Relationship between mass moment of inertia and second moment of area?

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Discussion Overview

The discussion revolves around the relationship between mass moment of inertia and second moment of area, particularly in the context of modeling a damped frame in SimMechanics. Participants explore how these concepts relate to structural dynamics and the requirements of simulation software.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks to understand the relationship between area moment of inertia and mass moment of inertia for modeling purposes in SimMechanics.
  • Some participants assert that mass moment of inertia and area moment of inertia are independent of each other.
  • Another participant challenges the independence claim, suggesting that they are related and can be expressed through a formula involving area density.
  • A proposed relationship is presented: Imass = ρarea * Iarea, where Imass is the mass moment of inertia, Iarea is the area moment of inertia, and ρarea is the area density.
  • Assumptions of constant density are noted as a condition for the proposed relationship.

Areas of Agreement / Disagreement

Participants express disagreement regarding the independence of mass moment of inertia and area moment of inertia, with some asserting they are independent while others propose a dependent relationship.

Contextual Notes

The discussion includes assumptions about constant density, which may affect the proposed relationship between the two types of inertia. The context of using simulation software adds complexity to the comparison of these concepts.

Fat Ryan
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I am trying to create a model in SimMechanics of a simple damped frame. I am very new to this software and structural dynamics as well. I have a copy of "Dynamics of Structures" 3ed by Chopra. In the textbook, the author uses the standard geometric and material properties that I am familiar with to obtain stiffnesses (modulus of elasticity, E & second moment of area, I). Simscape, however, asks for mass and inertia tensor. The latter of which has units of mass*length^2. Is there some sort of relationship between the area moment of inertia and mass moment of inertia? The reason it of importance is because I need to create this model and verify it somehow. If I replicate an example in the textbook, then obviously I'll know if I'm doing things correctly. Unfortunately, the textbook only provides area moment of inertia in it's examples.
 
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Sorry, the two are totally independent of each other.
 
viscousflow said:
Sorry, the two are totally independent of each other.

hmm, does anyone know why there's a difference between the book and simscape then?
 
viscousflow said:
Sorry, the two are totally independent of each other.

This isn't really true...

They are different, but still dependent/related to each other...
I've never found this in a book,
but one can show the relation between them by using balance of linear momentum...

The relation is the following:

Imass = \rhoarea * Iarea

where

Imass : Mass Moment of Inertia
Iarea : Area Moment of Inertia
\rhoarea : area density (kg/m²)
 
Assuming constant density...
 
enigma said:
Assuming constant density...
Yes, I forgot to mention that. Thanks!
 

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