When it comes to vessel design and optimization, computational fluid dynamics (CFD) can be game-changing, according to Wartsila.
Computational Fluid Dynamics
CFD uses advanced computational power to predict how water will flow in and around ship components. By analyzing how individual components work together in the water, experts can achieve significant savings in energy efficiency.
Using CFD helps to:
- optimize vessel performance
- increase efficiency
- troubleshoot design problems – and much more.
Norbert Bulten, Senior Product Performance Manager, is a CFD veteran. He has been working with CFD at Wärtsilä since the discipline was in its infancy – and he’s full of helpful facts about CFD that could benefit any vessel. Here are just six that may surprise you, all gained from Norbert’s decades of work in the field.
Perfecting Design
Before CFD, designing a component like a ship’s propeller took a long time and was very expensive. The only way to reveal how water flowed around your propeller was to build a model and test it in a tank. If your design wasn’t exactly right, it was back to the drawing board and then back to the tank for testing.
With CFD, the designer simply inputs the propeller geometry into the CFD software and the performance curve is ready in one or two hours. The designer can run CFD for 10 or 20 variants, then use this information to squeeze every last percentage of performance gain. This also means optimization can happen in the early design phases – when the real difference can be made.
Improve Performance
In its earliest days, CFD was used to improve the performance of individual components. Now it considers the vessel as a whole and how it behaves in the water. Understanding how components work together leads to even greater performance improvements, allowing greater optimization than would be possible individually.
For example, CFD can dramatically improve the way azimuth thrusters interact with the ship’s hull. Experts using CFD found that tilting the angle of the propeller shaft by 8° significantly reduces interaction with the ship. This is a game changer if you look at overall ship efficiency – a small change, made possible by CFD, that delivers up to 20% higher effective thrust.
These CFD-inspired changes help to minimize fuel consumption and contribute to the decarbonization of shipping.
Fixing Design Flaws
If an issue with your ship’s design comes to light during the sea trial, you must act fast. CFD can help to iron out design problems even at this late stage in the process. Wärtsilä’s CFD experts have often stepped in to find solutions to issues even when it hasn’t been the company’s responsibility.
In one case a propeller showed unexpected vibration levels. A detailed CFD simulation of the vessel showed the inflow causing the problems, due to poorly aligned brackets. Without CFD it could have been assumed that it was the propeller itself causing the issue, rather than something that could be fixed with a small modification.
In another case the shipyard didn’t use the right waterjet inlet duct design. Some quick simulations showed them how, with minimal welding and grinding, they could fix the problem. It was a subtle difference – but enough to get the performance over the design threshold and the vessel ready to be handed over to the customer.
In this case CFD was then used to design a new waterjet inlet duct for the sister vessel, which resulted in a top-performing ship that could accelerate from 0–55 knots (approx. 100 km/h) within 60 seconds.
Making Impossible Possible
For those who are used to relying on model-scale testing, it can be a leap of trust to believe in CFD analysis. That makes Wärtsilä’s decades-long successful track record very important – but seeing is believing. The best way to help people understand and visualize the results of CFD calculations is with virtual reality (VR).
Virtual dive inspections using VR glasses show things that would otherwise be impossible to demonstrate – letting anyone who wants to see where the water is flowing for themselves. In real life, a diver couldn’t go anywhere near a moving vessel, but in VR you can switch the propellers on and swim through them.
This gives you first-hand experience of how the water is flowing and affecting your vessel in a way that is clear and easy to understand.
Full-Scale Simulations
Model-scale measurements have been the industry standard for over 100 years. But CFD is changing the game again. As computing power has increased and CFD has advanced, it is often doing a better job than model-scale measurements. Crucially, it is also faster and cheaper.
For customers that want to test in a model basin, CFD can provide the performance curves for model scale and the model tests will confirm it.
CFD can also produce full-scale simulations. Why is this important? Well, the more we learn, the more we discover where the assumptions of model scale have got it wrong.
For example, in the case of a vessel with a duct, it’s crystal clear that model basins don’t accurately represent what’s happening. A full-scale CFD simulation is the only way to get the accurate data you need.
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Source: Wartsila
