With ground-based, impulsive acoustic sources, the initial blast wave can be followed by additional noise that is difficult to interpret. As outlined by Embelton [J. Acoust. Soc. Am. 100 (1996)], a porous ground can lead to creeping, ground, and surface waves. In a recent test on a grass-covered field, the blast noise from exploding balloons had evidence of a secondary arrival that in some cases was larger than the blast wavefront. The balloons were filled with oxy-acetylene gas and placed on the ground or in holes. The balloons were ignited, and the sound from the resulting explosions were measured at distances of 100, 130, and 160 m. At each of these stations, microphones were placed at four heights: 0.01, 1.2, 2.4, and 3.6 m. For every explosion, the blast wave amplitude increases with height, while the secondary arrival amplitude decreases with height. This variation in height can help identify the type of wave responsible for the secondary arrival. For example,the amplitude of surface waves propagating over grass exponentially decay with height. This study will help distinguish different types of acoustic signals produced by ground-based explosions, such as the Volcano Hazards Workshop in 2018.
The directionality of an explosion should be accounted for when estimating sound power. Our goal is to estimate the directionality of explosions from measurements on an arc not concentric with the origin of the explosion. To learn how to interpret such data, a test was conducted in a grass-covered field using exploding balloons. The balloons were filled with a stoichiometric mixture of oxy-acetylene and when ignited produced acoustic shock waves. The gas-filled balloons were placed in the ground in preformed “craters.” The craters were different shapes to hopefully produce different directionalities. Measurements were taken using both circular microphone arrays centered on each of the four crater locations and a single semi-circle array that was not concentric with any of the craters. The goal is to connect the two measurements by including the effective flow resistivity of the ground and determine how to interpret the directionality from data collected from the semicircle setup. This study was in preparation for a later volcano hazards workshop with buried explosives.
Sound power measurements are of interest in numerous applications, and several methods are available for obtaining the sound power of a system. A recent method that has been developed, referred to as the Vibration-Based Sound Power (VBSP) method, utilizes vibration measurements obtained from a Scanning Laser Doppler Vibrometer (SLDV). The VBSP method has previously been used to obtain the sound power radiated from flat plates, cylindrical shells and curved plates. This paper will present further developments to extend VBSP measurements to multiple coupled structures and investigate the acoustic coupling effects that may exist. Two coplanar flat plates separated by a distance d were modeled using the boundary element method. The sound power was determined within the boundary element software and the structural velocities were also exported and processed using the VBSP method. Computational and experimental results will be shown to demonstrate abilities and limitations for the VBSP method to accurately determine the radiated sound power for coupled structures. [Funding for this work was provided by the National Science Foundation (NSF).]
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.