Dear friends,
I'm trying to solve the following *equations *for the self-potential
distribution along a water injection in a well.
1) sigma * Laplace(V) + L * Laplace (h) = 0
2) L/sigma * grad(h) - grad(V) = 0
*Here h is the hydraulic head (pressure) distribution, V is the
Self_Potential signal*.
I'm using the *3d_cube_big_tetra mesh*. The code is attached.
The *boundary conditions* are:
Left and right side of the cube h=100m
Left side of the cube (reference point) V=0mV.
Center cells of the cube: h=1000m (injection of water)
In general it should be very easy to find a solution with sfepy FE but I
don´t get any relation between V and h, although both should be coupled via
the L/sigma parameter. L and sigma are constant in this *homogeneous case*(L=-1.5e-7, sigma=1).
Hydraulic head (h) is calculated correctly, but the SP signal (V) shows no
connection to h. Changing the parameters L or sigma has absolutely no
effect on the solution. It depends only on the boundary conditions.
So I tried to implement it with the following *equations*:
*
1 'SP' :
"""dw_laplace.i3.Omega( fluid.sigma, w, v ) + dw_laplace.i3.Omega(
fluid.C_sigma_rel, q, h ) = 0""",
2 'Coupling' :
"""dw_stokes.i3.Omega( fluid.C_sigma_rel, q, h ) - dw_stokes.i3.Omega(
w, v ) = 0""", *
A probe image through the middle of the cube is attached.
So my questions:
1) Am I using the right equations? I also tried it with dw_div_grad instead
of dw_laplace (should be the same, no?) but unfortunately the calculation
then doesn't converge.
2) Why is the coupling between both Laplacian eqn. not given? There should
be an effect of L and sigma even without defining eqn 2 (Coupling) but it
has no effect. This is not a SP problem but more a general issue because
there should be a coupling between both unless one part is zero.
That's why I'm afraid that having problems already with a homegeneous case
leads to much more problems with inhomogeneous sigma and L distributions.
Thanks very much for any hints and suggestions. I'm really out of ideas now.
Djamil

I am pleased to announce release 2013.2 of SfePy.
Description
-----------
SfePy (simple finite elements in Python) is a software for solving
systems of coupled partial differential equations by the finite element
method. The code is based on NumPy and SciPy packages. It is distributed
under the new BSD license.
Home page: http://sfepy.org
Downloads, mailing list, wiki: http://code.google.com/p/sfepy/
Git (source) repository, issue tracker: http://github.com/sfepy
Highlights of this release
--------------------------
- automatic testing of term calls (many terms fixed w.r.t. corner cases)
- new elastic contact plane term + example
- translated low level base functions from Cython to C for reusability
- improved gallery http://docs.sfepy.org/gallery/gallery
For full release notes see http://docs.sfepy.org/doc/release_notes.html#id1
(rather long and technical).
Best regards,
Robert Cimrman and Contributors (*)
(*) Contributors to this release (alphabetical order):
Vladimír Lukeš, Ankit Mahato, Matyáš Novák

Hi!
I am planning to release 2013.2 soon. Those that use the git version: let me
know, please, if things work for you. (Or if you have any patches ready, for
example issue 220 :))
r.

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

Dear sfepy group,
I defined a parameter field S and tried to use a function to assign certain
values to the parameter depending of the coordinates.
Like this (simplified):
variable_7 = {
'name' : 'S',
'kind' : 'parameter field',
'field' : 'pressure',
'like' : None,
'special' : {'setter' : 'Def_Sigma'},
}
def Def_Sigma(ts,coors,region=None):
x = coors[:,0]
y = coors[:,1]
val = x*y*10
return val
The field is:
field_1 = {
'name' : 'pressure',
'dtype' : nm.float64,
'shape' : (1,),
'region' : 'Omega',
'approx_order' : '1',
}
When I try to calculate the gradient of the parameter S field in a
post-process-hook I always get an error:
def post_process(out, pb, state, extend=False):
from sfepy.base.base import Struct
div = pb.evaluate('ev_grad.i2.Omega(S)',mode='el_avg')
out['Grad_S'] = Struct(name='output_data', mode='cell', data=div,
dofs=None)
return out
The error is:
Argument S not found.
Although I defined it before...
Thanks for help!
Djamil

Dear group,
I´m new with sfepy so please don´t mind when I ask stupid questions. It's a
great tool and before I ask thanks to all the developers!
*1. issue*: I already read the answers regarding the Darcy-flow question,
and I tried to solve it for a 2d homogeneous isotropic aquifer.
Unfortunately without success..
So what I want is the pressure (p, scalar) and fluid_flow (u, 2d vector) in
a simple rectangular mesh (here I used rectangle_fine_tri.mesh.
Variables: p pressure, static, and q the corresponding test variable
Similar: u fluid flow, static, and s the corresponding test variable
Successful is: Using Laplace eqn. for p gives me an expected distribution
with high pressure on the left side and low pressure on the right side of
the mesh. Fine. I used
equations = {
'Laplace' :
"""dw_laplace.i2.Omega( aquifer.const, q, p ) = 0""",
}
Now I tried to figure out how to get the fluid flow vector from this. I
tried it with the Darcy law in a weak formulation.
'Darcy' :
"""dw_volume_dot.i2.Omega( s, u) +
dw_diffusion_r.i1.Omega(aquifer.relation, q) = 0""",
I don´t know if this is correct. I added boundary conditions (no
perpendicular flow at the borders) but the resulting pressure distribution
and fluid flow is wrong, one would expect simply a flow in one direction
from left to right.
Has somebody an idea?
*2. issue*: My aim is actually to get not only pressure and fluid-flow, but
also the self-potential (SP) distribution at this 2d mesh. The governing
equation for this simple homogeneous case (constant electr. conductivity,
constant coupling coefficient(C)) is laplace(SP)=C*laplace(p)
I tried it with the same equation like the pressure distrib. (but as
Laplace(p) is already zero, I don´t get the interconnection between SP and
the pressure..). Is the interconnection for this simple case just defined
by the boundary conditions I chose? Like SP(left)=0 and
SP(right)=C*Delta(p)? If so, then the calculated pressure distribution in
between the borders has no effect, can this be true?
Thank you very much,
Djamil

Hi all,
My proposal for GSoC under SfePy is available in the project wiki -
https://github.com/sfepy/sfepy/wiki
Your feedback is welcome.
Thankx & Regards,
Ankit Mahato