optimal foam size rule of thumb?

[olika]

after years of simming, i still can find myself way too often,
wondering what a optimal foam size for a spezific scene would be.

I'm aware about the change i general from a small to a large scene.
But in detail i'm often wondering how it affects the end result etc.
I would love to know how you guys set it up.

Is there a rule of thumb i didn't found yet.
I.e. should it be a pixel in size or something?

Looking forward to your answers!

[Svetlin.Nikolov]

Hey, what I usually do is to imagine a bubble of the specific size in question and how it would look next to my sim. In your case, you have a bubble that is (on average, since you might also have variation), 0.006m -> 0.6cm. When I pick a size that sounds legit to me, I run the sim and of course if I find out that the bubbles are too small and I need to raise their number to millions of millions, then I raise their size instead so I don't simulate until I'm old.

Cheers!

[olika]

Hi Svetlin,
thx for the reply!

It is kind of confirming what i'm doing, isn't it
Realized i didn't mention that i'm using it for point foam later on.
How does it apply to that.
I.e. boat sim, foam is in point mode, how to find out if it's too small or large?

Found this in the tuts, and maybe it's somehow demonstrating the effect i'm wondering about.
Does the size parameter also influence how dense the foam gets,
i mean not spreading so much into separate particles?

You know what i mean?
Long story short, sometimes i wonder how to keep those separate foam particles more together to avoid the single foamis being so prominent

[Svetlin.Nikolov]

I see, so if you are rendering in Point mode, a lot of the cases where the size matters are not important anymore as Points are just a pixel wide on the screen by default. I.e. Point mode rendering is good if the foam amount is so high and the camera is so far away, that most foam particles would render smaller than a pixel if you used Bubbles mode.

The foam size is taken into account when you use the Foam Volume option, so bubbles would be able to calculate collisions. It also affects how quickly foam rises or falls down when there is flying foam or underwater foam in the scene. Also the Half Life "Vary" checkbox cares about the foam size. And this is pretty much it - if you are doing an ocean sim, the chances are that the foam size might not even be used in the actual simulation. If your foam is floating on the water surface, then the size doesn't play a role in how it would spread or bunch up together, unless you enable Foam Volume.

Cheers!

[olika]

cool, thx for the explanation Svetlin!
I think i understand what you mean although the last sentence made me wonder.

Let's say there's a splash hitting the surface and turns into foam.
What does influence how the foam particle behave then. (spread or bunch up)

(i wonder what are the forces responsible for moving the foam around)
Pattern strengh i guess, to move it into the patterns
The velocity is a factor too i guess, for how much it spreads, also in combination with droplet surfing.
etc.
and size is not such a factor?

I was assuming, i.e. particles spread away from each other instead of bunch up together(in the sim, not the render!) because size is propably to large.

Like bubble/foam size would be, lets say a 1cm.
So center to center distance of the particles is a 1cm,
bubbles will be aligned shell to shell. But foam points will be a cm away from each other.
Does that make sense? Or is just more B2B value needed to bunch it more up?

[Svetlin.Nikolov]

Oh, Droplet Surfing does not affect Foam, it's only working for Liquid and Splash.

If all your Foam options are turned off, then the foam outside the liquid voxels should stay still, and the foam inside them would just move with the speed of the liquid voxel.

Then, if you turn on the Rising and Falling Speed, the foam in the air should start falling down (larger bubbles would fall faster), and the foam inside the liquid would not only follow the liquid speed, but would also start rising up (again, larger bubbles would rise faster).

And then the more exotic options like Foam Volume and Foam Patterns would start pilling foam particles together or apart. BUT, if you don't have Foam Volume enabled, then two colliding foam bubbles would actually simply pass through one another - their size won't matter.