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[Solution]

This example is taken from Cornell University’s ANSYS AIM Learning Modules

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Contents

1. Problem Specification
2. Pre-Analysis
3. Geometry
4. Physics Setup
5. Results Evaluation

Problem Specification

This problem is intended to address the questions of force calculations as well as modeling of permanent magnets in asymmetric 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 (Neodymium Iron). 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)

where

f = force between magnet and coil i = current, R = horizontal displacement  s = vertical displacement

In case one, both s = 0 and R = 0.254mm are held constant. Therefore, f = f(i)

In case two, s = 0mm and i = 50mA are kept constant. Therefore 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 0.05mm intervals.

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Pre-Analysis

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.

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Geometry

Download the file here

In this video, you will learn how to import the geometry and how to define a parameter for the distance between the magnet and spool.

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Physics Setup

In this video, you will learn how to:

• Assign material properties
• Define boundary conditions and parameterize current
• Define output parameter for force magnitude
• Define design points

Design Point Study

Case 1: The current will vary from 0-100mA in 10mA intervals

As shown in the above video, all the 10 DEsign Points are updated. The force results will look as shown in below image.

Case 2: The axial displacement will vary from 0.0-.5mm in 0.05mm intervals. In the design parameters dashboard, 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. The results will look like shown below.

Results Evaluation

The following video shows how to compute Magnetic Flux Density