POTENTIAL FOR THE PRESENCE OF ADDITIONAL STOP BANDS IN THE MODAL RESPONSE OF REGULARLY RIBBED CYLINDERS

When, in a given frequency band, the magnitude of the line impedance o f the ribs approaches and exceeds the line impedance of a moderately d amped shell, to which the ribs are attached, a stop band emerges. This stop band need not coincide with any of the usual series of stop band s that are associated with the spacing regularity of the ribs. In this sense, this stop band is dubbed ''additional.'' The enhancement in th e magnitude of the line impedance of the ribs may be caused by a reson ance; e.g., if the line impedance of the ribs is commensurate with tha t of a sprung mass and the loss factor of this dynamic system is low, at resonance, the magnitude of the line impedance of the ribs is relat ively high. This resonance enhancement in the line impedance of the ri bs may contribute an additional stop band centered about the resonance frequency of the resonant ribs. Examples of additional stop bands in the response of regularly ribbed cylinders are cited and displayed in this paper. (C) 1998 Acoustical Society of America. [S0001-4966(98)062 08-0]