I need help with realistic fluid simulation

Hi all
Here is the story. I’m a complete noob in bledner, with only basic knowlege of Maya. Blenders interface and comunity tutorials taught me how to do fluids in 3D, cool.
BUT!
The real problem is I have to make this shot of a drop falling on the surface of water for my diploma work at art academy.:eyebrowlift2:
In two days I managed to get a basic understanding for the parameters in fluid simualtion and have setup a scene for this drop simulation. I understand that domain resolution is crutial, I already had blender crush because of too high resolution :eyebrowlift:
I made a simulataion in low res to see if it is violent enough for my purpose then when i was happy with everything I baked it it lasted around 2hrs it had res of about 200-250 and took 300mb of memory, which is ok i supose, baking proces went to the 190th frame just as I set it up, I saw blender calculating all the phases of the splash, then when it was all over and i tried to replay it it stopped at frame 83 (a moment before drop touches the surface) cursor in timline goes to the end at the frame 190 but animation stops at frame 83…
Is it a bug???, nothing crashed, directory where bake files are stored clearly has all 190 frames, but it seems that blender doesent read them all. What to do? I don’t know how to “reimport” or “reload” those bake files if it is posible.
Can somenone help me?
btw I think I’ll be posting questions in this thread all through the process of getting this scene, I didnt even come to the rendering think I’ll need help with it too, but first things first.
Thanks everybody in advance!

ps how can i make my scene look like a highspeed camera scene, will changing fps parameter make fluid simulation look like it is shot with a highspeed camera once i import rendered frames into some compositing software and play them at normal fps?

What do you mean exactly it “stops” at frame 83? Does it simply lag while playing? If this is happening right before the drop hits the water, you might be looking at the difference it takes to render (to your screen) a very different vertex count. Try running the animation in wireframe with the display qulaity (on the fluid tab) set to “Preview” and see if it helps.

I’ve spent a considerable amount of time testing the limits of my computers by seeing how complex a simulation I can bake and render before it crashes. What I can recommend, is making the domain as small as possible for what you absolutely need, and then just start cranking up the resolution until Blender crashes (or your computer)

Also, I believe turning the “start time” to below zero, should make the simulation start…before it starts… so basically you can make it start really doing the hard work only just before the drop hits the water.

thanks guys we’re getting somewhere.
To bugman:
I dont think its lagging, it goes like this I replay it it it goes to frame 83, the cursor in timeline goes further but nothing happens to the drop it just keeps displying frame 83, preview is set to preview (a lo res mesh), anyway i recon if it is lagging it should show any single frame while playback is paused, and it does to all frames before 83rd. And yes I’m previewing it in wireframe.
To J09:
There are few thing that are realy bugging me abut this whole thing, you mentioned some.
1st
What do you exactly mean by small domain? should it be small on the grid or should it be small in “realworld size” parameter? I dont dig this realworld prameter, to me it should be like a realy powerful parameter if i set it up to to be like 0.5m and the viscosity is set to water, and make a sphere roughly the size of a real drop to me it should look like a real drop but it seem it does not, because resolution is a key factor, that makes viscosity and realworld size almost irelevant.
2nd
can you please tell me some more about this:
“Also, I believe turning the “start time” to below zero, should make the simulation start…before it starts… so basically you can make it start really doing the hard work only just before the drop hits the water.”
does this mean that seting the start time in domain tab to let say a frame before drop hits the water should make blender somehow skip simulating drop falling through the air? if so it will actualy have to calculate the fall but won’t create the mesh?
3rd
i’m completely confused with the way some values are written in blender UI, for instance start and end frame im domain tab in fluid simualtion are writen like this 0.00
why puting a dot between numerals?? It woulkd be cool if it was writen in timecode format but it isnt 2.50 actualy means 250th frame
4th
linked to the 3rd after posting my original post I actualy baked a relatively hi res simulation it lasted like 12hrs i replay it and realise that drop hitting water actualy takes only 3 frames and the rest cca200 frames are just still water :smiley:
how to make a slow motion looking fluid simualtion??? will changing the fps value in scene panel make any difference like in realworld (when you record such things with highspeed cameras) or is it done differently.
5th
I want to make my drop hit the water realy hard with alot of secondary drops, should i change the viscosity? or will changing the resolution do?

once again thanks in advance

Hmm. It sounds like the simulation meshes for 83 on are not correct. You say you saw it actually simulate those frames?

u exactly mean by small domain? should it be small on the grid or should it be small in “realworld size” parameter? I dont dig this realworld prameter, to me it should be like a realy powerful parameter if i set it up to to be like 0.5m and the viscosity is set to water, and make a sphere roughly the size of a real drop to me it should look like a real drop but it seem it does not, because resolution is a key factor, that makes viscosity and realworld size almost irelevant.

Realworld size actually will only affect the speed of the fluid’s movement. Bigger realworld sizes will move more slowly. You’re right also that domain size makes no difference, at least in a way. The resolution divides the longest edge of the domain. What this does mean, however, is that non-cube shaped domains have fewer voxels (since voxels are cube shaped and the number of them is dependent on the longest edge). So basically a more oblong or flattish domain will be more efficient domain if your simulation doesn’t require a cube. [/quote]

can you please tell me some more about this:
“Also, I believe turning the “start time” to below zero, should make the simulation start…before it starts… so basically you can make it start really doing the hard work only just before the drop hits the water.”
does this mean that seting the start time in domain tab to let say a frame before drop hits the water should make blender somehow skip simulating drop falling through the air? if so it will actualy have to calculate the fall but won’t create the mesh?

You can’t set the start time below zero. Zero is the point at which the fluid starts to “flow” from the fluid mesh. Normally, the first frame is where this happens. If you set this to later, then the first frame will begin at what the shape of the fluid would be at the later time you set as start time.

3rd
i’m completely confused with the way some values are written in blender UI, for instance start and end frame im domain tab in fluid simualtion are writen like this 0.00
why puting a dot between numerals?? It woulkd be cool if it was writen in timecode format but it isnt 2.50 actualy means 250th frame

No, it means 2.5 seconds of “realworld time”. Think of dropping a rock in a bucket. You’ve got about a foot of water. You drop the rock. The water splashes. In a half a second the splash reaches its apex. The time depends on the size of the bucket (realworld size). The default time for fluid simulation is to start at the 0.00 time (read zero point zero) and go to 0.30 (just under one third of a second). The default realworld size is about 3 centimeters. So by default, you’re looking at the amount of movement a 3 centimeter square bit of water makes in 1/3 of a second. This is independent of the number of frames you are animating over. Since the default there is 250 frames at 25 fps (10 seconds) you’re looking at the water slowed down a factor of about 30 times by default.

4th
linked to the 3rd after posting my original post I actualy baked a relatively hi res simulation it lasted like 12hrs i replay it and realise that drop hitting water actualy takes only 3 frames and the rest cca200 frames are just still water :smiley:
how to make a slow motion looking fluid simualtion??? will changing the fps value in scene panel make any difference like in realworld (when you record such things with highspeed cameras) or is it done differently.

Maybe I already answered this last question. Basically, consider the time between the Start value and the End value the number of seconds of simulation time, and the number of frames/fps the number of seconds of “screen time”. If the screen time is longer than the simulation time, you’re going to see things in slow motion. Again, the “realworld size” makes a difference here, because if you’re looking at what is really a square centimeter, it is not going to seem slow motion if you are expecting it to behave like a 10 meter cube.

I want to make my drop hit the water realy hard with alot of secondary drops, should i change the viscosity? or will changing the resolution do?

once again thanks in advance

For this, add a non-zero Generate Particles value on the Par tab. Experiment a bit, but this will be the best way to do this.

Sorry I don’t know the solution to the original problem though.

By the way, there’s an extensive chapter on this stuff in the book in my sig, if you’re interested.

thats right I’ve seen it simulate those frames, but to heck with it… i made another one it was probably some one-time bug.

I understand this now thanks buddy! it somehow hints that because there can be no higher scene FPS tahn 120 relworld size coul efectivly make my simulatiom slower and therefore more “high-speed-like”?

I understand that now thanks to you it was bit confusing at first

its time for me to bake something :wink:
be shure I’ll post something as soon as i get it right, the whole thing is much clearer to me now. I think that these things you just told me are missing in those resources that I found so far, If everythings works as you said if you dont mind I’ll try to add them to some wiki tutorials on blender :smiley:

as for the book I am an audio specialist, I also do 2d and compositing. 3D was always a bit too much for my free time but it seem somehow that blender is starting to get under my skin :o

thank you very much, keep an eye open for some results!

Uh! I wrote a lenghty reply it somehow got lost, in short Bugman thanks alot It’s all so much clearer now, I’ll post as soon as i get some results, till then cheers mate!