Response spectrum method for fatigue damage assessment of aero-hydraulic pipeline systems

This paper proposes a response spectrum method to assess the fatigue damage of aero-hydraulic pipeline systems subjected to random airframe motion. A real-valued analytical formula for calculating the random stress response of a clamp-pipeline model transporting fluid is derived using the complex modal superposition method and random vibration theory. Based on our previous work on the response spectrum method for fatigue damage assessment, the authors establish a set of complex modal combination formulas for the expected damage rate, introducing new velocity-velocity and displacement-velocity combination coefficients. These formulas characterise the expected damage rate as a linear combination of the damage responses that are not reliant on the spatial distribution of the pipeline model. The fatigue damage assessment of different pipeline models is computationally efficient as only the natural frequencies and the mode shapes need to be calculated. The correctness of the complex modal combination equation is verified by the rain-flow counting method, and the effect of the fluid velocity on the expected damage rate is discussed.