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Found 77 results

1. ## Physically accurate friction settings

Hi all, I'm trying to create some physically accurate bullet sims using real world values for mass/density and friction, so I've been looking at some engineering tables for friction coefficients: http://roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm What I'm confused about is this: It seems that real world friction is calculated based on the coefficient of friction between two objects, eg wood & wood has a friction coeff of 0.25 - 0.5; wood and concrete 0.62; wood and metal 0.2 - 0.6. So friction is not a material specific attribute, so if I have 3 houdini objects, one wood, one concrete and one metal, how do I create realistic friction settings for each combination when I can only set a single friction value per object? Is it even possible? Also, how does Houdini calculate friction coefficient between two objects? Does it multiply the friction values? Or average them? Any help is much appreciated Thanks in advance!
2. ## Houdini constraint make the simulation freeze ?

Hello, i am currently working on my final student projet where i make a plane crash with Houdini. I base the workflow of this project around the RIGIDS III tutorial by Steven Knipping. Everything is working fine until i bring in a simple glue constraint, and when the simulation gets activated at a said frame the simulation simply does not happen. It works when i disconnect/disable the constraint. I already tried to unpack the alembics upon importation with the alembic node but that didnt change anything. What is weird is that everything was working fine when i used the model given with the course. I haven't really found anything that helped me online, so hopefully one of you can help me with this issue, i would appreciate it A LOT. I will attach the files down below. Thank you ! plane_sim.rar
3. ## OpenCL Sim caching with multiple gpus

Hi, is there anyway to cache my pyro sim in opencl with my 4 gpu (4xgt1080)? i couldn't find any preferences on houdini or topic in search. Thank you.
4. ## Guided Ocean Layer SIM missing frames

I'm trying to sim waves lapping up onto large rocks jutting out of an ocean. The sim appears to be working. However, when I write out to a bgeo sequence, some of the files have low byte counts, and are correspondingly missing when you play them back. This was simmed on a machine with 24 processors and 20GB of ram. I'm going to try to increase memory to see if this fixes the problem. But it would be helpful if the hip file could write out more informative diagnostic information. How would one go about doing this? As the geometry rop doesn't inherit any log info from the source DOP. thanks devilsRock.waveSim.h16p5p378.v007.hipnc
5. ## adding turbulence to flip sim

Hey! What is wrong with my setup? I am just trying to use a source volume node to add turbulence to my sim. However, I can't get it to work! Any help would be amazing. Thanks, flip.hipnc
6. ## fetchdata DOP

Hi, I wanted to know if the 'fetchdata' dop can be used to fetch the data from outside the dop. I'm trying to fetch a cached particle simulation into my pyro sim but for some reason it cannot fetch the data outside the pyros DOP. If the particle sim is in the same pyro dop then it fetches the data.
7. ## Cable Overheating

Hi everyone, For an upcoming project, I need to create the effect of an extension cable overheating. ie. holes being burnt in the plastic casing of a wire and then smoke emitting from them. This is a good reference, particularly the shot at 1:26 https://www.youtube.com/watch?v=jGPkkOU3Uf8 The problem I am currently having is that for smoke to emit from these little holes, the source volume has to be really tiny. This requires a ridiculously low division size just to get the sim to work, making it impossible to easily preview the simulation. I'm thinking there must be a better method for doing this, so if anyone has any suggestions, I'd be happy to hear them!
8. ## Cache Optimization

Hi All! Are there any ways to optimise/reduce the file size of Houdini caches. I'm caching a (very small) FLIP fluid sim with a 'File Cache' Node at the moment and each frame is about 100MB. Multiply by 500 frames and that's a BIG cache! - not to mention the time its taking! I am sure it shouldn't be this large considering this is only a very small fluid sim so any tips would be great! I know a lot of people have this issue with sims so hopefully kind people can help us out! Thanks in advance!
9. ## particles Rain particles going through the ground

Hi! Houdini beginner here, I am trying to make a basic rain sim of rain interacting with an object and splashing on the ground making puddles. I am having a problem with the particles splashing on the ground, they are acknowledging that the ground is there but 50% of the particles splash against it but the rest go through it and splash just under it, i have tried using different things for the ground like a groundplane and geo but i keep getting the same problem. Any suggestions or help would be amazing! I Have attached the scene file if anyone would be amazing enough to have a quick look? Thank you in advance! Rain_001.hipnc
10. ## Guided Ocean Questions

Hi there, I'm learning how to make guided ocean layer sims and I have a couple of questions: 1 - I'm not familiar with caching system from Houdini. In my guidedoceanlayer_sim I have output name - \$HIP/sim/\$HIPNAME.`opname("..")`.\$SF.sim - first newb question, should I use .sim or .bgeo? 2 - I've copied that name and after saving to disk, I 've pasted as relative references under DOP Network - playback simulation. I should see the sim, but I only see last frame of the sim and a bounding box around boat 3 - Under Ocean Source wavetank I have this expression under center - centroid("../mergefollow", D_Z) - How can I add or subtract a value since I don't need so much detail in the front of the boat and need more at it's back I'm learning Houdini so please be gentle. Thanks!
11. ## Render pyro sim with multiple smoke objects or source volumes separately?

Hi there, quite new to Houdini and I'm struggling to find documentation for something like this. I have a scene with a building where there are multiple fires starting at windows of varying sizes. This means I have different source volumes (fuel & temp, and a pump) for each window. I want to be able to render the pyro from each window separately and perhaps even have dynamic resizes for each source. The only way I could imagine doing this would be if it was possible to have multiple smoke object nodes that can reference different source volumes (the fuel & temp, and the pump). I saw that clustering exists but from what I understand it only accepts point sources? I am using a fluid source node building SDF from geometry to create the source volumes. What would be the best way of doing this? Thanks in advance and apologies if this has a very simple answer.
12. ## RBD Fractured Obj with FLIP?

Hello! I'm doing R&D for a project that will involve and egg breaking, releasing the yolk/white. Right now I'm just trying to get the principles down. I am currently just testing fluid inside an egg (making sure it stays inside when it's supposed to and falls with the egg in gravity) and am having issues with the fluid disappearing or leaking from the egg. I am used to using rbd packed objects for destruction so I started out my workflow with the egg as an rbd packed object, but saw some examples on here that suggested using an rbd fractured object so I have tried that as well. When I use the egg as a packed object, the fluid seems to just slowly disappear over time, and when I use a rbd fractured object the fluid sticks to the eggshell on the second frame and then flies out. I know the eggshell is thin geo for being a collision object (it is accurate to a chicken egg), but even when I thickened the geo I still had fluid disappearing. Any advice regarding using fluid inside rbd objects would be appreciated! egg.zip
13. ## "Upres Pyro" CPU not calculating SIM

Hello guys, when i upresing pyro sim, CPU not calculating sim. it's spending 9 hours only 7 frames. i'm using Explicit Caches. Cached frame file size is 3GB. i don't know what should i do. Help me guys. Sorry my bad english....
14. ## Detailed cloth?

Hey magicians, I saw a cool animation and I was wondering how to achieve this effect, is this made with cloth + constrains?, love the detailed look on the rugosity, any tip will be great! Thanks!
15. ## Slow down a Particle Sim for certain frames and then resume in normal speed.

Hello Pals, Hope you all are having a great year so far. I am trying to do a shot with particles which needs slow motion on a certain camera moment. Basically, I just want to slow down the motion of my particles for few frames. I dont want to mess with the velocity etc as I really like the motion of my sim. I looked into time-shift, time-warp etc. But they always feel like a cheat and not much of a high quality solution. There is a "Scale Time" option on the POP net. But for some odd reason its locked and we cant key-frame it at all. That would have been the best solution, where we can just lower the timescale for bunch of frames and then resume it in normal speed. Can anyone just give me a brief why Sidefx would want to make this such a big deal and lock it on POP nets? Thank-you and have a great day! HD
16. ## Fur Sim Issues with Scale and Settings H16

Hello, Using the latest version of Houdini 16.0.736. What is best scale to simulate fur on female jacket. Should I simulate real-world scale or scale it up very large for better fur simulation performance? For Example, should the fur coat match the scale of the test geometry like rubber toy or pig head? Should it be scaled to 2 meters or 200? I want to master the scale before tinkering with the Fur Sim settings. Otherwise, does anyone have dynamite fur sim settings for a specific scale? My sims either seem very static or dramatically broken with stretching fur. Thank you, Ryan
17. ## Flip Fluid Compression

Hello, I was wondering if anyone had any suggestions as to why my flip fluid sim seems to "compress" as my container moves. Any help would be appreciated. Thanks!
18. ## Flip Fluid Collision Problems

Hello! I am having a problem with collision for my flip fluid sim, frame 2 for some reason a chunk of particles falls through the bottom of my "cup" I've checked my collisions on my "cup" and I've also tried adding a sub d node in my tree. both didn't have any result. Also, as the sim continues my particles pretty much all disappear. I'm pretty new to water sims so I'm not really sure the problem. Thanks!
19. ## Best/most optimal way to load your packed geometry onto simulated points?

Hi, So I made an rbd sim where I had only 200 unique pieces. Then I made an rbd sim using 100s of each of these pieces. I cached the simmed points. After this, I want to place my unique pieces onto these points. What's the best and most optimal way to do this for the viewport and the renderer? I have seen many different techniques, I can't tell which one is the best. Should I just use Instance SOP? Should I save the first frame of the sim and use this instead? I can transform them using Transform Pieces SOP, but I don't know how to bring them optimally. Should the pieces be brought it as packed geometry, packed fragments, packed disk geo, or something else? I want Houdini to know everything is coming from these 200 unique pieces so it can show them more efficiently in the viewport and the renderer. I noticed if I save my pieces onto separate files as packed fragments, Houdini is saving the entire packed geometry onto each file that takes a lot of space. How do you do this? Thanks
20. ## two objects in a granular solid sim

I'm trying to set up two pig heads in a grain sim that collide together. an extension of the grainular solid example in Jeff Lait's h15 grains masterclass. in stead of one pig head i want to wire in two. I've set up two pig heads (skipping the bone group part for now) see attached file. Jeff shows how to override the P and v with from an animated version of the geo with a wragle. I've set the dop net up the same way with two sources. however for some reason one of the P values apparently collapses to 0. if i switch the merge order it switches which source goes to 0. see attached file. I'm obviously missing something here. help would be appreciated. twosolidpigs.hiplc
21. ## Gas Match Field (with field from different objects)

Hi I'm new to Houdini and recently I've been getting into DOPs. I have a question I've been trying different things out in dops to see how they work, been playing around with the "Gas Match Field" node and found that it works quite nicely when both fields you are supplying the node with are from the same object Like on picture 1, both the "myField" field and the "heat" field are part of the same object and the node works just fine But what I can't figure out is how to make the node work when I'm supplying it with fields from different objects. On picture 2 "myField" is part of an empty object and the "heat" field is part of the smoke object, I tried to reference them via their paths like on the picture 2 but unfortunately it doesn't seem to work. Does anyone have any insight into why this may be, I can see how referencing field from different objects can come in handy not just for this scenario.
22. ## FLIP sim refraction rendering artifacts

Hi all, I'm getting strange artifacts rendering a flip simulation with the PBR shader set to glass preset. As you can see there are lots of flickering and some features of the mesh even go in and out. If refractions are turned off the problem disappears, however the desired look is no longer achieved. The problem is not present on other presets such as gold, etc. Im guessing this has something to do with how the particlefluidsurface node meshed the sim, being inconsistent with the inner features or something like that. Is this a known issue or something anyone have come across? Can you think of anything to help me resolve it? Thanks in advance, Glass_Test_s.zip
23. ## Gradually switching between sim and animation

Hey there, how would you go about changing the animation/simulation state of e.g. a cloth sim? I tried the pin to animation attribute to release the cloth object from the animation; but bringing it back to follow the animation is harder. it just snaps into place when I put the attribute back to 1 in the sop solver (dops). Also does anyone know a way to mix between animations and simulations? Lets say the cloth object is meant to somehow follow the movement of a master object but also should react to some forces. Or in other words: object is moving fast = animation state; object suddenly moves very slow = simulation state; objects moves out of the frame again = smoothly go back to follow an animation. The pin to animation attribute isn't allowing 0.5 values or so.
24. ## Controlling particle count per voxel

Hi there, I'm trying to control flip particle count per voxel. The idea is to evaluate particle count per voxel on every step (Gas Particle Count) and then analyze the pcount field.. If pcount > n - delete some of particles (pcount - n) to make n numbers. And if pcount < n - add (n-pcount) particles. Any help is highly appreciated. Thanks,
25. ## SOP GEO - FIELD FORCE - BULLET

Hey guys, working on a destruction peice and wanting to take the velocity from my charachter and put it into my bullet sim - So decided to try and use a sop geometry node to bring in the calculated velocity (from a trail and fluid source) - which is working perfect. But my sop force doesnt update each frame, its static - ive tried changing the expression from \$T to \$F and other things, not sure if its a limitation or if im doing something wrong? i will attatch a file but will be missing the geo but atleast you guys can see the setup Any help would be great! Thanks Destruction_v3_t2.hip
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