Julie C. Slaughter
J. Adin Mann, III
Daniel O Adams
Aerosp. Eng. and Eng. Mech., 2019 Black Eng. Bldg., Iowa State Univ., Ames, IA 50011
The effect that spatial thickness variations of a beam has on the beam's far-field sound radiation was studied. The steel beams that were used in the initial tests show that at low-frequency ranges (500--1500 Hz) the thickness variations acted as discontinuities along the beam that increased sound radiation. However, at higher frequency ranges (2000--4000 Hz) the thickness variations, when spaced at certain intervals, acted as global stiffness changes and decreased the sound radiation. This decrease occurred when the spacing of the variations corresponded to a structural wavelength. Composite beams with thickness variations have also been built and tested. The spatial thickness variations appear to have a similar effect on the sound radiation as in the steel beams. The two data processing techniques used to evaluate the influence of the spatial thickness variations were a phase-speed tracking filter to quantify wave propagation in the structure and a wave-number domain filter to quantify far-field radiation. Results from these tests will be used to help determine how quieter materials can be designed. [Work supported by NSF.]