Using simulators and computer modelling will help the offshore industry overcome a new wave of challenges
Key issues with current dynamic positioning (DP) systems include low-quality failure mode effect analysis (FMEA), a lack of knowledge on fault alarm limits for propulsion thrusters, gyrocompasses and other sensors and a shortage of anomaly logging with DP systems. Whereas development trends include greater interest in open-bus-tie configurations and adding batteries for cutting emissions and adding redundancy.
Sandercott Project Engineering offshore DP consultant and director, Steve Sandercott, said these issues are causing headaches to system developers and vessel operators. This includes how many old systems have limited hardware and software support, development of new position reference technologies, such as targetless radar, issues with DP anomaly logging and lack of quality of FMEAs. There are also mismatches in displayed alarm limits for gyros, wind sensors and feedback-prediction errors.
“We need a longer snapshot of DP performance, so if a gyro drops out, this event is logged and put in a file,” said Mr Sandercott. This data could be used for trend analysis and preventing incidents in the future.
ABL Group principal engineer and DP surveyor, Nitin Thulkar, explained how different configurations of hybrid power systems influence DP operations. More OSV owners are converting vessels with batteries and generator sets and considering fuel cells for DP vessels. Mr Thulkar explained the challenges of managing power and energy from multiple power sources, the design issues in battery sizes for DP vessels and safety aspects of operating batteries.
The benefits of using batteries include reducing fuel costs and genset running hours, and providing redundancy in DP systems. But there are challenges to overcome in terms of reducing costs and raising the energy density of batteries, integrating batteries into vessel power-management systems and lowering safety risks.
“The way forward is to reduce the risk of fires and explosions, doing research into increasing battery density and chemical safety polymers, developing green offshore charging stations and introducing floating anchor areas for vessels,” said Dr Thulkar.
NJC Power director Nick Clarke explained the importance of simulating DP systems for performance and power faults, to diagnose issues and implement solutions.
“If rubbish goes in, then rubbish comes out”
Advanced DP systems 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.
He noted that simulators and computer modelling are only as good as the information fed into them: “If rubbish goes in, then rubbish comes out.”
Advanced simulations can uncover hidden failures, demonstrate how faults can propagate throughout the system and simulate the behaviour of intermittent faults.
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