OK, I can see now what are you trying to do. You would like to implement a
material nonlinearity (material parameters depending on state) and linearize
it by taking state from the previous time step in each time step, right?
I guess it can be done the way you try, i.e. each element has its own
region/material/term, but that is going to be utterly slow, as it would
completely negate the fact that the terms are evaluate in C for a number of
elements simultaneously.
So again, it's a good catch, as it is a common need and the code should
support that in a clean and easy-to-use manner. The solution is to pass the
state to the material update function, that a user could write. I am working
on this now.
Then you would evaluate all just over Omega (strain, stress, ...).
r.
On 12/16/10 18:18, Andre Smit wrote:
Robert
Yes, the materials are defined as:
# Dynamically assign materials
for i in range(NELS):
exec "material_%s = { \
'name' : 'mat_%s', \
'values' : { \
'lam' : youngpoisson_to_lame(young, poisson)[0], \
'mu' : youngpoisson_to_lame(young, poisson)[1], \
'D' : stiffness_tensor_youngpoisson(2, young,
poisson),},}"%(i+1,i)
So I have NELS number of materials in the model.
young will change depending on the strain rate in the individual elements
(I'm assuming the material is strain rate dependent) - so in effect the
material parameters change every time step when they are updated based on
young=f(strain rate). Each element is assigned a region and the equation
as:
# Fixed regions
regions = {
'Omega' : ('all', {}),
'Left' : ('nodes in (x< 0.001)', {}),
'Bottom' : ('nodes in (y< 0.001)', {}),
'Top' : ('node 2', {}),
}
# Dynamically assigned regions
for i in range(NELS):
exec "region_%s = {'name' : 'ele_%s', 'select' : 'element
%s'}"%(i+5,i,i)
# Dynamically assigned equation:
Eq=""
for i in range(NELS):
Eq+="dw_lin_elastic_iso.2.ele_%s(mat_%s.lam,mat_0.mu,v,u)+"%(i,i)
Eq=Eq.rstrip("+")
Eq+="=0"
equations = {
'balance_of_forces' : Eq
}
This brings up the issue of having different materials defined in the
model
- I can calculate the strain over Omega as before:
strain=pb.evaluate('de_cauchy_strain.2.Omega(u)') but stress needs to be
done for the individual elements (and materials) separately, right?.
s='de_cauchy_stress.2.ele_%s(mat_%s.D, u)' %i
stress = pb.evaluate(s)
So I don't think 'de_volume_average_mat.2.Omega( material, parameter )'
will
work as it needs a material parameter - but in this case the material is
not
defined over Omega. Am I missing something?
Andre
On Thu, Dec 16, 2010 at 3:49 AM, Robert Cimrman<cimr...@ntc.zcu.cz>
wrote:
Hi Andre,
I have some questions: how do you plan to use this D matrix? Do you
define
your material by a function? Note that to use a material parameter, it
has
to be evaluated in quadrature points, i.e. the coordinates passed into a
material function.
This code
Dstate=pb.create_state()
Dstate.set_full(Dmatrix)
assumes, that your state contains a single variable, which has the shape
like Dmatrix.ravel(). I doubt this is the case. SfePy unfortunately did
not
check this - I have just made a fix, so get the fresh git version.
Otherwise I would just use the term de_volume_average_mat, something like
the following code I use for the permeability tensor:
perm = pb.evaluate('de_volume_average_mat.2.Omega( m.K, pc )',
mode='el_avg',
copy_materials=False, verbose=False)
out['pperm'] = Struct(name='K', mode='cell', data=perm, dofs=None)
Otherwise, it's great you play/work with the code, it really makes it
better, if it is actively used by other people than me. :)
r.
On 12/16/10 06:27, Andre Smit wrote:
Hi guys
I've generated an array comprising material D matrix or stiffness tensor
values. It looks like this - where each block represents the material
value
for a cell or element (yes, they're all the same but will change in
subsequent time steps).
[[[ 1604.9382716 864.19753086 0. ]
[ 864.19753086 1604.9382716 0. ]
[ 0. 0. 370.37037037]]
[[ 1604.9382716 864.19753086 0. ]
[ 864.19753086 1604.9382716 0. ]
[ 0. 0. 370.37037037]]
[[ 1604.9382716 864.19753086 0. ]
[ 864.19753086 1604.9382716 0. ]
[ 0. 0. 370.37037037]]
...,
[[ 1604.9382716 864.19753086 0. ]
[ 864.19753086 1604.9382716 0. ]
[ 0. 0. 370.37037037]]
[[ 1604.9382716 864.19753086 0. ]
[ 864.19753086 1604.9382716 0. ]
[ 0. 0. 370.37037037]]
[[ 1604.9382716 864.19753086 0. ]
[ 864.19753086 1604.9382716 0. ]
[ 0. 0. 370.37037037]]]
I'd like to append this array to the vtk file generated by SfePy which
contains displacements, stress and strains, etc.
I was using the following to generate the array:
Dlist=[]
for i in range(NELS):
Dlist.append(pb.conf.materials.values()[i].values['D'])
Dmatrix=array(Dlist)
print "~~~~~~~~~~~~~~~~~~~~~~~~~~~"
print Dmatrix
Dstate=pb.create_state()
Dstate.set_full(Dmatrix)
outD=Dstate.create_output_dict()
out['D_matrix']=Struct(name='output_data',mode='cell',data=outD,dofs=None)
but get the following *numpy* error:
Traceback (most recent call last):
File "/home/grassy/sfepy/simple.py", line 120, in<module>
main()
File "/home/grassy/sfepy/simple.py", line 117, in main
app()
File "/home/grassy/sfepy/sfepy/applications/application.py", line 29,
in
call_basic
return self.call( **kwargs )
File "/home/grassy/sfepy/sfepy/applications/simple_app.py", line 112,
in
call
post_process_hook_final=self.post_process_hook_final)
File "/home/grassy/sfepy/sfepy/solvers/generic.py", line 216, in
solve_direct
nls_status=nls_status)
File "/home/grassy/sfepy/sfepy/solvers/generic.py", line 148, in
solve_evolutionary_op
ts=ts)
File "/home/grassy/sfepy/sfepy/fem/problemDef.py", line 535, in
save_state
out = post_process_hook( out, self, state, extend = extend )
File "its.py", line 102, in strain_rate
outD=Dstate.create_output_dict()
File "/home/grassy/sfepy/sfepy/fem/state.py", line 188, in
create_output_dict
var_info, extend)
File "/home/grassy/sfepy/sfepy/fem/variables.py", line 587, in
state_to_output
fill_value=fill_value))
File "/home/grassy/sfepy/sfepy/fem/variables.py", line 1468, in
create_output
(self.n_dof / self.n_components, self.n_components))
File "/usr/lib/python2.7/site-packages/numpy/core/fromnumeric.py",
line
170, in reshape
return reshape(newshape, order=order)
ValueError: total size of new array must be unchanged
Can I use existing SfePy methods to write this array to the vtk or
should
I
rather write my own?
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