Modal Analysis
Modal Analysis
(OP)
Could anyone explain to me, what is the crucial steps in developing modal analysis?
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RE: Modal Analysis
RE: Modal Analysis
First of all, thanks for your response.
Actually, i'm intended to develop experimental modal analysis of generator's end windings (Both DE & NDE sides).Bump tests already been done & the result shows that there are natural frequencies appeared on 95 - 115 Hz (area of interest: 2x of operating speed). Since this my attempt, hopefully you can guide me precisely....
thanks in advance
RE: Modal Analysis
Typically, the engineer will simplify the system to something that is idealized as a series of masses and springs. For a single degree of freedom system, this is a single mass and a spring. The spring stiffness is determined depending on the system configuration (for instance, a beam stiffness equivalent would be AE/L where A is the cross-sectional area, E is the modulus, and L is the length of the beam). The fundamental frequency is then calculated as the square root of k/m where k is the stiffness and m is the mass.
More complicated systems are more difficult, but all of this is covered in a basic vibrations course. Virtually any book on vibrations would have to cover this simplification methodology.
Someone more familiar with your particular application may be able to provide more specific examples.
RE: Modal Analysis
Tobalcane
"If you avoid failure, you also avoid success."
RE: Modal Analysis
Well, you are in luck. B&K have published a lot on the subject. I suggest you read the vibration and the two structural testing ones to start with, then search the rest of their site for the many articles and so on on modal analysis.
http://www.bksv.com/Library/Primers.aspx
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Modal Analysis
RE: Modal Analysis
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Modal Analysis
RE: Modal Analysis
RE: Modal Analysis
Tobalcane
"If you avoid failure, you also avoid success."
RE: Modal Analysis
Analysing the data, and displaying the mode shapes, and then doing some calculations based on the FRFs for whatever it is you want to do with them.
Strictly speaking it sounds to me that you may be able to jump to the third part straight away by using SMURF (structural modification using response functions), receptance theory, or from first principles.
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Modal Analysis
seems to have many articles that are directly relevant.
Nice link 2BC
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Modal Analysis
Could you please go in detail about the mode shapes & how to identify from FRF spectrum?
Thanks
RE: Modal Analysis
Cheers
Greg Locock
SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Modal Analysis
To obtain mode shape of a structure, a minimum set of FRF measurements must be taken either a single fixed input and many outputs or between a single fixed output and many inputs.Why not using many inputs and many outputs?
RE: Modal Analysis
The problem is that although the resulting model is more robust, it is also noisier.
A SIMO model linearises several sources of non linearity, and is easy to analyse channel by channel. A MIMO analysis is based on partial coherence, and the first step is to look at how to break the signals of interest up.
There's nothing really wrong with MIMO apart from complexity and time, in fact where you have large non linear structures it is likely to prove more reliable and less frustrating. For instance on a whole car, if you take two complete SIMO surveys using different excitation points you can spend weeks trying to reconcile the two resulting modal models. That's why we don't do that.
Cheers
Greg Locock
I rarely exceed 1.79 x 10^12 furlongs per fortnight