# MassMomentum sources

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 September 26, 2005, 13:30 Is there a way to setup mass/m #1 New Member   Ramiro Brito Willmersdorf Join Date: Mar 2009 Location: Recife, Pernambuco, Brasil Posts: 16 Rep Power: 10 Is there a way to setup mass/momentum point sources? Alternatively, can boundary conditions be assigned to single nodes? I'm asking because I have a very high speed jet flowing into a very large volume. If I model the inlet as a real inlet, I have to use very small elements (obviously), therefore I have to use itsy bitsy teeny weeny time steps to achieve stability (since there is no local time stepping, as I understand). We are talking element edge sizes from 0.020m to 10m here. (Obviously the mesh is nicely graded.) If I'm just interested in the global features of the flow, this is not so good, because I have to wait for thousands and thousands of time steps just for the flow information to propagate throughout the domain. I think I could get an adequate solution much faster if I could use a more uniform (with larger elements) mesh. Would it work to use a non-uniform input profile, with all nodes but one with the velocity I want? Many thanks!

 November 1, 2005, 11:46 Hi, I want to solve an equati #2 Member   olivier Petit Join Date: Mar 2009 Location: Göteborg, Sweden Posts: 67 Rep Power: 10 Hi, I want to solve an equation of momentum with an exterior force F (F doesn't depend on U, it is an volVectorField). should I make F like a source term (with fvm::Su)? because when I make : tmp UEqn ( fvm::div(phi, U) - fvm::laplacian(mu,U) ); UEqn().relax(); solve(UEqn() == -fvc::grad(p))-fvm::Su(F,U) ) I have a bad result. thanks for your help

 November 1, 2005, 15:20 no, you just add -F solve(UEq #3 Super Moderator     Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 22 no, you just add -F solve(UEqn() == -fvc::grad(p))-F) did you try that?

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