Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

AC/DC rmm module - bug report

Please login with a confirmed email address before reporting spam

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 ?

--
L. Queval


5 Replies Last Post 12 mar 2014, 08:55 GMT-4
COMSOL Moderator

Hello L. Queval

Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.

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


Please login with a confirmed email address before reporting spam

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

Please login with a confirmed email address before reporting spam

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.

--
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

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 12 mar 2014, 04:51 GMT-4
This bug has not yet been fixed (Comsol 4.3b). See enclosed model.

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


Walter Frei COMSOL Employee

Please login with a confirmed email address before reporting spam

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.

Please login with a confirmed email address before reporting spam

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.

--
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

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.