Calculate total force from cauchy stress
by Patricia Garcia Cañadilla

Dear Robert,
I have a 2D body of hyperelastic material which contracts and I would like
to compute the total force developed by the body from the cauchy stress. I
am trying to follow some of your indications I found in this group, but I
still couldn't make it works. Could you please help me to fix the problem?
I am getting the following error:
key = (region.name, integral.order, integration)
AttributeError: 'dict' object has no attribute 'name'
I am trying to do the following, inside stress_strain post-processing
function:
def stress_strain(out, problem, state, extend = False ):
from sfepy.base.base import Struct
from sfepy.mechanics.tensors import StressTransform
from sfepy.mechanics.tensors import transform_data
from sfepy.discrete.common.mappings import get_normals
ev = problem.evaluate
field = problem.fields['displacement']
region = problem.domain.regions['Gamma']
integral = problem.integrals['i2']
n = get_normals(field,integral,regions)
stress = ev('dw_tl_fib_a.1.Omega(f1.fmax, f1.eps_opt, f1.s, f1.fdir,
f1.act, v, u )',mode='qp', term_mode= 'stress');
F = ev('ev_def_grad.1.Omega(u)',mode='el_avg');
transform = StressTransform(F)
Cstress = transform.get_cauchy_from_2pk(stress)
T = Cstress*n;
Force = ev('ev_surface_integrate.2.Gamma(T)')
And here it is part of the problem configuration file.
fields = {
'displacement': ('real', 'vector', 'Omega', 1),
}
materials = {
'solid' : (None, 'get_elastic_pars'),
'load' : (None, 'linear_tension'),
'f1' : 'get_pars_fibres1',
}
variables = {
'u': ('unknown field', 'displacement', 0),
'v': ('test field', 'displacement', 'u'),
}
regions = {
'Omega' : 'all',
'Fix1' : ('vertices in x < %.10f' % (fix_point + eps2), 'facet'),
'Fix2' : ('vertices in x > %.10f' % (fix_point - eps2), 'facet'),
'Fix' : ('r.Fix1 *v r.Fix2', 'facet'),
'Gamma' : ('vertices of surface','edge'),
}
ebcs = {
'fixb' : ('Fix', {'u.all' : 0.0}),
}
integrals = {
'i1' : ('v', 1),
'i2' : ('s', 2),
}
3 months, 1 week

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

time-stepping solvers rewrite
by Robert Cimrman

Hi all,
I am just finishing a major rewrite of the time-stepping solvers in SfePy, with
the aim to make those solvers actually usable for more than just simple
quasi-static problems - for example, two elastodynamics solvers have been
implemented: the Newmark method and the Bathe method.
The new implementation is purely algebraic - the solvers do not "see" the
equations/problem etc., they work only with vectors and matrices. This should
make adding new solvers quite easy. On the other hand, it required significant
changes in Problem class and its handling of solvers, which in turn changed the
way of creating a script or a problem description interactively. For the
moment, see the updates in the "interactive" examples in git - the docs update
is in progress. One of the important changes is that Problem.__init__() does
not take solvers as arguments - Problem.set_solver() needs to be called instead.
The problem description files need not be modified, except two small changes
required in those that use a time-stepping ('save_steps' -> 'save_times' option
renamed and enhanced, 'verbose' option has to have a True value to see the
time-stepping info).
You can check the new code on github under the pull request #446 [1]. The new
solvers are used in examples/linear_elasticity/elastodynamic.py (work in
progress). Some rough edges are to be expected, so let me know under the PR or
by asking here.
r.
[1] https://github.com/sfepy/sfepy/pull/446
1 year, 2 months