A method for evaluating the acoustical properties of homogeneous and isotropic porous materials that may be modeled as fluids having complex is described here. To implement procedure, a conventional, two-microphone standing wave tube was modified to include: new sample holder; section downstream holder accommodated second pair microphone holders an approximately anechoic termination. Sound-pressure measurements at two upstream locations were then used estimate two-by-two transfer matrix...

In this paper the development of a two-dimensional elastic-absorption finite element model isotropic elastic porous noise control materials is described. A method for coupling elements with conventional acoustic also presented cases when interface between adjacent air space and foam either unfaced or sealed by membrane. The accuracy acoustic/elastic-absorption has been verified comparing its predictions analytical solutions case wave propagation in foam-filled waveguide. Further, used to...

Nearfield acoustical holography (NAH) is a useful tool for visualizing noise sources. However, to avoid spatial Fourier transform-related truncation effects, the measurement, or hologram, surface must extend beyond source region where sound pressure drops level significantly lower than peak within measurement aperture. Statistically optimized nearfield (SONAH), first derived by Steiner and Hald in planar geometry, based on formulation similar that of NAH. SONAH, surface-to-surface projection...

The metamaterial under investigation here consists of a periodic arrangement unit plates in grid-like frame such that there is contrast the local areal mass between cell interior and wall. In low frequency range normal incidence this panel exhibits sound transmission loss significantly larger than an unstructured with same homogeneous per area. However, when incident field diffuse, relative advantage barrier reduced or eliminated. A sequence experiments documented to demonstrate can be...

In this paper, methods for coupling both elastic porous material (i.e., foam) and structural finite elements with either modal or element representations of acoustical system are presented. addition, interface conditions described in various configurations. The foam is based on the theory Biot. By considering sound transmission through layered systems placed a waveguide, accuracy coupled acoustical-structural-foam model has been verified by comparing its loss predictions analytical solutions...

In previous studies, a sound field separation technique based on the equivalent source method (ESM) was successfully applied to separate incoming and outgoing fields composing non-free field. However, if wave is scattered by surface, not that would be generated in free The object of present work provide an allows recovery noisy environment. this approach, fields, including directly radiated measurement are separated obtain free-field pressure anechoic recovered then used reconstruct whole...

It has been previously shown that relatively simple computational fluid dynamics (CFD) models can be used to calculate the transfer impedances, including associated end corrections, of microperforated panels. The impedance is estimated by first calculating pressure difference across a single hole when transient input velocity imposed, and then Fourier transforming result obtain as function frequency. Since size dimensions inlet outlet channels are very small compared wavelength, flow through...

Topologically interlocked material systems are two-dimensional granular crystals created as ordered and adhesion-less assemblies of unit elements the shape platonic solids. The assembly resists transverse forces due to interlocking geometric arrangement elements. yet require an external constraint provide resistance under action load. Past work considered fixed passive constraints only. objective present study is consider active adaptive with goal achieve variable stiffness energy absorption...

Recent studies have demonstrated that granular aerogels with sub-50 μm particles surpass conventional acoustic materials like glass fibers and polyurethane foams in low-frequency sound absorption. However, incorporating such within practical structural solutions remains a challenge. In this study, we use additive manufacturing to overcome challenge by designing modular geometry allows us encapsulate 3D printed scaffold. Using the porous scaffold provides added benefits of tunability...

It has been noted that the absorption coefficient of a porous material sample placed in standing wave tube is affected at low frequencies by nature sample’s edge constraint. The constraint effect inhibiting motion solid phase material. latter can be strongly coupled to material’s fluid phase, and hence incident sound field, viscous means frequencies. Here earlier was demonstrated experimentally. main focus work, however, on corresponding transmission loss effect. considered aviation grade...

Practical holography measurements of composite sources are usually performed using a multireference cross-spectral approach, and the measured sound field must be decomposed into spatially coherent partial fields before holographic projection. The formulations by which latter approach have been implemented not taken explicit account effect additive noise on reference signals so strictly limited to case in superimposed is negligible. Further, when scanning subarray over number patches...

In the present study, patch near-field acoustical holography was used in conjunction with a multireference, cross-spectral sound pressure measurement to visualize field emitted by subsonic jet and predict its farfield radiation pattern. A strategy for microphone array design is described that accounts low spatial coherence of aeroacoustic sources self-noise resulting from entrained flow near jet. experiments, 0.8-cm-diameter burner produce subsonic, turbulent Mach number 0.26. Six fixed,...

Topologically interlocked materials (TIMs) are a class of 2D mechanical crystals made by structured assembly an array polyhedral elements. The monolayer can resist transverse forces in the absence adhesive interaction between unit properties system emerge as combination deformation individual elements and their contact interaction. present study presents scaling laws relating stiffness monolayered TIMs to characteristic dimensions. concept thrust line analysis is employed obtain laws, model...