kurzemnieks Posted January 26, 2015 Share Posted January 26, 2015 Hello! I'm quite new to Houdini - still trying to grasp some concepts. I need to create falling leaves simulation. I have been trying out different ideas but have some questions: 1. Is it possible to have normal/tangential drag (like in cloth objects) for RBD objects - to have some sort of aerodynamic effect ? I would like to use RBD to simulate a lot of leaves faster as I don't need soft deformations. Cloth sim gives very natural falling motion with normal drag active, but is very very slow for several thousand leaves. 2. I am creating my geometry using simple copy on scattered points and then doing Assemble to create individual leaf names. Partition to group them by name. Then feeding it all to DOP. The question is - what would be the best approach if I want to remove from simulation all the leaves which have reached certain condition - i.e. they have collided with the ground (or some other condition - i.e. leaf velocity is 0 for last N frames (For cloth it would be average velocity of all leaf points)). I need to keep the geometry around and render it, but I would like to remove it from Cloth/RBD simulation to speed things up. How are this kind of problems usually solved? Is it possible to remove objects/pieces from dynamic simulations? Quote Link to comment Share on other sites More sharing options...
kleer001 Posted January 27, 2015 Share Posted January 27, 2015 In the drag DOP the scale force and scale torque might be analogous to the normal and tangent drag in cloth, but I wouldn't think so. I would keep my leaves in cloth. I think you might want to use a sopsolver for that conditional managing, freeze, delete, etc. Quote Link to comment Share on other sites More sharing options...
Solitude Posted January 27, 2015 Share Posted January 27, 2015 The aerodynamic drag can work with the regular rbd solver, but it will probably be slower than the cloth solver. I don't think it works with bullet, however. In theory it wouldn't be too hard to implement since you can check the orientation in relation to the velocity to apply angular forces. I've yet to actually try it though. For the regular rbd solver, the sampling mode on the drag force set to circle will apply the drag based on the actual shape. I'd suggest adding a noise field as well to make it look good. http://www.sidefx.com/docs/houdini14.0/nodes/dop/drag#parameters Quote Link to comment Share on other sites More sharing options...
Artem Smirnov Posted January 27, 2015 Share Posted January 27, 2015 (edited) I think you can write your own air resistance force. Here is an example of where I've get so far... fakeAir.hiplc Edited January 27, 2015 by Artem Smirnov Quote Link to comment Share on other sites More sharing options...
kurzemnieks Posted January 27, 2015 Author Share Posted January 27, 2015 That is amazing, Artem - a bit too complicated for me to understand at first, but I will try!! Thank you guys for help. I will work on this and share the results. ps: there is a bug in H14 - forces are not working properly on cloth objects.. i.e. fan force not working, wind is very weak and noise is not working. The same scenes works properly ir H13. Wierd. Quote Link to comment Share on other sites More sharing options...
mawi Posted January 27, 2015 Share Posted January 27, 2015 Not sure it works with RBDs, but the pop propertys got a drag shape parameter that multiply drag in particles oriented frame. It wouldn't be to difficult to build your own if it doesnt work. Quote Link to comment Share on other sites More sharing options...
Atom Posted October 19, 2016 Share Posted October 19, 2016 So how would I add a leaf texture to these particles? I have replaced the box with a grid that has UVs and a Material but they still end up white when I issue a render. I have attached the texture set I am trying to leverage for this effect. ap_falling_leaves_fakeAir.hiplc Quote Link to comment Share on other sites More sharing options...
Atom Posted October 19, 2016 Share Posted October 19, 2016 (edited) Ok, after reading up a bit on PackedGeometry I can see that the Material node is not going to work in this case. Instead you must use an attribute wrangle or attribute create and create the path to the Mantra Surface as an attribute named shop_materialpath. Once you have done that you must also alter the Assemble node to let it know you want to transfer the shop_materialpath and uvs into the packed geometry. Once all that is in place Mantra can read the attributes and materialize the particles correctly. ap_falling_leaves_fakeAir.hiplc Edited October 19, 2016 by Atom 2 1 Quote Link to comment Share on other sites More sharing options...
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