Remotely operated underwater vehicle
A remotely operated underwater vehicle (ROUV) or remotely operated vehicle (ROV) is a free-swimming submersible craft used to perform underwater observation, inspection and physical tasks such as valve operations, hydraulic functions and other general tasks within the subsea oil and gas industry, military, scientific and other applications. ROVs can also carry tooling packages for undertaking specific tasks such as pull-in and connection of flexible flowlines and umbilicals, and component replacement.[1]
"Remotely operated vehicle" redirects here. For vehicles operating out of water, see remote control vehicle.
Submersible ROVs are normally classified into categories based on their size, weight, ability or power. Some common ratings are:
Submersible ROVs may be "free swimming" where they operate neutrally buoyant on a tether from the launch ship or platform, or they may be "garaged" where they operate from a submersible "garage" or "tophat" on a tether attached to the heavy garage that is lowered from the ship or platform. Both techniques have their pros and cons; however very deep work is normally done with a garage.[6]
Construction[edit]
Work-class ROVs are built with a large flotation pack on top of an aluminium chassis to provide the necessary buoyancy to perform a variety of tasks. The sophistication of construction of the aluminum frame varies depending on the manufacturer's design. Syntactic foam is often used for the flotation material. A tooling skid may be fitted at the bottom of the system to accommodate a variety of sensors or tooling packages. By placing the light components on the top and the heavy components on the bottom, the overall system has a large separation between the center of buoyancy and the center of gravity: this provides stability and the stiffness to do work underwater. Thrusters are placed between center of buoyancy and center of gravity to maintain the attitude stability of the robot in maneuvers. Various thruster configurations and control algorithms can be used to give appropriate positional and attitude control during the operations, particularly in high current waters. Thrusters are usually in a balanced vector configuration to provide the most precise control possible.
Electrical components can be in oil-filled water tight compartments or one-atmosphere compartments to protect them from corrosion in seawater and being crushed by the extreme pressure exerted on the ROV while working deep. The ROV will be fitted with thrusters, cameras, lights, tether, a frame, and pilot controls to perform basic work.[11] Additional sensors, such as manipulators and sonar, can be fitted as needed for specific tasks.[12] It is common to find ROVs with two robotic arms; each manipulator may have a different gripping jaw. The cameras may also be guarded for protection against collisions.
The majority of the work-class ROVs are built as described above; however, this is not the only style in ROV building method. Smaller ROVs can have very different designs, each appropriate to its intended task. Larger ROVs are commonly deployed and operated from vessels, so the ROV may have landing skids for retrieval to the deck.
Remotely operated vehicles have three basic configurations. Each of these brings specific limitations.
Tether management[edit]
ROVs require a tether, or an umbilical, (unlike an AUV) in order to transmit power and data between the vehicle and the surface. The size and weight of the tether should be considered: too large of a tether will adversely affect the drag of the vehicle, and too small may not be robust enough for lifting requirements during launch and recovery.
The tether is typically spooled onto a tether management system (TMS) which helps manage the tether so that it does not become tangled or knotted. In some situations it can be used as a winch to lower or recover the vehicle.[14]
Applications[edit]
Survey[edit]
Survey or inspection ROVs are generally smaller than work class ROVs and are often sub-classified as either Class I: Observation Only or Class II Observation with payload.[15] They are used to assist with hydrographic survey, i.e. the location and positioning of subsea structures, and also for inspection work for example pipeline surveys, jacket inspections and marine hull inspection of vessels. Survey ROVs (also known as "eyeballs"), although smaller than workclass, often have comparable performance with regard to the ability to hold position in currents, and often carry similar tools and equipment - lighting, cameras, sonar, ultra-short baseline (USBL) beacon, Raman spectrometer,[16] and strobe flasher depending on the payload capability of the vehicle and the needs of the user.