Launch vehicle avionics components must be designed and tested to withstand random vibration environments. These environments are often derived from flight accelerometer data of previous vehicles. This data tends to be nonstationary as shown in the figure above.
The typical method for post-processing is to divide the data into short-duration segments. The segments may overlap. This is termed piecewise stationary analysis.
A power spectral density (PSD) is then taken for each segment. The maximum envelope is then taken from the individual PSD curves.
The maximum envelope for a completed mission can be used to check the test levels for components which flew on that mission.
In addition, the maximum expected flight level (MEFL) for a future mission can be derived from the maximum envelope with the addition of an appropriate statistical margin. The component acceptance and qualification test levels can then be derived from the MEFL.
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A more realistic enveloping method is to use the damage potential based on rainflow cycles, which accounts for fatigue. This method is described in: Nonstationary Damage Potential. I developed this method in collaboration with Sam DiMaggio of SpaceX and with Vince Grillo of NASA Kennedy Space Center.
Here is the PowerPoint version.
The software programs for this method, both source code and executable files, are given at: Vibrationdata Nonstationary Page. The software is available on a subscription basis.
PS: After writing this paper, I learned that Scot McNeill had previously published a similar paper: FDS_FDET_McNeill.pdf. So I may have reinvented the wheel on this one. But I whimsically noticed that Scot used two of my previous papers as references in his own paper.
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