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Polar moment of inertia of cylinder with slit

Posted 17 avr. 2015, 08:38 UTC−4 Structural Mechanics Version 5.1 5 Replies

Andrei-Alexandru Popa
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Hello,

I am trying to obtain values for a complex shape (to begin with, a cylinder with a rectangular slit through it). How is it possible to do this? Thank you!

Andrei
5 Replies Last Post 20 avr. 2015, 03:45 UTC−4
Henrik Sönnerlind COMSOL Employee

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Posted: 10 years ago 17 avr. 2015, 10:50 UTC−4
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
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
Andrei-Alexandru Popa
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Posted: 10 years ago 17 avr. 2015, 17:01 UTC−4
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?
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?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 10 years ago 19 avr. 2015, 12:23 UTC−4
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
--
Good luck
Ivar
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 -- Good luck Ivar
Henrik Sönnerlind COMSOL Employee

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Posted: 10 years ago 20 avr. 2015, 03:40 UTC−4
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, 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
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 10 years ago 20 avr. 2015, 03:45 UTC−4
Hi Henrik

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

--
Good luck
Ivar
Hi Henrik I'm very pleased to hear this is now fully implemented :) Great news ! -- Good luck Ivar

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