Sound Attenuation In A Coarse Granular Medium

Particle Irregularity and Aggregation Effects in Airborne Suspensions at Audio- And Low Ultrasonic Frequencies

“…the viscous wave number) as the fractal dimension. The resulting predictions of attenuation agree closely with the results of the Wu et al experiments in water-saturated riverbed coarse sands [14]. Wu et al [14] found that the non-sphericity and surface roughness of particles have strong e!ects on the acoustic attenuation when Re is much larger than 1 and ka is smaller than 1.…”

“…The large discrepancies, shown in Figure 1, between predictions and data for attenuation in airborne suspensions of olivine sand imply that particle irregularity may have an important in#uence on attenuation of sound waves even when the acoustic Reynolds number is not as large as in the Wu et al experiments [14]. For sound propagation through airborne suspensions, Temkin and Dobbins [5] have distinguished the viscous and inertial regimes and the transition between them by using the dimensionless quantity T , where T is the viscous relaxation time denoted by…”

“…Wu et al [14] found that the irregularity of water-borne coarse sand particles cause the acoustic attenuation, for 60(Re(240, to increase signi"cantly over the values predicted for smooth spherical particles. It should be noted that, given sand particles with an average radius of 170 m, suspended in water, then, for frequencies where 60(Re(240, the particles are large compared with the viscous or thermal boundary layer thickness.…”

“…These are shown in terms of frequency and particle radius in Figure 2. The results of Wu et al's measurement [14] suggest that particle irregularity has a signi"cant in#uence on acoustic attenuation in the inertial regime.…”

“…In these measurements, the particles were quite large compared to the viscous or thermal boundary layer thickness. Consequently, these sand particles might not be regarded as smooth and spherical even through the Reynolds number was not as large as in the Wu et al experiments [14].…”