Re: [Getfem-users] Gradient of a velocity field using high level generic assembly, partial mesh fem and Interpolate transformation

[Yves Renard]

Dear Eleonora,

I don't see any problem in your formulation. This should a priori work.

Do you use Getfem 4.3 ?
If yes, can you try either the svn version or the link below

http://math.univ-lyon1.fr/homes-www/renard/temp/getfem-4.3.2.tar.gz

and tell me if it fixes the problem (some bug fix of this type have been done 
since 4.3 release).

Best regards,

Yves.
 

----- Original Message -----
From: "Eleonora Piersanti" <address@hidden>
To: address@hidden
Sent: Thursday, February 12, 2015 9:09:11 AM
Subject: [Getfem-users] Gradient of a velocity field using high level generic 
assembly, partial mesh fem and Interpolate transformation

Dear professor, dear all, 

I have to assemble a complicated term and I used the high level generic 
assembly. The problem is the following. 

I have a 2D mesh on which two fems are defined: mf_u that is P2 with qdim=2, 
for velocity, and mf_mult with qdim=2, for Lagrange multiplier, that is P1. 
This mesh is symmetric with respect to the x axis (y = 0). On the symmetry axis 
there is a filament represented by a 1D segment that for the 2D mesh is a 
boundary. On this segment an other mesh mesh made by 1D elements is defined and 
a fem mf_fil based on Hermite elements is defined. 

Now, for some reasons, I had to use the partial mesh fem object. I define 
mf_u_up on the upper part of the 2D mesh and on the dof on the symmetry axis 
(therefore on the filament too), and mf_u_dwn on the lower part of the 2D mesh 
and on the dof on the symmetry axis (therefore on the filament too). In the 
same way I define mf_mult_up and mf_mult_dwn. 

Then, I declare a model, varables and data: 

//-----------------------------------------------------------------------------------------------------------------------------------------------
 

getfem::model model_2; 

model_2.clear(); 

model_2.add_initialized_fem_data("vel_0_up", mf_u_up, vel_0_up); 

model_2.add_initialized_fem_data("vel_0_dwn",mf_u_dwn, vel_0_dwn); 

model_2.add_fem_variable("lambda_up", mf_mult_up); 

model_2.add_fem_variable("lambda_dwn", mf_mult_dwn); 

model_2.add_fem_variable("r", p.mf_fil); //r is the displacement y 

//Define the interpolate transformation from 2D mesh to 1D mesh 

add_interpolate_transformation_from_expression(model_2, "my_transformation", 
p.mesh_fil, p.mesh, "Print(X)"); 

getfem::add_linear_generic_assembly_brick(model_2, 
p.mim_fil,"Print(Interpolate(Grad_vel_0_up, my_transformation).[0.0; 
1.0])*r.Interpolate(Test_lambda_up, my_transformation)"); 

getfem::add_linear_generic_assembly_brick(model_2, 
p.mim_fil,"Print(Interpolate(Grad_vel_0_dwn, my_transformation).[0.0; 
1.0])*r.Interpolate(Test_lambda_dwn, my_transformation)"); 

model_2.assembly(getfem::model::BUILD_ALL); 

//------------------------------------------------------------------------------------------------------------------------------------------------------------//
 

I need to compute an integral on the filament that is 1D with some quantities 
that are 2D, therefore I use the Interpolate transformation. 
vel_0_up, and vel_0_dwn are data that are previously computed and I also 
exported them in .vtk so that I can obtain the terms Grad_vel_0_up.[0.0;1.0], 
Grad_vel_0_dwn.[0.0;1.0] on the filament with paraview. As you can see, I used 
the Print command so I could save the value of those quantities. Unfortunately, 
they do not seem to be correct. In particular, the first component of 
Grad_vel_0_up.[0.0;1.0] is the double than the one obtained with paraview while 
for Grad_vel_0_dwn.[0.0;1.0] on the filament I obtain something that is almost 
zero everywhere on the filament. I would expect something symmetric (maybe with 
differnt sign) due to the fact that vel_0_up and vel_0_dwn are symmetric. 

Am I doing something wrong? Is it possible that it is due to the fact that I am 
using partial mesh fem? 

I hope the question is clear. 

Kind regards, 

Eleonora. 


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