Re: Torque
by Robert Cimrman

In examples/large_deformation/hyperelastic.py a rotation by displacements is applied. By using a similar function the vectors defining the force couples could be defined for dw_surface_ltr (IMHO). Does it make sense?
r.
----- Reply message -----
From: "Andre Smit" <freev...(a)gmail.com>
To: <sfepy...(a)googlegroups.com>
Subject: Torque
Date: Sat, Dec 18, 2010 05:10
What is the best way to apply a torque load to a model?
--
Andre
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1 year, 1 month

1D line elements in SfePy
by Nimish

I am currrently looking for FEM packages to help me solve a system of
beams and columns, basically a collection of 1D bernoulli/timoshenko
line elements.
I started reading SfePy docs and i am getting the idea that doing the
above is not really possible here, am i right?
Are only 2D area elements permitted in SfePy?
Or is there any direct support for solving 1D line elements too..
Cheers
Nimish
3 years, 3 months

Evaluate a solution in the arbitrary point in the domain
by Alec Kalinin

Dear SfePy users,
Is it possible to evaluate a solution not only in the FEM mesh node, but in
any arbitrary point in the domain with the given (x, y, z) coordinates?
For example, consider Dirichlet problem for Poisson equation. We apply
essential boundary conditions on the surface nodes and after the problem
has been solved we have the solution vector, i.e. vector of values in the
FEM mesh nodes. But I want to know the solution in point v(x, y, z) that is
not FEM mesh node. What is the best way to obtain solution in this point v?
Sincerely,
Alec Kalinin
5 years

elliptical hole under isotropic stress
by David N. Mashburn

Hello sfepy developers and users!
I am modelling a simple linear elastic sheet under isotropic stress with
an elliptical hole in the center (and I have it working under sfepy,
great little platform!).
It is obvious the model should initially yield more easily in the
direction of the short axis of the ellipse. What is not so obvious to me
is what should happen in the limit as stress goes to infinity. Part of
me wants to believe that the hole should eventually become a circular,
but the results of the simulation show that the ellipse eventually
switches its aspect ratio with what was the the short axis becoming the
long axis and vice-versa.
My question is whether:
A: The finite element result is the product of a
small-displacement/non-moving mesh artifact (and if so, if there is a
way to get the correct behavior using sfepy...)
OR
B: My intuition about the physical behavior of this ideal system is
incorrect and the ellipse really wouldn't round out into a circle under
increasingly large stress (aka, the FE model is still physical/correct
with large displacements).
This might be obvious to people who have done more finite element
modeling than I have, but thanks anyway! I'm attaching a picture to make
it easier to see at a glance (quarter-ellipse with x and y symmetry
boundary conditions and equal tractions applied at the top and right
boundaries).
Thanks!
-David Mashburn
5 years, 3 months

GSoC Phase 1
by Ankit Mahato

Hi R,
I was very sick for the past few days.
Just got up from bed yesterday.
Earlier I went through the docs, samples, guide as you had instructed.
Also I got the weak form of the equations.
Kindly look at the attached PDF and suggest me the path I should take.
>From today onwards I will remain online all day and will ping you whenever
I get struck.
Regards
Ankit
5 years, 8 months

Re: [sfepy-devel] Re: 2d NS terms
by Robert Cimrman

On 07/04/2013 03:02 PM, Ankit Mahato wrote:
> Hi R,
>
> For our Navier-Stokes currently we use the Newton method with backtracking
> line-search.
Yes, in sfepy we use that.
> in OpenFoam and most of the CFD code the linearization
> approach is based on Patankar's SIMPLE algorithm.[1][2]
> I talked to my professor who told me that SIMPLE is used in commercial
> softwares like FLUENT too.
Do you think you could then try implementing SIMPLE in the FE context?
> I found few papers which tells us some other approaches. Do have a look at
> them and lend your views:
>
> -
> http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&...
> - http://numerik.iwr.uni-heidelberg.de/Oberwolfach-Seminar/CFD-Course.pdf
> -
> http://dspace.uta.edu/bitstream/handle/10106/5144/JIAJAN_uta_2502M_10764.pdf
> - http://www.reaction-eng.com/downloads/nksolver_pernice.pdf
> - http://aero-comlab.stanford.edu/Papers/birkenjamesonproceedings09.pdf
> - https://cs.uwaterloo.ca/research/tr/1993/02/CS-93-02.pdf
> - http://www.cs.sandia.gov/~rstumin/backtrack.pdf
> - http://repository.cmu.edu/cgi/viewcontent.cgi?article=1032&context=math
> - http://www8.cs.umu.se/kurser/5DA001/HT07/lectures/newton-handouts.pdf
>
>
> [1]:
> http://www.cfd-online.com/Forums/openfoam-solving/60167-how-nonlinear-dis...
> [2]: http://web.cecs.pdx.edu/~gerry/class/ME448/notes/pdf/SIMPLEslides.pdf
Nice list. I will try to look at it, but doubt that I will be of much help
in deciding what path to pursue. We need something that could be
implemented in a reasonable time. IMHO that rules out the multigrid-based
solvers, unless a prepared solution like pyamg could be used directly.
> PS: For the python 3 fix which I had forgotten earlier :( . While going
> through the codes I came across that we use output() in base.py to print.
> You have already called
> if sys.version[0] < '3':
> basestr = basestring
> else:
> basestr = str
> So basically we know the python version and call the print function
> according to the python version. If I am correct it is quite easy to fix
> then, am I?
In the sfepy codebase, there should be no print statements - output()
should be used everywhere (if it is not, it's a bug), so yes, updating
that for python 3 should be pretty easy.
r.
5 years, 9 months

Help regarding pressure gradient
by Ankit Mahato

Hi Guys,
I had formulated the problem combining Navier Stokes with Energy Equation.
For that I wanted to try out Couette flow with pressure gradient (*plane
Poiseuille flow*) with Thermal boundary conditions. For simple Couette Flow
( pressure gradient =0 ) the code is working fine and giving us the proper
velocity profile but how to do it with user defined pressure gradient.
See Link - http://www2.mech.kth.se/~luca/Smak/rec5.pdf
which will give us velocity profile for this flow.
I tried imposing pressure boundary condition but it is not working out.
I have attached the problem file.
Regards,
Ankit
5 years, 9 months

NS: algorithms to try
by Robert Cimrman

Hi Ankit,
I have contacted a friend who suggested some algorithms to try out for solving
the linear system:
1. algebraic brute force (does not address the nonlinearity, reported to work
on moderately sized problems): gmres with ILU(0) preconditioning.
2. If ILU(0) does not work:
We are solving K*x = b where K has a block structure:
K = | A B |
| B^T -C |
(C can be positive semi-definite or zero - our case)
Instead, an "augmented Lagrangian" technique would lead to
Q*x = b
with
Q = | A + alpha*B*B^t B |
| B^T -C |
alpha>=0, small
Either the augmented system can be solved, or Q could be used in ILU(0)
preconditioner.
3. Ultimately you want to solve a time-dependent problem, so try also the
Chorin-Temam projection method [1]. This could be used even for the stationary
case by solving in time until a steady state is (hopefully) obtained.
r.
[1] http://en.wikipedia.org/wiki/Projection_method_%28fluid_dynamics%29
5 years, 9 months

2d NS terms
by Robert Cimrman

Hi,
I have removed the "3d only" restriction from the Navier Stokes and related
terms. There is also a new example: examples/navier_stokes/navier_stokes2d.py.
r.
5 years, 9 months