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Hi

looks like you have not defined materials for all your domains, check again the material node, and then the physics node

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Good luck
Ivar

Dear Ivar,

Thanks for your soon reply. But I defined Concrete from library with density, young's modulus and poisson ratio.
In geometry scope, I selected All domains. Is it true?

Dear Ivar;

this is a screenshot from my model.
material properties and some other features are shown.

Hi

I missed the "edge" word in your error message, I stopped at "rho". The issue is that you use a "beam" phyiscs that is defined on edges only, while you are in 3D with a "domain" = volume, but the "domain" for "beams" are lines = edges.

So first of all you must define the material on the EDGES in the material node, as these are by default set to the highest order of the geometry = 3D volume = DOMAIN as you can see on your image too.

I agree this is confusing, the COMSOl developers could perhaps improve this, but it's far from obvious how, as "beam" phyiscs is special physics using geometrical entities 1 or 2 dimensions lower the the default geometrical domain entitiy.

So start to select edges for the material, as beams are lines=edges in 3D (or 2D if you have defined highest order = 2D)

And read through carefully the doc about geoemtrical objects, fem entities, physics on domains (but domains size depends on physics too) ...

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Good luck
Ivar

Thanks a lot Mr. Kjelberg
It is worked correctly. I selected all edges instead of all domain.

Now, natural frequencies is very greater than values expected. I calculated natural frequency of first mode about 274 Hz by means of formulas, but COMSOL results are shown 1382 Hz as fundamental frequency. units are same in both methods.

I think, if I choose "Solid mechanics" instead of "Beam", better results would be extracted. Is this true?

Thanks very much

Hi

Beam are slightly tricky in the beginning, but normally quite OK and solves so much faster. A common error is getting the inertia wrong as there is a coordinate mapping for beam, check the doc, where X,Y,Z are pointing in "beam Space"

It's true that solid is tempting for many cases, due to the power of our computer today

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Good luck
Ivar

Hi,

If the image shows a cantilever beam, then it is modeled as a 3D solid, and you should use a Solid Mechanics physics and define the material properties in the solid. If you use the Beam physics, COMSOL uses special beam elements, and you model the cantilever beam as a simple straight edge and define the cross-section properties in the physics settings (and the material properties for the single edge). Both approaches work and give the same eigenfrequencies, but a Beam model in general gives accurate results using much fewer elements than a full 3D model.

Best regards,
Magnus Ringh, COMSOL