Dear Andriy, Thank you for the advice. You understand correctly about what I am trying to achieve. The problems I am having now are to how to (1) use an updated deformed mesh and (2) consider the displacement/stress value of previous timestep as the initial condition at each new time step.
Could you please advise about the following?
1. If I use Isotropic_linearized_elastic_brick, how can I pass the
displacement and stress values from one time step to another? At each timestep,
I would like the initial condition to take into account the state (e.g.
displacement and stress) of last timestep. I am not sure maybe it does it
automatically or not.
2. I am trying to use high level assembly string language to carry out
linear elasticity. I am guessing, by doing this I can be more free. And maybe I
can consider the displacement/stress value of previous timestep as the initial
condition at each new time step.
Could you please have a look at the attached small code? I try to add the
assembly string of isotropic linear elasticity by
md.add_linear_term(mim,'(clambda*Trace(Grad_u)*Id(qdim(u)) +
cmu*(Grad_u+Grad_u’)):Grad_Test_u ')
but, when I run the code, it appear with some problem – although it does not
give error, but it does not proceed and the python shell is restarted. Could
you please advise about this issue?
Thank you very much
Regards
Zhenghuai Guo
From: Andriy Andreykiv <andriy.andrey...@gmail.com>
Sent: Friday, November 16, 2018 11:03 PM
To: Zhenghuai Guo <zhenghuai....@unsw.edu.au>
Cc: getfem-users@nongnu.org
Subject: Re: [Getfem-users] mesh_deformation
Dear Zhenghuai Guo,
If I understand correctly, you're trying to model creep with contact. If so,
then you can probably assume that your elastic properties are weakly coupled
with stress. In that case you can probably just update your elastic properties
every time step.
So, you need to write a loop where you change the properties every step. Here
are some ideas
1) Your elastic properties lambda and mu cannot be fixed sized constants, as
they will depend on stress values throughout the domain. The logical way to
handle this is
by setting them as a so-called im_data, which is a field defined on Gauss
points (on mesh_im class). Please look up documentation or source how to add
im_data.
2) Isotropic linearized elastic brick does not compute and store stress field.
You will need to define stress field as im_data too and compute it from your
solution
using probably high-level assembly
syntax<http://getfem.org/userdoc/interMM.html#interpolation-based-on-the-high-level-weak-form-language>
ga_interpolation_im_data(md, "lambda*Trace(Grad_u)*Id(qdim(u)) +
mu*(Grad_u+Grad_u'))" , im_data &imd_stress, base_vector &stress_result_vector);
3) The whole calculation should look like this:
initialize the elastic properties as im_data
create im_data for the stress
add contact bricks
while(t < T)
{
md.solve();
compute the stresses from the displacement field using high-level assembly
syntax interpolations
compute the new values for the elastic properties with high-level assembly
syntax interpolations
post-process;
t = t + delta T;
}
Best regards,
Andriy
On Fri, 16 Nov 2018 at 04:42, Zhenghuai Guo
<zhenghuai....@unsw.edu.au<mailto:zhenghuai....@unsw.edu.au>> wrote:
Dear Andriy,
I am planning to do a time dependent deformation with consideration of the
contact and friction. I would like to apply the elasticity theory with Young’s
modulus being a function of time and local stress value.
Could you please advise about the following?
1. If I use add_isotropic_linearized_elasticity_brick (mim, varname,
dataname_lambda, dataname_mu, region=None), how can I make the Young’s modulus
time and stress dependent? In the test examples e.g. in demo_tripod.py, Young’s
modulus is only added by the method add_initialized_data as a constant scalar
value.
2. If I carry out elasticity formulation by a approach like the one in
demo_tripod_alt.py using low level approach to building the linear system by
hand, can I in the meantime apply together the bricks framework e.g.
add_master_contact_boundary_to_large_sliding_contact_brick(indbrick, mim,
region, dispname, wname=None)?
Thank you very much
Best regards
Zhenghuai Guo
From: Andriy Andreykiv
<andriy.andrey...@gmail.com<mailto:andriy.andrey...@gmail.com>>
Sent: Thursday, November 8, 2018 8:56 PM
To: Zhenghuai Guo <zhenghuai....@unsw.edu.au<mailto:zhenghuai....@unsw.edu.au>>
Cc: getfem-users@nongnu.org<mailto:getfem-users@nongnu.org>
Subject: Re: [Getfem-users] mesh_deformation
Dear Zhenghuai Guo,
You can build getfem and getfem based programs using either GCC c++ compiler
for Linux based systems
(read Page 5 of the user doc:
http://download-mirror.savannah.gnu.org/releases/getfem/doc/gmm_userdoc.pdf)
or with Microsoft Visual Studio (you can use free Community edition). You can
find MSVC solution in msvc directory of the distribution.
Unfortunately, the solution for MSVC is not kept up-to-date and you would need
to re-add all getfem sources to it to make it work.
You can deform your mesh with a simple call:
auto deformator = temporary_mesh_deformator(mf, U, true, false);
//the first true means "deform on creation", the second false means "do not
restore the mesh back when temporary_mesh_deformator reaches the end of life"
mf - is the mesh_fem for your displacement field and U is the displacement
vector with gmm::vect_size(U) = mf.nb_dof();
Best regards,
Andriy
On Thu, 8 Nov 2018 at 01:15, Zhenghuai Guo
<zhenghuai....@unsw.edu.au<mailto:zhenghuai....@unsw.edu.au>> wrote:
Dear Andriy,
Thank you for your explanation.
Regarding creep, at the moment I only use liner_elasticity_brick with young’s
modulus being changed on each time-step. This is just to start with. I am new
in Getfem in fact.
Could you please advise about the follows?
1. Are you using c++ to run getfem? If so, can you give some hints how I
can to it? I can’t see any instruction about setting up for c++.
2. If you don’t use c++, how do you normally use the
getfem::temporary_mesh_deformator (from getfem_deformable_mesh.h) or other C
functions?
I was trying to see if it is possible to use this function in Python interface
by using SWIG or Python.Boost. But it is far beyond my knowledge.
Thank you very much
Regards
Zhenghuai Guo
From: Andriy Andreykiv
<andriy.andrey...@gmail.com<mailto:andriy.andrey...@gmail.com>>
Sent: Wednesday, November 7, 2018 8:32 PM
To: Zhenghuai Guo <zhenghuai....@unsw.edu.au<mailto:zhenghuai....@unsw.edu.au>>
Cc: getfem-users@nongnu.org<mailto:getfem-users@nongnu.org>
Subject: Re: [Getfem-users] mesh_deformation
Dear Zhenghuai Guo,
I don't use Python interface much, but your assumption is correct, using
getfem::temporary_mesh_deformator (from getfem_deformable_mesh.h) you can
apply displacement field to the mesh.
By default temporary_mesh_deformator will deform the mesh and un-deform it in
the destructor, unless you build it with the argument to_be_restored=false.
I only assume that you can do it with Python too.
I'm not really experienced with creep, but intuitively I would assume that you
can also use large deformation formulation to account for the change in
geometry.
Or it's not how you intend it?
In your follow up email you are asking about the usage of mesh slices. From
what I know it's used primarily for post-processing, not calculation. If you
intend to use it solely for
post-processing than you can easily achieve it nowadays with Paraview, were you
import a vtk file, warp the result with a displacement field and take a desired
slice.
Best regards,
Andriy
On Sat, 3 Nov 2018 at 12:33, Zhenghuai Guo
<zhenghuai....@unsw.edu.au<mailto:zhenghuai....@unsw.edu.au>> wrote:
Dear Sir or Madam,
Could you please advise how I and deform a mesh according to a displacement
field?
I am trying to simulate a time dependent deformation of a cylinder like object
using python-interface. After applying stress the object creeps with time.
I think I can just go with many small time steps. In each time step, I would
like to update and deform the mesh according to the displacement calculated as
a function of time. And the deformed mesh will be an input for next time step.
I can see there is some related information such as (1)
‘getfem_deformable_mesh.h’ in page 18 in
https://download-mirror.savannah.gnu.org/releases/getfem/doc/getfem_project.pdf
(2) ‘getfem::slicer_apply_deformation’ in
http://getfem.org/userdoc/export.html#getfem::slicer_apply_deformation . But I
can find details examples.
Thank you very much
Zhenghuai Guo
Tyree Xray CT network facility, School of Minerals and Energy Engineering
Resources, UNSW Sydney
Test.py
Description: Test.py
