Jittery fluid sim stream

Hi,
I’m very new to Blender. I’ve been using it for a few months to edit drone footage and also to animate the 3D models I produce from drone photogrammetry. I’m trying to animate a sequence where a small dam gets removed from a stream in Yorkshire (UK). I’ve got drone flights before and after the removal and I want to use Blender for the fluid sim rather than a full on CFD code. Latest results are here:

Good things are that, with some faking of the slope and the gravity, the water stays in the stream. I’ve also figured out how to get the water to stop at the little dam (made it an outflow) and then I morph the dam and pull it under the surface. It works! The water breaks through. So my remaining problems are the jittery aspect of the water and the shading of the flow. For the jitters, the flow looks like it’s a timelapse shot. I tried to play with the time of the bake, but I don’t understand the use of seconds instead of frames? Does the fluid sim pull the frame rate when it runs? Any suggestions to fix this?
About the shading, because this uses a mesh produced from the drone data, the stream is a dark streak in the model. So I don’t think clear water would look right, anyway, this water should be a bit muddy. Any suggestions on what to do to improve the shading of the water?

Thanks
Pat

It looks like very low resolution meshes. Are you sure you are not rendering preview resolution instead of final high resolution ?

If it is not the case, you should to try to limit difference between X, Y, Z scales of domain and try to bake a fluid sim at an higher resolution.

be sure to set the fluid worlds “real world size” option to something appropriate, as it is at the moment it looks like someone spilled water on a model trainset :smiley:

the default fluid sim size is 0.5m meaning the fluid simulations domain size is half a meter in “real world” length.

if you set this value to something more appropriate , like 200m , it will reduce the apparent speed of the simulation, and should help with the jittteryness, keep in mind you probably will need to bump up the fluid resolution a fair amount as well. for a high quality large scale fluid sim like what you seem to be going for, it should probably take around 12 hours to bake on a modern PC… that’s a ballpark figure i plucked from thin air, but fluid baking on that scale is a very slow process so make sure everything is perfect before you leave it to bake overnight. and make sure its saving the cache to disk :slight_smile:

materials and stuff can be done later, but baking the sim should be done once… so measure twice (make sure its running at the right speed and stuff by doing a much much lower quality bake before bumping up the domain resolution to a much much higher value (400 for resolution wouldn’t surprise me)

:smiley:

its worth keeping in mind that a movie studio doing water simulations for blockbuster movies would typically break the simulation into as many smaller parts as possible and composite them together in post… it could be done here but you will have to be very creative in working out how to break up the sim while keeping it coherent.