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Thread: VDB Gas Solver

  1. #1

    VDB Gas Solver

    Hi all,

    Never posted here, but maybe you'll see me sometime now.
    Does anyone knows how to stop gas emission in a gas solver ?

    I tryed animating gas solver settings down to 0. I tryed cutting the mesh to volume that emits in gas solver with booleen (CSG). I tryed scaling the target mesh of the mesh to volume down to 0 (this crashes lightwave when simulating).
    All this does not work. It emits forever.

    The setup is very simple : I only plugs a mesh to volume in the source grid of a gas solver.


    Any idea ?

    Thanx.

  2. #2
    RETROGRADER prometheus's Avatar
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    Was about to test it, but to my surprise, I canīt even add a gas solver, it crashes lightwave 2019.1.1
    and I canīt even reload old gas solvers either, it crashes too.

    I canīt recall that being the issue the first time I tried 2019.1.1 something must have happened to my installation.
    O well..I better reinstall and do that with 2019.1.5 instead.

  3. #3
    Same problem here (lw 2019.1.5).
    Lot of crashes and scenes that can't reload.
    I have to delete gas solver after every simulation and remember settings for the next one. It seems it keeps cached datas (I don't know where. Not on disk anyway) and If I unplug everything on it and go back to first frame then plug again and activate visibility, there's still something that appears on one frame. If I don't do that (deleting it and creating a new one, then entering settings again), other simulations are odd then I get sometime crashes.
    I have problem with saver that often don't want to open new grid after plugin the first one. Hard to plug velocity grid.
    And I can't figure how saving this velocity grid (it seems to save 0 value on every cells when saved).

    And if I use result with octane, it is flipped in Z axis (I have to scale Octane null by -1 in Z axis).


    Anyway, thanx for looking at it Prometheus ! I really need to stop emission at some point.
    Last edited by TorTor; 03-11-2020 at 01:01 PM.

  4. #4
    Registered User 3dhotshot's Avatar
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    What type of gas are you making ?

  5. #5
    Registered User squarewulf's Avatar
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    Quote Originally Posted by 3dhotshot View Post
    What type of gas are you making ?
    oh that wasn't me that was the dog i swear

  6. #6
    Electron wrangler jwiede's Avatar
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    Well, using 2019.1.5 on Mac (OSX 10.13) I was able to take a mesh, hook it up using mesh to volume into gas solver's source volume, started timeline running, and it ran fine for a few dozen frames. Was quite difficult getting timeline to stop, but other than that didn't encounter any crashes.

    What I don't see is any easy/direct means to convince the gas solver to _stop_ making gas from the source volume.
    John W.
    LW2015.3UB/2019.1.5 on MacPro(12C/24T/10.13.6),64GB RAM, NV 980ti

  7. #7
    I'm not making gas (neither my dog ), but gas solver has the kind of behavior I need for what I'm doing.

    But I can't stop emission. And this is needed ...

    Crashes and problems don't happen when testing quickly.
    But when adding forces, refining, saving caches, canceling, refining again. Gas solver seems not to reset well without deleting it. It seems that some kind of ram cache don't reset well and sometime new simulations start without a fresh empty grid.
    And when saving scenes. The worst thing is when you reload a scene that crash and can't be loaded again. Or when it crashes when saving scenes.

    Anyway I worked around those bugs (even if this is not a way for production, I have enough time on this one, so I test the tool).

    My bigger problem now is to stop emission when I need it. Like in any other grid simulator.


    What I'm doing is not gas:
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    Last edited by TorTor; 03-11-2020 at 04:18 PM.

  8. #8
    RETROGRADER prometheus's Avatar
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    Oki..just installed 2019.1.5 since something must have been screwed up with 2019.1.1, I know it used to work..but suddenly crashed by only trying to add the gas solver node.

    Anyway..no crashing now so I could set up a gas solver.
    And a solution could be, enter the gas solver node and simply add an envelope for the Gas density, that should stop it, though it doesnīt shut it down exactly at desired cutoff keyframe...takes a bit longer, will have to look in to this more..perhaps it does, itīs just the appearance of it dying off is not sharp, since it has to fade away.




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  9. #9
    I thought I tried this.
    I probably put the envelope on an other channel.
    This will be perfect.

    Thanx prometheus !

    Aren't you have problems when trying to plug all 3 output grid on a saver ?
    I have to plug first velocity grid. If not, saver does not open new input when trying to plug it.
    Or is there a needed order when plugin those output grids ?
    And when plugged, does the saved velocity grid have other values than 0 ? it seems I had only 0 values.

  10. #10
    Electron wrangler jwiede's Avatar
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    Quote Originally Posted by TorTor View Post
    I thought I tried this.
    I probably put the envelope on an other channel.
    This will be perfect.

    Thanx prometheus !

    Aren't you have problems when trying to plug all 3 output grid on a saver ?
    I have to plug first velocity grid. If not, saver does not open new input when trying to plug it.
    Or is there a needed order when plugin those output grids ?
    And when plugged, does the saved velocity grid have other values than 0 ? it seems I had only 0 values.
    Well keep in mind that the boundary regions for the grid will be mostly 0 values because the gas is located towards the middle, not at the edges (at least in the beginning). It's quite possible there's data hiding in there, but unless you check rather thoroughly, you could miss it because most of the grid is initially "empty" in that regard. If you can figure out roughly where the middle of the dataset is, and aren't seeing values there either, that could indicate something is amiss. However, just seeing large quantities of zeroed entries initially in the dataset isn't so unusual, because the only actual data is right at the center of the bounded volume.
    John W.
    LW2015.3UB/2019.1.5 on MacPro(12C/24T/10.13.6),64GB RAM, NV 980ti

  11. #11
    RETROGRADER prometheus's Avatar
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    I like the quality of the gas solver, and itīs fairly easy to color as you need..these factors is actually harder to control in my opinion for blender fluids, another factor is that I can use the particles velocity motion as force input to drive the gas intial direction, without actually using the particles as fluid emitters and having blobs because of just that, I donīt think blender can do that, blender got smoke flow for particle advection though..so that is something I miss in lightwave.
    And blender doe simulate seemingly much faster, but hard to tell due to so different solvers and grids and resolutions, and blender at least got proper voxel slicing for the openGL, where we got a horrible tick presentation, often in need to zoom out to see anything decent.

    Since I had to install the latest version and try gas solver out again, I Just had whipped up a little neb, stars are just clones lensflare (which I also would have natively directly in viewports in blender) background is volumetric scattering and some procedural textures on weight channel and fed in to a gradient as well, the actual sim was driven by particles pushing it in the direction I needed.
    The image is too clear though, should add noise to it, and I would need to adress more darkness deepness in the plume.



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  12. #12
    Really pleased to post on this forum.
    Nice to have people who helps as fast as you did.

    So thanx prometheus and jwiede !


    Next step I need to solve is how to reiterate gas solver simulations for refinement.

    My problem is that when I stop a simulation test because I want to tweak something before simulating again, I don't know how to go back to first simulation frame and get a new fresh solver without deleting it and creating a new one. Last simulated frame appears in the first frame when I go back to simulate again.
    I searched for a "clear" button, I tried to unplug and replug everything on the solver, I tried to deactivate, reactivate it. Nothing I did worked for me.
    And keeping a fresh unplugged solver which I clone for getting a new one seems to be the problem which makes saved scenes crashing when reloading (not sure this is the only cause, but I had some scenes with this bug which I cured by deleting every unplugged node).

    There should be a way to do that without deleting solver and creating a new one and entering again every setting in it, but I can't find how to do that.


    Hope you're not tired to help ...
    Last edited by TorTor; 03-12-2020 at 04:09 AM.

  13. #13
    GAS SOLVER NOT RESETING : SOLVED

    For the gas solver to reset, you must go to frame 0 in the time-line.
    My fluid animation is not beginning at frame 0 (it is around frame 1000). So for convinience I had set up my first time-line frame at the beginnng of the fluid animation. And when coming back to this first fluid animation frame, gas solver was keeping in cache the last computed grid state (or sometime only a part of it).
    So, for it to reset correctly, I have to go back to frame 0, then jump to the first simulation frame again and then I can simulate without having to delete gas solver. Not very convinient, but not bugged.
    (I hope I won'thave bad surprises when jumping on the fisrt simulation frame. For now it seems to work).
    Last edited by TorTor; 03-12-2020 at 09:03 AM.

  14. #14
    RETROGRADER prometheus's Avatar
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    Quote Originally Posted by TorTor View Post
    GAS SOLVER NOT RESETING : SOLVED

    For the gas solver to reset, you must go to frame 0 in the time-line.
    My fluid animation is not beginning at frame 0 (it is around frame 1000). So for convinience I had set up my first time-line frame at the beginnng of the fluid animation. And when coming back to this first fluid animation frame, gas solver was keeping in cache the last computed grid state (or sometime only a part of it).
    So, for it to reset correctly, I have to go back to frame 0, then jump to the first simulation frame again and then I can simulate without having to delete gas solver. Not very convinient, but not bugged.
    (I hope I won'thave bad surprises when jumping on the fisrt simulation frame. For now it seems to work).

    Isnīt clearing the cache good enough? in the end tab of the gas solver, if you constant test the sim..you may need to turn of to cache it, but that means much slower playback..and if you cache it..you obviously need to clear it when tweaking a new simulation.

  15. #15
    Clearing cache clears only disk cache. Not what is stored in ram when refining your simulation.
    Clear cache is greyed if you don't load a cache from disk. And so with no effect.

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