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Found 33 results

  1. Simulating flip from bottle

    Hello everyone. Long time since last post here when i was dealing with the same thing. After watching some tutorials and learning some more in houdini i decided it was time to go back and see if i could get some better results. There is still some big questionmarks that im seeking answers for. Here goes. This is the simulation i want to do. Animating a beer bottle (prefferable in maya since i have a rigged character and i have made a animation that matches footage so i know that the animation is timed correctly and so on. The bottle will be pouring beer into a pretty standard glass. When i have a stable flipsim i would want to go on and simulating bubbles and foam. So on to the questions. 1. I have noticed some differences between using collision geometry made in houdini or imported geometry. Making the geometry in houdini seems to work much better for some strange reason. Can anyone confirm this? It seems that i get away with much higher settings on particle separation and gridscale then using similar objects imported from maya. 2. Scale seems very important here. Simulating in real scale gives a lot of trouble. therefor i scaled the bottle up so that it is around 1 meter high. However, this gives some problems when it comes to actually using the animation i made in maya. Everything in maya is done in centimeters and when importing it to houdini its way to big. I ended up matching the animation inside houdini from the imported file and used that instead. Wich is the best way to get around this? Usually in production everything is modeled in correct scale in maya. 3. Setting up the flip source. Is this the correct way? Import the fbx file with the bottle. --> create a new geo node --> create a box big enough to cover the bottle and up to the level where the liquid should end at the bottleneck. Object merge the bottle into this geo and connecting a boolean with subtract b-a settings. Then i blast the exterior so i have only the interior of the box minus the bottle. 4. In the bottle geo i have a transform and after that a null. i put the displayflag on the null and then create a deforming object from that. 5. finally i create a static object from the imported glass. Now all is setup to start simulating. ofcourse there is alot of tweaking of particle separation and collision settings to be done but overall is this a good setup? I can post a file if that helps. Finally some other questions. When caching out the flip to simfiles i only want the particles to be cached. where do i set this up? Regarding substeps, if i raise the substeps INSIDE the dopnet on the flipsolver will this generate more substeps when caching it out or is it only the substes on the dopnode that sets substeps in caches? Sorry for kinda of a long post but if anything can be answered i would be grateful! THX!
  2. I have a meshed FLIP sim (cached out, .bgeo files read back in) that I want to use as a "solid" object and have a rigid body rest on top of it (the idea is that something solid "ripples" psychedelically and the objects resting on top of it move as the ripples go underneath--but the original object is still a solid, and the objects don't sink into it). I just can't get it to hold up, however--when the RBD object is initially "dropped" onto the fluid mesh, it bounces and settles as expected, and does okay with simple early movement, but eventually the collisions become less and less precise and the RBD object just sort of sinks in. How can I get the mesh to read as just a run-of-the-mill deforming object? I've tried RBD solver, bullet solver (obviously doesn't work with the shape of the mesh), volume and surface collisions, jacking up collider volume resolution to make sure all the little waves are getting captured, and boosting the substeps, but the result has been pretty consistent (except more substeps = super jittery RBD as it's reading all of the little pre-big-movement mesh ripples). On the attached setup (a simpler version of the project giving me trouble) I even ran the meshed surface through a "clean" just in case any of the lingering velocity attributes were throwing it off, but that didn't help either. I'm wondering if the fact that the topology itself changes so much might be the problem, but if so I'm not sure how to fix that. Thanks for any suggestions! flipmeshtest.mp4 meshtest.hiplc
  3. Hi everyone, Can't get why the RBD solver doesn't take all the geometry generated with Copy to points. It only take the first object and ignore the others that coming in later. Also collisions don't work either even though it looks like it's setup correctly. Please, help! geo_collisions.hip
  4. 238/5000 hello, can anybody help me? I have a problem in this scene, I have a necklace that I want to collide with the body moving, at first it collides and becomes good, but when the body begins to dance, the necklace breaks and enters the body mesh. untitled.mp4
  5. Drooling Creature

    Hi there, I'm trying to use the condensation shelf tool to create a drooling saliva effect for a lizard. So far the results are... well, a little off: My main issue is that the rig isn't watertight and is composed of separate meshes that aren't closed and intersect, so the liquid is falling through the mesh although it does collide with it in some areas. I have the different components separated into groups: So my questions would be: 1. Any advice on how to make this mesh watertight for collisions 2. How to handle collisions from animated geomettry in the DOP network so that liquid doesnt explode everywhere and fall through its neck. 3. How to adjust the pop fluid settings to get long, thin strands of saliva I'll keep working on it and upload a hip file once I have done some more work. Still new to Houdini so any help or pointers are very much appreciated. Thanks, H
  6. How do pyro collisions work?

    Hello, Could anyone explain exactly how pyro collisions work? In some cases, it doesn't seem like collisions with the smoke solver are "real" when using moving colliders. It seems like 2 things happen when using an animated static object: 1. Takes the velocity from the collider and advects the smoke with it 2. Delete any density that goes inside collision object (can be disabled) Look at my gif. If I disable velocity from the collision nothings happens. The density just gets deleted. In the example I turned off correct collisions for better visualization. If the collisions were "real", I would expect the density to move when the collider moves, then stop once the collider stops since no velocity from the collider is being applied. Any ideas? smoke_collision_test.hip
  7. I'm having problems in my scene trying to have dust particles and rigid body "stones" attracting to a moving point in world space. I have the stones set up so they attract to a point and collide with a sphere which seems to work just fine, however once i start introducing the particles to the DOP network the stones start to get influenced by the particles and start to gain a high velocity whenever a collision is made. Any thoughts on how to make the stones velocity not be effected by the particles while still having them collide. ParticleCollision.zip
  8. Hi friends, I've been searching for this for a while but have come up empty handed. Is there a way to create a collision detection (frame) attribute for flip fluids. I am currently developing a splash element that requires the colliding particles to emit smaller splashes upon collision similar to what you see in this clip. The kicker is, I am doing this without a tank and hence cannot use something along the lines of a crown splash. I plan on taking the frame the flip particles collide with a surface, and copy stamp instance geo to those points and then emit through another flip sim. It sounds complicated and it has become so as the element takes shape. I would attach a file but the project is under non disclosure. Any help would be greatly appreciated. Thanks in advance.
  9. Is there anyway other than changing the "velocity scale" under flipsolver->volume->collisions to change the influence scale of an animated collision object with the FLIP fluids? I'd like to try and have a by-object control... I tried changing the velocity of the SOP that I am using as deforming object but with no effect...
  10. Hi there, I have been fighting with this for a while. I want to fill a geometry with a flip fluid but the geometry is watertight. the fluid is a stream comming from outside and colliding on the inside and filling up the geometry. one would think that inversed normals could do the trick but it doesnt seem to work that way. the other solution would be to disable collisions before the particles are inside the object. but i could not figure out how to disable the collisions per particle before they enter the volume. it seems like a very common problem but i could not find a straight answer anywhere. any suggestions? thanks
  11. Smoke interaction

    I would like to make 2 smoke sources to interact with each other. How can I set up my scene to make it happen? smoke.hipnc
  12. Random pop bounce direction

    Hi, I'm trying to achieve a simple effect, but am struggling to get my head around it. I'm sure I'm overthinking it but if anyone could help me that would be great! I'm trying to get a random bounce direction on particles when the collide with the ground plane. As if the particles were small stones bouncing randomly due to a bumpy road surface. I've attached a hip file with the basic setup. I was thinking maybe you could inherit a random vector as the collision happens, but couldn't seem to figure a way to do it. I know various sources have mentioned the old "gain normal" parameter, but this no longer exists. Any help would be much appreciated. odforce_randompopdirection.hip
  13. Hi people, I got some problem with color loss in my balls array attached to point box. Everything is working as intended until I transform my array to RBD Object. In my scene I would like to have balls bounce around and collide with everything but I would like to have some materials and distribute them randomly on them as well. Everything is working but color is lost inside Assemble node at the end in Attribute Wrangle node called : add_name_attribute. I have no idea what happens but this node is making additional groups from my balls and in the end there are many groups which I don't need. All balls are turning grey in viewport as well. If you could have a look I would be grateful. ajz3d_randomize_materials2.hipnc
  14. FLIP Collision and behaviours

    Hello, I come from a Realflow background where you adjust the collision settings like roughness and bounce within the menus of the object of collision. In houdini there are 2 places where I see the same settings, and I don't know if both of them affect the simulation (if not, then wich one?): FLIP Object -> Properties -> Physical. Static Object -> Physical. In Realflow there was a parameter that easily let me escalate the intensity of the collisions, meaning that some objects would create bigger disturbance and higher splashes (not affecting the global forces on the scene). In Houdini I thought the equivalent was Velocity Scale on collisions, and I tried to change the value to 0 only to find out that not much changed in the splashes generated by the collisions... Any idea how to achieve this difference in intensity? Thanks
  15. FLIP Spray not colliding

    Hello every one, I am doing a regular FLIP simulation where I have my particles colliding properly with a passive object. I have added a whitewater dopnetwork from shelf, and I re-created the collision setup in there. When I add foam and spray, everything goes as expected, but the spray just goes ballistic and completly ignores th collision borders. In the capture below you have an example of the overshooting particles (the ones making the correct form are the regular corefluid FLIP particles).
  16. Particle movement and collisions?

    Hey guys! I'm trying to make some floating particles inside a geometry. I need the geo to be a collision object and the particles to kinda have a buffer area before they touch anything, not very obvious but enough so nothing actually collides. However, I'm having trouble getting the particles to actually treat the geo as a collision object, and also stopping some of the random ones that like to go super fast. I thought that the popspeedlimit would the trick for the fast ones, however, it kinda clamps the whole speed of all the particles, rather than clamping the velocity of the fast ones. Anyway, here is the scene file with the alembic, if anyone has an idea of how to fix this please let me know! underwater_particles.009.hipnc blockoutForSim.abc
  17. Pyro Collisions

    Hi, I am dealing with some pyro collision problems. I have an explosion that is penetrating the roof collision shape. Part of the trouble is that the collision is fairly thin and the pyro sim is moving fast. I can make the collisions perfect by setting the substeps to a ridiculously high number, such as 10. What is a better way to deal with my problem other than high substeps? As you can see, most of the fire is colliding, but some seems to seep through. Thanks
  18. Pyro collision velocity leak

    Hello guys, maybe anyone knows why on pyro collisions, velocity still leaks? Density works properly, but not velocity. Maybe there is some simple checkbox or it's by design and I should delete those velocities by some advanced hacks? Any ideas? Thank you! collision_pyro.hip
  19. Dealing with FEM + Static Body

    Good night, people: I'm a newbie with Houdini. I've tried lots of tutorials but, I'm still having problems with collisions. I made a simple setup, a growing fem ball inside a static collider, but, it interpenetrates the walls of the static object. I tried to get more substeps, to have more detail in collision guides, but I'm not sure what I'm doing wrong. I attach the file that I'm working on. Thanks! testme.hipnc
  20. Partial collision detection

    hey, little problem here. I have a piece of cloth made out of grains. Its colliding with an object. Here I use a collision detection in combination with a collision behaviour. The collision detection shall only detect a few polygons of the whole object to stop the motion there. Referencint the polys in dops. Its giving me a correct collision guide but during the sim it keeps ignoring it. Insteat it freezes the grains along the whole 'main collision object'. So that are the areas to collide with, just a few squares.
  21. Hair Collisions

    Hi guys, I have a hair sim that im trying to do, i've got everything setup and working with the exception of collisions with other objects. The hair will collide with the skin surface, but im trying to add collisions with his clothing. I've created an external dopnet and merged in a static object (his coat). I've verified that the collision guide is accurate but i can't get it to collide with the hair wire object. Collide Independent and Collide Codependent are enabled on the wire object. Any help would be gratefully appreciated Thanks
  22. Sporadic Particle Motion Blur

    Houdini FX 15.0.313 Im working towards creating a stream of particles that hits two characters in the scene, mimicking water from a small hose at high pressure. Everything looks great in the view port but when I render the motion blur is sporadic and showing up as if the particles have very jittery motion when all they should be doing is travelling in one general direction. I tried using a trail node to generate velocity data but it doesnt seem to fix the issue. Any ideas as to what is causing this? Any way to get around it? waterSpray.hip
  23. Hi, Im working on a desert scene with a dust cloud blowing over some nice sand dunes geo. No matter what I do the pyro keeps clipping straight through the geo. The weird thing is this did happen with particles. Heres some of the things I've tried: Selecting the geo and making it a Static Object, Selecting the geo and making it a Terrain Object, Ticking the Use Deforming Geometry box, Ticking the Create Active Object box, Unticking the 'Use Volume Based Collision Detection' in the Collisions/RBD Solver tab. Changing Offset Surface from 0 to 1, 2 or 3. Im guessing there are some nodes that I will need to work with and connect up in order to produce a better collision but I do not know where to start. Any help appreciated, Thankyou Charlie
  24. Chain Links?

    Hello, I've been trying to create wrecking ball that I can use to smash into a brick wall. I made one using torus' and a big sphere. However, when I try to simulate it as an RBD packed object in a dopnet they just fall through eachother. Sometimes one will hold for a few seconds but it just falls afterwards. Does anyone have any advice? The objects are blue because collision geometry is on.
  25. Hi, folks. I need to set up a simulation where dynamically-generated arrows fly, then collide with a deforming surface and stay stuck to that surface (shields carried by moving soldiers). Importantly, the arrows should NOT just align along the prim normal on collision; they should protrude at the angle at which they collided. This is a topic that's come up before, but I haven't been able to find a satisfactory answer about it. Some suggestions don't quite hit all the elements I need; some are for older versions of Houdini and so might not be as relevant/accurate (I'm on H14). The approaches I've considered are: 1. Particle-based arrows that stick. It's easy enough to copy arrow geo onto a particle sim, and have the particles stick to the collisions surface. However, then the particles have to start inheriting the orientation of the collision prim as it continues to move. This could be handled two ways: The collision geo is deforming. In this case I'll somehow have to calculate how the collision prim has transformed from the moment of impact to the current time. The collision geo is transforming. In this case I'd use rivets to attach non-deforming stand-in geo to the moving collision objects (which don't change shape). Not ideal, but it might make it easier to work with the orientation values? 2. Particle-based arrows that create geo. Having already grown sick of the mathematical jungle of quaternions, matrices, and dihedrals, I wondered if a better approach might be to make each particle spawn some geo in the colliding object's network instead (presumably using a SOP Solver?) , then die. This would hopefully eliminate the need to continuously update orientation. 3. RBD-based arrows with constraints. Moving away from particles altogether, I wondered about using simple Bullet geo for the arrows, and dynamically creating constraints to pin them to the shields when they impact. An advantage of this method would be that it would allow realistic stick-like collisions and bounces for loose arrows--something particles can't really do. If anyone has any thoughts about which of these methods is most promising, or has any specific advice about how to implement them, I'd be extremely grateful to hear. Thanks in advance!
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