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AC/DC rmm module - bug report

Posted Jul 23, 2012, 11:48 a.m. EDT Low-Frequency Electromagnetics Version 4.3b 5 Replies

L. Queval
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In the 2D generator tutorial, I changed the prescribed rotational velocity from 'rpm' to 'rpm*tri1(t[1/s])'. tri is a triangle function. Therefore the rotation speed should first increase, then decrease. As a consequence, the amplitude of the induced voltage should first increase, then decrease.
But the rotation speed first increases positively till tri(t) is maximal, then stops, then increases negatively. As a consequence, the induced voltage increases, then goes back to 0, then increases again.
What can I do to correct this ?

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L. Queval

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5 Replies Last Post Mar 12, 2014, 8:55 a.m. EDT
COMSOL Moderator

Hello L. Queval

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If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.

Nils van der Blij
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Posted: 1 decade ago Aug 19, 2013, 3:50 a.m. EDT
Dear L. Queval,

Have you been able to solve this? I'm having a similar problem. I'm doubting if Comsol was designed to be able to handle variations in rotational velocity.

Kind regards,
Nils
Dear L. Queval, Have you been able to solve this? I'm having a similar problem. I'm doubting if Comsol was designed to be able to handle variations in rotational velocity. Kind regards, Nils
L. Queval
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Posted: 1 decade ago Aug 26, 2013, 11:50 a.m. EDT
Dear Nils,

I dont know if this bug has been fixed in 4.3b. If not, you can probably get around this problem by using "prescribed rotation" instead of "prescribed velocity". It worked for me.

Good luck.

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L. Queval
Dear Nils, I dont know if this bug has been fixed in 4.3b. If not, you can probably get around this problem by using "prescribed rotation" instead of "prescribed velocity". It worked for me. Good luck. -- L. Queval
L. Queval
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Posted: 1 decade ago Mar 12, 2014, 4:51 a.m. EDT
This bug has not yet been fixed (Comsol 4.3b). See enclosed model.

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L. Queval
This bug has not yet been fixed (Comsol 4.3b). See enclosed model. -- L. Queval

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Walter Frei COMSOL Employee

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Posted: 1 decade ago Mar 12, 2014, 8:48 a.m. EDT
This is a slight misunderstanding of the functionality of the prescribed rotational velocity feature. From the documentation (p. 239 of the AC/DC User's Guide, v4.4)

"The Prescribed Rotational Velocity node imposes a coordinate transformation to the selected domain that effectively rotates it a prescribed angle that grows linearly with time. It is used to model a rotating part at a constant rotational velocity.
...
Enter a constant value for the Revolutions per second rps (SI unit: Hz) and the X and Y coordinates for the Rotation axis base point rax (SI unit: m). "

Note that the feature expects a *constant* velocity. If you want to vary velocity in time, then use the prescribed rotation feature.
This is a slight misunderstanding of the functionality of the prescribed rotational velocity feature. From the documentation (p. 239 of the AC/DC User's Guide, v4.4) "The Prescribed Rotational Velocity node imposes a coordinate transformation to the selected domain that effectively rotates it a prescribed angle that grows linearly with time. It is used to model a rotating part at a constant rotational velocity. ... Enter a constant value for the Revolutions per second rps (SI unit: Hz) and the X and Y coordinates for the Rotation axis base point rax (SI unit: m). " Note that the feature expects a *constant* velocity. If you want to vary velocity in time, then use the prescribed rotation feature.
L. Queval
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Posted: 1 decade ago Mar 12, 2014, 8:55 a.m. EDT
Thank you for the precision. The name of "prescribed rotational velocity" should then be "prescribed constant rotational velocity". Nevertheless it would be more useful if one could acutally apply a time dependant rotation speed.

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L. Queval
Thank you for the precision. The name of "prescribed rotational velocity" should then be "prescribed constant rotational velocity". Nevertheless it would be more useful if one could acutally apply a time dependant rotation speed. -- L. Queval

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