The initial conditions: overview

TM application: reminder

A transient application is a physical application characterized by:

  • properties that vary in function of time: variable sources, variable material characteristics…
  • a time equation (differential equation of the 1 st order) : d/dt ≠ 0 (transient regime or variable regime).

The resolution consists of a sequence of resolutions in time. The solutions are not independent from each other: each solution is linked to the previous one by the temporal equation.

Initialization « at zero »

In the most general case, state variables are initialized to zero (for t = 0). The 1st step of time (t = t1) corresponds to the first Flux solving step as presented in the table below.

  Initial instant 1 st time step
Flux solver t = 0 t = t1  
Result B, H… null everywhere * B, H… calculated  
Note: * In 3D, if there are non-meshed sources (non meshed coils or imposed field), the values of B and H are those related to these sources (Hj field).

Initialization by static computation

In the presence of magnets or sources of non null current/voltage at t = 0 s, the zero initialization in Flux is not carried out « in real accordance with the physical reality ». The starting is accompanied then by a “numeric transient”, which distorts the solving process.

To prevent from this problem, it is possible in Flux to take into account initials conditions of the static computation initialization type.

Initialization by FE solution

It is possible to initiate a transient computation by using as initial state the result of a Magnetostatic, Magnetoharmonic, or Transient Magnetic problem.

This permits for example :

  • to study a variation around an average value without being obliged to carry out all the time steps permitting to attain the steady state regime
  • to resume a computation after the modification of the value of a physical size (current...)