How to create a velocity field from pyro?

[violalyu]

Hi houdini friends,

I'm here again for the car and leaves projects... I tried several methods using RBD only but it won't give me the ideal movements. So I'm thinking of maybe use a box of volume and have the car as collision object, so that the volume will imitate the change in the air. However, I don't know how to create the velocity field from the pyro sim and take that into another dop and use that to affect the movement of the leaves? Does anyone have any advice on this? Thank you so much!!!

[shawn_kearney]

11 hours ago, violalyu said:

Hi houdini friends,

I'm here again for the car and leaves projects... I tried several methods using RBD only but it won't give me the ideal movements. So I'm thinking of maybe use a box of volume and have the car as collision object, so that the volume will imitate the change in the air. However, I don't know how to create the velocity field from the pyro sim and take that into another dop and use that to affect the movement of the leaves? Does anyone have any advice on this? Thank you so much!!!

iirc isn't it a matter of activating it in DOP I/O??

Edited November 28, 2016 by shawn_kearney

[violalyu]

12 minutes ago, shawn_kearney said:

iirc isn't it a matter of activating it in DOP I/O??

Hi Shawn,

I'm thinking about using the pyro simulation to act as the wind for the actual simulation of leaves affected by the car, so I thought maybe there's a way to turn a pyro sim to a vector field and use that to drive the movement of the leaves?

[shawn_kearney]

Yeah. If you used the shelf tool inside the pyro_import sopnet there is a dopio sop labeled "import pyro fields"

By default the field "vel" it's not visible, but it is being imported, so all you need to do is point your secondary DOP to that node and import the "vel" field. You can optionally not import the other fields and if you like set the visualization of the velocity field to "rainbow" or "smoke" and set the render tag to display.

Once you have that,  you can use Pop Advect by Volumes DOP to either drive fluid or to drive particles on which your leaves are instanced. I'd imagine there would be a way to prevent them from colliding, I can think of at least one way to do it with a SOP Solver DOP, though using a low resolution fluid interacting with a RBD geometry might be a quick and dirty solution as well, if a little inefficient.

Anyone know if there is a more direct route here to advect RBD as you with POP?? 

Edited November 29, 2016 by shawn_kearney

[shawn_kearney]

@violalyu I decided to try this out since my "wind" project I did earlier this semester does not work very well. I am not sure if this solution is well-suited for you, and I am not totally familiar with how instancing works in Houdini yet, so there is very likely a better solution to get the leaves onto the support geometry. But for a few thousand leaves, this should work OK.

wind.hiplc

[nigelgardiner]

The last Flip fluid webinar covers advecting a flip fluid with a vel field from a smoke sim. That may be a useful watch.

[violalyu]

On 11/29/2016 at 9:56 PM, shawn_kearney said:

@violalyu I decided to try this out since my "wind" project I did earlier this semester does not work very well. I am not sure if this solution is well-suited for you, and I am not totally familiar with how instancing works in Houdini yet, so there is very likely a better solution to get the leaves onto the support geometry. But for a few thousand leaves, this should work OK.

wind.hiplc

Thanks Shawn! I checked it and it works great!

[violalyu]

On 11/30/2016 at 0:12 AM, nigelgardiner said:

The last Flip fluid webinar covers advecting a flip fluid with a vel field from a smoke sim. That may be a useful watch.

Thanks nigel! I'll check it out!!!

[shawn_kearney]

On 1/5/2017 at 0:08 PM, violalyu said:

Thanks Shawn! I checked it and it works great!

Just be aware that the orientation is calculated completely wrong. You'll want to use the orient vop node iirc.