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catchyid last won the day on November 20 2016

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About catchyid

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    Khaled Abdelhay
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    Montreal, QC

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  1. Some FLIP questions

    Thanks, Ikon also hinted me to this video! Thanks guys, I will watch it, hopefully it will answer my questions
  2. Hi, I have some FLIP questions, any help is appreciated 1- In particles reseeding, how is "Particle reseeding -> Particles per Voxel“ useful? meaning, what difference does it make to set it to 4,8 or 16? 2- ”FLIP Object->Grid Scale“ and ”Particle reseeding->Particles Per Voxel" seem to define the same thing? i.e a bigger grid will have more particles per voxel, so why redefine the number of particles per voxel again? 3- What does mean that particles are “unresolved” ? 4- I understand that the “pressure projection” solve is the process that changes particles velocities to compensate for pressure differences (i.e. move particles from high to low pressure). My question: if the number of particles per voxel can change freely (i.e. particles reseeding, voxel size, …) what really defines pressure? i.e. what makes some areas of fluid have more pressure than others? 5- According to docs, Particles reseeding will increase spawn particles if they are below a certain count per voxel and vise versa. My question: what makes particles diseapear in the first place? I understand they are moving, but so what? If they leave a voxel then the voxel becomes empty and it's even “wrong” to create particles just to meet the minimum particles count per voxel? The same question applies on having “too” many particles per voxel, what this happens in the first place and what does it mean? Thanks...
  3. Hi, I have a heavy FLIP simulation, my machine has 64 GB RAM and it can barely finish the sim! Anyways, the sim result is stored as surface and vel VDB and packed geo for particles. I using these VDB and particles for whitewater simulation, however it's terribly slow (e.g. it takes couple seconds just to create source particles for whitewater sim). My question : is there a way to simplify the results coming out from FLIP simulation? I've tried using VDB LOD but it's seems to be broken (it changes volumes names randomly and nothing works after), also I've tried VDB Resample, and it did lower the VDBs resolution, but I got the same particles count which still makes whitewater sim very slow?? Thanks
  4. FLIP Divergence Question

    Apologies, I followed your steps/hints and it does work Thanks for your
  5. FLIP Divergence Question

    Hi, I've set FLIP divergence to high positive and negative numbers and it had not effect on the FLIP simulation, is this normal? I understand Divergence measures expanding/shrinking of the fluid (and it does work in pyro this way as far as I remember), but in FLIP I don't see any effect for it. Am I missing something? If has no effect, why it's there in the first place? Thanks
  6. Okay, some general FLIP questions a-Default value for particles per voxel is 8. Question: Let's say I double it to 16 or half it to 4, in essence, what difference does it make? I am asking this question because I understand that FLIP is voxels based (and not particles based), particles are just used for some intermediate computation, and finally voxels are where the physics computations are done, so what difference does it make to have 1 or 100 particle per voxel? For example, should I except sharper results with higher particles count per voxel? b-Let's say, I want to a thick fluid to have initial creases as show in the images below (sorry, they are gross :)), what's the best way to initially have these creases? If it's a simple spherical creases, then I can do that geometrically and create FLIP Particles based on the modified mesh, but in the images below, they are not symmetrical (specially the dog and fish images) Cheers,
  7. Different ways of FLIP collisions ...

    Another thought: I think there is one advantage of using collision and collisionvel which is one can control the impact of the collision individually for each object (i.e. customize each volume independently), however when using RBD object there is only one universal control for all collisions (i.e. in flip solver -> volume -> collision -> velocity scale)...
  8. I found a solution...basically using instance RBD objects + SOP solver to copy positions into animated instances... instanced_rbd.hip
  9. Hi, I am using a single RBD Fracture object to create many RBD pieces at once inside a dop network (these pieces are all independent objects and are created and driven by a POP Solver, actually they are spawned as static pieces as I am controlling their animation from the POP network). In principle, it works, however I am having one problem: any piece that gets created after the first simulation frame is ignored, i.e. RBD Fracture Object only creates the pieces that exist in the first simulation frame, and any other pieces that get created after is ignored! My goal is to spawn the new RBD objects as they are get created by the POP solver ... Attached shows a simple network where particles create the RBD objects. I've tried to use a SOP Solver but it does not work (things work only if I emit the first frame), however you can ignore the SOP solver altogether, it was just a failed trial Any feedback is appreciated rdb_fractured_question.hip
  10. Different ways of FLIP collisions ...

    Thanks Alejandro I remember collisionmask was slowing my sim a lot with method (a) which agrees with what you say, and yes method (b) was faster, but my problem with it was that creating collision and collisionvel for many objects were too slow which defeated the whole purpose of using it (maybe I need to do more research to find a better way to create collision and collisionvel faster)... Once more, thanks
  11. Hi, I can introduce collision into a FLIP sim using either: (a) RBD collision (e.g. use static or RBD object), or (b) FLIP source configured as collision (i.e. it has both collision and collisionvel volumes) My question: what's the difference? why have two methods? Why (b) method requires two volumes (meaning, why it needs collisionvel volume while RBD does not need)... Any insights or thoughts are appreciated Cheers,
  12. Also, there is a tutorial on pops by side effects , I think it's a master class, that talks about these issues in details.... I am sure you can find it if you still need more info on this topic
  13. Ocean Spectrum question

    Hi I was able to fix the problem earlier...I remember it was a matter of grid size, grid resolution, amplitude scale ...just playing with these parameters fixed the problem ...Thanks for your help as well
  14. Hello, I have two questions regarding Ocean Spectrum and how it works: 1) If I set an ocean spectrum resolution to 8 I get facet surface (i.e. as if points normals are not interpolated between faces), and If I increase the resolution to 10 then I get a smoother surface but with too many frequencies (see attached). My question: Is there a way to keep the lower resolution but with smoother shading (i.e. remove these facet)? Note: I am using Mantra Ocean Shader (maybe another way to phrase the question: why conversion from ocean spectrum frequencies to mesh displacement produces such facet look? I am not expert here, but my understanding is changing frequencies should change the frequencies in the produced mesh, so even if we have low resolution spectrum, it should produce "smooth" low frequency mesh ...) 2) If I want to ignore the ocean shader altogether and displace the mesh before rendering (using ocean spectrum evaluate), how to compute the minimum mesh resolution/division (i.e. the minimum primitive dimension) in order to capture the spectrum highest frequencies (i.e. I need to subdivide the input mesh high enough to capture high frequencies before feeding it to Ocean spectrum evaluate)? Thanks,
  15. Thaaaaaaanks Janis I have tested volume slice and it does work exactly like you described. However, when it comes to Volume VOP, I am not sure exactly how to do this test : if density > 0 execute the addpoint command? plz, see attached image where you can see what I have done... Once more thanks for your help vop_question.hip