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This has nothing to do with rendering. I am designing a solar oven and would like to see how the "sunlight", meaning rays falling straight down into the oven, bounces off the parabolic walls of the solar oven and into the oven itself. What I'm imagining something that would look like this:

enter image description here

Pictured is the solar oven (the actual "hotbox" being the bottom part, while the top is the parabola that will concentrate the sunlight)

Is there perhaps an addon that makes this possible?

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  • $\begingroup$ Do you need to animate this or a static image only? Animation Nodes or Sverchock addons might be able to do this easily, though i don't have any experience with them. Not sure how to do it natively though, maybe particles with physics. $\endgroup$ – Duarte Farrajota Ramos Apr 9 '17 at 18:25
  • $\begingroup$ Light travels in straight lines. The angle of reflectance equals the angle of incidence. $\endgroup$ – Dontwalk Apr 9 '17 at 19:06
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I don't think you need any simulation or other visualization than this:

enter image description here

Every straight ray has to go through the focal point, which for a parabola is a single point. You can construct this point for any parabolic solar oven like this [pdf link].

Every ray coming through this focal point will also leave straight up after hitting the opposite side (if the parabola is big enough). The food (or anything else) is supposed to be placed directly at the place of the focal point.

The design with the bottom parabola part under the focal point replaced with (usually) black box is not very efficient if you are trying to heat directly from rays. Usually such design is meant to heat up the whole box, and the food off of this box.

For direct ray focusing a double parabola design with shared focal point will focus the rays much more efficiently:

enter image description here

The pattern of the rays coming through is of doughnut shape, so it is best to place the food in a small circle. You are also able to further focus these rays into a single point with some lens.

If you really need to plot lot of rays, I suggest using CAD software for this (like freeCAD, etc..), where you are able to easily create geometric entities and constrain them to each other.

You can do the same inside Blender with* Constraints* on bones or empties, but it is much more work to setup. The geometry math is very easy though.

You can also preview the caustic pattern of any curved mirrors, but Cycles is not very efficient for this task. Any bi-directional path-tracing renderer is a better choice.

To make cardboard parabolas with Blender you need the Export: Paper Model plugin. You can create parabola meshes with the bundled Add Extra Objects plugin. There are multiple ways to make parabolas, but I like this one:

enter image description here

  • it is an icosphere mesh Shrink Wrapped to parabolic mesh
  • it can be disassembled into 5 stackable pieces for easy storage
  • I marked 1 possibility of gluing flaps placement on one of the pieces, but the Paper Model plugin can figure this out itself. If the cardboard is thick enough, I believe there is no need for flaps, just cuts to be glued together.
  • it can be sprayed with reflective paint (Mirror Spray Paint cca $5), imho much better choice than gluing aluminium to paper

A popular idea is also to use an umbrella..

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  • $\begingroup$ Yes, I am aware of the parabola focal point. In fact I designed the oven after I plotted the parabola in another program. My oven is square in shape, not circular like a satellite dish. The reason I asked the question was because I was wondering what path the light rays at the corners would take. I appreciate the advice, though! My oven is designed at a very hobby-level, as I plan to build it myself with cardboard and tin foil. It was also intended to be a solar oven (with the black box) rather than a solar cooker, as I do want to heat the whole box evenly. $\endgroup$ – Espen Sales Apr 9 '17 at 20:48
  • $\begingroup$ I believe the square shape also eliminates the possibility of a double-parabola solution. $\endgroup$ – Espen Sales Apr 9 '17 at 20:51
  • $\begingroup$ @EspenSales It will be hard to focus the light into the box evenly - I believe most will hit the top of the sides of the box. If the parabola is of square cross section, the focused pattern will be a cross-like shape (at focal point, then blurred). You can render the caustics how they will turn out in Cycles, but it won't give you the rays themselves. In CAD you could do the rays on 3D surfaces. $\endgroup$ – Jaroslav Jerryno Novotny Apr 9 '17 at 21:37

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