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more sand/grain question

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As nobody answered my previous post (no hard feelings ^_^), here I am again.

I have made some progress with sand/grain but I'm still not sure of the process.

In this new file I'm trying to have the sand to gradually blow away .

I'm using a PopForce to move my particles and I'm controlling the v@Force Attribute with a voppop.

I'm using a ramp based on Y and a turbulence noise to set the @force value as I would like the sand to start blowing randomly from the top and slowly go down the pile of sand.

But I have 2 problems.

1- because the noise and the ramp are based on position, the particles enter and exit the noise/value

2- the noise is fading to quickly, I think I need to add a fit node to compensate.. but I can't figure it out.

Here is my ramp/noise test (on a volume).



PS: my previous post was about sand disintegration.


and I attached a Hip of my scene.

Please Help me out!



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Here's one way of doing it.   If you want the sand to gradually blow away, you probably dont want to reference @P.y inside the simulation  to drive the force, because thats going to dynamically change during the sim, and if a particle gets outside of the threshold, the force could stop affecting it.

So I here created a group in SOPs that grows over time based on the Y bounding box.  It gets referenced in the DOP sim, and then particles always stay in the group once they have joined.  If you want to add more forces using a POP VOP, make sure the noise is set to 3D noise, and then add that to @force, and put force_grp in the group parameter of the VOP.


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Hi Loudsubs,

thanks a lot for your reply and file, very interesting stuff going on in there.

it took me a little bit of time to understand what was going on, and how you were animating the growth  (still not sure I understand at 100%):)

You pointed out exactly my problem I'll bring my vop to sop level and set a group there and see how it goes.

Thanks again and I'll update shortly...


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So I tried to reproduce and change a little my file to see if I understood your process.

but I'm stuck again.

In the attached file I tried, in sop, to first use a pointVOP to generate color and then use a group node to generate the force_grp.

And bring that to the dop network and use your technique to dynamically update the group. but for whatever reason I only get the first frame of the group.

I can see my group being updating in SOP (advance a few frame, middle mouse to check the number of pt in my group, advance a few frame...etc).

but I think I'm not doing something right in dop...??



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I think I'm getting closer, I found out why I couldn't see the group updating in DOP .... wrong naming in the SopSolver, DUH!

now I fixed that and it looks better, but I have some weird behavior at the end of the sim,

Not sure if the particles are "swimming" in the texture again, or what... any idea?


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I haven't looked at loudsubs file but this is how I would apply forces to the sand using SOPS to control it.

Hope it helps.
Cheers Jake.


Edited by Malf

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Hi Jake,

thanks a lot for your scene! I like the simplicity of it. very clean! 

and that's exactly what I was looking for.


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