# Transient magnetic coupled with transient thermal

## Transient magnetic – transient thermal

The cosimulation « transient magnetic – transient thermal » can be used when:

• The electromagnetic problem is represented by a transient control, particularly for the study of a motor start up. The considered losses are then instantaneous values.
• The thermal problem relates to a temperature field that is time dependent

## Caution

The time constants of thermal and electromagnetic phenomena are generally of a completely different size order. This difference is dependent on the studied device. The total calculation time can therefore be very important.

For this reason it is then advisable to:

• Study a motor model which is characterized by thermal and electromagnetic response times that do not differ greatly.
• Consider a value for the thermal time step that is a multiple of the electromagnetic time step (or the reverse) and choose the «number of steps between each data exchange» (in the «cosimulation» box) to synchronize the electromagnetic/thermal exchanges. Example: if a thermal step is equal to twice the electromagnetic step, then choose an exchange at each two time steps in the electromagnetic project (see image below)
• Carefully choose the value of the time step (avoid too long time steps) etc.

## Non considered iron losses

In the case of transient magnetic (not in steady state), it is impossible to calculate the instantaneous value of iron losses. These are therefore not taken into consideration in the cosimulation.

## Cosimulation proceedings

The different internal steps implemented during the cosimulation of magneto transient with the transient thermal are :

Step Electromagnetic Thermal
0 The initial temperature is set by the user The initial source terms (losses) are null
1 Solving Magnetic transient at current step ti *
2 Export of the instantaneous losses field
Import of losses
3 Solving transient thermal at step ti
4 Export of the temperature field
Import of the temperature field
5 Verification of the convergence of the temperature field solution as to accuracy: at the same step ti *
6
• If the convergence is attained : Passage to the next magnetic (then thermal) time step ti+1
• Return to step 1 if not, to iterate on the same time step ti
7 End of the cosimulation having solved all the time steps of the magnetic and thermal projects

*As explained in the caution measures below, it is the user's responsibility to choose a number of steps between each exchange, in the cosimulation box, to make sure that the exchange is synchronized for the same time step.

** The verification of the convergence of the imported temperature field at a time step ti is done in relation with the last imported temperature field. As long as the accuracy is not reached, a loopback is repeated on the same time step. Once the accuracy has been attained, the electromagnetic and the thermal problems pass to the next time step.