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about the L parameter in AC/DC module
Posted 5 ago 2010, 10:04 GMT-4 3 Replies
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Hi, I try to use COMSOL to simulate a DC motor and I use the rotating machinery model under AC/DC module. I found there is a length parameter labelled L in the subdomain dialogue box and its default value is 1m. I think this is the lenght of the motor in z axis that I simulated, is that correct? I tried to change the value of this parameter to 0.1m, but nothing happens to the result, it is the same as before, so I wonder if somebody can tell me something about this parameter.
thanks!
thanks!
3 Replies Last Post 5 ago 2010, 14:01 GMT-4
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Posted:
1 decade ago
Hi
if you are in 2D, in fact you are still solving for 3D but by default COMSOL considers 1[m] depths (depends on the application mode/physics) this has it's importance if you calculate forces or torques as the units must remain consistent and a motor of 10cm depth or 1m depth should give you 10x more torque, if you keep the rest idntical. now COMSOl often renormalises over the depth too, that is why it's so important to always consider the units. Loads are mostly applied as presures [N/m^2=Pa] so ifyou have total forces in [N] you need to divide the value by the active surface,. before you enter tzhis value into a comsol load defined in pressure. thereis a good similitude with the 2D-3D relation via the depth. All depends if you are looking on a variable that scales with "z" the in plane dimension
Hope this helps
--
Good luck
Ivar
if you are in 2D, in fact you are still solving for 3D but by default COMSOL considers 1[m] depths (depends on the application mode/physics) this has it's importance if you calculate forces or torques as the units must remain consistent and a motor of 10cm depth or 1m depth should give you 10x more torque, if you keep the rest idntical. now COMSOl often renormalises over the depth too, that is why it's so important to always consider the units. Loads are mostly applied as presures [N/m^2=Pa] so ifyou have total forces in [N] you need to divide the value by the active surface,. before you enter tzhis value into a comsol load defined in pressure. thereis a good similitude with the 2D-3D relation via the depth. All depends if you are looking on a variable that scales with "z" the in plane dimension
Hope this helps
--
Good luck
Ivar
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Posted:
1 decade ago
Hi, thanks for your reply.
As you said, I am doing simulation in 2D and the value I want to get is the torque of a rotating machine. if I leave the L to be 1m, the torque I get is 104 N*m. AfterI changing L to 0.1m, I still get 104 N*m, but it should be 104/10=10.4 N*m, right? So how can I setup the variable to see this change in torque as the length of the machine varies?
As you said, I am doing simulation in 2D and the value I want to get is the torque of a rotating machine. if I leave the L to be 1m, the torque I get is 104 N*m. AfterI changing L to 0.1m, I still get 104 N*m, but it should be 104/10=10.4 N*m, right? So how can I setup the variable to see this change in torque as the length of the machine varies?
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Posted:
1 decade ago
Hi
Notfully I believe, because the reply from COMSOL is obviously normalised since it does not change when you change the depth.
To get the absolute force you need to divide by 0.1[m] as you write out phyiscally in your equation.
This is so, I believe, to allow easy trsansfer from one physics to another
--
Good luck
Ivar
Notfully I believe, because the reply from COMSOL is obviously normalised since it does not change when you change the depth.
To get the absolute force you need to divide by 0.1[m] as you write out phyiscally in your equation.
This is so, I believe, to allow easy trsansfer from one physics to another
--
Good luck
Ivar