Problem in Hybrido - ship sail in ocean

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3dkobi
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Joined: Sun Mar 03, 2019 2:34 pm

Problem in Hybrido - ship sail in ocean

Postby 3dkobi » Sun Mar 03, 2019 2:43 pm

Hi guys,
I'm trying to make a very simple simulation - a ship sailing in a straight line, and I'm having a little problem - No matter what settings I use, the water level at the end of the ship is always too low and the ship is a bit "above the water". The only thing that helped a little bit was to raise the Time Factor from the default 1 to 2, but it is still not perfect.

Any idea how to solve this ?

Kobi


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Oldcode
Posts: 789
Joined: Thu Nov 03, 2011 11:28 pm

Re: Problem in Hybrido - ship sail in ocean

Postby Oldcode » Mon Mar 04, 2019 2:33 pm

Are you trying to make the ship actually float on the Hybrido water?

If you are, I would say don't do that. It never really works well for models like a ship. Animate the ship yourself to the level you want it to be in the water, but in some rocking motion, and then have the Hybrido fluid flow around the ship as it moves.

Good Luck,
"My sword and my service are yours."

"Then forever remind him of his vow, Knight of the Old Code."

3dkobi
Posts: 8
Joined: Sun Mar 03, 2019 2:34 pm

Re: Problem in Hybrido - ship sail in ocean

Postby 3dkobi » Mon Mar 04, 2019 5:52 pm

Sorry if that wasn't clear - I animated the ship, it moves 10 meters per second (the ship is 45 meters long). The fluid (particles) isn't behaving as water - as if when the ship moves 1 frame the particles doesn't fill the gap that the ship left quick enough ( I hope I explained myself good enough)
I'm soing another test now and I think it's a little bit better now - I changed the Hybrido MAX substeps to 4

https://imgur.com/LZK9EjI
https://imgur.com/u4gMOh5
https://imgur.com/gg5fECu

3dkobi
Posts: 8
Joined: Sun Mar 03, 2019 2:34 pm

Re: Problem in Hybrido - ship sail in ocean

Postby 3dkobi » Tue Mar 05, 2019 7:19 am

After changing the MAX substeps to 4 and running a simulation over night - it's still not good - Still the same problem - the water level in the area of the back of the ship is still too low

https://imgur.com/DBNYkC6

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tsn
Posts: 924
Joined: Fri Oct 27, 2006 10:36 am

Re: Problem in Hybrido - ship sail in ocean

Postby tsn » Tue Mar 05, 2019 6:26 pm

Quick question: did you try to increase the ship's "Grid friction" parameter already? And I can also imagine that it might help to make the water slightly deeper. More substeps won't help you here, I'm afraid.

3dkobi
Posts: 8
Joined: Sun Mar 03, 2019 2:34 pm

Re: Problem in Hybrido - ship sail in ocean

Postby 3dkobi » Wed Mar 06, 2019 5:25 am

The water depth is now 4 meters, about half of it is below the ship's lowest point (pics attached). Should it be even deeper ?
https://imgur.com/vtwoUIO
https://imgur.com/UmndGNv
About the "Grid friction" & "Friction bandwidth" - I already tried several settings but I didn't saw it affects the overall level of the water too much

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tsn
Posts: 924
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Re: Problem in Hybrido - ship sail in ocean

Postby tsn » Wed Mar 06, 2019 7:47 am

A depth of 4 m should be ok for that. Another thing I can think of: are the checkboxes under the domain's "Particle Sampling" active? These options are there to control particle-object interaction and in many cases it's better to deactivte them, because they often remove particles in certan areas of an object What's the cell size of the domain and the ship?

3dkobi
Posts: 8
Joined: Sun Mar 03, 2019 2:34 pm

Re: Problem in Hybrido - ship sail in ocean

Postby 3dkobi » Wed Mar 06, 2019 7:57 am

All those check boxes were set to the default "yes" (active)
I unchecked all of them and I'm running another simulation now - I will have a result in about 2-3 hours and will post it

3dkobi
Posts: 8
Joined: Sun Mar 03, 2019 2:34 pm

Re: Problem in Hybrido - ship sail in ocean

Postby 3dkobi » Wed Mar 06, 2019 10:31 am

Well, it's worst now - In addition to the main problem now there's a big gap between the ship and the fluid (the ship has a low cell size and the Isosurface looks very good and matching the original model)
https://imgur.com/BSgSVJ2

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tsn
Posts: 924
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Re: Problem in Hybrido - ship sail in ocean

Postby tsn » Wed Mar 06, 2019 11:13 am

I see... I had many projects where disabling particle sampling was my rescue, so I though it might be worth trying.

My guess is that this is more a structural problem - either with the ship's shape or the Hybrido solver - or both. It could be that the particles along the bow are pretty fast, so that they simply move away from ship's body. And the stream they create prevents the surrounding fluid from moving back towards the ship's body again. Vortices, produced around the ship's stern, might also prevent the fluid from touching the body in this area. So this might be a problem with the ship's own speed and/or its shape.

Have you made some tests with more simplified ship models, smaller scale and smaller Hybrido domain cell sizes. Not sure if this will have any impact and I have to leave it up to you if you want to give these ideas a go nor not.


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