Sea Technology

NOV 2013

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Multibeam Sonar For ROV Control MBIS Enables Object-Relative Positioning, Movement By Dr. Ioseba Tena • Ed Cheesman R ecent advances in automation have seen the introduction of navigation systems which are able to fuse data from navigation sensors and use the extracted information to control UUVs. Driven initially by the development of AUVs, the solutions have found their way to the workhorse of the underwater space, the ROV. The ROV has been instrumental in the development of subsea felds. So much so that when new subsea infrastructure is designed an important requirement is to allow seamless ROV operations. From drilling (where the ROV is used to monitor the blowout preventer and riser) through construction support (surveys, touch-down monitoring, interfacing, tooling, etc.), IRM (inspection, repair and maintenance) and even in the decommissioning phase, the ROV presents the easiest and safest way to interact with the subsea environment, enabling truly amazing feats of engineering and ingenuity. From their initial development to their current form, ROVs have seen many changes and improvements. They have become more capable, going deeper and tackling a greater variety of tasks. Today, there is also a greater range of ROVs, from small, one-man portable systems to large, sophisticated work-class systems operating at thousands of feet from dedicated offshore vessels. The extensive use of ROVs has created a need for expert operators with extensive training. Their skills are required as much to pilot the systems as they are to service and maintain them. Ultimately, the bottom line is tied to how effciently and expertly an operator can fy the ROV. Until recently, the control of the ROV remained tied to the joystick commands affected by a pilot looking at a video monitor. This is an extremely challenging task, as the pilot is deprived of many sensors and is restricted to the use of 2D video monitors and some gauges. Thus, the introduction of automation has been a welcome addition. By fusing the navigation data, the ROV user can now command the ROV to hover in one place for extended periods of time, to cruise at a given velocity and even to follow a set of predefned waypoints. All of this is done in Example of a diver being tracked by an MBIS mounted on a VideoRay Sonar CoPilot. relation to coordinates in a local or global set of references, meaning that the ROV can be made to move to a position or distance measured relative to the ground. For the most part, the ROV interacts with objects, not with the ground. Many of the objects are static on the seafoor but others are fexible and may not be in a known position, so the ability to estimate their position and then control the ROV relative to them stands to improve operations radically. From monitoring loads as part of construction support at the initial stages of a feld development and inspecting risers from seabed to surface during its life all the way to inspecting the structure before a decommissioning job, object-relative positioning for ROVs adds undisputed value to operations. In order to achieve reliable control, the user must be able to obtain reliable positioning information, measuring the distance and orientation between the object and the ROV. This challenge has been met with the use of a new generation of sonar known as multibeam imaging sonar (MBIS). Multibeam Imaging Sonar MBIS are active devices which use electrically excited ceramic arrays to emit pulses of sound into the water and listen November 2013 / st 39

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