5,897 research outputs found

    Aerodynamic instabilities in high-speed air intakes and their role in propulsion system integration

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    High-speed air intakes often exhibit intricate flow patterns, with a specific type of flow instability known as ‘buzz’, characterized by unsteady shock oscillations at the inlet. This paper presents a comprehensive review of prior research, focused on unraveling the mechanisms that trigger buzz and its implications for engine stability and performance. The literature survey delves into studies concerning complex-shaped diffusers and isolators, offering a thorough examination of flow aerodynamics in unstable environments. Furthermore, this paper provides an overview of contemporary techniques for mitigating flow instability through both active and passive flow control methods. These techniques encompass boundary layer bleeding, the application of vortex generators, and strategies involving mass injection and energy deposition. The study concludes by discussing future prospects in the domain of engine-intake aerodynamic compatibility. This work serves as a valuable resource for researchers and engineers striving to address and understand the complexities of high-speed air induction systems.EU Erasmus+ Progra

    A review of topology optimisation software for additive manufacturing: capability comparison

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    The topology optimisation method has gained significant attention in recent decades due to the extensive development and implementation of additive manufacturing, an advanced technology applied to fabricate complex geometries and structures. By following the topology optimisation methodology, the existing geometry can be effectively optimised by minimising or maximising objective functions, such as stiffness, volume, or weight reduction. This paper provides an overview of the topology optimisation algorithm and compares the capabilities of computer-aided software designed to conduct topology optimisation procedures. Four different software are analysed using case studies from various industries. The case study models are categorised based on important parameters for the topology optimisation and evaluated in terms of availability, optimisation method, objective function, and other factors

    Influence of door gap on aeroacoustics and structural response of a cavity

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    Numerical aeroacoustic analysis using the Shear Stress Transport–Scale Adaptive Simulation turbulence model was conducted on a weapon bay model based on the M219 geometry with doors incorporating radar cross-section reduction features. The effect of the introduction of a gap between the doors and the cavity edge on the aeroacoustic and structural response of the cavity was analyzed at Mach 0.85. The effect of introducing 3 deg of sideslip was also investigated. Both mean and unsteady flow analyses were conducted. The results showed a strong palliative effect of the door gap with and without sideslips. The overall analysis of the spectral signature on the forces and moments acting on the doors indicated the possibility of fluid–acoustic coupling, as all acoustic spectra showed a predominant tone located at the same frequency of the first structural mode

    A cyber-physical prototyping and testing framework to enable the rapid development of unmanned aircraft

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    A cyber-physical prototyping and testing framework to enable the rapid development of UAVs is conceived and demonstrated. The framework is an extension of the typical iterative engineering design and development process, specifically applied to the rapid development of electric fixed-wing UAVs. Unlike other development frameworks in the literature, the presented framework allows for iteration throughout the entire development process, from design to construction, using a mixture of simulated and real-life testing as well as cross-aircraft development. For specific aircraft or application requirements, methods and tools can be added, removed, or modified as need to be within the framework. Additionally, the framework still enables traditional aircraft development and system engineering principles. The framework presented includes low- and high-order methods and tools that can be applied to a broad range of fixed-wing UAVs and can either be combined and executed simultaneously or sequentially. As part of this work, 7 novel and enhanced methods and tools were developed that apply to electric fixed-wing UAVs in the areas of: flight testing, measurement, emulation and modeling, and optimization. These methods and tools include: (1) data acquisition, (2) flight testing automation, (3) 3D scanning, (4) moment of inertia measurement, (5) modular emulation, (6) electric aircraft power modeling, and (7) propulsion system optimization. Capturing accurate flight testing data is a fundamental component of UAV development, and doing so requires high-fidelity flight data from a large range of sensors. Two data acquisition systems were developed that showed superior capabilities and performance compared to those developed by comparable research institution and commercial systems. The latter of the data acquisition systems was further enhanced to enable flight control, which was then used to develop and demonstrate a flight-testing automation technique. Compared to other unmanned flight testing efforts in the literature, automating the data collection process, as opposed to the previous manual status quo, has allowed for improved airspace utilization (up to double) and more efficient flight testing through precise maneuvering, minimal trial-and-error, and, more importantly, decreased flight time required (as little as 1/10th). Knowledge of aircraft parameters, including geometric, inertial, and subcomponent properties is vital in the analysis of flight testing results; however, in the case of UAV development, developers, especially researchers, often use existing COTS airframes that have limited parameters available. The 3D scanning methodology enabled accurate geometry data collection, yielding a CAD model used to develop a flight model for the high-fidelity emulation. Along with model generation, the geometry was used to compute the aircraft's aerodynamic characteristics using several computational tools of varying order: the lifting-line theory aerodynamic tools, XFLR5 and AVL, and the computational fluid dynamics (CFD) tool Ansys Fluent; these computed aerodynamic characteristic values were also compared to values estimated from flight testing data. In order to enable practical high-fidelity emulation as well as processing of flight data, a moment of inertia testing rig and methodology was developed that enables very accurate measurement of an object, i.e., within 5%, which is an order of magnitude less error than the existing "low-effort" methods from the literature; the accuracy of the developed testing method is comparable to high-effort, complex methods with geometric-based drag or other types of corrections. In order to decrease development time, modeling and emulation became an important component of the developed framework. Instead of prototyping, testing, and analyzing through the many stages of aircraft development in hardware, which is resources and time intensive, a virtual aircraft and its sub-systems were modeled and then implemented into an emulation environment, i.e., creating a "Virtual Twin". The uavEE emulation environment integrates a high-fidelity simulator with layers of modeling (e.g. aircraft power model), flight control software (e.g. autopilot software), and interfaces to hardware components (e.g. flight control board and sensors). A high-fidelity, low-order power model for electric, fixed-wing UAVs was developed that incorporates propulsion system power consumption and solar power generation. Both models were evaluated through flight testing and showed very close agreement with experimental flight data. Finally, as the propulsion system consumes a significant portion of onboard energy, a propulsion system optimization tool was developed that determines optimal propeller and motor combination(s) for electric, fixed-wing UAVs, given desired mission requirements and profile. Flight testing validation showed that an optimized propeller-motor combination requires approximately 20% less power than a default manufacturer-recommended combination. Simulations of agricultural survey and infrastructure inspection missions showed potential for greater efficiency gains of 50% to 75%, relative to the default combination, yielding 2-4 fold increases in coverage. Two demonstrations of the development framework are presented. The first demonstration showed how to rapidly develop an unmanned aircraft for agricultural field surveillance based on an existing platform, with general and mission-specific methodology. The second demonstration showed the full development of a computationally-intensive, long-endurance solar-powered unmanned aircraft for visually intensive applications; this framework application required 4 iterations, from conception to flight demonstration of the desired aircraft capabilities. A comparison of the developed solar unmanned aircraft to a similar aircraft developed using a different methodology shows a significantly reduced development timeline and resources requirement. The cyber-physical prototyping and testing framework, tools, and methods developed in this work enable users to rapidly design, develop, and modify UAVs to desired aircraft and mission specifications. The UAV development framework can be applied to clean-sheet designs or utilize existing airframes and other components. The tools and methods developed enable rapid aircraft development, testing, and optimization, to significantly improve their performance, efficiency, and endurance. Finally, the aircraft development demonstrations performed provide a foundation for future UAV development. This is especially true for future long-endurance, solar-powered UAVs, which can build off of the aircraft developed in this work and take advantage of incremental improvements in energy capture and storage capabilities.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    High-Performance Piezoelectric Nanogenerators Based on Hybrid Perovskite Nanomaterials for Energy-Harvesting

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    With the increasing drive to create self-powering nano/micro-electromechanical systems (NEMS/MEMS), maximizing the output performance of piezoelectric nanogenerators (PENGs) is essential. Organic-inorganic halide perovskites (OIHP) have unique advantages over century-old ceramic piezoelectrics, including mechanical flexibility, low-temperature processing, bio-friendliness, structural tunability and low cost, making them ideal candidates for electromechanical energy conversion devices and a wide range of applications. This research explores the piezoelectric properties of OIHPs and applies them to designing efficient piezoelectric nanogenerators. The novel perovskite materials which are studied here include cesium lead halide (CsPbX3), (4-aminotetrahydropyran)2 lead bromine chlorine ((ATHP)2PbBr2Cl2), (trimethylchloromethylammonium)2 tin chloride ((TMCM)2SnCl6), N-ethyl-1,4-diazoniabicyclo [2.2.2] octonium copper chloride (EDABCO-CuCl4), formamidinium (FA) lead bromine iodine (FAPbBr2I), and polystyrene (PS) functionalized FAPbBr2I. The perovskites are used to fabricate 0-3 type of piezoelectric composites (random distribution) and the PENG operation is assessed under 3-3 operational mode. The perovskite-polymer nanocomposites are employed to harvest mechanical energies from the vibration (< 50 Hz) to produce electricity and to use those nanogenerators as the power source to realize self-powered wireless sensing systems. Firstly, the dissertation discusses the piezoelectric and dielectric properties of different OIHP nanomaterials and the fundamentals of PENGs (Chapter 1). It also provides insights on halogen regulation, the synergistic effect of molecular dipole rotation with octahedral displacement, and quasi-spherical cation with Jahn-Teller distortion, thus transforming blind material search into a guided design strategy for piezoelectrics. The influence of nanomaterial distribution, geometry, porosity, dielectric constants, force, frequency, and ferroelectric manipulation of the composite film is then systematically analyzed (Chapter 2). Through a series of PENGs that are fabricated, characterized, and evaluated from halogen-tuned (I/Br) piezoelectric CsPbX3 (X=Br/Cl) (including piezo response force microscopy (PFM) and electric measurements), it is revealed that the highest piezoelectric charge constants (d33 ~ 47 pC/N) and output power density (24 μW/cm2.N) come from the CsPbBr2I PENG. This performance enhancement is attributed to the anisotropic lattice strain and elastic softness. The findings of this research emphasize the potential of inorganic CsPbX3-based PENGs in self-powered NEMS/MEMS (Chapter 3). The second part of the dissertation outlines the use of novel OIHP nanorods of (ATHP)2PbBr2Cl2 to improve piezoelectric coefficients. These nanorods are synthesized through a ligand-assisted reprecipitation (LARP) method, which confers superior in-plane polarization, leading to d31 (transverse piezoelectric coefficient) of 3 times higher (~ 64 pC/N) than that of a commercial piezoelectric polymer of polyvinylidene fluoride (PVDF). Experiments also show that the nanorods can be dispersed in a flexible polydimethylsiloxane (PDMS) polymer, which leads to a large output voltage. The high output performance of the PENG is a result of the large surface area and bending of nanorods, which contribute to the d33 and d31 coefficients (Chapter 4). The third part provides a design and synthesis route of a novel vacancy-ordered halide double perovskite of (TMCM)2SnCl6 to improve the d33 and g33 of piezoelectric materials simultaneously. The molecular dipole moment and atomic displacement in the inorganic [SnCl6]2- are influenced by the halogen bond between them, resulting in a large spontaneous polarization. Meanwhile, the presence of insulating molecules reduces the relative permittivity, leading to a high d33 of 137 pC/N, and g33 of 980×10-3 V•m/N. Experiments also demonstrate a high output voltage of 81 V at 40 Hz, 4.2 N in the PENG. This design showcases the potential of a heavy-metal free, highly piezoelectric materials in PENG design, which can potentially be integrated with batteries/capacitors to power an electrical circuit (Chapter 5). The fourth part presents a green organic-inorganic metal halide EDABCO-CuCl4 to fabricate PENGs. This study on symmetry breaking highlights the independent roles of quasi-spherical molecules and spherical molecules with Jahn-Teller active and inactive metal ion complexes. With its highly confined 0D architecture and large tetrahedral distortion, it possesses a high d33 of 165 pC/N, and a massive g33 of 2,110 ×10-3 V•m/N, and its performance remains unchanged till ~ 180 oC. The high transduction coefficient produces an output power density of 43 μW/cm2 in a PENG at 50 kPa. The energy generation is also stably maintained up to ~ 160 oC. This study further demonstrates the design and fabrication of green PENGs capable of producing electrical energy in harsh environments (Chapter 6). The fifth part presents a PENG design from the in-situ grown OIHP of FAPbBr2I nanoparticles (NP) that create a highly porous structure inside a piezoelectric polymer composite. The mechanism of pore formation, its characterization, and its implications on the PENG performance are explored. The porous composite increases the output piezo potential by 5-fold, while the OIHP nanoparticles enhance the relative permittivity by interfacial polarization, reduce the film conductivity and thus increase the output current by ~ 15-fold higher than the commercially available analog of PVDF. The PENG is used as a power source, successfully showcasing a self-powered wireless communication application between a PENG and smartphone, potentially realizing a proof-of-concept for future battery-independent IoT systems. The PENG is also capable of efficiently harvesting energy from the vibration of a car engine and storing it in capacitors- potentially applicable to other vibrating parts such as airframes, or the engine of an aircraft (Chapter 7). The sixth part aims to enhance the output current by fabricating a cascade-type PENG structure. The research improves the OIHP's stability by functionalizing its surface with the polystyrene. As a result, the fundamental performance limiting factors of the perovskites, such as ion migration, crystallinity, and grain sizes are improved, all of which are conducive to PENG performance. The cascaded architecture by the newly designed piezoelectric composites results in a large current density of ~ 100 μA/cm2, an enhancement of more than an order of magnitude for the OIHP-based PENGs (Chapter 8). This dissertation is devoted to deepening our understanding of the piezoelectric behaviour of the new perovskite nanomaterials in a soft and flexible polymer. The findings of exciting piezoelectric and dielectric properties in novel perovskite material will also have a substantial impact on many areas, including the field of energy harvesters, sensors, actuators, flexible optoelectronics, and soft robotics. At the art at which this research is developing, it is anticipated that PENG-based power sources will soon be driving portable electronics

    Spin Recovery Analysis on a Simulation Model of the NASA F-18 High Alpha Research Vehicle (HARV) Using Thrust Vectoring

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    In the early years of aviation, spins were poorly understood and frequently fatal. With just over a century of research and experiments dedicated to spins, today’s aviation world has a very firm grasp on spin aerodynamics. Most fighter aircraft have airframes and control surfaces specifically designed to ensure the ability of departure from the possible spin modes the aircraft can enter. An alternative and/or additional approach is given by thrust vectoring. Implementing thrust vectoring into spin recovery can potentially save an aircraft and/or the life of the pilot in situation where control-surface-only spin recovery is not able to recover the aircraft due to non-adequate recovery time and/or altitude restrictions. This work investigates the efficacy of implementing thrust vectoring alongside the control surfaces into spin recovery on the NASA F-18 HARV. A total of 396 different thrust vectoring configurations were tested by applying them on a single, leftward flat spin mode that was attainable by the NASA F-18 HARV. The thrust vectoring configurations are defined by three variables: specific vanes deflected, the magnitude of vane deflections, and the throttle deflection. These spin recovery trials were evaluated by two main criteria, time of recovery and loss of altitude during recovery. The overall results have shown that implementing thrust vectoring along with the control surfaces into spin recovery greatly decrease both the recovery time and the loss of altitude during recovery

    World War Two Glider Borne Forces: The Role of British Doctrine in Effective Military Change

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    The United States’ National Defense Strategy has shifted from fighting an asymmetrical, fourth generation adversary utilizing counterinsurgency and unconventional warfare to preparing for a peer/near peer conventional conflict focused on the Pacific and Central Europe. Modern maneuver commanders and operational planners can apply the economy of force, criticality of speed plus precision in kinetic engagements, value of highly trained, task organized small units, and technological incorporation knowledge gathered from analyzing the World War II glider operations executed by Germany, Great Britain, and the United States. Gliders were sailplanes that had a higher ratio of lift to drag than a motorized airplane. They were lightweight aircraft snatched fully loaded from the ground by towplanes, pulled to a high altitude, released by disengaging a towrope, then glided silently and stealthy over many miles before landing in small open spaces or conducting controlled crash landings on rough terrain. The research is not attempting to make an anachronistic case for gliders as a modern vertical envelopment mobility asset. It is empirically examining which nation best leveraged the glider borne force capabilities using the analytical tools of PEST (Political, Economic, Socio-Cultural, and Technology) and M from DIME (Diplomacy, Information, Military, and Economic). Therefore, a study that assesses the degree of effectiveness by which World War II belligerents employed the new glider technology can yield lessons for the development of modern strategy. War drives strategic, tactical, and technological change. Vertical envelopment concepts were initiated in World War Two due to the lessons learned from trench warfare in the First World War. Gliders were a vertical envelopment change that had to be managed, tactics-techniques-procedures (TTPs) developed and codified, and operationally implemented. How each nation accomplished that varied. Clausewitz saw the nature of warfare as defined by the interplay of passion, chance, and creativity. He also felt that war reflected the nature of the societies waging it. This thesis will examine the German, American, and British glider capability integration, doctrine development, manning-training-equipping processes, proponent and opponent mindsets’ within the respective military hierarchies, and technological innovations that emerged from each country’s program. It will provide an empirical, comparative analysis revealing how Great Britain succeeded over the others at implementing and pre-eminently leveraging glider capabilities in World War II

    Towards Robust and Efficient Communications for Urban Air Mobility

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    For the realization of the future urban air mobility, reliable information exchange based on robust and efficient communication between all airspace participants will be one of the key factors to ensure safe operations. Especially in dense urban scenarios, the direct and fast information exchange between drones based on Drone-to-Drone communications is a promising technology for enabling reliable collision avoidance systems. However, to mitigate collisions and to increase overall reliability, unmanned aircraft still lack a redundant, higher-level safety net to coordinate and monitor traffic, as is common in today's civil aviation. In addition, direct and fast information exchange based on ad hoc communication is needed to cope with the very short reaction times required to avoid collisions and to cope with the the high traffic densities. Therefore, we are developing a \ac{d2d} communication and surveillance system, called DroneCAST, which is specifically tailored to the requirements of a future urban airspace and will be part of a multi-link approach. In this work we discuss challenges and expected safety-critical applications that will have to rely on communications for \ac{uam} and present our communication concept and necessary steps towards DroneCAST. As a first step towards an implementation, we equipped two drones with hardware prototypes of the experimental communication system and performed several flights around the model city to evaluate the performance of the hardware and to demonstrate different applications that will rely on robust and efficient communications

    30th Annual Willem C. Vis International Commercial Arbitration Moot

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    31st March – 6th April 2023 in Vienna, Austri

    Optical Measurement of Airborne Particles on Unmanned Aircraft

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    Aerosols and clouds are persistent causes of uncertainty in climate and weather models, which is due to their heterogeneous suspension and occurrence within the atmosphere, and complex interactions which are chaotic and exist on small scales. Unmanned aerial vehicles (UAVs) have grown in popularity, and are becoming more commonly used for general atmospheric measurement, particularly measurement of aerosols and clouds. This thesis presents and evaluates a synergy between two UAVs, a multi-rotor: the UH-AeroSAM octocopter and a fixed-wing: the FMI-Talon, and an optical particle instrument: the Universal Cloud and Aerosol Sounding System. Computational fluid dynamics with Lagrangian particle tracking (CFD-LPT) was used as a tool for the characterisation of the velocity fields and particle trajectories around both UAVs. In both instances CFD-LPT was used to develop an operational envelope, with particular attention to angle of attack constraints and size distribution perturbation, for the UAV – instrument synergy. UCASS was the first open path instrument to be used on a UAV, and a good case has been made for its continued use, particularly on fixed-wing UAVs, which exhibit less complex aerodynamics and superior stability in the induced sampling airflow through the instrument