RESUMO
Cylindrical containers, such as liquid tanks and pressure vessels, are ubiquitous in storage applications. Traditional lines of non-destructive evaluation (NDE) are mostly focused on the integrity of containers, but studies on solid contents within using external sensors are lacking. In previous work, metrics were developed to estimate the structural integrity of mock-up fuel assemblies inside a lab-scale nuclear dry storage cask. Linear acoustic resonance techniques were shown to be sensitive down to single assembly level. In this work, this problem is further examined by studying contact nonlinearity in a simplified system using Nonlinear Ultrasound Resonance Spectroscopy (NRUS). This system consists of a single layer of identical spheres with varying composition and size evenly distributed at the bottom of a cylindrical aluminum container. The resonance frequency shifts due to varying amplitudes were mostly affected by the total mass of spheres inside, while diameter and composition of spheres played minor roles. A phenomenological model was developed based on the resulting shifts and was studied numerically using finite element simulations. The agreement between simulations and experiments suggests that the contact nonlinearity is predominated by a contact loss mechanism. This NRUS technique may complement linear acoustic techniques for solid cargo NDE inside sealed vessels.
RESUMO
We observe that our experimentally measured emission power enhancement of a speaker inside a previously proposed metacavity agrees with our numerically calculated enhancement of the density of states (DOS) of the source-cavity system. We interpret the agreement by formulating a relation between the emitted sound power and the acoustic DOS. The formulation is an analog to Fermi's golden rule in quantum emission. The formulation complements the radiation impedance theory in traditional acoustics for describing sound emission. Our study bridges the gap between acoustic DOS and the acoustic Purcell effect for sound emission enhancement.
RESUMO
This paper investigates the wind noise pressure spectra measured by aerodynamically designed devices in turbulent flow. Such measurement probes are often used in acoustic measurements in wind tunnels to reduce the pressure fluctuations generated by the interaction of the devices with the incident flow. When placed in an outdoor turbulent environment however, their performance declines noticeably. It is hypothesized that these devices are measuring the stagnation pressures generated by the cross flow components of the turbulence. Predictions for the cross flow contribution to the stagnation pressure spectra based on measured velocity spectra are developed, and are then compared to the measured pressure spectra in four different probe type devices in windy conditions outdoors. The predictions agree well with the measurements and show that the cross flow contamination coefficient is on the order of 0.5 in outdoor turbulent flows in contrast to the published value of 0.15 for measurements in a turbulent jet indoors.
