Correctly Interpret Random Vibration Analysis Results Using Ansys Mechanical — Lesson 3

Consider an airplane in flight or a train on its tracks — both experiencing random vibrations. To study such models with uncertain loads, we utilize random vibration analysis. The input of this analysis follows a Gaussian distribution and is statistically represented as a power spectral density. Because the input is uncertain, the output of this analysis is statistical in nature as well. As a result, unlike others, the directional outcomes (such as stresses) cannot be combined in the usual way; therefore correctly interpreting the results is crucial. In this video, we will discuss the importance of interpreting the results of a random vibration analysis correctly and how to do so.

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0:00 - Intro
1:06 - Statistical nature of the results/ output
2:15 - Scale factor for RMS Results (1 sigma, 2 sigma, & 3 sigma)
2:58 - Derived Results/ Derived Quantities
4:38 - Solution Coordinate System
5:08 - Importance of Element Orientation
5:43 - Response PSD Tool and benefits
5:58 - RPSD Definition
6:29 - RMS Definition
6:44 - Expected Frequency Definition
8:39 - Setting Element Orientation
9:04 - Requesting Sufficient Modes
10:01 - Participation Factor Listing
10:35 - Input PSD Specification
11:30 - Random Vibration Results
15:10 - Relative vs Absolute Results
16:33 - Frequency Clustering

[michapiersa]

Does multiplying-by-3 method for equivalent stress applies for all 1, 2, and 3 sigmas? For example, in 13:40, if I would like to report equivalent stress in 3 sigma, I should multiply 283.35 MPa by 3 (because of Segalman-Fulcher algorithm) and state, that actually equivalent stress is 850.05 MPa?

[Dineshkumar]

11:05 how the G acceleration value is calculated?

[SoulfullSpace]

We can also get the same results using harmonic response, whats the difference then?

[adreasdinos]

can we get an RPSD graph for multiple points?