Vibroacoustical sensitivities of stiffened structures due to attached mass-spring-dampers with uncertain parameters

The slightest manufacturing tolerances and variances of material properties can have a significant impact on structural modes. An unintentional shift of eigenfrequencies towards dominant excitation frequencies, however, may lead to increased vibration amplitudes of the structure resulting in radiated noise, which will reduce the passenger comfort inside an aircraft cabin. The focus of this paper is on so-called non-structural masses, also known as the secondary structure, that are attached to the primary structure via clips, brackets as well as shock mounts and which constitute a major part of the overall structural mass. Using the example of a simplified fuselage panel the vibro-acoustical consequences of parameter uncertainties in linking elements is studied. For the specification and quantification of parametric uncertainty, the Fuzzy Arithmetic provides a suitable framework. It is capable of creating deterministic parameter combinations, which then are re-transformed into fuzzy outputs and which subsequently can be used for the evaluation of the simulation results regarding target quantities and influence of each parameter on the overall system behaviour. To assess the vibrations of the fuzzy structure and by taking into account the excitation spectra of engine noise, modal and frequency response analyses are conducted.