[Getdp] Linear Elasticity Examples
geuzaine at acm.caltech.edu
Wed Nov 10 21:03:36 CET 2004
m.fenner at gmx.net wrote:
> Dear Christophe,
> I rerecently discovered the linear elasticity examples in the wiki -
> and immediately ran into a few problems with the 3D-example.
> 1. the ukulele.geo produces a number of errors when loading. The
> variables in the Layers command are missing:
> Error :
> '/cygdrive/d/MF/Programme/FEM/Problems/Elasticity-01/parts.geo', line
> 15 : Unknown variable 'Peg'
> Nevertheless a mesh can be generated with a few parts of the ukulele
> missing. Next I completed the ukulele by assigning the missing
> variables at random.
> I tried both meshes with the .pro files but neither gives a solution:
> GetDP : Warning : Generated system is of dimension zero .. GetDP
> : Warning : No equations in linear system
Seems like I forgot to put the "parts.geo" file in the wiki. Should be
> 2. I also tried a simple model (rectangular beam). I fix the bottom
> face of the beam and apply a transverse force either at the top
> surface or a top edge without further constraints. The solver is
> hardly converging, just stopping at NB_Max_Iter. The solution gives
> an "S"-shaped displacement as if there was a z=0 constraint on the
> top surface. Despite the warning in the Wiki to use the exmples and
> operators at own risk: Do you have an idea about where this goes
> wrong? (I shall attach the files.)
Actually, it looks good to me: you impose a zero displacement on the
face z=0 and a force along the x-axis direction on the face z=0.05. This
will lead to an S-shaped deformation.
To speed up the convergence, just increase the size of the incomplete LU
factorization (used as a preconditionner for GMRES). You can have a look
at the sample solver.par file I've added in the wiki for an example.
> Another question:
>> From the Elasticity_3D.pro file I assume that the non standard D1
>> and D2 operators also work with the Lanczos algorithm. Is that
>> right? I am quite interested in mechanical Eigenmodes.
>> ohyeahq at yahoo.co.jp has sent a patch for the Lanczos functionality
>> recently. But I fear that it shall take me ages to set up all the
>> stuff (cygwin, GSL, LAPACK ...) required - not to speak of
>> implementing the patch and building my own binaries. Do you intend
>> to implement this patch into a distribution soon? I guess I'd
>> rather wait for that.
Not sure when we will distribute a new binary. But since the patch is
merged in the main tree, I would recommend that you compile the nightly
source archive (http://geuz.org/getdp/src/). Cygwin is actually pretty
easy to install, and it provides precompiled packages for GSL and LAPACK
(just select them in the cygwin installer, along with gcc and g77).
Applied and Computational Mathematics, Caltech
geuzaine at acm.caltech.edu - http://geuz.org
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