modes & its significance
modes & its significance
(OP)
What is mean by modes & its significance in structural analysis?
why i need to perform mode based structural analysis?
why i need to perform mode based structural analysis?
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RE: modes & its significance
B) mode based methods significantly reduce the computational effort, due to uncoupling/orthogonality
RE: modes & its significance
Mike McCann, PE, SE (WA)
RE: modes & its significance
@csk62 mathematically modes means eigenvectors but what is its physical meaning. Imaginary of stiffness & mass distribution in the entire structure is my interpretation of modes.How it will reduce computational costs?
@msquared48 If my excitation has same frequency as natural frequency of the structure also direction of application is same as mode shape then it will leads to resonance & uncontrolled vibration will occur so whether direct frequency analysis without considering modes is senseless?
Once againg thanks for spare your time, please through some light on above mentioned queries.
Regards
Krishna
RE: modes & its significance
RE: modes & its significance
RE: modes & its significance
The free (unforced) motion of a linear system can always be descrigbed as a linear combination of its modes. That is a pretty basic physical significance of a mode. It describes the way the system vibrates when no external forcing remains.
While above paragraph focused on free behavior, these same modes are remarkably helpful for predicting forced behavior.
Additionally a modal model of a system provides more physical insight than other models for example state space model. (knowing the frequencies and modeshapes we can often qualitatively guess the responses much better than if we knew the state space coefficients… example: you said yourself a system will have high vibration near resonance).
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(2B)+(2B)' ?
RE: modes & its significance
A) I would say the physical meaning of a mode is the displacement behaviour of the structure at a particular natural frequency. Modes are usually normalized by disp when showing a plot, for ease of understanding. I believe they need to be mass normalized to calculate participation factors (how much each mode participates).
B) As electric pete mentioned, any system can be described as a linear combination of its modes. If we say that 90% of the structure can be represented by a reduced number of modes (say three for example), then you can accurately estimate forced analyses using only these three modes, since the remaining modes are less important. Analyzing the structure by using just these three modes will probably be much more practical computationally than a timemarching solution for the entire structure.
Aside:
One professor once told me: Never say "N factorial", just scream "N" at the top of your lungs. :)
RE: modes & its significance
It is embarrasing to design a housing with a large panel eager to sing a song at gear mesh frequency.
RE: modes & its significance
Good Point. The rule of thumb the good people at Abaqus told me was that the maximum frequency extraction range should be twice the maximum frequency sweep range in SSD. (if you want to do a sweep from 50100Hz, you should probably extract all eigenvalues between 50200Hz)
RE: modes & its significance
http://commons.wikimedia.org/wiki/Category:Drum_vi...
here are a couple:
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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
RE: modes & its significance
Example look at the two modes in IRStuff's link.
One the left is the first natural frequency.
On the right is the 2nd natural frequency.
If you were to apply that excitation at that 2nd natural frequency but located spatially at the exact middle of the disk, then you would not excite the resonance. The reason is that you are applying excitation at the node of the 2nd mode.
So it is not just relationship between excitation frequency and system mode frequency that leads to resonance response, it is also relationship between excitation spatial distribution and system mode shape.
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(2B)+(2B)' ?
RE: modes & its significance
Those new Koni shocks sitting in their boxes on the back seat can not contribute much to wheel control.