M. Strasberg D. Feit
David Taylor Res. Ctr., Bethesda, MD 20084-5000
It is well known that the observed vibratory behavior of large and complicated structures usually indicates much more damping than can be accounted for by the inherent dissipation in the structural material. Several investigators have pointed out that greatly increased damping may result from vibratory power dissipated by the numerous small resonant substructures usually attached to the large main structure; C. Soize called them the ``structural fuzzy'' [J. Acoust. Soc. Am. 92, 2365 (A) (1992)]. This paper presents a simplified procedure for estimating the effect of these substructures when they have many resonances at frequencies near the excitation frequency. In this case, the increased damping of the large structure depends mainly on the total effective mass of all the substructures resonating within a frequency band (say a half-octave) centered at the excitation frequency, and is relatively independent of the specific amount of dissipation in the individual substructures. The effect of the substructures on the frequency response and vibration pattern of the main structure can also be accounted for in simple fashion. The influence of nonuniform spatial distributions of the attached substrates on the estimates is also discussed in terms of specific examples. [Work supported by ONR.]