Abstract:
Systems and methods for longitudinally restraining a movable structure disclosed herein include, but are not limited to, providing a rack attached to a first structure and a chock attached to a second structure, wherein the rack and chock are configured to engage one another. Upon engagement, the chock may be locked into place with extendable jack screws, thereby restraining the movable structure in the longitudinal direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims the benefit of U.S. Provisional Application 61/665,210 filed on Jun. 27, 2012. 
     
    
     TECHNICAL FIELD 
     Background of the Invention 
       [0002]    The present invention relates to a locking system for movable structures. Large structures such as drilling facilities on offshore platforms are periodically repositioned as necessary for drilling operations. A typical repositioning method is to skid the facilities on skid beams or capping rails. Once positioned, these facilities must be stabilized and secured against external loads caused by such things as seismic events or high wind loadings. A need exists to quickly and securely lock the structure in position. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    An object of the present disclosure is directed to a system and method for locking movable structures. According to one aspect of the present disclosure, there is provided a longitudinal restraint system comprising a rack attached to a first structure, a chock coupled to a second structure, an actuating device configured to move the chock in relation to the rack, and a jack screw coupled to the second structure, wherein a portion of the jack screw is configured to engage a portion of the chock. In the exemplary embodiment, the rack comprises a plurality of teeth and the chock comprises a plurality of matching teeth, such that the rack and the chock may engage, thereby resulting in high friction along the longitudinal direction of the rack. 
         [0004]    In the exemplary embodiment, the rack is affixed to the deck of a vessel through welding, bolting, or other means known to those skilled in the art. The rack may have a longitudinal direction according the longitudinal direction of the skid beams. For example, it would be known to one skilled in the art of platform drilling, that a movable structure such as an offshore rig may be moved in the stern to bow direction but also in the port to starboard direction. Racks may be placed accordingly. In the exemplary embodiment, the racks follow the direction and location according to the placement of skidding beams along the surface of a vessel. The racks may also be placed on the side or undercarriage of the skidding beam itself, according to one embodiment of the disclosure. 
         [0005]    In one embodiment, the longitudinal restraint system is employed in regions, both land and sea, of high seismic activity. In still another embodiment of the present disclosure, the restraint system may be used in areas of high wind. 
         [0006]    In one embodiment, the longitudinal restraint system comprises a self-contained chassis, wherein the components of the longitudinal restraint system are housed. The chassis may be built around, or be part of a skid guide devised to skid along a skidding beam or capping rail. A person skilled in the art would recognize the benefit of a chassis as allowing the entire longitudinal restraint system to be disconnected from, and reconnected to, a movable structure. Therefore, longitudinal restraints engineered for higher or lower loads may be swapped out as required. 
         [0007]    The longitudinal restraint system, according to one embodiment of the present disclosure, comprises jack screws. Jack screws may be hydraulic, but are preferably mechanical. Jack screws are coupled to the movable structure such that a portion of the jack screw may be extended to engage the chock, thereby seating the chock into the rack, and locking the chock in the longitudinal direction. Jack screws may be provided on any side of the chock, as required to prevent motion in the longitudinal direction, and may be torque limited to prevent damage to the screw mechanism or the chock. In one embodiment, the jack screw may also assist in moving the movable structure in the longitudinal direction. 
         [0008]    According to one embodiment of the present disclosure, there is provided at least one vertical jack screw. A vertical jack screw may be hydraulic, but is preferably mechanical. The vertical jack screw may be extended to engage the chock in the vertical direction to assist the actuating cylinder in maintaining engagement between the rack and the chock. The vertical jack screw also provides additional means of preventing disengagement of the chock and the rack during external events like wind loading, wave activity, or seismic activity. In one embodiment, the vertical jack may also assist in moving the movable structure in the vertical direction. 
         [0009]    There is provided, in one embodiment, remote actuation of the elements of the present disclosure. For example, at least one of the group consisting of the actuating device and the jack screw and the vertical jack screw is remotely actuated. 
         [0010]    In one embodiment, the rack comprises a high friction surface, and the chock comprises a high friction surface, wherein the chock high friction surface is configured to engage the rack high friction surface. Optimally, the high friction surfaces comprise teeth. 
         [0011]    According to the present disclosure, the movable structure may be skid along the skidding beam or capping rail via the skid guides. The entire movable structure may be coupled to only one longitudinal restraint system, or many longitudinal restraint systems may be employed. When the movable structure is in place, the actuating cylinder maneuvers the chock to engage the corresponding rack. In one embodiment, the actuating cylinder may pivot about a pivot point to align the chock with the rack. Multiple actuating cylinders may be provided. Jack screws may assist in placement of the chock and engagement of the chock to the rack. Upon engagement, horizontal jack screws may extend from either side of the chock to lock the chock in place longitudinally. Vertical jack screws may extend in the vertical direction to lock the chock to the rack in the vertical direction. The jack screws may be pitched or yawed around a pivot point as well in order to assist in locking the chock. The movable structure is thus restrained. 
         [0012]    When it comes time to move the movable structure, the jack screws may be reversed to disengage the screws from the chock. The actuating cylinder may then disengage the chock from the rack, allowing the movable structure to be skid along the skidding beam in the longitudinal direction. 
         [0013]    In one embodiment, a method for longitudinally restraining a movable structure comprises attaching a rack to a first structure, attaching a chock to a second structure, wherein the face of the chock is configured to engage the face of the rack. The chock is then positioned along the face of the rack such that the teeth of the rack align with the teeth of the chock, and the chock and rack are engaged. A locking mechanism attached to the second structure can be used to restrict the chock from moving along the longitudinal axis of the rack. Preferably, the locking mechanism is a jack screw. However, one skilled in the art would understand other types of locking mechanisms could be used. Optimally, such locking mechanisms would not depend on electrical power or hydraulic pressure to remain engaged. 
         [0014]    The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
           [0016]      FIG. 1(   a ) is a side view of an embodiment of the locking system of the present disclosure; 
           [0017]      FIG. 1(   b ) is an exploded view of an embodiment of the rack portion of the locking system of the present disclosure; 
           [0018]      FIG. 2  is a top view of an embodiment of the locking system of the present disclosure; 
           [0019]      FIG. 3  is an end view of an embodiment of the locking system of the present disclosure; and 
           [0020]      FIG. 4  is a side view of an embodiment of the locking system of the present disclosure. 
       
    
    
       [0021]    It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The locking system of the present disclosure allows a movable structure to be temporarily restrained to a desired position on a fixed structure. In one embodiment, the fixed structure is a deck of a vessel, such as an offshore platform, the floor of any built structure, or any flat surface that is in a fixed position, and the desired position is a horizontal position along the deck, floor, or flat surface. Alternatively, the fixed structure is a wall, and the desired position a vertical position on that wall some distance above the floor or ground. In the preferred embodiment, the locking system of the present disclosure provides locking in the longitudinal direction of movement of a movable structure in the forward and aft or port and starboard direction on board the vessel. 
         [0023]    Referring to  FIGS. 1(   a ),  1 ( b ) and  2 , rack  102  is shown attached to a fixed structure  126  along its length. The attachment can be done through welding, bolting, or other means known to those skilled in the art. Referring to  FIG. 1(   b ), rack  102  includes a body  103  that defines a longitudinal axis extending there through. Body  103  is shown with a series of teeth  104  that extend away from the fixed structure  126 . In the preferred embodiment where rack  102  is secured on the floor or deck of a vessel, teeth  104  face upward opposite the fixed structure. In an alternative embodiment, rack  102  may be secured on any available surface. For example, rack  102  may be positioned on a vertical wall or the bottom of a horizontal surface, such as a ceiling or the underside of a skidding beam. A person skilled in the art would understand how to rotate elements of restraint system  100  about the longitudinal axis to maintain the integrity of the invention. Multiple racks may be present in a given longitudinal direction, for example, along a skidding beam. 
         [0024]    The locking system shown in  FIG. 1(   a ) further comprises chock segment  106 . Chock segment  106  is coupled to movable structure  108 . In the embodiment of  FIG. 1(   a ), movable structure  108  is movable relative to fixed structure  126 . In one embodiment, chock segment  106  is coupled to movable structure  108  through at least actuating cylinder  110 . When movable structure  108  is positioned at a certain location and it is desired that movable structure  108  be temporarily fixed or locked at that location, certain embodiments of the locking system of the present disclosure can be used to allow temporary immobilization of movable structure  108 . While there are many applications for the embodiments of the locking system of the present disclosure, they are particularly useful for securing items on vessels due to the constantly moving nature of a floor or deck of that vessel or due to external forces such as wind loading or seismic activity. 
         [0025]    Chock segment  106  includes teeth  107  shaped to engage teeth  104  of rack  102 . When chock segment  106  is closed against rack  102 , teeth  107  engage teeth  104  to lock chock segment  106  in position with respect to fixed structure  126 . In the alternative, chock segment  106  may rest to the side of or underneath rack  102 , such as where rack  102  is secured to a vertical surface or a horizontal surface above. 
         [0026]    In the preferred embodiment, actuating cylinder  110  moves chock segment  106  into engagement with rack  104 . Actuating cylinder  110  may be pivotally attached to movable structure  108  and chock  106 . In embodiments in which movable structure  108  moves relative to chock  106 , actuating cylinder  110  pivots at pivot points  130 . Actuating cylinder  110  is configured to maintain pressure sufficient to ensure chock  106  remains engaged to rack  102  as actuating cylinder  110  pivots. Although one actuating cylinder  110  is shown, it is understood that multiple actuating cylinders could be used. Further, actuating cylinder  110  is shown in perpendicular alignment with rack  102 . However, one skilled in the art understands the angle between the actuating cylinder  110  and rack  102  changes when movable structure is moved. In the case of multiple actuating cylinders, the angles of the actuating cylinders may be offset such that one cylinder is always in a perpendicular alignment with rack  102 . 
         [0027]    Chock segment  106  is disposed between a locking mechanism. The locking mechanism is configured to engage chock  106  in the longitudinal direction so that forces imparted on movable structure  108  by external events are transferred through chock  106  into rack  102 . The locking mechanism may be hydraulic, but is preferably mechanical. It may be engaged electronically or manually. 
         [0028]    In the exemplary embodiment shown in  FIG. 1(   a ), the locking mechanism comprises two jack screws  112 , configured to move or actuate in the direction parallel to the longitudinal direction of rack  102 , which is generally perpendicular to the direction of movement of actuating cylinder  110 . Actuating cylinder  110  and jack screws  112  are preferably actuated electrically or hydraulically. Jack screws  112  are preferably coupled to reaction plates  114 , but can be affixed to any rigid component coupled to structure  108 . After chock  106  is in position and is interlocked with the teeth of rack  102 , drive or jack screws  112  can be actuated to extend a body of jack screws  112  until drive or jack screws  112  engage chock segment  106 . Once jack screws  112  engage with chock segment  106 , loads acting in the longitudinal direction along the body of rack  102  can be transferred between reaction plates  114 . In this manner, jack screws  112  can be used to secure or move movable structure  108 . When securing movable structure, jack screws on both sides of chock  106  are extended to engage chock  106 . When moving movable structure  108 , jack screws on one side of chock  106  are extended to push movable structure  108 . 
         [0029]    In the preferred embodiment, the pitch angles of rack  102  and chock segment  106  are such that forces in the longitudinal direction of motion (along the body of rack  102 ) are insufficient to overcome friction. Therefore, when load is applied in the longitudinal direction, friction via the vertical force along the engagement between rack  102  and chock  106  prevents longitudinal slide of the components in the restraint system. In this way, chock segment  106 , along with movable structure  108  coupled to it, is locked in the longitudinal direction in a desired location through its engagement with stationary rack  102 , which is attached to the fixed structure  126 , even when load is applied in the longitudinal direction. Jack screws  112  become lock screws when load is applied. 
         [0030]    For the teeth design shown in  FIGS. 1(   a ),  1 ( b ), and  4 , rack teeth  104  match chock teeth  107 . One skilled in the art would understand that various rack and chock designs are available. For example, the top land of either set of teeth may be flat or involute, as can be the bottom land. Teeth on either the rack or chock (or both) may have an edge round. The chordal thickness of the teeth need not match between the rack and the chock. The pitch angles of the teeth may be of varying degrees, depending on the preferred ease of engagement. In one embodiment, a saw tooth design is contemplated. In another embodiment, rack  102  and chock  106  do not have teeth, but rely on high friction surfaces as well known by those skilled in the art. 
         [0031]    In the embodiment shown in  FIG. 2 , actuating cylinder  110  is configured to react to any additional load perpendicular to the longitudinal that may occur, for instance, from vertical vessel motion. In other words, actuating cylinder  110  can be configured to maintain engagement between chock  106  and rack  102  irrespective of the vertical load. In the present disclosure, the term “vertical” can mean the direction vertical to the horizontal floor or ground as well as a direction normal to the face of rack  102 . It is understood that actuating cylinder  110  and jack screws  112  are configured to provide the appropriate force to support chock  106  and movable structure  108  in the lock position. 
         [0032]    In one embodiment, jack screws  112  are also coupled to movable structure  108  to spread the load transfer between chock segment  106  and movable structure  108  to provide a more secure lock when chock  106  engages rack  102 . Jack screws  112  can be welded or bolted to movable structure  108  or coupled through other appropriate means known to those skilled in the art. For example, jack screws  112  may be mounted on reaction plates  114 . 
         [0033]    In the embodiment shown in  FIG. 4 , additional jack screws are provided in the vertical direction. These vertical jack screws  111  can be coupled to movable structure  108  directly (not shown) or via a longitudinal restraint chassis  117 . Chassis  117  may comprise skid guide  116  and reaction plates  114 . It is understood that chassis  117  allows longitudinal restraint  100  to be disconnected from, and reconnected to, movable structure  108  without having to remove each component of longitudinal restraint  100 . After chock segment  106  is in position and is interlocked with the teeth of rack  102 , vertical jack screws  111  are actuated to extend a body of vertical jack screws  111  until vertical jack screws  111  engage chock segment  106 . The vertical jack screws  111  assist actuating cylinders  110  in reacting to any additional load perpendicular to the longitudinal that may occur, for instance, from vertical vessel motion. Vertical jack screws  111  can be configured to mechanically assist in retaining chock  106  engaged and locked to rack  102  in the event that vertical load is applied in addition to or in place of the longitudinal load. Additionally, vertical jack screws  111  can be used to lift movable structure  108  or restraining system  100  relative to fixed structure  126 . 
         [0034]    In one embodiment, jack screws  112  impart enough force on chock  106  in the longitudinal direction to effectively slide movable structure  108  along skidding beam  118 . This allows for the restraint system to facilitate minor tweaks in the position of movable structure  108  without engaging the main jack skidding system. 
         [0035]    In another embodiment, certain elements of the locking system of the present disclosure are operated remotely and/or automatically. In the preferred embodiment, the movement and actuation of actuating cylinder  110 , jack screws  112 , and vertical jack screws  111  are remotely controlled so that the locking system of the present disclosure can be locked or unlocked remotely. The locking system of the present disclosure is particularly applicable to hold the footing of a large structure, such as a mobile drilling rig used in the oil and gas industry, on a vessel whether on land or sea. In other aspects, the embodiments of the present disclosure can be used to secure smaller items in environments that are subject to changing load applications. 
         [0036]    In one exemplary embodiment, referring to  FIG. 3 , movable structure  108  is a footing of a structure coupled to skid guide  116  and vertical skid guides  122 . Skid guides  116  and vertical skid guides  122  slide along skidding beam  118 . The upper half of vertical skid guides  122  also serve as vertical restraints for attachment of restraint system  100  to movable structure  108 . Where movable structure  108  is to be secured to a deck  126  of vessel (not shown), movable structure  108  coupled to restraint system  100  is skidded to the desired position along skidding beam or capping rail  118  guided by skid guide  116  and vertical skid guides  122 . Rack  102  is attached to the vessel at the desired location. When the desired position is achieved, chock  106  is engaged to rack  102  thus immobilizing structure  108  in the longitudinal direction. 
         [0037]    In one embodiment, there are provided lateral restraints  120  comprising a fixed wedge  121 , a travelling wedge  123 , and a lateral restraint actuating cylinder  124 . Referring to  FIG. 2 , fixed wedge  121  is firmly coupled to movable structure  108 , preferably mounted on to the skid guides  116  or vertical skid guides  122  or chassis  117  of the longitudinal restraint. Travelling wedge  123  is coupled to lateral restraint actuating cylinder  124 , and exists in the space between fixed wedge  121  and the lateral edge of skidding beam  118 . As lateral restraint actuating cylinder  124  retracts, travelling wedge  123  is sandwiched in between fixed wedge  121  and the lateral edge of skidding beam  118 , thereby making contact with said edge. Movable structure  108  is thus restrained in the lateral direction, perpendicular to the longitudinal axis of the skidding beam. When the movable structure  108  is to be relocated, lateral restraint actuating cylinder  124  extends, moving travelling wedge  123  away from the lateral edge of skidding beam  118 . One skilled in the art would recognize that additional lateral restraints  120  may be added as required to constrain movable structure  108  in the lateral direction. 
         [0038]    Coupled to movable structure  108  are actuating cylinder  110  and jack screws  112 . In the unlock configuration, actuating cylinder  110  holds chock segment  106  above rack  102 . Cylinder  110  can be remotely actuated to lower chock segment  106  until it engages rack  102 . In the preferred embodiment, chock  106  is configured to be placed next to one jack screw  112 . If chock segment  106  is lowered so that its teeth  107  properly align with teeth  104  of rack  102 , the system can sense this when jack screw  112  next to chock segment  106  is actuated but cannot be moved beyond the specified maximum force. Jack screw  112  is torque limited. If chock segment  106  is lowered and its teeth are not properly aligned, when jack screw  112  closest to chock  106  is actuated, its specified force is sufficient to push chock  106  into proper alignment. After it is determined that chock  106  is properly aligned with rack  102 , the other jack screw  112  can be actuated, preferably remotely, until it engages chock  106 . In one embodiment, vertical reaction screws  111  are then engaged to mechanically resist vertical loads on chock  106 . Vertical reaction screws  111  may also be torque limited. The locking system of the present disclosure is now in the lock configuration where movable structure  108  is secured to the vessel. 
         [0039]    To unlock, each jack screw  112  can be actuated to withdraw from chock  106  sequentially or simultaneously. Vertical jack screws  111  are actuated to withdraw from chock  106  in the vertical direction. Cylinder  110  then can lift chock  106  to disengage it from rack  102 . If movable structure  108  has four footings, there would be four corresponding movable structure  108  attachment points, four chock segments  106 , and four racks  102  placed at the appropriate locations on the vessel for locking movable structure  108  to the vessel as described. In one embodiment, cylinder  110 , jack screws  112 , and vertical jack screws  111  can be programmed to operate remotely and automatically without manual control or user input during the locking and unlocking process. 
         [0040]    As described, certain embodiments of the present disclosure allow for temporary locking of an object, large or small, in a location that can withstand loads in the horizontal (side to side) and vertical (up and down) directions. The embodiments of the locking system of the present disclosure are particularly applicable for securing structures of all sizes on a vessel, which often experiences loads in all directions (e.g., waves, wind, seismic, etc.). Further, certain embodiments of the present disclosure allow for the convenience of remote operation to lock or unlock the system. 
         [0041]    Although the embodiments of the locking system of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the future claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.