Hi guys, wonder if anyone might have an idea that could help me out on what im doing wrong.
I'm going through Applied Houdini Volumes 4 and trying to recreate with the new volume sourcing. Running into a problem where a short particle burst is the source which works great initially, but as soon as the particles in the source sim die out (and therefore their point velocities too) the smoke in the sim just runs into a brick wall and goes lifeless, with gravity just pulling it straight down. It's like the smoke created didn't gain any momentum from the particle source and when they disappear, so does all the velocity in the smoke.
In the tutorial, where Steve uses the old sourcing workflow with ‘fluid source’, he gets a sort of rolling edge along the ground from the pressure of the initial velocity burst and can't figure out why my smoke is losing all its momentum. Any thoughts?
Looks to me like you aren't sourcing velocity at all. You are just sourcing smoke which has no velocity, which is why when the source dies, the smoke just falls down. Try adding velocity to your source fields. Also if you crank up the shape parameters, you will at least get movement during that time, whether or not velocity is inherited.
Hey thanks for getting back. I think I sourced in the right way, i rasterised the V attribute on the particles and then imported ‘v’ volume into ‘vel’ field in the dopnet.
When I do a volume slice on the Vol Rasterize attrib sop, I see the velocities while the particles are alive. It just seems like after those velocities from the particles go, the smoke has no interest in carrying on moving. Im not really experienced with Houdini or volumes, so maybe they don't work like this, I just assumed that the smoke created would have inherited the initial velocities and had some momentum.
When I cranked up the vel field on the source, it gets a more powerful initial burst, but still just stops after the source sim stops.
I did get some movement adding in turbulence /shape settings you're right, but stripped them away to try and sort this issue, which really having no luck so far!
Post a hip file and Ill check it out. That'll be the best way for me to diagnose this. If you can't share the file for whatever reason, then try and replicate the problem in a simple file you can share.
hey, thanks a lot for that. Posted the file here. Did a few caches along the way which I've disabled, but isn't very heavy, just simple RBD smash sim, points on the broken pieces which feeds into a particle sim to create the burst for the pyro.
I don't think there is anything wrong with your setup. You are getting velocity while there are particles, and when there are no more particles, there is no more velocity being sourced, just as there is no more density being sourced. The smoke definitely gains momentum from the initial velocity burst, because if you disable your gravity and drag, you will see that it continues moving in its initial direction, just with a loss in velocity over time. I'd probably need to see the tutorial you are mentioning to see what he did differently. Perhaps something as simple as reducing the timescale so that velocity is lost slower might do the job. It does feel like everything is working as intended though.
I made some tweaks to your file to show you what happens when you increase the source velocity, and tweak how your velocity is being sourced a bit. Here, you can see the velocity die off over time, as opposed to just disappearing when your source disappears at 1018. Here, you can see a more gradual loss of velocity, which makes sense as velocity is only sourced as the points that are sourcing it exist.
Hi, thanks for taking a look. Ok cool that’s helpful that I’m sourcing correctly.
Watching through and having a think, I never used the old fluid source as only started learning with H17, but there was an option to add curl to velocity in the fluid source, which Is then masked out by density in dop sim. So maybe that’s why it keeps moving out in the tutorial. Mainly the difference is a rolling edge that moves out along the ground that I’m not seeing in mine.
I’ll try the timestep idea thanks, yeah I think some way to loosen up the smoke is what I’m after, but adding the shape parameters to give it some extra movement will also help.
Thanks for your time and all the help, much appreciated.
km6064 Hi, thanks for taking a look. Ok cool that’s helpful that I’m sourcing correctly.
Watching through and having a think, I never used the old fluid source as only started learning with H17, but there was an option to add curl to velocity in the fluid source, which Is then masked out by density in dop sim. So maybe that’s why it keeps moving out in the tutorial. Mainly the difference is a rolling edge that moves out along the ground that I’m not seeing in mine.
I’ll try the timestep idea thanks, yeah I think some way to loosen up the smoke is what I’m after, but adding the shape parameters to give it some extra movement will also help.
Thanks for your time and all the help, much appreciated.
Have you been able to resolve this? I'm having the same problem. In fact, I registered here because of this problem. Thanks
Hey Learna, ummm sort of, I think as Midasssilver was right in that the setup is ok, so after that, having a think and speaking to Steve himself about it generally, I figure it's part and parcel of the new sourcing method. Since we are adding velocity now to particles and making a volume from them instead of the old way (which I guess) was making a general volume and adding attributes within it.
When I watched Steve play with the fluid source settings and there were different noises like ‘curl’ and ‘turbulence’ I guess they are applying noise within the general volume as a whole, not just to the source areas, so when the particles disappear and take their velocities with them, those noise fields are still being affected by those noise fields, since Steve ‘masks’ the velocity by density within the dopnet, and the source has already created density, so it carries on through the curl field. At least I guess this is what's happening.
So…. other than micro-solvers and scaling the source velocity up, I also created a large box of points, the size of my sim, added a curl velocity field with a pointvop, and ‘volume rasterised’ the v as a volume.
I then added a second ‘volume source’ within the dopnet, mixing in this general curl velocity and masking it with the density.
Probably a terrible idea, and not much different than adding in micro solvers but I gave it a go and seemed to get somewhere. I haven't gone back to the file too much over the last week or so tbh
km6064 Hey Learna, ummm sort of, I think as Midasssilver was right in that the setup is ok, so after that, having a think and speaking to Steve himself about it generally, I figure it's part and parcel of the new sourcing method. Since we are adding velocity now to particles and making a volume from them instead of the old way (which I guess) was making a general volume and adding attributes within it.
When I watched Steve play with the fluid source settings and there were different noises like ‘curl’ and ‘turbulence’ I guess they are applying noise within the general volume as a whole, not just to the source areas, so when the particles disappear and take their velocities with them, those noise fields are still being affected by those noise fields, since Steve ‘masks’ the velocity by density within the dopnet, and the source has already created density, so it carries on through the curl field. At least I guess this is what's happening.
So…. other than micro-solvers and scaling the source velocity up, I also created a large box of points, the size of my sim, added a curl velocity field with a pointvop, and ‘volume rasterised’ the v as a volume.
I then added a second ‘volume source’ within the dopnet, mixing in this general curl velocity and masking it with the density.
Probably a terrible idea, and not much different than adding in micro solvers but I gave it a go and seemed to get somewhere. I haven't gone back to the file too much over the last week or so tbh
hope that helps at all.
Thanks for your help, I remember it had something to do with the new workflow. I have been offline since I last posted this. I only log on when I have a problem. Bad, but it's what it's.
