Mixing / advecting Cd in FLIP sim with multiple objects

[j00ey]

Hello all

 

I have a problem with a FLIP sim I'm working on. I'm trying to set something up where randomly coloured painballs get thrown at a wall. I have a custom stick field to stick the paint where there is some text on the wall - that's working ok so far.

 

The problem is really that I want the different coloured paints to mix and I can't get that to work.

 

To start with I had several DOP objects, 1 for each paintball but I read on here someone said merge everything in SOPS first and just have the one DOP object. So I've sort of done that - I have a single FLIP object node but it's creating a new DOP object every 10 frames, I think this is part of my problem but I'm struggling with how to get the same effect with a single DOP object. Really I'd like a system that sits there throwing randomly coloured paintballs at the wall without having to manually add another one each time...

 

 

I am using a Gas Match Field DOP to get the Cd from the particles, then I advect Cd volume using vel, then I transfer the Cd back to the particles. This isn't working, and when I import the sim back into SOPs I have a set of Cd volumes for each paintball [as well as vel for each]. How can I just have 1? Also for some reason I have 2 surface volumes for each and I can't figure out why.

 

Attached is the hip file, also a link to a movie of the sim as is. I'd be very grateful for any advice or pointers.

 

 

Many thanks..

 

paintball_01.hiplc

[pbarua]

Can you make it hipnc? My Houdini is older than Indie. Can't update in between project.

[j00ey]

Hi Pradeep

So fast! I love this forum!

Here's a hipnc, I didn't realise Indie files wouldn't open, thanks for the tip..

paintball_01.hipnc

[j00ey]

I just realised I should just be using a source volume DOP with intermittent activation rather than thinking of it as separate objects. I'll give it a go and post again if I get stuck, or in case it's useful to anyone else

[pbarua]

There you go..........

paintball_pbarua.hipnc

[pbarua]

I bypassed gasadvactfield dop and used gasblur to smooth out result.

[j00ey]

Hi

 

Yes I thought of doing that but I would still get all the different sets of vel and Cd and surface volumes in SOPs.

 

I switched it around to have just a single flip object and that fixed that. I had to turn off the gas advect  because that just blew away the colour with the velocity but with a single set of Cd volumes the colour mixes anyway.

 

Thanks for having a look. I'll post the file later in case it's useful for anyone.

[pbarua]

Why am I getting these volumes called surface?

 

 

Because you are importing surface field from DOPs using dopio sop.

surface field is important for secondary sims like whitewater and it's not useful in meshing at all. You don't need that. Just click on cross(X) to delete it. 

[pbarua]

Hi

 

Yes I thought of doing that but I would still get all the different sets of vel and Cd and surface volumes in SOPs.

 

I switched it around to have just a single flip object and that fixed that. I had to turn off the gas advect  because that just blew away the colour with the velocity but with a single set of Cd volumes the colour mixes anyway.

 

Thanks for having a look. I'll post the file later in case it's useful for anyone.

As I mentioned for flip surfacing you do not require "surface" and "vel" fields. Just ingore those by uncheck import or click on cross.

You only need "Geometry" and "Cd" from DOPs. 

[pbarua]

I thought of doing that but I would still get all the different sets of vel and Cd and surface volumes in SOPs.

 

 

Did you check my file?

I'm getting single set per field. By using only single flip object.

I'm using sourcevolume dop with activation set to:

if($FF%ch("../interval")==1,$FF,0) 

what you used in flipobject creation frame.

I set that to 1 and Initial data to default.

[j00ey]

But in the first set up I was getting 2 volumes called surface per DOP object. I know I should be getting one, and one of them looks as you'd expect but the other seems to be using the centroid of the simulation[?] but isn't evolving at all. I must have set something up wrongly on the Fluid Source SOP but when I was trying to figure it out yesterday I couldn't find what it was.

 

Here's a video showing the 2 surface volumes

 

[pbarua]

Here's a hipnc, I didn't realise Indie files wouldn't open, thanks for the tip.. 

 

 

.hiplc wouldn't open up older build (before Indie was introduced) only. In newer build you can open those without any problem like hipnc.

Only thing you can't save it. 

Edited December 14, 2014 by Pradeep Barua

[j00ey]

Hi Pradeep

That's what I did last night yes and it worked - and yes I only got the volumes I was expecting.

I was just trying to figure out what I did wrong before.

I have to go out now but I'll return to this tomorrow when I get chance.

Thanks very much for the taking the time to help out.

 

Edit - ps no I didn't check your file yet but I will later, thanks

Edited December 14, 2014 by j00ey

[pbarua]

I was just trying to figure out what I did wrong before.

 

 

You were creating multiple flip object after certain interval that was creating separate (multiple) fields for each object.

Edited December 14, 2014 by Pradeep Barua

[pbarua]

You can clearly see it in Detail View.

[j00ey]

Hi Pradeep

 

I had a look at your file - I'd done the same modifications as you except for the gas blur - good idea to add that in for a bit more control of the colour mixing.

 

As you say I saw all the sets of volumes in the details view - I can see why there would be one set of Cd volumes, one set of vel, one surface etc for each DOP object but I still don't understand why there were TWO surface volumes for each. One day it will become clear I hope!

 

Thanks again for the help.