Wave transmission in multi-panel structures

Large engineering structures for transport, from passenger ships and super tankers to aircraft and spacecraft structures, are designed for low weight, powerful propulsion system and higher speed. Along with this tendency is a progressively more stringent requirement of higher comfort with respect to noise and smooth ride quality. Prediction of noise and vibration at the design stage is therefore becoming increasingly important. Unfortunately, there is no single prediction method that covers the entire audible frequency range, and the mid-frequency range is currently difficult to estimate. The objective of this project is to develop a technique for predicting the vibrational response of structures in this frequency range. Computational routines such as the finite element method are used successfully at low frequencies, and statistical energy analysis (SEA) in its present form is applicable at high frequencies. However, the newly proposed wave intensity analysis appears to be capable of closing the mid-frequency gab, because it allows two of the SEA assumptions to be relaxed. In the development of this technique Langley has shown that this applies to the diffuse field assumption and the equipartition of modal energies. This means that reliable predictions can be made in the mid-frequency range. In this project the wave intensity analysis has been examined, and it is found that the technique can be improved by using transmission coefficients that include the effects of finite subsystems such as damping, modal density and length-wise boundary conditions. This has been demonstrated in predictions of vibration levels in small assemblies of plate panels. The wave intensity technique in its original form has also been used for calculating the structural wave transmission and energy distribution in extended plate structures with idealised boundary conditions. Comparison with experimental results from a moderately damped box-structure of aluminium shows a good agreement.