Thank you gentlemen for the comments.
Just to highlight the practical aspect of my question. When generator is opened (end shield/bell) is removed, there is dust (if there is oil than - dark grease) visible on end winding. This is result of insulation wear. If insulation wears out – sooner or...
Hello All
One of the most important aspects of any vibration analysis is Vibration Limit. So one may expect that for most powerful generators (steam turbine driven generators) these data are readily available. It is not true.
What is available - Vibration Limits on bearings and rotor...
Michael,
Is it already defined how non-linearity will be modeled in FE?
I cannot agree on you estimation of the error distribution. Let us conceder impact testing (SISO or SIMO).
If resonance pike is identified, then for a mode at 50-200 Hz error in frequency cannot be more then 5%...
Michael,
I will vote to give you the job if somebody is to ask me.
Can you tell how you are modeling output of nonlinear system: in FE code or in MatLab thru the system of equations?
How is error distributed between modal parameters in case when SISO applied to non-linear system? I think...
Michael,
I really appreciate you help. Now the issue is clear.
Since at least some of my modes call for force appropriation analysis, can you explain the base principle of it and how new is the method?
Thanks,
Dmitry
...mode shapes from an FE analysis, but I am trying to figure out if all curve fitting is already done or not.
Judging from yours and Greg postings:
* In case of AMPLITUDE - I am working with mode shape, eigenvector or "modal vector in real mode format"
* In case of AMPL/PHASE...
I do have three spectrums. Each is the sum of signals for all the accelerometers in the specified direction. So they are not for a single point. They give only an idea about FRF.
Regards,
Dmitry
Hi Greg,
I have access only for animated mode shapes. They are animated in STARReport system. Complete help on the topic is:
METHOD DESCRIPTION
AMPLITUDE Displays the modal vector in a derived real mode format.
AMPL/PHASE Displays the complete modal vector both real and imaginary coefficients...
Hi All,
I'm doing analysis of modal test data. I found that mode shapes look different depending on method for deriving/visualization!
For particular frequency:
By First method - Amplitude ("Displays the modal vector in a derived real mode format.") - I see bending of the...
Hi, Lotten!
I think you are right. Applying sine signal and wiring its frequency also can do it. But to do test??? – It never came to my mind because some one should know the answer with appropriate accuracy.
Regards,
D.Semenov
Hi Greg!
You are a bit late, I have already developed one :) and probably a month earlier I received curve fitter (CF) evaluation copy from Vibrant Technology, Inc.
http://www.vibetech.com
But CF development and usage is interesting but quite separate question that deserves independent tread...
ANTOINE,
I wold like to use “… appropriate formula…”, but Formula is solution of certain equation (as usual) and equation implies existence of a set of assumptions on account of system properties. If I do not like any one of these assumptions, then usage of the Formula becomes questionable.
As...
Bradh,
I’m after the modal parameters (characteristics). My goal is predict modal parameters of real system by the most simple model. In fact this task is quite similar to devising a one-degree of freedom curve fitter for particular pike of experimental mobility function.
The difference.
In...
Hi thierrybelge!
As I think, this way we do can describe system behavior under external load. In this case beam deformation in the point of interest is dependent from end conditions (as you said), as well as, from external force type (for example distributed or point applied).
But what...
...model which amplitude (in the middle of span) and frequency will be the same as for the beam first bending mode.
The model described as: M * x" + C * x' + K * x = 0.
How model parameters are related to parameters of the real system?
I think in this case:
M = m;
K = 1/ (E*I)...
Hi All
I feel like the initial question was about more simple problem then the answers are. It was about behavior of the model.
If modeled structure is I-beam, then the bigger inertia moment – the bigger rigidity and so – natural frequencies.
If cross-section of modeled structure...
...APS, Linear APS, PSD and Linear PSD:
MySignalFFT=fft(MySignal);
% Ns – sampling frequency
% N – lengths of time realisation
% APS
plot((0:N/2-1)*Ns/N,
(conj(OutputFFT(1:N/2))/N*2.* MySignalFFT(1:N/2)/N*2));
% Linear APS
plot((0:N/2-1)*Ns/N,
sqrt(conj(OutputFFT(1:N/2))/N*2.*...
Hi ronfrend!
Can you say how high mast be frequencies to be affected by nominal impedance of 10 m cabel? The accelerometer is a Piezo-Electric type with built in amplifier.
Regards
D. Semenov
Greetings ronfrend!
Doing cable repair, I have found out, to my surprise, that its screen is not connected to anything. So it cannot be grounded. Is it normal?
I would like to learn if cable entrance resistance is of importance. How to choose entrance resistance of a cable?
Regards...
