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AC/DC rmm module - bug report

Posted 23 lug 2012, 11:48 GMT-4 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 12 mar 2014, 08:55 GMT-4
COMSOL Moderator

Hello L. Queval

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Nils van der Blij
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Posted: 1 decade ago 19 ago 2013, 03:50 GMT-4
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 26 ago 2013, 11:50 GMT-4
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 12 mar 2014, 04:51 GMT-4
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 12 mar 2014, 08:48 GMT-4
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 12 mar 2014, 08:55 GMT-4
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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