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

michael.asam at infineon.com michael.asam at infineon.com
Mon Oct 15 11:07:51 CEST 2012

```Hi John,

I think the missing Dt implementation is not the root cause for the not working B formulation.
GetDP uses DtDof instead which will deliver a result (in your case probably the wrong one).
The calculation of the time derivative in a function could be done by using there the function
Dt (see manual page 16) or you can calculate it manually by using the variable \$DTime (page 21).

The main problem is that you give the Dof as an argument to a function:  B[Dof{H}].
I think, this is not allowed. (Otherwise you could build nonlinear Galerkin equations ...)
Instead you should give H from the last iteration to the function: B[{H}].

Dof{H} means the unknown values of H you are looking for in the actual iteration
in contrast to {H}, which represents the known values from the last nonlinear iteration.
(Have a look in your first formulation where the usage of {H} and Dof{H} is correct.)

Cheers
Michael

From: Velasco Alvarado Jonathan [mailto:jonathan.velasco at aalto.fi]
Sent: Monday, October 15, 2012 9:34 AM
To: Asam Michael (IFAG ATV BP PD 1 M1); getdp at geuz.org
Subject: RE: Time-dependent non-linear problem and time derivatives

Hi Michael,

Thanks for your prompt reply. I am actually interpolating B for each calculated value of H with my own measured data and I am building my Jacobian matrix using the JacNL function. The derivatives have been carried the way you've mentioned, as an external calculation in the Function field by applying the dAkimaInterpolation scheme. The first formulation (using permeability) gives me reasonable results. The formulation with B doesn't work though still. The fact that Dt has not been implemented might be the reason. How can the time derivative calculated in the Function block?

Best Regards,

Jonathan

________________________________
From: michael.asam at infineon.com [michael.asam at infineon.com]
Sent: Monday, October 15, 2012 9:57 AM
To: Velasco Alvarado Jonathan; getdp at geuz.org
Subject: RE: Time-dependent non-linear problem and time derivatives
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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