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Changing material does not change electric field distribution!

Posted 2017年11月27日 GMT-5 08:45 1 Reply

Hossein Nili
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Hi, I am simulating a 2D domain, wherer there is an electrode as a half-line at bottom of a rectangular domain. I apply a potential (fixed, DC) to the electrode, and the domain is filled with water. I am using the Electric Currents module under AC/DC. The simulation works and I get results. The trouble is that changing the material from water to 'anything' (drastically altering the relative permittivity and the conductivity) does not give the slightest change in the results. It would help a lot if you could please guide me as to where the problem comes from. Many thanks

1 Reply Last Post 2017年11月27日 GMT-5 09:25
Jeff Hiller COMSOL Employee

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Posted: 7 years ago 2017年11月27日 GMT-5 09:25
Updated: 7 years ago 2017年11月27日 GMT-5 10:17

Hello Hossein,

In some cases, the solution of a PDE is independent of the material properties.

In your case, it sounds like you're solving the steady-state electric currents equation with a spatially-independent conductivity , and with your boundary conditions being all Dirichlet or zero flux. In that case, you can see that , the conductivity, is the only material property that appears in the equation and the BCs, and that it can actually be removed from the equation (because is spatially-independent and can therefore be taken out of the divergence and eliminated from the equation by dividing both sides by ) and the BCs (by dividing both sides of those BCs by ).

Best regards,

Jeff

PS: While in your model the voltage and electric potential (which is defined solely in terms of the voltage) do not depend on , some other quantities do, for instance the current density.

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Jeff Hiller
Hello Hossein, In some cases, the solution of a PDE is independent of the material properties. In your case, it sounds like you're solving the steady-state electric currents equation with a spatially-independent conductivity \sigma, and with your boundary conditions being all Dirichlet or zero flux. In that case, you can see that \sigma, the conductivity, is the only material property that appears in the equation and the BCs, and that it can actually be removed from the equation (because \sigma is spatially-independent and can therefore be taken out of the divergence and eliminated from the equation by dividing both sides by \sigma) and the BCs (by dividing both sides of those BCs by \sigma). Best regards, Jeff PS: While in your model the voltage and electric potential (which is defined solely in terms of the voltage) do not depend on \sigma, some other quantities do, for instance the current density.

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