Utah Aurora - May 10/11 2024

Advanced construction technologies are creating opportunities to design and fabricate non-traditional concrete structural geometries. While removing structurally unnecessary material can aid in sustainability efforts, it can also reduce a structure’s ability to attenuate impact sound. An assessment of the impact sound insulation performance of custom concrete floors has often been excluded from previous studies because of the large computational cost for simulating radiated sound at high frequencies. In response, this paper presents a hybrid, computationally efficient method to approximate the impact sound performance of floors by strategically using the air-hemisphere method for a subset of low frequencies, while relying on the structure’s radiation efficiency at higher frequencies. This method improves upon existing strategies to discretize the receiving side of the floor for impact sound performance. To demonstrate this method, six anthropometric walking paths are simulated on four non-traditional floor geometries and three conventional floor slabs. The simulated results are compared to experimentally obtained dynamic behavior for the custom slabs and full-scale tests of impact sound for the conventional slabs. The proposed method is much more efficient than maintaining high resolution discretization across all frequencies, leading to significant computational time savings. Efficient simulations for determining the impact sound insulation of non-traditional structures may further enable the design of novel floor geometries, potentially accelerating their implementation in buildings.

Spatiospectral lobes are significant contributors to noise radiated from full-scale tactical aircraft. Prior studies have explored lobe frequency-domain characteristics, but a joint time–frequency domain analysis has the potential to further describe these phenomena and connect them to source-related events in the time waveform. This paper uses acoustical data collected from a 120-microphone array near a T-7A-installed F404 engine to characterize the spatiospectral lobes in combinations of the time, frequency, and spatial domains. An event-based beamforming method is used in conjunction with a wavelet transform to determine propagation angles and event source locations corresponding to each of the lobes. Temporospectral events in the wavelet transform are then analyzed using Markov chains. Finally, spatiospectral maps created from the measured data are decomposed into individual lobes using events in the wavelet transform as a guide. The spatiospectrotemporal combination of these three analyses shows that the lobes originate from multiple, overlapping regions along the jet lipline and that each lobe has its own peak radiation angle. Additionally, events corresponding to the spatiospectral lobes occur intermittently and at different times from each other, leading to bursts of acoustic energy with rapidly changing directivities.

ANSI/ASA standard S12.75 (2012) provides guidance on allowable meteorological conditions for acoustical measurements of installed high-performance jet engines. This paper investigates meteorological effects on acquired acoustical data by analyzing recent measurements of a T-7A-installed GE F404 engine. During this measurement, the aircraft was run up six times at engine powers from idle to full afterburner, with test conditions following those prescribed by S12.75. However, far-field spectra are surprisingly variable, despite a morning measurement with low wind conditions. Analysis of the vertical temperature gradient shows a correlation between the gradient and spectral characteristics at distances as short as 38 m from the aircraft. The results suggest that local temperature profiles must be considered more carefully in future full-scale measurements and the results studied to establish guidelines for inclusion in the standard.

The SpaceX Falcon-9 rocket is a partially-reusable vehicle with a first-stage booster that lands propulsively after launch. As the booster falls toward the landing site, it produces a sonic boom. These sonic booms have unique properties and, so far, the ability to model them using current methods remains unclear. This paper presents findings from three Falcon-9 flyback sonic booms and highlights some features and trends that will be important to future modeling efforts. At every measurement location, a triple boom is recorded. This triple boom appears to propagate stably to at least 25 km from the landing pad. Within 1–2 km of the landing pad, the calculated sonic boom metrics tend to plateau. Outside 1–2 km of the launch and landing facility, the sonic boom is the highest-pressure event of the entire flight, including the launch. The Perceived Level 1 km from the landing pad is around 128 dB and at 25 km is around 87 dB. An appendix is included that discusses the benefits and challenges of attempting to correct for hardware low-frequency rolloff using digital pole-shift filtering.

Solute segregation in materials with grain boundaries (GBs) has emerged as a popular method to thermodynamically stabilize nanocrystalline structures. However, the impact of varied GB crystallographic character on solute segregation has never been thoroughly examined. This work examines Co solute segregation in a dataset of 7272 Al bicrystal GBs that span the 5D space of GB crystallographic character. Considerable attention is paid to verification of the calculations in the diverse and large set of GBs. In addition, the results of this work are favorably validated against similar bicrystal and polycrystal simulations. As with other work, we show that Co atoms exhibit strong segregation to sites in Al GBs and that segregation correlates strongly with GB energy and GB excess volume. Segregation varies smoothly in the 5D crystallographic space but has a complex landscape without an obvious functional form.

Carbon nanotubes (CNTs) possess many unique properties that make them ideal for field emission. However, screening due to high density and poor substrate adhesion limits their application. We tested the field emission of various patterned vertically aligned carbon nanotube (VACNT) arrays adhered to copper substrates using carbon paste. After many fabrication steps to improve uniformity, we found that the field emission was dominated by individual CNTs that were taller than the bulk VACNT arrays. After testing a sample with silver epoxy as the binder, we found that the failure mechanism was adhesion to the substrate. Using energy dispersive xray spectroscopy (EDX), we found that the carbon paste migrated into the VACNT bulk volume while the silver epoxy did not. The migration of carbon paste into the volume may explain why the carbon paste had greater adhesion than the silver epoxy.