center of buoyancy

[MikeMarcoux]

Does anyone have a good method of calculating center of buoyancy?

We've tried several different methods with mixed results.  We have a multi-component assembly which contains flooded and sealed compartments.  Shrink wrapping doesn't always work so well (parts won't solidify), or doesn't seem to give us a level of accuracy that is acceptable.   We've also calculated the buoyancy on a part to part level, but that take a long time, and when designs are constantly in flux, multiple iterations can take too much time.  Ideally, it would be great to have an analysis that could be run as a design is evolving.

I've heard that it's possible to use Behavioral Modeling, but I have found no literature in terms of using for determining center of buoyancy.  If anyone has a technique or approach that has worked well for them, I'd be curious to hear the details of their solution. 

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[dschenken]

Try BMX Feasibility, Free Pro/E Wildfire Video Tutorial, Consumer Product Design/Development, E-Cognition Inc

You may have to buy his DVD, but I can vouch for his tutorials - they are well done and easily understood. Others are available at ECognition - YouTube

I don't know if his method requires BMX or not. It's right there in the page title; BMX it is. I'm downloading the movie file as it doesn't play in my browser for want of some plug-in.

[pperrin]

Hello Mike,

Isn't possible to design a variable height horizontal plane in the assembly and remove (cut) the volume of the assembly over the plane (with empty, completely filled and partially filled volumes).

The volumes under the plane are empty if sealed, filledl if competely under it and partially filled if the plane cut the volume.

When the weight of the kept volume is equal to the equivalent volume of water the center of buoyancy is in the plane : this would give the height of the center of buoyancy.

Using the bahaviour modeler is not necessary but could be usefull by finding the correct height to balance the weights of the assembly and of the "moved water".

Am I clear enough ?

Pierre

[pperrin]

Works fine with a simple boat including 2 balasts (blue) plus 2 empty (full of air) cylindrers. (red)

Sensitivity studies for both weights (full boat with partially filled cavities and empty cavities).

In this simple example, the "boat" will be around 70.8 mm deep in the water.

When the level in the partially filled cylinders is 60.8 mm (the thickness of the bottom is 10 mm) the mass of the moved water is equal to the mass of the boat + the air + the water Inside.

The empty volume must be full of "air" to be taken in account when the water volume is calculated.

The boat "cut" at the level of the water inside the cylinder => give the volume of the moved water (of the sea) => when both masses are identical, the steady state is reached, giving the buoyancy level.

Hope this could help !