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## Comsol 4.0 : electric currents - el. potential V continuity between two adjacent domains?

Posted Jun 12, 2014, 11:36 AM EDT AC/DC & Electromagnetics, Geometry Version 4.0 5 Replies

Hello all,

I have a fairly simple yet bizarre problem with my Comsol model.

I am using Comsol 4.0, 2D, Electric Currents.

I have an annulus (a ring) that's split in two domains, each with a different conductivity and permittivity (but constant).

On one side of the annulus for the boundaries there I have an Electric Potential set, and on the other side of the annulus for the boundaries there I have a Ground set.

That's pretty much my model. When I run it in stationary mode, I have a bizzare solution, which can only makes sense if the potential isn't continuous between the internal boundaries inside the ring, between the two domains. Even more so, if I do a plot of Electric Field I notice the huge discrepancies at the borders of the domains, like E(domain1) ~= E(domain2) which should be false!

Analitically, I should have the potential as:

For the innermost part of the ring, the one that has a boundary with electric potential, the potential inside this domain is defined as:

V1(r) = V_boundary + (V_boundary - V_ground) * log(r / r_min) / log (r_min/ r_max )

For the outermost part of the ring, the one that has a boundary with ground set, the potential inside this domain is defined as:

V2(r) = V_ground + (V_boundary - V_ground) * log( r / r_max ) / log ( r_min / r_max )

Where V_boundary is the potential, V_ground is the ground, r is the radius of the point where I want to calculate the potential, r_min is the innermost part of the ring and r_max is the outermost part of the ring.

Plotting this for

1) V_boundary of 40.000 V,

2) r_min = 0.02 m,

3) r_max = 0.10 m

4) each domain having 0.04 m

(so 0.02 -> 0.06 m is domain 1, and 0.06 -> 0.10 m is domain 2)

5) sigma_domain1 = 1e-15 S/m

6) sigma_domain2 = 1e-16 S/m

7) epsilon_r_domain1 = 2.2 -

8) epsilon_r_domain2 = 3.5 -

I **should** have something like this:

-- Attached file : Image_analytical

Using this model, or using its counterpoint axi-symmetric 2D model, I keep getting this result:

-- Attached file : Image_comsol

I've tried using Union mode and Assembly mode for creating the geometry, but alas, it's still the same. I've attached all 3 models which basically all give the same result, different than the one I should be getting analytically.

Am I doing something wrong?

Please advise.

Thank you!

I have a fairly simple yet bizarre problem with my Comsol model.

I am using Comsol 4.0, 2D, Electric Currents.

I have an annulus (a ring) that's split in two domains, each with a different conductivity and permittivity (but constant).

On one side of the annulus for the boundaries there I have an Electric Potential set, and on the other side of the annulus for the boundaries there I have a Ground set.

That's pretty much my model. When I run it in stationary mode, I have a bizzare solution, which can only makes sense if the potential isn't continuous between the internal boundaries inside the ring, between the two domains. Even more so, if I do a plot of Electric Field I notice the huge discrepancies at the borders of the domains, like E(domain1) ~= E(domain2) which should be false!

Analitically, I should have the potential as:

For the innermost part of the ring, the one that has a boundary with electric potential, the potential inside this domain is defined as:

V1(r) = V_boundary + (V_boundary - V_ground) * log(r / r_min) / log (r_min/ r_max )

For the outermost part of the ring, the one that has a boundary with ground set, the potential inside this domain is defined as:

V2(r) = V_ground + (V_boundary - V_ground) * log( r / r_max ) / log ( r_min / r_max )

Where V_boundary is the potential, V_ground is the ground, r is the radius of the point where I want to calculate the potential, r_min is the innermost part of the ring and r_max is the outermost part of the ring.

Plotting this for

1) V_boundary of 40.000 V,

2) r_min = 0.02 m,

3) r_max = 0.10 m

4) each domain having 0.04 m

(so 0.02 -> 0.06 m is domain 1, and 0.06 -> 0.10 m is domain 2)

5) sigma_domain1 = 1e-15 S/m

6) sigma_domain2 = 1e-16 S/m

7) epsilon_r_domain1 = 2.2 -

8) epsilon_r_domain2 = 3.5 -

I **should** have something like this:

-- Attached file : Image_analytical

Using this model, or using its counterpoint axi-symmetric 2D model, I keep getting this result:

-- Attached file : Image_comsol

I've tried using Union mode and Assembly mode for creating the geometry, but alas, it's still the same. I've attached all 3 models which basically all give the same result, different than the one I should be getting analytically.

Am I doing something wrong?

Please advise.

Thank you!

Attachments:

5 Replies Last Post Jun 13, 2014, 10:36 AM EDT