Cannon smoke tips/help

[olajay]

Hi all,

 

I'm new to the forums and have been learning Houdini for the last 1-2 months. I've totally fallen in love with Houdini's procedural workflow and was surprised how intuitive and logical it feels contradicting my beliefs :-)

 

Anyways been trying to make a smoke sim of a cannon fire. Only the smoke, no burst of fire (ill add that in comp). Problem I'm facing is directing the smoke the way I want. Tried making the inside of the barrel a volume and pushing it out with forces and a RBD sphere. This way its hard to get the timing right, smokes too slow and it gives a ugly mushroom shape.

 

Looking at this clip: https://www.youtube.com/watch?v=5bYRc0nm8WQ&t=1m5s the smoke fills the front of the cannon instantly, making me think I should combine two sims; one that's the shape of the the large diffuse smoke, and one more billowy blown out of the cannon. Then write to disk and time-warp and offset as needed.

 

So questions are as follows:

 

Could I model the initial shape of the big diffuse smoke as poly in front of the cannon, make it a volume and simulate it to blow away (no emmision)?

What is the best way to add velocity to the thicker smoke coming out the barrel? forces?

Anyone done something similar have any tips for making this effect?

How to avoid the infamous mushroom shape?

 

I'll see how far i get with the "two-sim" solution tomorrow and post my findings.

 

All the best,

 

Ola

 

PS: I'm aiming for a less dramatic effect than the one in the video. Less smoke, but still realistic. 

 

 

 

[yashpolke]

 For the shape of the smoke :

 

What you can do is create a geo shape that will be the source of your smoke. eg: When i did cannon fire i had make a line, transformed it and copied a bunch around the origin of the line, which gave me a cone like appereance and then i just added some noise on it to make it a little curly.

Then I gave it some density and velocity using a VOPSOP and then used the cluster points node. This node automatically gives you cluterpoints and averagepoints. I used the averagepoints to make a bounding box for the curly lines geo for smoke and used the fluid source to make a volume out of it and put that into the sim.

 

Remember you have to source the bounding box in the smoke object which you use in the sim. I used the resize also but sometimes its good not to use the resize since it messes the smoke shape.

 

And i think this method itself will prevent the mushroom shape you are talking about

 

Then you can do all sorts of things like wind and drag to your smoke in the DOP network and manage the look of the smoke with the solver, I used a Pyro solver.

 

For controlling the emmision time of the smoke I used Python, gave it a fire frame attribute, and made a digital asses out of it so that you can just enter the frame you want the cannon to fire.

 

I hope this helps!

 

Yash