1. FEMM 4.2 = CAD program for electromagnetic field

2. steady-state heat flow problems.
Introduction to FEM
FEMM is a suite of programs for solving lowfrequency electromagnetic problems on two-dimensional planar and axisymmetric domains. The program currently addresses
linear/nonlinear magnetostatic problems,
linear/nonlinear time harmonic magnetic problems
linear electrostatic problems,
steady-state heat flow problems.
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3. FEMM is divided into three parts:
Interactive shell (pre-processor and a post-processor for the various types of problems solved by FEMM 4.2 .
CADlike interface for laying out the geometry of the problem to be solved and for defining material properties and boundary conditions.
Field solutions can be displayed in the form of contour and density plots.
The program allows the user to inspect the field at arbitrary points, as well as evaluate a number of different integrals and plot various quantities of interest along user-defined contours.
Triangle.exe  breaks down the solution region into a large number of triangles, a vital part of the finite element process.
Solvers (fkern.exe for magnetics; belasolv for electrostatics); Each solver takes a set of data files that describe problem and solves the relevant partial differential equations to obtain values for the desiredfield throughout the solution domain.
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4. The idea of finite elements
to break the problem down into a large number of regions, each with a simple geometry (e.g. triangles).
over these simple regions, the “true” solution for desired potential is approximated by a very simple function.
the advantage of breaking the domain down into a number of small elements:
the problem becomes transformed from a small but difficult to solve into a big but relatively easy to solve.

5. Example of the planar electrostatic model
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6. FEM analysis, example of discretization
Presentación
FEM analysis, example of discretization
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7. Presentación
Some posibilities
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8. FEM
The finite element method (FEM) (finite element analysis (FEA)) is a numerical techniques for finding approximate solutions of partial differential equations (PDE) as well as of integral equations.
The solution approach is based either on eliminating the differential equation completely (steady state problems) or rendering the PDE into an approximating system of ordinary differential equations, which are then numerically integrated using standard techniques such as Euler's method, Runge-Kutta,….

9. Tipos de problema
Electrostatic problems
The behavior of electric field intensity E, and electric flux density (alternatively electric displacement or induction) D.
The program solves
for voltage V over a user-defined domain with user-defined sources and boundary conditions.
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10. New problem  initial data
Diseño
New problem  initial data
Problem types:
planar (cartesian coordinates);
axisymmetric (cylindrical coordinates)
Length units: mm, cm and m..
“Depth” = third dimention of the investigated object.
Minimum angle of the triangle element, (value from 1 to 33,8 deg)
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11. Grid properties button
New problem definition, GRID
Grid on/off
Snap to grid
Grid properties button
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12. and mesh sizing for each section..
Preprocessor Drawing ModesPreprocessor Drawing Modes
Adding “Block Label” markers into each section of the model to define material properties
and mesh sizing for each section..
Drawing the endpoints of the lines and arc segments that make up a drawing.
Connecting the endpoints with either line segments or arc segments
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13. shortcuts and mouse buttons (for point properties)
Double click: Display coordinates of the nearest point
Select the nearest point
Create a new point at the current mouse pointer location
Delete selected points
Unselect all points
Display dialog for the numerical entry of coordinates for a new point
Edit the properties of selected point(s)
SPACE KEY
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14. Some operations Parameters for moving, copying, rotating
Example of 60º element rotation
Copy
Rescale
Move
Symmetry
Area selection
Delete
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15. Materials choosed for actual analysis
Electrostatic problems
Materials choosed for actual analysis
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Transparencia nº 15

16. Properties of the materials
New material creation.
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17. Line properties for electrostatic problems
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18. allow the user to apply constraints on the total amount of charge carried on a conductor.
Alternatively, conductors with a fixed voltage can be defined, and the program will compute the total charge carried on the conductor during the solution process.
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19. boxes for defining the voltage at a given point, or prescribing a point charge density at a given point.
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20. Electrostatic analysis
Manual choice of mesh size
Output (graphical postprocessor)
Start calculations
Building triangles (meshes)
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21. Possibilities of the electrostatic postprocessor
Posprocesador
Possibilities of the electrostatic postprocessor
Zoom in/out
Result visualisation (density plots, equipotential lines, vectors)
Shifting the screen
Selection of numerical method and visualisation
Selection of points, lines or blocks for numerical analysis and graphical presentation
Grid parameters
Open problem or start a new problem
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22. Output selection: point
Point properties (electrostatic postprocessor)
Output results
Output selection:
point
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23. Choose the type of field value
Graphical postprocessor
Plot the function
plot
Choose the type of field value
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24. Start of the integration
Line integral
Definition of the line
Options
Integral results
Start of the integration
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25. The selected region will appear highlighted in green.
Block Integrals
To select the regions over which a block integral is to be performed, left-click with the mouse in the desired region.
The selected region will appear highlighted in green.
Posprocesador
Block element
options
result
Start button
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26. Electrostatics Postprocessor:
Equipotential lines
options
Visualisation dialog box
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27. Electrostatics Postprocessor: Density plots
Electric field area
Legend
Menu
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28. Electrostatics Postprocessor: Vector plots
Posprocesador
Electrostatics Postprocessor: Vector plots
Vectors
START
Dialog box
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29. Step by step EXAMPLE 1
Capacitor with a Square Cross-Section

30. The outer square has a 4 cm size, the inner square 2 cm size.
The geometry extends for 100 cm in the “into-the-page” direction.
The dielectric between the plates  air.
TASK: build the FEMM problem (model), analyze it, and determine the capacitance.

31. Procedure Physical problem description. Model design.
Boundaries definition.
Materials description.
Boundary conditions application.
Mess generation.
Finite Element Method application.
Results extraction and analysis.

32. The finished model
Remark: Because of the symmetry, only one quarter of the device need to be modeled.

33. Create model Start FEMM "File|New" from the main menu.
Select "Electrostatics Problem" in the "Create a new problem" dialog that appears.
After you hit "OK", a blank electrostatics problem will appear.

34. Entered POINT (0,2) Press <TAB> BUTTON Enter x=0, y=2
Select „nodes”
Press <TAB>
BUTTON
Enter x=0, y=2
Entered POINT (0,2)

35. Select „lines” and try to connect all points
To select the endpoint of a line, click near desired endpoint with the left mouse button!
Select „lines” and try to connect all points

36. Add materials to the model
Select „Properties|Materials”
Click Add Materials”
Change the name of the property to „AIR”
Confirm by clicking „OK.”

38. Define materials for each region
Click „Block Labels”
It can be done via <TAB> dialog or by click on the left button
Make block label red (right click)
Press space to „oopen” the selected block label
Set to AIR
Uncheck „Let Triangle….”
Choose Mesh Size „0.025”

39. SPACE BUTTON
Right click

40. Define conductor voltages
Select „Properties| Conductors”
Click „Add Property”
Replace „New Conductor” with „ZERO”
Select „Prescribed Voltage”, enter „0”, confirm
Repeat the above procedure to the new boundary condition „ONE”
Attribute conductor voltages to the segments
When segment turns to red press SPACE BAR and change the selction from „none” to „ZERO” or „ONE”

44. PRESS
SPACE BAR

46. Set PROBLEM Characteristics
Select „Problem”
Choose „planar”
Set the length units to „Centimeters”
Depth = 100
Default solver precicion (10-8 )

48. GENERATE MESH and RUN! Save the file Click button with yellow mesh
If the mesh seems to be to fine or too coarse select mesh size again
„TURN the CRANK”

51. To chenge mesh size select block labels and adjust new mesh size

52. TURN THE CRANK  RUN!

53. DISPLAY RESULTS Click on the glasses to open a postprocessor window
Click Edit|Preferences to change selection on the main menu of both preprocessor and post processor

61. Ejemplo
EXAMPLE
4 MV
Ground 0 V
Maximum value
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62. Point with maximum value
Two spheres
Sphere potencial 30000
Equipotential line
Point with maximum value
Sphere with 0 V
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63. EXAMPLE 3
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