The frequency range of interest of an aircraft Ground Vibration Test (GVT) depends on the size of the structure but rarely surpasses the 80 Hz region. Evidence suggests that there is a strong coupling of structural vibration and the surrounding fluid in the range of 100 Hz and 500 Hz. At this frequency range, the aircraft structure acts as an efficient transmitter of structure-borne sound. Vibratory forces introduced into the structure will be transmitted as structure-borne noise which is radiated as airborne-noise into the surrounding fluid. In particular the sound radiated into the cabin largely affects acoustic cabin comfort. During aircraft operation, the sound field inside the cabin is influenced by tonal sources (e.g. engine and system related vibrations, vortex shedding at fuselage mounted antennas) and broadband sources (turbulent boundary layer) of vibrations. Implementation of highly efficient measures for cabin noise reduction require to localize the areas of high sound radiation as well as the transfer paths of vibration associated with the sources. Knowing these transfer paths and source mechanisms, specific economically viable measures to mitigate the cabin noise can be proposed. The measurement of high frequency vibrations even of smaller structures is a highly complex and time-consuming problem. In order to accurately map the structural vibrations, thousands of sensor positions need to be measured. To reduce the effort involved in performing such measurement task, the institute prototypes and develop contactless vibration measurement systems.
Literature: