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, 2 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

possible GSoC project ideas
by Robert Cimrman

Hi,
we are trying to sign up under the PSF umbrella for this year's Google Summer
of Code because of an e-mail from Ankit Mahato, who expressed interest to help
developing SfePy as his GSoC project this summer.
So let us discuss possible project ideas here. I will post results of the
discussion to [1].
Ankit's ideas are (my summary):
#1 parallelization - cluster support using mpi4py
#2 pre- and post-processing GUI frontend
#3 incorporating phase changing materials (his research area)
Ankit, could you post full text your ideas into this thread? The pdf you sent
me does not allow selecting text.
My comments:
For me, #1 is something that I was planning to do "soon" anyway as I am going
to need it for my research work - a help would come really handy, but we will
have to think carefully about the implementation. I think I prefer having a
parallel layer above the current serial FEM, so that the current code can stay
as it is, unaware that it runs in parallel. I am not sure yet how difficult it
is going to be, but it won't be trivial.
#2 would be nice, but IMHO it is not so important as having a solid and
reasonably fast FEM core.
#3 would IMHO be the most useful for Ankit, and a nice addition to modelling
capabilities of SfePy.
Other possible topics can be found in our issues list ("enhancement" label).
IMHO it would be good to prospective student(s) to try tackling some of the
issues listed below to get acquainted with SfePy code before the GSoC starts:
#196 Document properly term evaluation modes and postprocessing/probing.
#195 describe how to add Neumann BC in a diffusion example and tutorial
(tutorial part done by Alec)
#167 improve gallery page
#164 Python 3 compatibility
#154 automatic testing of terms
#140 test schroedinger.py
#133 Provide examples for SfePy Terms
Implementing the other enhancements would be, of course, also very useful, but
those IMHO too difficult for someone trying to learn the code. They are
certainly quite difficult for me, as they are not done yet =:) (shell elements!)
Cheers,
r.
[1] http://sfepy.org/doc-devel/development.html
5 years, 10 months

Modeling an adjustable X-ray optic
by Tom Aldcroft

I'm working on modeling a next-generation X-ray mirror for which the
shape can be actively controlled by use of many thin piezo-electric
actuators mounted on the mirror surface. The mirror is basically a
glass conical paraboloid with a 1 meter radius and 200 micron
thickness (e.g. http://en.wikipedia.org/wiki/X-ray_optics). Our
project is currently using a proprietary FEA package, but the model
setup and turnaround time is slow, in part because there is only one
part-time engineer who can run it.
SfePy looks like a great package and we're hoping that it could be
used to automate running a large number of different cases. I've
spent some time reading the documentation but I have a few questions
that I hope can be answered before going too much further. I want to
apologize in advance if some of my wording is imprecise, I have a
physics background but this topic is a bit outside my realm...
- Is SfePy appropriate for this problem?
- If a specify a grid with about 800 x 400 points (azimuthal, axial)
and about 10 boundary conditions (corresponding to mount points), what
is the rough order of magnitude of time to compute the solution? Is
it seconds, minutes, hours, or days?
- The linear elastic examples show a problem with a specified
displacement. How do I specify an input force? The piezo essentially
provides a tensile force along the surface.
- Is there a way to specify the problem and solve in cylindrical
coordinates? This is the natural coordinate system.
- How do I specify 6-DOF constraints which correspond to the mirror
mounts?
Thanks in advance for any help!
Tom Aldcroft
5 years, 11 months

elastic contact plane term
by Robert Cimrman

FYI: A new elastic contact plane term has been implemented. Its use is
demonstrated by a new example - try:
$ ./simple.py examples/linear_elasticity/elastic_contact_planes.py
$ ./postproc.py cube_medium_hexa.vtk -d'u,plot_displacements,rel_scaling=1'
--wireframe --view=-6.24e+01,5.04e+01,2.86e+00,0.00e+00,0.00e+00,0.00e+00
--roll=-2.95e+01
r.
5 years, 12 months

Question about solving a problem with SfePy
by Demian Wassermann

Hello SfePy-ers!
I'm starting to work with the tool. I found it great, very nice to use.
I have a problem that I can not wrap my head around:
I have a cylinder close to a sphere, both with different elasticity
properties (the cylinder is rigid and the sphere is more elastic).
I'm trying to rotate the cylinder about the centre of its bottom cap and
thus hit the sphere deforming it.
To do this I put the sphere and the cylinder close, I put them in a
bounding box representing the media in wich both are inscribed (air, water,
etc), I calculate a mesh for this domain with tetgen having a different
material for each object (cylinder, baloon, media)
and then use a function in the ebcs conditions to move the rod. Similar to
the large deformations hyperelastic example (rotate_yz), where the rotation
angle increases with time.
My problem is that if my cylinder rotates more than ~.1 degrees, I get a
"warp violation" error.
How could I solve this? By making the elements of my mesh smaller? Taking
smaller steps, increasing the order of the balance integral holding the
elasticity properties?
Any help will be great
Thanks
Demian
--
Demian Wassermann, PhD
dem...(a)bwh.harvard.edu
LMI / PNL / SPL Labs
Harvard Medical School
Brigham and Women's Hospital
1249 Boylston, Boston, MA, USA
http://lmi.bwh.harvard.edu/~wassermann/
6 years