Thomas D. Rossing
Phys. Dept., Northern Illinois Univ., DeKalb, IL 60115
Uwe J. Hansen
Indiana State Univ., Terre Haute, IN 47809
In oval cylinders, the familiar vibrational modes of a circular cylinder are split into doublets, one new mode having a node in the region of greatest curvature and the other having an antinode there. Since increasing the curvature increases the effective stiffness and thus raises the speed of bending waves, the bending wavelengths are generally longer (and the nodes further apart) in the region of greater curvature. This phenomenon is the basis of the ``two-tone'' phenomenon in ancient Chinese bells. The mode splitting in a variety of noncircular cylinders and bells, observed by means of holographic interferometry and experimental modal testing with impact excitation, is described. By using two mirrors, it is possible to view simultaneously the front, end, and top of a vibrating cylinder in holographic interferograms.