# Discussion Forum

## Calculating of torque

RSS feed   |   Turn on email notifications   |   4 Replies   Last post: May 4, 2012 5:02pm UTC

Artem Polunin

May 1, 2012 10:29pm UTC

Calculating of torque

Hi

I have COMSOL 4.2a and I'm new in COMSOL. I'm simulating in AC/DC module Switched Reluctance Motor and I need to calculate torque of rotor and build plot of torque depending on angle of rotation. In user guide I found only equations how to calculate torque using Maxwell’s stress tensor and any example how to do it. Does someone have an example or user guide how to calculate torque.

Thank you in advance,
Artem

Jens Krause

May 2, 2012 9:43am UTC in response to Artem Polunin

Re: Calculating of torque

Hi Artem

You need to add to your model tree a node "Force Calculation" under "Magnetic Fields" and select
the regions you want to compute the torque. Then after solving there is a
global variable for forces and torque.

In the hel look for
AC/DC Module > The Electric Field Interfaces > The Electrostatics Interface
which is applicable also in the magnetic case

Cheers

Jens

Artem Polunin

May 3, 2012 10:49pm UTC in response to Jens Krause

Re: Calculating of torque

Hi

Thanks for the reply. I've calculated the torque, but when I do Global Evaluation I can choose Axial torque, Torque x, y, z components. So I always get ZERO for all torques, except torque z component, but I don't understand what is this torque mean and this torque much bigger than I calculated it analitically. As I understand z axis in 2d models mean length (depth) of the motor, but I needed the torque that lies on the x-y axes. Also z torque doesn't depend on lenght of the motor, I have length in Global Definitions, but I think I must somehow make torque depending on legth. I also tried to change Torque axis and Torque rotation point, but z torque changes when Torque rotation point much bigger than diameter of the rotor. How can I find a normal torque?

I attached my model.

Thank you in advance,
Artem

Ivar Kjelberg

May 4, 2012 6:57am UTC in response to Artem Polunin

Re: Calculating of torque

Hi

that looks nice, the forces are high but that is also for a 1m long (deep in Z) device, so 12 N/cm is not that much, or ?

Check your depth in the main physics node.

A few comments: why not add the shaft to the magnetic iron domain and give it some mu_r > 1, also I often check my action/reaction forces hence also measure the force of the complementary parts (stator in your case).

The best force/torque values are obtaines when the part is fully surrounded by air (or the same material) I noticed only a few N difference if I add the air all around so its not really significant in your case. but dor the rotor, I would add the axis too if you add it to the magnetic domain.

Last thing, if you want to get a better mesh in tha thin air gap, add a circle with an inner boundary splitting the air in the middle of the gap and have some 4 nodes over the gap. You can then also use this boundary as a rotating one, in Geometry Assembly mode

Force/torque values are very sensitives to the mesh, I have often noticed that using "boundary mesh" can improve the values, to be tested carefully

Nice model

--
Good luck
Ivar

Artem Polunin

May 4, 2012 5:02pm UTC in response to Ivar Kjelberg

Re: Calculating of torque

Hi

Thank you very much Ivar. I've computed the torque and everything looks correct.

Cheers
Artem

Rules and guidelines