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Liquid source term with unit 1/s?
Posted Jun 20, 2010, 8:47 p.m. EDT 1 Reply
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Hi everyone
I'm working with Earth Science Module, Darcy law, however the equation that is being solved is the PDE coefficient form so my question maybe is valid for other modules as well. I'm working with a 2D domain on x-y plane, and I want to assign a uniformly distributed liquid source vertical to x-y plane (i.e. rainfall) over the whole domain. I think that the right way to do is to assign the appropriate value to f term (if I use the PDE coefficient form) or the Qs term if I use the earth science module. In other softwares usually one defines the liquid source as m/s or m^3/s which makes sence. Here in comsol the unit for the term Qs is 1/s, which I cannot understand. What does it mean "In my domain I have a Liquid source x per second"
Thanks you comsol users in advance
Giorgos
I'm working with Earth Science Module, Darcy law, however the equation that is being solved is the PDE coefficient form so my question maybe is valid for other modules as well. I'm working with a 2D domain on x-y plane, and I want to assign a uniformly distributed liquid source vertical to x-y plane (i.e. rainfall) over the whole domain. I think that the right way to do is to assign the appropriate value to f term (if I use the PDE coefficient form) or the Qs term if I use the earth science module. In other softwares usually one defines the liquid source as m/s or m^3/s which makes sence. Here in comsol the unit for the term Qs is 1/s, which I cannot understand. What does it mean "In my domain I have a Liquid source x per second"
Thanks you comsol users in advance
Giorgos
1 Reply Last Post Jun 21, 2010, 1:17 a.m. EDT
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Posted:
1 decade ago
Hi
I do not have the Earth Sience module so I cannot reproduce your case, but if you model in 2D, you should still think in 3D, and say it's per depth probably by default 1[m]. Just as in 1D its per Area by default usually 1[m^2] this affects the units too. So I suspect that ir what is happening.
This means also that often one sould multiply by these values (in 2D-axi it's often 2*pi*r the "loop length" that must be taken into account i.e. for coupling integration variables, and I believe only "r" in V4 there is a a slight change there, pls check carefully the doc.
Now, normally there are somewhere a field to define the default "depth" (Z or out of plane value), as for your case it might not be "per meter"
Think it over, and check the differences for 1D, 2D and 3D cases, I believe you would quickly find out.
Checking the units is an unique feature of COMSOL, and really it takes away many stupid errors, not always easy to spot.
Have fun Comsoling
Ivar
I do not have the Earth Sience module so I cannot reproduce your case, but if you model in 2D, you should still think in 3D, and say it's per depth probably by default 1[m]. Just as in 1D its per Area by default usually 1[m^2] this affects the units too. So I suspect that ir what is happening.
This means also that often one sould multiply by these values (in 2D-axi it's often 2*pi*r the "loop length" that must be taken into account i.e. for coupling integration variables, and I believe only "r" in V4 there is a a slight change there, pls check carefully the doc.
Now, normally there are somewhere a field to define the default "depth" (Z or out of plane value), as for your case it might not be "per meter"
Think it over, and check the differences for 1D, 2D and 3D cases, I believe you would quickly find out.
Checking the units is an unique feature of COMSOL, and really it takes away many stupid errors, not always easy to spot.
Have fun Comsoling
Ivar