why normalization has been doing in modal analysis?

[suryamadduri]

why normalization has been doing in modal analysis?
Ex. 1 mode displacements showing like 250(more than actual value) units.

Thanks,
madduri.surya

 

[GregLocock]

Displacements in a linear FEA modal are arbitrarily scaled, typically the programmers scale the maximum displacement as 100%, but there are several other choices.

Cheers

Greg Locock


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[electricpete]

What he said.

An eigevector (modeshape) x is a solution to Ax = Lambda*x
If Ax = Lambdax is true than A*c*x = Lambda*c*x will also be true (since both sides scale linearly with c) and c*x is also an eigenvalue... so you can see the eigenvalue is only determined to an arbitrary multiplicative constant.

You can take the modal solution (eValues, eVectors) and combine thenm with an assumed excitating force to compute a total solution as a weighted sum of modes... the weighting factors also called participation factors take the normalization into account and the calcualted magnitude of each weighted modal response should match the real world to the extent your model is accurate.

What do you mean by "actual value". Can you describe your experiment and comarison some more?



=====================================
(2B)+(2B)' ?

 

[suryamadduri]

Generally mode shape scaling done for modal analysis.why?

 

[suryamadduri]

because of normalization

 

[nanobot29]

I'm not sure i fully understand the question but i do agree with Greg and Elec's statements. FEA modal analysis does not calculate exact displacements. You would need to run a transient or harmonic analysis where you can input forcing functions and system damping to calculate an accurate response.