SIGMA frigate 9813


there is a good role for CFD here, together with Precal (3D potential flow panel code) and Shipmo (strip theory). It is not replacing but adding to the possibilities.”


ART Many ships use Anti-Roll Tanks (ART) as a roll-damping device. CFD can help in the design of these tanks to provide more insight into the influence of complex inter- nal structures.


In 2014, DSNS and MARIN did model tests with the Anti-Roll Tanks on a hexapod. Re- action forces and moments were measured for different roll frequencies and amplitudes, with a variety of internal structure configu- rations. “This has provided a huge database and test matrix, with a lot of validation material. And we will be able to use it to optimise our ships,” he says.


Following the tests, MARIN did the ReFRESCO calculations for the model and it will help train people at DSNS so they can do the calculations themselves in the future.


CFD is also being used to examine the above water smoke hindrance on the aft part of ship. Exhaust gas can sometimes get trapped in the wake behind the superstruc- ture. Here, DSNS is currently applying open source software. “This enables us to investi- gate the risks of smoke hindrance in the early design stage, rather than carrying out the tests in a wind tunnel.”


“We believe a good place to start with ReFRESCO is for the bare hull resistance, without the shaft lines and then in the next phase apply it with the appendages and in a few years, with the propeller and ship together. This is all still in calm water but waves will be added later on.” Damen is investigating how far we can get with CFD and which tool suits our needs, he says.


“We can already see that some of the tests that used to be done at MARIN are now being replaced by CFD such as the paint smear tests. And I think bare hull resistance tests will be replaced by CFD. Coupled with this there is more pressure to reduce the design time and building process.” Mr van


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Straten outlines where he expects CFD to play a role going forward. For DSNS, it will for sure be significant in the ‘resistance and propulsion train’ (bare hull, with appendag- es and the ship/propeller combination), he comments.


Ship motions And if considering ship motions and seakeeping, again CFD has a valuable role to play. “For example when examining roll damping one of the traditional tests at MARIN is ‘roll decay’ – where the roll angle is applied to the model and then measured to see how quickly the roll motion decays. We want to do this using CFD. The damping of roll motions is currently covered by some generic formulations but I think


Good relationship There are plenty of areas where CFD will increasingly be used, he stresses, and the nature of model tests will change. “I think there will be a shift in the type of problem looked at by model testing and the scope of the testing phase will be reduced in the earlier phases. But there are areas that are still difficult to tackle with CFD alone – cavitation for instance. Although there have been some recent cavitation tests within Cooperative Research Ship, which look quite promising.”


Overall, whether working on model test campaigns or CFD calculations, DSNS and MARIN will continue to partner each other in the future. “The R&D teams all know each other very well. MARIN is always willing to help with any intermediate questions between test campaigns. Having a good relationship with such a research institute is very important to us.”


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