Investigation of passive control devices for potential application to a launch vehicle structure to reduce the interior noise levels during launch: Report for Stage 4, Tasks 1 and 2

The work completed in this stage involves the application of the tools developed in the previous stages to the Representative Small Launch Vehicle Fairing (RSLVF). An improved mathematical framework is developed for calculating the vibro-acoustic response of the system, which reduced the calculation time by approximately 50\%. This faster technique was used to identify trends on an example problem of a rectangular cavity with a simply supported rectangular plate, which had tuned vibration dampers attached to the plate to reduce the sound transmission into the cavity. The results showed that for a fixed added mass to the plate, the greatest noise reduction was achieved by attaching a large number of light-weight tuned vibration dampers to the plate, compared to a small number of heavy-weight tuned vibration dampers attached to the plate. This also had the advantage that the noise reduction that was achieved was relatively insensitive to the location of the dampers on the plate. This method was also applied to the RSLVF and similar trends were identified as shown in the example problem of the rectangular cavity and plate. The second task in this stage involved developing mathematical tools to analyse multiple degree of freedom tuned vibration dampers that are capable of transmitting both translational forces and rotational moments to the structure. Optimisations were conducted to determine the noise reduction that could be achieved with these multiple degree of freedom absorbers. The results showed that for the same added mass to the fairing, the same amount of noise reduction was obtained when 20 PVADs with multiple degrees of freedom, and 500 PVADs with a single degree of freedom were used. However, further investigation is required to assess the sensitivity of these solutions to variations in the acoustic excitation of the fairing, which is the subject of a future task in this project. It is hypothesised that the use of a large number of light-weight single degree of freedom absorbers will provide the most robust solution.

Carl Q. Howard, Colin H. Hansen, Rick Morgans, Anthony C. Zander