Acquiring statistical energy analysis damping loss factor for complex structures with low to high damping characteristics

The present study has its root in a need of the aircraft industry related to modeling of aircraft structures by the statistical energy analysis method. The measurement of the damping loss factor is more particularly addressed for complex structures showing low to high damping characteristics. The first part of this work is totally dedicated to the damping loss factor. Two much used methods are scrutinized: the decay rate method and the power input method. The efficiency of those methods is somewhat validated by the aid of the half-power bandwidth method. A parametric study using the finite element method is proposed and focuses on constant thickness panels and ribbed panels. The conclusions of this parametric study are further put to test by experimenting on various structures like flat aluminium panels, composite trim panels, sandwich panels and flat and curved ribbed aluminium panels. The boundary conditions are whether free-free or clamped. Different damping levels are added to the structure via viscoelastic constrained layer materials or by sound packages. The excitation is provided by both a hammer and a shaker. Notwithstanding the fact that the decay rate method does systematically under evaluates the damping level, it is nevertheless the most constant method as proven by both the numerical study and the experimental measurements. This conclusion is also valid for all tested structures. It evolved for ribbed panels that the physics of the structure plays a fundamental role for the power input method ability to measure damping loss factor. The second part of this work is devoted to two SEA applications. The first one compares structure-borne insertion loss and air-borne insertion loss of sound packages applied to a ribbed curved panel installed in the transmission loss facility. It is demonstrated that under high damping characteristics, both indicators are equivalent. The frame radiation influence on transmission loss of ribbed panels is also presented. The second SEA application presents the complete modeling of a fully furnished Q400 aircraft. A total of four models are proposed. The biggest difference between the models resides in the sound package modeling strategy. The model leading to the best correlation is the single wall model where the trim panel is included in the noise control treatment applied onto the skin. The results are well correlating with the experimental results. It is demonstrated that the weaker link of the panel is the windows. Modeling the windows using an insertion loss in conjunction with conveniently measured damping loss factor yielded the best correlation