Transmission loss characteristics of an annular cavity with arbitrary port locations using Green's function method.
The prediction of transmission loss characteristics of a short chamber requires the study of both longitudinal as well as transverse modes. This prompts the development of a three-dimensional (3D) transfer matrix, which can address the wave propagation in all three directions. Accordingly, an analytical methodology for transmission loss characteristics of an annular cavity using Green's function method is presented in this paper. The 3D wave equation is used to derive the mode shape functions for the cavity. The average pressure on the inlet and outlet ports is predicted using the Green's function derived from the mode shapes. Three different port location configurations of the annular cavity are considered for establishing the analytical methodology, viz., face-inlet-face-outlet (FIFO), side-inlet-side-outlet (SISO), and face-inlet-side-outlet (FISO). Numerical model results are used to corroborate the analytical results. The effects of geometrical parameters on the transmission loss are studied.
General formulation of four pole parameters for three-dimensional cavities utilizing modal expansion, with special attention to the annular cylinder
Abstract Four poles for three-dimensional cavities were simulated in terms of eigenfunctions of these cavities, first for general curvilinear co-ordinates, then for the specific example of an annular cylindrical cavity. As an application example, this formulation was applied to an annular cylindrical cavity connected to an anechoic pipe, with a single and a double input. Various responses are illustrated. Many applications come to mind, for example in three-dimensional muffler theory, but application examples were chosen in such a way that they contribute to the understanding of pressure pulsations inside a shell enclosing a refrigeration compressor, with the acoustic input being the suction port of the compressor and the output being the evaporator pipe. The relative locations of input and output ports, pressure distributions in the cavity at resonance condition, and phase cancellations when two input ports are used, are discussed.
Acoustic attenuation performance of circular expansion chambers with offset inlet/outlet : II. Comparison with experimental and computational studies
Abstract This is the second of two papers investigating the acoustic attenuation performance of asymmetric, circular expansion chambers with respect to the chamber length and the relative location of the offset inlet/outlet. Three approaches are employed to determine the transmission loss: (1) the three-dimensional analytical approach developed by the authors in a companion paper (Selamet and Ji, 1998,Journal of Sound and Vibration,213, 601–617) [1]; (2) the three-dimensional computational solution based on the boundary element method; and (3) experiments on an extended impedance tube set-up with expansion chambers fabricated with fixed inlet, outlet, and chamber diameters, varying chamber length to diameter ratios, and varying offset locations of the inlet and outlet. The results from the three approaches are shown to agree well. The effect of geometry, particularly that of the offset angles of the asymmetric configurations, on the multidimensional wave propagation and acoustic attenuation performance is discussed in detail.