Experiments carried out at NUWC's Seneca Lake facility in the summer of 2020 demonstrate efficacy underwater navigation via a single spiral wavefront (SWF) acoustic beacon. An SWF beacon is transducer array that has capability generating signal whose phase varies linearly with angular aspect along reference constant phase. unmanned vehicle (UUV) operating under various channel conditions receives regular from fixed position The UUV's relative to and its radial velocity can be determined by...

Abstract Recognizing challenges to developing undergraduate engineering students’ writing, our College of Engineering invited instructional innovation proposals tackle this issue. Bringing together faculty and graduate students from writing studies, team proposed first researching current instruction in at large research university. We applied a mixed methods approach, including administering surveys, conducting discourse-based interviews, collecting course documents, analyzing curricular...

The authors consider the retrieval of Green functions G from correlations non-stationary non-fully diffuse noise incident on an array sensors. Multiple schemes are proposed for optimizing time-varying weights with which may be stacked. Using records created by direct numerical simulation waves in a two-dimensional multiply scattering medium, cases shown conventional stacking does poor job and substantially improve recovered G, rendering it more causal and/or symmetric, similar to actual G....

Slow dynamic nonlinearity describes a poorly understood, creep-like phenomena that occurs in brittle composite materials such as rocks and cement. It is characterized by drop stiffness induced mechanical conditioning, followed log(time) recovery. A consensus theoretical understanding of the behavior has not been developed. Here we introduce an alternative experimental venue with which to inform theory. Unconsolidated glass bead packs are studied rather than or cement because structure...

Slow dynamic nonlinearity is widely observed in brittle materials with complex heterogeneous or cracked microstructures. It seen rocks, concrete and glass blocks. Unconsolidated structures show the behavior as well: aggregates of beads under pressure a single bead confined between two plates. A defining feature loss stiffness after mechanical conditioning, followed by logarithmic-in-time recovery. Materials to exhibit slow dynamics are sufficiently different microstructure, chemical...

Slow dynamic nonlinearity is ubiquitous amongst brittle materials, such as rocks and concrete, with cracked microstructures. A defining feature of the behavior logarithmic-in-time recovery stiffness after a mechanical conditioning. Materials observed to exhibit slow dynamics are sufficiently different in microstructure, chemical composition, scale (ranging from laboratory seismological) suggest some kind universality. consensus theoretical understanding universality general log(time)...

Providing contextualized, effective writing instruction for engineering students is an important and challenging objective. This article presents a needs analysis conducted in large college introduces the faculty development program that was created based on analysis. The authors advocate sustained interdisciplinary collaboration to promote contextualized adoption adaptation of best practices testing scalable strategies.

Recently wide frequency band gaps were observed in an experimental realization of a multiresonant metamaterial for Lamb waves propagating thin plates. The rose from hybridization between the flexural plate (A0 waves) and longitudinal resonances rods attached perpendicularly. Shortly thereafter theory based on considering one-dimensional periodic array scattering matrix single rod successfully described observations. This letter presents alternative simpler theory, arguably accurate at high...

SUMMARY Due to the partly diffuse character of ambient noise, retrieval amplitude information and attenuation from noise cross-correlations has been difficult. Here, we apply temporal reweighting method proposed by Weaver & Yoritomo seismic data USArray in central-midwest US. The results show considerable improvements retrieved Green's functions both symmetry causality. is able make effective incident field more isotropic (though not yet truly isotropic). It produces robust measurements...

Inasmuch as ambient noise fields are often not fully diffuse the question arises to how, or whether, cross-correlations converge Green's function in practice. Well-known theoretical estimates suggest that quality of convergence scales with square root product integration time and bandwidth. However, correlations from natural environments show random features too large be consistent fluctuations insufficient time. Here it is argued empirical seismic suffer practice spurious arrivals due...

We report measurements and theory on the distribution evolution of diffuse ultrasonic waves in elastic bodies with weakly broken axisymmetry. Aluminum cylinders dimensions large compared to wavelength were excited by transient point sources at center one circular faces. The resulting power spectral density PSD was then examined as a function time frequency position that face. It found showed marked concentration early times, subsequently slowly diminished towards state uniformity across...

The elastic behavior of rocks and other composite materials cannot be entirely captured by the traditional theory nonlinear elasticity, where stress field is related to powers strain field. Rather, these display non-classical behavior, such as hysteresis, end-point memory, fast dynamics, slow dynamics. Slow dynamics (SD) characterized a drop in material stiffness due minor mechanical conditioning, followed recovery back original macroscopic state. SD has drawn particular attention because...

Abstract The Accreditation Board for Engineering and Technology (ABET) has identified effective communication as a critical competency; however, STEM instructors are often not well prepared to assist students in developing writers or respond student writing effectively. Recognizing this challenge, Writing Studies faculty graduate created long-term collaboration, Across (WAE), the college of engineering at large R1 university. By participation WAE, instructional staff writing-intensive...

We report measurements on the distribution and evolution of diffuse ultrasonic waves in elastic bodies with weakly broken axisymmetry. Aluminum cylinders dimensions large compared to wavelength were excited by transient point sources at center upper circular face. The resulting power spectral density was then examined as a function time frequency position. It found that this energy showed marked concentration early times, subsequently slowly diminished towards state uniformity across face,...

Inasmuch as ambient noise fields are often not fully diffuse the question arises to how, or whether, cross-correlations converge Green’s function in practice. Well-known theoretical estimates suggest that quality of convergence scales with square root product integration time and bandwidth. However, correlations from natural environments show random features too large be consistent fluctuations insufficient time. Here, it is argued empirical seismic suffer practice spurious arrivals due...

We consider the retrieval of Green functions G from correlations non-stationary non-fully diffuse noise incident on an array sensors. Multiple schemes are proposed for optimizing time-varying weights with which may be stacked. Using records created by direct numerical simulation waves in a two-dimensional multiply scattering medium, cases shown conventional stacking does poor job and substantially improve recovered G, rendering it more causal and/or symmetric, similar to actual G. It is...

• Walter Grotrian in 1939 and Bengt Edlen 1943 discovered that the temperature corona is a few million degrees Kelvin. If only process involved was thermal nature, this would violate second law of thermodynamics, namely heat cannot flow from colder area to hotter one. There must be some other physical mechanism heats such high temperatures. It as if outer region surround light bulb really hot, but you move closer surface bulb, it got cooler.

Much information about wave propagation in a variety of structures has been obtained from Green's function retrieval by noise correlation. Here it is examined how dispersion affects and, particular, its signal-to-noise ratio (SNR). On recalling the inherent spread signal due to band limitation augmented and distance, both affect amplitude, argued that SNR highly dispersive media can be substantially lowered strong dispersion. It this most relevant for gravity waves over large distances ocean...

A number of one-dimensional models have been developed to inform the design piezoelectric transducers. The majority these are in frequency domain. In this paper, we develop a time-domain model for mechanical response layer. Secondary effects, resulting from feedback between acoustic and electric variables, included model. Our approach utilizes Green's function Helmholtz equation with radiation boundary conditions methods complex analysis. predictions validated by comparison finite-difference...

A number of one-dimensional models have been developed to inform the design piezoelectric transducers. The majority these are in frequency domain. In this paper, we develop a time-domain model for mechanical response layer. Secondary effects, resulting from feedback between acoustic and electric variables, included model. Our approach utilizes Green's function Helmholtz equation with radiation boundary conditions methods complex analysis. predictions validated by comparison finite-difference...

The parabolic equation method is an accurate and efficient approach for solving nonseparable problems in ocean acoustics which there are horizontal variations the environmental parameters. Many range-dependent may be solved using 2-D models that ignore coupling of energy between planes constant azimuth. When azimuthal must taken into account, splitting used to efficiently solve a 3-D handles depth operator higher order but azimuth only leading order. Despite fact this approximation provides...

Slow dynamics (SD), a type of non-classical nonlinear elastic behavior, is characterized by (i) material softening due minor mechanical conditioning and (ii) subsequent slow recovery that approaches the original macroscopic state. Early work in sandstones other consolidated granular materials—and more recent unconsolidated materials—have found to be logarithmic-in-time, at least for seconds hours after conditioning. However, studies have observed recoveries materials deviate from log(time),...

It is shown that if vibrational energy put into one substructure and allowed to diffuse other weakly coupled substructures (as in the case of statistical analysis or reverberant sound diffusing from room others through small windows), at infinite time density starting will still be above its equipartition value. We offer a theory predict amount this Anderson localization such systems substructures. compare these predictions with numerical results obtained using random matrix