Dennis Sedov Posted October 23, 2008 Share Posted October 23, 2008 I have dont a fluid simulation, that I am pretty happy with, the only thing I want is it to be 3 times slower, but following the same paths. Resizing, changing forces does not work, as the fluid blend together and looses all the detail created by noise fields. I am really ran into a wall, and don't know where to go from here rather then retiming rendered images. What I am trying to simulate is a wispy smoke that goes from a sewer on a street at night. So I have two problems - there is not enough "whispiness" and the simmulation is too fast for what is should be Any help would be much appreciated. Hip file is attached fluid_smoke6.hip Quote Link to comment Share on other sites More sharing options...
aracid Posted October 24, 2008 Share Posted October 24, 2008 Hey man Have u tried using the time scale on the dopnet ? not inside the dopnet but at obj level? Quote Link to comment Share on other sites More sharing options...
Dennis Sedov Posted October 24, 2008 Author Share Posted October 24, 2008 Gotta try that now. But I have tried doing a flip book with .5 stepsize, and every other frame was empty, so I assume that fluid sims don't scale like that. Quote Link to comment Share on other sites More sharing options...
Allegro Posted October 24, 2008 Share Posted October 24, 2008 the only thing I want is it to be 3 times slower Wow, and here we normally have people complaining that they want faster fluids Yes, you can try the time scale in your simulation to make things behave slower. The reason you wouldn't have had any frames in .5 because you probably aren't substepping while simulating (change the substep parameter on the dopnet to do this). Quote Link to comment Share on other sites More sharing options...
Dennis Sedov Posted October 24, 2008 Author Share Posted October 24, 2008 tried everything. I have increased substep, and whenever I tri to put Scale Time to 0.5 - fluids just go up a if there are no forces applied to it. Rendering a flip book with 0.5 timestep also produces weird results Like every fourth frame is blank Quote Link to comment Share on other sites More sharing options...
Dennis Sedov Posted October 25, 2008 Author Share Posted October 25, 2008 Any help? It is really weird that fluids dont scale, as everywhere I read, dop node's time scale is used to achieve "slow motion", but for some reason does not work with fluids =((( Quote Link to comment Share on other sites More sharing options...
mangi Posted October 25, 2008 Share Posted October 25, 2008 Hi there, well at there moment I am baking out the smoke sim , Its gona take a while , My idea is getting this into the chops. can't do nothing until the sim is complete . will give it a shot in the morning , it is 12 pm here in madrid. A while back there was a series of videos tutorials on the chops and you could do retiming , atleast with dop rbd's have you looked into this , cheers , I will try and do something in the morning , mangi Quote Link to comment Share on other sites More sharing options...
mangi Posted October 26, 2008 Share Posted October 26, 2008 (edited) Hi there. well i did bake the sim ran out of disk space. It looks like the chops , it's not a good idea as the dynamic node import is for the transformation. it was a while back that I looked at this. However, I did a simple sim and tried the Scale Timer 0.5 and Time Step 0.02 in the dop and was able to to some retiming as what allegro had mentioned. cheers. I will do some testing to see what the issue may be cheers mangi Edited October 26, 2008 by mangi Quote Link to comment Share on other sites More sharing options...
Dennis Sedov Posted October 26, 2008 Author Share Posted October 26, 2008 See - I have exactly the same behavior on a simple scene like this. Download the hip file I have attached with my first message and see the difference in how the forces are applied. I have several fans in the scene. So in at full speed I get the result I want. However, when I put the time scale at 0.5 the sim behaves as there are no fans or forces in the scene - the smoke just goes up. Before you play the sim down the size of the container resolution ( I have like 120 there) to 20 so you'd see the feedback and be able to make a difference between a full speed simmulation and the time scaled one. Hi there. well i did bake the sim ran out of disk space. It looks like the chops , it's not a good idea as the dynamic node import is for the transformation. it was a while back that I looked at this. However, I did a simple sim and tried the Scale Timer 0.5 and Time Step 0.02 in the dop and was able to to some retiming as what allegro had mentioned. cheers. I will do some testing to see what the issue may be cheers mangi Quote Link to comment Share on other sites More sharing options...
Allegro Posted October 27, 2008 Share Posted October 27, 2008 See - I have exactly the same behavior on a simple scene like this. Download the hip file I have attached with my first message and see the difference in how the forces are applied. I have several fans in the scene. So in at full speed I get the result I want. However, when I put the time scale at 0.5 the sim behaves as there are no fans or forces in the scene - the smoke just goes up. Before you play the sim down the size of the container resolution ( I have like 120 there) to 20 so you'd see the feedback and be able to make a difference between a full speed simmulation and the time scaled one. I think part of the problem is that you have $F as the seed in your noise. As soon as you add substeps, or scale the time you're going to have different results in your simulation because of this noise so offhand, I'm not entirely sure how you would get it to have an identical look, yet behave slower. I've reworked your file slightly however, and you can see that by multiplying your noise by the timestep, you can at least get identical results when either doubling the substepping or halving the timestepping (identical to each other, not identical to your original simulation) fluid_smoke7.hip Quote Link to comment Share on other sites More sharing options...
Dennis Sedov Posted October 27, 2008 Author Share Posted October 27, 2008 Thank alot! Now I see what I did wrong. Also replaceing $F with $FS would yeld similar results! Another question offopic. Is there a way to control amount of fluids generated? In maya you can set amount of density, heat and fuel generated per second. Is it possible to set in Houdini. I only found how to set up temperature, which just makes smoke go up really fast, but I'd rather set density. I think part of the problem is that you have $F as the seed in your noise. As soon as you add substeps, or scale the time you're going to have different results in your simulation because of this noise so offhand, I'm not entirely sure how you would get it to have an identical look, yet behave slower.I've reworked your file slightly however, and you can see that by multiplying your noise by the timestep, you can at least get identical results when either doubling the substepping or halving the timestepping (identical to each other, not identical to your original simulation) Quote Link to comment Share on other sites More sharing options...
Allegro Posted October 27, 2008 Share Posted October 27, 2008 Thank alot! Now I see what I did wrong. Also replaceing $F with $FS would yeld similar results!Another question offopic. Is there a way to control amount of fluids generated? In maya you can set amount of density, heat and fuel generated per second. Is it possible to set in Houdini. I only found how to set up temperature, which just makes smoke go up really fast, but I'd rather set density. If you convert your torus to a fog volume using an iso offset sop before sending it into dops as a source, I believe you can control the density that gets emitted with a volume mix or volume ramp sop. Quote Link to comment Share on other sites More sharing options...
Dennis Sedov Posted October 28, 2008 Author Share Posted October 28, 2008 If you convert your torus to a fog volume using an iso offset sop before sending it into dops as a source, I believe you can control the density that gets emitted with a volume mix or volume ramp sop. Nope - have not found that unfortunatelly. And there is nothing in the docs eather. Don't really want to do this with heat, as it becomes less controlable =( Quote Link to comment Share on other sites More sharing options...
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