Mode splitting in an inflated polyimide cylinder with circumferential asymmetry

In the past, a good deal of the research on the feasibility of inflatable structures for space applications has focused on the behavior of inflated cylinders. In many cases, especially in theoretical and numerical studies, the cylinder has been assumed to be uniform across its circumference. In the case of many thin-film structures, this assumption does not hold. These structures often contain at least one seam that produces localized changes in film thickness and stiffness. Experimental evidence of the effect of this seam in the form of mode splitting and the accompanying divergence of repeated eigenvalues was seen during modal testing of a polyimide cylinder at NASA Marshall Space Flight Center (MSFC). This paper will examine the effect of asymmetry through the inspection of experimental data and the use of finite element methods.