Power Spectral Density
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Utilities
The scripts on this page require the utility modules
PSD of a Time History
The PSD of a time history may be calculated using psd.py
The psd.py script uses the FFT function.
from scipy.fftpack import fft
It includes options for retangular and Hanning windows.
Matplotlib PSD
An alternate method would be to use the matplotlib psd function.
Spectrogram PSD
A script for a spectrogram PSD of a time history is given at: spectrogram.py
The script uses the Matplotlib function specgram.
This function is useful for tracking the frequency change with time.
Overall GRMS Level
The overall GRMS level for a PSD function can be calculated via: psdint.py
Synthesize a Time History to Satisfy a Specified PSD
A sample time history can be synthesized via: psd_syn.py
This script also requires: velox_correction.py
Note that a given PSD does not have a unique time history, because it discards the phase angle.
SDOF Response
This script calculates the response of a single-degree-of-freedom system to an acceleration PSD base input: sdof_ran.py
The method is more accurate than Miles equation, because it performs a point-by-point multiplication of the power transmissibility function times the base input PSD. It thus allows the PSD to vary with frequency.
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