[Paraview] How to find the nearest quad element?

[Marco Nawijn]

What about the following:

Generate two additional datasets, one containing (an approximate of) the
center of the hex elements, the second the center of the quads. Then create
a vtkKdTreePointLocator object based on the center points of the quad
elements. Than loop over the centers of the hex elements and use one of the
Find* methods to get the closest quad.

Marco




On Fri, Aug 21, 2015 at 2:21 PM, Dennis Conklin <dennis_conklin at goodyear.com
> wrote:

> Sam,
>
> Thanks for responding.  You have helped me several times in the past and I
> am always grateful for your insights.  In this case there is considerable
> refinement in the model, so only a very small portion of the hex elements
> are in immediate contact with quads.   Also you could think of places like
> the tread in the tire where there is no reinforcement whatsoever.
>
> Another approach which I have considered is a wave propagation technique,
> where in the first wave every hex immediately adjacent to a quad gets
> direction cosines assigned (as you suggest).   Then you loop thru the
> remaining elements and assign cosines from any adjacent quad or hex that
> has cosines.   Eventually the direction cosines will propagate throughout
> the model.   A major complication is that wavefronts will collide and then
> you will have to choose which of several conflicting neighbor cosines to
> adopt.  Averaging is one approach but certain structures give adjoining
> cosines which are 180 degrees reversed, so averaging would give you an
> indeterminate direction.
>
> I am toying now with some pseudo-variables, such as combinations of radius
> and lateral location, combined with zoning, to try to find a quantity that
> is unique for a local section of the geometry, to reduce the  search size
> for each hex element.
>
> I am still hoping for a very clever scheme which someone may suggest
> before I proceed with these much more brute force methods.
>
> Dennis
>
>
>
> *Sam Key Wrote:*
>
> *Dennis, *
>
> *Assuming for the moment that each quad 4-tuple is a finite element that
> contains one or more tire reinforcement items, and that each quad 4-tuple
> is "sandwiched" in between two hex 8-node finite elements, then the quad's
> 4-tuple is also a surface facet of two different 8-node hexahedrons. Both
> hexhedrons are the 'closest' hexhedrons to the quad. Given the usual
> organization of 'element blocks' in the Exodus-II datum structures, the two
> closest hexahedrons will be located on the surface of their respective
> element blocks. *
>
> *Using material ID's which are also element block ID's, have the software
> generate surface side-sets for each of these two element blocks specified
> with these two material ID's. With luck, each member in the side-set will
> be specified as a 2-tuple, (Elem# in the block, Quad-Face# in the hexah) *
>
> *With his info, you can confine your search to finding the side-set item
> that has a 4-tuple that matches your quad's 4-tuple. The search is reduced
> to a relatively small collection of hexahedral surface 4-tuple faces.  *
>
> *Hope this helps. *
>
> *Samuel W Key FMA Development, LLC 1005 39th Ave NE Great Falls, Montana
> 59404 USA *
>
>
>
>
>
> *From:* Dennis Conklin
> *Sent:* Thursday, August 20, 2015 3:52 PM
> *To:* Paraview (paraview at paraview.org)
> *Subject:* How to find the nearest quad element?
>
>
>
> All,
>
>
>
> I have an Exodus, multi-block model.  Most of the blocks are hex elements,
> and some are layers of quads (tires are composite structures).  I would
> like to establish local strains which are oriented in the direction of the
> nearest quad layer.  To do this I need to identify, for each hex in the
> model, which quad element in the model is closest to the hex.    Then I can
> extract directions from the quad element and rotate the strain tensor in
> the hex to these local coordinates.
>
>
>
> My question is,  is there some clever and efficient way to quickly
> determine the nearest quad for each hex in the model.  Keep in mind that
> there are multiple blocks of quads, but if there is some way to address the
> quad blocks one at a time, I could make this work.
>
>
>
> The brute force way is:
>
> Loop over every hex in the model:
>
>       Loop over every quad in the model:
>
>              Calculate the distance between hex and quad
>
>              Smallest distance wins!
>
>
>
> That is a pretty brutally inefficient calc (several million hex elements)
> that I am trying to avoid – any ideas about how best to approach this.
> I’m hoping for some elegant way to use connectivity or something of that
> sort.
>
>
>
> Thanks for looking
>
>
>
> Dennis
>
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