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--- simple_electrostatic_simulation_in_femm_-_step-by-step_tutorial [2021/05/11 20:15]
stanzurek [Step 8 - circuits]
+++ simple_electrostatic_simulation_in_femm_-_step-by-step_tutorial [2021/05/11 22:08] (current)
stanzurek [Step 19 - that's it!]
@@ Line 42: / Line 42: @@
 {{enter_point.png}} Fig. 3-2. Entering point with coordinates (0,0)
-Click on the ''Zoom extents'' button (Fig. 3-3), which is the third one (white rectangle with a magnifying glass). (//If not sure - hover a mouse over the buttons and see their description in the botoom left of the FEMM window.//)
+Click on the ''Zoom extents'' button (Fig. 3-3), which is the third one (white rectangle with a magnifying glass). (//If not sure - hover a mouse over the buttons and see their description in the bottom left of the FEMM window.//)
 Then click on the ''Zoom out'' button once (magnifying glass with a minus).
@@ Line 90: / Line 90: @@
 {{el/conductors_el.png?500}} Fig. 8-1. Menu for "Conductors"
-Several currents can be specified and used for separate windings or conductors. A new circuit can be added by ''Add Property'' (Fig. 8-2), and filling the value of current in the ''Circuit Property'' pop-up window.
+Several "Conductors" can be specified and used for separate electrodes. A new conductor can be added by ''Add Property'' (Fig. 8-2), and filling the value of current in the ''Circuit Property'' pop-up window.
-The phase of the current is specified by using complex notation. For example, the value of ''0.7071+I*0.7071'', means that there is ''0.7071'' of the real component (0 deg. phase) and ''+I*0.7071'' means the imaginary component (90 deg. phase), so this combination represents a peak current of 1.000 A at 45 deg. phase.
+The conditions can be prescribed either by voltage (value in volts, V) or as imposed electric charge (in coulombs, C).
-FEMM only solves with current as the input variable. It is not possible to set voltage. If the voltage needs to be used then some iterative calculations are required (especially with non-linear materials). External calculations are required. See an example here: https://www.femm.info/wiki/MyTransformer
+(In FEMM calculation of capacitance is independent of voltage, so sometimes setting a voltage difference of 1 V is beneficial because it simplifies calculation of capacitance, as it is done in this example.)
 {{el/circuit_property_el.png?600}} Fig. 8-2. Add Conductor
@@ Line 105: / Line 105: @@
 FEMM contains a library / database of materials, which can be used in the model, Fig. 9-1.
-{{material_library.png?500}} Fig. 9-1. Acessing Materials Library
+{{el/material_library_el.png?500}} Fig. 9-1. Accessing Materials Library
-The library window has two parts. On the left ("database" in Fig. 8-2), there are all the available materials as provided by FEMM. New materials can be added ot it if needed.
+The library window has two parts. On the left ("database" in Fig. 9-2), there are all the available materials as provided by FEMM. New materials can be added to it if needed.
 The part on the right is for all the materials which will be accessible within the given model. Simply use the mouse to drag-and-drop method to drag the given material from the left to the right sub-window.
-{{material_library2.png?500}} Fig. 9-2. Database (left) and model (right), drag-and-drop
+{{el/material_library2_el.png?500}} Fig. 9-2. Database (left) and model (right), drag-and-drop
 ----
 ==== Step 10 - boundary ====
-FEM equations require boundary conditions to be solved. They act as a reference point. Many different conditions can be specified, but for a simple magnetics simulation it is typically most useful to use the built-in "open boundary" feature. This boundary simulates an infinitely large volume (hence "open"), even though it can be positioned quite close to the simulated objects.
+FEM equations require boundary conditions to be solved. They act as a reference point. Many different conditions can be specified, but for a simple electrostatic simulation it is typically most useful to use the built-in "open boundary" feature. This boundary simulates an infinitely large volume (hence "open"), even though it can be positioned quite close to the simulated objects.
-This "open boundary" method (Fig. 10-1) should be done only afer all other geometry was created, because it can automatically set the right size of the boundary, suitably larger thatn the rest of the model. If this is the case then nothing needs to be changed in the pop-up window, and all the default values can be accepted with "OK".
+This "open boundary" method (Fig. 10-1) should be done only after all other geometry was created, because it can automatically set the right size of the boundary, suitably larger than the rest of the model. If this is the case then nothing needs to be changed in the pop-up window, and all the default values can be accepted with "OK".
-{{open_boundary.png?500}} Fig. 10-1. Create open boundary automatically
+{{el/open_boundary_el.png?500}} Fig. 10-1. Create open boundary automatically
-After accepting there will be many cirles created automatically, Fig. 10-2. There will be some block names appearing in the circles (as shown by the red arrows). These should be ignored, because they are needed for correct operation of the boundary.
+After accepting there will be many circles created automatically, Fig. 10-2. There will be some block names appearing in the circles (as shown by the red arrows). These should be ignored, because they are needed for correct operation of the boundary.
-{{open_boundary2.png?500}} Fig. 10-2. Open boundary created
+{{el/open_boundary2_el.png?500}} Fig. 10-2. Open boundary created
 ----
 ==== Step 11 - block labels, materials, currents ====
-Every part in the model must have a material data assigned to it, so FEMM know how to solve it. Each area completely surrounded by blue lines or arcs represtents a "block", and each such block has to have the material specified for it. This is done by using the gren icon //Operate on block labels//, Fig. 11-1.
+Every part in the model must have a material data assigned to it, so FEMM know how to solve it. Each area completely surrounded by blue lines or arcs represents a "block", and each such block has to have the material specified for it. This is done by using the green icon //Operate on block labels//, Fig. 11-1.
-After selecting the option click somewhere (anywhere) inside of each block, as shown in Fig. 11-1. A green point called ''<none>'' will appear with each click. To remove it, just right-click on it (to select it, changes colour to red) and press Delete (on keboard).
+After selecting the option click somewhere (anywhere) inside of each block, as shown in Fig. 11-1. A green point called ''<none>'' will appear with each click. To remove it, just right-click on it (to select it, changes colour to red) and press Delete (on keyboard).
-{{block_labels.png?500}} Fig. 11-1. Add block points
+{{el/block_labels_el.png?500}} Fig. 11-1. Add block points
 Then each green point has to be configured. Right-click on a given point and press **''Space''** (on keyboard). Alternatively, after selecting (it turns to red) use: ''menu > Operation > Open selected''. A pop-up window will appear, Fig. 11-2.
-In the window, use the drop down list to select material type or "Block type". For example, ''Air'' is chosen for the point in Fig. 11-2. If the material is passive (no current flowing, not a magnet), then nothing more needs to be configured. Press OK to accept.
+In the window, use the drop down list to select material type or "Block type". For example, ''Air'' is chosen for the point in Fig. 11-2. Click OK to accept.
 The drop down list will also contain the ''u1, u2, u3...'' materials for the open boundary. These should be ignored.
@@ Line 147: / Line 147: @@
   * The "In group" variable can be used to group some objects. All objects have by definition group = 0. But this can be set to other value so that several objects can be a part of the same group. This is useful for editing (move, copy, rotate) or results analysis (select all objects in the group easily).
-{{block_labels2.png?500}} Fig. 11-2. Configure block labels
+{{el/block_labels2_el.png?500}} Fig. 11-2. Configure block labels
-If the given block has some imposed current flowing through then it is also set in the same window. Fig. 11-3 and Fig. 11-4 show how to set current in the circular wires. FEMM uses the approach of "positive turns" and "negative turns" for the same current. So just one current needs to be defined and the values have to be assigned as shown in the figures.
+The geometry represents a capacitor with two plates. The inside of each plate will have by definition the same potential, so it does not matter which material is assigned (but it needs to have some material, so Air will do).
-There is no need to draw each individual wire. It is sufficient to draw the whole rectangular cross-section shape of the coil and assign a number of turns the the whole area (such that N > 1).
+{{el/block_labels3_el.png?500}} Fig. 11-3. Configured labels for all blocks
-{{copper_and_current.png?500}} Fig. 11-3. Set current
+Now each plate needs to have the voltage assigned to ALL the lines and arcs which belong to that plate. Lines and arcs need to be set separately.
-The frame core is configured as "Pure iron" in the final model, Fig. 11-4.
+Select the "line" icon and right click on both lines of the left plate, and press Space. Then choose the previously defined "zero" voltage option to configure the conductor.
-{{plus_minus_n.png?600}} Fig. 11-4. Final model
+{{el/block_labels4_el.png?500}} Fig. 11-4. Assign voltage to lines
+{{el/block_labels5_el.png?500}} Fig. 11-5. Assign voltage to arcs
+Repeat the same for the right plate, to assign "positive" voltage.
+{{el/block_labels6_el.png?500}} Fig. 11-6. Assign voltage to arcs
 ----
@@ Line 168: / Line 174: @@
 If some block label was left undefined then this message will say something like:
-| //Created mesh with 12239 nodes.// \\ //Grey mesh lines denote regions that have no block label.//  |
+| //Created mesh with 11957 nodes.// \\ //Grey mesh lines denote regions that have no block label.//  |
 It is necessary to define ALL block labels.
-{{mesh.png?500}} Fig. 12-1. Mesh (automatically generated)
+{{el/mesh_el.png?500}} Fig. 12-1. Mesh (automatically generated)
 ----
 ==== Step 13 - analyse / solve ====
-Analysis is executed by clicking the "cranked cog" icon (red arrow in Fig. 13-1). A pop-up window appears which shows the progress of calculations. Just wait until it finishes. No message is shown if all finishes correctly.
+Analysis is executed by clicking the "cranked cog" icon (red arrow in Fig. 13-1). A pop-up window appears which shows the progress of calculations. Just wait until it finishes. No message is shown if all finishes correctly, which for small models it can be less than 1 second.
-As soon as the small window dissapears the results can be viewed by clicking the "glasses" button (black arrow).
+As soon as the small window disappears the results can be viewed by clicking the "glasses" button (black arrow).
+If there are errors in the model or material data the solution might not converge. If the computation time is excessive typically there is a problem somewhere in the model (block labels, double labels, wrong boundary, etc.)
-For all-linear models the calculation finishes in one step. For non-linear models it takes many iterations. For highly non-linear models (e.g. with deep saturation) or with large very dense mesh, the calculatiations can take very long time.
+{{el/analyse_el.png?500}} Fig. 13-1. Analyse / solve
-If there are errors in the model or material data the solution might not converge. If the computation time is exessive typically there is a problem somewhere in the model (block labels, double labels, wrong boundary, etc.)
-{{analyse.png?500}} Fig. 13-1. Analyse / solve
 ----
@@ Line 197: / Line 200: @@
 These two options can be accessed also through: ''menu > View > Contour plot'' and ''menu > View > Density plot''.
-{{solution1.png?500}} Fig. 14-1. Results window, with field lines, no colour map
+{{el/solution1_el.png?500}} Fig. 14-1. Results window, without equipotential lines, and colour map
-Clicking the "rainbow" button shows the small window, which which the type of variable can be selected: Flux density B, Magnetic field intensity H, or Current density J. Limits are scaled automaticaly betwen the min. and max. value present in the model, but they can be adjusted manually as needed, Fig. 14-2.
+Clicking the "rainbow" button shows the small window, which which the type of variable can be selected: Voltage V, Flux density D, or Field intensity E. Limits are scaled automatically between the min. and max. value present in the model, but they can be adjusted manually as needed.
 Don't forget to tick the "Show Density Plot" box!
-{{solution2.png?500}} Fig. 14-2. Choosing Flux density B |T| density plot
-Flux density |B| plot with the flux lines disabled is shown in Fig. 14-3.
-{{solution3.png?500}} Fig. 14-3. Flux density |B| plot
@@ Line 213: / Line 210: @@
 ==== Step 15 - plot data along line ====
-In the solution window, use the "red line" icon (Fig. 15-1) to draw a path of lines or arcs, between any two existing points (left-click of mouse) or between any arbitrary points (righ-click of mouse). Once the path is created, various values can be plotter along that line, from the beginning to its end, in the same order as it was drawn.
+In the solution window, use the "red line" icon (Fig. 15-1) to draw a path of lines or arcs, between any two existing points (left-click of mouse) or between any arbitrary points (right-click of mouse). Once the path is created, various values can be plotter along that line, from the beginning to its end, in the same order as it was drawn.
+Use "line" icon (red arrow), draw the line between the points of interest, then click on the "graph" icon (black arrow), and select the type of plot in the pop up window.
 The path can end at the same point it started.
-To plot, press the "graph" icon (Fig. 15-1). A pop-up window will open and the variable to be plotted can be selected, Fig. 15-2. N
+To plot, press the "graph" icon (Fig. 15-1). A pop-up window will open and the variable to be plotted can be selected. The graph will be plotted in a new window.
 Note that there is an option to export/write the data to a file, which can be then used with any spreadsheet software.
-{{graph_of_line.png?500}} Fig. 15-1. Draw path to plot data
+{{el/line_el.png?500}} Fig. 15-1. Draw path to plot data
-{{graph_js_plus_je.png}} Fig. 15-2. Select data to plot or export to file
+{{el/line_el2.png?500}} Fig. 15-2. Plotted graph
-The graph will be opened in a new window. For AC simulations, black curve means the absolute value (total amplitude), blue is the "real" component (0 deg), and green is the "imaginary" component (90 deg).
+----
+==== Step 16 - line integral ====
-{{eddy_current_graph.png?500}} Fig. 15-3. New window with plotted data
+Some values can be integrated over lines or blocks. Draw a line, and then chose the integral icon, Fig. 16-1.
-----
+The calculated voltage is exactly -1 V, as defined in the conductors. Because the line was drawn from left to right, from "zero" to "positive", so the integral is evaluated correctly.
-==== Step 16 - block integral ====
-Some values can be integrated over the whole blocks. To select a block use the "green square" button, and then click anywhere within a block of interest, Fig. 16-1.
+{{el/line_integral_el.png?500}} Fig. 16-1. Select block
-Then click on the "integral" icon.
-{{block_integral1.png?500}} Fig. 16-1. Select block
-A pop-up window will appear (Fig. 16-2), and the drop-down list can be used to select the value of interest. After accepting, the value will be evaluated and shown in another pop-up window, Fig. 16-3.
-{{block_integral2.png}} Fig. 16-2. Select type of integral
-{{block_integral3.png}} Fig. 16-3. Calculated value of integral
 ----
 ==== Step 17 - conductor info ====
-The losses in the ciruict (energised coil) can be integrated with the block method described above, but much reacher information is provided with the "Circuit properties" icon, Fig. 17-1.
+Info about the given conductor with the "Conductor properties" icon, Fig. 17-1.
+If there is more than one conductor defined then it can be selected from the drop-down list.
-If there is more than one current/circuit defined then it can be selected from the drop-down list.
+Capacitance is charge over voltage, C = q/V, and because the voltage was set to 1 V, the capacitance of this capacitor is 3.6e-13 F, or 0.36 pF.
-{{conductor_info.png?600}} Fig. 17-1. Circuit properties
+{{el/conductor_properties_el.png?600}} Fig. 17-1. Conductor properties
 ----
@@ Line 262: / Line 257: @@
 If snap-to-grid is enabled then only the grid positions will be available.
-{{data_at_any_point.png}} Fig. 18-1. Click anywhere to get values
+{{el/point_props_el.png}} Fig. 18-1. Click anywhere to get values
 ----
@@ Line 268: / Line 263: @@
 ==== Step 19 - that's it! ====
-And that's all - now you can run a simple FEMM magnetics simulation!
+And that's all - now you can run a simple FEMM electrostatic simulation!
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Unofficial FEMM documentation by Dr Stan Zurek

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Unofficial
FEMM
documentation
by Dr Stan Zurek