Comparison of Vibro-acoustic Performance Metrics in the Design and Optimization of Stiffened Composite Fuselages

Optimization of composite aircraft fuselages with respect to acoustic requirements is an emerging engineering problem. Late-stage design solutions such as the application of the additional insulation layers may be undesirable since they would add additional mass to the structure. Moreover low-frequency sound transmission loss through cylindrical shells is dominantly governed by the stiffness properties of the structure. Therefore, investigation of the stiffness distribution effect on sound insulation performance is important. Structural optimization for the acoustic performance can be performed using different approaches. One method is to model both structure and acoustic cavity, and conduct coupled structural-acoustic analyses to predict the sound pressure levels at certain locations. Another method is to carry out the design only in structural level to reduce structural vibrations therefore structural-born noise. This is a relatively coarse approach compared to the first method, but it has considerably lower computational cost and it produces more versatile results. In this paper, optimization studies for stiffened fiber-reinforced composite fuselages for vibro-acoustic requirements are presented. Optimum stiffness distributions are found using aforementioned two preliminary design methodologies. The results obtained by sole structural analyses are tested together with the acoustic cavity and compared with the coupled simulation results.