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Keep it fluidKjell Magne Gjerde Associate Fellow Fluid Mechanics Hydrodynamics and Thermo-Fluid Modelling

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Aship delivering critical supplies to an offshore drilling platform battles gale force winds and six metre high waves and still holds its position steady, to an accuracy of within two metres. In such demanding conditions how can the

captain be certain he has the right propulsion systems and the right amount of power to do the job?

Kjell Magne Gjerde knows. He is a Rolls-Royce Associate Fellow in Fluid Mechanics and Hydrodynamics. He and his team’s calculations have played a significant part in predicting the power the ship will need. Using very powerful computers they have modelled the complex forces: wind conditions; current; waves; all interacting with every aspect of the vessel.

And when he says they model every aspect, he means it, right down to the smallest detail. According to Gjerde: “If you were sitting in a chair on the deck we would have included you in the model.”

“Power predictions,” says Gjerde, “are the main parameter for determining the engines on a vessel. Knowing this at an early stage can have a significant impact on the build and operating cost of the vessel.”

AutomatedThe ability to create such complex models comes as a result of an advanced approach to the use of computational fluid dynamics (CFD). Gjerde and his team of experts have created specialist computer software that has automated some of the more standard CFD calculations allowing designers to perform them for themselves and freeing up CFD specialists to undertake ever more advanced projects.

“The first step to creating such software is to model the domain you want to study. In terms of hull resistance, for example, the complex interaction of water and the air with the vessel.” To do this a ‘computational mesh’ is constructed. This allows the calculations used to

create the model to be broken down into lots of separate small parts. A very powerful computer then solves the relevant calculations for each individual part of the mesh and its neighbours. The results from each set of calculations are combined until a complete picture is obtained of how air and water flow around the ship as it moves through the water.

Sophisticated“Historically,” Gjerde says, “this has been an obstacle. It has been difficult to model the complexity of the domain because a ship has

various appendages such as rudders, tunnel openings, propellers etc.” The development of increasingly sophisticated meshes has allowed the modelling of very complex geometry and allowed non-specialist ship designers to perform calculations that would once have been the domain of experts.

Thanks to Gjerde’s software, a ship designer can log onto a secure Rolls-Royce website, anywhere in the world, type in a small number of input values; for example, speed and range of the vessel and a couple of draughts. At the push of a button, overnight powerful computers generate a report simulating results and containing information about flow detail, pressure detail, velocity, turbulence and wave pattern.

The same web based automatic process has been adopted to model the performance characteristics of

all the propulsion/thruster range in Rolls-Royce. The software for this automatic design process has been named Propulsion template and Ship template respectively. The ultimate goal is to merge the templates into a single design template. The template components are modularised in order to be vendor independent and thus the most suitable component can be selected for specific tasks.

“This is groundbreaking. I don’t think anyone else has moved this kind of task from specialists to the designers in a fully automated way like we

Career•Kjell Magne Gjerde has a Degree in Hydrodynamics and joined Rolls-Royce in 1997 when the Ulstein Group was acquired.

•He has worked with hydrodynamics throughout his career working first on rotating machinery in water and (marine) gas turbines before specialising in rotating propellers.

•He heads a small team, based in Ulsteinvik, responsible for delivering CFD across Rolls-Royce marine sites.

CFD analysis of a UT755 vessel.

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have done. That makes the whole process much cheaper, much faster. Previously designers would have to go to a specialist for each design, now they can go through a lot of design iterations in search of the optimum design. This frees up specialists to do more advanced modelling.”

ExploringOne area where such advanced techniques are needed is modelling the interaction of multiple thrusters, such as the 12 found on the Rolls-Royce powered vessel Allseas “Pioneering Spirit.” Gjerde and his team are exploring how the thrusters interact with the hull, the vibration and noise which can be created by pressure pulses and the flow conditions into the thruster to identify the best alignment and orientation of the thrusters to maximise power.

With a wider range of vessels now using Liquefied Natural Gas (LNG) as fuel, modelling the behaviour of LNG in fuel tanks is another increasingly important area of advanced research.

Whether creating “ground breaking” software to allow non-specialists quickly and efficiently to arrive at the optimum hull design for a customer, or modelling the extreme conditions encountered delivering supplies to North Sea oil platforms, computing power is critical. Increased computing power allows more complex studies to be done better, earlier and faster than ever before, helping to push the boundaries of ship design and performance.

Author: Simon Kirby consults and lectures in marketing communications with a particular interest in technology. He has worked in communications roles extensively in both the public and private sector.

Above Vortex structures generated from a UUC thruster operating at 12 knots.

Below Thrusters being designed for installation on a vessel.