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Distance between two plates in a boundary condition

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Dear Comsolers,

using only the Solid Mechanics physics, I try to simulate the mechanical behaviour if a capacitor made out of a rubber-like silicone. The dielectrica as well as the electrodes are soft and compliant. When a voltage is applied to the electrodes, the dielectrica between the two electrodes gets compressed by a mechanical pressure and the electrodes move closer together. The electrical field causes this mechanical pressure (maxwell stress) which can be described by the following equation:

where is the vacuum permittivity, is the relative static permittivity, the applied voltage (a fixed value, say 2.5kV) and the distance between the two electrodes.

How can I access the distance between the two electrodes? I would like to use it in order to set up a boundary load condition on the electrode-surfaces using as a pressure. As I define the geometry, the distance is well known at first, but becomes unknown when the capacitor is deformed. Also, the distance has not the same value over the whole geometry, so I need to access a scalar field containig all distances at every node.

I attached a picture of the unformed capacitor, where the elctrodes (blue) are volumes (and not surfaces). I am interested in the distance between the inner surfaces of the two electrodes.

Any help or hint is much appreciated, thanks a lot in advance!

My comsol version: 5.3

P.D.: I don't want to use the Electrostatics module. I think it is unnesessary in this case. Also, I am simply interested in learning how to access the distance d as in my question.



5 Replies Last Post 21.05.2018, 08:36 GMT-4
Edgar J. Kaiser Certified Consultant

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Posted: 7 years ago 18.05.2018, 12:44 GMT-4

Hi,

as the distance d extends in z-direction, would d-w be what you need? This can be evaluated on the surfaces.

Cheers Edgar

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Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Hi, as the distance d extends in z-direction, would d-w be what you need? This can be evaluated on the surfaces. Cheers Edgar

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Posted: 7 years ago 19.05.2018, 08:51 GMT-4

Dear Edgar, thanks a lot for your reply!

Yes, is exactly what I need. To be more precise, I need , where is the displacment on the upper electrode and the displacment of the lower electrode.

How can I evaluate and on the surfaces so it gets updated in every iteration of the solver?

Dear Edgar, thanks a lot for your reply! Yes, d-w is exactly what I need. To be more precise, I need d - (w_2-w_1), where w_2 is the displacment on the upper electrode and w_1 the displacment of the lower electrode. How can I evaluate w_1 and w_2 on the surfaces so it gets updated in every iteration of the solver?

Edgar J. Kaiser Certified Consultant

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Posted: 7 years ago 19.05.2018, 09:18 GMT-4

Freed,

you might use it in a coupling operator, e.g. an average operator that works on the respective boundary.

w1 = aveop1(w) on one electrode w2 = aveop2(w) on the other electrode

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Freed, you might use it in a coupling operator, e.g. an average operator that works on the respective boundary. w1 = aveop1(w) on one electrode w2 = aveop2(w) on the other electrode Cheers Edgar

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Posted: 7 years ago 21.05.2018, 07:19 GMT-4
Updated: 7 years ago 21.05.2018, 07:21 GMT-4

Hey Edgar, I'm a beginner in Comsol and almost embarassed to ask, but how do I evaluate w on just one surface and store its values in a variable which I can access somewhere else? I tried it with a surface-probe, but that doesn't seem to work during the calculation (only after the calculation has terminated).

Also, I'd need a point- or knotwise evaluation of w and not an average value. How could I access w pointwise?

Thanks again

Hey Edgar, I'm a beginner in Comsol and almost embarassed to ask, but how do I evaluate w on just one surface and store its values in a variable which I can access somewhere else? I tried it with a surface-probe, but that doesn't seem to work during the calculation (only after the calculation has terminated). Also, I'd need a point- or knotwise evaluation of w and not an average value. How could I access w pointwise? Thanks again

Henrik Sönnerlind COMSOL Employee

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Posted: 7 years ago 21.05.2018, 08:36 GMT-4

Hi,

You are looking for one of the extrusion coupling operators, under Defintions->Component Couplings.

Regards,
Henrik

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Henrik Sönnerlind
COMSOL
Hi, You are looking for one of the extrusion coupling operators, under Defintions->Component Couplings. Regards, Henrik

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