Centre of buoyancy and C of G 2

[Rich944]

Hi all,

I am modeling up a concept for a submerged 'aerofoil' type shape. This will be made of GRP and house some metalic components.

We want to try to insure the centre of buoyancy is in the same position as the centre of mass/gravity. To do this we can play around with the size/position of some foam blocks within the structure, note: the shape will be free flood.

Two things:

1. I want to confirm that when I do analysis > measure bodies and select the 'Radius of gyration' tab that this shows the centre of gravity/mass?

2. Is there an easy way to find the centre of buoyancy?
The only way I can think of doing this is to 'save as' the assy and all components and make sure all the densitys are set the same then find the of gyration.

Cheers,

Rich

 

[Rich944]

NX 7.5 btw

 

[JohnRBaker]

If you perform the Measure Body routine with the Associate option toggled ON, an associative point object will be created at the Mass Center of the part and it will automatically update as changes are made to the model (as long as you make sure that the Measure Body feature is always moved, which you can do by 'dragging' the feature in the Part Navigator, to be the last feature in the model tree).

As for how be determine 'center of buoyancy', since I have no experience in that area of engineering (I'm a machine designer by education and work experience). I'll leave that discussion to someone else.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
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Cypress, CA
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[petulf]

As John say the associative measure body command (analysis-> measure bodies ...) is the one you want, to find the center of buoancy i would do as follows

1 - Create a top assembly for the craft.
2 - Create a displacement component and link the displacement envelopes as solids or in the case of hollow components as faces.
3 - In the displacement component sew together any linked faces into solids, then assign water as the material property of all solids.
4 - In the top assembly create one associative body measurement feature for all the solids in the displacement component, and one for all the solids in the craft assembly.

an alternative method would be to create a displacement solid in each component and add it to a displacement reference set, that would remove the need for a displacement component.