Indirect blocked force measurement of a hydraulic power pack for structural vibration transmission into an airframe

Centralization of electrically driven hydraulic power packs into the body of aircraft have increased the attention on the noise and vibration characteristics of the system. A hydraulic power pack consists of a pump coupled to an electrical motor, accumulator, reservoir, and associated filter manifolds. In previous studies, the characteristics of the radiated acoustic noise and fluid borne noise were studied. In this paper, we focus on the structure borne forces generated by the hydraulic pump characterized through blocked force measurements. The blocked force of the pump was determined experimentally using an indirect measurement method. The indirect method required operation with part under test fixed to an instrumented receiver structure. Measured operational accelerations on the receiver plate were used in conjunction with transfer function measurements to predict the blocked forces. Blocked forces were validated by comparing directly measured accelerations to predicted accelerations at positions on the receiver plate that were not used for the inverse calculation. To build further confidence in the results, two receiving structures were used to calculate the blocked forces and blocked forces were compared. The determined blocked forces can be used by aircraft OEM’s for further acoustic evaluation.