In AS1418 Cl 4.5.3.3 there is a table categorizing hoisting application group for cranes (H1 to H4). One of the properties is the fundamental natural frequency of structure (vertical plane)- see table below.
However the standard do not discuss much about this "vertical plane fundamental natural...
jgKRI can you enlighten me under what circumstances strain gages can be used? Did you try to measure load of equipment without isolation system?
I have a feeling that this topic opened up a large can of worms. It belongs to ill-conditioned inverse problem which recent research can be...
sk_cheah hopefully I will be able to setup an experiment to validate on that (not so soon)
BrainE22 strain-gauging is more complex in operation but worth a try too on a scale down experiment, thank you for the suggestion.
jgKRI do you get the dynamic load in frequency domain? What are your...
@burningDiesel
How do you related the allowed vibration (which is a response change according to the foundation the equipment lays on) to dynamic load (which is usually constant regardless of foundation).
@ sk_cheah
You are right that the amplitude of the response in this circumstance is generally low (5um/s - 50um/s). Can this be compensated by moving the floor response sensor closer to the forced hammer?
From my experience a 1000g/mV sensor are likely to pick up the signal in such scenario.
It...
How does one accurately measure the effective dynamic load in frequency domain exerted by heavy equipment (huge vacuum pump, multistage centrifugal pump, and etc.) transmitted to arbitrary floor without reallocating the equipment?
One method I can think of is to work out the FRF of the floor at...
Thanks for your input Greg! You are always the first few to reply.
I have reduced the sampling frequency to the minimum and the sample time to the maximum and test it on a harmonic excitation (built an experiment to verify it). The problem is still exist because we are dealing with extremely...
As pointed out in the old thread below, it's sort a norm to use 1/3 octave band for environment vibration assessment.
"One-Third-Octaves for Dummies"
Link
The bandwidth increases as central frequency so spectral leakage in high frequency band (>20Hz)is not a concern.
But then it come to very...
Can't agree more! As I learn more on this topic I found I know less than I imagined.
Upon testing on a signal composed of 1, 10 , 50 Hz, using hanning window with the correct energy correction give an excellent match on high freq band (10, 50), where leakage on low frequency band (1) persists...
Thanks for your brainpower Steve and Greg!
Looking back at your comments after a few months of learning and practice I found them extremely helpful.
The error mentioned previously could be caused by spectral leakage where the signal block is not an integer period of its frequency component...
No window is used.
I have been using this code modified from Embedded Lab. I found out If we choose the sample size in the power of 2 it gives very small error (~0.1%). If we not, eg. 1000, then there is still 1024 bins and ifft go flat after the 1000th point, the error grows.
The other weird...
Did tests on a signal composed of sinusoidal waves of different phase in the same octave band (center 25Hz)
x(t)=2*sin(2pi*23*t)
y(t)=5*cos(2pi*24*t)
z(t)=15*cos(2pi*25*t+pi/5)
The sum of fft line values are 260, very close compared to hand calc, 2^2+5^2+15^2=254, a discrepancy ~ 2.4% in...
Greg,
By energy point of view, total energy in octave equals to total energy in narrowband.
Both my fft amplitude term and octave band amplitude need to be in rms velocity term (mms-1).
So:
1. square the fft lines (vi->vi^2)
2. assign them to bin and sum them, Sum(v1^2+ v2^2+...)
3. square root...
Lately I have came across a vibration design criteria with 1/3 Octave Band. Been doing a lots of dynamic analysis on narrowband but this 1/3 octave band is rather new to me. Some suggest we assign narrow band amplitude (fixed interval) into octave bin and sum them, some suggest to average them...
