# CFX Momentum Inputs Question

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 September 27, 2013, 13:50 CFX Momentum Inputs Question #1 New Member   G. Smith Join Date: Sep 2013 Posts: 3 Rep Power: 5 Hi all! I am new to using CFX and a novice with CFD analysis. I'm working on a problem with a moving tank. To simulate the movement of the tank in the fluid, I am trying to input momentum source information. The momentum info I am using was calculated from Reynolds Transport. However, for a general Reynolds Transport in Momentum, the units come out to be kg*m/s. The CFX Momentum input asks for a momentum source coefficient with units kg/(m^3 s) and a vector with units kg/(m^2 s^2). How do I go from a general momentum case to the needed values/equations for the CFX momentum input? Thank you, G. Smith

 September 27, 2013, 17:09 #2 Senior Member   Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 566 Rep Power: 11 Don't use the momentum source coefficient. That is for making it a function of velocity. Just use the Component option, which has units of kg/(m^2 s^2) = momentum per unit volume per second = (kg*m/s) / (m^3 s)

 October 21, 2013, 10:46 #3 New Member   G. Smith Join Date: Sep 2013 Posts: 3 Rep Power: 5 Thank you for the reply! The per unit volume makes sense if I divide the general momentum case by the total fluid volume. But I still don't understand how to go from general momentum to the per time. Is the general momentum divided by the timestep? or by the overall time of the run?

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