WAVE-NUMBER SPACE RESPONSE OF A NEAR PERIODICALLY RIBBED SHELL

Employing near-field acoustic holography measurements, the wave-number space response of a ribbed shell to a point drive is investigated. Th e data show the dominance of flexural vibration in the mid-frequency r ange, and demonstrate the prominent role played by the eigensolutions of the periodic structure. The supersonic region of frequency-wave-num ber space is examined in detail and the fast membrane waves, although suppressed in level relative to the subsonic bending waves, provide a clear highlight in this domain at frequencies below the first radiatin g flexural passband. The results are also examined in k(z)-k(phi) spac e for several frequencies. This representation enables an interpretati on of the results in terms of the slowness surface of the flexural wav es and provides a simple explanation for the various complex beaming a nd focusing phenemena which occur in this system.