Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

436 Centrifugal Pumps: Design and Application
The mechanical natural frequencies of the piping spans should not occur
in the same range as the acoustic response frequencies. The analysis
aids in determining the allowable frequency range that can be used to establish
the proper design of the piping supports and span lengths to minimize
the potential for exciting a piping resonance, lite acoustic analysis
can be used to redesign the piping to modify the frequency response and
particular acoustic modes that may be predominant.
Acoustic Resonance. When a dynamic pressure pulse propagates down
a pipe and reaches a restriction or pipe size change (flow area), the pulse
is reflected [13, 15]. As the series of pressure pulses continue to be reflected,
a standing wave is generated; that is, at a point in the pipe, the
pressure periodically rises above and drops below the average line pressure
(simple harmonic variation). The super-position of an incident pulse
and a reflected pulse, being the sum of two pulses traveling in opposite
directions, produce the standing wave.
If the timing (phasing) of a reflected pulse matches a new pulse, the
two pulses will add, or amplify. The timing of the pulses are dependent
Figure 18-0. Passive acoustic response of piping system.