Thin Wall Model L/D Ratio

[will_roe]

Hi,

I just noticed that the thin wall model L/D ratio is substantially different between Inventor Stress Analysis and Nastran. I don't understand what's going on behind the scenes enough to know why this is the case.

Simple question- Are these ratios the correct assumption to make when working in each analysis?

Nastran-

https://knowledge.autodesk.com/support/inventor-nastran/learn-explore/caas/CloudHelp/cloudhelp/2019/...

Stress analysis-

https://knowledge.autodesk.com/support/inventor/learn-explore/caas/CloudHelp/cloudhelp/2020/ENU/Inve...

[will_roe]

Hi,

I just noticed that the thin wall model L/D ratio is substantially different between Inventor Stress Analysis and Nastran. I don't understand what's going on behind the scenes enough to know why this is the case.

Simple question- Are these ratios the correct assumption to make when working in each analysis?

Nastran-

https://knowledge.autodesk.com/support/inventor-nastran/learn-explore/caas/CloudHelp/cloudhelp/2019/...

Stress analysis-

https://knowledge.autodesk.com/support/inventor/learn-explore/caas/CloudHelp/cloudhelp/2020/ENU/Inve...

[John_Holtz · Accepted solution]

Hi @will_roe 

The 100/1 L/D ratio (Inventor Stress Analysis, ISA) seems very large to me. Personally, I would not use a solid mesh when the L/D ratio is close to that large. But ISA does have higher order elements (high order than parabolic in Inventor Nastran), so perhaps it can compensate for such thin parts.

I suspect the 20/1 L/D ratio (Inventor Nastran) is based on the engineering approximation of thin-wall cylinders versus thick-wall cylinders.

[John_Holtz · Accepted solution]

Hi @will_roe 

The 100/1 L/D ratio (Inventor Stress Analysis, ISA) seems very large to me. Personally, I would not use a solid mesh when the L/D ratio is close to that large. But ISA does have higher order elements (high order than parabolic in Inventor Nastran), so perhaps it can compensate for such thin parts.

I suspect the 20/1 L/D ratio (Inventor Nastran) is based on the engineering approximation of thin-wall cylinders versus thick-wall cylinders.