Few Questions

[hstone2003]

Hi, I’ve only just started using Phoenix so still trying to learn all the right settings of what to do and what not to do.
I’ve been testing out a scene with a simple cube dropping into the ocean and creating splashes and foam. It's almost there however there is just a few issues that are bothering me...

1. Default settings for conservation is set to “Symmetric” When I was playing with the 2.1 demo the default was “Smooth” Which would be a better option to use?
The issue I’m having is that with Symmetric, the stability of the ocean is really good, however when the cube hits the ocean there are a few crazy splashes that always shoot outside the grid. It’s a very unnatural splash. (only with a few droplets) but the good side is the ocean seems to calm down and settle. I changed conservation to smooth and the now the drops/splashes work perfectly however the grid does not settle. It ripples a lot. Any idea why this might happen? Also, is there a way to get the fluid to settle back to a rest quicker?

2. With demo 2.1, when you enabled liquids the voxel mode was automatically changed to inscribed. Should I always need to change the voxel mode to inscribed when using fluids? Or can you leave it on default mode?


https://www.youtube.com/watch?v=k9ky4kmG7Sc

I've included a video to show what I mean. First part is smooth conservation, as you can see a swell is created at the grid edge and then at the end it is very unstable motion. The second part is with symmetric conservation, when the cube hits there is a few strange splashes that hit the back of the grid (spray falls diagonally) the grid is a decent size for this test so those particles really fly unnaturally out the grid.

Thanks and any help would appreciated.

Thanks
Hayden

[Ivaylo Katev]

the content must settle with both the conservation method, can you send the scene to check this?
the voxel mode is changed to inscribed to avoid rendering artifacts related to liquid-geometry contact points. when the mode is not inscribed, the liquid is kept outside the object and this forms gaps, see the images here
seeing the video i have the feeling that the scale is too small. like few centimeters. this may be the reason for the stability problem
the weird splash is a known issue, water droplets flying slower than the particle droplets. the best solution is just to hide them by the good amount of splash particles, and you can try to increase the air friction of the splash too, this will prevent the fast falling.

[hstone2003]

see post above...

[hstone2003]

Splash_Test.zip

Thanks very much for your quick reply.
The size may be the issue then as I've kept to default generic units. What would you recommend as the default unit setup to use? I prefer working with generic units compared to metric, can I just adjust the size each unit represents? will that still work.

Thanks for the link to that help file, it seems to not be included with the nightly installs.

[Ivaylo Katev]

the units are not important, the size of the simulator is the only thing that matters.
for example when you simulate a swimming pool, you can make it 100 meters, or 4000 inches, but not 1 meter or 10 inches

[hstone2003]

So then will it be ok to change the generic unit scale to something like 1unit = 1 meter then instead of the default inches. So a grid of 300 x 300 should now equal 300mx300m instead of 300inches.
This way you should still be able to have smaller grid sizes.

[Ivaylo Katev]

well, i think i found the scene scale problem
actually your scene is not too small, 300 inches is about room size and is pretty enough. however you have modified the velocity of the displacement texture. this produces the feeling that something is wrong, actually this happens because the waves in the container are moving faster than the displacement waves.

[hstone2003]

Ah ok thanks so much again for such quick reply. Yeah I changed the velocity on the map as it was moving too fast so I slowed it down. But seeing as the grid scale was on the smaller size I see how it would create that effect. I'm testing out a sim quickly with the units changed to meters, so should be a 300m grid instead of 300 inches and will see what the results look like.

Thanks again for your help, really appreciate it. Will post an update when I get the results.

[Ivaylo Katev]

300m is huge, good for meteorite impact
actually what scale are you targeting? if you imagine something like a falling car, 1000 inches container is good , no need to go up to 300 meters

[hstone2003]

HAHA ok thanks for the heads up. Yeah I ended up changing the grid to about 100m after making the unit change and realised the cube was now falling from over 100m in just a few frames so the splashes just exploded.

At the moment I haven't got a scale in mind for this test, it's probably around a car size, so will use your measurments. For the shot I'll need to do for work I have a character about 6m big emerging from the water.

[Ivaylo Katev]

don't forget to use the reynolds parameter when you have emerging from the water object

[hstone2003]

Thanks Wouldn't have thought of using it.

[hstone2003]

Hi,

I haven't had much time to work with this again but I did some tests yesterday and today and just have a few more questions. It seems the scale of my original scene didn't cause any issues, I had the same effects regardless of scene scale. With Symmetric conservation I still get the splashes flying out my grid unnaturally but my issue at the moment is the instability with smooth conservation.

I did a test with the standard download version of phoenix and the ocean is smooth no issues, I change back to the nightly version and suddenly I have a swell created on the edges of my grid (same scene). Any idea why this happens and how to stop it from happening? I hope you can see from my video I posted.

https://www.youtube.com/watch?v=KoOOfTJS1Ng


Another question, I was just testing out a basic scene with liquid poured into the grid (showed at end of video). The grid is 1m x 1m with cell size of 0.005m. Settings I changed were:
Timescale 0.75
SPF 8
Vorticity 0
Viscosity 0.001
Surface tension 1

The current result isn't too bad however I still think it's a little bit turbulent. Is there any way to get this to settle quicker?

Splash_Test.zip
Added scene file

Thanks
Hayden

[Ivaylo Katev]

in the official 2.11 the initial fill up builds underwater supporting walls (to prevent the water leaking), this was a big problem for the ocean simulations and we replaced them with pressure. this is the reason for the different behavior, however, this water surface instability is just temporary and you have to wait about 30 frames to settle.

[hstone2003]

Thanks for the explanation

Just realised I attached the wrong file.
Did a test last night with a new scene and let it simulate for 300 frames. Seems to have settled nicely from after 100 frames. So that's probably my issue with my other file as it's only 120 frames long and doesn't have enough time to settle (only gave it about 20 frames to settle).