Theme: Phonons and Shockwaves
Faculty Mentor: Philip Marston
Example Project: Environmental effects on solid-object modal dissipation for UXO detection
There is a significant effort to use low-frequency acoustics in water to locate and eventually recover lost munitions before they endanger the pubic [1]. Such munitions are often referred to as unexploded ordinance (UXO). Some of the acoustic signatures used in the development of that approach are associated with the low-frequency modes of solid objects on or in sand. One justification for that approach is that for simple metallic objects such as cylinders and bullet-shaped objects, the distinct modal structure appears to be detectable for situations investigated in field measurements that mostly involved fully exposed objects simply resting on sand [2-4]. However modeling each mode as if it were a driven harmonic oscillator, it is currently poorly understood how environmental factors alter each modal quality factor (or Q) of even the most prominent modes. We aim to investigate the environmentally induced reduction in Q in controlled laboratory-based measurements.
The REU scholar, faculty member, and graduate student will investigate these issues. The REU scholar will use tone-burst magnetic fields to excite modes. Maxwell-stresses associated with eddy currents drive the modes [5]. The modal decay will be recorded with a hydrophone [5,6]. This should be possible for UXO models having different burial depths in sand in a tank of water. Others involved will use specialized acoustic sources to excite the modes [6]. It should be feasible to model observed dissipation.
Undergraduate Research
Marston’s research program at WSU has been externally funded since 1979 and he has involved undergraduates (ugs) in research on numerous occasions (including on NASA aircraft). For example Williams (see [1]) got his first research experience as a ug working with Marston & over 7 ugs having worked with Marston went on to earn graduate STEM degrees. Recently: One undergraduate (Smith) presented a poster at the annual WSU Showcase in 2018 & was also part of a meeting paper [7]. During summer 2019 Smith (still as a ug) demonstrated the excitation of low-frequency mechanical modes at the difference frequency of high-frequency currents [8].
References
[1] https://www.serdp-estcp.org/News-and-Events/Blog/Low-frequency-Acoustics-for-Munitions-Response
[2] Williams … J. Acoust. Soc. Am. (2010) DOI: 10.1121/1.3419926
[3] Zampolli … J. Computational Acoustics (2012) DOI: 10.1142/S0218396X12400073
[4] España … J. Acoust. Soc. Am. (2014) DOI: 10.1121/1.4881923
[5] Hefner … J. Acoust. Soc. Am. (2000) DOI: 10.1121/1.428188
[6] T. Daniel, Ph. D. Thesis (WSU, Pullman, July 2019).
[7] T. Daniel … J. Acoust. Soc. Am. (2018) DOI: 10.1121/1.5036085
[8] Smith … J. Acoust. Soc. Am. (manuscript in preparation).