Tutorial 1

Simple Rotor

In this tutorial we analyse a rotor that is moving between two permanent magnets. First we apply a forced speed of 5.000 turns per minute and then we analyse the free motion behaviour.

Different techniques are shown here, so we use 2D as well as 3D modeling. And we use two different motion techniques for rotation: ’General Motion’, a feature that can be used for 3D rotation and translation. And the ’Moving Band’ technique, that is capable for 2D rotation only. Also we show free (dynamic) motion as well as enforced motion. Thus, the tutorial is split into four parts:

1. 2D enforced,

2. 2D dynamic,

3. 3D enforced,

4. 3D dynamic.

Two permanent magnets are positioned near the rotor. This leads to time dependent variations of the magnetic field and therefore eddy currents will appear in all electric conducting parts. In reality such eddy losses will lead to temperature rise, an effect that is neglected in this basic tutorial but could be simulated by a coupled thermal solution. Those eddy currents shall be displayed and resulting power loss shall be computed. The enforced analysis shall be done over 45 degrees, the dynamic one over a time period that allows observing the expected oscillations. The CAD models of both the 2D and 3D base on the same ’Skelett.prt’ file.

2D Enforced Driver

The following example a pure 2D example; and thus not designed to work in 3D. In this example, an iron rotor rotates between two permanent magnets. The example shows how to perform analysis’ that couple electromagnetics and mechanical movement. In the present scenario the motion is simulated with an enforced motion; however, it can also be simulated with dynamic motion. This is done in the next tutorial. Then, the movement would have one degree of freedom in the mechanical sense. The example is executed in 2D because of the shorter solution time but it would be similar in 3D as is shown in a further example.

Main goal is to model the enforced motion effect of the rotor. Other results like eddy currents can be requested additionally if desired.

Estimated time: 45 min.

Follow the steps to reproduce it:

1. Download the model files for this tutorial from the following link:
   https://www.magnetics.de/downloads/Tutorials/6.CouplMotion/6.2SimpleRotor3D.zip

2. Open the part file ’rotor2D.prt’.

   • Here, the start position of the rotor is set to -20 degrees.

   • Also, there is a ’Moving Band’ visible. This has two circular edges, one connected to the moving part and one to the stator regions. At each time step the solver will rotate the moving regions and create a mesh between the two edges automatically.

3. Start Simcenter Pre/Post, create a new Fem and Sim file for 2D Electromagnetics.

   • Switch off ’Create Idealized File’,

   • Choose Solver ’MAGNETICS’ and Analysis Type ’2D or axisym Electromagnetics’, OK,

   • Set the ’Analysis Type’ to ’Magnetodynamic Transient’ and name the solution ’Enforced’.

   • In register ’Output Requests’,’Table’ activate ’Motion Data’ and in ’Plot’ activate ’Displacement’ as well as ’Magnetic Fluxdensity’. Others can be activated if one is interested.
     

   • In register ’Time Steps’ set the ’Time Increment’ to 1/(60*360/60). This formula corresponds to a rotor speed of 60 rpm (1 rps).
     

   • In register ’2D’ set the ’Thickness’ to 10 mm.
     

   • OK.

4. Switch to the Fem File.

   • When using the Moving Band technique the band elements should have about the same element size. Therefore, create a ’Mesh Control’ , use type ’Size on Edge’, select the outer and inner edges of the moving band, set the ’Element Size’ to 1.5 mm and click OK.
     

   • Create a Tri-Mesh on the Magnets. Use the suggested element size and assign material ’N30EH at 100C’. The permanent direction of north is X by default, so we can stay with the default for our example. Assign the name ’Magnets’.
     

   • For the Rotor also create a tri mesh with the suggested size and assign the material ’Iron_Sample1’. Also set the ’Inertia RZ’ to ’87 \(Kg mm^{2}\)’. Assign the name ’Rotor_Iron’.
     

   • For the inner air (2 faces) create a tri mesh with suggested element size and assign a ’FluidPhysical’ with material ’Air’. Name it ’innerAir’.
     

   • For the outer air create a tri mesh and assign one more ’FluidPhysical’ with material ’Air’. Name it ’outerAir’.
     

   • Notice: Do NOT mesh the air gap between rotor and stator. When using the MovingBand feature this will be done automatically inside the solver.

   • Check that all mesh collectors have a meaningful name. Then, click the button ’Rename Meshes and Physicals from Collectors’ from the Magnetics toolbar.
     

5. Switch to the Sim File.

6. Assign a constraint of type ’Flux tangent (zero a-Pot)’ on the circular edge of the infinity air.
   

7. Now create a new Simulation Object ’Enforced Motion 2D’. Use the type ’Revolute by Moving Band’. Hint: The type ’Revolute by General Motion’ would also work, but this would use a different motion technique.
   

   • At ’Airgap Rotor Edge’ select the 8 inner circle edges as shown below. These must be those edges, that belong to the moving part. Maybe the selection filter with option ’Tangent Continuous Edges’ is helpful here.
     

   • At ’Airgap Stator Edge’ select the 8 outer circle edges as shown below.
     

   • Under the box ’Airgap, auto meshed’ select from the list the Air, that already resides in the Fem file. Accept the default 1 at ’Number of Air Gaps’.
     

   • Under ’Rotor Geometry’, click ’Create Moving Parts’ and select the Rotor and the inner air and add these to the list. Then click ’Close’ as shown below. If the names do not appear in the list take care that in the Fem file the Physicals have such names assigned.
     

   • At ’Angular Step’ key in 1 deg. Because we have defined 45 time steps we will compute for 45 degrees of motion with these settings. OK.

8. Solve the solution. The solution monitor indicates the progress and successful end.
   

9. Plot the Magnetic Flux Density and observe the result. For a smoother display set the ’Combine At’ option at ’Edit Post View’ to ’Nodes’ and at ’Average Across’ deactivate ’PID’.
   

10. The plot with magnetic flux density, arrows and contour, then will look like the following for increment 1.
    

11. Cycle through the time steps by using the green button ’Next Iteration’ . Alternatively, use the ’Animation’ function and set the option ’Animate’ to ’Iterations’. If you want to see more movement repeat the solution with more time steps.

12. Display the eddy current losses on the rotor. This graph shows nicely the eddy current effect when rotor and magnets move near to each other.
    

This ends the tutorial.

2D Dynamic Driver

The following example is a pure 2D example; and particularly is intended to be a follow-up example of the previous example ’Simple Rotor, Enforced’. In this example, the rotor oscillates between two permanent magnets. The example shows how to perform an analysis that couples electromagnetics and mechanical movement. In the present scenario the magnet is simulated with a dynamic motion. Here, the movement has one degree of freedom in the mechanical sense. The example is executed in 2D because of the shorter solution time but it would be quite similar in 3D.

Main goal is to find the oscillation behavior of the rotator. Other results like eddy currents can be requested additionally if desired.

Estimated time: 25 min

Follow the steps to reproduce it:

1. Start from the previous example and clone the solution,
   

2. then remove the enforced joint.

3. Name the new Solution ’Dynamic’.

   • Chose Analysis Type ’Magnetodynamic Transient’.

   • In register ’Output Requests’, Table activate ’Motion Data’ and in Plot activate Displacement as well as ’Magnetic Fluxdensity’. Others can be activated if desired.
     

   • Modify the ’Time Increment’ to 0.001 and the ’Number of Time Steps’ to 100 resulting in a total simulation time of 0.1 sec.
     

4. Change to the Sim file, if not already there.

   • If a new solution is created, add the constrain ’Flux Tangent’ to the solution.

   • Create a ’New Simulation Object’ of type ’Dynamic Motion 2D’. Remove the old one, if the solution was cloned.
     

   • Select Type ’Revolute by Moving Band’ (the default)
     

   • Select the ’Airgap Rotor Edge’ and the ’Airgap Stator Edge’ in the same way as already done in the previous enforced example.
     

   • Again select Air for the material at the Airgap
     

   • At ’Rotor Geometry’: Select the Rotor and the inner air.

   • All other settings can stay at the defaults. There is no step size necessary because this will be computed from the dynamics of the system: Electromagnetic forces and mass inertia of rotor.

5. Solve the Solution. This will take about 1 min.

6. Now verify the oscillating behaviour of the rotor. To do so, open the results and display the ’Total Displacement’ of the dynamic joint as in the below picture.
   

7. Also plot the graph showing the eddy current losses on the rotor.
   

8. Then plot the Magnetic Flux Density.
   

This ends the tutorial.

3D Enforced Driver

In this example we will use an enforced driver and 3D geometry.

Estimated time: 1 h. The following picture shows the geometry and the named CAD bodies.


To set up the model, follow these steps:

1. Download the model files for this tutorial from the following link:
   https://www.magnetics.de/downloads/Tutorials/6.CouplMotion/6.2SimpleRotor3D.zip

2. Open the file ’rotor3D.prt’.

3. Switch to Simcenter Pre/Post

4. Create a new FEM and Simulation. Choose Solver ’MAGNETICS’ and Analysis Type ’3D Electromagnetics’. Switch off the ’Create idealized Part’.

5. Choose Solution Type ’Magnetodynamic Transient’. Name the solution ’Enforced’.

   • In register ’Output Requests’ under ’Plot’ activate ’Current Density’ and ’Eddy Current Losses Density’ to enable the calculation of eddy currents. Also enable ’Nodal Force - virtual’ to check for these results.

   • Under ’Table’ activate ’Eddy Current Losses’ to enable the calculation of integrated current losses and to get them written into a tabular file. Also enable ’Motion Data’ to get results of displacement and velocity of the motion driver.
     

   • In register ’Time Steps’ set the ’Time Increment’ as shown. This corresponds to a rotor velocity of 5.000 U/min if the step size is 1 deg. We will use this later.
     

   • In register ’Initial Conditions’ accept the defaults. Hint: The option ’Set back after Solve’ can be deactivated to allow restarting from a previous run.
     

   • Click Ok.

6. Switch to the Fem file.

7. Mesh the rotor:

   • Use (3D) tetrahedral elements and the half of the suggested element size.

   • Assign material ’Iron_Sample1’ from the Magnetics material library.

   • Key in the value 87 Kg \(mm^{2}\) for Inertia RZ. This is necessary only in case of dynamic motion of the rotor because the forces acting on the rotor will be transformed into a motion step by Newtons law.

   • name the collector ’Rotor_Iron’, click OK to finish.
     

8. Mesh the two magnets:

   • Use (3D) tetrahedral elements with half of the suggested element size.

   • Assign material ’N30EH at 100C’. Name the collector ’Magnets’. OK. Hint: For the north direction, we want x. Because x is the default, there is nothing to do now.
     

9. Mesh (2D) the three outside faces of the body ’AIR’.

   • Use (2D) tri elements with a quarter of the suggested element size.
     

   • In the mesh collector of this 2D mesh, set the Type to ’ZeroPotential’ and click ’Create Physical...’. and OK. This setting will impose a boundary condition at the mesh level, so there is no need to give a zero potential condition in the Sim file.

   • name the mesh collector ’Outer_ZeroPot_Meshes’. OK.
     Notice: This 2D mesh will be used two times: First it serves as boundary condition and second it is used as border for the following air mesh (Solid-from-Shell Mesh).
     

10. Now create 2D Surface Coat meshes on the parts:

    • Blank the 2D meshes and also the air body.

    • Choose the meshing function ’Surface Coat’,
      

    • Select the bodies of the two conductors and the rotor,

    • Set the ’Mode’ to ’Geometry’, activate ’Export Mesh to Solver’ and ’Automatic Creation’, Check that the ’Type’ is set to ’Tri’.
      

    • The system creates by default a physical of type NotToSolver what is correct because we want to use these 2D meshes only as borders for the following air mesh (Solid-from-Shell Mesh).

    • Assign the name ’Inner_Coat_Meshes’ to this mesh collector.
      

11. We want to have all collector names written to the corresponding physicals and meshes because this is easier to use. Therefore click the button ’Rename Meshes and Physicals from Collectors’ from the Magnetics toolbar.
    

12. Next we create a new 3D mesh collector that will later hold the 3D air mesh. We will set up this collector in a way that it automatically updates the air mesh at every new rotor position. It will automatically use the ’Solid from Shell’ mesher, therefore it is necessary to have meshed the 2D border of this 3D air.

    • First choose the function to create a new collector.
      Name this collector ’UpdatingAirMesh’.
      

    • In box ’Physical Property’ set the ’Type’ to ’FluidPhysical’. Use the button ’Create Physical’ to create a new physical. In the new physical choose the material Air. OK.
      

    • Back in the mesh collector dialogue expand the box ’Auto Mesh’ and set the option ’Activate’ to ’Auto Mesh at Solve’.

    • Next choose the button ’Shell Boundary for 3D Mesh’. In the following dialogue select the two border physicals and click on ’Add’.

    • Then press Close and Ok to close all dialogues.
      

    • The navigator now shows the new collector. Notice that there is no mesh in it. This mesh will be created at solve time automatically through the function ’Solid from Shell Mesh’. The mesh will also be updated at every motion step.
      

13. Switch to the Sim-file.

14. Create ’Simulation Object’ for the rotor movement:
    

    • Choose the function ’Enforced Motion’. The following dialogue appears
      

    • At ’Rotor Geometry’ click on ’Create Moving Parts’ . In the following dialogue select the physical Rotor_Magnet and click Add, Close.

    • Notice that the ’Angular Step’ is set to one degree for each step. This is already what we want so there is no change necessary. Leave all other settings at their defaults. OK.

    • Hints: By this procedure the MAGNETICS Solver will rotate the 3D Rotor mesh at each timestep for the desired amount and will automatically create ’Solid from Shell’ meshes for the air using the previously created 2D boundary meshes.

15. Model setup is now done. Save your parts, blank the meshes (maybe you leave the rotor mesh visible because this will nicely show the motion). Decrease the window size, because it will pop up to foreground at every time step.

16. Solve the solution. This will take 5-10 minutes because of the 45 steps to run. A progress bar at the bottom of the Simcenter window shows the current and the remaining steps.
    

17. The finishing of the solve is shown by the information window as below
    

18. After the solve finishes you can post process the results.

    • Open the plot results. All motion steps are stored in the result file. This allows running animations over the iterations and creating movies if desired.

    • The following picture shows the magnetic flux density result (left) and the nodal forces (right) at time step 9. (Results are set to averaged at nodes and element edges are blanked).
      

19. After this General Motion run the moving meshes are set to ’Locked’. If an update of the meshes to the original situation is desired, unlock the moving meshes and perform a mesh update.

The tutorial is complete.

3D Dynamic Driver

The completed Sim file, that resides in the tutorial folder, contains also a solution (named ’Dynamic’) with a dynamic joint. This can be used for further studies. (Set the ’Number of Time Steps’ to 100 before solving the complete period.) The following result graphs are made with a larger number of time steps. Of course, that solution needed much more time.

The following picture shows the resulting displacement of the previous 2D dynamic (blue) and the 3D dynamic (red) rotor.
The next picture shows the resulting eddy current losses of the 2D dynamic (blue) and the 3D dynamic (red) rotor.

When comparing the 2D and 3D results one will find out that the simulated forces and torques are higher in the 3D case, even if the 2D is set to the same z thickness. Therefore, also the dynamic rotation speed becomes higher in 3D. This effect can be explained as follows: The magnetic forces appear mainly on the border faces between air and magnetic material. Because the 3D model has additional side faces, and these are used in the simulation, the forces here are higher. The following picture illustrates this: It shows the force distribution on the 3D rotor. It can be seen, that forces are not homogeneously distributed. At the side faces they are higher. Also the magnetic flux density result shows this effect. This is one reason why 3D simulations can be more realistic.

The tutorial is complete.