Mass per unit length

[davidbl1419]

I have created a 3D geometry but I only have the ''mass per unit length''. How can I apply it in order to study its normal modes? I have tried everything but I can't find it
Thanks!

 

[cohoman]

If you want to calculate the normal modes of a 3D FEM in Nastran, you will need to define the density of the material for the elements in your FEM. What are you modeling? Is it made of bar or beam elements, or solid/shell elements?

 

[davidbl1419]

Thanks for the answer.
I am modeling a wing but with a simple geometry. The problem is that, I don't have the density of the material, only the mass per unit length (it's for an essay). So I don't know how to apply it

 

[BlasMolero]

Dear David,
The easy way is to mesh with 1-D CBEAM elements and in the properties of the beam elements simply add the value of non-structural mass per length.
You can create the center line of the solid members and mesh with beam elements, easy!!

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

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[davidbl1419]

Thanks for the answer.
I have done that by defining 1D elements using the property CBAR (we are free to use the elements we want). I have used a bar orientation that is perpendicular with the union I want to make and a ''random'' area. To not waste too much time I've only tried that on a part of the structure.
Como veo que eres español aprovecho a explicarme en castellano también.

The problem I see now is that in the analysis the elements act very strange, as they were different parts of the structure. I'm used to use only 3D elements and the performance is very different.
El caso es que mi estructura no se comporta como si fuese un sólido, es decir, si yo le aplico una fuerza en una esquina (que es lo que he probado) debería deformarse conjuntamente de una forma ''lógica''. En este caso parece que cada elemento va por libre respecto al resto. Posiblemente esté diciendo barbaridades pero dada la inexperiencia con este programa y estar atascado en esto...

 

[cohoman]

Can you upload your Nastran bdf file?