Simulating Subsea Scenarios
by Dr. Jason Tisdall
CEO, General Robotics Limited
Just a generation ago subsea oil deposits were being discovered and exploited at depths of around 300 metres. Today, as readily accessible oil becomes exhausted, attention is being transferred to oil reservoirs at depths of 3,000 metres and beyond. This presents a range of challenges which require the use of autonomous and remotely controlled equipment and techniques. To an ever increasing extent Visualisation and Simulation technologies are playing a key role in the remote operation of subsea and ocean floor equipment.
Visualisation and Simulation are distinct technologies with different but complementary applications. Visualisation ranges from a simple graphic model of a field to a complex graphic model in which objects can be moved around relative to each other by an operator, and can be both 2D and 3D. Visualisations can show live data input, so GPS and USBL inputs give the position of a support vessel and its ROV or a pipelay barge and its anchor lines. This allows operations to be shown in real-time such as tracking an ROV's manoeuvres near a subsea structure, or monitoring touchdown during cable or pipeline deployment.
Simulation, rather than just showing inputs, incorporates a physics engine so objects move in response to their environment (e.g. complex water currents and swell) and may also include user interactive inputs in parallel.
A pilot training simulator should reproduce the actual subsea conditions that an ROV pilot has to work with. Hydrodynamic modelling of objects in the water is important, so that the ROV simulator responds to the controls just like its real counterpart, with behaviour based on actual physical properties like: mass, density, drag, taking account of currents and ROV speed and the resultant forces acting on the tether and the ROV. Different visibility conditions can also be simulated, with varying light levels, water fogging and suspended particles together with an accurate sonar system to provide realistic support data. An ROV trainer simulates the subsea environment which pilots must “fly” through interactively and presents complex situations where the pilot’s decisions directly affect the success of a mission.
Subsea services providers like Sonsub and DeepOcean AS are increasingly making use of simulators. DeepOcean uses a simulator to train pilots for its KystDesign Installer and Supporter ROVs, working from ships and oil platforms in the North Sea and the Mediterranean.
DeepOcean used to recruit experienced ROV pilots and then cross-train them on the ROVs offshore, but as the volume of work grew, on-the-job training became too slow and expensive. It takes a new pilot, with no prior ROV experience, around two years of training to gain DeepOcean's certificate of competence. Using the simulator, pupils can notch up the training hours far more quickly and cheaply than using the ROVs at sea; in addition, a real work environment is not the best place to train new pilots.
"We believe the simulator is paying for itself - more qualified pilots can be deployed more flexibly, which is making our offshore operations more efficient," said Sven Storesund, Superintendent ROV/Survey at DeepOcean. "We can now give existing pilots refresher and scenario training on-shore. A unique aspect of the simulator is that you can play around with new techniques which would be prohibitively expensive, and possibly dangerous, using the ROV for real."
Sonsub expects its ROV operators to be able to take the machines apart offshore, change components and reassemble them. As a result simulator training also involves learning to troubleshoot problems using diagnostics software included in the simulator, which replicates hardware failures offshore so trainees can practise fault finding.
An important benefit of a simulator integrated with an ROV is the capacity to rehearse subsea projects down to the level of individual tasks. Sonsub’s project teams can prepare a complete 3D virtual scene of the subsea facility, and pilots and other offshore personnel are given a chance to perform the planned operations in a simulated environment. This gives an invaluable opportunity to practise the best way of carrying out the planned tasks, exposing possible problems and allowing alternative strategies to be developed before going offshore.
There is a clear trend towards using visualisation and simulation tools in ROV and other offshore operations, for both task planning and crew training. In the future, engineering tools and planning tools will continue to converge, so not only will the deployment of equipment to the seabed be visualised taking in live inputs, but control and simulation will come together to allow the operator to respond to events and drive what happens in the real world. Such developments promise huge benefits not just in improved training and reduced operation timescales but in greater operational predictability and reliability, leading in turn to improved safety, lower costs and lower environmental impact in all offshore tasks.
Dr. Jason Tisdall is CEO of UK-based General Robotics Limited, a leading and vastly experienced provider of subsea visualisation and simulation systems since 1988. To contact Tisdall, email jason-tisdall@generalrobotics.co.uk.
