PFA Module Glossary
Much of the terminology associated with pulsation analysis is specific to time-frequency analysis and/or to vibrational analysis. The following words have been defined for ease of comprehension when working with the PFA module. Note that most of the defined words include page numbers and, occasionally, equation numbers. All of these references can be found in the document referenced at the end of this page.
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Sample Rate - The inverse of the time step (Page 14)
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Harmonic Frequencies - Multiples of the base frequencies that excite the system
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Forcing Function - The function that will be used to “ring” the system. This function can be the pulse in a non-low-pass-filtered system, or can be determined by the cutoff frequency that is determined by using Fast Fourier Transform (Page 7)
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Pulse - The near-instantaneous increase, then normalization, of flow
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Fast Fourier Transform (FFT) - A method used to transpose the time-domain (flow vs. time) into the frequency-domain (magnitude vs. frequency)
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Cutoff frequency (fc) - This is the maximum frequency that will be shown in the frequency analysis results.
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Detectable Frequency - This is the maximum frequency which will be recognized by xStream during the transient solution. If frequencies exist above this frequency they will be aliased to lower frequencies in the final solution.
References
Blanding, James M., Ph.D., and Trey Walters, PE. Pulsation Analysis in Positive Displacement Pump Systems Using Waterhammer, Modal, and Animation Software. Houston, TX: 45th Turbomachinery & 32nd Pump Symposia, Sept. 2016.
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