Help with Scipy07 abstract and project planning for the summer
by Ryan Krauss

So, I have a small university grant to work on a research project this
summer focused on impact dynamics. The project has two parts:
1. Designing an impact test device to extract material properties at
impact speeds
2. Coming up with a Python based, FEA simulation of the impact test
I have learned just enough about SfePy to believe that it is a good
fit for my project. But not enough to know all that I am going to
have to do to make this project work. And not even really enough to
write an intelligent abstract. But the abstract is due next Monday.
So, while I am still learning SfePy, I could use some help and
direction in writing my abstract and planning my summer project.
I am planning on trying to contribute contact modeling capabilities
eventually. I believe my project will also need the following, which
SfePy may or may not already be capable of:
- a nonlinear material model (or at least piece-wise linear) for the
stress vs. strain material behavior
- modeling two bodies, one with an initial velocity and one that is
initially stationary (they could initially start at the instant of
contact, so that an algorithm for describing when contact happens
could be put off for now)
I put together a description of the problem and an high-speed video of
an impact test here:
http://www.siue.edu/~rkrauss/research_project3.html
The entire impact event last 10 or so milliseconds.
Can you help me understand what it will take to model this test, what
SfePy can already do, and what I will need to contribute to make this
project come together?
Thanks,
Ryan
10 years, 9 months

release
by Robert Cimrman

Hi,
we should make a release to get some attention, as both EuroScipy08 and
SciPy08 conferences are approaching. Also lots of things were updated
and improved since the last one (already three months ago). We are still
far from 1.0, so it has not to be perfect, but are there any critical
issues with the hg version that you feel should be fixed now?
cheers,
r.
10 years, 9 months

status of testing with manufactured solutions
by Robert Cimrman

Hi,
for reference, look at tests/test_msm_symbolic.py.
Currently, the symbolic derivation of right-hand sides corresponding to
manufactured solutions works only for scalar variables - briefly, we can
test just Poisson or diffusion problems, where the symbolic description
of what each term does is:
Laplace term: 'c * div( grad( u ) )' (c is scalar)
Diffusion term: 'div( K * grad( u ) )' (K is matrix)
I would like to discuss here how to approach the problems involving
vector fields, e.g. the linear elasticity. The linear elastic term is
defined (LaTeX notation, summation convention - same indices sum
together) as
d/dx_j D_{ijkl} e_{kl}(u), or div( D e ), where e is the small strain
tensor.
I am thinking of two ways of describing this in SfePy:
1. matrix notation (this is used for scalar terms)
expr = """
e = 1/2 * (grad( vec( u ) ) + grad( vec( u ) ).T)
D = map( D_sym )
s = D * e
out = div( s )
"""
... ok, but some more complex terms may be difficult to express in this
was. Anyway I will try this first.
2. indicial notation
"""
e[i,j] = 1/2 * (der[j]( u[i] ) + der[i]( u[j] ))
map = ?
D[i,j,k,l] = map( D_sym )
s[i,j] = D[i,j,k,l] * e[k,l]
out[i] = sum( der[j]( s[i,j] ))
"""
... better in a sense that one sees immediately how the operations look.
But as I would like to avoid writing
for i in range( 3 ):
for j in range( 3 ):
e[i,j] = ...
i.e. writing the cycles explicitly, some parsing would have to be included.
-> my question (Ondrej) - would it be possible to add to sympy some
capabilities of Einstein summation convention? maybe a module that would
expand names like e_i_j into proper cycles.
r.
10 years, 10 months

FEA books
by Ryan Krauss

So here is the list of what I have checked out so far:
Segerlind, Larry J., 1937- Applied finite element analysis.
Kikuchi, Noboru. Finite element methods in mechanics / Noboru Kikuchi.
Norrie, D. H. Introduction to finite element analysis, D. H.
Norrie and G. de Vries.
Finite element primer / published by the National Agency for
Finite Element Methods and Standards.
Irons, Bruce. Finite element primer / Bruce Irons and Nigel Shrive.
Huebner, Kenneth H., Finite element method for engineers / Kenneth
H. Huebner, Earl A. Thornton, Ted G. Byrom.
What every engineer should know about finite element analysis /
edited by John R. Bauer.
White, R. E. (Robert E.) Introduction to the finite element method
with applications to nonlinear problems / R.E. White.
Becker, Eric B. Finite elements : special problems in solid
mechanics / Eric B. Becker, Graham F. Carey, and J. Tinsley Oden. v.1
Becker, A. A. (Adib A.) Introductory guide to finite element
analysis / A.A. Becker.
Finite element methods : fifty years of the Courant element /
edited by M. Krizek, P. Neittaanmaki, R. Stenberg.
Bathe, Klaus-Jurgen. Finite element procedures in engineering
analysis / Klaus-Jurgen Bathe.
Martin, Harold Clifford, 1913- Introduction to finite element
analysis: theory and application [by] Harold C. Martin [and] Graham F.
Carey.
Cheung, Y. K. Practical introduction to finite element analysis /
Y. K. Cheung and M. F. Yeo.
Norrie, D. H. Finite element method; fundamentals and
applications, [by] Douglas H. Norrie [and] Gerard de Vries.
If you can recommend the best starting point(s), I am open to
suggestions. If you have a favorite (especially for beginners), that
isn't on this list, I can almost certainly get it (we are a smallish
school, but all university libraries in the state of Illinois
cooperate). So, I am open to recommendations.
Thanks again,
Ryan
10 years, 10 months

.mesh file documentation
by Ryan Krauss

I am trying to create a .mesh file as an input to SfePy, and all the
links I can find for it in google are broken, for example:
http://www-rocq.inria.fr/gamma/medit
Looking at simple.mesh, the format seems fairly straight forward.
After a couple of header lines, it seems to contain coordinates of
vertices. I assume this are X Y Z, but I don't understand the 4th
column which is always 0. Then there are a bunch of lines describing
tetrahedrons. I assume these are being described based on numbers
assigned to vertices. But again there is an extra final column I
don't understand. One tetrahedron row seems to contain 4 vertices and
then the number 6. What does the 6 represent?
So, I am slightly stuck. Can anyone direct me to documentation on
.mesh files? Also, are there free utilities or Python scripts for
generating them? I don't want to reinvent the wheel and might go a
little crazy trying to visualize too many tetrahedra. I don't want to
reinvent the wheel.
Ryan
10 years, 10 months