Discussion Forum

Hmm. If I move your magnet up to the vertical center (pos z = -.01 instead of pos z = -.09) of your model, then the force drops by a factor of about 20x. This suggests that this asymmetry in the force was due to imperfections (the vertical asmmetry) in your model. Boundary conditions can never truly represent free space. Also, using finer meshes and higher order discretization reduces the force even further. So... it looks like you have numerical effects involved. You'll likely never get a "true" zero. This is a finite-element method based code.

By the way, why are you doing a time-dependent study on what seems to be a steady-state problem? Did I miss something?

Thank You,

Yes I need to make a time-dependent study of a linear motor. The previous file was a simplified version to show just one issue.

In the file linked below, the magnetic field force is used for computing the displacement of shaft. The problem with the simulation is that magnetic force is non zero even when the coil current is set to zero. The shaft moves, but the applied forced is expected to be zero.

The file below does not have assymetry but the issue remains.

The lab file

All models have numerical errors. In time-domain models, the errors can grow over time, sometimes even washing away the real physics. Thus, you need to configure your model so that the physics of interest to you dominates over the numerical errors. In some cases, this is very easy to do. In others, it takes a great deal of effort. Linear motor models are a bit outside my primary areas of investigation, so I encourage the more knowledgeable members of this forum to contribute their specific suggestions about how your model can be improved. Good luck.

Thamk You