EoW May 2009

technical article

delivered to the work site via a manned submersible, more like the Deep-Sea ROV. Additionally, the vehicle’s autonomous capability provides a means to recover the vehicle if the fibre optic tether were to sever or break during the operation. The vehicle can be pre-programmed prior to the start of the operation with a geodetic location to return to if communication is lost. This could be as simple as a single location or instruction to swim out on the same path as was used to reach the work site. To assist with autonomous navigation the Hybrid AUV/ROV is equipped with a GPS (Global Positioning System). The vehicle can be programmed to come to the surface during transit to the work site to obtain a navigational fix. Once the fix has been obtained the vehicle can correct its course and proceed to the next waypoint. The vehicle is also equipped with high-frequency sonar, as seen in Figure 6 , which is employed for obstacle avoidance and to help locate the work site.

vehicle’s activities and allow the operator to take control of the vehicle at any time. Additionally, if the fibre optic tether were to break, the vehicle is pre-programmed to return to a selected location for recovery. In the ROV mode, the operator can take control of the vehicle to conduct inspections such as to check damage on hulls of ships, potential faults in dams, and leaks in potable water tunnels. 4.2 Description The shape of the Hybrid AUV/ROV is drastically different from that of the original Deep-Sea ROV. The profile of the vehicle mimics the contours of a standard submarine or torpedo design. The body shape allows the vehicle to speed (> 3.5 knots) through rough waters and heavy currents. The Hybrid AUV/ROV is 6" in diameter and over 62" in length. Though larger than the Deep-Sea ROV, it has the agility needed to position itself for near field inspections. The vehicle has a main propulsion screw for forward and reverse motion as well as vertical and lateral thrusters located in the fore body. Refer to Figure 5 for a schematic of the AUV/ROV. The Hybrid AUV/ROV is similar to the Deep-Sea ROV in that it has an onboard power supply and is tethered to the command station via the same Deep-Sea ROV cable. Cable is paid out of the vehicle in a more simplistic manner than the original Deep-Sea ROV, storing up to 2,000metres of cable within its hull. The tether leaves the vehicle via a small tube called the stinger, so as to prevent the cable from getting caught up in the propulsion system. The Hybrid AUV/ROV has improved electronics and sensors to allow it to perform its role as a piece of inspection equipment. 4.3 Advantages The Hybrid AUV/ROV has the capability of travelling long distances without any human intervention via its autonomous operation mode. The advantages of the autonomous mode are that: (1) it provides a stand-off capability from the work site and (2) it eases operator loading by not having to steer the vehicle at high speed over a long distance. Without a stand-off capability, the Hybrid AUV/ROV would have to be Figure 5 ▲ ▲

Another advantage of the ROV was its ability to provide real-time high-resolution video images via a high-resolution camera and sophisticated lighting, as seen in Figure 3 .

Figure 3 ▲ ▲

Since the ROV’s buoyancy, yaw and pitch could be adjusted on the fly, this ROV could be very effective on missions requiring tricky manoeuvres. 3.4 Disadvantages The Deep-Sea ROV was designed for a niche application. Because it was a slow moving vehicle (< 3 knots) and it had a finite amount of battery life, the ROV had to be placed in very close proximity to the inspection site. A majority of the time it would be carried to the site via a manned submersible in a launch and recovery enclosure (LARE) as seen in Figure 4 . The BOT could operate in currents of 2 knots or less.

Figure 6 ▲ ▲

Once the Hybrid AUV/ROV has reached its destination the operator shifts to the ROV mode and monitors the high-resolution imagery available from the two video cameras. One camera is located on the nose and the other on the GPS mast. The camera located on the GPS mast is used both surfaced and submerged. This camera can assist with navigation when surfaced and provide a different perspective when submerged since the nose of the vehicle is visible in the viewing area. In addition, the Hybrid AUV/ROV has two lasers located on the nose, used to provide a fixed reference frame for sizing objects seen through the nose camera. 4.4 Disadvantages The Hybrid AUV/ROV was not designed to penetrate shipwrecks or small void areas; the long length of the vehicle offsets the small diameter size.

Figure 4 ▲ ▲

4 Hybrid AUV/ROV 4.1 Purpose The purpose of the hybrid vehicle is to take the advantage of the Deep-Sea ROV technology and couple that with the advantages of an autonomous, free swimming vehicle. This was achieved by using a Myring hull design vice the box shape of the first generation Deep-Sea ROV. The Hybrid AUV/ROV is capable of greater distances as well as the handling of strong water currents. The Hybrid AUV/ROV has two modes of operation: (1) autonomous and (2) ROV. In the autonomous mode, the vehicle can be programmed via mission planning software to operate using waypoint navigation. In this mode the fibre optic tether can be used to monitor the

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EuroWire – May 2009