Initialization by FE solution: operation

Starting by FE solution

It is possible to start a transient computation by using as initial state the result of a Magneto Static, a Steady State AC Magnetic or a Transient Magnetic problem.

MH-TM relevance/ example

The MH applications permit the study of the steady state regime, but it has the following drawbacks:

  • approximations in the taking into consideration of the magnetic saturation*
  • no possibility to compute the harmonics in space and time

The TM applications compensate for the limits quoted above, but it has the drawback of requiring a computation time that can be quite long. Then, the number of time steps is important.

Starting a TM application on the basis of the MH solution permits to rapidly reach the steady state regime without being forced to solve all the time steps of the TM problem until the steady state regime is reached.

Remember: *With a Steady State AC Magnetic application, the approximations are carried out in order to take into consideration the non linear materials. We deal then with the equivalent B(H) characteristics (B sinus, H sinus…). The local values obtained with such equivalent curves get more or less accurately close to the real result (Example of the asynchronous machine).

Relevance TM-TM / example

As with a MH application, the TM application permits to obtain the steady state regime more rapidly without the need for the user to make again the computation of the transient phases or those for start-up (starting up of a synchronous machine with magnets, for instance).

It also permits to reach a certain specified point of the steady state regime – for example the passage at zero of the current of one of the phases of an electric alternator.

Finally, and mainly, it gives the possibility of an initialization by FE problem when the system comprises permanent magnets, which is not possible with an initialization by an MH problem.

Operation

The operation principle is described in the table below in the case of a MH – TM sequence.

Phase Description
1 Construction of the Flux project 1 (MH application)
2 Solving of the Flux project 1 (MH application)
3

Export of the FE solution:

Creation of an exchange file (format FTS)
Phase Description
1

Construction of the Flux project 2 (TM application) on the basis of the Flux project 1 (MH application)
2 Modifications of the physical properties
3

Choice of the initial conditions:

  • Initialization of the type «by file »
  • Exchange file
4 Solving of the Flux project 2 (TM application)