floating platform

[gbon]

Hi alls,

I needto simulatea floating platform.

The structure weight is not uniformly distributed.
It's supported by plastic floating tanks.
For stability and equilibrium, each float have to be partially filled with
water.

So, my aim is to dimension those "floats" and how to fill them.

I don’t really know how to do this with Mechanica.

For example, if my platform is squared and if I have a float at each corner,
I can simulate it on a rigid floor and calculate reaction.
Then, I don't know how to simulate floating phenomenon and tanks filling...

Any idea?

Thanks,
GB





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[iceblink1]

On Fri, 4 May 2012 10:35:32 +0200, g bon wrote:
> Hi alls,
>
> I needto simulatea floating platform.
>
> The structure weight is not uniformly distributed.
> It's supported by plastic floating tanks.
> For stability and equilibrium, each float have to be partially filled
> with
> water.
>
> So, my aim is to dimension those "floats" and how to fill them.
>
> I don’t really know how to do this with Mechanica.
>
> For example, if my platform is squared and if I have a float at each
> corner,
> I can simulate it on a rigid floor and calculate reaction.
> Then, I don't know how to simulate floating phenomenon and tanks
> filling...
>
> Any idea?
>
> Thanks,
> GB
>

Do an analysis with gravitation as the load, and single point supports
instead of your floats.
Make sure you can get reaction forces from the supports (it may require
creating measures, i'm not sure).
Then do hand calculations to see how much displaced water you need at
each float.

The actual floating will be difficult to simulate. It's probably better
to create a curve in Excel for depth of the float in the water versus
upward reaction force versus volume of water inside the float, and then
use those curves together with your reaction forces.

If you really must simulate the floating, I guess you would model the
air volume inside the float (excluding both the water inside the float
and the air inside the float that is above water level) and apply water
density and negative gravity to those volumes. (Actually I'm not sure
Mechanica can assign different gravity accelerations to different
volumes, so check that before you start).

Make sure to let us know how you solved it in the end!

Best regards,
Patrick Asselman

[AndreasVlahinos]

GB,

There is a simpler way using BMX.
1. Assume an equilibrium position by establishing the sea level plane with 3
parameters (i.e. theta1, theta 2, height)
2. Create a datum point (model analysis feature) at the CG of the submerged
volumes and compute the submerged volume (with the same model analysis
feature)
3. Extract the cg distances from some reference axes (i.e. x and y) measure
analysis feature
4. Write in relations the 3 equilibrium equations using the buoyancy and
gravity forces
5. Build a design optimization feature that automatically solves the
equilibrium equations and repositions the platform on a static equilibrium
position. If you don't like the optimization feature you can solve these
equations (they are all linear) in a relation feature.
6. Finally you can run one more optimization in order to make
Obj=abs(theta1)+abs(theta2) zero by adjusting the vertical forces (water
weight) at your floats

We use this process for a submarine deployment and it worked great.
Actually we use the submarine deployment problem as an example in our BMX
class.

Let me know if you have any quick questions.


Cordially,

Dr. Andreas Vlahinos

Advanced Engineering Solutions, LLC
4547 N. Lariat Dr.
Castle Rock, CO 80108
303-814-0455 Office
720-838-0455 Cell