Random response analysis of hydraulic pipeline systems under fluid fluctuation and base motion

Aero hydraulic pipeline systems are subjected to internal fluid fluctuations and random base motions during operation, resulting in time-varying system parameters and nonstationary random responses. To analyse this situation, a nonstationary random response analysis method and a fatigue damage assessment formula for periodic time-varying systems under stationary random excitations are proposed. The nonstationary random response is described by a time-varying power spectral density function, which is strictly characterised by a set of pseudo responses of a periodic time-varying system under a series of harmonic excitations. A frequency-domain iterative solution format for the pseudo responses is constructed and combined with the fast Fourier transform to obtain the time-varying power spectral density function. A fatigue damage assessment formula is derived by discretising the time-varying power spectral density function of the pipeline stress in both the time and frequency domains. The proposed method only requires a few iterations at specific frequency points to calculate each pseudo response in a wide-band random airframe motion environment, showing high computational efficiency. A practical application concerning a section of the wingtip hydraulic pipeline is presented to demonstrate the correctness and efficiency of this method. The variations of pipeline responses and fatigue damage rates under fluid fluctuations and random base motions are also discussed.