Structural response of an aircraft fuselage to hydraulic system - A wave and mobility approach

In-flight sound pressure levels can sometimes be intense which cause fatigue to the cabin crew, communication failures and discomfort to the passengers. This is often caused by the turbulent boundary layer flow over the aircraft body, engine noise and vibration and internal aircraft systems. Most of these issues have been dealt with; however, little attention was directed towards understanding the effect of the hydraulic system which comprises a pump located at the back of the aircraft and pipes which run along the fuselage. The pipes are connected to the fuselage using rubber mounts. Experimental measurements show that the hydraulic system, on its own, does not contribute to the in-flight sound pressure level in the aircraft cabin; it is its connection to the fuselage that is problematic. In this paper, a relatively simple model is presented to analyse the power flow from the piping of the hydraulic system to the fuselage. Two models of the mount are presented, and various plate models are utilised to represent the fuselage. The models are augmented with experimental measurements of a section of a typical aircraft fuselage. Experimental results show that the internal resonances of the mount interfere with those of the fuselage around the pumping frequency. The proposed model can be further used to conduct sensitivity or optimisation studies at the design stage of the piping or aircraft fuselage.