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[FAQ]

Neither Mechanical nor Mechanical APDL provides an automated method for performing a sine-on-random vibration analysis. A harmonic response analysis is deterministic (real + imaginary results), where as a random vibration analysis is statistical (1-sigma results). So, it is not clear how to combine the results. Two methods employed sometimes employed to simulate the sine-on-random effect are: 1. Include the harmonic loading (sine) as a ‘spike’ in the PSD input spectrum (area of sine loading should have same energy content) and then perform a single combined PSD analysis. 2. Perform a separate harmonic response and random vibration analysis and convert the harmonic response results to “RMS”” values. Then statistically add the RMS results from the harmonic analysis to random vibration results.