Cascading explosion

[jstrob]

Hi,

I'm trying to simulate and explosion with many sim boxes. But when i use brush (100%) it creates too much fire in the second sim box and when I use inject (0.001) it creates just very thin smoke. I am using the temp, smoke and fuel maps in the source so why aren't they transferred correctly?

[Svetlin.Nikolov]

Hey Strob,

Unfortunately the cascade simulation of fire/smoke has not yet received the full makeover it deserves. Right now you basically have the isosurface representation of the fluid from the first sim act like a source in the second sim. You can check what the emissive volume would be if you switch to mesh preview of the first sim. It is going to emit the exact values you specified in the source in the second simulation, homogeneously inside the whole volume of the smoke. This is why you get a lot of temperature and fuel in the second simulator - they are not copied from the voxels of the first sim, but instead are taken from the source.

However, I think you might get a much better result if you plug a different grid texture in each of the temperature, smoke and fuel channels. Keep the emit mode to brush. Each grid tex should read the respective channel from the first sim - temperature, smoke and fuel. Use world coordinates for the grid texture.

Try this approach and ping me if there are still issues with it.

Cheers!

[jstrob]

I had everything already setup as you described except I didn't think of setting the uv coordinates of the grid texture to world instead of the default object. I also changed the temperature of the source for the second sim until we don't see much difference in the amount of fire.

But now i am trying to simulate the second sim and it's always crashing after the first frame. Max just disapear. My ram doesn't seems to be maxed out... Any idea?

[Svetlin.Nikolov]

Oh, can you please send the scene over? We gotta fix this ASAP.

[jstrob]

It was crashing on first frame all the time on my i9 dell alienware system but on my supermicro dual xeon it could simulate entirely without crashing. i can't send that scene I would have to reproduce on a dummy scene...

[jstrob]

In fact I had an older version of phoenixfd in my dual xeon. The one I had on my i9 was the one for vray 4. so it may due to that. I try to reproduce when I finish my job.

[Guest]

If you're using V-Ray 4 you should install Phoenix for V-Ray 4 otherwise crashes are almost а cеrtain thing.

[Svetlin.Nikolov]

This is not an issue since if you are using V-Ray 4 with Phoenix for V-Ray 3, Phoenix won't be able to load in the first place.

[Svetlin.Nikolov]

Mmmm, yeah, could not repro it with a new scene here

However, I got the temperature transfer working, but there were a few things:

- First off, a very important limitation is that the Source clamps the texture values between 0-1. So smoke and fuel will naturally transition fine, but temperature which goes waaay above 1 - up to several thousand Kelvin - will need to be squashed before being plugged into the source. This is why I added and Output map after the grid texture reading the temperature channel, set the temperatures for the source for sim 1 and for the brush source to 2000K, and set the Output Amount of the Output map to 1/2000 = 0.0005.
- You need to enable Motion Velocity on the Brush source so that the velocities will be transferred as well and of course you need to have velocity exported from the first sim.
- The area which overlaps will be rendered twice, unless you put a box as a render cutter for the first sim.
- Grid-based self-shadowing won't work between the cascade grids - you need to switch to the slower but more robust Ray-Traced self-shadowing.
- There was a bug with using a grid texture from one sim in a source which acts on another sim in world coordinates - the fix will be in tomorrow's nightly.

Here is the scene I tested with (Max 2018 ) : fire_cascade_grid_tex.zip

[jstrob]

Cool thanks Svetlin I will take a look!

[jstrob]

Hi Svetlin, Is there a way to launch a cascading sim (or part of it) on the network via deadline?

Also I prepared a scene that is always crashing when trying to simulate the second part (with wolrd coordinates for the texture) I tried also with the nightly from today and it still crashing. Can I send it to you by email?

[Svetlin.Nikolov]

Absolutely! Please send it over and we'll check it ASAP. My work mail is my names separated by a dot, at chaosgroup dot com

You can run a cascade sim with multiple simulators just like you run only a single one. You can chain simulators after one another by enabling Script and uncommenting the part that launches another sim when this one finishes, just replacing the sim name

Cheers!

[cb LLC]

can a future phoenix not calculate empty grid cells? it looks like new 3ds max liquid uses grids too but it does not matter how far liquid travels like a lazy river around a water park you wont need a large giant grid. thanks

[Svetlin.Nikolov]

All fluid sims use grids more or less - FLIP liquid sims use them for velocity, while the Phoenix fire/smoke solver uses them for all channels - smoke, temperature, etc. This is a topic of a much larger conversation and it's not something we could simply turn off

[Svetlin.Nikolov]

Note that fluid solvers before FLIP either relied only on grids, or used no grids at all and thus produced worse results and could not simulate some effects at all. If it comes to managing the sizes of the grids - yes, simulations can run in sparse grids, but would usually mean slowing them down in many other situations because having box shaped grids is a great helper to performance.

Especially for Phoenix, there are two important things to note - for fire and smoke you really need too simulate the velocity of the air around smoke plumes and explosions because this is where their rolling and realistic appearance comes from - this is the way closest to how nature works. For liquids you often don't need the velocity around, unless you are doing a very large scale, epic simulation. Only in this case you can check Simulate Air Effects - if it's unchecked, Phoenix knows to ignore empty space and all it does is to occupy RAM.

Hope this helps shed some light on the general situation