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Defining Torque axis and torque rotating point

Posted Feb 10, 2011, 6:57 a.m. EST Low-Frequency Electromagnetics Version 4.0a 3 Replies

Jose Luis Sebastian
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I am trying to calculate the torque around the z axis on a dielectric sphere subjected to a non uniform E field, but I am not sure how do I have to specify the torque axis and the torque point coordinates. I have tried writing x = 0, y =0, z = 1 in the force calculation field, but it does not give the correct value. Is this the correct procedure?.
I will wellcome any advice on how I enter the torque axis and values for the torque point.

J.L. Sebastian
3 Replies Last Post Feb 10, 2011, 4:08 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 10, 2011, 7:32 a.m. EST
Hi

for the reactions forces and torques, you need to efine the point of action (origine) and then you get out the three compoonents in the solution frame used. If your axis is different you must recalculate it correspondingly from the x,y,z coordinates (or X,Y,Z depending on your settings)

The moments are calculated from the reaction forces taking into acount the "origine of the action point" see the corresponding intenal equations. For me this has always worked OK

--
Good luck
Ivar
Hi for the reactions forces and torques, you need to efine the point of action (origine) and then you get out the three compoonents in the solution frame used. If your axis is different you must recalculate it correspondingly from the x,y,z coordinates (or X,Y,Z depending on your settings) The moments are calculated from the reaction forces taking into acount the "origine of the action point" see the corresponding intenal equations. For me this has always worked OK -- Good luck Ivar
Jose Luis Sebastian
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Posted: 1 decade ago Feb 10, 2011, 11:05 a.m. EST
Thanks so much Ivar for your prompt reply.
I know that I have to define a rotating point as well as the rotating axis. The problem is that I do not know how to specify these data in the "Force calculation fields rax and ro".
If I want the rotation axis to be the "z axis", and my sphere is placed in x =, y =0 z = 20 (all dimensions in microns), what should I write in the torque axis "rax" and in the torque rotation point ro? .
I have tried writing x = 0, y =0 and z = 20 (in microns) for ro and x =0, y =0 and z = 1 for rax, but the result is not correct for the torque z component..
If I write x = 1, y =0 and z = 0 (in microns) and keep the same values for ro, I GET the same value for trhe torque z component. How would this be possible?.
It is clear to me that I am entering the wrong values, as it seems that COMSOL is not identifying the correct axis torque (z axis).

Could you please specify more clearly how should I enter the values for the rotating point and the torque axis?.

I have looked carefully through the manuals, but the information provided is very scarce.

I am really stucked with this calculation, therefore i will sincerely appreciate any further help you may give me.

Regards

Jose L. Sebastian
Thanks so much Ivar for your prompt reply. I know that I have to define a rotating point as well as the rotating axis. The problem is that I do not know how to specify these data in the "Force calculation fields rax and ro". If I want the rotation axis to be the "z axis", and my sphere is placed in x =, y =0 z = 20 (all dimensions in microns), what should I write in the torque axis "rax" and in the torque rotation point ro? . I have tried writing x = 0, y =0 and z = 20 (in microns) for ro and x =0, y =0 and z = 1 for rax, but the result is not correct for the torque z component.. If I write x = 1, y =0 and z = 0 (in microns) and keep the same values for ro, I GET the same value for trhe torque z component. How would this be possible?. It is clear to me that I am entering the wrong values, as it seems that COMSOL is not identifying the correct axis torque (z axis). Could you please specify more clearly how should I enter the values for the rotating point and the torque axis?. I have looked carefully through the manuals, but the information provided is very scarce. I am really stucked with this calculation, therefore i will sincerely appreciate any further help you may give me. Regards Jose L. Sebastian
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 10, 2011, 4:08 p.m. EST
Hi

are you talking about the RBC rigid Body Connector (input for which you define a point and an axis and you apply a moment M) or the postprocessing "Reaction forces and Moments" for the latter you define a centre, but no axis, as the three components are RMx,RMy,RMz and its up to you to combine these to get your arbitrary angle axis output.

By the way you can alsomcreate a coordinate system and access the matrix elements, check the underlaying equations to see how to use them

--
Good luck
Ivar
Hi are you talking about the RBC rigid Body Connector (input for which you define a point and an axis and you apply a moment M) or the postprocessing "Reaction forces and Moments" for the latter you define a centre, but no axis, as the three components are RMx,RMy,RMz and its up to you to combine these to get your arbitrary angle axis output. By the way you can alsomcreate a coordinate system and access the matrix elements, check the underlaying equations to see how to use them -- Good luck Ivar

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