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Design of acoustic coating for underwater stealth in low-frequency ranges
Get PDFIn this study, it is aimed to protect underwater vehicles against active sonar systems by anechoic coating. A matrix material with close acoustic impedance to water, resistivity to hydrostatic pressure, suitability for the marine environment, and high material loss factor is selected. At low frequencies, the inclusions in different shapes and sizes are added to the matrix material. Since solid inclusions will increase the coating mass considerably, air cavities are preferred as inclusions. More attention is paid to low-frequency absorption, especially below 1 kHz, because of advancing sonar technology. The acoustic performance of the designed models is compared in three frequency ranges: low (below 3 kHz), middle (3–6 kHz), and high (6–10 kHz). The designed models are constructed by considering hydrostatic pressure; hence, volume of air cavities is tried to decrease, while absorption performance is aimed to increase. Therefore, a conical cavity which commonly used in the literature is optimized by chancing its dimensions and location. Also, novel approaches, gong shape cavity, and sandglass cavities are introduced. The results show that, not only cavity shape, but also its location and dimensions are highly influential on absorption performance. High-volume cavities increase the absorption performance at the low-frequency range, but they are not effective at high frequencies. The gong shape and sandglass air cavities show broadband absorption; also, gong shape cavity volume is less than literature models. Thus, its usability increases at deep waters. The results of this study provide novel underwater acoustic coating models for various applications.Journal of the Brazilian Society of Mechanical Sciences and Engineerin
Operational data for the risk management of victim operated explosive devices in humanitarian mine action: a practitioner’s perspective
Get PDFSince Mine Action's inception at the end of the 1980s, operators have collected limited data on the Victim Operated Explosive Devices (VOEDs) they clear. This includes not only data on the explosive ordnance itself but data on how they were found, where they were found and how they were processed and ultimately destroyed. In a context where detection of mines, boobytraps and certain Victim Operated Improvised Explosive Devices (VOIEDs) is an ongoing humanitarian and military challenge, significantly expanded operational data collection provides an achievable way to facilitate enhanced operational risk management. Risk decisions inherent in the clearance of VOEDs are better if made on the basis of extensive operational data. In the absence of a technological solution to detect and positively discriminate VOEDs from false positive indications, the collection of operational data offers the best prospect for “managing” if not “solving” the problem.Heliyo
Developing organizations’ dynamic capabilities and employee mental health in the face of heightened geopolitical tensions, polarized societies and grand societal challenges
Get PDFThe year 2023 witnessed intensified geopolitical tensions, military conflicts, and international economic sanctions, with heightened risks and uncertainties for businesses, especially multinational enterprises. In this editorial for 2024, we focus on two phenomena—international sanction and mental health—as critical issues for human resource management research and practice. These two issues are closely related to the United Nations Sustainable Development Goals (Goal 3: Good health and wellbeing and Goal 16: Peace, justice and strong institutions). We draw on dynamic capability theory to illustrate how organizations can develop corporate capabilities to survive and thrive in a volatile global business environment. We suggest sets of research questions to inform policy decisions and practice. We also outline practical implications for human resource professionals
A comment on the pursuit to align AI: we do not need value-aligned AI, we need AI that is risk-averse
No full textAI Safety, AI Alignment, and the eventual demise of society due to superintelligent beings have recently become topics of public and even political interest. So much so that there were calls to halt all development on Artificial Intelligence until these issues had been addressed (see BBC News, May 2023), Elon Musk has established another organisation (‘xAI’) aimed at tackling such issues, and global leaders have organised global summits to prioritise research in the area. Needless to say; with the introduction of ChatGPT, there has been a growing interest in and precedence to solve issues to prevent the AI dystopian scenarios we might be familiar with from science fiction.AI & SOCIET
Wave-assisted propulsion: an experimental study on traveling ships
No full textA submerged hydrofoil interacting with incoming waves produces combined heaving and pitching motion, facilitating the conversion of wave energy into thrust. When the foil is attached to the ship hull, the generated “green” power from wave energy could assist the ship's propulsion system and significantly reduce fuel costs. This study experimentally assesses thrust generation from a fixed mid-hull foil by comparing towing force at different wave and traveling speeds. The optimal mid-hull foil demonstrates a fuel cost reduction ranging from 10.3% to 20.4% at diverse traveling speeds and wave parameters. Thrust generation increases at higher traveling speeds. Additionally, this study mathematically describes the hydrofoil motion with an outer pivot, which better suits the ship–foil model. This study then introduces a Strouhal number (StA,S) specifically for the ship–foil model, considering ship travel, ship response, and the hydrofoil's rotation around its outer pivot.Physics of Fluid
Control layer security: exploiting unobservable cooperative states of autonomous systems for secret key generation
Get PDFThe rapid growth of autonomous systems (ASs) with data sharing means new cybersecurity methods have to be developed for them. Existing computational complexity-based cryptography does not have information-theoretical bounds and poses threats to superior computational attackers. This post-quantum cryptography issue indeed motivated the rapid advances in using common physical layer properties to generate symmetrical cipher keys (known as PLS). However, PLS remains sensitive to attackers (e.g., jamming) that destroy its prerequisite wireless channel reciprocity. When ASs are in cooperative tasks (e.g., rescuing searching, and formation flight), they will behave cooperatively in the control layer. Inspired by this, we propose a new security mechanism called control layer security (CLS), which exploits the correlated but unobservable states of cooperative ASs to generate symmetrical cipher keys. This idea is then realized in the linearized UAV cooperative control scenario. The theoretical correlation coefficients between Alice's and Bob's states are computed, based on which common feature selection and key quantization steps are designed. The results from simulation and real UAV experiments show i) an approximately 90% key agreement rate is achieved, and ii) even an Eve with the known observable states and systems fails to estimate the unobservable states and the secret keys relied upon, due to the multiple-to-one mapping from unobservable states (pitch, roll and yaw angles) to the observable states (3D trajectory). This demonstrates CLS as a promising candidate to secure the communications of ASs, especially in the adversarial radio environment with attackers that destroys the prerequisite for current PLS.IEEE Transactions on Mobile Computin
Wave interaction with multiple adjacent floating solar panels with arbitrary constraints
Get PDFThe problem of wave interaction with multiple adjacent floating solar panels with arbitrary types and numbers of constraints is considered. All the solar panels are assumed to be homogeneous, with the same physical properties, as well as modeled by using the Kirchhoff-Love plate theory. The motion of the fluid is described by the linear velocity potential theory. The domain decomposition method is employed to obtain the solutions. In particular, the entire fluid domain is divided into two types, the one below the free surface, and the other below elastic plates. The velocity potential in the free surface domain is expressed into a series of eigenfunctions. By contrast, the boundary integral equation and the Green function are employed to construct the velocity potential of fluid beneath the entire elastic cover, with unknowns distributed along two interfaces and jumps of physical parameters of the plates. All these unknowns are solved from the system of linear equations, which is established from the matching conditions of velocity potentials and edge conditions. This approach is confirmed with much higher computational efficiency compared with the one only involving eigenfunction expansion for the fluid beneath each plate. Extensive results and discussions are provided for the reflection and transmission coefficients of water waves, maximum deflection, and principal strain of the elastic plates; especially, the influence of different types and numbers of edge constraints are investigated in detail.Physics of Fluid
Opportunities and challenges organo-mineral fertiliser can play in enabling food security
Get PDFFood security is a growing challenge related to an increasing global population.
The agricultural sector is key for a secure supply of food but relies up to 50%
on mineral fertilisers to meet crop nutrient demands. As mineral fertilisers
production is energy intensive, causing close to 2% of global greenhouse gas
(GHG) emissions, this poses greater challenge to meet net zero targets. Other
challenges include extreme weather patterns, GHG during fertiliser applications
and diffuse pollution, declining soil health, pest, disease, and loss of soil
biodiversity. As mineral fertilisers’ price increases and the state of soil health
decreases, innovative solutions are needed to meet crop nutrient demands
while ensuring that sufficient organic matter is conserved in the soil. One
solution to achieve net zero in agriculture can be in the form of organo-mineral
fertilisers (OMF). OMFs are a new concept that take organic feedstock (such as
biosolids, livestock manure, crop residues, food waste) and combines them with
reduced amounts of mineral fertilisers resulting in a balanced fertiliser product.
This Perspective piece discusses a Strength-Weakness-Opportunities-Threats
(SWOT) analysis on OMF and summarizes how OMF applications can play a role
to improve food security. This is further linked with short, medium and long
terms policy interventions that can be deployed to achieve a more sustainable
approach by balancing between protecting the wider environment and meeting
food security.The author would like to acknowledge funding received from UKRI Innovate UK Defra Farming Innovation Programme (10026016). The policy aspect of this work was carried out as part of a separate project that received the Research England Policy Support Fund.Frontiers in Sustainable Food System
Battery temperature prediction using an adaptive neuro-fuzzy inference system
Get PDFMaintaining batteries within a specific temperature range is vital for safety and efficiency, as extreme temperatures can degrade a battery’s performance and lifespan. In addition, battery temperature is the key parameter in battery safety regulations. Battery thermal management systems (BTMSs) are pivotal in regulating battery temperature. While current BTMSs offer real-time temperature monitoring, their lack of predictive capability poses a limitation. This study introduces a novel hybrid system that combines a machine learning-based battery temperature prediction model with an online battery parameter identification unit. The identification unit continuously updates the battery’s electrical parameters in real time, enhancing the prediction model’s accuracy. The prediction model employs an Adaptive Neuro-Fuzzy Inference System (ANFIS) and considers various input parameters, such as ambient temperature, the battery’s current temperature, internal resistance, and open-circuit voltage. The model accurately predicts the battery’s future temperature in a finite time horizon by dynamically adjusting thermal and electrical parameters based on real-time data. Experimental tests are conducted on Li-ion (NCA and LFP) cylindrical cells across a range of ambient temperatures to validate the system’s accuracy under varying conditions, including state of charge and a dynamic load current. The proposed models prioritise simplicity to ensure real-time industrial applicability.This work was funded by the UKRI Faraday Battery Challenge project called Next Generation LFP Cathode Material (NEXLFP). In addition, Abbas Fotouhi acknowledges funding from the Faraday Institution (Industrial Fellowships FIIF-003 and FIIF-014).Batterie
A comprehensive survey on Delaunay Triangulation: applications, algorithms, and implementations over CPUs, GPUs, and FPGAs
Get PDFDelaunay triangulation is an effective way to build a triangulation of a cloud of points, i.e., a partitioning of the points into simplices (triangles in 2D, tetrahedra in 3D, and so on), such that no two simplices overlap and every point in the set is a vertex of at least one simplex. Such a triangulation has been shown to have several interesting properties in terms of the structure of the simplices it constructs (e.g., maximising the minimum angle of the triangles in the bi-dimensional case) and has several critical applications in the contexts of computer graphics, computational geometry, mobile robotics or indoor localisation, to name a few application domains. This review paper revolves around three main pillars: (I) algorithms, (II) implementations over central processing units (CPUs), graphics processing units (GPUs), and field programmable gate arrays (FPGAs), and (III) applications. Specifically, the paper provides a comprehensive review of the main state-of-the-art algorithmic approaches to compute the Delaunay Triangulation. Subsequently, it delivers a critical review of implementations of Delaunay triangulation over CPUs, GPUs, and FPGAs. Finally, the paper covers a broad and multi-disciplinary range of possible applications of this technique.IEEE Acces