Objective
Noise is one of the important limiting technical factors in modern aircraft design. Community as well as passenger acceptance is essential for the commercial success of a new aircraft. Hence, a reduced internal noise level is becoming more and more important as a market factor.
In an aircraft structure vibration induced noise may be caused directly by the engines or indirectly by external noise sources, eg the propellers. The interior noise field caused by the vibrating structure is a result of the noise transmission through the aircraft wall assembly, which in essence is a double shell system. To accurately predict the internal noise levels, in such a complicated system, is difficult for a number of reasons. The main problem, however, lies in the prediction of the transmission of propeller or rotor noise through the fuselage into the cabin; it applies equally to fixed wing aircraft as to helicopters.
The main achievement of the BRAIN project is the development of fundamental building blocks for a complete design methodology in aircraft interior noise. These building blocks are based on two major aspects of the research work:
Modelling the mechanisms responsible for the damping increase in an aircraft when interior trim is mounted, ie increasing knowledge and understanding
Development of suitable prediction methods to model these mechanisms. ie addressing prediction capability
and acceptance of these results by industry will be dependent on both the accuracy of the methods and the required computational effort.
The results from the performed research show that the thermal insulation is the by far most important source of the high damping levels observed in these systems. There are two phenomena which occur in the double wall which are central to the modelling of this damping:
high damping in the deformation of the porous medium itself
radiation/air pumping, induced by a vibrating surface.
As a consequence of the results discussed above, the core part of the development work in BRAIN came to be focussed on the thermal insulation and material damping modelling. For these particular aspects, improved prediction methods have been developed which allow predictions of the transmission of sound and vibrations through a double wall with thermal insulation filling.
The new models developed in BRAIN require some specific material parameters, which in some cases are quite new. In BRAIN vibration testing in vacuum was developed, and used, to get damping parameters associated with the porous material frame deformations and for the plexi glass Neural Network based estimation of the AHL parameters was also developed. In addition, dedicated procedures for extraction of the static moduli of the thermal insulation were also developed together with techniques for estimation of equivalent linear properties of weakly non-linear mechanical systems.
The BRAIN project is focussed on a detailed, fundamental, investigation of the mechanisms of noise transmission through fuselage structures. It is aimed at identifying, understanding and quantifying these mechanisms, and on this basis developing accurate models that describe the transmission process. Through the usage of accurate prediction methods, applicable at the design stage of a new aircraft, designs exhibiting an optimum balance of low weight and low cabin noise would then be possible to reach.
Topic(s)
Data not availableCall for proposal
Data not availableFunding Scheme
CSC - Cost-sharing contracts
Coordinator
3001 Heverlee
Belgium
Participants (7)
81043 Capua
161 11 Bromma
8316 PR Marknesse
92322 Châtillon
2 Dublin
Southampton
26500 Patras