[Paraview] Gauss points

Thu Dec 5 15:19:05 EST 2013

Hi Burrlen,

Thank you for your help

Marios

On Wed, Dec 4, 2013 at 10:50 AM, Burlen Loring <bloring at lbl.gov> wrote:

>  Hi Marios,
>
>          If I apply the InterpolatetoQuadraturePoints filter as shown in
> Figure 2 the output result is
> basically empty.
>
> If you write the data arrays containing the scalar values at the Gauss
> points to the file then you do not want to apply the "interpolate to qp"
> filter. This filter's purpose is to generate these array from nodal values.
> This means that you have to have the nodal values. You mentioned that
> you've removed them so that you won't get confused, and that will prevent
> this filter from working.
>
> If I apply the GenerateQuadraturePoints filter as shown in Figure 3 the
> field data
> transformed to point data. Hence after the application of the
> GenerateQuadraturePoints the previous 9
> point data and 4 cell data are not exist anymore but together with the
> field data they transformed to 16
> point data representing the 16 Gauss points. Those 16 points have the
> correct coordinates and T values.
>
> yes, that's what should happen. You're visualizing a different geometry -
> the Gguass points - so data arrays on the original geometry will not be
> available.
>
>
>          I tried to reproduce the same example using the GID software and
> the results are shown in
> Figure 4. Can I do something similar with Paraview? I want to have these
> contour lines instead of just
> point’s information. I want to continue use Paraview because has some
> really powerful features that I
> like and I am sure this is trivial but I cannot find some way to do it.
>
> you can't generate the contours on a point set, you first need to mesh it.
> One way to do this would be to apply "delaunay 2d" to the point set. Other
> approaches would be more efficient and produce better results but would
> require you to write some code. eg. write out the mesh on the Gauss points
> directly from your simulation.
>
>
> On 12/04/2013 10:30 AM, Marios Mavros wrote:
>
> Hi Burlen,
>
>  Thank you for your help and for your example that you have provided. I
> followed your instructions and I prepare a small pdf explaining what I did
> and what I expected as a final result. I thought that this procedure was
> the solution to my problem but maybe I have to do something extra or
> something different. Attached you will find also the file that I used.
>
>  Thank you again for your help
>
>  Marios
>
>
> On Tue, Dec 3, 2013 at 2:46 AM, Burlen Loring <bloring at lbl.gov> wrote:
>
>>
>> 1. What the numbers 0 4 8 12 (line 24) represent?
>>
>>  This is the offset array used by VTK for random access into data on the
>> quadrature points data. To generate it you go cell by cell and accumulate
>> the number of quadrature points used by each cell. The next cell's data
>> offset is the sum of the previous cell's number of quadrature points.
>>
>> note that the documentation says that each array has a quadrature scheme
>> dictionary, but this changed. the dictionaries are stored in the offeset
>> array. we did this so that you only need to define one quadrature scheme
>> dictionary for many arrays.
>>
>>
>> 2. What the QuadratureWeights are all zero (line 37)?
>>
>>  Those aren't currently used in VTK but we have a place holder for them
>> in case they are needed in user developed custom filters or later in VTK.
>>
>>
>> 3. In your example there are 4 cells with 4 Gauss points in each cell. In
>> total 16 Gauss points. If I want to assign to each Gauss point one value of
>> stress or strain how I have to write those 16 values in xml format.
>>
>>  in my example you would read this file into PV and apply  "interpolate
>> to quadrature points" and then "generate quadrature points".
>>
>> You're asking about writing the data on the Gauss points into the file.
>> You have to store them in VTK FieldData and add an information key to each
>> array that names the offset array. You have to order them correctly
>> according to the offsets array and quadrature scheme. for example the pdf I
>> sent before shows how each cell's quadrature points are ordered for one
>> scheme. you won't write the points themselves, just the data values.
>>
>> the T FieldData array in the following file is an example of containing
>> scalar values at quadrature points (watch out there's also a PointData
>> array named T that stores the nodal values),
>> http://www.hpcvis.com/vis/images/vtk-quadrature-points-example/quadrature-points-example-2.vtu
>>
>> after reading such a file into PV, you could see the arrays in the
>> spreadsheet view but to see them in the 2d/3d view you'll need to apply the
>> "generate quadrature points" filter to produce the point set and transfer
>> the data onto it.
>>
>>
>> On 12/01/2013 10:26 PM, Marios Mavros wrote:
>>
>> Hi Burlen,
>>
>>  Your example was really helpful to understand many thing about the xml
>> format and I want to thank you about that, but I still have some questions.
>>
>>  1. What the numbers 0 4 8 12 (line 24) represent?
>> 2. What the QuadratureWeights are all zero (line 37)?
>> 3. In your example there are 4 cells with 4 Gauss points in each cell. In
>> total 16 Gauss points. If I want to assign to each Gauss point one value of
>> stress or strain how I have to write those 16 values in xml format. Can you
>> please sent me an example with this information?
>>
>>  Thank you very much
>>
>>  Marios
>>
>>
>> On Sat, Nov 30, 2013 at 4:28 PM, Burlen Loring <bloring at lbl.gov> wrote:
>>
>>>  Hi Mario,
>>>
>>> sending again to the list. the weights have 2 dimensions i (node id) and
>>> j (Gauss point id), so to generate ShapeFunctionWeights for a new
>>> QuadratureSchemeDefinition  what you do is evaluate each shape function at
>>> each Gauss point. For the linear quadrilateral you'll end up with 16
>>> weights. For example see the example
>>>
>>>
>>> http://www.hpcvis.com/vis/images/vtk-quadrature-points-example/vtk-quadrature-points-example.pdf
>>>
>>> http://www.hpcvis.com/vis/images/vtk-quadrature-points-example/quadrature-points-example.vtu
>>>
>>> Burlen
>>>
>>>
>>> On 11/29/2013 3:34 PM, Marios Mavros wrote:
>>>
>>> Hi Burlen,
>>>
>>>  I want to thank you for the information that you send me. I read the
>>> paper and I try to made a simple example in xml format for a 4 node
>>> quadrilateral element but it didn't work for me. Attached you will find the
>>> element formulation that I used with the shape functions and a .vtu file
>>> with my example. If I want to give 4 stress values in the 4 Gauss points (
>>> lets say 0.1 0.2 0.4 -0.1) can you please write in the .vtu file the
>>> missing information in order to understand haw I have to write a correct
>>> file in xml format.
>>>
>>>  Thank you very much
>>>
>>>  Marios Mavros
>>>
>>>
>>> On Wed, Nov 27, 2013 at 2:56 PM, Burlen Loring <bloring at lbl.gov> wrote:
>>>
>>>>  You'll need to use an XML file format. There's some documentation in
>>>> the following link. It's slightly dated but should get you started.
>>>> http://www.vtk.org/Wiki/images/7/78/VTK-Quadrature-Point-Design-Doc.pdf
>>>> The ctest, VTK/Filters/General/Testing/Cxx/TestQuadraturePoints.cxx,
>>>> could be used as an example.
>>>>
>>>>
>>>> On 11/27/2013 02:32 PM, Marios Mavros wrote:
>>>>
>>>>  Hi
>>>>
>>>>  I have wrote a simple program in Fortran that transform the output of
>>>> a finite element software in vtk Legacy Format. I don't know how to handle
>>>> the Gauss points values. For example in my case my cells have 4 Gauss
>>>> points and I have 4 values (for example strain in x-direction) for each
>>>> cell. How I have to write the vtk file taking into account that each cell
>>>> has many Gauss points?
>>>>
>>>>  Thank you
>>>>
>>>>  Marios
>>>>
>>>>
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>>>>
>>>
>>>
>>
>>
>
>
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