Modeling ideas 1

[snegi]

Hi there, i am new here and i am new with femap, so i have some problems...

I made a model in femap and i need to make some analyses so i need a little help.

I made model (sections of the ship that sholud be lifted with cran) with plates and beams. So i made all structural geometry and now i need to put elements under deck (such as cabins, some ship gears etc ) that have mass but does not contribute any strength to the structure.

Part of my model (one deck) is in attachment

any advice how to made such elements? thanks (and sorry on my english )

 

[rb1957]

if you only want to model the mass effects ... use a mass element (at the cg of the mass), which is connected to the rest of the structure with RBE3 rigid elements (at as many points onthe structure as you like).

 

[BlasMolero]

Hello!,
I nice trick in FEMAP is to use command "Tools > Mass Properties > Solid Properties" that will ask you to select a solid and the next question is "OK to create a representative node and mass element?", the next prompt is the density (by default 1.0), and finally will ask you "OK to link mass to mesh?".

Well, at this point I suggest to cancel command because FEMAP don't allow you to specify what type of RIGID element to create (RBE2 or RBE3), then is better to make this process "by hand": after cancel command, FEMAP will create a 0-D MASS element (named CONM2) + node at the center of gravity of the solid. FEMAP also will create the property associated to this element. Simply edit the property to enter the correct mass value.

The final step will be to connect the above MASS element with your supports: simply use command "Model > Element > TYPE = RIGID" and make sure to select RBE3 (interpolation): here select the MASS NODE as DEPENDENT and all the support nodes as INDEPENDENT. Click on NODES to select nodes using METHOD = BY CURVE, etc..

Regarding DOF, make sure to select TX,TY,TZ only in both DEPENDENT & INDEPENDENT fields (desactivate rotations).

And you are done, you have created your first SPIDER RBE3 element.

This method runs OK when you have imported the geometry from a solid CAD 3D package. If this is not the case, you will have to create the node & mass element by hand, OK?.

Good luck!!.
Best regards,
Blas.



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Blas Molero Hidalgo
Ingeniero Industrial
Director

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[rob768]

If you want an even distribution of the mass over the floors, you might want to use non-structural mass, added to the plate elements. You can enter the mass per area.