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Found 10 results

  1. Divergence field in FLIP fluids

    Hi, I'm trying to understand how the divergence field works in Houdini, and how it interacts with FLIP fluid particles. Positive divergence should cause the fluid to expand but there seems to be a difference between having positive values in the divergence field and having positive values of divergence in the particles attribute: -If I have positive values of divergence in the particles attribute, the field copies this values (or does some other math operation) and the fluid expands. -If I have positive values of divergence in the field, the particles don't inherit any divergence and the fluid stays the same. -If I disable the option "Divergence by attribute" and have positive values of divergence in the field, the fluid also stays the same. Another thing I can't understand: If I want to fill a volume of 1m^3 using the gasequalizevolume micro-solver with the paramater "Scale Goal Volume" set to 0 then, according to Houdini's Documentation I have to change the parameter "Add Goal Volume" and set it to 1. I tried this and the FLIP solver simply copied the value 1 to the divergence field which doesn't result in any change on the fluid surface. Could some one shed some light on this behaviour, and what is the correct approach to fill specific volumes knowing the total volume value? EDIT: The divergence field is actually working as intended, I was modfying it in the sourcing input rather than in the velocity volume input...
  2. di- vs. convergence in Particles

    Hi, what is a plausible way to reverse the divergence of particles? The classic example, a glass champagne. After a period of n frames the divergence have to stop cause my wife hate stains on the floor.. ;-) . A Particlesystem is filling the glass. I realiced the foam with popgroup node with the expressioin ingroup = !(@id%10) && @age > 0.35; What is the apropriate way to reverse the expansion of the divergence in the foam group wich was defined in @Cd = 0; @density = 1000; @viscosity = 1; @divergence = 0.0; if(@group_foam) { @Cd = 1; @density = chi("density"); // ch = 9 @viscosity = chi("viscosity"); @divergence = chf("divergence"); // ch = 0.4 if(@age>4) { @divergence = 0; } } After that I give the foam group age dependend a lift on top via a popforce. So I have my foam slowly but surly on top. The problem is that the particles wich was influenced from the divergence stay in place even if the divergence becomes 0 again. I need a way wich leave the volume exypansion of the concerned particles (group_foam) behind - a convergence would be fantastic. Is there a way to do that without another elabrorated sophisticated sim? The concerned particle should behave as they never had a divergence. should I increase the density, hmm, na... foam group wil sink on bottom... the best way would be a mixer but after using it the champagne will taste stale, naa... ;-). AND: Interesting problem how houdini realize the rejection power of the divergented particles. How this perhaps work under the hood? Any ideas for this? Thanks in advance EDIT: found a solution: with a balanced interaction of divergence, density and viscosity its a good solution to simulate foaming and collapsing liquids. Only reamins to solve the real bubbles, its expansion and collapsing paralel to the liquid di- and convergence. Still thea are just particles.
  3. I was trying to expand the some smoke simulation using divergence field. the divergence field create a big hole in the smoke simulation. any idea why is this happening Test Smoke.hiplc
  4. Greetings, I'm currently working on a large scale FLIP animation and I'm running into a question, I need to fill with liquid a very large object (like a house), and I figure that the divergence was doing a great fob until I reduce my particle separation for a higher definition. Sim look different, but that it's fine. The main problems is the volume that doesn't fill anymore, so is there any kind of equation or technique that I can apply to ensure the same result persist over particle separation. Any advice is welcome I made a video of the difference using the same divergence value over time Thanks for your time
  5. Hello fellow magicians, I'm trying to better understand gasequalizevolume DOP inside FLIP Fluids and so far I haven't found anything usefull outside of the Houdini documentation and example files. So I tried to create a simple example file to test it out. So far, I can't seem to create one of the necessary fields for gasequalizevolume to properly work, the goal field. I used a gasmatchfield DOP and imported a pre-created fog vdb with the name goal, and nothing happened. To debug I setup a multifieldvisualization DOP and set the density field to goal, but it doesn't display anything... If some one could have a look at the file and point what I'm doing wrong... Also, if you any information or tutorials on this subject I'd be very gratefull! Thank you Gas_Equalize_Volume_RnD.hip EDIT: The Gasequalizevolume was wired in the wrong input. It needs to be wired into the volume velocity. Still can't get the gasmatchfield to work though...
  6. Divergence Problem

    Hi Guys. I'm trying to create a kind of 'expanding foam' effect (like an Elephant's Toothpaste chemical reaction). Expanding out of a teacup. But my FLIP fluid is hitting a weird shelf and not overflowing the edges of the cup properly (see below). My emitter is a sphere at the bottom of the cup. .hiplc file also attached. Any pointers hugely appreciated. Elephant_Foam_02.hiplc
  7. FLIP Divergence

    Hey guys, I'm trying to use divergence with flip but things get kinda unstable. I'm using only the point attribute, should I use a volume field as well somehow? Thx FLIP_Divergence_v0100.hip
  8. Advice needed for pyro sim

    Hi Guys, I am currently working on a shot where I need to simulate an object falling slowly through deep water whilst bleeding (The more blood the better). Initially I began with a pretty simple setup, An emissive object, a collision object and a divergence volume which is being used for expansion. The problem I am running into is that I need the smoke to continually expand, whilst becoming more diffused and transparent, but to always remain in the sim. So I have disabled dissipation as I don't want to lose density, but this leaves me with a dense volume which isn't transparent or diffused. I would like the density that is in the sim to have an aged based blurring. I did try to achieve this with a gas dissipate and heat field but this still wasn't right. I have also spent time trying to tweak the pyro shader to achieve the desired effect but I am not having much luck. Below is an example of the look I am trying to achieve. Between 0:21 and 0:34 Any advice will be greatly appreciated. Many thanks, Clive Blood_in_water_odforce.hip
  9. Fluid question: Gas compression

    Hi, I search and read a lot of post on google/ODForce without really finding a answer to that. I trying to see how I can compress a fluid correctly. Just to illustrate one case from many others , I try to compress gas with a piston in to a cylinder. I know Houdini is more a artistic tool than a fluid analysis software but there a way to make divergence, density and pressure interact correctly ... or what I thinking is a correct bihavior? In the example hipfile I attach to this post , I expect to see the density and pressure increased proportionnally to the changed volume of the cylinder by the pushing piston (SIM_Compress geometry at obj level). I figured out a lot of way to connect , inject , add , multiply combinations of density/divergence source without any good result ( "best" one attached to the post ). Somebody have a idea ? Thanks compression_test_v001.hip
  10. Hey folks, Does anybody know how to use the "Goal Divergence" and the "Pressure" in the "Gas Project Non Divergent"? Whenever I try to inject a field the particles go crazy. Would be nice to get something like a explanation or example file. Thanks
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