matrix cures and becomes substantially more rigid. The properties of the resin matrix can be adjusted for manufacturing convenience and/or for a particular intended operating environment of the final composite rope structure. 
         [0030]    The example impregnated yarns  122  comprise approximately 90% by weight of fibers and approximately 10% by weight of resin. The fibers may be in a first range of substantially between 85% and 95% by weight of the yarn but in any event should be within a second range of substantially between 70% and 98% by weight of the yarn. The resin may be in a first range of substantially between 5% and 15% by weight of the yarn but in any event should be within a second range of substantially between 1% and 30% by weight of the yarn. Other combinations of resin and fibers can be used to implement the principles of the present invention. 
         [0031]    In particular, another example of the impregnated yarns  122  comprises approximately 80% by weight of fibers and approximately 20% by weight of resin. The fibers may be in a first range of substantially between 75% and 90% by weight of the yarn but in any event should be within a second range of substantially between 50% and 95% by weight of the yarn. The resin may be in a first range of substantially between 10% and 25% by weight of the yarn but in any event should be within a second range of substantially between 5% and 50% by weight of the yarn. 
         [0032]    The example fibers are glass fibers but may be one or a combination of carbon fibers, aramid fibers, polyester fibers, HMPE, basalt, Vectran, PBO, PBI, and ceramic fibers. The resin is a thermoplastic polyurethane, but other thermoplastic materials or the combination of thermoplastic and thermosetting resin systems may also be used. Other suitable thermoplastic materials include polyester, polyethylene, polypropylene, nylon, PVC, and their mixtures may also be used. Other compositions of resins and fibers can be used to implement the principles of the present invention. 
         [0033]    The example twisting system  120  comprises a first bobbin  124   a  for storing the untwisted impregnated yarns  122   a  and a second bobbin  124   b  for storing the twisted impregnated yarns  122   b . The untwisted impregnated yarn  122   a  is unwound from the first bobbin  124   a , twisted, and taken up on the second bobbin  124   b  as the twisted impregnated yarn  122   b.    
         [0034]    In the example twisting system  120 , the second bobbin  124   b  rotates about a primary axis of rotation A and also rotates about a twist axis of rotation B defined by the impregnated yarn  122 . The rotation of the second bobbin  124   b  about the primary axis A and the twist axis B converts the untwisted impregnated yarn  122   a  into the twisted impregnated yarn  122   b  and winds the twisted impregnated yarn  122   b  on the second bobbin  124   b . Where the fibers forming the untwisted impregnated yarn  122   a  are substantially straight and parallel, the fibers forming the twisted impregnated yarn  122   b  take on a generally helical configuration. 
         [0035]    The untwisted impregnated yarn  122   a  may be twisted at room temperature. However, to facilitate the twisting process, the twisting system  120  further optionally comprises a heating stage  126  for heating the untwisted impregnated yarns  122   a  before, as, and/or after they are twisted. The heating stage  126  increases the temperature of the resin matrix of the untwisted impregnated yarns  122   a  to a temperature that is elevated but below the cure temperature of the resin matrix. 
         [0036]    By softening the resin forming the matrix portion of the untwisted impregnated yarns  122   a , the fibers can more easily be twisted into the substantially helical configuration. Also, when preheated prior to, as, and/or after they are twisted and then allowed to cool, the resin matrix portion of the twisted impregnated yarns  122   b  is more likely to maintain the fibers in the substantially helical configuration. 
         [0037]    The example twisting system  120  further optionally comprises a release agent stage  128  for applying a release agent to the twisted impregnated yarns  122   b  as they are taken up on the second bobbin  124   b . The release agent or similar chemicals help to prevent the binding among the twisted impregnated yarns at the elevated temperature or when curing in the subsequent combination of the twisted impregnated yarns  122   b  with other rope components as will be described below. 
         [0038]      FIG. 4  illustrates a first example combining system  130  for combining multiple uncured twisted impregnated yarns  122   b  into an uncured strand  132 . The example strand  132  comprises seven twisted impregnated yarns  122   b  in what will be referred to as a 1×7 configuration. The twisted impregnated yarns  122   b  may, however, be combined using fewer or more yarns and in combination structures other than a 1×7 configuration. 
         [0039]    To form the example strand  132 , seven of the second bobbins  124   b  are supported by a first rotator assembly  134 . The first rotator assembly  134  is or may be conventional and will be described herein only as necessary for a complete understanding of the present invention. The example first rotator assembly  134  comprises a central bobbin mount  136  and a six perimeter bobbin mounts  138 . The central bobbin mount  136  allows the second bobbin  124   b  supported thereon to rotate about its primary axis A. The second bobbins  124   b  are supported by the perimeter bobbin mounts  138  for rotation about their primary axes A. 
         [0040]    The perimeter bobbin mounts  138  further support the second bobbins  124   b  for rotation together about a system axis C defined by the first rotator assembly  134 . The central bobbin mount  136  may be supported with the perimeter bobbin mounts  138  such that the second bobbin  124   b  supported thereby also rotates about the system axis C with the second bobbins  124   b  supported at the perimeter bobbin mounts  138 . Alternatively, the central bobbin mount  136  may be supported independent of the perimeter bobbin mounts  138  such that the second bobbin  124   b  supported thereby rotates only about its primary axis A and not about the system axis C. 
         [0041]    As the twisted impregnated yarns  122   b  are withdrawn from the first rotator assembly  134 , the twisted impregnated yarns  122   b  unwound from the second bobbins  124   b  at the perimeter bobbin mounts  138  are combined with the twisted impregnated yarn  122   b  unwound from the second bobbin mount  124   b  at the central bobbin mount  136  to form the strand  132 . In the example system  130 , the strand  132  is taken up on a strand bobbin  140 . 
         [0042]    The twisted yarn  122   b  unwound from the second bobbin mount  124   b  at the central bobbin mount  136  forms a core impregnated yarn of the strand  132 . The fibers in the core impregnated yarn maintain the substantially helical configuration created by the twisting system  120 . The twisted impregnated yarns  122   b  around core yarn will be referred to as the perimeter yarns. The fibers in the perimeter yarns maintain the substantially helical configuration created by the twisting system  120  but will also have a secondary helical configuration centered about the core yarn. The fibers in the perimeter yarns thus have a substantially double helical configuration. 
         [0043]    The twisted impregnated yarns  122   b  may be combined to form the strand  132  at room temperature. However, to facilitate the combination process, the first combination system  130  further optionally comprises a heating stage  142  for heating the twisted impregnated yarns  122   b  before and/or as they are combined. The heating stage  142  increases the temperature of the resin matrix of the twisted impregnated yarns  122   b  to a temperature that is elevated but below the cure temperature of the resin matrix. 
         [0044]    By softening the resin forming the matrix portion of the twisted impregnated yarns  122   b , the twisted impregnated yarns  122   b  can more easily be combined into the strands  132  with fibers of the core yarns in the substantially helical configuration and the fibers in perimeter yarns in the substantially double helical configuration. Also, when preheated prior to, as, and/or after they are twisted and then allowed to cool, the resin matrix portion of the twisted impregnated yarns  122   b  is more likely to maintain the fibers of the core impregnated yarn in the helical configuration and the fibers in the perimeter impregnated yarns in the substantially double helical configuration. 
         [0045]    The example combination system  130  further optionally comprises a release agent stage  144  for applying a release agent to the strand  132  as it is are taken up on the strand bobbin  140 . The release agent or similar chemicals help to prevent the binding among the strands  132  at the elevated temperature or when curing in the subsequent combination of the strand  132  with other rope components as will be described below. 
         [0046]    The example second combination system  130  further comprises an optional shaping die  146 . The shaping die  146  is arranged where the ends are twisted and joined together. 
         [0047]      FIG. 5  illustrates a second combining system  150  for combining multiple strands  132  into a rope structure  152 . The example rope structure  152  comprises seven strands  132  in what will be referred to as a 7×7 configuration. The strands  132  may, however, be combined using fewer or more yarns and in combination structures other than a 7×7 configuration. 
         [0048]    To form the example rope structure  152 , seven of the strand bobbins  140  are supported by a second rotator assembly  154 . The second rotator assembly  154  is or may be conventional and will be described herein only as necessary for a complete understanding of the present invention. The example second rotator assembly  154  comprises a central bobbin mount  156  and a six perimeter bobbin mounts  158 . The central bobbin mount  156  allows the strand bobbin  140  supported thereon to rotate about its primary axis. The strand bobbins  140  supported by the perimeter bobbin mounts  158  are supported for rotation about their primary axes. 
         [0049]    The perimeter bobbin mounts  158  further support the strand bobbins  140  for rotation together about a system axis D defined by the second rotator assembly  154 . The central bobbin mount  156  may be supported with the perimeter bobbin mounts  158  such that the strand bobbin  140  supported thereby also rotates about the system axis D with the strand bobbins  140  supported at the perimeter bobbin mounts  158 . Alternatively, the central bobbin mount  156  may be supported independent of the perimeter bobbin mounts  158  such that the strand bobbin  140  supported thereby rotates only about its primary axis and not about the system axis D. 
         [0050]    As the strands  132  are withdrawn from the second rotator assembly  154 , the strands  132  unwound from the strand bobbins  140  at the perimeter bobbin mounts  158  are combined with the twisted impregnated strand  132  unwound from the strand bobbin  140  at the central bobbin mount  156  to form the rope structure  152 . In the example system  130 , the rope structure  152  is taken up on a rope bobbin  62  described above. 
         [0051]    The strand  132  unwound from the strand bobbin  140  at the central bobbin mount  156  forms a core strand of the rope structure  152 . The fibers in the core strand maintain the shape created by the first combination system  130 . The strands  132  around core strand will be referred to as the perimeter strands. The fibers in the perimeter yarns of the perimeter strands maintain the shape created by the first combining system  130  but will also have a tertiary helical configuration centered about the core strand. The fibers in the perimeter yarns thus have a substantially triple helical configuration. 
         [0052]    The strands  132  may be combined to form the rope structure  152  at room temperature. However, to facilitate the combination process, the second combination system  150  further optionally comprises a heating stage  162  for heating the strands  132  before, as and/or after they are combined. The heating stage  162  increases the temperature of the resin matrix of the strands  132  to a temperature that is elevated but below the cure temperature of the resin matrix. 
         [0053]    By softening the resin forming the matrix portion of the strands  132 , the strands  132  can more easily be combined into the strands  132  with fibers of maintaining the appropriate helical configurations. Also, when preheated prior to, as, and/or after they are twisted and then allowed to cool, the resin matrix portion of the strands  132  is more likely to maintain the fibers in the appropriate helical configurations. 
         [0054]    The example second combination system  150  further comprises an optional shaping die  164 . The shaping die  164  is arranged where the ends are twisted and joined together. 
         [0055]    Referring now to  FIG. 6 , depicted therein in more detail is the onsite curing system  60  described above with reference to  FIG. 2 . The onsite curing system  60  was described above in the context of deploying anchor lines used by an deepwater drilling system  20 , but the onsite curing system may be used to deploy cured composite rope structures in other environments, for other purposes, and at other locations. 
         [0056]    The example curing assembly  64  is shown to comprise infeed rollers  170 , a heating element  172 , an intermediate roller  174 , a shaping die  176 , and outfeed rollers  178 . 
         [0057]    As the uncured composite rope structure  22   a  is unwound from the rope bobbin  62 , the uncured composite rope structure  22   a  first passes through the infeed rollers  170 . The infeed rollers  170  support and direct the uncured composite rope structure  22   a  as it is unwound from the rope bobbin  62 . 
         [0058]    The uncured composite rope structure  22   a  is next fed through the heating element  172 . The heating element  172  is typically an elongate oven capable of raising the temperature of the resin matrix of the uncured rope structure  22   a  to above the cure temperature of the resin matrix. The heating element  172  may control the pressure and/or other environmental factors that may affect the curing of the resin matrix. 
         [0059]    As the uncured rope structure  22   a  leaves the heating element  172 , the temperature of the resin matrix has been elevated to above the cure temperature, which begins the chemical process that causes the resin matrix to cure. Some time may be required for the resin matrix to fully cure. Accordingly, the composite rope structure  22   a  is still identified as being in the uncured state as it leaves the heating element  172  in  FIG. 6 . 
         [0060]    The uncured composite rope structure  22   a  leaving the heating element  172  is thus passed over the intermediate roller  174  to change the direction of the composite rope structure  22   a . In the example shown in  FIG. 6 , the still uncured composite rope structure  22   a  is fed through shaping die  176  which maintains the rope structure  22   a  in a desired geometry and directs the rope structure  22   a  in a desired direction as the resin matrix fully cures. After passing through the shaping die  176 , the composite rope structure is cured as indicated by the use of solid lines. The cured composite rope structure  22  is supported by outfeed rollers  178  as the rope structure  22  is deployed from the curing assembly  64 . 
         [0061]    Given the foregoing, it should be apparent that the present invention may be embodied in forms other than those described above. The scope of the present invention should be determined with reference to the claims appended hereto and not the foregoing detailed description of examples of the present invention.