art3mis Posted October 22, 2016 Share Posted October 22, 2016 Hi Trying to create a very simple simulation with a torus falling into a FLIP tank. Instead of trying to add a buoyancy force to the torus I want to simply change the gravity when the torus impacts the water, so it will still sink, but at a much slower speed. Much googling and checking the DOP references turned up nothing but came upon a reference in a book Houdini on the Spot which I think is the right direction. The solution is to use dopnumrecords within a Modify Data DOP like so dopnumrecords("/obj/dopnet1", "objectname", "Impacts","Impacts") where you would use the name of the object you wanted to test instead of objectname and the name of the DOP network for dopnet1. Being a newcomer to the world of DOPs I am stumbling in actual implementation. Can any DOPs experts possibly help with my attached .hip? 10.19.16_DropClock - Copy (2).zip Quote Link to comment Share on other sites More sharing options...
Atom Posted October 22, 2016 Share Posted October 22, 2016 (edited) Changing gravity will also affect the splash portion of the fluid as well. You may want to simply add a buoyancy force to affect the RBD objects. This image shows the setup. The fetchdata1 gets it's input from the result of the fliptank surface. You can also preview the surface as well. Buoyancy force needs large numbers to have affect. In this animation I have used 3000 force in the Y axis. This causes the torus to raise back up quickly, out of the fluid, where it is no longer affected by the buoyancy force. But then gravity takes over and it falls into the fluid again. ap_dropClock_008.hiplc.hipnc Edited October 22, 2016 by Atom 3 Quote Link to comment Share on other sites More sharing options...
galagast Posted October 22, 2016 Share Posted October 22, 2016 Hi, here's an alternative method. I added notes inside the hip file. RED: Current movement. BLUE: With drag force after entering water. I also added a simpler version, where instead of reading the fliptank's surface field. I simply create a custom Scalar field with manually-set size and dimensions to be used by the drag. dropClock_008_jlim.zip 1 Quote Link to comment Share on other sites More sharing options...
art3mis Posted October 22, 2016 Author Share Posted October 22, 2016 (edited) Wow..thanks guys. this make my weekend! One gotcha I'm noticing with the buoyancy method is that Particle Separation, Buoyancy Force and Feedback Scale seem to be interdependent. Changing one affects the others. Edited October 22, 2016 by eco_bach Quote Link to comment Share on other sites More sharing options...
galagast Posted October 24, 2016 Share Posted October 24, 2016 Yeah, Feedback Scale seems to be largely affected by the Particle Separation. Particle Separtion: Varies Water Desnity: 1000 Ball Density: 500 Looking at the comparisons above, I suppose it's safe to say that a minimum separation of 0.1 would get you roughly the same result as a separation of 0.025. 3 Quote Link to comment Share on other sites More sharing options...
art3mis Posted October 24, 2016 Author Share Posted October 24, 2016 (edited) Great test! Even more surprising to me is the extra level of detail when going from .05 to .025! One parameter I've been ignoring is density. How did you come up with those values? I want objects to sink. S L O W L Y Does this mean my ball or torus density must be equal to or greater than the water? No buoyancy force in this example? From quick tests I've surmised buoyancy force is somewhat interchangeable with feedback. and I've found altering timescale on the solver seems to affect feedback as well Edited October 24, 2016 by eco_bach Quote Link to comment Share on other sites More sharing options...
galagast Posted October 24, 2016 Share Posted October 24, 2016 Quote One parameter I've been ignoring is density. How did you come up with those values? I did multiple tests to find a value that would make the ball float Quote Does this mean my ball or torus density must be equal to or greater than the water? I suppose you'll need to set the density of your torus a bit lower than the water for it to slowly sink. Any density greater than the default 1000 might make it sink faster. Quote No buoyancy force in this example? Yup, didn't use buoyancy on those tests. Quote Link to comment Share on other sites More sharing options...
art3mis Posted October 24, 2016 Author Share Posted October 24, 2016 And forgot to ask, feedback scale, was it 0 or 1 or? Quote Link to comment Share on other sites More sharing options...
galagast Posted October 25, 2016 Share Posted October 25, 2016 Feedback Scale is set to 1 Quote Link to comment Share on other sites More sharing options...
art3mis Posted October 25, 2016 Author Share Posted October 25, 2016 galagast...your test needs to be in the wiki and or documentation! Extremely frustrating trying to simply slow down a FLIP sim. I'm using a timescale vlaue of .1 on the actual solver node inside my AutoDopNetwork but when I try and go even slower by changing it to say 0.05, the entire look of the sim changes! Feedback, Buoyancy, Particle Separation and Timescale all seem inter connected. Change just one and the others are affected! Also confusing is the use of "Scale Time" and "Sub Steps" on the actual AutoDop node. How are these different and or connected with the similarly named parameters inside on the solver node? Quote Link to comment Share on other sites More sharing options...
galagast Posted October 26, 2016 Share Posted October 26, 2016 That's interesting Jim, I haven't honestly played around timescale yet. I'll try and do some round of tests with it this weekend Quote Link to comment Share on other sites More sharing options...
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