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Data is key for DP simulation and design
As dynamic positioning (DP) systems on offshore vessels, drilling rigs and shuttle tankers become more advanced, there is an increasing need for thorough simulation for greater reliability
Experts explained why the quality and veracity of data was important for enhanced simulation and modelling at Riviera Maritime Media’s European Dynamic Positioning Conference, in London, UK, 7 February 2023.
NJC Power director Nick Clarke explained the importance of simulating DP systems for performance and power faults to diagnose issues and implement solutions to rectify problems.
Advanced DP systems, such as those under DP3 class for offshore semi-submersible drilling rigs and drillships, require complex levels of testing and simulation. Modelling potential power faults, such as short circuits, grounding faults, over or under voltage and load imbalances, means vessel owners and charterers can be assured DP systems are reliable and resilient.
“Systems need to ride through faults and healthy systems should remain online to provide assurance of power to DP systems,” said Mr Clarke. “Simulations will need to be all encompassing,” but as DP systems become more advanced, “the quality of simulations becomes significant.”
He said simulators and computer modelling are only as good as the information fed into them. “They are only as good as the data input,” said Mr Clarke. “If rubbish goes in then rubbish comes out.”
Advanced simulation can uncover hidden failures, demonstrate how faults can propagate throughout the system and simulate the behaviour of intermittent faults.
OneStep Power Solutions president Mark Craig said data from remote trials, DP testing and annual testing should be used to improve power and DP system design using multiple sources of information, such as real-time data, images and regular measurements.
“We need multiple points of data and cannot just rely on one source,” Mr Craig said. “We need better data from DP and power systems testing.”
Validating data enables vessel owners to demonstrate predictability and reliability of DP systems to charterers. There are also benefits for owners with large fleets of ships.
“Owners can identify hidden failures on vessels and retest others in the fleet,” said Mr Craig. “Charterers should help to fund the costs of these advanced and complicated tests.”
Wärtsilä has developed methods of analysing performance using computational fluid dynamics (CFD) and other simulation for its range of thrusters.
CFD was used to design azimuth thrusters, their tilt and configuration on various ships and offshore support vessels. Their performance was then validated through model testing and real ship operations.
“Our azimuth thrusters were optimised using full-scale CFD,” said Wärtsilä product performance manager for thrusters Petra Stoltenkamp.
One of the main CFD studies involved analysing the tilt of thrusters for optimal performance and minimal losses.
“There is minimal friction with the hull and power losses from the thruster,” said Ms Stoltenkamp. The optimal tilt was 8˚ with the flow from the thruster not hindered by the vessel hull or other thrusters.
Wärtsilä also developed the OPTI-DP tool for analysis of thrusters’ 360˚ performance, loadings, allocations and configurations.
“We have shown less power is needed by optimising propulsion, reducing design costs and lead times and providing better assurance of full-scale performance,” said Ms Stoltenkamp.
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