Frequency response - Hydraulic network

[LordCatG]

Hello everyone,

i have a measured signal of a high pressure oscillation in a hydraulic network. Performing a FFT of said signal shows two dominant frequencies, a and b.
After performing a linear analysis of the hydraulic network i found out that the network has two eigenvalues at those frequenices a and b. If i assume that the hydraulic network is excited at those two eigenvalues and that is what causing the high pressure oscillation, that should mean that excitation signal should have those two frequencies included?

 

[FactChecker]

If I understand your question, yes, the frequency must have come from somewhere, at least initially. If the eigenvalues have magnitude greater than 1, the frequency may have only been there for an instant and grown from that. In that case, the initial disturbance may have been very small and undetectable.
If the eigenvalue magnitude is less than 1, then the excitation signal must continue to include some of that frequency in order to keep it from fading away.