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05-04-2012
04:35 AM

05-04-2012
04:35 AM

floating platform

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

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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2 REPLIES 2

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05-04-2012
07:06 AM

05-04-2012
07:06 AM

floating platform

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

> 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

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05-04-2012
12:46 PM

05-04-2012
12:46 PM

floating platform

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

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