Experimental Identification of Transmissibility Functions of Passenger Seats

Abstract

This report describes the experimental identification of transmissibility functions from the floor of an aircraft cabin through a typical passenger seat to the pelvis, chest and shoulder of a sitting test dummy. For this purpose, a multi-axial vibration test facility was utilized. A typical passenger seat with test dummies was mounted on the vibration table. All six axes of the vibration table were excited with three levels of sine sweep and random excitation signals. The responses at specific positions on the test dummy were measured. The transmissibility FRF were computed with two approaches. First, the response signals were related to the respective excitation axis. Second, an improved approach was used which takes into account the motions of all base axes. Both approaches delivered transmissibility FRF which were nearly identical. However, in most cases the transmissibility FRF, which were computed with the improved approach, were more noisy. The reason for this might be the spill-over effect of some cross-talk motions. An investigation of possible nonlinear effects showed that an increase of the excitation level of the sine sweep excitation resulted in a shift of the resonance peaks to lower frequencies and a reduction of the resonance amplitudes. The verification of computational models should therefore be mainly accomplished with data of the low level, if the models are assumed to be linear. Medium and high levels of sine sweep excitation should only be used for the verification of nonlinear models.