Piezo shunts and eigenfrequency analysis

Jacopo Marconi
Hi all,
I'm modelling a beam with a piezo attached on the top, and an electrical circuit attached to the patch: to do so I used the solid mechanics (solid), electrostatic (es) and circuit (cir) modules. I used successfully this model in both frequency domain and time domain analysis, but now that I want to perform the eigenvalue analysis (I want to extract the dispersion using my model as a periodic cell...) it doesn't work and it says that one equation is missing ("Singular matrix. - Detail: There are 1 void equations (empty rows in matrix) for the variable comp1.es.term1.Q0_ode. at coordinates: (0,0), ... "). The implementation is ok I think, in fact removing terminals and circuit it works... any idea?
Thank you all in advance,
Jacopo

Some more details:
The piezo-shunt is implemented as follows: the bottom face of the piezoelectric patch (attached to the beam) is grounded (es.ground), the upper one is connected to a circuit terminal (es.terminal 1 - type circuit), then a capacitor (in cir) is connected from node 0 (ground) to node 1 which is in turn connected to the terminal (in es) through a "External I - Terminal" connection (selecting terminal 1 for the electric potential). This layout always worked for me, I don't know what is going wrong this time...

2 Replies Last Post 2017年6月22日 GMT-0400上午10:12
Magnus Olsson COMSOL Employee
Posted: 4 months ago 2017年6月19日 GMT-0400上午3:38
Hi Jacopo,

This is because the electrical circuit interface does not explicitly support the eigenfrequency study. There is a simple workaround:

* In the Model Builder, select the Electrical Circuit node.
* In the Settings window, expand the Equation section.
* Set the Equation form to Frequency domain.
* Set the Frequency to User defined and type freq in the f field.

Now, the Electrical Circuit will have the right equation form and variables to perform eigenfrequency analysis.

N.B. Do not forget to switch back to Study controlled before running a stationary or time dependent study.

Best regards,
--
Magnus
Hi Jacopo, This is because the electrical circuit interface does not explicitly support the eigenfrequency study. There is a simple workaround: * In the Model Builder, select the Electrical Circuit node. * In the Settings window, expand the Equation section. * Set the Equation form to Frequency domain. * Set the Frequency to User defined and type freq in the f field. Now, the Electrical Circuit will have the right equation form and variables to perform eigenfrequency analysis. N.B. Do not forget to switch back to Study controlled before running a stationary or time dependent study. Best regards, -- Magnus

Jacopo Marconi
Posted: 4 months ago 2017年6月22日 GMT-0400上午10:12
Hi Magnus,

thank you very much for your answer. I did what you suggested, but unfortunately it didn't work. Here the error:

"Error in sweep. The following feature has encountered a problem:
Singular matrix.
- Detail: There are 1 void equations (empty rows in matrix) for the variable comp1.es.term1.Q0_ode.
at coordinates: (0,0), ...
There are 1 void equations (empty rows in matrix) for the variable comp1.es.term2.Q0_ode.
at coordinates: (0,0), ...
- Feature: Eigenvalue Solver 1 (sol1/e1)"

I even tried change the settings in the electrostatic node as I did in the electric circuit node, but without success. Could it be due to the sweep analysis? I'll keep trying, thank you for the help!

Jacopo
Hi Magnus, thank you very much for your answer. I did what you suggested, but unfortunately it didn't work. Here the error: "Error in sweep. The following feature has encountered a problem: Singular matrix. - Detail: There are 1 void equations (empty rows in matrix) for the variable comp1.es.term1.Q0_ode. at coordinates: (0,0), ... There are 1 void equations (empty rows in matrix) for the variable comp1.es.term2.Q0_ode. at coordinates: (0,0), ... - Feature: Eigenvalue Solver 1 (sol1/e1)" I even tried change the settings in the electrostatic node as I did in the electric circuit node, but without success. Could it be due to the sweep analysis? I'll keep trying, thank you for the help! Jacopo

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