Abstract:
A system that can be used for inspecting underwater structures. The system allows a user to gain a better understanding of the condition of an underwater structure. The system is a self-contained, modular system that can be operated by divers, coupled to an AUV, ROV or other host platform vehicle deployment platform, towed by a ship, pole mounted, or hull mounted. All of the components necessary to achieve the desired scanning functions are incorporated onto the self-contained, modular system. The system can include and fully utilize a 3D sonar system and an inertial navigation system. This combination of features permits the system to be used to, for example, generate 3D models of underwater structures, detect changes in underwater structures by comparing the generated 3D model against an a priori 3D model, and provide navigational updates to the host platform based on the observed features of an underwater structure.

Description:
[0001]    This application claims the benefit of U.S. Provisional Applicant Ser. No. 61/406309, filed on Oct. 25, 2010, the entire contents of which are incorporated by reference. 
     
    
     FIELD 
       [0002]    This disclosure relates to a system for conducting inspections of subsea and other underwater structures. 
       BACKGROUND 
       [0003]    There are a number of underwater structures for which one might need to gain a better understanding of the underwater structures. One example is the inspections of the subsea support structures of offshore oil and gas platforms that are conducted on a routine basis or after an extreme event such as a hurricane. Current methods of inspecting underwater structures include inspections using divers, remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs). 
       SUMMARY 
       [0004]    A system that can be used for inspecting underwater structures is described. The system allows a user to gain a better understanding of the condition of an underwater structure. The system is a self-contained, modular system that can be operated by divers, coupled to an AUV, ROV or other host vehicle deployment platform, towed by a ship, pole mounted, or hull mounted. All of the components necessary to achieve the desired scanning functions are incorporated onto the self-contained, modular system. 
         [0005]    The system can be used to scan any type of underwater structure composed of material dissimilar enough from water to provide sonar reflections. Underwater structures include man-made objects such as offshore oil platform support structures and oil-well related equipment, as well as natural objects such as geological and biological formations. Scanning an underwater structure may be desirable, for example, to inspect the structure as part of a routine inspection schedule or after an extreme event such as a hurricane, or to generate a model of the underwater structure. As used herein, the term underwater includes any type of underwater environment in which an underwater structure may be located and may need to be scanned using the system described herein, including, but not limited to, salt-water locations such as seas and oceans, and freshwater locations. 
         [0006]    The system can include and fully utilize a 3D sonar system and an inertial navigation system. This combination of features permits the system to be used to, for example, generate 3D models of underwater structures, detect changes in underwater structures by comparing the generated 3D model against an a priori 3D model, and provide navigational updates to the host platform based on the observed features of an underwater structure, although other uses of the system are possible. 
         [0007]    In one embodiment, a modular system for use in scanning underwater structures includes a modular support frame, a 3D sonar system mounted on the modular support frame, an Inertial Navigation System (INS) mounted on the modular support frame, and an electronics pressure vessel mounted on the modular support frame. The INS can include a Doppler Velocity Log (DVL) and a Conductivity Temperature and Depth (CTD) sensor. The electronics pressure vessel can include one or more data processors, one or more non-volatile storage device, and other associated components required to operate the 3D Sonar, INS, CTD, and interface to the host platform, which optionally includes power and communication connections. The 3D sonar system, INS, and CTD are electrically connected to the electronics pressure vessel. Optionally a GPS system can also be connected to the electronics pressure vessel and mounted on the modular support frame. This modular system is self-contained and in one embodiment needs only to be connected to a host platform, such as an AUV or ROV, for electrical power and locomotion. The electrical power requirement can be alleviated through the use of optional submersible battery assemblies which can also be mounted on the modular support frame. 
         [0008]    The modular system may also contain one or more additional sonar systems of different frequencies to collect different data about the structure being inspected. One example is to include a low frequency sonar system, such as the one described in U.S. Provisional Patent Application Ser. No. 61/406479, filed on Oct. 25, 2010, and titled Remote Flooded Member Detection, which is incorporated herein by reference in its entirety, to inspect the structure for flooded members. This second sonar system would also be mounted on the modular support frame and would be electrically connected to the electronics pressure vessel. 
         [0009]    The modular system may also contain one or more cameras and/or lights for use in collecting visual data of the structure being inspected. The cameras, if present, can be still and/or video, color and/or black and white, cameras. The lights, if present, can be flash/strobe and/or sustained lights. These cameras and lights would also be mounted on the modular support frame and electrically connected to the electronics pressure vessel. 
         [0010]    As used herein, an ROV is a remotely operated underwater vehicle that is tethered to a host, such as a surface ship. The ROV is unoccupied and is operated by a pilot aboard the host. The tether can carry, for example, electrical power (in place of or to supplement battery power on the self-contained system), video and data signals back and forth between the host and the ROV. 
         [0011]    As used herein, an AUV is an autonomous underwater vehicle that is unmanned and is not tethered to a host vessel. 
     
    
     
       DRAWINGS 
         [0012]      FIG. 1  depicts a system described herein scanning an underwater structure. 
           [0013]      FIG. 2  is a perspective view of a modular scanning package that forms part of the system described herein. 
           [0014]      FIG. 3  is another perspective view of the modular scanning package. 
           [0015]      FIG. 4  illustrates a variation of the modular scanning package. 
           [0016]      FIG. 5  illustrates an example of an ROV that can employ the modular scanning package. 
           [0017]      FIG. 6  illustrates a diver operated version of the modular scanning package of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  illustrates a body of water  10  in which an underwater structure  12  is disposed. The body of water  10  can be any body of water, saltwater or freshwater. In this illustrated example, the structure  12  is a support structure of an oil platform  14 , where the support structure  12  is mounted to the floor of the body of water. However, the depiction of an oil platform support structure is exemplary only, and it is to be understood that the underwater structure can be any type of underwater structure, man-made or naturally occurring, anchored to the floor or floating. 
         [0019]    A system  16  is shown submerged in the water  10  and in position relative to the structure  12  for scanning the structure. The system  16  is illustrated in  FIG. 1  as being incorporated into an AUV. However, as described in more detail below, the system  16  is not limited to operation as or with an AUV. 
         [0020]      FIGS. 2 and 3  illustrate the system  16  in the form of a modular package. The package forms the core of the system and includes a support structure  20 , and a 3D sonar  22 , an Inertial Navigation System (INS)  24  and an electronics pressure vessel  26  mounted on the support structure  20 . 
         [0021]    In the illustrated example, the support structure  20  is a modular support frame composed of a plurality of individual hollow frame member  30  made from a suitable material such as aluminum. Each frame member  30  is generally rectangular in shape, with a plurality of holes  32  along the frame members to facilitate assembly of the support frame, to facilitate changes in the shape of the support frame, and to facilitate mounting the support frame to a host platform if desired. Gusset plates  34  or other suitable connectors connect the frame members  30  to each other. 
         [0022]    A plurality of optional eye-bolts  36  can be connected to support frame at suitable locations to facilitate attachment of lifting devices to the support frame for lifting the system. In addition, a plurality of optional handles  38  can be connected to frame members  30  at the top of the support frame, which can be to assist diver handling when the package is used in the diver operated version shown in  FIG. 6 . In addition, a plurality of optional adjustable feet  40  can be provided at the base of the support frame, which can be used for leveling the support frame while sitting on deck. 
         [0023]    With continued reference to  FIGS. 2 and 3 , the 3D sonar  22  is mounted on the support structure  20 . The 3D sonar  22  can be any sonar that creates a 3D image. An example of a suitable 3D sonar is the CodaOctopus Echoscope available from 
         [0024]    CodaOctopus Products. In the illustrated embodiment, the sonar  22  is mounted so that the sonar  22  points toward or out the side of the support structure so as to send pings out to the side. The sonar  22  is also oriented at a desired angle relative to vertical as evident from  FIG. 2 . For example, the sonar  22  can be tilted downward at an angle relative to vertical. However, it is to be understood that in appropriate circumstances, the sonar  22  could be mounted so as to point in other directions and have other orientations relative to vertical. 
         [0025]    The 3D sonar  22  is electrically connected to the electronics pressure vessel  26  and to the data processing electronics and data storage devices therein, so that data produced by the sonar  22  as it sends out and receives returning pings are routed to the pressure vessel. In addition, the 3D sonar  22  receives power from the pressure vessel  26 . 
         [0026]    The INS  24  is also mounted on the support structure  20 . The INS  24  determines the position, orientation, and velocity (direction and speed of movement) of the support structure  20 . The INS  24  includes a Doppler Velocity Log (DVL) unit that faces downward for use in determining velocity. The INS  24  can be any system that can determine position, orientation, and velocity (direction and speed of movement). An example of a suitable INS is the Sea DeVil available from Kearfott Corporation. 
         [0027]    A Conductivity, Temperature, Depth (CTD) sensor  70  for sensing salinity of the water, water temperature, and depth is also provided. The CTD sensor improves the operation of the 3D sonar  22  and the INS  24  by providing speed of sound information and a reference depth measurement. It is understood that any sensor providing this information can be substituted in place of the sensor  70 , and that the system can be operated without the sensor CTD sensor  70 . 
         [0028]    The electronics pressure vessel  26  is also mounted on the support structure  20 . The pressure vessel  26  comprises a water-tight, pressure resistant canister that includes a hollow can closed at each end by end caps. At least one of the end caps is removably connected to the canister to allow access to the interior of the canister. 
         [0029]    The interior of the electronics pressure vessel  26  contains the data processing capability (hardware and software) suitable for the scanning tasks being performed by the system  16 . In one example, the electronics pressure vessel  26  includes one or more data processors, one or more non-volatile storage device, and other associated components required to operate the sonar  22 , the INS  24 , and the CTD sensor  70 , and to interface to the host platform, which optionally includes power and communication connections. For each data processor, there is preferably at least one of the non-volatile storage devices associated with the data processor. 
         [0030]    The modular package may also contain one or more additional sonar systems of different frequencies to collect different data about the structure being inspected. For example, a low frequency sonar system having a frequency lower than the sonar system  22  can be provided. As described in U.S. Provisional Patent Application Ser. No. 61/406479, filed on Oct. 25, 2010, and titled Remote Flooded Member Detection, the low frequency sonar system can be used to inspect the structure for flooded members. This low frequency sonar system would also be mounted on the modular support frame and would be electrically connected to the electronics pressure vessel  26 . 
         [0031]    The modular package may also contain one or more cameras and/or lights for use in collecting visual data of the structure being inspected. The cameras, if present, can be still and/or video, color and/or black and white, cameras. The lights, if present, can be flash/strobe and/or sustained lights. These cameras and lights would also be mounted on the modular support frame and electrically connected to the electronics pressure vessel. Optionally a GPS system can also be connected to the electronics pressure vessel and mounted on the modular support frame. 
         [0032]      FIG. 4  illustrates a variation of the modular scanning package that includes all of the components illustrated in  FIGS. 2 and 3 . In addition, a camera platform  80  is mounted at the rear of the support structure  20  having a diver&#39;s video camera  82  mounted on the platform and pointed out the same side of the support structure as the 3D sonar. Blocks of flotation foam  84  or other buoyant members can be attached to the support structure to make the system neutrally buoyant. In the case of use with an AUV or an ROV, neutral buoyancy would not be required and the blocks of flotation foam need not be used. One or more rechargeable batteries  86  can provide power to the system  16 , and a junction box  88  can be provided for use in linking multiple batteries together and connecting them to the electronics pressure vessel  26 . 
         [0033]    The embodiment of the system in  FIG. 4  is especially suited for use as a diver operated version of the system as shown in  FIG. 6 . In this version, the system is towed by a diver operated tow vehicle  100  that is tethered to the system. A second diver can grasp handles provided at the rear of the support structure for operating the system. An umbilical  102  can extend from the system to a host platform  104 , for example a surface ship, via which data and/or power (if suitable battery power is not provided on the support frame) can be transmitted between the system and the host platform. However, the system in  FIG. 6  can be operated by divers with or without the umbilical  102 . 
         [0034]      FIG. 5  illustrates an example of an ROV  120  on which the system  16  can be used. The system  16  would be mounted to the bottom  122  of the ROV  120  in the manner of a tool skid, for example using the mounting holes  32 . 
         [0035]    The system described above can be used in a number of different ways for a number of different purposes. The system functions as a self-contained system for scanning an underwater structure which can be diver operated, or mounted on a host platform such as an AUV or ROV. In one embodiment, the self-contained system operates 3D sonar, collects inertial navigation data, logs and processes the data from the 3D sonar and inertial navigation system to construct a full 3D model of the scanned structure which can be used for a number of purposes including change detection and feature based navigation. The collection, logging and processing of the data to construct the 3D model would be performed using the data processing electronics in the pressure vessel. In another embodiment, the self-contained system can be used to detect changes in an underwater structure by using the pressure vessel electronics to compare the latest scans from the 3D sonar to a previous scan or to an existing 3D model of the structure. In still another embodiment, the self-contained system can be used to navigate relative to an underwater structure based on features of the underwater structure from the 3D sonar scans. 
         [0036]    In the case of the self-contained system mounted on an ROV, the ROV pilot can use the live 3D sonar picture (which can be transmitted to a host vessel via the umbilical connected to the ROV or via other suitable transmission methods) to help navigate the ROV relative to the underwater structure. If an existing model of the structure is available, then the self-contained system can be used for feature based navigation and report to the ROV pilot the ROV&#39;s current position very accurately. 
         [0037]    Although the data processing is performed in the pressure vessel, the collected and processed data can be extracted from the pressure vessel. For example, when the system is brought on board a host vessel, a suitable connection such as Ethernet connection between the host and the pressure vessel can be used to extract the data. 
         [0038]    The examples disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.