3.3. Identification and evaluation of vibration sources based on
acceleration values
Noise is generated by air friction as well as by vibrations. In
rotating machines such as the suction housing, there is a great deal
of vibration that, when emitted, causes noise. The correlation
between part-specific vibration values and noise levels can be evaluated
using contributions. Contribution evaluation helps determines
whether the vibration that occurs in a specific part
influences the overall noise. Measurements of 14 areas (r–14 in
Fig. 4) revealed that the 3000 Hz vibration component occurred
in the impeller area and not in other areas. In addition, the measured
contribution of this area to the overall 3000 Hz vibration
component was 0.9 or higher, nearly 1. This is confirmed by the
results shown in Figs. 10 and 11. Fig. 10 presents the vibration
value and contribution at the position v; Fig. 11 shows the same
data for position12, showing that it had no 3000 Hz vibration component.
In addition, in silencer parts, a 57.5 Hz vibration component
appeared, demonstrating the influence of the silencer on the
noise. Fig. 12 presents the vibration value and contribution at the
position10 and shows that the peak value (57.5 Hz) measured at
silencer outlet was greater than that at positions v and12 (refer
to Figs. 10 and 11), and had a greater contribution to the overall
noise. The 57.5 and 3000 Hz components are the objective frequency,
which also showed higher sound pressure levels. When
compared to the sound intensity results, the higher level agreed
with the silencer at 57.5 Hz and with the impeller at 3000 Hz. Thus,
the sound occurring in the silencer and impeller areas was found to
contribute greatly to the overall noise level.