truss structure normal modes: low frequencies?
truss structure normal modes: low frequencies?
(OP)
I have a 3D solid model of a truss, and I'm using Nastran to determine the normal mode frequencies. Nastran is giving me results for modes 1-10. The first 6 modes are effectively 0 Hz, but my understanding is that those correspond to rigid body translations and rotations and that 0 is the expected result for a 3D model. Modes 7-10 all fall between 1-2Hz. I'm not sure what to make of this, as I was expecting much higher numbers. Is this result typical for a the normal modes of a complex structure like a truss? Is this telling me that I don't need to be concerned about, say, a 100Hz disturbance exciting the fundamental modes of the structure?
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RE: truss structure normal modes: low frequencies?
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Greg Locock
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RE: truss structure normal modes: low frequencies?
RE: truss structure normal modes: low frequencies?
Thanks
RE: truss structure normal modes: low frequencies?
what are the low freq modeshapes like (i.e. i mean the non rigid ones)?
RE: truss structure normal modes: low frequencies?
(It's a bit disconcerting if there is an aerospace company somewhere, where the dynamic analysts are unfamiliar with the concept of unconstrained modes!)
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