Abstract:
A method and apparatus of operating an autonomous underwater vehicle (AUV) may include receiving an AUV in a receptacle of a submersible station. The AUV and the submersible station may be launched to an underwater location. The AUV may engage with the submersible station before, after or during a mission, and may return to the same or a different submersible station after part, or all, of the mission has been completed.

Description:
RELATED APPLICATIONS AND CLAIM OF PRIORITY 
     This patent application claims priority to GB Patent Application No. 0719946.6, filed Oct. 12, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
     NOT APPLICABLE 
     BACKGROUND 
     Autonomous underwater vehicles (AUVs) are normally launched into the water from a surface support vessel by a simple wire hoist. The AUV does not have an umbilical, and thus there are no hard wire/live links with the vehicle, which can be used to facilitate the launch and recovery process to and from the vessel. Once an AUV has been lowered from the deck of the support vessel to the water surface, the AUV is manually released from the hoist so it can then submerge and accomplish its mission. The hoist line is manually attached to the AUV for recovery to the deck after the mission. 
     Both launch and recovery to and from the vessel are difficult in rough weather. 
     SUMMARY 
     In an embodiment, a method of operating an AUV may include providing a submersible station that may engage with the AUV, submerging the submersible station and engaging the AUV with the submersible station before, after or during a mission. 
     The AUV may engage with the station on the deck of a support vessel from which it is launched, and the AUV and station may be launched into the water as a unit. In an embodiment, the AUV can return to the same or a different station after part or all of its mission has been completed. 
     In an embodiment, the AUV can be launched separately from the station, from the same or a different vessel, and can be docked with the station when underwater, prior to commencement of the mission. 
     In an embodiment, the AUV can be deployed on a mission direct from the vessel without engaging with the station before commencement of the mission, and can engage with the station only after part (or all) of its mission has been completed. 
     In an embodiment, an apparatus for operating an AUV, may include a submersible station having a receptacle to receive the AUV, the station being adapted to be lifted by a lifting device to facilitate deployment of the station and AUV from a vessel to an underwater location. 
     The submersible station may be launched from the vessel to a location on the sea bed or on a fixed structure, so that the station is static at the times of engagement and disengagement of the AUV. The station may house the AUV within a protective housing and thereby may provide a “garage” which provides protection from the elements as the AUV is launched through the air/water transition zone, and a static base on the sea bed which the AUV can engage before, during or after its mission. 
     The station can have a receptacle for the AUV, which can have a shape adapted to receive the AUV being used, which may vary in different embodiments. The receptacle can be set in a square base plate. The station can incorporate weights or ballast, and can incorporate flow paths configured to enhance the hydrodynamics of the station when being lowered from a surface vessel. In an embodiment, the station can have a base plate with a lattice construction to facilitate its passage through the water. 
     The station can have guide surfaces that are sloped, channeled or funneled towards the receptacle, which can facilitate engagement of the AUV with the station, by guiding it passively to the edge of the receptacle. In an embodiment, the guide surfaces can include flat sloping faces arranged at an angle to the base plate, adapted to guide movement of the AUV up to the level of the entrance to the receptacle. The AUV can then enter the receptacle by advancing until in alignment with an opening for the receptacle, and then optionally descending into engagement with an optional latch mechanism. 
     The station can have at least one lifting eye, arranged on a frame and can be lifted by a crane connected to the eye. The frame may span the receptacle and may have a connection mechanism for cooperation with the crane provided on the upper surface of the frame. The frame may have upright side portions and a cross bar that defines an opening that is adapted to allow passage by the AUV. 
     The station may include shock absorbers to provide a soft landing on the seabed, thus, the shock absorbers can configured to facilitate damage-free landing on the seabed. Once landed, the station can be decoupled from the vessel motion by a float device in the lift line which can be left slack because it is held clear of the seabed by the float device. 
     The AUV may be loaded into the receptacle on the deck of the vessel at the surface, and the assembly of the AUV and the station may be launched as a unit into the water from the vessel using lifting devices such as, but not limited to, a winch, a hoist, a crane, an A-frame and/or any other suitable and available lifting device, such as a wire hoist, on the vessel. The lifting device may have a lift line which may be, but is not limited to, a wire and/or a rope. The initial launching operation of this type may be quite similar to a routine lift to the seabed, avoiding the need to use any particular form of specialized lifting equipment. In an embodiment, other suitable locking devices can be used. 
     The apparatus may incorporate a signaling system adapted for communication between the station, the AUV and a receiving vessel. The receiving vessel may be the vessel from which the station is deployed. The station can incorporate a signaling system to communicate (one-way or two-way) with the AUV or with the receiving vessel. The signaling system can include an acoustic beacon for determining the station&#39;s position relative to a known marker using a relative positioning system such as, but not limited to, a conventional ultra short base line system (USBL), provided on the receiving vessel. Other relative positioning systems can be used instead. The known marker may be the receiving vessel. The known marker may have a known fixed position, and thus it may take the form of an offshore and/or marine installation, for example, a wellhead installation, a navigation buoy or a lighthouse. This information can be combined with vessel global positioning system (GPS) coordinates to provide an accurate position of the station on the sea bed. This can provide the AUV with a datum start point for an optional on-board navigation system. 
     In the event that the support vessel does not have a USBL, the absolute station position can be estimated by other means, such as, but not limited to, observed lift line position, and the vessel GPS coordinates. 
     In an embodiment, the station can be disconnected from the wire hoist after lowering the assembly of the AUV and the station to the desired position, although it can optionally remain connected during the mission of the AUV, if desired. Disconnection can be by a remotely operated underwater vehicle (ROV) operated hook or by an acoustic release system. Reconnection of the station to the wire hoist of the vessel after the AUV has been deployed (and optionally recovered) can be by an ROV operated hook. 
     The station can have a self operating latch mechanism for retaining the AUV optionally within the receptacle. This can advantageously be centrally placed in the receptacle, in the floor. Latching can be achieved by the AUV entering the receptacle and driving a built in socket over the latch. The latter can have spring loaded locking levers that can automatically retract and then extend behind an inwardly extending rim on the AUV socket. 
     The AUV/station engaging operation can compress a spring loaded collar, which can remain energized against the AUV socket after the latch has operated to retain the vehicle. The AUV can optionally release itself by extending a probe that retracts the locking levers and the AUV is then pushed clear of the latch by the action of the energized spring. 
     In order to extend the mission time of the AUV, an embodiment of the garage can include a power supply such as a battery. The power supply can optionally be used to charge the on-board battery or other power supply on the AUV. In an embodiment, the power supply can include a generator and an embodiment can incorporate a water flow driven generator. The water flow driven generator may include, but is not limited to, a turbine or an oscillatory generator. The water flow driven generator may be a tidal generator which can be removed or installed on the base plate as necessary. The tidal generator can be mounted on and/or connected to a battery pack. The battery pack may be configured to provide a reservoir of power for recharging the AUV thereby extending its mission time. The level of charge in the station and in the AUV can be monitored and optionally compared by the operator. This can allow the AUV operator to optimize the recharging regime, for example, by directing the AUV to engage a particular station with sufficient power to recharge the on-board AUV batteries and to avoid engagement with stations that have depleted power supplies. The provision of a power supply in the station may mean that AUV missions can in principle be extended indefinitely, as the AUV can simply return to a recharging station every time its on-board power supply drops below a certain level. The AUV may be triggered to return to a selected station for recharging upon reaching a threshold of power depletion. The reaching of the threshold value may trigger the return of the AUV to the station. The threshold may be set sufficiently high to enable the AUV to reach the station under the remaining power stored in the AUV power supply. 
     The level of charge in the station and vehicle can optionally be monitored by the vehicle and/or station, and in an embodiment, the vehicle itself can optionally determine the charging regime so that an operator is not required. 
     The power supply can be configured to drive a data handling package, that can accept data transmitted or downloaded from the AUV for acoustic transmission to a surface facility or vice versa. A number of these stations can be strategically positioned in the AUV mission area (e.g. around a field development) to allow the AUV to complete an extensive and comprehensive survey or other tasks, without being recovered to surface. 
     The station can include a stab connector that can be accessed by the AUV to provide signal and power transfer. In an embodiment, transmission of signals and power between the AUV and the station can be wireless, for example, by an induction or an acoustic mechanism. In an embodiment, the AUV may include a matching connector that can be mated on command with its counterpart on the base plate, by means of a hydraulic cylinder (or similar extensor). 
     In an embodiment, a system for operating an AUV may include a submersible station, an AUV and a lifting device, wherein the lifting device is configured to deploy a vessel to the submersible station from an underwater location and the submersible station includes a receptacle configured to receive the AUV before, after or during a mission. 
     In an embodiment, a method of operating an AUV may include engaging an AUV with a submersible station, connecting the submersible station to a lift wire of a lifting device located on a vessel, deploying the submersible station from the vessel to an underwater location using the lifting device and decoupling the station from motion of the vessel during a mission. 
     The method may include fitting a floatation device to the lift wire wherein the flotation device may be configured to decouple the submersible station from motion of the vessel. The method may include disconnecting the lift wire from the station. 
     In an embodiment, a method of deploying an AUV may include receiving an AUV in a receptacle of a submersible station, lowering the station and the AUV as a unit from a vessel to an underwater location and moving the AUV from the station to perform a mission. 
     In an embodiment, a method of operating an AUV may include submerging a first submersible station and engaging the AUV with the first submersible station before, after or during a mission. 
     In an embodiment, an apparatus for operating an AUV may include an AUV, a submersible station adapted to engage with the AUV before, after or during a mission and a lifting device adapted to deploy at least one of the AUV and the submersible station from a vessel to an underwater deployment location. 
     One or more embodiments including the embodiments disclosed above may be combined within the scope of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects, features, benefits and advantages of the embodiments described herein will be apparent with regard to the following description, appended claims and accompanying drawings where: 
         FIG. 1  depicts a schematic side view of the method and vessel for operating an AUV according to an embodiment. 
         FIG. 2  depicts a schematic perspective view of a station used in the method of  FIG. 1  according to an embodiment. 
         FIG. 3  depicts a schematic side view of a latching mechanism connecting the AUV to the station in  FIGS. 1 and 2 , showing the latching sequence according to an embodiment. 
         FIG. 4  depicts a more detailed view similar to  FIG. 3 , showing the releasing sequence according to an embodiment. 
         FIG. 5  depicts a schematic side view of an alternative embodiment of the station with an optional power supply according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Before the present methods are described, it is to be understood that this invention is not limited to the particular systems, methodologies or protocols described, as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present disclosure which will be limited only by the appended claims. 
     As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. As used herein, the term “comprising” means “including, but not limited to.” 
     Referring now to  FIGS. 1 and 2 , a station  1  for engagement with an AUV  2  may includea base plate  3  with a general pyramid structure having a flat lower surface  3   s  and at least three (or four) sloped side walls  3   w . The sloped side walls  3   w  may be formed in panels and attached to a frame  3   f  that defines the pyramid structure. The side walls  3   w  may have flat faces that converge towards the apex, but the wide walls  3   w  may not meet at the apex, but instead define an aperture in the upper surface of the pyramid structure, on the opposite face to the flat lower surface  3   s . The aperture may be defined by portions of the frame  3   f  and may define the entrance to an AUV receptacle  4  having sides  4   s  and a floor  4   f . The receptacle  4  may be adapted to receive the AUV  2 , and optionally may have a latching mechanism  15  to latch the AUV  2  into place within the receptacle. The latching mechanism  15  can be located in the floor  4   f  of the receptacle, but other locations (side wall  4   s  or frame  3   f ) can be used for this purpose. 
     Referring now to  FIGS. 1 and 2 , a station  1  for engagement with an AUV  2  may include a base plate  3  with a general pyramid structure having a flat lower surface  3   s  and at least three (or four) sloped side walls  3   w . The sloped side walls  3   w  may be formed in panels and attached to a frame  3   f  that defines the pyramid structure. The three (or four) sloped side walls  3   w  have flow paths  3   p  through which water can pass. Collectively the flow paths  3   p  provide a lattice construction  3   c  to facilitate passage of the station  1  through water. The side walls  3   w  may have flat faces that converge towards the apex, but the wide walls  3   w  may not meet at the apex, but instead define an aperture in the upper surface of the pyramid structure, on the opposite face to the flat lower surface  3   s . The aperture may be defined by portions of the frame  3   f  and may define the entrance to an AUV receptacle  4  having sides  4   s  and a floor  4   f . The receptacle  4  may be adapted to receive the AUV  2 , and optionally may have a latching mechanism  15  to latch the AUV  2  into place within the receptacle. The latching mechanism  15  can be located in the floor  4   f  of the receptacle, but other locations (side wall  4   s  or frame  3   f ) can be used for this purpose. The base plate  3  may include a lifting frame  6  with uprights  6   u  and a cross bar  6   b , having a lifting eye  6   e  suitable for cooperating with a wire hoist on a vessel to be used for launching and recovering the AUV  2 . Once the AUV  2  is latched into the receptacle  4  on the deck of the vessel, the lifting eye  6   e  may be connected to the wire hoist of the vessel and the combined assembly of the station  1  and the AUV  2  may be lifted by the wire hoist, swung outboard and lowered into the water as shown in  FIG. 1 . 
     The assembly of the station  1  and the AUV  2  may be lowered into the water quickly, thereby minimizing the time for transit through the air/water interface. Thereafter, the assembly may be lowered to a fixed location on the sea bed. The actual landing of the station can be timed to minimize the effects of ship motion on the wire hoist. Optionally, the base  3  can include shock absorbers  5  mounted on the lower surface  3   s  of the base in order to minimize the impact on landing. Once landed, the lift wire may be slackened, but may remain supported above the frame  6  by a flotation device  14 . This may decouple the station  1  from the motion of the vessel. 
     The absolute position of the base  1  can be determined optionally using GPS combined with the vessel&#39;s USBL or by GPS and an estimated seabed location based on the lift line position. The datum for the AUV navigation system can be updated accordingly (and other mission details also transmitted/updated if necessary). 
     On command from the vessel, or from a timer, the AUV  2  may unlatch itself, and proceed on its mission, at the end of which it may return to the station  1 . In the meantime, the station  1  can be recovered for subsequent redeployment elsewhere or at the same place, or disconnected from the support vessel and left on the sea bed in the same location for subsequent reattachment of the AUV  2 . In an embodiment, disconnection of the wire hoist and the station  1  can be by ROV or by acoustic release, and reconnection can optionally be by ROV. The facility to disconnect or recover the garage may allow the support vessel to leave the site and undertake additional tasks whilst the AUV  2  executes its mission. 
     When the AUV  2  has completed its mission or when its available on-board power has dropped to a certain level, the AUV  2  may be triggered automatically to return to the location of the station  1  under the power remaining on the battery of the AUV  2 . This trigger can be provided by an on-board system such as, but not limited to, a battery sensor or a timer, or can be a command from the vessel. When the AUV  2  is nearing the station, the geometric configuration of the lifting frame with the two uprights  6   u  and the cross bar  6   b  may assist in the AUV&#39;s identification of the correct target and in its assessment of, but not limited to, an approach vector, a speed and a distance. The AUV  2  can be programmed to approach the station from a predetermined angle that is favorable to the docking procedure in the receptacle  4 , for example, where the uprights  6   u  and cross bar  6   b  are arranged in a plane that is perpendicular to the approach of the AUV  2 . The sloped side walls  3   w  of the base plate  3  may assist in guiding the AUV to the entrance of the receptacle  4 , as it swims up the ramps and into the entrance of the receptacle  4 . Other guiding surfaces that control the lateral deviation from the optimal docking path of the AUV can be used to funnel the AUV into the entrance of the receptacle on approach. Other configurations of station can be used to guide the approach of the AUV  2 . 
     The AUV  2  and the station  1  can have acoustic beacons  30  to communicate with the vessel&#39;s USBL system. 
     In an embodiment, the AUV  2  or the station  1  can have a disengagement mechanism that is energized by the docking process. As shown in  FIG. 3 , the AUV can be docked with the receptacle by a docking sleeve  12  and latching probe  11  which can mate with a latching mechanism  15  with a spring  13 . When the sleeve  12  passes over the latching mechanism, it may compress the spring  13  between a collar  17  and the floor of the receptacle  4   f  as shown in  FIG. 3 . When the AUV is released from the latching mechanism, the AUV may insert the latching probe  11  into the bore of the latching mechanism on the receptacle  4 . This may retract the locking levers  16  and may release the sleeve  12  of the AUV from the latching mechanism. The spring  13  may be free to expand and push the AUV away from the floor of the receptacle  4  as shown in  FIG. 4 . 
     An alternative embodiment of a station  21  is shown in  FIG. 5  in which an optional power supply may be provided. In the station  21 , similar components are used to the station  1 , and like reference numbers have been used, with the prefix “ 2 ”, so AUV  22 , base plate  23  and lifting frame  26  are all basically similar to the corresponding components described above. In the station  21 , the difference may reside in the connections between the station  21  and the AUV  22 , and in the power supply. The power supply may include a tidal generator  27  and an optional battery pack  28 . The tidal generator  27  may have a rotor with vanes turned by tidal movements, which is converted to electrical energy by the generator  27 . The generator may charge the battery  28  whenever the rotor is turned at sufficient speed. The battery can be connected to the AUV  22  by the power and signal connectors  29  in the receptacle  24 , so the AUV  22  can be charged after docking with the station  21 . The battery  28  may be kept charged by the generator  27  so that if the AUV&#39;s on board battery is depleted during a mission it can return to the station  21  and the on-board battery on the AUV can be recharged from the battery  27  and/or directly from the generator. Thus, the AUV  22  can remain submerged for numerous missions without returning to the vessel. This frees the vessel from remaining on station during each mission of the AUV  22 . 
     In an embodiment, a single AUV (or multiple AUVs) can be deployed from a number of stations  1 ,  21  strategically located around a field site and an AUV can be programmed to locate the nearest power station  21  when its on-board battery is depleted to a set level. The AUV can be provided with a navigation device to determine its position and on-board communications systems such as an acoustic beacon  30  needed to transfer acoustic data between the AUV and the vessel. When the AUV has docked with a base station (or is within wireless or acoustic range) it can optionally download data and update its mission parameters through the stab connector  29  or via the acoustic beacon  30 . 
     Using the stations  1 ,  21  can save on the AUV power consumption as it is not necessary to drive the AUV from the surface to the seabed. By handling the AUV in an underwater “garage” the commencement and conclusion of missions may be significantly less weather dependent as the need for “manual” surface release/reconnection arrangements during conventional launch and recovery operations may be avoided. It follows from this that the need to terminate a mission, in order to safely recover the vehicle in the event of bad weather, may also be avoided. Because the stations can be recovered to the vessel after disengagement of the AUV or just left on the seabed, the AUV support vessel can be freed to accomplish other tasks in parallel with the AUV mission. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. It will also be appreciated that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.