Re: [Libmesh-users] [Libmesh-devel] Elastic Solid Examples?

[Robert <li...@ro...>]

On Thu, Jan 12, 2012 at 10:13:03AM +0100, Robert wrote:
> On Wed, Jan 11, 2012 at 02:10:30PM -0600, Roy Stogner wrote:
> > On Tue, 10 Jan 2012, Robert wrote:
> > > I have just tested this with the default configure options. Any
> > > suggestions for improvements are of course welcome.
> > 
> > Would you try running it in parallel?  The serial results look
> > sensible in my eyeball norm, but with 'mpirun -np 6' (with SerialMesh)
> > I seem to get mesh tangling before the first time step is even begun.
> 
> I just checked this, the calculation runs fine, although it hits an
> assertion in fem_system.h:346 when running in parallel. It would fail
> with a "negative jacobian/deformation gradient"-error if there are any
> serious problems.
> 
> The problem here is the output. If you are using paraview try attaching
> a "Calculator" filter to the reader, input "x*iHat+y*jHat+z*kHat" and
> check the "Coordinate Result" box. This uses the x,y,z solution
> variables instead of the provided node coordinations and the result
> should look fine again. The VTKIO just uses one processor for writing
> the node coordinates, so the output just contains the coordinates of
> this first processor and zeros all other values. This behaviour was 
> the reason for my earlier patch for VTKIO to write in parallel.
> 
> But maybe using the node coordinates (and marking it as mesh_vars) as
> primary variables is not the way to go anyway as it causes trouble with
> the periodic boundaries also.
> 
> Just another thought: It would be nice to have a own FEType for storing
> values at quadrature points instead of abusing the MONOMIALs for this.
> This would allow a correct method for projecting the values from
> quadrature points to the nodes. Additionally it would allow output
> filters for formats which support this to write solutions on gausspoints
> to the files (There is an output filter for GiD[1] on my disk which
> looks at the variable name to identify variables with gauss point data).
> The cauchy stress, which is computed at gauss points in a postprocessing
> routine, is usually the most important result of a calculation
> involving solids.
> 
> And finally I found a small error in my patch:
> 
> libmesh/examples/fem_system/solid_ex2> diff -r Makefile Makefile.p1
> 33c33
> < target           := ./solid_ex2-$(METHOD)
> ---
> > target           := ./solid_ex1-$(METHOD)
> 
> Robert

The missing link is
[1] http://gid.cimne.upc.es/