Posts made by Propeer

hmmz.. Based on your example, it seems that the laws of physics of buoyancy haven't been programmed quite flawless yet. I think I'll wait voor SP4.0. Maybe things have changed by then

Thnx both of you for your time and help.

@TIG: I actually do use your CoG tool! I like it a lot. I used it already to check my calculations for the center point and the weight of the concrete shape and used this weight to calculate the volume of the displaced water. Then again I used your tool to find the buoyancy point.
I'm now thinking of the right way to make one group of concrete with one rectangeled shape cut out and make one group of air. What I've tried already was to have separate groups of air in the hollow spaces of the concrete element. To bad it resulted in up flying air groups and a falling concrete tunnel element. Somehow I can't get the air groups to be enclosed in the tunnel. The just fly through the roof..

@mptak: Thanks for your input. I've already tried to make separate groups, but I can't find a way to make torque tightened connections between these objects. They just fall apart.

Does someone know how to solve this?

Hi TIG,

Thanks for your quick reaction. Though I'm not sure what you're saying :O.

"Your objects are non-solid groups."
My solids tool says they are.

"You don't need SP to do this ?"
I'll admit I don't need SP for the calculation, but it would be great to test my calculations with SP.

I understand your calculation with the result of app. 50% draft and i know how the system works with ballast water tanks to get the result of no pitch or roll or a preferred draft. But as mentioned in my first post, I don't want the 'sealed assembly' to have a homogeneous mass. I want to see if there is any roll while floating. With the given model I know there is, so now I'm trying to simulate that with SP. I guess it's not jet bug free.

When I just tried again, the 'air volumes' just went trough the roof of the tunnel.

I don't know how to glue two groups together with both of them with there own density..

Hi you all,

First post on this forum, so please correct me if i'm violating any rules.

I'm using SU8PRO and recently installed SP3.2. Now my challenge is to model a tunnel element for a to be immersed tunnel and sea of salt water and check if it floats and if it's stable. FYI an immersed tunnel is built by shipping floating tunnel elements to the right location en let them sink onto the right place on the bottom of the sea by making them heavier.

Now the density (or the weight) of water is app. 1.025 and the density of armored concrete is 2.500. Because the tunnel element has got closed hollow spaces it's supposed to float. I modeled these hollow spaces as groups with a density of 0.000, placed inside the tunnel element.

By my calculations the weight of the tunnel element is less then the weight of the displaced water, so the tunnel should float. But in Sketchup, it doesn't. Not even close. See my attached model.

Has someone any clue on where i'm going wrong? How SHOULD I model a heavy object with air inside?

Off course what I can do is add up the volume of the concrete and the hollow spaces, divide them by the weight of the concrete and give the complete tunnel element that weight. Actually that's not what I want, because that eliminates the differences in thicknesses - and thereby the weight - of each wall or roof.

Hope to get some help.

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Buoyancy Tunnel element.skp