Electric Shielding

This is a tutorial application that shows how to model isolated highly conductive objects in the Electric Currents interface. The analysis includes the current terminal and electric shielding boundary conditions.

Model Definition

The modeling domain is a seawater filled box containing an electrode. The sides of the box are insulated while the top has an assigned electric potential of 1 V and the bottom is set to ground.

Boundary Conditions on the Electrode

The first version of the application uses the terminal boundary condition with a zero net current. The electrode then assumes a constant potential determined by the surrounding field. This condition, also known as a floating potential condition, can be a good approximation if the electrode is a much better conductor than the surrounding medium. It can also be used for metal surfaces in electrostatics, where the zero current condition is replaced by a zero total charge.

The second version uses an electric shielding condition instead of the terminal boundary condition. The electric shielding condition requires the specification of the material constituting the thin layer and its thickness. When used for describing thin sheets of conducting materials, the electric shielding condition results in a potential that is assumed to be constant across the depth of the material, but varies on its surface.

Results and Discussion

Figure 1 shows the potential distribution when using the electric shielding condition. The electrode is modeled as a 1 mm thick sheet of titanium bent to form three quarters of a cylinder. The cylinder has a radius of 0.2 m and is centered in a cube with a 1 m side. The result, as seen in the surface plot, is a potential that varies between 0.472 V and 0.476 V on the conductor.

Figure 1: The electric potential distribution on the conductor and in the water when using the electric shielding condition.

For a comparison, with the zero current terminal condition, the potential on the conductor evaluates to a constant 0.474 V.

ACDC_Module/Resistive_Devices/electric_shielding

Modeling Instructions

From the menu, choose .

New

In the window, click .

Model Wizard

In the window, click .

In the tree, select .

Click .

In the tree, select .

Click .

Geometry 1

Create the model geometry, starting with the electrode.

Cylinder 1 (cyl1)

In the toolbar, click .

In the window for , locate the section.

From the list, choose .

Locate the section. In the text field, type 0.2.

In the text field, type 0.2.

Locate the section. In the text field, type 0.4.

In the text field, type 0.5.

Locate the section. From the list, choose .

In the text field, type 1.

In the text field, type 0.

Click .

Next, delete the segment of the cylinder that lies in the octant y ≤ 0, z ≥ 0.

Delete Entities 1 (del1)

In the window, right-click and choose .

Select the boundary shown in the figure below by clicking on it.

In the window for , click .

In order to facilitate applying materials and boundary conditions, create a selection of the electrode object.

Explicit Selection 1 (sel1)

In the toolbar, click and choose .

In the window for , locate the section.

From the list, choose .

In the window, click on the three boundaries constituting the electrode.

Right-click and choose .

In the dialog box, type Electrode in the text field.

Click .

Finish the geometry by adding a block for the salt-water domain surrounding the electrode.

Block 1 (blk1)

In the toolbar, click .

In the window for , click .

Click the button in the toolbar.

Materials

Having created the geometry, proceed to assign materials.

Add Material

In the toolbar, click to open the window.

Go to the window.

In the tree, select .

Click in the window toolbar.

In the toolbar, click to close the window.

Materials

Titanium beta-21S (mat1)

In the window for , locate the section.

From the list, choose .

Material 2 (mat2)

In the window, right-click and choose .

Right-click and choose .

In the dialog box, type Sea Water in the text field.

Click .

Select Domain 1 only.

In the window for , locate the section.

In the table, enter the following settings:


Property	Variable	Value	Unit	Property group
Electrical conductivity	sigma_iso ; sigmaii = sigma_iso, sigmaij = 0	5	S/m	Basic
Relative permittivity	epsilonr_iso ; epsilonrii = epsilonr_iso, epsilonrij = 0	85	1	Basic

Electric Currents (ec)

Ground 1

In the window, under right-click and choose .

Select Boundary 3 only.

Electric Potential 1

In the toolbar, click and choose .

Select Boundary 4 only.

In the window for , locate the section.

In the V0 text field, type 1.

Terminal 1

In the toolbar, click and choose .

In the window for , locate the section.

From the list, choose .

Next, apply an node to the electrode for use in the second study. To prevent it from overriding the node just added, it will be excluded in the first study.

Electric Shielding 1

In the toolbar, click and choose .

In the window for , locate the section.

From the list, choose .

Locate the section. In the ds text field, type 1[mm].

Mesh 1

Free Tetrahedral 1

In the window, under right-click and choose .

Size

In the window for , locate the section.

From the list, choose .

Click .

Study 1

Before solving, disable the node.

Step 1: Stationary

In the window, under click .

In the window for , locate the section.

Select the check box.

In the tree, select .

Click .

In the tree, select .

In the window, click .

In the window for , locate the section.

Clear the check box.

This setting is useful if you want full control over which plot groups to create.

In the toolbar, click .

Results

Before adding a to use for reproducing the plot in Figure 1, add a selection to the solution data set to hide the block obstructing the view of the electrode.

In the window, expand the node.

Study 1/Solution 1 (sol1)

In the window, expand the node, then click .

Selection

In the toolbar, click and choose .