[zyfsoton]

Dear All,

I am simulating ship in waves using interFoam (OpenFOAM v7). My customized case is based on DTCHull tutorial. In setFields, the free suface is set at z=0.244m. I am wondering if I need to change the hull, eg changing to KCS hull, how I can determine the free surface position? what value I should input for z?

Any help is appreciated!

Many thanks,

Tony

[Ship Designer]

Hello Tony, in the DTC Hull tutorial, the z coordinate corresponds to the draft of the model used in the towing tank, whereas they left the z = 0 coordinate at the baseline of the model. For the KCS hull you can find the draft of the model in literature or on a website of any of the workshops that used it. You would also need to adjust href accordingly.

I prefer to shift the geometry of the hull down the z axis, so that the free surface becomes z = 0. The results are the same but it has several advantages for post-processing. It is easier e.g. in ParaView to set up the free surface elevation and wave contours, because their z-coordinates simply become positive for crests and negative for troughs and you can read the heights directly. Otherwise you have to always remember to correct the z-coordinates or you would need to shift the entire domain first to obtain the still water surface at z = 0.

I think for seakeeping and manoeuvring simulations the z axis is defined to be positive downwards and the origin close to amidships, so there are many ways to define the coordinate system and there's no right or wrong. The choice depends on the application and what makes more sense for post-processing. The important thing is to not get confused.

Hope this helps. Cheers, Claudio