Clouds

[brit_bunkley]

I am trying to make clouds move slowly across a landscape in a smooth, slow fashion with a surrealist
out of whack scale....using 3ds Max 2024 and Corona.

But using the final file "Animated_Clouds_max2020_final-bonus-step" downloaded from the tutorial https://docs.chaos.com/display/PHX4MAX/Animated+Clouds, extending the simulations to 400 frames and running it, gets a very jerky cloud formation animation https://mega.nz/file/chIDnDxa#6WvYjP...qwdOZMlpvdx8AM, a bit better slowed down to 10% https://mega.nz/file/E5pGTawY#EKAZZ5...nWb4TWp680pfzE. But how to I make a seamlessly smooth cloud moving across the road? ... I just saw this https://docs.chaos.com/display/PHX4M...onSetup-Clouds but there is not enough information

[zdravko_pavlov1]

Hello,

As I can see in the tutorial the "Animated_Clouds_max2020_final-bonus-step" explains how to set the clouds shader and back lighting. I followed the tutorial and started with the "Animated_Clouds_max2020_final". The bonus one might still work, but I didn't try it.
As I was following the tutorial I also recorded an explanation that I hope might make things a bit clearer - https://www.youtube.com/watch?v=faCcv13QrlM
It's a bit clumsy and I apologize in advance

Cheers

[brit_bunkley]

Thanks so much! It might still be a bit fast but it is smooth now. I tried rescaling time again and resimulating. It has been several days rendered and it looks good so far when using slow motion. I brought the rendered clip into Premiere and set it to 50% speed using the optical flow time interpolation.

[zdravko_pavlov1]

Yup. When you use the Playback Speed to slow down a simulation it is very similar to what Premiere does with footages. The Grid Blend -> Interpolation is basically a frame blending. Where if it is slowed down by half, every other frame will be a 50/50 mix of the one before and the one after. And if you switch the Grid Blend to Velocity, it is similar to what the Optical Flow in Premiere or AE is trying to do. And Optical Flow might also give you some "broken" frames if it misses some data or if you are trying to slow it down to extreme values like 15, 10 or 5 percent of the original speed. And that's why you need to go through this resimulation process. And indeed the new cache could be stretched once more and resimulated again.

[brit_bunkley]

Thank you. This was very helpful! I just received info from Chaos support on using dynamics They say: "Select your Phoenix simulation and go to the Dynamics rollout and then adjust the "Time Scale" value.
Using low values such as 0.01 will result in much slower movement (slow-motion effect) while increasing it will result in faster movement." It worked as well with no resimulations with few simulation files.

[zdravko_pavlov1]

Hello,
Glad that you sorted it out. Yes that's what the Time Scale is for. It also changes the behavior of the fluid, so you need to adjust the steps per frame accordingly. The Time Scale value can also be animated. You can start the sim in normal speed (1) and once the cloud is formed, then bring the time scale down.
Resimulations are used when you have a simulation and movement that you already like and just want to:
1. Amplify the resolution
2. Adjust the speed on already existing sim.

(Resimulation usually runs faster than the original sim.)

[brit_bunkley]

Thanks. This is very helpful. So to adjust the speed on an already existing sim one rescales the time and re-simulates using time-bending?

These cloud simulations seem to make a flat-bottomed cumulous. How would one make a rounder "cotton-ball" using these settings in the tutorial? It seems to work by changing the grid size to more of an even sided box. I'm looking to add some virtual clouds like the Dutch artist Smilde does non-virtually in real-time using a smoke machine https://www.floornature.com/design-t...-clouds-16912/

Also, you seem to be able to get a fast preview. I have to render overnight to see if they are at the right rate. How do you do that?

[zdravko_pavlov1]

Hello,

So to adjust the speed on an already existing sim one rescales the time and re-simulates using time-bending?

Yes this is pretty much the steps you need to take. Resimulation can be used to amplify the resolution as well. Here's the page that describes all of the settings and what you can do using it: https://docs.chaos.com/display/PHX4M...e+Resimulation

The cumulus clouds are usually flat at the bottom in real life, so that's the look Hammer was aiming for when creating the tutorial.
If you want another shape, you can make another geometry (a sphere for example) and use it as an emitter source. When you create a phoenix source, you can pick a geometry object (Phoenix also supports particle systems) as an emitter. The default emission mode is set to Surface Force. And by default, the polygon ID is set to 0. That means that fluid will be created out of all polygons (the entire object). You can of course change that and tell phoenix which polygons you want to be used by specifying the IDs.
The fluid created on the object's surface will be ejected along the surface normal with a given speed.

There is also a Volume Inject mode, that will fill the entire volume of an object with fluid. The object needs to be set to non-solid, so that the fluid can escape. Phoenix will ask you if you want to change the object from solid to non-solid for you, when you switch the modes.

In other words you can create a sphere. Create a phoenix source. Select the sphere as an emitter inside the Phoenix source. Change the sphere to non-solid or let Phoenix change it for you when you switch the emission mode to Volume Inject. The object will start filling up and the pressure will expand the fluid outwards. You can also disable the temperature emission and leave only the smoke. That way, the fluid won't start raising up. By default, the phoenix source creates temperature of 2000 Kelvins. The default temperature of the Phoenix container is 300 Kelvins which is roughly 27 degrees Celsius or ~80 deg. Fahrenheit (in other words it is a room temperature on a warm summer day). If the temperature of the fluid is below that value it will go down. And if it is above it will rise up (just like in real life). By unchecking the temperature emission from the source, you can make sure that the smoke will stay at 300 K and will spread evenly in every direction.

About the preview. You can enable the GPU preview inside the Preview rollout. You have to make sure that the detail reduction stays at 0, to see the full resolution. In case that your GPU can't handle it you can reduce the details a bit. This only affects what you see in the viewport, but it will always render in full res. MAX can make a preview of what you see in a viewport so you can use that to quickly visualize your animation and get sense of the general motion and speed without doing a render.

I'll allow myself to give you an advice if you don't mind of course. Forget about the tutorial and start in a clean scene. Work your way through the settings. In each rollout there is a question mark button on top that will open the documentation page where every parameter is explained.. If you are not sure what a given parameter does, you can always hop there and check. I do it all the time.

And of course you can always ask here for assistance.
I hope this was helpful.
Cheers.

[brit_bunkley]

I managed to make a rounder puffy cloud by importing the final tutorial cumulus cloud simulation. I then made a more or less even-sided smaller grid and then began a simulation - on the left below. The one on the right is the original cumulus cloud. So first I had to make a new simulation folder and move those simulation files to that folder while directing the input into that new folder in order to keep that older cloud animation intact (otherwise the new simulation would overwrite the older one). The Puffy Cloud new simulation (bottom left) then went into the original folder. I then could animate two separate and distinct clouds using the tutorial set-up with 2 slight modifications (dynamics at a speed of .1 and a different grid setup for both).

My eyes soemtimes gloss over at the immense amount of technical information on simulations. There must be at least 200 different variables in a Phoenix simulation of which 5-10 are crucial, so the easiest and most intuitive solution is best for me.

[brit_bunkley]

I am able to get a GPU image, but I guess that my GPU is not fast enough for an animation sample when scrolling the animation bar, so it is not possible to see the rate of movement before a long rendering (https://mega.nz/file/gtI2VQgI#EFxQ-z...zpIFNhCYA8v4rU). You used something called ty... to get a quick sample rendering?

[zdravko_pavlov1]

No, no. I don't know what your GPU is, but most likely you can't scrub through the timeline in real-time not because the GPU is slow, but because each cache file needs to be loaded from your hard drive. The cache files are quite big so this takes some time and playing back the animation in real-time is impossible. Most likely it's the HDD that is slowing things down and not the GPU. And If you have two simulators reading two separate cache sequences, most likely it will be twice as slow. It really depends on the size of the files that needs to be loaded for each frame.

You can always generate quick viewport previews without rendering the animation. Just go into the main menu - Tools - Preview - Grab Viewport - Create Preview Animation... Make sure the viewport you want to "grab" is selected.

Alternatively you can click on the + icon at the top of the viewport and in the drop down menu you can find the same function there as well.

There is a third-party particle system called TyFlow. It is installed in MAX as a plugin. It has a free version so maybe you can try it out. Besides the really robust and powerful particles, you also get a bunch of extra modifiers. Some of them are versions of modifiers that already exist in MAX, but you have improved functionality, performance and sometimes some extra features. They are quite handy so I prefer using it, but this has nothing to do with Phoenix. By installing TyFlow you also get something called TyPreview. It is the same function as the standard Preview in MAX that I described above, but with a slightly nicer interface and some extra features like versioning and so on. But nothing that you can't already do with the standard MAX standard preview.

Here is a link to the Autodesk page that explains the preview function:
https://help.autodesk.com/view/3DSMA...955B99B18FA

[brit_bunkley]

Thanks. That is very helpful! I did a simulation of those 2 clouds with a long render. Parts of the larger cloud to the right flickered (as if there was a lightning storm). I re-rendered with a lower noise level (below 3 plus the denoiser) and then again using append save to file UHD and there was only little difference https://mega.nz/file/NhhwTZYK#1-HZH-...GlyEAaR9b_-3j0. any suggestions? I managed to make it less noticeable with a mask in Premiere

[georgi.zhekov]

Can you show us your render settings? How about if you disable the Volume Light cache checkbox in the Smoke options for the Phoenix simulator?

[brit_bunkley]

Thanks, I'll turn off the volume Light cache (under simulation object > rendering >volumetric options > smoke colour) for my next rendering.

[brit_bunkley]

It seemed to be the same in the new rendering.https://mega.nz/file/Iw4GHTCQ#RFzrN4...Wqpls0skxdKxlk However, it smoothed out with the optical flow in Premiere. It might need the noise limit lowered. Would 2 steps help?