# [Getdp] Time-dependent non-linear problem and time derivatives

michael.asam at infineon.com michael.asam at infineon.com
Mon Oct 15 08:57:09 CEST 2012

```Hi John,

regarding the first formulation:
The term-op-type Dt is actually not implemented. GetDP uses DtDof instead, which is
in many cases wrong. The newest version (nightly build) gives here now a warning.

You can overcome this problem when you calculate the time derivative of the complete
(nonlinear) expression in a separate function (located in the Function{ ... } block).

Regarding the 2nd formulation with B:
The Galerkin equation has to be linear with respect to the Dof, which is not the case
here. You have to linearize it, either with functional iterations (Picard iteration)
or with Newton's method.
Please have a look in the reference manual at page 22, chapter 4.10 Fields -> Dof.

Best regards,
Michael

From: getdp-bounces at ace20.montefiore.ulg.ac.be [mailto:getdp-bounces at ace20.montefiore.ulg.ac.be] On Behalf Of Velasco Alvarado Jonathan
Sent: Friday, October 12, 2012 3:29 PM
To: getdp at geuz.org
Subject: [Getdp] Time-dependent non-linear problem and time derivatives

Hello everyone,

I am currently working on a time-dependent non-linear magnetodynamic case. The permeability is my non-linear term but I don't want it to be included in my calculations for simplicity. For this reason, I am using the flux density instead of permeability times field strength (B = mu*H). I am currently using this formulation (T-ohm) and it seems to work:

Galerkin { Dt[ mu_non[{H}]*Dof{H}                ,  {H}] ; In Stack    ; Jacobian JMat ; Integration GaussIntegration ; }
Galerkin { [ 1/sig[]* Dof{Curl H}        , {Curl H}] ; In Stack    ; Jacobian JMat ; Integration GaussIntegration ; }

However, if I substitute B into my equation:

Galerkin { Dt[ B[Dof{H}] , {H}] ; In Stack ; Jacobian JMat ; Integration GaussIntegration ; }
Galerkin { [ 1/sig[* Dof{Curl H} , {Curl H}] ; In Stack ; Jacobian JMat ; Integration GaussIntegration ; }

It doesn't seem to do anything. I was wondering if there is a way to take the time derivative of my non-linear term in terms of a magnetic flux density as shown above.

BR,

John
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