Boat simulation; issues with active body

[JuhaHo]

I'm doing my first boat project with Phoenix FD 4 and I have some issues with simulation.
1. The boat is rotating to left and it looks a bit funny when it travels right side in front. It's not turning, it's traveling to original direction, but not the bow ahead.
2. I can't link emitter geometry to active body geometry. I have two emitters for propulsion linked to active body hull, but once the simulation starts the link is broken and the emitters are left to start position.

Anyone else having these?

[georgi.zhekov]

Hey,

For the first one - try to play around with the center of mass for the original boat and make sure that the checkbox for Override Center of Mass in the Phoenix properties is on. You can find more about it in our guide here - https://docs.chaosgroup.com/display/...e+Bodies+Guide
If you're using a simulator linked to the animated boat, can you try with a large static simulator.

For the second issue - this is still in the to do list I'm afraid.

Thanks!

[JuhaHo]

Thanks Georgi,

I deleted the Center of Mass helper and it helped with turning. I see the boat going now straight ahead. However, it seems the stern is too deep. When the helper causes problems I have to avoid using it. To straighten the boat, I think I need to create a small bulge near bow to get the running angle within given degrees. Then I noticed, it swims overall to deep. I have defined the weight by given mass. Is it possible that the simulator doesn't lift planing boat accordingly and I should reduce the weight to get the position correct? If so then there's a problem when boat is not moving; the waterline would be too low.

To my other issue, I guess if I can freeze the active bodies hull animation maybe just by disabling it in simulator. Then I'd run the simulation again. Now the boat hull would follow previous simulation and propulsion emitters would work correctly if linked to fixed active bodies?

[JuhaHo]

What I'm doing wrong here?

[JuhaHo]

Now the boat wants to turn to the right, to starboard as they say. Bow is also diving. So what I did, I once again deleted the CoM helper and reduced the hull weight a bit. I wish there was a way for steering the boat.

Anyway I deleted the Z-rotation keys, which turned the boat again to steering direction.

And I deleted more keys: X-rotation and Y position. Now I wonder, what would happen, if the weight parameter was animate able.

[georgi.zhekov]

Hey,

Offsetting the CoM should help for the turning, ideally there shouldn't be need of deleting the keyframes (although you can totally do that).

For the linked emitters, if you don't mind running the sim twice, you can first run the sim with Active Bodies, after the first sim is done, disable the Active Bodies solver from the Dynamics rollout of the simulator and hide the original boat (or you can make it non-solid so it won't interact with the simulation).
Then link your emitters to the Boat clone that was created during the first sim.

For the boat steering - you can animate the original boat to follow a spline and using the Animation influence option you can control how precise the clone would follow the original boat. You can keyframe this value as well.

As for the animated weight - I will log this as a feature request as it is currently not possible.

Thank you!

[JuhaHo]

For me it's beginning to look obvious that Phoenix FD cannot do the job without some workarounds. Is there any lifting force taken into account when processing activebodies? It looks like there isn't For instance on Chaos demoreel the boat seems to swim way too deep in the water, which makes it very unnatural. I was thinking that since manipulating the weight doesn't do the trick, I might next concentrate finding correct placing for CoM helper to get the riding position within given limits. Then I should reduce the ocean level to match the given height position. Should I animate the height somehow so when not moving the boat would float correctly?

I'm not sure if animating the weight or ocean level would solve the problem. Instead there could be additional parameter for speed dependent lifting force.

I think there's no point sharing here my latest failed simulation runs.

[Svetlin.Nikolov]

Oh, please do share, it would definitely help to see how it looks in motion.

Btw, we're missing some important info - are you using the newer 4.1 or a nightly, or the older Phoenix 4.0?

Another important question - the lower the grid resolution, the higher chance the active body will get strongly affected by small disturbances. How many voxels do you have in that grid?

[JuhaHo]

Thanks Svetlin,

Here's my latest screenshot on finished simulation. It was done by using one very long static simulator wit 53 million cells of 62 mm in size. Version is 4.10.02. I think it would be a good idea to save the *_phx_done object to be used when simulating the actual boat wake. Then I will use smaller animated simulator with smaller cells. But there's long way to go before we can try that. Actually would it be a good idea to make the simulator more narrow to increase the cell amount at this point, because at this stage I'm not simulating the boat wake - I'm trying to do only the hull animation?

However, I'm not finished with this one, because the ride angle is too high according specifications. So I need to move the CoM helper forward a bit before the next simulation. Also one minor thing is that the boat has moved 300 mm sideways during the simulation,

[Svetlin.Nikolov]

Oh yes, looking much better now! Indeed, we are not happy with how currently the active body gets voxelized at the Simulator's resolution in order to interact with the fluid, meaning that fine details get lost and symmetry of vessels can also be impacted by this process, resulting in improvement by increasing the grid resolution which can make iteration times huge. We have some ideas about how to change this in the next updates...

[JuhaHo]

I wonder how to create an independent copy of simulated active body. At the moment the animated geometry is deleted when I start new simulation. My idea was to create several animated boat hull copies so I can pick the best animated boat to be used with boat wake simulation.

[kaloyan.darmonev]

Hello, if you want to preserve a simulated copy of an active body, you can make a copy of the simulated AB clone and then move the copy out of the Active Body Solver's layer in 3dsMax's Layer Explorer (everything in that layer gets deleted when the sim is restarted, so it does not interfere with the next simulation).
You will also probably want to add the copy to the Phoenix Simulator's exclude list, so it does not interfere with the sim.

[JuhaHo]

Thanks Kaloyan,

I solved it this way. I created a copy of the original active body hull. Then I copied the keys from simulated active body to hull copy by using the Dope sheet. This way I can link the XRef render geometry to the animated hull copy. Also I could now permanently link the propulsion emitters to the hull copy as well.

Here the latest simulation. Bow is still too high, so I moved the CoM forward a bit and hit the start button again. We'll see tomorrow if it helps.

[JuhaHo]

Finally, I got it within limits.

My first test simulation with wave force is about to be finished. I think it's not responding to the waves very well. I wonder if moving CoM upwards a bit, would help. At the moment it's near to keel, because it was that way more stable. Maybe it's too stable for wave force.

[JuhaHo]

Yet another iteration. Now I managed to simulate slight 0.9 degrees variation for bow angle. I think the ocean is beginning to look too rough in renderings so I moved the CoM upwards a bit and the made the hull mass a bit lighter for next simulation run.

I wonder what parameter I should change If I want to use more rough ocean during simulation and reduce the roughness when rendering in a way that doesn't change the basic surface shaping too much. That way the boat animation should still match the sea waves.