Momentum source term problem

kdarc · February 10, 2009, 13:00

Hi. I have a momentum source I need to use (in 2d) that operates with a positive value in the x-direction, but a negative value in the y-direction.

Is there a way to apply source terms to individual components of vectors???

I want to do something along the lines of:
+ fvm::Sp(S,U.component(0)) - fvm::Sp(S,U.component(1))

Any ideas??

thanks,
Ken

eugene · February 10, 2009, 14:53

As far as I know its not currently possible. The diagonal coefficient always has to be a scalar, you are trying to make it a vector.

kdarc · February 10, 2009, 16:17

One way to do this may be to simply specify Ux and Uy as scalars, and solve them separately with their own different source terms. The U vector can simply be recomposed afterwards for other standard operations.

Any obvious problems (that aren't occurring to me!!) with doing this???

Thanks.

eugene · February 11, 2009, 08:52

Well the Laplacian operator that you need for the pressure equation, is not defined for a vector. I am not sure how you would get around this problem. Perhaps use a sparse tensor?

Other than this I don't see anything fundamental, but I'm sure there will be a lot of operational issues that will complicate the problem.

I have a vague recollection that someone else wanted to do this kind of thing a few years back. Have you tried searching the forum?

February 10, 2009, 13:00	Hi. I have a momentum source	#1
kdarc Member Ken Darcovich Join Date: Mar 2009 Location: Ottawa, Canada Posts: 34 Rep Power: 17	Hi. I have a momentum source I need to use (in 2d) that operates with a positive value in the x-direction, but a negative value in the y-direction. Is there a way to apply source terms to individual components of vectors??? I want to do something along the lines of: + fvm::Sp(S,U.component(0)) - fvm::Sp(S,U.component(1)) Any ideas?? thanks, Ken

February 10, 2009, 14:53	As far as I know its not curre	#2
eugene Senior Member Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 21	As far as I know its not currently possible. The diagonal coefficient always has to be a scalar, you are trying to make it a vector.

February 10, 2009, 16:17	One way to do this may be to s	#3
kdarc Member Ken Darcovich Join Date: Mar 2009 Location: Ottawa, Canada Posts: 34 Rep Power: 17	One way to do this may be to simply specify Ux and Uy as scalars, and solve them separately with their own different source terms. The U vector can simply be recomposed afterwards for other standard operations. Any obvious problems (that aren't occurring to me!!) with doing this??? Thanks.

February 11, 2009, 08:52	Well the Laplacian operator th	#4
eugene Senior Member Eugene de Villiers Join Date: Mar 2009 Posts: 725 Rep Power: 21	Well the Laplacian operator that you need for the pressure equation, is not defined for a vector. I am not sure how you would get around this problem. Perhaps use a sparse tensor? Other than this I don't see anything fundamental, but I'm sure there will be a lot of operational issues that will complicate the problem. I have a vague recollection that someone else wanted to do this kind of thing a few years back. Have you tried searching the forum?

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