Splash flip simulation

[Arvin]

Hello everyone! I hope everyone is doing well.

 

Before I start I'd like to apologies for my English.

 

I'm creating a flip sim of a ship rising from underneath the ocean and splashing pretty much similar to this type of shot and I'm following this tutorial from Escape Studios on Youtube

The problem I'm getting is that the splash is too big ( https://imgur.com/a/jpd1KsI ) What would be the solution to get just the right splash for this type of shot? The boat has been scaled and animated in Meters before I've imported it to Houdini. I have attached the hip file so everyone could take a look.

Also, the flip simulation seems to move very slow compare to the animation of the boat. Here's the preview 

 

Thanks all!

Boatsplash.hipnc

Edited April 28, 2020 by Arvin

[Whatsinaname]

Without looking at your file:

 

- deactivate Reseeding in your FLIP solver > Particle Motion > Reseeding. Are the Splashes still way too extreme?
- You might be over smoothing your sim, this is why it feels too slow. FLIP Solver > Volume Motion > Velocity Smoothing. When using the Splashy Kernel, the default is 0.1, which I think is way too much, try something like 0.01 or 0.005...or maybe change to FLIP/APIC by changing the Kernel to Swirly. 
 

[Arvin]

On 01/05/2020 at 12:11 PM, Whatsinaname said:

Without looking at your file:

 

- deactivate Reseeding in your FLIP solver > Particle Motion > Reseeding. Are the Splashes still way too extreme?
- You might be over smoothing your sim, this is why it feels too slow. FLIP Solver > Volume Motion > Velocity Smoothing. When using the Splashy Kernel, the default is 0.1, which I think is way too much, try something like 0.01 or 0.005...or maybe change to FLIP/APIC by changing the Kernel to Swirly. 
 

The reseeding under flip solver seems to be greyed out so I cannot deactivate it. I'm using the default flip tank from the shelf tool.

[Whatsinaname]

I took a quick look at your scene. 

 

As it seems, you are using the default values Houdini is setting up for you when using the shelf tool. Unfortunately, these auto-generated setups are often very messy.
The boat object in your scene was missing, so I couldn't test anything. However, it feels to me your tank is huge. 

How are you bringing in the boat? Has it been modelled in a different application and then brought into Houdini? If so, check it's scale...it could be 10 times larger than real-world scale, leading to some extreme forces accumulating during the simulation.
Just check the Houdini grid...the units displayed on the grid are meters. If you want, you can also create an object called 'Tommy', which gives you a human-sized model. 
So first and foremost...is your scale set up properly?

 

[Arvin]

2 hours ago, Whatsinaname said:

I took a quick look at your scene. 

 

As it seems, you are using the default values Houdini is setting up for you when using the shelf tool. Unfortunately, these auto-generated setups are often very messy.
The boat object in your scene was missing, so I couldn't test anything. However, it feels to me your tank is huge. 

How are you bringing in the boat? Has it been modelled in a different application and then brought into Houdini? If so, check it's scale...it could be 10 times larger than real-world scale, leading to some extreme forces accumulating during the simulation.
Just check the Houdini grid...the units displayed on the grid are meters. If you want, you can also create an object called 'Tommy', which gives you a human-sized model. 
So first and foremost...is your scale set up properly?

 

Aha! The scale of the boat is way too big after comparing it to the Tommy Object but the boat was modelled and scaled in meters in Maya before exporting it as an alembic file.

Boat.abc

[Whatsinaname]

Maya is using a different interpretation when it comes to scaling and units. For the scale to work in Houdini, you have to scale it inside Houdini so that 1m of your boat equals one Houdini unit, no matter what it says it was in Maya. Try it, I suppose it will work.

[Arvin]

On 07/05/2020 at 1:32 PM, Whatsinaname said:

Maya is using a different interpretation when it comes to scaling and units. For the scale to work in Houdini, you have to scale it inside Houdini so that 1m of your boat equals one Houdini unit, no matter what it says it was in Maya. Try it, I suppose it will work.

After changing the scale and redoing the sim it seems like I'm getting a weird interaction with the fluids. Any ideas on how to fix this?

https://imgur.com/a/XrLXSzh

Boat3.abc

Splash.hipnc

[Whatsinaname]

Inside your FLIP sim, look for the FLIPobject > VIsualisation > Collision. Turn that on. 

Run a few frames of the sim, so you can see how the solver sees your collision object. My guess is that it might be all over the place. 
Ideally, you want a closed (no holes) model for this purpose, therefore you will have to create a proxy of your boat to make it collide.

 

 

[Arvin]

On 11/05/2020 at 2:58 PM, Whatsinaname said:

Inside your FLIP sim, look for the FLIPobject > VIsualisation > Collision. Turn that on. 

Run a few frames of the sim, so you can see how the solver sees your collision object. My guess is that it might be all over the place. 
Ideally, you want a closed (no holes) model for this purpose, therefore you will have to create a proxy of your boat to make it collide.

 

 

Thanks for the help so far. I've managed to make a sim until the part where I have to surface it using the particlefluidsurface node.

The problem here is that I'm getting this weird geometry. Any idea as to how to fix this? Some frames have this and some don't.

Boat3.abc

Boat_splashdown_7.hipnc

[Whatsinaname]

That weird pyramid in the bg? My first guess would be some rogue particles at arbitrary positions making the meshing algorithm go crazy. Try creating a bounding box around the area of you want to mesh and kill everything that is outside that area. On top of that, delete any attribute that you don't need for meshing, using an attribute delete before using the particle surface SOP.

It could also be a weird hiccup...try adding a slightly different number to your Particle Separation value, something like 0.11 instead of 0.1. See if the odd structure is generated with slightly different settings.