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Quasi-Static or Inertial Terms

Posted Mar 21, 2012, 8:31 a.m. EDT Version 4.2a 3 Replies

Delwar
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Dear moderator and COMSOL user,
I built up a model for time dependent analysis of Structural mechancis module of COMSOL 4.2a. I am more interested to see the time dependance behavior of this piezo. When I compute the time dependent study, it is working but the pressure in the Ti does not changing with time(for 1D plot).
In the structural transient behavior of Piezo Devices, there are Quasi-static and Include inertial terms. When I select the ''Quasi-static'', the simulation results for pressure or displacement of PZT doesn't changnig with time(shows const. value) but for ''include inertial terms'' , it is changing with time.

What should I select to see the change of pressure or displacement of PZT with time for 1D Plots?


Regards
D Bhuyan


3 Replies Last Post Apr 15, 2012, 4:15 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 Mar 21, 2012, 2:04 p.m. EDT
Hi

check the equations of your physics when you turn on and off the inertial terms, you wil lsee the d^_u_/dt^2 term drops out, then check how this influences the pressure term

Nromally it's better to use the inertial terms if you look for the transient response, the only thing is that you need then to have smooth and coherent initial conditions, else you get large transient ringings that might mask your effects, or the del might just not converge

--
Good luck
Ivar
Hi check the equations of your physics when you turn on and off the inertial terms, you wil lsee the d^_u_/dt^2 term drops out, then check how this influences the pressure term Nromally it's better to use the inertial terms if you look for the transient response, the only thing is that you need then to have smooth and coherent initial conditions, else you get large transient ringings that might mask your effects, or the del might just not converge -- Good luck Ivar
Delwar
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Posted: 1 decade ago Apr 12, 2012, 8:19 p.m. EDT
Dear User,
I am interested to see the transient behaviour of thesimulation model. For example, If I apply electrical potential in the piezo and time range(0 to 400us, stepsize 1us). 1) How can I define the variable for transient analysis of piezo?
2) How can I build up the PZT response for simply pulse excitation? I have attached the model for your consideration.

Please give me a feedback.

Thanks
D Bhuyan
Dear User, I am interested to see the transient behaviour of thesimulation model. For example, If I apply electrical potential in the piezo and time range(0 to 400us, stepsize 1us). 1) How can I define the variable for transient analysis of piezo? 2) How can I build up the PZT response for simply pulse excitation? I have attached the model for your consideration. Please give me a feedback. Thanks D Bhuyan

Attachments:

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Apr 15, 2012, 4:15 a.m. EDT
Hi

the include inertial terms, adds (keep) the "rho*d^2 _u_ / dt^2" term in the equation, you have all transient behaviour, including the ringing from any inconsistent initial conditions w.r.t. to the steady state at solving start

in your case I'm not sure what to use as I do not fully uderstand your model, the fixyed part of the PZT seems bizarre for me as its the domain that should deform, and I do not see any time varying voltage, only a 100V steady state, which from the "0" initial conditions gives a "bang" hence ringing with the inertial terms, which dissapear if you remove the inertial terms, but this is the same as a statonary case.

aanother thing your puls/rect defined is symmetric (plot it to check), so you need to use an time offset when you call it to start at "0" and get the pulse in the positive time domain (i.e. "V=100[V]*Pulse((t-2*Pulse_hw)[1/s])

Finally do not forget to use an "intermittent" or "strict" time stepping, and choose a smaller time (i.e.0.1[us]) step if you include the inertial terms as its ringing at quite a high frequency ;)

--
Good luck
Ivar
Hi the include inertial terms, adds (keep) the "rho*d^2 _u_ / dt^2" term in the equation, you have all transient behaviour, including the ringing from any inconsistent initial conditions w.r.t. to the steady state at solving start in your case I'm not sure what to use as I do not fully uderstand your model, the fixyed part of the PZT seems bizarre for me as its the domain that should deform, and I do not see any time varying voltage, only a 100V steady state, which from the "0" initial conditions gives a "bang" hence ringing with the inertial terms, which dissapear if you remove the inertial terms, but this is the same as a statonary case. aanother thing your puls/rect defined is symmetric (plot it to check), so you need to use an time offset when you call it to start at "0" and get the pulse in the positive time domain (i.e. "V=100[V]*Pulse((t-2*Pulse_hw)[1/s]) Finally do not forget to use an "intermittent" or "strict" time stepping, and choose a smaller time (i.e.0.1[us]) step if you include the inertial terms as its ringing at quite a high frequency ;) -- Good luck Ivar

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