Re: [Pyode-user] lifting forces.

[tim r. <bla...@ya...>]

Markus Wondered:
>Hi All,
>
>i am new to pyODE.
>
>Can i use pyODE for Problems like lifting force at
>Water.
>For Example i have got a empty Bottle which will be
>swim on the Water,
>but will be sink if it is filled with Water. My
>Programm should calculate
>what will happen. Or if something lies on the bottle
>and push the Bottle
>into the Water.
>
>Bye Markus

I think it's unlikely that you'd find a library to do
buoyancy for you.  There are, however, libraries to
make it relatively easy.  Google 3d boolean
operations. There is likely an operation that would
allow you to find the section of your bottle that is
below the water. Then, you find a library to help you
find the volume and geometric center of the bottle.
multiply the density of the fluid by the volume, and
you get the magnitude of the force. Of course it will
be pointed straight up, and applied at the center of
the underwater portion.

This is where ODE comes in. It's possible to feed in
the buoyancy force you found, the force of gravity,
and whatever other forces you have(an outboard
engine?!?) and ODE will tell you exactly what's
happening.

ODE can easily handle setting soemthing on top of your
bottle. It's just a matter of creating something to
set on top, detecting collisions, and creating a
contact joint as long as they are touching. ODE does
all these things easily

The other thing ODE can do is detect collisions
between the neck of the bottle and the water. This
will allow you to use some other method to calculate
how much water flows in.

I'm not sure what you'd do about the Free Surface
Effect of the water inside the bottle(google it if you
don't know what I'm talking about). You would
certaintly have to add it to your center of gravity
for the bottle, and thus to your gravitational force.
You may not want to get this detailed.

There are calculus methods for calculating how much
water goes through a given opening in a given time. I
could help you with that if you like. It's a fair bit
of work, though, so I'll only help you if you want me
to.  I really do want you to ask me, because I enjoy
this sort of thing, and tend to work problems like
this at the slightest provocation :)

--Tim Rau


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