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Modal Analysis

wmay
2-Guest

Modal Analysis

I am attempting my first modal analysis. I am checking a flat plate with
holes around the edge for bolts. I have constrained the holes. The plate is
1/8" thick aluminum. I used the PTC material library for the 6061-T6
aluminum. The analysis says that my first mode is 389 Hz. I don't believe
it. I had a coworker check it with Patran/Nastran and he gets 13 Hz. That I
believe. I can't figure out what I am doing wrong. Any help?
1 REPLY 1
RodGiles
1-Newbie
(To:wmay)

Dear Wade,

Try checking your units - I bet the density is too low because you're using
the default ProE units. Always use IPS for inch parts or mmNs for metric
parts. (Dividing your answer by sqrt(386.4) gives 19.8 Hz, which is in the
right area). The hole constraints may be slightly over-constraining in
comparison to the Nastran results. Check the Mechanica Verification Manual
(included in the help files under Simulation: Additional Information). It
gives a number of examples where a comparison is made to Nastran.


Regards,

Rod Giles
Elite Consulting Ltd - The Mechanica Specialists - since 1992


_____


To: PTC/USER Simulation (Pro/Mechanica) and Behavioral Modeling Discussion
Subject: [sim] Modal Analysis


I am attempting my first modal analysis. I am checking a flat plate with
holes around the edge for bolts. I have constrained the holes. The plate is
1/8" thick aluminum. I used the PTC material library for the 6061-T6
aluminum. The analysis says that my first mode is 389 Hz. I don't believe
it. I had a coworker check it with Patran/Nastran and he gets 13 Hz. That I
believe. I can't figure out what I am doing wrong. Any help?


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