On 06/09/2016 09:02 AM, Patricia Garcia Cañadilla wrote:
Hi Robent,
Yes, it was one oh the error, thanks. Now, my problem is I do not how to perform the T = stress \cdot n. and to finally obtain the force (sorry I am very new with python). I have this:
ev = problem.evaluate field = problem.fields['displacement'] region = problem.domain.regions['Gamma'] integrals = problem.get_integrals()['i2'] n = get_normals(field,integrals,region)
Try using:
geo, _ = field.get_mapping(region, integral, 'surface')
then geo contains both normals and the jacobians, and you can integrate it just by something like
np.sum(np.dot(stress, geo.normal) * geo.det)
but first you need to restore the stress to matrix form - it is stored as a vector with 11, 22, 12 components (in 2D). For that you can use [2].
Also you might want to convert the stress to Cauchy stress first [1] - the 2nd Piola-Kirchoff stress that is used in the total Lagrangian formulation has no direct physical meaning.
And there is a catch, see below.
[1] http://sfepy.org/doc-devel/src/sfepy/mechanics/tensors.html?highlight=cauchy... [2] http://sfepy.org/doc-devel/src/sfepy/mechanics/tensors.html?highlight=get_fu...
stress_aux = 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'); T = stress_aux*n; Force = ev('ev_surface_integrate.2.Gamma(T)')
and the shapes are stress_aux = (9699,1,3,1) n=(299,2,2,1)
This is because you evaluate the stress in Omega, while the normals on Gamma. Evaluation of stress on surface is not directly supported for the moment. But one could use some workaround(s) here - could you send me the input file (+ a small mesh, if needed) to try something?
r.
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'),
}
Thanks again :)
El miércoles, 8 de junio de 2016, 17:12:09 (UTC+2), Robert Cimrman escribió:
Hi Patricia
Dear Robert,
I have a 2D body of hyperelastic material which contracts and I would
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
On 06/06/2016 03:27 PM, Patricia Garcia Cañadilla wrote: like 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)Here you probably meant using 'region' instead of 'regions', right? regions are the dict in the module name space of the problem description file, so the error is pretty easily overlooked :)
If that does not help, try sending a complete file that reproduces the problem.
r.