Translation or rotation with compressible air area


This paragraph deals with rotation or translation motion of a moving part in a compressible air area.

Example: presentation

The example presented in this paragraph represents a simple model of a switch that has two operation modes: translating motion along an axis and rotating motion around an axis.

Assignment of regions

The assignment of regions in mechanical sets is done in the following way:

  • moving mechanical set: the upper magnetic core
  • fixed mechanical set:
    • the lower magnetic core
    • the two coils
    • the “external” area of air (not affected by the displacement)
  • compressible mechanical set: the area of air surrounding the device (affected by the displacement)

Compressible mechanical set

Different methods of defining the compressible area are presented in the table below. The first case corresponds to the most common one.

1st case 2nd case
Geometry scheme
Compressible mechanical set Maximum area, corresponding to the air region Minimum area, in which the moving part moves
Advantage No need to create a specific region

Reduced area to remesh

reduced requirements for mesh storage


Larger area to remesh

larger requirements for mesh storage

Requires creation of a specific region


Any contact between the moving part (the upper core) and the fixed part (the magnetic circuit) is not allowed.

Mechanical stops

For translating motion the user must make sure that contact between the fixed and moving parts will not occur.

To overcome the problem of contact, it is possible to define mechanical stops in order to prevent motion within certain areas.

Rules to be respected (in 3D only)

In the “automatic formulations” mode, the formulations for different regions are automatically chosen by Flux 3D. However, some rules must be respected.

The rules to be respected are the followings:

  • Conducting materials in contact with the dissociation surface are not authorized.
  • For regions with conductive materials, the user must comply with some additional rules detailed in the table below.
Conductive region inside a … with
translating motion rotating motion


mechanical set

There are no additional constraints for choosing the formulations Choose only advanced formulations (edge formulations)


mechanical set

There are no additional constraints for choosing the formulations

* A reminder about field formulations: formulations available for regions with conducting materials are the following:

  • nodal formulations (normal): Mx3TOM, Mx3TSCRHJ
  • edge formulations (advanced): Mx3TWOM, Mx3TWSCRHJ


  • x = T, for Transient Magnetic application
  • x = D, for Steady State AC Magnetic application