sebkaine Posted May 12, 2015 Share Posted May 12, 2015 (edited) Hi guys , i have to do SPH like liquids with surface tension that help to keep cohesion beetween particle. as i am doing this in H i prefer to use FLIP. but we don't have this tension parameter in FLIP. i would like to know if divergence could be use as an alternative. i am not sur i have perfectly understand divergence but from what i get. - FLIP is by default non divergent so each voxel tend to modify his pression to respect this rules - you can hack pression in your fluids by playing with divergence - if you put a positive value your fluid will tend to push outward and make your fluid explode - if you put negative divergence it will push inward and in theorie help keep cohesion is that correct ? and if yes can we use this as a B-Plan for surface tension. i haven't find any exemple or precise info in the doc about how to use it in practice. any advise on the subject would be appreciated ! Cheers E Edited May 12, 2015 by sebkaine Quote Link to comment Share on other sites More sharing options...
anim Posted May 12, 2015 Share Posted May 12, 2015 ..- if you put negative divergence it will push inward and in theorie help keep cohesion.. not quite in a way you would expect, it will simply loose the volume and possibly disappear have you tried Sergei's asset? http://www.orbolt.com/asset/vosiloB_%3A%3Aparticle_surface_tension%3A%3A1.0 1 Quote Link to comment Share on other sites More sharing options...
sebkaine Posted May 12, 2015 Author Share Posted May 12, 2015 Thanks Tomas ! very cool link i didn't know this asset i'm gonna check this ! After testing divergence you are right , it's more like a swiss army knife tool that you can use for certain ponctual things but basically you hack your pressure grid and you loose volume cohesion. Could be cool for pyro explosion i guess .... Quote Link to comment Share on other sites More sharing options...
anim Posted May 12, 2015 Share Posted May 12, 2015 ..Could be cool for pyro explosion i guess .... yes, for simulating gas expansion or vacuum suction for volumes, playing with divergence is essential there is as well quite handy tool in Populate Containers shelf, Expand From Objects, which allows you to easily source positive or negative divergence to your sim 1 Quote Link to comment Share on other sites More sharing options...
sebkaine Posted May 13, 2015 Author Share Posted May 13, 2015 (edited) i have test Sergei asset , it's interesting but it's not surface tension like in sph. it's more like a point proximity attractor cause at the end you have only small spherical agregated point. what i need is some true surface tension. basically for each point of the flip sim - for each point you evaluate all neighbour under a certain threshold distance - for each neighboor under this threshold you create a spring connection - you define the stiffness factor beetween each point the goal is to keep both - the dynamics - the cohesion like in Realflow I don't know how to efficiently attack those kind of problem in H. Edited May 13, 2015 by sebkaine Quote Link to comment Share on other sites More sharing options...
sebkaine Posted May 13, 2015 Author Share Posted May 13, 2015 (edited) i find this http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=25343 by Jeff Lait in the text : The problem with the SPH elasticity is that it was some stiff forces that required a higher order integrator to be stable.It is possible with a lot of node surgery to get them to work with FLIP - Nick had them working here with the old FLIP Solver. You have to open up the FLIP solver and wire into the gas integrator a force-update version of the elastic forces.I think the right way for viscoelastic for FLIP is with the Gas Strain Force & Gas Strain Integrate style approach, as per "A Method for Animating Viscoelastic Fluids". You'll have to move the strains between particles and fields in a sensible way.We've not had a chance to experiment ourselves with this to see how it shakes out, however. But in theory all the nodes are there. Edited May 13, 2015 by sebkaine Quote Link to comment Share on other sites More sharing options...
anim Posted May 13, 2015 Share Posted May 13, 2015 I feel like you are talking about 2 different things viscoelasticity is completely different from surface tension Sergei's asset is pretty much what surface tension is a force acting toward surface, he is using actual surface SDF of the flip to generate that source. The problem with that is that that kind of surface is many times not precise enough and can cause unballanced forces that break up your sim more than they should, so it really depends on what kind of shot you have and how well you can tweak it (you can as well try using Gas Surface Tension DOP, which has as well it's faults) However I fully agree, that there is a need for high quality surface tension solver for FLIP Quote Link to comment Share on other sites More sharing options...
sebkaine Posted May 13, 2015 Author Share Posted May 13, 2015 (edited) Thanks for your answer Tomas ! You are right i must be confusing surface tension and viscoelasticity ... to be honest i don't know precisly the difference ... I need to get similar behavior : Basically paint behavior ... Edited May 13, 2015 by sebkaine Quote Link to comment Share on other sites More sharing options...
sekow Posted May 13, 2015 Share Posted May 13, 2015 (edited) I am pretty sure that those examples do not make use of surface tension like we all are eager to have one day, instead using the sheeter demon to fill out gaps, like sergei tools does very well. Ive come very close to believable splashing paint by using a bit viscosity, gas surface tension dop and the gap filling technique by sergei. and some clever custom forces to shape that crown/ tendrils. Edited May 13, 2015 by sekow 1 Quote Link to comment Share on other sites More sharing options...
sebkaine Posted May 13, 2015 Author Share Posted May 13, 2015 (edited) Thanks Sebastian ! i have find many tools here and there to help making those nice viscous stuff i can centralise them here : - sheeters deamon to feel the hole by pavel : http://forums.odforce.net/topic/18111-flip-smorganicsheeter-effect/page-3?hl=smorganic - surface tension by sergei http://www.orbolt.com/asset/vosiloB_%3A%3Aparticle_surface_tension%3A%3A1.0 - viscoelastic behavior by johner http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=25343 - stick liquid to object by alejandro https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=137275#137275 well i think that by combining all those stuff i will be able to get the job done ! Edited May 13, 2015 by sebkaine Quote Link to comment Share on other sites More sharing options...
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