The heart signal: An acoustic signature observed during a second-bubble entrainment

The presence in operation of many prototypes of UAVs with propeller propellers, the use of such devices at relatively low altitudes and flight speeds makes the problem of noise reduction from UAVs urgent both from the point of view of acoustic imperceptibility and ecology.The aim of the work is to determine a set of methods that help to reduce the visibility of UAVs in the acoustic range. It is shown that the main source of noise from the UAV on the ground is the power plant, which includes the engine and the propeller. The parameters of the power plants influencing the processes that determine the acoustic signature of the UAV were investigated. A comprehensive analysis of the factors affecting visibility was carried out. The power plants include two-stroke and four-stroke engines, internal combustion and two-blade propellers. The use of silencers on the exhaust of the internal combustion engine was considered. The spectral characteristics of the acoustic fields of the propeller-driven power plants for the operating sample of the UAV "Eco" were obtained. The measurements were carried out in one-third octave and 1/48 octave frequency bands under static conditions. The venue is the KhAI airfield. Note that the propellers that were part of the power plants operated at Reynolds numbers (Re0,75<2*105), which can significantly affect its aerodynamic and acoustic characteristics. It is shown that when choosing a UAV control system, one should take into account the fact that two-stroke piston engines are the dominant source in the noise of propeller-driven control systems in the absence of a hood and mufflers in the intake and exhaust tracts. The use of a four-stroke internal combustion engine significantly reduces the noise of the control system. In the general case, the position of the boundaries of the zone of acoustic visibility of a UAV at the location of the observer is determined by the ratio between the intensity of acoustic radiation perceived by the observer from the UAV and the intensity of sound corresponding to the natural acoustic background and depends on the degree of manifestation of acoustic effects accompanying the propagation of sound in a turbulent atmosphere - the refraction of sound waves. Absorption and dissipation of acoustic energy. The calculation and comparison of the UAV detection range was carried out taking into account the existing natural maskers.The results of experimental studies are presented that allow assessing the degree of acoustic signature of the UAV. A set of measures aimed at reducing the intensity of the acoustic signature of the UAV in various regions of the radiation spectrum has been determined.

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Acoustic signature reduction using feedback of piezoelectric layers

10.1117/12.388757 ◽

2000 ◽

Author(s):

Johan Hamberg ◽

Anders Malmgren

Keyword(s):

Acoustic Signature ◽

Piezoelectric Layers

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Multiple point contact wear prediction and source identification scheme using a single channel blended airborne acoustic signature

IFAC-PapersOnLine ◽

10.1016/j.ifacol.2020.11.046 ◽

2020 ◽

Vol 53 (3) ◽

pp. 283-288

Author(s):

Muhammad Atayyab Shahid ◽

Tariq Mairaj Khan ◽

Kevin Lontin ◽

Kanza Basit ◽

Muhammad Khan

Keyword(s):

Source Identification ◽

Single Channel ◽

Point Contact ◽

Multiple Point ◽

Wear Prediction ◽

Identification Scheme ◽

Contact Wear ◽

Acoustic Signature

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A survey on acoustic signature recognition and classification techniques for persistent surveillance systems

10.1117/12.919872 ◽

2012 ◽

Cited By ~ 2

Author(s):

Amir Shirkhodaie ◽

Amjad Alkilani

Keyword(s):

Surveillance Systems ◽

Classification Techniques ◽

Acoustic Signature ◽

Signature Recognition

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Cavity and flow measurements of reproducible bubble entrainment following drop impacts

Experiments in Fluids ◽

10.1007/s003480100320 ◽

2001 ◽

Vol 31 (6) ◽

pp. 664-673 ◽

Cited By ~ 17

Author(s):

P. A. Elmore ◽

G. L. Chahine ◽

H. N. Oguz

Keyword(s):

Flow Measurements ◽

Bubble Entrainment ◽

Drop Impacts

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Acoustic signature based discrimination of drinking water

2012 Sixth International Conference on Sensing Technology (ICST) ◽

10.1109/icsenst.2012.6461741 ◽

2012 ◽

Cited By ~ 1

Author(s):

R. S. Chouhan ◽

A. H. Kiranmayee ◽

P. C. Panchariya ◽

P. B. Prasad

Keyword(s):

Drinking Water ◽

Acoustic Signature

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Acoustic Signature Based Intelligent Health Monitoring of Air Compressors with Selected Features

2012 Ninth International Conference on Information Technology - New Generations ◽

10.1109/itng.2012.67 ◽

2012 ◽

Cited By ~ 12

Author(s):

Nishchal K. Verma ◽

Tarun Maini ◽

Al Salour

Keyword(s):

Health Monitoring ◽

Acoustic Signature ◽

Air Compressors

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Air Bubble Entrainment, Breakup, and Interplay in Vertical Plunging Jets

Journal of Fluids Engineering ◽

10.1115/1.4039715 ◽

2018 ◽

Vol 140 (9) ◽

Cited By ~ 3

Author(s):

Numa Bertola ◽

Hang Wang ◽

Hubert Chanson

Keyword(s):

High Speed ◽

Point Explosion ◽

Air Bubble ◽

Bubble Breakup ◽

Jet Impact ◽

Bubble Entrainment ◽

Bubble Interaction ◽

Onset Velocity ◽

Air Cavities ◽

Interaction Behaviors

The entrainment, breakup, and interplay of air bubbles were observed in a vertical, two-dimensional supported jet at low impact velocities. Ultra-high-speed movies were analyzed both qualitatively and quantitatively. The onset velocity of bubble entrainment was between 0.9 and 1.1 m/s. Most bubbles were entrained as detached bubbles from elongated air cavities at the impingement point. Explosion, stretching, and dejection mechanisms were observed for individual bubble breakup, and the bubble interaction behaviors encompassed bubble rebound, “kiss-and-go,” coalescence and breakup induced by approaching bubble(s). The effects of jet impact velocity on the bubble behaviors were investigated for impact velocities from 1.0 to 1.36 m/s, in the presence of a shear flow environment.

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