Eigenfrequencies without any restriction 1

[naeng]

Has some sense extract the eigenfrequencies of a structure, or mechanical part, without any restriction in displacements?. If so, which is the reason?.

I do this question, because i´ve seen do this in a very, very important analysis of a mechanical component in a very, very important company in its field, and i don´t understand it.

Thanks in advance.

 

[ztengguy]

I think your translator is broke. Your looking for the eigen frequencies of a structure or part?

 

[naeng]

yes, the question is looking for the eigen frequencies without some restriction

 

[PicoStruc]

What do you mean by restriction ?

Eigenvalue is only function of stiffness for stability analysis ?

Eigenvalue is only function of stiffness and Mass for dynamic analysis ?

 

[PicoStruc]

Eigenvector or eigenvalue are not displacements at all ?


If I remember correctly, for the eigenprobem formulation i am used to, the eigenvector values are amplitude generally scaled with a generalized coordinate and eigenvalue correspond to

1) square of the mode frequency in dyanmic analysis
2) load scale factor in stability analysis.

 

[naeng]

What i mean is in a dynamic analysis looking for the eigenfrequencies (natural frecuency) without any boundary condition as a displacements constraints, etc.

 

[GregLocock]

We call that a free-free test. The memebers of this forum may not have come across it, it is a standard approach for automotive and aerospace.

As you say it identifies the resonant frequencies of the test part unconstrained. This is accurate for items in space, and fairly accurate for those where their constraints are very soft compared with the stiffness of the part, such as an engine on its mounts, or the car body on its suspension.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[naeng]

Thanks Greg, your answer is what i´m looking for, i saw that analysis in an aerospace company, and in that moment i didn´t understand it. Thanks, again.