[Radiance-general] modelling perforated materials

[Greg Ward]

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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