Density of an Assembly

[rdiederich]

I'm trying to find the moment of inertia of an assembly, but I'm having a problem. I don't know how to find the density of the assembly. There are two parts in the assembly, both of which have the proper densities. Every time I try to find the mass properties of the assembly, it automatically sets the density of the assembly to 1. So, I'm a bit stuck at this point.

Thank you for any help you can provide.

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[Chris3]

If you are using the calculated mass properties it will average the densities of all of the components in the assembly. If you used assigned mass properties it will report whatever you typed in. Did you type in mass properties manually? File-> Prepare -> Model Properties -> Mass Properties

[rdiederich]

Since the materials were not assigned to the parts, I'm guessing that the densities were put in manually.

I just did a quick test of two 1cm x 1cm x 1cm cubes in an assembly, manually setting the density of one to 25, and the other to 35. After putting them in an assembly (both parts fully constrained), the density was still set at 1.000000e+00, without the ability to change it.

As another test, I set the material of the two cubes. One had a density of 0.00786, the other had a density of 0.00282. After saving the changes to the cubes, I regenerated the assembly just to be safe, but the density of the assembly was still 1.000000e+00, and I still couldn't change it.

At this point, I'm honestly stumped. I'm using Wildfire 5, if that makes any difference.

Thank you for any help you can provide.

[StephenW · Accepted solution]

REGEN may not get mass related items updated. Do a ANALYSIS - MASS PROPERTIES on the assembly and then regenerate. Depending on your model and your config, you may need to force a full regen. I do this by dragging the insert here to the top. Then back down again. Usually quick and easy unless your model is large.

My last resort is to go to File-> Prepare -> Model Properties -> Mass Properties change and then GENERATE REPORT, then regenerate.

Depending on your models, sometimes it can be stubborn.

[rdiederich]

That did it! Thank you. For whatever reason, before I press the "Compute Current Analysis for Preview" button, it lists the density option grayed out and set at 1.000000e+00, but when the report is actually generated, it lists the density correctly. I don't know if I'm just misinterpreting the window incorrectly or something else, but it works fine.

Again, thank you.