Smoke extraction throught fans

[MANUEL_MOUSIOL]

Hi,
I am trying to do a smoke extraction sim in a staircase where air is sucked through two fans in a wall.
I am driving this with a Followpath helper, but I need two paths since it is two fans that the smoke has to go through (first floor, second floor).
It doesnt really seem to work though. Either the first one attracts too much or the second one does...is it just my settings or are two followpath helpers not working properly?

Another question:
I would like to let the fans suck the air. The smoke (that comes from the bottom floor) is not supposed to try to go through the wall to get to the follow path. Any idea how to solve this?

If you need more info, please ping me. Attached are two screens of the setup.

I appreciate any help! THanks!

[georgi.zhekov]

Hey,

When having more than 1 Path Follow forces in the scene you will have to set the Influence option below 1 or the forces will start to compete for domination. Set it to something lower like 0.1, 0.2...

As for the fans sucking the smoke - how do you do that at the moment? Is it only the Path Follows?

If the smoke from the two floors shouldn't interact with the other one - maybe you can make two simulators - one for each floor.

[MANUEL_MOUSIOL]

Ok, I'll give it a shot. Thanks.

The idea is that one fan won't suck all the smoke out so that the rest of the smoke keeps going up and then is sucked in by the second fan. So a second simulation... Is not the best idea in this case, right?

Is there a way to let walls be obstacles for forces? In tyflow it's possible at least..

[MANUEL_MOUSIOL]

Ideally I would prefer something else than followpath. It seems a little artificial. Something like another force sucking from behind the walls into the hole... do you have any suggestions?

[MANUEL_MOUSIOL]

You can see how the smoke is pressed against the wall. If it would only be sucked in by the fan, this obviously wouldnt happen..

[MANUEL_MOUSIOL]

Ok, I got it. Feel stupid for not checking enough with the docs.
I had to lower the max distance and the influence.
Still the question remains and is interesting: can other objects be obstacle for forces so there influence is limited? Like a wall that doesnt let wind through..

[Paul Oblomov]

I think you should try to create custom velocity field. With voxel tuner I think... maybe.

[georgi.zhekov]

For the fans sucking up the smoke, you can add the fan as an emitter to a Phoenix Source and then set the discharge to a negative value - this way instead of emitting smoke it will consume it.
In order to get good results with such scenes where the smoke is swirling around in closed space - you will need to increase the conservation quality. You can find more about it along with some examples here - https://docs.chaos.com/display/PHX4M...y(Conservation)

Using the negative source should give you the result you're after I guess. Here is a simple scene how this works. It is saved for Max 2019, let me know if you need it downsaved.

As Paul mentioned using the Voxel Tuner you can make forces affect the simulation using complex conditions. You can check how this works here - https://youtu.be/Z-EF6t5uXik

Cheers!

[MANUEL_MOUSIOL]

Hi Paul and Georgi,
thanks a lot for the tips. Using the negative discharge really helped to get closer to my attended affect. I was starting out with the large smoke preset btw and already had a high conservation quality.
I am playing now to get the smoke extracted more by the fan. In reality there is air blowing into the staircase, bringing the smoke up and into the direction of the fan. Unfortunately I dont even have good reference and have to work with my own logic, which is never good LOL
The voxel tuner looks awesome but I still have to find a way to use it - again, I have to work with my logic and i am not the most logically thinking person hahaha

[Svetlin.Nikolov]

Hey guys, dropping in with a setup that would simulate the fan more properly.
- The problem with Path follow is that it is indeed very forced and can make the fluid behave artificial for shots such as yours.
- The problem with a negative source is that it draws the fluid into a point volume, while in the case of a fan, we want to have it draw fluid from one direction and shoot it the other way, and leaving it to do its fluid thing after.

So here is how Paul's suggestion for creating a velocity field with the Voxel Tuner would look like:


There is a box inside the opening, non-solid and not-renderable. I picked it in to the Voxel Tuner and told it to create velocities inside the box, along the positive X axis - this points from the emitter sphere, through the opening:



So here is how the simulation looks like (note that the number 300 for velocity is calibrated via trial and error - I was not sure in the beginning how strong the "fan" should be. 300 in this case is the strength of the fan. Also note that the distance the "fan" should affect is controlled by the Conservation Quality in the Dynamics rollout - I chose quality of 100, Direct Symmetric and also used 2 steps per frame because the ejected smoke through the opening was getting too voxelated:



And finally, here it is in motion:

Hope this helps!

[MANUEL_MOUSIOL]

Hey Svetlin,
thanks so much for the detailed answer, the setup and the video. Always stunned how helpful you guys are.
This looks indeed pretty good and I will try out the setup. What i am also imagining is that the fan does not only suck in one direction but has indeed a spread so that even the smoke at, lets say, a 15 degree angle beneath the x axis will be sucked in. Probably something like that can be achieved with additional voxel tuners or maybe a combination of a path follow or vortex space warp? Still a lot to test here...

[Svetlin.Nikolov]

Hmmm, yes, maybe the vortex force can draw in the smoke the same way and its advantage would be that you can direct it any way you want, not just along some axis