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Dolphin-Inspired Target Detection for Sonar and Radar

Timothy Leighton Paul White
Archives of Acoustics | 2014 | vol. 39 | No 3 | 319-332 | DOI: 10.2478/aoa-2014-0037
Keywords sonar radar cetacean dolphin whale mines explosives nonlinear wake
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Abstract

Gas bubbles in the ocean are produced by breaking waves, rainfall, methane seeps, exsolution, and a range of biological processes including decomposition, photosynthesis, respiration and digestion. However one biological process that produces particularly dense clouds of large bubbles, is bubble netting. This is practiced by several species of cetacean. Given their propensity to use acoustics, and the powerful acoustical attenuation and scattering that bubbles can cause, the relationship between sound and bub-ble nets is intriguing. It has been postulated that humpback whales produce ‘walls of sound’ at audio frequencies in their bubble nets, trapping prey. Dolphins, on the other hand, use high frequency acous-tics for echolocation. This begs the question of whether, in producing bubble nets, they are generating echolocation clutter that potentially helps prey avoid detection (as their bubble nets would do with man-made sonar), or whether they have developed sonar techniques to detect prey within such bubble nets and distinguish it from clutter. Possible sonar schemes that could detect targets in bubble clouds are proposed, and shown to work both in the laboratory and at sea. Following this, similar radar schemes are proposed for the detection of buried explosives and catastrophe victims, and successful laboratory tests are undertaken.

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Authors and Affiliations

Timothy Leighton
Paul White

Numerical Investigation on the Gas Field Generated by High Pressure Gas Atomizer Focused on Physical Mechanisms of Gas Recirculation and Wake Closure Phenomenon

Mingxiang Liu Shan Zhou
Archives of Metallurgy and Materials | 2022 | vol. 67 | No 1 | 167-174 | DOI: 10.24425/amm.2022.137485
Keywords Gas field Aspiration pressure Recirculation mechanism Wake closure Atomization
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Abstract

Physical mechanisms of gas recirculation and wake closure were investigated by modeling the gas field generated by High Pressure Gas Atomizer using computational fluid dynamics. A recirculation mechanism based on axial and radial gas pressure gradient was proposed to explain the gas recirculation. The occurrence of wake closure is regarded as a natural result when elongated wake is gradually squeezed by expansion waves of increasing intensity. An abrupt drop could be observed in the numerical aspiration pressure curve, which corresponds well with the experimental results. The axial gradient of gas density is considered as the reason that results in the sudden decrease in aspiration pressure when wake closure occurs. Lastly, it is found that a shorter protrusion length and a smaller melt tip diameter would lead to a smaller wake closure pressure, which could benefit the atomizer design to produce fine metal powder with less gas consumption.
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Authors and Affiliations

Mingxiang Liu
1
ORCID: ORCID
Shan Zhou
2
  1. Shanghai University, School of Materials Science and Engineering, Center for Advanced Solidification Technology, Shanghai 200444, China
  2. Shanghai Jiao Tong University, Institute of Forming Technology and Equipment, 1954 Huashan Road, Shanghai 200030, China

Analysis of wake structures in bubbly flows using Particle Image Velocimetry (PIV)

Björn Lewandowski Michał Fertig Georg Krekel Mathias Ulbricht
Chemical and Process Engineering | 2019 | vol. 40 | No 1 | 49-55 | DOI: 10.24425/cpe.2018.124996
Keywords bubbly flow Particle Image Velocimetry wake analysis flow characteristics high-speedimaging
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Abstract

The flow structure around rising single air bubbles in water and their characteristics, such as equivalent diameter, rising velocity and shape, was investigated using Particle Image Velocimetry (PIV) and Shadowgraphy in a transparent apparatus with a volume of 120 mL. The effect of different volumetric gas flow rates, ranging from 4 μL/min to 2 mL/min on the liquid velocity was studied. Ellipsoidal bubbleswere observedwith a rising velocity of 0.25–0.29m/s. It was found that a Kármán vortex street existed behind the rising bubbles. Furthermore, the wake region expanded with increasing volumetric gas flow rate as well as the number and size of the vortices.

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Authors and Affiliations

Björn Lewandowski
Michał Fertig
Georg Krekel
Mathias Ulbricht

Numerical investigation of vortex wake patterns of laminar flow around two side-by-side cylinders

Van Luc Nguyen Duy Knanh Ho
Archive of Mechanical Engineering | 2022 | vol. 69 | No 3 | 541-565 | DOI: 10.24425/ame.2022.141517
Keywords viscous fluid vortex shedding vortex wake pattern vortex-in-cell method two side-by-side cylinders
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Abstract

The laminar flow around two side-by-side circular cylinders was numerically investigated using a vortex-in-cell method combined with a continuous-forcing immersed boundary method. The Reynolds number (Re) of the flow was examined in the range from 40 to 200, and the distance between the cylinders varies from 1.2 D to 6 D, where D is the cylinder diameter. Simulation results show that the vortex wake is classified into eight patterns, such as single-bluff-body, meandering-motion, steady, deflected-in-one-direction, flip-flopping, anti-phase-synchronization, in-phase-synchronization, and phase-difference-synchronization, significantly depending on the Re, the cylinder distance, and the initial external disturbance effects. The anti-phase-synchronization, in-phase-synchronization, and phase-difference-synchronization vortex patterns can be switched at a low Re after a long time evolution of the flow. In particular, the single-bluff-body and flip-flopping vortex patterns excite the oscillation amplitude of the drag and lift coefficients exerted on the cylinders.
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Bibliography

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Authors and Affiliations

Van Luc Nguyen
1
ORCID: ORCID
Duy Knanh Ho
1
  1. Institute of Engineering and Technology, Thu Dau Mot University, Binh Duong Province, Vietnam

Life cycle assessment of the alternative fuels in the light of the International Maritime Organization initial GHG reduction strategy

Krzysztof Kołwzan
Prawo Morskie | 2022 | No XLIII | 59-78 | DOI: 10.24425/pm.2022.143405
Keywords LCA – Life Cycle Assessment GHG – Greenhouse gas GWP – Global warming potential CO2 – Carbon dioxide CO2eq – Carbon dioxide equivalent WtW –Well-to-Wake TtW – Tank-to-Wake WtT – Well-to-Tank
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Abstract

The article aims to increase knowledge on methods for assessing Greenhouse Gases (GHG) emissions throughout the life cycle of marine alternative fuels. The life cycle of new marine alternative fuels and the assessment of GHG emissions resulting not only from their combustion is one of the new topics that are currently being discussed by the IMO, under the ‘Initial IMO GHG Reduction Strategy’ announced by the Organization in 2018. The IMO Marine Environment Protection Committee (IMO MEPC) is currently working on the development of Guidelines for Life-Cycle Assessment of GHG emissions for marine fuels from their extraction, through transport, processing, bunkering on board and end use in vessels propulsion systems, what is often called ‘from Cradle-to-Grave’. The use of fossil hydrocarbon fuels is common throughout the shipping industry, but in recent years ships with alternative energy sources have begun to be successfully introduced. Alternative fuels, although they may have low, zero or zero net GHG emissions in use (Tank to Wake or TtW), GHG emissions during their production, processing and distribution (Well-to-Tank or WtT) can vary widely. While a range of low-carbon and zero-carbon energy sources are potentially available for shipping, currently there is no clear decarbonization path or paths, and is likely that in the future a range of solutions will be adopted according to different vessel and operational requirements.
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Authors and Affiliations

Krzysztof Kołwzan
1
  1. Centre for IMO Affairs, Polish Register of Shipping

An Innovative Multiple Attribute Based Distributed Clustering with Sleep/Wake Scheduling Mechanism for WSN

Shankar D. Chavan Shahaji R. Jagdale Dhanashree A. Kulkarni Sneha R. Jadhav
International Journal of Electronics and Telecommunications | 2021 | vol. 67 | No 3 | 437-443 | DOI: 10.24425/ijet.2021.137831
Keywords advanced distributed energy efficient adaptive clustering clustering lifetime sleep-wake cluster head scheduling throughput wireless sensor networks
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Abstract

Wireless sensor network is a dynamic field of networking and communication because of its increasing demand in critical Industrial and Robotics applications. Clustering is the technique mainly used in the WSN to deal with large load density for efficient energy conservation. Formation of number of duplicate clusters in the clustering algorithm decreases the throughput and network lifetime of WSN. To deal with this problem, advance distributive energy-efficient adaptive clustering protocol with sleep/wake scheduling algorithm (DEACP-S/W) for the selection of optimal cluster head is presented in this paper. The presented sleep/wake cluster head scheduling along with distributive adaptive clustering protocol helps in reducing the transmission delay by properly balancing of load among nodes. The performance of algorithm is evaluated on the basis of network lifetime, throughput, average residual energy, packet delivered to the base station (BS) and CH of nodes. The results are compared with standard LEACH and DEACP protocols and it is observed that the proposed protocol performs better than existing algorithms. Throughput is improved by 8.1% over LEACH and by 2.7% over DEACP. Average residual energy is increased by 6.4% over LEACH and by 4% over DEACP. Also, the network is operable for nearly 33% more rounds compared to these reference algorithms which ultimately results in increasing lifetime of the Wireless Sensor Network.
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Bibliography

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Authors and Affiliations

Shankar D. Chavan
1
Shahaji R. Jagdale
1
Dhanashree A. Kulkarni
1
Sneha R. Jadhav
1
  1. Dr. D. Y. Patil Institute of Technology, Pimpri, Pune

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