Experimental evaluation of backscattering from finite internally loaded cylindrical shells.

Abstract

Dynamic interaction between a shell and internal structural elements may be significant in backscattering. These interactions are of particular interest to us at frequencies where wavelengths are comparable to characteristic discontinuity lengths of the structure. Scattering by three cylindrical shell models has been measured to delineate regimes where the influence of internal structures is significant, and to highlight fundamental backscattering processes common to more complex structures. The models are: an empty shell, a duplicate empty shell with unequally spaced ribs, and a duplicate ribbed shell with resiliently mounted, wave-bearing internal structural elements. The measurements were conducted with wide-band pulses covering the frequency band of 2.75<ka<10.5 corresponding to 3/4 to 3 times the ring frequency of the empty shell. The internal structures are found to cause significant changes in target strength at all angles of incidence away from beam aspect, and throughout the frequency range studied. The backscattered signature in the time domain shows an increased initial peak response induced by the internal structures, as well as group delay and decay rate properties induced by shell discontinuities and by interaction between the shell and the internal structures. [The authors acknowledge valuable inputs from J. R. Fricke and Y. P. Guo of MIT, and NRL for acquisition of the backscatter data. Research sponsored by ONR.]