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# Compressible Region for Linear Motion

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Hello

I have modelled two permanent magnets, one fixed (disc) and the other translating away from the first (spherical) in the z-direction. Please see below:

From this I plotted the force acting on the spherical magnet in the z direction at each deflection step.

My results correlate quite well to experimental data, but the simulation forces are all slightly smaller than the experimental.

My first question is: would creating a compressible region surrounding these magnets improve the accuracy of the simulation?

I quickly tried to model and mesh one, please see below:

• As you can see, the mesh is very coarse
• I used the automatic mesh generator for the compressible region and I cannot figure out how to manually make these elements smaller
• It doesn't even look like the mesh in the compressible region has been created to interact with the meshes of the two magnets inside
• When I ran the solution, the results were much worse. They were all over the place, with some force values not making sense

I assume these results are due to how coarse the compressible mesh is. However, without it, surely the mesh inside the infinite box must have similar sized elements, so I don't understand how having the compressible region has made the results worse.....

The reason I originally modelled it without a compressible region was because I followed the linear actuator tutorial, which does not require one. But another simulation I've been running, involves rotating magnets and I can't even get that to run without a compressible region. As this confuses me, my second/third question is....

What criteria requires the use of a compressible region in a simulation and in what instances should you avoid using them?

Many Thanks

Rory

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Hi,

The results depend on the quality of the mesh and not on the type of mechanical sets. In your case you need to refine the mesh. To do it you can create your own mesh generator (create point and line discretization). To do it:

• Select mesh from general data

• Select mesh tool (there are three options: mesh point, line and mesh generator)

• For each option you can create your own mesh tool

• Once you have create your mesh tool, assign this mesh tool to your device (point, line, face and volumes)

Other thing, you can create an air(vacuum) region around the device (magnets) before creating the infinite box. Like this you can control easily the mesh around the magnets.

Best regards.

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Hello

Great, Thank you! I will give it a go

Kindest Regards

Rory

You are welcome.

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