Discussion Forum

Hi,

If you add a 'Mass Properties' node under 'Definitions', you can compute mass, center of gravity, and mass moments of inertia.

For a 2D case, using the Beam Cross Section interface is another option.

Regards,
Henrik

Thank you very much!

I have added the Mass Properties Subnode, could I kindly ask you to be a bit more specific on how to obtain the mass moment of inertia/ cog/ etc?

Hi

check the Results - Derived Values - Global Variables and then the list from COMSOL ("CNTRL + Space" shortcut key), you will find the names and components therein, but you might use these names anywhere in your model set up, but they get defined only once you start solving your model.

One thing: by default COMSOL assumes a "standard density" for all materials of 1[kg/m^3], so if you want the true mass, change the scalar "1" to your material density i.e. for Solid Physics "solid.rho" this is the field variable name for COMSOL to map the different domains you choose to their respective solid.rho(x,y,z,t) values (the "t" time might not be relevant here, in your case, I just added it for completeness)

the mass is mass1.Mass or mass2.Mass ... if you have 2 masses defined
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Good luck
Ivar

Hi,

In version 5.1, you can also select to take the mass properties from the physics interface. When doing that, the appropriate mass densities are automatically set, and you will also get other types of contributions than the volume integral of the mass density. Such contributions can be for example point masses, added mass, or rotational inertial around the axis of a beam.

Note that you do not have to do a full solution to get the mass properties computed. It is sufficient to do a 'Get Initial Value', which is a fast operation.

Regards,
Henrik

Hi Henrik

I'm very pleased to hear this is now fully implemented :)
Great news !

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Good luck
Ivar