Can you model real physics? Parabolic dishes and their focused light?

If a parabolic dish and a “compound” parabolic dish can be rendered in blender, and a light “shone” on them from different directions to light up a cooking vessel, that would be SO useful! It could demonstrate the differences and the advantages of compound parabolic dishes all at once.
A parabolic dish only concentrates the light properly when it is pointing directly at the sun. At other times it does not concentrate well.
A compound parabolic dish is an attempt to correct this problem.
I have made several contrbutions to solar cooker research. (only because companys and “real” science is not interested).
The mechanical mathematician, some trackers (low tech) and a “compound” parabolic reflective dish for concentrating the sunlight on a cooking vessel. (Also I have contributed really low tech methods for making that compound parabolic dish). The best solar cookers are parabolic dishes but there are problems. The point of light they produce is dangerous and aparently there is also a secondary focus possible if the light shines on them from an angle.
A parabolic dish must be moved often (every 15 to 20 minutes) as the sun moves. A compound parabolic dish, on the other hand, is designed to concentrate the light on a different part of the cooking vessel as the sun moves. So 1,2 or 3 hours without moving the dish is possible! The overall aim is to to help people in poor countries to cook without burning all their forests. I am incompitent with software, and I could not do the blender stuff myself. Anyone want to try it and put it as a response to one of my videos or as a response to a popular parabolic dish video?
(People are stuck on the idea of parabolic dishes even though they are dangerous). The compound parabolic dish does not produce a point of light but rather an area where the light shines. The area of light is closer to the dish itself so that keeps it safer too.
Much of my stuff has been accepted at solarcooking dot org so if your blender demo was reasonably good, I am pretty sure they would put it on there. (Its the main solar cooking site in the world).
http://www.youtube.com/user/gaiatechnician is my videos for more information.
You can also find information on compound parabolic dishes on instructables dot com and elsewhere.
Brian White BC Canada

I don’t think Blender can do that type of rendering, although there have been many improvements to it’s raytracer recently. You would probably want to model the stove in blender and export it to render in indigo or yafray. Look on the wiki (wiki.blender.org) for more info.

Yafaray can do this. So model in Blender and export i YAFARAY and enjoy!

caustics will allow you to see where focused beams of light hit a surface:

http://www.geomerics.com/screenshots/thumbs/nice-caustic.jpg

there’s a patch for blender for ‘faked’ caustics, not sure if it’d support physically accurate effects like a parabola. if you want to visualise the beam in space however, you need volume caustics:

http://features.cgsociety.org/stories/2003_10/Rendering%202/volume_caustic.jpg

mentalray supports this, haven’t been able to find evidence if indigo or yafray do too.

mentalray supports this, haven’t been able to find evidence if indigo or yafray do too.

You can do it in indigo, put the whole scene inside an object with a low scattering coefficient. There is an example that comes with indigo :slight_smile:

For something with really complex caustics, I’d advise something like indigo/luxrender, because you’ll be able to see the result very quickly (though high quality results will take some time) and be able to correct for errors without having to wait for photon map calculations.

But how do you draw a mathemtically accurate parabola in Blender? I’ve often wanted a script that could produce mathematically accurate 2D curves and dump them in my scene, either as a mesh with a selected number of vertices, or as Beziers. Unfortunately I don’t have the scripting skills to do the job myself.

I’d like to be able to add:

a) A sine wave.
b) A parabola
c) A cosh curve (a.k.a. catenary, or the shape of a naturally hanging rope)

There’s probably lots of other curve types that could be included by a mathematically gifted scripter (that excludes me on all counts! :o).

Volumetric caustics in Indigo:

http://www.indigorenderer.com/joomla/forum/files/im1189492285_527.png

many of the curves you talked about exist already in the list of script on wkli

like paraboloid 3D from which you can loop select and get a parabola

mind you i would like to see a GUI which allow to select from a menu different curves

but i’m having problem to find one

i already done may script to do different type of curves and wish to put all of them inside one script to allow selections and execution with a menu like the scritp for spirals

but this script use and old technic of global variables which may not be the best way to do it nowaday

so i you see a script with menu please Pm me and i’ll prepare a new scipt for all kind of curves - mind you i may need 6 months to complete it but i’ll work on it

Salutations

For a script to model parametric surfaces (i.e. surfaces where the co-ordinates x, y and z are expressed as functions of independent parameters), see an old post of mine here.

Coincidentally, the reason I originally posted that was because I was looking for a way to make off-axis parabolic mirrors (where a parallel beam comes in and is reflected to a focal point at an angle to the original direction of the beam). I did in fact make some Indigo renders of light focusing from a such a parabolic mirror in a smoke-filled environment. But that was a while ago, and I can’t seem to find them now.

Hi, thanks for all your answers. I just re found the thread a while ago. In September 2008 I made my first “compound” parabolic reflective dish. This one (as far as I know) reflects all the light to an area between the focal point and the bottom of the dish. It is more useful for solar cooking because the light stays on this area for a long time. (up to 3 hours in the dish I made). I tested it and it gave results comparable to a commercially produced sk14 parabolic solar cooker in India!
But I guesstimated a lot of the reflections. I do not really “know” anything
Anyone want to model it with the sun crossing the sky for 2 or 3 hours and put the model or video on utube? If your model compared it to a similar parabolic dish that would be super!
Anyone able to do it?
I have more info at http://www.youtube.com/user/gaiatechnician
and at
http://www.instructables.com/id/Compound_parabolic_dish_making_a_template_with_te/
Do not worry about getting stuff perfect for this project.
If I had waited to get my “compound” parabolic dish perfect, it would never have been done!
Thanks for any attempts that you make, I certainly cannot do it.
Brian White.

Is yafaray and yafray the same thing? My verson of blender has yafray as an option to render built in.
I have fired up blender recently and I have no clue what I am doing. Has anyone a link to where and how I can get one of those parabolic dish surfaces mentioned in the thread? Readymade to download into my blender as an object? Thanks for the help
Brian

Yafaray is the newer version of Yafray. Yafray has basic support in Blender that has broken in the last few releases. If you want to use Yafaray go download it from their site and it will tell you how to install and use it with Blender.

As for the parabolic dish: thay ought to be extremenly easy to model unless I’m missing something.