Capturing Dynamic Effects in Ship Tanks - A coupling between HydroD™ and OpenFOAM®
Abstract: When a ship with partially filled tanks is subjected to waves with frequencies in the vicinityof the natural period of the fluid inside the tanks, sloshing occurs. Sloshing influences theseakeeping properties of a ship but can be hard to capture when using softwares inseakeeping. DNVs software HydroD has this problem and cannot capture the dynamic forcesfrom the tank, as it is today. The dynamic forces can be captured by using CFD and that iswhy a coupling between HydroD and a CFD software is interesting to investigate. By usingalready existing CFD software, that is able to give these dynamic forces as a force input, theproblem might get solved. If choosing OpenFOAM which has the advantage of being easyavailable and free, it could also be beneficial from an economical point of view, since itwould cost DNV more to develop a CFD feature in HydroD than using this software.The idea was to run HydroD initially to get a motion output from a barge model that would beused as motion input for the tank simulated in OpenFOAM. In turn, OpenFOAM wouldoutput forces to be used as force input in HydroD. This data exchange between the twoprograms would make an iterative process that would go on until the motion in HydroDconverged.When investigating this problem, the results were verified against a known experiment wherea model of a barge with a tank was subjected to beam sea and free to move in sway, heave androll.Two particular cases were studied, one where the tank had no free surface effect and could beconsidered “closed”, and one where the tank was partially filled having a free surface. For thecase without any free surface, results agreed well with the experimental one but for the casewhere there was a free surface present, the results were not as satisfying. Still, these resultsgave an indication that it could be possible to use OpenFOAM together with HydroD, butunfortunately time was a restricting factor which is why further work will be needed forobtaining better agreement, as described in recommendations.
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