Modelling of fuselage/floor structures and associated cabin acoustics for the prediction of propeller induced interior sound fields

Wei, Jiantao (1995) Modelling of fuselage/floor structures and associated cabin acoustics for the prediction of propeller induced interior sound fields. University of Southampton, Doctoral Thesis.

Abstract

An analytical model of fuselage/floor structures and associated cabin acoustics has been developed. In the model, a fuselage is idealised as a thin circular cylindrical shell stiffened by equally spaced ring frames and stringers. The stiffeners are treated as discrete members. A floor may be mounted in the fuselage either through uniform constraints or at discrete points. The constraints may have an offset from the skin of the fuselage. This represents the situation where a floor is attached to ring frames. The floor is a rectangular plate with equally spaced stiffeners along both dimensions of the plate. The structure is assumed to be simply supported at the two extreme ends. The Rayleigh-Ritz and extended Rayleigh-Ritz energy methods are used to derive the equations of motion of the structure. Several techniques have been developed to cope with the complexity of the model and to reduce the size of the problems. These include the treatments of stiffeners, the use of the coupling relationships caused by equally spaced stiffeners and the replacement of the geometric constraints with a set of equivalent constraint equations which are much easier to implement. The cabin acoustics is analysed using the acoustic finite element method. The analysis is of a three-dimensional acoustic cavity is reduced to a two-dimensional problem. The acoustic finite element mesh is generated using either quadratic or curvilinear isoparametric elements. The prediction of the interior sound pressure field is based on an uncoupled solution.

The model was validated by applying it to numerical examples found in the literature to evaluate the structural and acoustic natural frequencies. The comparisons demonstrated the advantages of the present approach in handling large numbers of stiffeners and discrete geometric constraints. It showed that the analysis is a very efficient method to analyse frequency pass bands of periodic structures both finite and infinitely long.

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