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pulse generation

Posted Apr 26, 2012, 8:47 a.m. EDT Low-Frequency Electromagnetics, Heat Transfer & Phase Change Version 4.2a 3 Replies

Mohammad Arif Saber
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Hi,

I am new to comsol and I want to generate a single pulse of 0.7 v of 20us . this will act as a voltage to a structure and the structure will get heated up. Now my point is to see how fast the structure cools down.

I have no idea how to do this. what I did is defined a rectangle function with lower limit as 20 us and upper limit as 40 us and then i try to use 0.7*rect1(t1) as a input voltage. I tried to follow the suggestion in the other threads but could not understand. Can anybody help me? BTW I am using V4.2a.
3 Replies Last Post Apr 30, 2012, 1:57 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 26, 2012, 2:34 p.m. EDT
Hi

the rect() or pulse function, just as he step function has a rise time defined in the dvanced tab (normally "closed") you need to adapt this parameter too when you have such short pulses, do not make it too steep, or then at least define enough time stepping (or parameter stepping) points in the solver definition to catch the rise time (I would say at least 5 step during the rise and fall time. If you are doing time dependent studies, as I understand, check also the solver stepping settings and use an "intermediate" and NOT automatic stepping scheme, as you have a rise and a fall time here. Then if the default BDF does not converge, you could also try the Gen-alpha solver, it's sometimes more stable, but often somewhat slower, all depends ...

--
Good luck
Ivar
Hi the rect() or pulse function, just as he step function has a rise time defined in the dvanced tab (normally "closed") you need to adapt this parameter too when you have such short pulses, do not make it too steep, or then at least define enough time stepping (or parameter stepping) points in the solver definition to catch the rise time (I would say at least 5 step during the rise and fall time. If you are doing time dependent studies, as I understand, check also the solver stepping settings and use an "intermediate" and NOT automatic stepping scheme, as you have a rise and a fall time here. Then if the default BDF does not converge, you could also try the Gen-alpha solver, it's sometimes more stable, but often somewhat slower, all depends ... -- Good luck Ivar
Mohammad Arif Saber
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Posted: 1 decade ago Apr 30, 2012, 3:35 a.m. EDT
Hi Ivar,

Thanks a lot for your reply. I started reading the user's guide after your reply but could not find any advanced tab. how can I activate this advanced tab ?
Hi Ivar, Thanks a lot for your reply. I started reading the user's guide after your reply but could not find any advanced tab. how can I activate this advanced tab ?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 30, 2012, 1:57 p.m. EDT
Hi

my fault it's not the advanced it's the "smoothing" tab (I get also confused, and I'm not always behind my WS ;)

You are right that many of the "advanced" tabs are hidden,by default you must turn them on from the the Options Preferences View tab

--
Good luck
Ivar
Hi my fault it's not the advanced it's the "smoothing" tab (I get also confused, and I'm not always behind my WS ;) You are right that many of the "advanced" tabs are hidden,by default you must turn them on from the the Options Preferences View tab -- Good luck Ivar

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