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derivative and units
Posted 2009/09/09 12:48 GMT-4 Geometry Version 4.1 2 Replies
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Hello!
I am wondering how exacly comsol calculate derivative?
If all the constants are in SI system, but insted of meter [m] I use centymeter[cm]. I don't inform comsol what are the units I just leave it blank. Then I run my simulation and i want to evaluate a psix - the space derivative of psi potential in Volts [V] with respect to x being space coordinate. The resoult is in [V/cm] or in [V/m] as comsol dosn't know that the basic unit of x is cm ??
Best regards
Piotr
I am wondering how exacly comsol calculate derivative?
If all the constants are in SI system, but insted of meter [m] I use centymeter[cm]. I don't inform comsol what are the units I just leave it blank. Then I run my simulation and i want to evaluate a psix - the space derivative of psi potential in Volts [V] with respect to x being space coordinate. The resoult is in [V/cm] or in [V/m] as comsol dosn't know that the basic unit of x is cm ??
Best regards
Piotr
2 Replies Last Post 2011/07/22 7:05 GMT-4
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Posted:
2 decades ago
Hello
Be careful with the units, as ANY tool having implicit units (for Comsol it's SI if you do not say anything else) then the results are in coherent SI units.
a usual garbage in => garbage out, but this is not specific to COMSOL
It's rather easy in COMSOL you can mostly add the units with a [cm] and it will transform internally to the default units you have asked for in the general model property GUI.
But, some fields do not accept units, then you have to do the transformation manually.
In anycase the result will mostly be wrong by a given scaling factor if you use [cm] when the system expect [m]. Then you have to translate the COMSOL proposed units of [V/m] into V/[cm] because you in fact want to make 1[cm] = 1[m]
Good luck
Ivar
Be careful with the units, as ANY tool having implicit units (for Comsol it's SI if you do not say anything else) then the results are in coherent SI units.
a usual garbage in => garbage out, but this is not specific to COMSOL
It's rather easy in COMSOL you can mostly add the units with a [cm] and it will transform internally to the default units you have asked for in the general model property GUI.
But, some fields do not accept units, then you have to do the transformation manually.
In anycase the result will mostly be wrong by a given scaling factor if you use [cm] when the system expect [m]. Then you have to translate the COMSOL proposed units of [V/m] into V/[cm] because you in fact want to make 1[cm] = 1[m]
Good luck
Ivar
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Posted:
1 decade ago
Hello,
I have three problems with units in Comsol.
I am trying to simulate a MEMS device in Comsol. I prepared my 3D model in Inventor and I used "mm" as my unit. When I want to transfer my model to Comsol 4.1, before I transfer my model, should I change the unit to "mm" (when Comsol asks abut the unit) or should I just transfer it to Comsol and it realizes that the units are in "mm"? If I have to define it in Comsol that my units are in "mm", how about if I draw in "m" in Inventor, and transfer it to Comsol and define "mm" as the unit in Comsol. Would it work?
Since I am modeling a MEMS device, the dimensions are very small (MAX=100 um). When I draw my model in Inventor with "micro meter" as my unit, as soon as I transfer it to Comsol, when I want to define the material, I get an error, saying it has problems in Geometry. It seems that it is TOO SMALL. What should I do?
I really appreciate if anyone can guide me.
Thank you,
Sincerely,
Keivan
I have three problems with units in Comsol.
I am trying to simulate a MEMS device in Comsol. I prepared my 3D model in Inventor and I used "mm" as my unit. When I want to transfer my model to Comsol 4.1, before I transfer my model, should I change the unit to "mm" (when Comsol asks abut the unit) or should I just transfer it to Comsol and it realizes that the units are in "mm"? If I have to define it in Comsol that my units are in "mm", how about if I draw in "m" in Inventor, and transfer it to Comsol and define "mm" as the unit in Comsol. Would it work?
Since I am modeling a MEMS device, the dimensions are very small (MAX=100 um). When I draw my model in Inventor with "micro meter" as my unit, as soon as I transfer it to Comsol, when I want to define the material, I get an error, saying it has problems in Geometry. It seems that it is TOO SMALL. What should I do?
I really appreciate if anyone can guide me.
Thank you,
Sincerely,
Keivan