Re: [deal.II] Output multiple fields with different discretization

[Wolfgang Bangerth]

>dataOutDisp.add_data_vector(solution.block(0), [...]
> ...
A probable solution could be to create a new DOfHandler during each output 
call for both the displacement as well as the phase-field and attach the 
respective solution blocks to their DofHandlers. Not sure this would work 
since the mapping which would be used for the phase-field would be based on a 
different DoFHandler. Also, this would probably be computationally expensive 
(not sure?)


Just output the whole vector (not just one block). If you don't want to 
visualize the fields that are in the other blocks, just don't visualize them 
even though they are in the output file :-)


Cheers
 W.


--

Wolfgang Bangerth  email: bange...@colostate.edu
   www: http://www.math.colostate.edu/~bangerth/

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Re: [deal.II] Output multiple fields with different discretization

[Paras Kumar]

 

Hi Wolfgang,


Thank you for the quick response.


I am fine with writing the displacement and the crack phase-field in 
separate files, as long as the objective of visualizing the phase-field on 
the deformed mesh is achieved.


Listed below are two possible ways of doing this (along with the 
issues/queries regarding them).


1. Write the phase-field in a separate file using a MappingQEulerian type 
object based on the displacement with nSubdivisions equaling the polynomial 
degree for FE ansatz of phase-field. The problem with this approach is that 
the command


dataOutDisp.add_data_vector(solution.block(0),

dispNames,

dealii::DataOut::type_dof_data,

dataCompIntepretationDisp);

dataOutDisp.build_patches(qMapping, polyDegrees[0]);


results in the following error:


An error occurred in line <1069> of file 

 
in function

void dealii::DataOut_DoFData::add_data_vector_internal(const DoFHandlerType*, const 
VectorType&, const std::vector >&, 
dealii::DataOut_DoFData::DataVectorType, const 
std::vector&, 
bool) [with VectorType = dealii::Vector; DoFHandlerType = 
dealii::DoFHandler<2, 2>; int patch_dim = 2; int patch_space_dim = 2]

The violated condition was:

data_vector.size() == dof_handler->n_dofs()

Additional information:

The vector has size 132372 but the DoFHandler object says that there are 
198558 degrees of freedom and there are 65731 active cells. The size of 
your vector needs to be either equal to the number of degrees of freedom, 
or equal to the number of active cells.


A probable solution could be to create a new DOfHandler during each output 
call for both the displacement as well as the phase-field and attach the 
respective solution blocks to their DofHandlers. Not sure this would work 
since the mapping which would be used for the phase-field would be based on 
a different DoFHandler. Also, this would probably be computationally 
expensive (not sure?)


2. Another idea could be to write both of them in the same file as done in 
Step-44, but use nSubdividisions equaling either min or max of the 
polynomial degrees of the FE ansatz for the two variables. Since, I 
probably not yet fully understand the implication of the parameter 
nSubdivisions in the definition of build_patches() 
[https://www.dealii.org/9.0.0/doxygen/deal.II/classDataOut.html#a5eb51872b8736849bb7e8d2007fae086],
 
could you please explain what happens in the below example.


Let pDisp=2 and pPF=3 (it is known that pPF >= pDisp always) be the 
polynomial degrees used for the FE ansatz of displacement and phase-field 
respectively. 


a) What information would we loose for phase-field, if nSubDivisions=pDisp, 
since, there are 16 values available per cell, and we only visualize 9 in 
PARAVIEW? Are the non-vertex values used for interpolation of the 
phase-field on the 4 sub-cells or are they completely neglected?


b) If we use nSubDivisions=pPF, then we would have the best “possible” 
visualization for the phase-field, but how would the values of the 
displacement field be interpolated for the 27 sub-cells since in reality 
only values for 9 points per cell are known. Could this lead to incorrect 
visualization of displacement?


Best regards,

Paras 


On Friday, August 7, 2020 at 8:15:06 PM UTC+2, Wolfgang Bangerth wrote:
>
> On 8/7/20 11:20 AM, Paras Kumar wrote: 
> > 
> > I have a query regarding writing the solution to a VTK file for 
> visualization 
> > with PARAVIEW.  If one wanted to do this via a mapping based on the 
> > displacement field, then one could simply follow the output_results() 
> function 
> > of step-44. 
> > My question is that, Is it possible to write to the same vtk file, 
> fields 
> > based on different MappingQEulerian 
> > <
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.dealii.org%2F9.0.0%2Fdoxygen%2Fdeal.II%2FclassMappingQEulerian.html=02%7C01%7CWolfgang.Bangerth%40colostate.edu%7Ccbd1a9a17b8540f0018708d83af62a7b%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C0%7C637324176247361942=0fDQN1511kXggwdxcB8jf%2FO05Wn8ghyd3QzReWpRrqc%3D=0>
>  
>
> > objects and with different values of n_subdivsions for the 
> > data_out.build_patches 
> > <
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.dealii.org%2F9.0.0%2Fdoxygen%2Fdeal.II%2FclassDataOut.html%23a5eb51872b8736849bb7e8d2007fae086=02%7C01%7CWolfgang.Bangerth%40colostate.edu%7Ccbd1a9a17b8540f0018708d83af62a7b%7Cafb58802ff7a4bb1ab21367ff2ecfc8b%7C0%7C0%7C637324176247371938=d1P5xlbOdyblD2C38dcCkBaFpm2sCqSI8HWRFvKNYtw%3D=0>()
>  
>
> > function? 
>
> Paras: 
> No, you can't. But there is nothing that prevents you from creating two 
> .vtu 
> files that contain different things, and visualizing the at the same time. 
> Both paraview and visit allow you to open several .vtu files at the same 
> time 
> and showing their contents in the same window. 
>
> Best 
>   W. 
>
>
> -- 
>  
> Wolfgang Bangerth  email:  

Re: [deal.II] Output multiple fields with different discretization

[Wolfgang Bangerth]

On 8/7/20 11:20 AM, Paras Kumar wrote:


I have a query regarding writing the solution to a VTK file for visualization 
with PARAVIEW.  If one wanted to do this via a mapping based on the 
displacement field, then one could simply follow the output_results() function 
of step-44.
My question is that, Is it possible to write to the same vtk file, fields 
based on different MappingQEulerian 
 
objects and with different values of n_subdivsions for the 
data_out.build_patches 
() 
function?


Paras:
No, you can't. But there is nothing that prevents you from creating two .vtu 
files that contain different things, and visualizing the at the same time. 
Both paraview and visit allow you to open several .vtu files at the same time 
and showing their contents in the same window.


Best
 W.


--

Wolfgang Bangerth  email: bange...@colostate.edu
   www: http://www.math.colostate.edu/~bangerth/

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[deal.II] Output multiple fields with different discretization

[Paras Kumar]

Dear Deal.II Community,

I am trying to model the phase-field fracture problem, which, essentially 
is a multi field problem involving a vector valued displacement field 
coupled with a scalar crack phase-field. Both the variables are 
approximated using FE_Q type ansatz but the polynomial degree could be 
different.

I have a query regarding writing the solution to a VTK file for 
visualization with PARAVIEW.  If one wanted to do this via a mapping based 
on the displacement field, then one could simply follow the 
output_results() function of step-44.
My question is that, Is it possible to write to the same vtk file, fields 
based on different MappingQEulerian 
 
objects and with different values of n_subdivsions for the data_out.
build_patches 
()
 
function?


Best regards,
Paras 

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