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Dynamics and Vibrations of Mechanical Systems

Relatore: Prof. Roberto Corradi

Tutor: Prof. Andrea Bernasconi

Università di Provenienza: Politecnico di Milano - Ingegneria Meccanica

Titolo della Tesi: Modelling and testing of trim panels for rotocraft interior noise prediction

Modelling and testing of trim panels for rotorcraft interior noise prediction

Introduction

  • Interior noise enhancement in rotorcraft is particularly challenging due to the multiple vibro-acoustic sources of mechanical and aerodynamical nature contributing through multiple transfer paths to noise in the cabin
  • Interior noise improvement can be pursued acting at the source, along the transmission path between the source and the cabin, or at the receiver
  • With reference to the transmission path, interior trim panels confine the passenger cabin, realizing the very last attenuation stage for vibrations and noise before reaching the cabin.

Objectives

  • The present work aims at developing mathematical models suitable for predicting the vibro-acoustic response of trim panels in the mid-high frequency range, accounting for both structure-borne and airborne paths.
  • With reference to the airborne path the trim panel Transmission Loss needs to be predicted under diffuse field excitation.
  • Structure-borne path needs to be investigating considering an incoming broadband vibration on the fuselage side. Influence of the vibration isolators needs to be assessed, accounting for the vibration isolator dynamics as well.
  • The models developed in this framework need to be fast and accurate in order to be suitable for supporting the design of the trim panels and vibration isolators in an industrial context.

Results

Two main models have been developed accounting airborne and structure-borne paths:

  • The sound transmission model is suitable for predicting the Transmission Loss of arbitrarily layered trim panels. The model has been experimentally validated.
  • The hybrid deterministic/SEA model is suitable for assessing the structure-borne response of trim panel-isolator systems. In particular, the isolator dynamics is included through an isolator model based on a dynamic stiffness characterization up to 6 kHz.

Conclusions

  • Development of isolator and trim panel models, tuned on the results of experimental tests performed on the single components
  • Development of integrated models for the prediction of the vibroacoustic behaviour of the trim panel
  • Investigation of the structure-borne noise in trim panels supported by vibration isolators accounting for the isolator dynamics
  • Investigation of the airborne noise in trim panels by means of both simulations and experimental tests
  • The models developed are suitable for supporting the design of trim panel-isolator systems

References

S. Baro, R. Corradi, Investigation of Structure-borne Noise In Plates Supported By Vibration Isolators Through A Hybrid Deterministic/SEA Approach, Proceedings of the Inter-Noise, 2018.
S. Baro, R. Corradi, A. Parrinello, G. Ghiringhelli, Numerical and experimental assessment of the transmission loss of honeycomb sandwich panels, Proceedings of the Inter-Noise, 2018.
A. Nilsson, S. Baro, E. Piana, Vibro-acoustic properties of sandwich structures, Applied Acoustics, 2018