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Naming convention

Posted Apr 11, 2011, 5:39 a.m. EDT Version 4.1 3 Replies

M R
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In comsol 4.1 I want to access cp(longitudinal wave velocity) in solid mechanic , I define cp as:
mod1.solid.cp
but it gives me error why?
how should I define it?

cheers

3 Replies Last Post Apr 11, 2011, 7:29 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 11, 2011, 6:18 a.m. EDT
Hi

I'm not sure I catch your explanation correctly, are you referring to a COMSOL internal variable "cp" (I do not know that one) that appears in "solid" physics in your fist model hence can be accessed as "model1.solid.cp" ?

Or is it that you have defined a variable under the "model1" node, of

cp = someting

(and not mod1.solid.cp = something) and you want to refer to it ?

--
Good luck
Ivar
Hi I'm not sure I catch your explanation correctly, are you referring to a COMSOL internal variable "cp" (I do not know that one) that appears in "solid" physics in your fist model hence can be accessed as "model1.solid.cp" ? Or is it that you have defined a variable under the "model1" node, of cp = someting (and not mod1.solid.cp = something) and you want to refer to it ? -- Good luck Ivar
M R
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Posted: 1 decade ago Apr 11, 2011, 6:57 a.m. EDT
Hi Ivar,

cp is comsol internal variable for longitudinal wave velocity under material-solid mechanic-linear elastic material model.
Due to help of comsol I shoudl define it mat1.def.cp
but when I refer to results the expression assigned for it is mod1.solid.cp!!

when I am going to define maximun mesh size I want maximum mesh size to be cp*T (T is a number in seconds).
when I am defining maximun elemet size by mat1.def.cp*T or mod1.solid.cp*T I get error Unknown model parameter.

It is wierd because it should be correct!!
I look forward to hearing from you.

Thank you

Hi Ivar, cp is comsol internal variable for longitudinal wave velocity under material-solid mechanic-linear elastic material model. Due to help of comsol I shoudl define it mat1.def.cp but when I refer to results the expression assigned for it is mod1.solid.cp!! when I am going to define maximun mesh size I want maximum mesh size to be cp*T (T is a number in seconds). when I am defining maximun elemet size by mat1.def.cp*T or mod1.solid.cp*T I get error Unknown model parameter. It is wierd because it should be correct!! I look forward to hearing from you. Thank you
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 11, 2011, 7:29 a.m. EDT
Hi

"mat1.def.cp" is referring directly to the material, and #1, check the "tags" to see if your material is "1" or "2" or... It changes depending on how many an the order you create the material properties in your model. I try to avoid accessing directly the material properties, as these may change when you adapt the model and you easily forget that. So, "my way" is to copy the value from the particular material and make a Parameter "my_cp" and dump the numerical value and units therein. then I know where I have the variable I might need to change explicitly in front of me.

Now if you use the cp variable in your physics, then COMSOL copies the material value into the "model1.solid.cp" value FOR THAT SPECIFIC ENTITY WHERE DEFINED ! (that means that cp is not necessarily a scalar and is only defined on the domains or boundaries where the material + correct physics applies. That is why you might find the variable in the postprocessing/Results as mod1.solid.cp.

Turn on the equations (see the "Options Preferences") and check what is going on thereunder, it often helps

And another comment careful with variables names with only 1 letter, they are mostly already used by COMSOL and you might get confusion/conflicts (and often these are NOT flagged, as COMSOL allows you to fiddle with its internal variables) so "T" is normally the Temperature, use rather "tt" or "my_t". This can also easily lead to undetected errors

--
Good luck
Ivar
Hi "mat1.def.cp" is referring directly to the material, and #1, check the "tags" to see if your material is "1" or "2" or... It changes depending on how many an the order you create the material properties in your model. I try to avoid accessing directly the material properties, as these may change when you adapt the model and you easily forget that. So, "my way" is to copy the value from the particular material and make a Parameter "my_cp" and dump the numerical value and units therein. then I know where I have the variable I might need to change explicitly in front of me. Now if you use the cp variable in your physics, then COMSOL copies the material value into the "model1.solid.cp" value FOR THAT SPECIFIC ENTITY WHERE DEFINED ! (that means that cp is not necessarily a scalar and is only defined on the domains or boundaries where the material + correct physics applies. That is why you might find the variable in the postprocessing/Results as mod1.solid.cp. Turn on the equations (see the "Options Preferences") and check what is going on thereunder, it often helps And another comment careful with variables names with only 1 letter, they are mostly already used by COMSOL and you might get confusion/conflicts (and often these are NOT flagged, as COMSOL allows you to fiddle with its internal variables) so "T" is normally the Temperature, use rather "tt" or "my_t". This can also easily lead to undetected errors -- Good luck Ivar

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