Unwanted "strings-like" effect in fluid sim

[lazza79]

Hi Guys,

I noticed that my simulation generates some "string-like" agglomerates of water that act weirdly.

As you can see in the video and in the screenshot, these strings are generated and they remain almost intact until they fall together.
I would expect them to separate or act in a more "random" way...

Is there a way to avoid the formation of these effects? How can I prevent/limit them?

Thank you for your help!
Cheers!

Andrea

untitled.mp4

Edited May 14, 2016 by lazza79

[Zybrand]

Hi Andrea,

In my experience FLIP has always had an element of stringiness to but there is some stuff you can try to help minimize it. I don't know what your machine constraints are but just lowering the the particle separation will help, its hard to tell from your clip but it looks a bit lowres to me. You can also play with the droplet detection settings on the particle tab that can help break up the splashes a bit more. And lastly if that sup is smashing through the water quickly you could add an extra substep to solver the collisions a bit better.

Hope that is helpful.

cheers

Zybrand

[lazza79]

Thank you Zybrand.

You can see the speed of the submarine in the video I attached in my previous post.
The sim is in fact low res 0.08 because I am still in the set-up phase.

What you mean by playing with the droplet detection? Right now my droplet setting are the default ones ( min 0.5 - max 1 - blend with fluid - velocity blend 0.2)

Anyway, right now I am re-simming everything since I have raised the velocities on the lower front part, in order to have more forward-oriented splashes

Cheers!
Andrea

[Zybrand]

OK well then you can expect it to get better and less stringy as you upres after you set-up phase. On a lowres sim there is very little detail in the underlying velocity grid so it wont advect the the particles with much variation.

About droplet detection I meant test different min ma density settings. Here is an example of some droplet settings Igor tested: https://vimeo.com/99057854

Cheers,

Zybrand

[lazza79]

Unfortunately I am still having these strings.

Can these being caused by having set surface extrapolation to 0.7 (default 0.5) and velocity smoothing to 0.5 (default 0.1) ?

My sim resolution is 0.065 and tank is 42x68

I see that Igor's part sep is way higher than mine (0.15) so I think my problem is elsewhere

Cheers,
Andrea

sub_v21.mp4

Edited May 20, 2016 by lazza79

[Zybrand]

Don't think surface extrapolation would cause that. The velocity smoothing is high though keep that at default for now.

Well particle separation is relative to the size of your domain so you can't just compare 0.065 with 0.15. Igor's domain is a lot bigger so there will be more voxels and particles even with 0.15.
 You can test it for your self scale your domain up to be double the size but keep the separation the same and see what happens.

Any chance of sharing a .hip file? would be easier to find a solution if the setup is clear.

Cheers,

Zybrand

 

[lazza79]

Sure!

Find the setup attached.

sub_tests_AL.hip

alembic_sub_anim_3.abc

[lazza79]

My friction is also quite high...

[Zybrand]

Hi Andrea,

Had a look at your scene and I think you can get better result not using the splash tank setup you currently have there. I made an example setup for you with a flat tank and a optional velocity volume if you need waves. Then I made some changes to your collider like adding timeblends so you get the correct sub-frame positions for your collisions. I only ran a very lowres test on a few frames to make sure everything works so you will have to run the sim your self to see if the results are what you are looking for.

cheers,

Zybrand

sub_tests_AL_zy.hip