# Hulls and COB calculation

This topic is 2558 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

I have some questions on calculating COB for a mesh. Assume that the hull density is non uniform. Knowing the total mass of the hull, how can I calculate COB?

My instincts tell me that I will need to integrate the volume starting from the lowest part of the keel up, along the +y axis, until I arrive at d for a plane p(<0,1,0.>,d) where the volume of the hull below p * density of water = mass of hull. If so than the centroid of that mesh should be the COB. I'm also aware that it should be possible to use some sort of binary subdivision to speed this up.

Am I on the right track.

##### Share on other sites

I have some questions on calculating COB for a mesh. Assume that the hull density is non uniform. Knowing the total mass of the hull, how can I calculate COB?

My instincts tell me that I will need to integrate the volume starting from the lowest part of the keel up, along the +y axis, until I arrive at d for a plane p(<0,1,0.>,d) where the volume of the hull below p * density of water = mass of hull. If so than the centroid of that mesh should be the COB. I'm also aware that it should be possible to use some sort of binary subdivision to speed this up.

Am I on the right track.

No one has anything to share? ( my polite bump)

##### Share on other sites
I've done COB calculations before but only as a weighted sum of point masses type integration rather than anything more fancy...

##### Share on other sites
Have you looked at S.Melax here: http://www.melax.com/volint.html.

There are also papers from Mirtich and Eberly. Google for polyhedral mass properties.

##### Share on other sites

Have you looked at S.Melax here: http://www.melax.com/volint.html.

There are also papers from Mirtich and Eberly. Google for polyhedral mass properties.

link is broken, will work my google...Thanks for the hints about the papers... off to citeseer i go.

##### Share on other sites

I've done COB calculations before but only as a weighted sum of point masses type integration rather than anything more fancy...

That is how I'm getting the masses of each object that makes up the hull or lies inside it. This is also why the density of the hull varies, depending on where in the hull i'm looking. Thanks for coming out though(seriously the fact that someone answered at all brings hope)

##### Share on other sites

That is how I'm getting the masses of each object that makes up the hull or lies inside it. This is also why the density of the hull varies, depending on where in the hull i'm looking. Thanks for coming out though(seriously the fact that someone answered at all brings hope)

In LBP PSP we had two material types which were buoyant, and it was possible to glue multiple convex objects together (each one had its own material type). I knew the buoyancy of the material, the area of the polygon (this was in 2d) and the COM of each sub-object so I could do some weighted sum type calculations to work out where the COB was in the overall object, and then apply an impulse at that location to make the object float (or not)...

1. 1
2. 2
Rutin
19
3. 3
4. 4
5. 5

• 9
• 9
• 9
• 14
• 12
• ### Forum Statistics

• Total Topics
633300
• Total Posts
3011267
• ### Who's Online (See full list)

There are no registered users currently online

×