Experimental Modal Analysis and Damping Estimation for an Inflated Thin-Film Torus

Experimental modal testing of an inflated torus is examined. The principal focus of this investigation is an evaluation of the use of conventional dynamic testing tools in modal testing of a thin-film inflated structure. Because thin-film structures are inherently flexible and lightweight, precautions must be taken in the test procedure. Challenges in testing and identifying natural frequencies and modal damping are detailed. The experimental study shows that whereas localized flexible body dynamics is predominant at higher frequency, the structure behaves in a fashion similar to that of a solid elastic structure for the low-order modes. In addition, natural frequencies and modal damping are shown to be dependent on the level of internal pressurization. Furthermore, viscous (air) damping and structural (strain-rate) damping coefficients are estimated from the experimentally measured modal parameters to provide a more complete assessment of the damping behavior of this structure.