Re: [Getfem-users] boundary conditions on nodes

[julien pommier]

Hello Julien,

You have to use the generic "constraints" brick for that purpose. Here 
is an example of use (supposing b3 is a previous brick):

b4 = MdBrick('constraint',b3, 'penalized');
H=Spmat('empty',1,mfu.get('nbdof'));
H[0, 143] = 1
R = [41.42];
b4.set_constraints(H,R);

Here we impose the constraint H*u = R , where H is a row matrix (only 
one constraint), and R is a vector with only one element. Here, the dof 
number 143 is forced to be equal to 41.42

However there was a bug in the python interface which prevented the use 
of this function (it only accepted matlab sparse matrices). This is 
fixed now:

http://svn.gna.org/viewcvs/getfem/trunk/getfem_matlab/src/gf_mdbrick_set.cc?r2=2505&rev=2505&r1=2426&dir_pagestart=50

Best Regards,
Julien


Julien Sylvestre wrote:
> Hello,
>    I am trying to impose a fixed value to the z-component of 
> displacement in a linear elastic problem, on a specific node, leaving 
> the x- and y-components untouched. The only thing I'm currently able 
> to do is something like
>
> mfu = getfem.MeshFem(mesh, 3)
> ...
> lower_boundary = 1+len(mesh.regions())
> mesh.set_region(lower_boundary, fbot) # fbot is a list of element ids
>
> b3 = getfem.MdBrick('dirichlet', b2, lower_boundary, mfu, 'penalized')
>
> This doesn't do what I want:
> 1. I need to set the boundary condition only on one component of the 
> displacement field (i.e., z, and not x or y)
> 2. I need to set the boundary condition only on one node; I couldn't 
> find a way to create a region on a single node. Best I can do is to 
> create a region on one element.
> 3. I want a fixed value for the specified component of the 
> displacement field which is not zero, but rather some other arbitrary 
> (fixed) number.
>
> I was unable to get the information in a format I could understand 
> from the documentation. Any help would be greatly appreciated.
>
> Regards,
> JS
>
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