Frequency domain input identification for vibration testing of flexible structures

Electronic equipments in flexible slender aerospace structures are subjected to severe vibration environments during the course of flight. In order to qualify the equipment for real life environment, they are subjected to vibrations levels using electrodynamic shaker tables on ground. Control sensors are placed at the critical locations and desired spectra are achieved on the electronic packages at the section level testing. During this testing, the flexible modes of the structure are ignored. In this present study, a methodology of vibration testing is described to achieve the desired spectra at the specified locations on the structure. The article discusses a frequency domain identification of the required input forces to achieve desired acceleration spectra at the specified control locations on the structure. A generalized formulation of input force identification for multiple input multiple output is presented for the vibration testing methodology. Three different configurations like single input single output, multiple input single output, and multiple input multiple output are simulated and verified with the experiments at collocated and non-collocated control sensor-exciter combinations. From the experiments, it has been observed that the desired acceleration spectra at the specified locations are achieved to a good degree of accuracy. Moreover, the efficacy of the proposed method is experimentally verified for the structure with closely spaced modes. Apart from the acceleration control, velocity control approach is also presented in this article.