Topological pumping in acoustic waveguide arrays with hopping modulation

Thouless pumping is the adiabatic transportation of quantized charge, which is regarded as the dynamic version of the quantum Hall effect. Here we propose the design of an acoustic system to demonstrate the topological pumping characterized by transporting acoustic energy from one side to the opposite. The system is composed of coupled acoustic waveguide arrays with modulated coupling along both cross-sections and the propagating direction. We explore multiple topological phases by introducing rich spatial frequency or enlarged range of the hopping modulation. Such distinct topological phases are evidenced by adiabatic evolution of the edge states, where the acoustic system varies continuously and slowly along the state propagating direction. The robustness behavior of the edge states transport is also verified with numerical simulations to imply their topology origin. Our work provides a route to realize topological phases and utilize the corresponding edge states in waveguide arrays that can lead to versatile acoustic wave manipulation applications.

Quantification of Wide-Area Norwegian Spring-Spawning Herring Population Density with Ocean Acoustic Waveguide Remote Sensing (OAWRS)

Norwegian spring-spawning herring are a critical economic resource for multiple nations in the North Atlantic and a keystone species of the Nordic Seas ecosystem. Given the wide areas that the herring occupy, it is difficult to accurately measure the population size and spatial distribution. Ocean Acoustic Waveguide Remote Sensing (OAWRS) was used to instantaneously measure the areal population density of Norwegian herring over more than one thousand square kilometers in spawning grounds near Ålesund, Norway. In the vicinity of the Ålesund trench near peak spawning, significant attenuation in signal-to-noise ratio and mean sensing range was observed after nautical sunset that had not been observed in previous OAWRS surveys in the Nordic Seas or in other regions. We show that this range-dependent decay along a given propagation path was caused by attenuation through dense herring shoals forming at sunset and persisting through the evening for transmissions near the swimbladder resonance peak. OAWRS transmissions are corrected for attenuation in a manner consistent with waveguide scattering theory and simultaneous downward directed local line-transect measurements in the region in order to produce instantaneous wide-area population density maps. Corresponding measured reductions in the median sensing range over the azimuth before ambient noise limitation are shown to be theoretically predictable from waveguide scattering theory and observed population densities. Spatial-temporal inhomogeneities in wide-area herring distributions seen synoptically in OAWRS imagery show that standard sparsely spaced line-transect surveys through this region during spawning can lead to large errors in the estimated population due to spatial and temporal undersampling.

The Effect of Attenuation from Fish on Passive Detection of Sound Sources in Ocean Waveguide Environments

Attenuation from fish can reduce the intensity of acoustic signals and significantly decrease detection range for long-range passive sensing of manmade vehicles, geophysical phenomena, and vocalizing marine life. The effect of attenuation from herring shoals on the Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) of surface vessels is investigated here, where concurrent wide-area active Ocean Acoustic Waveguide Remote Sensing (OAWRS) is used to confirm that herring shoals occluding the propagation path are responsible for measured reductions in ship radiated sound and corresponding detection losses. Reductions in the intensity of ship-radiated sound are predicted using a formulation for acoustic attenuation through inhomogeneities in an ocean waveguide that has been previously shown to be consistent with experimental measurements of attenuation from fish in active OAWRS transmissions. The predictions of the waveguide attenuation formulation are in agreement with measured reductions from attenuation, where the position, size, and population density of the fish groups are characterized using OAWRS imagery as well as in situ echosounder measurements of the specific shoals occluding the propagation path. Experimental measurements of attenuation presented here confirm previous theoretical predictions that common heuristic formulations employing free space scattering assumptions can be in significant error. Waveguide scattering and propagation theory is found to be necessary for accurate predictions.

Oscillations of elastic plate, located at the end of semi-infinite cylindrical acoustic waveguide

Получено точное аналитическое решение задачи о гармонических изгибных колебаниях тонкой круглой упругой пластины, расположенной в торце полубесконечного цилиндрического акустического волновода. Кромка пластины жестко заделана в стенку волновода. Волновод с жестким корпусом заполнен идеальной сжимаемой акустической средой. Колебания пластины возбуждаются набегающими на неё нормальными волнами волновода, распределение акустического давления для которых имеет цилиндрическую симметрию. Проведено численное исследование смещения пластины на разных частотах возбуждения. Показано, что наличие сжимаемой среды существенно влияет на форму колебаний пластины. Совместные колебания акустической среды и упругой пластины носят резонансный характер. На резонансных частотах имеет место значительное увеличение амплитуды колебаний пластины. На форму колебания пластины влияют как распространяющиеся, так и неоднородные нормальные волны в волноводе, что приводит к увеличению узловых линий в распределении смещения пластины. An exact analytical solution to the problem of harmonic bending oscillations of a thin round elastic plate located at the end of a semi-infinite cylindrical acoustic waveguide has been obtained. Plate edge is rigidly embedded in waveguide wall. The waveguide with rigid housing is filled with an ideal compressible acoustic medium. The plate oscillations are excited by the normal waveguide waves running to the plate. The distribution of acoustic pressure for waves has cylindrical symmetry. Numerical study of plate displacement at different excitation frequencies was carried out. It has been shown that the presence of a compressible medium significantly affects the waveform of the plate oscillation. Joint oscillations of acoustic medium and elastic plate are resonant. There is a significant increase in amplitude of plate oscillations at resonant frequencies. The waveform of the plate oscillation is influenced by both propagating and inhomogeneous normal waves in the waveguide, which leads to an increase in the nodal lines in the displacement distribution of the plate.