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Re: [Getfem-users] mesh_deformation

 From: Andriy Andreykiv Subject: Re: [Getfem-users] mesh_deformation Date: Fri, 16 Nov 2018 13:03:22 +0100

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

3) The whole calculation should look like this:

initialize the elastic properties as im_data
create im_data for the stress
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 <address@hidden> 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.

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

Sent: Thursday, November 8, 2018 8:56 PM
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

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 <address@hidden> wrote:

Dear Andriy,

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.

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

Sent: Wednesday, November 7, 2018 8:32 PM
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 <address@hidden> wrote:

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