# dfbi,resistance calculation

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 January 13, 2014, 20:48 dfbi,resistance calculation #1 New Member   Join Date: Jan 2014 Posts: 3 Rep Power: 4 Dear all, I would really appreciate your help in a question that may sound a bit 'stupid'... I model the half of the geometry in STAR CCM+ in accordance with the DFBI tutorials and everything is set up properly. The resistance that I will calculate will be for the half model or for the whole? I haven't really cleared in my mind the function of the symmetry plane. And another thing,how many cells do you usually use just to calculate the calm-water resistance? Thank you again.

 January 14, 2014, 13:07 #2 New Member   Join Date: Jan 2014 Posts: 3 Rep Power: 4 Well, seeing no reply I thought to elaborate a little. When I started messing with Star CCM+ an experienced on CCM+ friend's friend (which I cannot reach anymore),advised me not to use more than 2M cells to simulate my cases (for the half of the geometry-symmetry plane,model size).Having domain dimensions equal to -2L

 January 14, 2014, 23:18 #3 Senior Member   KHB Join Date: Aug 2010 Location: Singapore Posts: 109 Rep Power: 8 Dear Antares, If you are simulating half of the domain, the Resistance value that you will obtain is only half of the 'real' resistance. This is because the pressure and shear force will be integrated and since only half of the surface that is present hence half of the total force that you will be getting. You need to remember that the mass, inertia that you need to include in the DFBI is also half of the physical thing. Regarding the sinkage value, make sure the sinkage is using the same reference, some tank test result based their sinkage on the static VCG, and maybe your simulation reference is from certain reference line, just make sure the simulation and test both are using the same reference. Mesh count I believe is largely dependent on your geometry complexity as well the speed that you are running. But I think 1-2M you should be able to get sensible result for simple shape (not like 100% error )

 January 14, 2014, 23:32 #4 New Member   Join Date: Jan 2014 Posts: 3 Rep Power: 4 Dear Lava, I was hoping that you would reply, thank you very,very much.

 January 15, 2014, 02:27 #5 Senior Member   KHB Join Date: Aug 2010 Location: Singapore Posts: 109 Rep Power: 8 You are welcome

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