A simple analytical method is developed to estimate frequencies of longitudinal modes in closed hard-walled ducts with discontinuities in a cross-sectional area. The approach adopted is based on a general expression for the acoustic impedance for a plane wave motion in a duct and conditions of impedance continuity at duct discontinuities. Formulae for mode frequencies in a form of transcendental equations were found for one, two and three discontinuities in a duct cross-section. An accuracy of the method was checked by a comparison of analytic predictions with calculation data obtained by use of numerical implementation based on the forced oscillator method with a finite difference algorithm.

JO - Archives of Acoustics L1 - http://journals.pan.pl/Content/107547/PDF/91.pdf L2 - http://journals.pan.pl/Content/107547 IS - No 3 EP - 435 KW - longitudinal duct modes KW - discontinuity in duct cross-section KW - contraction ratio ER - A1 - Meissner, MirosÅ‚aw PB - Committee on Acoustics PAS, PAS Institute of Fundamental Technological Research, Polish Acoustical Society VL - vol. 35 JF - Archives of Acoustics SP - 421 T1 - Effect of Cross-Sectional Area Discontinuities in Closed Hard-Walled Ducts on Frequency of Longitudinal Modes UR - http://journals.pan.pl/dlibra/docmetadata?id=107547 DOI - 10.2478/v10168-010-0034-0