Re: [Getfem-users] 3D truss element

[Renard Yves]

Dear Roman,

I am not an expert at all for this kind of (rather simple) element.  
What I do not understand in 3D is what kind of degrees of freedom this  
element will link ? Is this element have a nonlinear behavior due to  
the geometrical nonlinearity or is it considered in small  
displacements ?

There could be several way to implement this. The first one is to use  
the transformation matrix M of the non-tau equivalent elements (see  
the doc). A second way, especially if it is non-linear and since the  
elementary matrix is very simple, would be to create an small model  
brick dealing with such an element.

Of course, It would be interesting to add such an element in Getfem.

Yves.


Roman Putanowicz <address@hidden> a écrit :

> Dear All,
>
> Has anyone of you implemented 3D truss element (or 2D) within the
> framework of GetFEM++? Not that this element is any special --
> I could calculate its stiffness matrix explicitly and use generic
> assembly routines. However I have problems if figuring out if there
> is some sort of support in GetFEM for "structural elements" as I call them.
>
> To be more explicit: one usually  defines the truss element in
> local coordinate system that reduces the problem to 1D.
> Then in case of 2D one uses the transformation matrix:
>
>   T = [ c  s 0 0
>         0  0 c s ]   c -- cosine between local and global X axis
>                      s -- sine between local and global X axis
>
>  that transforms global degree of freedom Q_i (2 per node) into the
>  local one.
>  Of course element stiffness matrix in global coordinate system boils down
>  to :
>    E*A *   T' * [1,-1;-1,1] * T     where E*A is the bar stiffness.
>
>  The question essentially is -- what is the most "GetFEMic" way of handling
>  the matrix T?
>
>
>  Regards
>
>  Roman
> --
> Roman Putanowicz, PhD  < address@hidden  >
> Institute for Computational Civil Engng (L-5)
> Dept. of Civil Engng, Cracow Univ. of Technology
> www.l5.pk.edu.pl, tel. +48 12 628 2569, fax 2034
>
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