Re: [Getfem-users] Transient analysis-dirichlet conditions

[Andriy Andreykiv]

Sebastien,

 

  Why don't  you try to use   

 

getfem::assembling_Dirichlet_condition(K,RHS,mf,region=0,DIRICHLET_VECTOR);

 

As you can check in the documentation, this way you're imposing

A Dirichlet condition on a sysmem K*u=RHS.

The above function modifies your stiffness matrix K and your RHS, without resizing them.

DIRICHLET_VECTOR is the imposed values on a region of your finite element object mf.

Best regards,

                    Andriy

________________________________
 Andriy Andreykiv (PhD, Msc)
 Delft University of Technology
 Department of Precision Engineering
 Group of Fundamentals of Microsystems
 Mekelweg 2
 2628 CD  Delft
 The Netherlands

 

 E-mail  :  address@hidden
 Tel.    :   (31) 15 2786818
 Fax.    :   (31) 15 2789475
 www     :   http://www-tm.wbmt.tudelft.nl/~andrico
 private:  (31) 6 47376804

----- Original Message -----

From: "Sébastien Janas" <address@hidden>

To: "Yves Renard" <address@hidden>

Cc: <address@hidden>

Sent: Wednesday, June 04, 2008 10:31 PM

Subject: Re: [Getfem-users] Transient analysis-dirichlet conditions

Le 04-juin-08 à 16:01, Yves Renard a écrit :

> On Wednesday 04 
June 2008 10:30, Sébastien Janas wrote:
>> Hi 
all,
>>
>> I want to solve the transient linear equation of 
diffusion.
>>
>> It seems that there is no function pre-build 
in getfem for the
>> transient problems. So I assemble the mass matrix 
(MM) and stiffness
>> matrix (SM) "manually", and then construct the 
linear system A*X=B
>> using the backward euler
>>
>> 
A = (MM + delta t * SM)
>> B = MM * X(t-1)
>>
>> Then 
I have to impose dirichlet conditions on the surface. I import  
>> my
>> mesh from gmsh, where the surface are tagged with a 
number (in my  
>> case
>> 200). How can I modify my 
linear system to take into accompt the
>> dirichlet conditions? All the 
functions I found in the documentation
>> are in the case where you use 
model bricks or standard assembly
>> 
procedures...
>>
>> If I can have the list of node numbers 
tagged by 200 I would use the
>> penalty method. But I am not able to 
obtain these list.
>>
>> I am using the python interface of 
getfem.
>>
>> Thanks for your help,
>>
>> 
Best regards,
>>
>> Janas Sébastien
>
>
> 
This is true that there is no general strategy proposed for transient
> 
problems, especially with the matlab or python interfaces.  This is  
> however
> not easy to build such a general strategy since the 
situation can  
> vary a lot
> for differente time integration 
schemes.
>
>
> However, You can have the list of nodes on a 
boundary with the command
>
> gf_mesh_fem_get(MF, 'dof on region', 
[bnum]);
>
>
> but you have first to tag the boundary with the 
command
>
> gf_mesh_set(M, 'region', int bnum, imat 
CVFLST);
>
> (see the Matlab examples).
>
> 
Yves.


Is there any systematic procedure to impose the dirichlet 
conditions  
on my system A*X=B ?

I have tried with the penalty 
method, but the sparse matrix format  
included in getfem set it very 
difficult (we can't make B[i] += A[i,i]  
* BIG * val because A[i,i] 
give an 1x1 array and not a scalar...)

>
>
>
> -- 
>
>  Yves Renard (address@hidden)       tel : (33)  
> 
04.72.43.87.08
>  Pole de Mathematiques, INSA de 
Lyon          fax : (33)  
> 04.72.43.85.29
>  20, rue Albert Einstein
>  
69621 Villeurbanne Cedex, FRANCE
>  http://math.univ-lyon1.fr/~renard
>
> 
---------
>


_______________________________________________
Getfem-users 
mailing list
address@hidden
https://mail.gna.org/listinfo/getfem-users