Finite Element Analysis Of Wedges Used In Anechoic Chambers

On the Acoustic Absorption of Porous Materials With Different Surface Shapes and Perforated Plates

“…Figure 5 illustrates the "nite element mesh and dimension of the wedge "brous absorber, where s"1)32 m, h"0)28 m, q"0)2 m and the #ow resistivity "24,000 N s/m. Figure 6 reveals the correlation among various methods [10,16] where Easwaran and Manjal [10] used 432 triangular elements (259 nodes) and present work uses 85 eight-node isoparameteric elements (253 nodes). Comparing these two "nite element solutions with experimental data, it reveals that present results are even better when the sound frequency exceeds 150 Hz.…”

“…Similar to the formulation procedure as used by Easwaran and Munjal [10], the present "nite element model is developed as follows. Considering the impedance tube domain as shown in Figure 1, the Helmholtz wave propagation equation can be written as…”

“…However, the surface shape of above acoustic absorbers is limited to plate shape. Recently, Easwaran and Munjal [10] used Galerkin "nite element method combining bulk reaction of "brous absorbers to explore the sound re#ection coe$cient of wedge "brous absorbers. Kang and Bolton [11] further discussed the acoustic absorption of porous materials and sound transmission through foam-lined double-panel structures by conventional acoustic "nite elements.…”

“…To examine how surface shapes and sizes of porous materials with perforated plates a!ect acoustic absorption, a "nite element procedure, derived from the Galerkin residual method and Helmholtz wave propagation equation [10], is established in this work. For measuring the parameters of porous materials that are required for "nite element analysis, say, complex wave propagation constant, characteristic impedance and #ow resistivity, the two-microphone transfer function method [12] and the modi"ed Ingard and Dear impedance tube testing systems [13] are employed.…”

Acoustic Transmission Analysis of Multi-Layer Absorbers

“…where Z P is the back surface acoustic impedance of the "rst layer of airspaces or porous materials backed with a rigid wall, and is taken as R. Similarly, the surface acoustic impedance of the next layer of airspaces or porous materials can also be evaluated by equation (11) except that the back surface acoustic impedance Z P is substituted by the surface acoustic impedance H ( j"a or m). Thus, the e!ects of various combinations of airspaces and porous materials between adjacent perforated plates can be accurately described in the same way.…”