Page 47 - Shock and Vibration Overview

Response Spectrums

mount in excess of a couple hundred hertz natural frequency to at least not amplify the
vibration levels in the environment.

Let’s take this example a step further and develop a test standard PSD from the
experimental data. That data that was captured with the Slam Stick represents actual
data; but can a simplified PSD be developed off that experimental data? Again using the
MATLAB GUI package, a simplified PSD can be created that envelopes the maximum
expected flight level plus some margin. This is a more prudent approach because
conditions experienced experimentally may vary in the future (the weight of the

passenger in the seat, temperature in the cabin, engine speed etc.). Using a trial-and-
error approach the script derives the least possible PSD that meets the VRS requirement
of the raw data shown in Figure 29.

Figure 29: An enveloped PSD is calculated using a vibration response spectrum to ensure it meets
or exceeds the VRS of the experimental data.

The vibration response spectrum of the simplified PSD is shown in Figure 30. It still
envelopes the same levels as that shown in Figure 28; but it does so more

conservatively. This PSD may be distributed to customers so that they can design their
components accordingly and test them to appropriate vibration levels. Note the relative
displacement shown in Figure 30; if isolator mounts are used then it’s important to
ensure they can withstand the expected relative displacement levels so they don’t
bottom out.

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