[Radiance-general] modelling perforated materials

[Germán Molina Larrain]

What I have done a few times is to mix a metal or plastic material with
Void. (in this case, 40% void). That passed the few simple tests I made, at
least... but maybe what Greg suggests is more accurate.


2015-07-22 2:44 GMT-03:00 Greg Ward <gregoryjward at gmail.com>:

> OK, this helps.  What you probably want to do is compute the average
> behavior as a BSDF, which requires explicitly modeling a small section of
> the material.  You can do this using antimatter to get the holes perfectly
> cylindrical.  Start with a slab from genbox as you suggested, then use
> antimatter like so:
>
> void metal aluminum
> 0
> 0
> 5 0.7 0.7 0.7 0.9 0.02
>
> !genbox aluminum slab 140 140 4 | xform -t 0 0 -4.01
>
> void antimatter hole_mat
> 1 aluminum
> 0
> 0
>
> !xform -n even -t 10 10 0 -a 10 -t 12 0 0 -a 6 -t 0 20.78461 0 cylinder.rad
>
> !xform -n odd -t 16 20.392305 0 -a 10 -t 12 0 0 -a 6 -t 0 20.78461 0
> cylinder.rad
>
> ------------
>
> The file "cylinder.rad" contains:
>
> hole_mat ring cyl.top
> 0
> 0
> 8
> 0 0 0
> 0 0 1
> 0 4
>
> hole_mat cylinder cyl
> 0
> 0
> 7
> 0 0 0
> 0 0 -4.02
> 4
>
> hole_mat ring cyl.bot
> 0
> 0
> 8
> 0 0 -4.02
> 0 0 -1
> 0 4
>
> -----------
>
> You then need to run genBSDF on the whole thing, keeping your sampling
> region within the appropriate zone:
>
> genBSDF -t4 5 +geom millimeter +f +b -dim 10 70 10 72.35383 -4.02 0
> perf.rad > perf.xml
>
> This creates a tensor tree, which is probably better for this material.
> If you need a Klems matrix, just leave off the "-t4 5" setting.
>
> To apply the resulting XML file in a model, you can put this in your
> rendering file:
>
> void BSDF perf_mat
> 6 0 perf.xml 0 1 0 .
> 0
> 0
>
> perf_mat polygon perf_shelf
> 0
> 0
> 12
> {coordinates in horizontal plane with normal aligned with Z}
>
> -----
>
> I hope this works for you.  If you need the shelf to have a different
> alignment, just change the "up" orientation for the BSDF (set to XYZ == 0 1
> 0 in the above example).
>
> Best,
> -Greg
>
> *From: *John Ford <john at relume.com.au>
>
> *Subject: *Re: [Radiance-general] modelling perforated materials
>
> *Date: *July 21, 2015 9:23:04 PM PDT
>
>
>   Greg,
>
> The spec at the moment is 4mm thick aluminium with 8mm diameter holes at
> 12mm pitch in a hexagonal pattern. The open area is 40%. The viewing
> position is at a distance, so correct average behaviour might work, however
> I am relying on the inside surface of the holes to reflect light to the
> viewer, so I’m not sure how using a trans material or suchlike would work
> in this case. The plan was to render one panel to show effect of being
> internally when veiwed from below on ground level.
>
> Thanks,
> John.
>
> (may be duplicated- replied from wrong address)
>
>
> On 22 Jul 2015, at 1:51 pm, Greg Ward <gregoryjward at gmail.com> wrote:
>
> Hi John,
>
> How big are the holes relative to the thickness of the material?  What
> percentage of "holiness" does the surface possess, on average?  Are the
> wholes aligned in a grid or a hexagonal pattern?  Are you going to be in a
> rendering position where you actually see the holes, or do you just want
> the correct average behavior with a minimum of noise?
>
> Cheers,
> -Greg
>
> From: John Ford <john at relume.com.au>
> Subject: [Radiance-general] modelling perforated materials
> Date: July 21, 2015 8:35:44 PM PDT
>
> Hi,
>
> I’m trying to find the best way to model a perforated aluminium panel and
> struggling with antimatter materials and such like. Could someone please
> advise how to do this without ending up with a massive number of surfaces?
> I haven’t found many examples of how to use the antimatter material apart
> from the glass lotus in Rendering with Radiance.
>
> My initial assumption was that the panel should be made with genbox then
> an array of antimatter holes should be added using cylinders of antimatter
> material, slightly longer than the thickness of the panel. Would it also be
> possible to genbox the panel then insert tubes into it or would the face of
> the panel still be present?
>
> Thanks,
>
> John Ford.
>
>
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