Ink in Water

[ben_hamburg]

Ok, after some more testing I´m afraid I´ll have to cheat around the tearing object. I just rendered a small preview and the smoke just goes crazy, looks like very strong turbulence or wind, but there is non included in the sim.
I had a phoenix turbulence object in the scene, but I got rid of it.
So my guess ist that the cloth sim has too much influence on the smoke sim, that the verts move to fast from frame to frame or something like that and the sim goes crazy. I´ll try and make a snapshot of the finished tear and use that as a collision object for the smoke. Might not be 100% accurate this way, but the weird behaviour is most definitely linked to the cloth object.
I could still try and lower the objects velocity in the phoenix properties or increase the step size (its currently at 3), but I guess this is just how I´ll have to deal with it.

[Svetlin.Nikolov]

Hey,

Sorry to redirect you, but you should check the help site for some of those https://docs.chaosgroup.com/display/P220N

You should note that the smoke will render denser or thinner depending on the scene scale - it's quite similar to the fog color of the VRayMtl - we have to add a setting with which you can turn this on and off, because it could happen so that at low scale you can't make the smoke thick, and at high scale you can't make it more opaque...

In order to make the smoke pump out quick and the stop quickly, it really sounds like a good idea to use high discharge for a single frame and then animate the time scale. Do you have a video of how it looks?

Cheers!

[ben_hamburg]

No problem, manuals are my friend...

The explanations just don´t go deep enough sometimes, I guess its something you just have to learn from experimenting sometimes.
But mostly I don´t get the scale/time/gravity options.
I do a lot of medical animations with microscopic environments, so real world scale just isn´t an option. I read the according info in the manual, but I´m still confused:

I looked at the nuke example and there you have a scale of 1 Unit=3 meters. The emitter object therefore has a real world radius of around 40meters.

So now I´m working in a scene with a unit scale of 1 unit=1 meter and my emitter object is something like 0.1m in radius.
What happens now, if I change the scene scale? lets say I scale it up to 400 -does the sim now consider my emitter object to be as big as the one in the nuke scene? I think the confusion comes from the way its described in the manual as "You can use this multiplier if you need to adjust your simulation's behavior separately from the scale of the other objects in the scene."

And whats the difference in scaling up the gravity multiplier?

And one more question:
How does the new plain force work? Does it work like a wind force in the way, that it just "blows" in the direction of the logos arrow? And is the damping option similar to the wind forces decay?

The problem with simulations is always, that you got more time to ask questions than to actually answer them...

[Svetlin.Nikolov]

Ah, I sent you to the docs just to check on the rendering questions - the sim part is kinda outdated for the smoke/fire part and is heavily outdated for the liquids - we will publish the new help site together with the release of Phoenix 3.0 soon.

The Scene Scale will make Phoenix think the container is bigger in world units than it actually is, so 400 should equalize the emitter with the nuke scene. The simulation will act accordingly for all scale-dependent parameters - reducing the effect of gravity, but not only.

The plain force adds velocity in the direction of the icon, yes - you can also enable applying the force behind the icon. It has damping in order to balance and counteract the effect of repeatedly adding velocity by the force, so the force and the drag will reach equilibrium at a certain speed. The Max Distance would be the equivalent of the Wind's decay.

Cheers!

[Svetlin.Nikolov]

I missed what you posted about the cloth object - it's very likely that it would cause issues if it's not a closed geometry - Phoenix generally doesn't support anything that has no volume, except for the 3ds max Plane just because it's a standard primitive. If you can shell it somehow, this would do the trick.

[ben_hamburg]

Yeah, I already gave the cloth object some volume by adding a shell modifier, that isn´t the issue here. I really think its about the speed the vertices have. Like I said: I could probably do some more tests with higher SPF, but unfortunately I ran out of time again and I gotta wrap it up. I ended up going the Fake-way and used a snapshot of the cloth object in its torn state as collision dummy. I´m missing a bit of dynamics now (I couldn´t get the plain force to work like I wanted to) and I´m still missing detail, as you can see:

https://vimeo.com/acolori/review/180002480/70fd8cd8bf

Here are my settings:



Vorticity is at 0.1, so maybe upping that might give me that extra level of detail. Or my scale is still off and I need to adjust that, OR I need to increase my grid resolution...

[ben_hamburg]

And I´m also not using any buoyancy, I don´t really want the smoke to rise up, but rather sink down (towards the camera), not sure how that influences the look of the sim...

[ben_hamburg]

Hm, I´m also not sure about my opacity curves now. I just switched to simple smoke with smoke factor at 1.0 and it looks much more massive now...I´ll play around some more with the render settings.
I also just read about the displacement option in the manual. I only used this for liquid sims before, I didn´t know, that it was possible to use it for smoke and fire aswell, the added detail looks great in the examples!
I couldn´t figure out how to make it work though, I used the Phoenix tex map, used the velocity of the sim, then plugged the map into a composite map and multiplied it with a noise map and used the composite map in the displacement slot, but the result looked in no way different.
Do I need to consider anything else here?

[ben_hamburg]

Ok, I didn´t check the velocity channel in the Output settings of the sim, thats probably why I don´t get any results with the displacement...

[Svetlin.Nikolov]

Hey,

Sorry for the late reply! In the video the velocity acts like the discharge still continues after the first frame.. If you like, you may drop the scene to Support and we'll have a look.

Cheers!

[ben_hamburg]

No problem, I finished the project already and am quite happy with the final look (see attached file).



The discharge isn´t actually stopping after one frame, I just dropped it from 20 down to 2, so thats why it looks like its still emitting...
The smoke could have looked even denser, but that was probably just the render settings and maybe I could have simmed with even more grid cells and increased the vorticity a little further. Also I´d still have liked the smoke to slow down even more after the first burst. Wasn´t there a setting like "air restistance" in a previous build or am I imagining things? Because increasing that value would probably be the closest thing to simulating an underwater environment. Or would it actually be possible to simulate smoke in a liquid container?

I also realized at some point, that I already had made the exact same setup in a previous project, I was even happier with the result back then, so I´m gonna take a look at those settings again...(see other attached file).

[Svetlin.Nikolov]

Sweet! Very organic looking

There wasn't an air resistance, but maybe we need to add a similar option. I was just experimenting with ways to increase the inertia of rolling smoke, so this might be a single control that goes both ways...

Cheers!

[Ivaylo Katev]

the air resistance is directly controllable by the smoke temperature when uniform density is disabled.
cold and hot smoke produce very different result, the hot smoke expires bigger air resistance than the cold one

[Svetlin.Nikolov]

This would be a very indirect way to approach it and won't work in all cases though.

[ben_hamburg]

Thanks, I´ll give it a try next time! Uniform density was always enabled I think, so I guess the smoke temperature didn´t do anything. Its always hard to get dynamics right, when your don´t know much about physics...
But I have to say it once again: I just love how versatile Phoenix is! I´m constantly trying new ways to squeeze phoenix into our projects and from the feedback we´re getting I know that our clients love it...