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ejenner1-Visitor
1-Visitor
July 16, 2014
Solved

Moment of inertia

  • July 16, 2014
  • 1 reply
  • 17861 views

I would like to be able to find the rotational moment of inertia of an assembly (that is, to disegnate which parts move around the axis and get the moment for those parts together). There are several different materials involved in these parts. I have the density (kg/m^3) of all the materials. I tried setting mass poperties but everthing in the window is greyed out or locked. And even if I could set that, I am unsure how to find the moment. How do I go about doing this? I could do it one part at a time and sum if needed, since inertia about the same axis is additive.

    Best answer by tbrotherhood

    Initial thoughts are the first part needs to be fixed. There are two constraints on this part but it is still 'packaged' and free to move.

    Also, the first part has no material applied to it. For a Mass Properties analysys you need to assign a material or density to every single component. Which parts was the material property greyed out?

    So I put together a few of the parts I think should be in the rotor sub-assembly and added this to the housing with a pin connection. The attached model should be self-explanatory. You should then be able to check the moments of intertia of the rotating parts as they will be in one sub-assembly.


    1 reply

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    tbrotherhood12-Amethyst
    12-Amethyst
    July 17, 2014

    With the model open in PTC Creo, open the Analysis tab and click Mass properties. Click on the glasses button and the dialog will report moments of inertia. For this to work you must assign materials to every component in the assembly/

    Mass_props.jpg

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    ejenner1-VisitorAuthor
    1-Visitor
    July 17, 2014

    The entire assembly is not moving (that is, the assembly includes the stationary parts in which the item is moving). How do I get the moment for only the parts that will move? Also, the density entry boxes for some of the items in the assembly are greyed out; what do I do with these items?

    T
    tbrotherhood12-Amethyst
    12-Amethyst
    July 17, 2014

    Can you make the moving parts into a sub-assembly?

    Rather than change the density apply a material definition. File > Prepare > Model Properties > Material. In the dialog choose a material and apply it to the part.

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