1. Unit 44
Vibrationdata
Sine Filtering

2. Introduction Vibrationdata
We have covered time-domain, sine curve-fitting in previous units for signal identification
This unit will use this method for a new purpose, to separate sine and random components of a signal
The curve-fitting is done using random number generation and trial-and- error, with some convergence built-in
A measured sine vibration typically has some slight variation in amplitude and frequency, thus require a few sinusoids to match the data
The following method works best for “short “ time segments
Could be used to remove 60 Hz noise from measured data

3. Vibrationdata Exercise 1 Generate white noise Add sine component
Then separate sine and random components

4. Vibrationdata
Save as: white

5. Displacement
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6. Displacement
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Save as: combined

7. Sine-on-Random Signal
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8. Sine-on-Random Histogram
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9. Vibrationdata Displacement
Time History > Filters, Various > Remove Sine Tones

10. Vibrationdata Comparison Results Case Amplitude fn(Hz) Phase(rad)
Standard Deviations
original:
synthesis:
residual:

11. Comparison, Close-up
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12. Original minus Sine Synthesis
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13. Vibrationdata Exercise 2 Bombardier Q400 Turboprop Acoustics
The PW150A engine/propeller rotation rate during takeoff and climb is 1020 RPM, but is throttled back at cruise altitude to 850 RPM, or Hz
There are six blades on each engine, so the blade passing frequency is 85 Hz

14. Displacement
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Read in file: Q400

15. Vibrationdata

16. Vibrationdata Spectral Peaks
Next step: Separate blade passing frequencies from background noise

17. Displacement
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18. Vibrationdata Results for 85 Hz Component Results
Case Amplitude fn(Hz) Phase(rad)
Diminishing returns effect as additional cases are included for a given frequency

19. Vibrationdata Comparison
Difference is due to background noise and some spectral components unrelated to blade passing frequency

20. Original minus Synthesis
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21. Vibrationdata Residual FFT
Peak at Hz is unrelated to blade passing frequency
Could repeat exercise with more aggressive sine removal