Discussion Forum

Hi

the "mess" you are seeing is a mixture of natural oscillations undersampled and aliasing with a not fine enough mesh compared to the time sequence and sample size.

First you can improve by turning OFF the inertial terms and stay in +Quasi static", at least unti lyou model is working and better tuned, its often difficult to get around all the physics in one go when starting, this is so for all of us ;).

I have a few other comments, you second PZT does not have any + electrode defined, you are hitting the device hard with a 10V step starting from initial conditions 0V this puts the device into oscillations when you use the inertial terms (rho*d^2_u_/dt^2 ones). Then you need to define some coordinate orientations as I do not expect the PZD are aligned with the main coordinate system, (add one per PZT as these are oreiented differently, as you need to add one PZT physics per device to use the different orientations

Then do not forget that if you want to simualte a rapid time hange, in full dynamic you must consider the speed of sound or waves in your material to get a mesh fine enough to sample that wave

And pls use the latest version forget old 4.0 (you will be less frustrated with the newer one)

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Good luck
Ivar

Hello Mr. Ivar,
Thanks for your encouraging reply.
The previous model was in COMSOL 4.0a but now, I am using COMSOL version 4.1. I did not see the Quasi-Static for time dependent analysis. I think it behaves by default as a Quasi-static.
But how can I turn off the inertial terms? Please tell me how to define some coordinate orientations so that PZD are aligned with the main coordinate system?

I want to simulate the model for the time range(0 to 10ms) and step size 1 microsecond(1us). So what should be the proper mesh for this model? I rebuild the model in COMSOL 4.1and attached for your kind consideration

Regards
D Bhuyan

Hi
the inertial terms/quasi static appears in the main physics node (if you do not see it you might need to turn on advanced features in the view section) at least I ave it in my 4.2a version. When you check the main physics node equation view you will see that the rho*d^2_u_/dt^2 is dropped in quasi static mode

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Good luck
Ivar

Hello Mr. Ivar,
Thanks for your reply. I did not find the Quasi-Static in Comsol 4.1 but I found it in COMSOL 4.2a and replaced the model in 4.2a. But when I compute the study, it shows error(Failed to find consistent initial values). I have attached the model for your kind consideration. If you have time, can you please check this one?


Thanks
D Bhuyan

Hi

have you cehced that you have enough BC's for all physics, I see no "fixed" part so your model is flaoting in free air, that makes the life too tough for the solver it integrates away, adda fixed constraint and it will work, I'm sure ;)

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Good luck
Ivar

Dear Mr. Ivar,
Thanks a lot for your response. Now it is working. But the problem is, the simulationn results(1D plot for pressure) shows constant value, it is not changing with time. But, I want to see the pressure/displacement in the material with respect to time(for example 0 to 5ms, stepsize 1us). I have attached the model for your kind consideration.

Regards
D Bhuyan

Hi

strange, once I deleted your solver (for 2.model) and recreated them with default COMSOL settings, then changed the frequency domain sweep to range(9000,100,10000) to catch the first eigenfrequency, then changed the "Piezo material model Coordinate System" to Y-Z plane and looked at point "9" (because you have fixed point 3) I get pothe a pressure change (assymetric) and a displacement peak up in my scan

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Good luck
Ivar

Dear Mr. Ivar,
Thanks a lot. Your previous feedback was frequency domain analysis. I did it according to your instructions and it's working fine for frequency domain anlysis. Now, I can easily observe the impedance analysis of the piezo.

For your kind consideration, I am more interested to see the time dependance behaviour of piezo. So, I am trying to see the simulation results for time dependent analysis (for example range 0 to 5ms, step size 1us). When I compute the time dependent study, it is working but the pressure or displacement in the Ti does not changing with respect time(for 1D plot). If you have time can you please look at my model.