## Simple boat buoyancy demo

Show what you made with Bullet Physics SDK: Games, Demos, Integrations with a graphics engine, modeler or any other application
robagar
Posts: 48
Joined: Fri May 21, 2010 1:49 am

### Simple boat buoyancy demo

Here's a short demo of a boat sailing through waves on an unbounded ocean. Buoyancy is modelled by attaching floats to the body which simply apply a force acording to their depth below the surface at discrete points. The ocean surface is functionally generated, so it is infinite in extent. Replacing the quick + simple but completely wrong sine waves with something more physically correct is on my todo list, as is making a better boat model

Note this is not using the technique demonstrated in HeightFieldFluidDemo, which models the water as a finite heightfield.
Flix
Posts: 456
Joined: Tue Dec 25, 2007 1:06 pm

### Re: Simple boat buoyancy demo

Nice video and physic effect !

Code: Select all

``Buoyancy is modelled by attaching floats to the body which simply apply a force acording to their depth below the surface at discrete points.``
Could you please explain a little further the approach you used ? From what you've written I presume you attached some rigid bodies (how many, which shape, where, with which constraint?) to the boat rigid body so that you can apply a force on each of them at every internal timestep proportional to the body distance from the water surface. Correct?

I'm not asking any source code, just a further explanation of one line or two. Thank you in advance.

Flix.
robagar
Posts: 48
Joined: Fri May 21, 2010 1:49 am

### Re: Simple boat buoyancy demo

Cheers!

The floats are not real Bullet bodies - they are imaginary things attached to points on my boat object.

Code: Select all

``````boat
+ btRigidBody
+ Ogre renderable
+ floats
``````
But yes, in the timestep the each float tests the water level at their position, then applies a force to the boat's rigid body at their position relative to the boat. I imagine each float as a cylinder which is always vertical, regardles of the orientation of the boat. The force is proportional to how deeply immersed they are, up to a maximum defined by their volume.

At the moment the boat has just 4 floats - bow, stern, port & starboard. I manually set their volumes to provide enough force to counteract gravity, and then adjust the positions and cylinder lengths to tweak the way the boat moves. I've got a vague idea to generate the floats by packing cylinders into the rigid body volume somehow, but that's something for the future
Flix
Posts: 456
Joined: Tue Dec 25, 2007 1:06 pm

### Re: Simple boat buoyancy demo

Thank you for your explanation !
robagar
Posts: 48
Joined: Fri May 21, 2010 1:49 am

### Re: Simple boat buoyancy demo

jinij123
Posts: 1
Joined: Wed Aug 18, 2010 1:17 pm

### Re: Simple boat buoyancy demo

Could anybody send me a sample code on how to proceed to make a similar sample as shown by robagar?
I would like to use OgreBullet framework for making this.

gtafan
Posts: 14
Joined: Tue Jul 16, 2013 2:57 pm

### Re: Simple boat buoyancy demo

I would also like to see the sorcecode of this boat buoyancy demo.
c6burns
Posts: 149
Joined: Fri May 24, 2013 6:08 am

### Re: Simple boat buoyancy demo

Considering his last visit to the forum was 2 years ago, you might have to be contented with his explanation instead of his source.
gtafan
Posts: 14
Joined: Tue Jul 16, 2013 2:57 pm

### Re: Simple boat buoyancy demo

c6burns wrote:Considering his last visit to the forum was 2 years ago, you might have to be contented with his explanation instead of his source.
I don´t realy expected the topicstarter to give me the sorces, but may be the sources, even posible modified, are avaible somewhere and someone can say where to find them.
Leith
Posts: 2
Joined: Mon Mar 25, 2019 9:13 am

### Re: Simple boat buoyancy demo

I'm happy to follow this up, if nobody else cares to, and hi, Erwin!
wanglei
Posts: 1
Joined: Mon Nov 15, 2021 8:53 am

interesting！