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Frequency Domain Analysis

Posted Oct 31, 2012, 11:47 a.m. EDT Parameters, Variables, & Functions, Structural Mechanics Version 4.3 3 Replies

Zhangxian Deng
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Hi,

I am trying to simulate a 3-D beam in COMSOL v4.3. This beam is free in one end, and in the other end, I want to applied a sinusoidal boundary displacement input D(t)= Damp*sin(2*pi*f*t).

In the Frequency Domain study, I can add varying frequencies, but how to apply that boundary excitation? I am not using structural mechanics modulus but using PDE weak forms instead.


Thank you very much

Dan
3 Replies Last Post Nov 1, 2012, 2:55 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 31, 2012, 3:50 p.m. EDT
Hi

a frequency domain solver expects only amplitudes as external loads, there is no "t" time variabe,
For the equations it's using standard harmonic notations: d/dt is replaced by j*omega, and d^2/dt^2 by -omega^2, where omega = 2*pi*freq.

--
Good luck
Ivar
Hi a frequency domain solver expects only amplitudes as external loads, there is no "t" time variabe, For the equations it's using standard harmonic notations: d/dt is replaced by j*omega, and d^2/dt^2 by -omega^2, where omega = 2*pi*freq. -- Good luck Ivar
Zhangxian Deng
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Posted: 1 decade ago Oct 31, 2012, 5:36 p.m. EDT

Hi

a frequency domain solver expects only amplitudes as external loads, there is no "t" time variabe,
For the equations it's using standard harmonic notations: d/dt is replaced by j*omega, and d^2/dt^2 by -omega^2, where omega = 2*pi*freq.

--
Good luck
Ivar


Thanks a lot, Ivar.

Are "omega" and "j" the default variables defined inside COMSOL, or should I define by myself somewhere?

Dan
[QUOTE] Hi a frequency domain solver expects only amplitudes as external loads, there is no "t" time variabe, For the equations it's using standard harmonic notations: d/dt is replaced by j*omega, and d^2/dt^2 by -omega^2, where omega = 2*pi*freq. -- Good luck Ivar [/QUOTE] Thanks a lot, Ivar. Are "omega" and "j" the default variables defined inside COMSOL, or should I define by myself somewhere? Dan
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Nov 1, 2012, 2:55 a.m. EDT
Hi

these are defined by COMSOL when you change the solver type, just as COMSOl defines "t" for time when you do a time solver analysis

--
Good luck
Ivar
Hi these are defined by COMSOL when you change the solver type, just as COMSOl defines "t" for time when you do a time solver analysis -- Good luck Ivar

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