Ohlrich M., Friis L.

In machine installations vibratory power is being transmitted as structureborne sound via the machine’s feet and into its supporting structure. The paper examines this injection of vibratory power from sets of point forces that act on a periodic-type support structure, as is found in ship and aircraft foundations. A developed analytical model of a finite periodic structure formed by beam-type elements [JASA 118 (6), 3607-3618] is used for determining the injected power. The model is furthermore used for examining what effect the spatial cross-coupling between excitation points has on the power injection, which often occurs in several transmission coordinates. The comb-type foundation being considered herein comprises of a waveguide with structural side-branches – or supports – attached asymmetrically at regular intervals. Allowing for three motion-coordinates this tri-coupled periodic structure experiences flexural-longitudinal wave coupling. This phenomenon is taken into account when determining all the mobilities at driving force locations that govern the power injection into the periodic assembly. These results are used for examining the effect of spatial cross-coupling on the power injection for cases of ‘distributed’ excitation by sets of point forces with variable phases.