Modeling of Elastomeric Engine Isolators for Prediction of Aircraft Cabin Noise

The paper describes a unique dynamic characterization modeling process of Lord Corporation’s isolation system for an executive jet aircraft. It was performed as part of a Joint Plan of three companies to build a global acoustic model of the aircraft, engines and engine isolators, which would allow for prediction of the cabin noise. The objective of the isolator modeling process was to calculate the dynamic stiffness matrices of the three isolators, which are made of metal and rubber materials, as functions of frequency for the working point conditions. The Modal analyses of the metal components and rubber packs showed that their dynamics would not affect the dynamic behaviors of the isolators in the frequency range of interest. Isolator Model C, which is a hybrid model, had an analytical part and an experimental part. The analytical part was based on nonlinear hyperelastic FE models of the rubber packs. The outputs of these models were six stiffnesses per rubber pack for the working point static loads. These stiffnesses served as input to model B, which is a spring FE model that allowed for the calculation of the full 6X6 isolator static stiffness matrices. The experimental part of Model C was based on dynamic shear tests of rubber samples, which addressed the effects of the working point temperature, static and dynamic strains, as well as, frequency on the rubber properties. The test results were used to scale the six stiffnesses per rubber pack, which were obtained from the hyperelastic models. The scaled stiffnesses served as input to Model B, which was used as an engine to generate the dynamic stiffness matrices of the isolators as functions of frequency for the working point conditions.

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