clever_beast Posted June 30, 2015 Share Posted June 30, 2015 Hello there, i'm stuck in a particle simulation, here is my issue : I have an animated bird geometry that goes through a cloud of particles, and I want his wings to create wind and swirls. I managed to compute velocity with a trail node... but i can't find a way to have a vector field simulation out of it. Can anyone help me ? (it may be a stupid question... but i'm new with houdini and i'm a bit lost between the different tools) Quote Link to comment Share on other sites More sharing options...
rtep Posted June 30, 2015 Share Posted June 30, 2015 Here's one way to build a vel volume from a trail. You can then use the vel volume in an advect by volume node in your dop pop. Check it out. This might be enough for your project. vel field from points_v001.hip I find you get a better result if you create a big container of smoke and let your vel volume disturb that. Have your points floating in the big container and they will be affected by the disturbance of the big object. But that's a little more involved and this file will be simpler to understand and hopefully get you going in the right direction. Let me know if it helps. Quote Link to comment Share on other sites More sharing options...
clever_beast Posted June 30, 2015 Author Share Posted June 30, 2015 (edited) Thank you for your quick answer. Your vel volume technique works well (thus, i don't really understand how the velocity affects the visibility of the volume)... I was wondering if there was a way to add a feather to the volume. I tried to add a volume feather/volume blur, but it didn't seem to work. I guess I can manage to do it with a volumeVOP or something. When you talk about a container of smoke, you talk about a smoke object and a smoke solver, right ? I created a container, collision with the object works, but how can i manage to affect my particles with the smoke container's vectors ? I tried with a "POP advect by volume", with velocity source set to "DOP data", but it doesn't work... I let you check my setup, if you have time Thanks vel field from points_B_v002.hip Edited June 30, 2015 by clever_beast Quote Link to comment Share on other sites More sharing options...
sadhu Posted July 1, 2015 Share Posted July 1, 2015 You need to import vel field using dopimport field sop from SMOKE_VECTORS dopnet. Then specify the path of this dopimport field in PARTICLE_FIELD dopnet/popadvectbyvolumes1 dop. set the velocity source to sop. Refer the attached file. There are other solutions as well, I just continued with your existing setup. Hope this helps. vel field from points_B_Solution.hipnc Quote Link to comment Share on other sites More sharing options...
rtep Posted July 1, 2015 Share Posted July 1, 2015 (edited) Howdy, I can take a look at the files tomorrow but sadhu might have you covered. But I'll jump in and answer your other questions quickly. The volume won't be visible when the velocities are negative but they are still there. The volume, by default, will only display positive values. I'm not sure if there's a node or parameter directly used for feathering but as far as controlling your velocity volume there are 2 important things to remember, the resolution of the volume and the amount of points that are being sampled. The resolution of the volume node will define how fine your vel field is. By increasing the voxels you will get more samples of vel data and the particle motion will match closer to the animating geo, which will become more apparent with deforming geo. Resolution works in tandum with the number of points you are sampling the vel attr from. A higher res volume won't do much without more points to sample vel from. So you can scatter points in your geo or scatter points on the surface of the geo, get your vel attr and then use a vop to add noise to the vel or feather the field based on distance from an sdf of the animated geo... it's pretty limitless once you get it going. Edited July 1, 2015 by rtep Quote Link to comment Share on other sites More sharing options...
clever_beast Posted July 1, 2015 Author Share Posted July 1, 2015 YES ! That is exactly what i needed. With your answers and your explanations, it becomes clearer. Thank you so much ! Quote Link to comment Share on other sites More sharing options...
clever_beast Posted July 2, 2015 Author Share Posted July 2, 2015 Hi again, Even if a solution has already been explained, I just found a tutorial from Peter Quint where he just uses an Advect by Volume node. It's a pretty simple setup : part 1 : https://vimeo.com/12092711 part 2 : https://vimeo.com/12093352 The only "issue" you might have with this solution : you can't really have control on the effect (volumefeather for instance...). Quote Link to comment Share on other sites More sharing options...
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