ANSYS AIM Tutorial Modeling Forces in Permanent Magnets Author(s):Joshua Wallace Created using ANSYS AIM 18.2 Problem Specification Pre-Analysis & Start Up Governing Equation Start Up Geometry Physics Set-Up Specify Material Boundary Conditions / Forces Solution/Result Verification
Problem Specification This problem is intended to address the questions of force calculations as well as modeling of permanent magnets in axisymmetric and three dimensional geometries.the spool is made out of brass, the coil is made out of copper and the magnet is made of NdFe30. In this demonstration two cases will be considered and the force between the magnet and the coil will be determined. f = f(i, R, s ) f = f orce between magnet and coil i = c urrent, R = h orizontal displacement s = v ertical displacement I n case one, both s = 0 and R = 0.254mm are held constant. T herefore, f = f (i) I n case two, s = 0 mm and i = 50mA are kept constant. T herefore f = f (R)
In the first case the current will vary from from 0-100mA in 10mA intervals. In case two the axial displacement will vary from 0.0-.5mm in.05mm intervals.
Pre-Analysis & Start Up Governing Equation Magnetostatics is the study of magnetic fields in devices where the magnetic field is generated from DC (steady) currents and/or permanent magnets. Magnetostatics is a special case of Maxwell s equations, which form the basis of electromagnetism. For magnetostatics the electric field inside of a current carrying coil is completely decoupled from the magnetic field, and the following Maxwell s equations are solved for magnetostatics - Where denotes divergence, H is the magnetic field intensity, J is the current density and B is the magnetic flux density.
Start Up A few words on the formatting on the following instructions: 1) Notes that require you to perform an action are colored in blue 2) General information will be colored in black, but do not require any action 3) Words that are bolded are labels for items found in ANSYS AIM 4) Most important notes will be colored in red Now that the the pre-calculations are finished, we are ready to begin the simulation in ANSYS AIM. Open ANSYS AIM by going to Start > All Apps > ANSYS 18.2 > ANSYS AIM 18.2. Once starting page has opened, select the Magnetics template as shown below.
Geometry You will be prompted to either Define new geometry, Import geometry file, or connect to active CAD session. Select import new geometry and downloaded the file here. AIM will prompt again asking to select your calculation type, physics coupling and options. Under options, check compute force and then click Finish. Creating geometric parameters In order to vary the horizontal distance between the coil and magnet a parameter must be created. Once AIM has loaded click on Geometry > Edit Geometry. Hide the enclosure by deselecting the checkmark.
Triple click on the magnet to select the body. Select the move tool and click on the origin. Drag the origin onto the face of the magnet closest to the spool.
Once the origin turns into a square, select the blue axis of the Move tool. The other axis will be greyed out and in the General sidebar select the Ruler tool. The Ruler tool will then follow the cursor, at which point click the face of the spool closest to the inside the gap.
To create the parameter click on the P next to the highlighted dimension box. Once the parameter is created, click the x in the top right corner to begin the physics set up. ANSYS Inc.
Physics Set-Up AIM will automatically create an enclosure around the geometry. In order to see the inside geometry click on Physics > click on the box > right click on the box > Hide Body. Specify Material Click on Add, next to Material Assignments > Material Assignment > Copper (Material Samples). Next, click on body selection in top right corner. Select the coil and click Add. This assigns copper to the coil.
Then click on next step and repeat the process. Assign NdFe30 to the magnet and brass to the spool. (You can use Type to Search to find NdFe30 and Brass in the material library.)
Boundary Conditions / Forces Now force computation must be set up. Click Next Step > Fix > Force Computation. Select the magnet using body select and click the +. Leave all other setting in default condition. Since a current is running through the copper coil, a current condition will need to be created. Right click > Add > Electromagnetic Conditions > Current. Select the surface by looking for the line in the line that runs perpendicular to the spool face.. Click on the plane below the line by using the plane selector. Then input a Current of.01 amps and 280 for the Number of Conductors. Click on the arrow below to parameterize the Operating current.
Then click on Generate Conduction Paths, this will show the solver interpretation of the coil. If the solver s interpretation of the coil is incorrect (current is flowing outside of the coil) insulating boundary conditions must be added to ensure that the current stays within the coil. Since the solvers interpretation of the coil is incorrect (current is also flowing in the brass spool), insulated boundary conditions will be added.
Right click > Add > Electromagnetic Conditions > Insulating. Click on the three inside faces of the brass spool. Hiding the coil geometry will make this step easier.
In order to check that insulating condition worked, click on Physics > Electromagnetic Conditions > Current 1 > Generate Conduction Paths. ANSYS Inc.
The solvers new interpretation of the coil is correct. Case one will now be set up. ANSYS Inc.
Setting up case 1: The last parameter we need to define is the force on the magnet. Go to Results in the workflow. Under Objects, click on results again. Select Value Force Magnitude 1. Click on the arrow horizontal from undefined and select parametrize. Click on the design points dashboard in the upper right hand corner. The first table that comes up is the design points. Under Current 1 Operating current, iterate the input by 10 ma up to 100mA. Use the image below for reference. In the other column, input.254mm for the horizontal(r) distance. Once this is done, click Update All in the top right corner of the design points dashboard. AIM will solve each case for the force on the magnet and the force outputs for each current input can be seen in the design points dashboard.
Setting up case 2: In case two, the force of the magnetic is a function of horizontal(r) distance. In the design parameters dashpoint, change all the current data points to 50mA. Then iterate the horizontal data points from 0.05mm-.5mm by 0.05mm. Click update all to see results.
Solution/Result Click on Results in the Workflow and add a vector plot. Choose Magnetic Flux Density for the variable and click Evaluate. The results are shown below.
Verification ANSYS Inc.