An analysis of Feature extraction and Classification Algorithms for Dangerous Object Detection

One of the important practical applications of object detection and image classification can be for security enhancement. If dangerous objects e.g. knives can be identified automatically, then a lot of violence can be prevented. For this purpose, various different algorithms and methods are out there that can be used. In this paper, four of them have been investigated to find out which can identify knives from a dataset of images more accurately. Among Bag of Words, HOG-SVM, CNN and pre-trained Alexnet CNN, the deep learning CNN methods are found to give best results, though they consume significantly more resources

Анализа, моделирање и оптимизација беспилотне летелице за велике висине на соларни погон

High-altitude long-endurance (HALE) or High-altitude platform station (HAPS) are aircraft that can fly in the stratosphere continuously for several months and provide support to military and civilian needs. In addition, HAPS can be used as a satellite at a fraction of the cost and provide instant, persistent, and improved situational awareness. Solar energy is the primary source of energy for these types of unmanned aerial vehicles (UAVs). Solar panels mounted on the wing and empennage capture solar energy during the day for immediate consumption and conserve the remainder for use at night. The main challenges to the successful design of HAPS are finding an appropriate model to calculate airframe weight, materials for structural analysis, designing a wing and propulsion system so that they can be integrated successfully into a unique aircraft configuration and these problems need to be solved. Therefore, this thesis investigates /focuses on the concept of HAPS, optimization of the airfoil, wing design and aerodynamic analysis, experimental analysis of different materials used in the wing structure, structural analysis of the wing and design of novel optimized propeller. The topics covered in the chapters are mentioned below. The first three chapters of this thesis deal with the introduction, review of available literature and previous relevant research, and background of existing high-altitude aircraft and their configurations. Then, in Chapter 4, the initial mission requirements, mission profile, basic characteristics of solar panels, rechargeable batteries, assessment of daily power consumption and battery mass as well as methodologies for the initial estimation of aircraft structural mass and wing loads are discussed. Chapter 5 is dedicated to selecting and defining the appropriate airfoil by using potential flow model and the multi-criteria optimization process. The aerodynamic analysis of wings performed by computational fluid dynamics is shown in Chapter 6. Calculations of aerodynamic coefficients of the wing and the flow field around the wing are presented in this chapter. Chapter 7 is dedicated to the structural design of high-performance slender wings. Tensile tests of a variety of 3D printed polymers and composite materials as well as the effect of ageing and heat treatment on the tensile properties of PLA are presented to investigate their mechanical characteristics. Structural analysis of the wing is presented in Chapter 8. Two different possible solutions of the aircraft's wing structure for high altitudes are presented and their performance is compared through static and modal analyses. Chapter 9 deals entirely with the methodology for designing the optimal propeller intended for highaltitude unmanned aerial vehicles. Coupled aero-structural optimization was performed using a genetic algorithm where input and output parameters and constraints were defined from a set of geometric, aerodynamic, and structural characteristics of the propeller. Finally, main conclusions are presented in chapter 10.Беспилотне летелице за велике висине (ХАЛЕ, ХАПС) су авиони који могу да лете у стратосфери непрекидно неколико месеци и пружају подршку војним и цивилним потребама. Поред тога, ове летелице се могу користити и као економични сателити и обезбеђивати тренутни, стални и побољшани увид у дешавања на Земљи. Сунчева енергија је главни извор енергије овог типа беспилотних летелица. Соларни панели распоређени по крилу и хоризонталним стабилизаторима упијају сунчеву енергију током дана за тренутну потрошњу док се остатак чува за лет током ноћи. Основни изазови успешном пројектовању ХАПС летелица су изналажење одговарајућег модела за процену тежине летелице, материјала за структуралну анализу, пројектовање крила и погонског система који се могу успешно интегрисати у јединствену конфигурацију летелице и ови проблеми морају бити решени. Стога, ова теза истражује/је фокусирана на концепт ХАПС-а, оптимизацију аеропрофила, дизајн и аеродинамичку анализу крила, експерименталну анализу различитих материјала коришћених у структури крила, структуралну анализу крила и дизајн нове оптимизоване елисе. Теме обрађене по поглављима наведене су у наставку. Прве три главе ове тезе баве се уводом, прегледом доступне литературе и претходних релевантних истраживања, као и прегледом постојећих ХАПС летелица и њихових конфигурација. Затим, у глави 4, разматрани су полазни захтеви и мисија, основне карактеристике соларних панела и пуњивих батерија, процена дневне потрошње енергије и потребне масе батерија, као и методологије за почетну процену масе конструкције авиона и оптерећења крила. Глава 5 посвећена је одабиру и дефинисању одговарајућег аеропрофила коришћењем модела потенцијалног струјања и вишекритеријумског оптимизационог поступка. Аеродинамичка анализа крила спроведена методом прорачунске механике флуида приказана је у глави 6. Овде су такође приказани и прорачунати аеродинамички коефицијенти крила као и струјно поље око крила. Глава 7 посвећена је унутрашњој структури високоперформантних витких крила. Описана су спроведена мерења затезних карактеристика различитих 3Д штампаних полимера и композитних материјала, као и ефекти старења и термичке обраде на механичке карактеристике 3Д штампаних епрувета. Структурална анализа крила представљена је у глави 8. Приказана су два различита могућа решења структуре крила авиона за велике висине и упоређене су њихове перформансе кроз статичку и модалну анализу. Глава 9 се у целости бави методологијом пројектовања оптималне елисе намењене беспилотној летелици за велике висине. Овде је спроведена спрегнута аеро-структурална оптимизација помоћу генетског алгоритма где су улазни и излазни параметри и ограничања дефинисани из скупа геометријских, аеродинамичких и структуралних карактеристика елисе. Коначно, основни закључци дати су у глави 10

Conceptual design of solar-powered high-altitude long endurance aircraft

The design of high-altitude unmanned aerial vehicles is one of the most current research topics today in the field of aviation. The possible purposes of such flying platforms are numerous, from communication hubs, terrain observations, performing various measurements in the upper layers of the atmosphere, to various military uses. However, these are complex systems that involve many unresolved scientific and research challenges such as: the necessity of extremely low airframe weight, low air pressure and density cruising at high altitudes where air pressure and density are much lower than in the Earth’s vicinity, sub-zero temperatures, exposure to increased radiation, low Re implying accentuated viscosity effects and decreased aerodynamic characteristics, assuring complete flight autonomy, need to generate the required energy for flight solely from solar energy, adequate sizing and control of rechargeable batteries, etc. At the beginning, the initial mission requirements, mission profile, assessment of daily power consumption and battery mass as well as methodologies for the initial estimation of aircraft structural mass and wing loads are discussed. Then a novel high-lift airfoil specially designed for low-Re high-altitude flight through multi- objective optimization was designed by using genetic algorithm. Subsequently, aerodynamic analysis of the wing carried out by the methods of computational fluid mechanics, specifically by solving Navier-Stokes equations averaged by Reynolds statistics and closed by a 4-equation turbulent model is shown. Finally, static analyses of the behavior of wing structures under the combined action of calculated aerodynamic and gravitational loads were performed, as well as dynamic, modal analyses (important for knowing the response of the structure in non-stationary operating conditions) using the finite element method

Towards viable flow simulations of small-scale rotors and blade segments

The paper focuses on the possibilities of adequately simulating complex flow fields that appear around small-scale propellers of multicopter aircraft. Such unmanned air vehicles (UAVs) are steadily gaining popularity for their diverse applications (surveillance, communication, deliveries, etc.) and the need for a viable (i.e. usable, satisfactory, practical) computational tool is also surging. From an engineering standpoint, it is important to obtain sufficiently accurate predictions of flow field variables in a reasonable amount of time so that the design process can be fast and efficient, in particular the subsequent structural and flight mechanics analyses. That is why more or less standard fluid flow models, e.g. Reynolds-averaged Navier—Stokes (RANS) equations solved by the finite volume method (FVM), are constantly being employed and validated. On the other hand, special attention must be given to various flow peculiarities occurring around the blade segments shaped like airfoils since these flows are characterized by small chords (length-scales), low speeds and, therefore, low Reynolds numbers (Re) and pronounced viscous effects. The investigated low-Re flows include both transitional and turbulent zones, laminar separation bubbles (LSBs), flow separation, as well as rotating wakes, which require somewhat specific approaches to flow modeling (advanced turbulence models, fine spatial and temporal scales, etc). Here, the conducted computations (around stationary blade segments as well as rotating rotors), closed by different turbulence models, are presented and explained. Various qualitative and quantitative results are provided, compared and discussed. The main possibilities and obstacles of each computational approach are mentioned. Where possible, numerical results are validated against experimental data. The correspondence between the two sets of results can be considered satisfactory (relative differences for the thrust coefficient amount to 15%, while they are even lower for the torque coefficient). It can be concluded that the choice of turbulence modeling (and/or resolving) greatly affects the final output, even in design operating conditions (at medium angles-of-attack where laminar, attached flow dominates). Distinctive flow phenomena still exist, and in order to be adequately simulated, a comprehensive modeling approach should be adopted

Optimal Propeller design for future HALE UAV

Osnovne uloge bespilotnih letelica podrazumevaju: osmatranje, nadzor, prenos robe, daljinsko očitavanje i različite bezbedonosne zadatke. Poboljšana klasa bespilotnih letelica su one koje su posebno projektovane za velike visine leta i duge istrajnosti (uglavnom pri podzvučnim brzinama krstarenja). Do sada je probano nekoliko varijanti koje se razlikuju kako po dimenzijama tako i po primenjenim tehničkim rešenjima. Uobičajeni pristup podrazumeva standarnu konfiguraciju krilotrup-zadnje repne površine i let pomoću elise koja je najefikasnija u tom opsegu brzina. Rad ukratko prikazuje preliminarnu aerodinamičku analizu glavnih uzgonskih površina, ali i detaljniji opis izvedene višekriterijumske optimizacije elise sposobne da obezbedi dovoljni potisak na zadatoj visini i brzini krstarenja. Aerodinamičke performanse razmatranih elisa procenjene su kombinovanim modelom. Izabrani optimizacioni metod, genetski algoritam, pogodan je za probleme koji uključuju veliki broj ulaznih promenljivih.The main roles of unmanned air vehicles (UAVs) include: observation, surveillance, transportation, remote sensing and various security tasks. Improved, augmented type of UAVs are high-altitude long-endurance (HALE) aircraft capable and designed, as their name suggests, for lengthy flights at higher altitudes (which also usually implies subsonic cruising velocities). Different variants, in both size and applied technical solutions, have been tried. Common approach incorporates standard wing-fuselage-aft empennage configuration and propelled flight as the most efficient for the required speed range. The paper gives a brief overview of a preliminary aerodynamic analysis of the main lifting surfaces as well as a detailed description of the performed multi-objective optimization of the propeller capable of producing a sufficient amount of thrust at the cruising altitude and speed. Aerodynamic performances of the investigated propellers are estimated by a simple blade element momentum theory (BEMT). The chosen optimizing method, genetic algorithm (GA), is suitable for dealing with a large number of input variables

Effects of Hard Real-Time Constraints in Implementing the Myopic Scheduling Algorithm

Myopic is a hard real-time process scheduling algorithm that selects a suitable process based on a heuristic function from a subset (Window) of all ready processes instead of choosing from all available processes, like original heuristic scheduling algorithm. Performance of the algorithm significantly depends on the chosen heuristic function that assigns weight to different parameters like deadline, earliest starting time, processing time etc. and the size of the Window since it considers only processes from processes (where, knnk≤). This research evaluates the performance of the Myopic algorithm for different parameters to demonstrate the merits and constraints of the algorithm. A comparative performance of the impact of window size in implementing the Myopic algorithm is presented and discussed through a set of experiments

Optimal Propeller design for future HALE UAV

Osnovne uloge bespilotnih letelica podrazumevaju: osmatranje, nadzor, prenos robe, daljinsko očitavanje i različite bezbedonosne zadatke. Poboljšana klasa bespilotnih letelica su one koje su posebno projektovane za velike visine leta i duge istrajnosti (uglavnom pri podzvučnim brzinama krstarenja). Do sada je probano nekoliko varijanti koje se razlikuju kako po dimenzijama tako i po primenjenim tehničkim rešenjima. Uobičajeni pristup podrazumeva standarnu konfiguraciju krilotrup-zadnje repne površine i let pomoću elise koja je najefikasnija u tom opsegu brzina. Rad ukratko prikazuje preliminarnu aerodinamičku analizu glavnih uzgonskih površina, ali i detaljniji opis izvedene višekriterijumske optimizacije elise sposobne da obezbedi dovoljni potisak na zadatoj visini i brzini krstarenja. Aerodinamičke performanse razmatranih elisa procenjene su kombinovanim modelom. Izabrani optimizacioni metod, genetski algoritam, pogodan je za probleme koji uključuju veliki broj ulaznih promenljivih.The main roles of unmanned air vehicles (UAVs) include: observation, surveillance, transportation, remote sensing and various security tasks. Improved, augmented type of UAVs are high-altitude long-endurance (HALE) aircraft capable and designed, as their name suggests, for lengthy flights at higher altitudes (which also usually implies subsonic cruising velocities). Different variants, in both size and applied technical solutions, have been tried. Common approach incorporates standard wing-fuselage-aft empennage configuration and propelled flight as the most efficient for the required speed range. The paper gives a brief overview of a preliminary aerodynamic analysis of the main lifting surfaces as well as a detailed description of the performed multi-objective optimization of the propeller capable of producing a sufficient amount of thrust at the cruising altitude and speed. Aerodynamic performances of the investigated propellers are estimated by a simple blade element momentum theory (BEMT). The chosen optimizing method, genetic algorithm (GA), is suitable for dealing with a large number of input variables

Towards viable flow simulations of small-scale rotors and blade segments

The paper focuses on the possibilities of adequately simulating complex flow fields that appear around small-scale propellers of multicopter aircraft. Such unmanned air vehicles (UAVs) are steadily gaining popularity for their diverse applications (surveillance, communication, deliveries, etc.) and the need for a viable (i.e. usable, satisfactory, practical) computational tool is also surging. From an engineering standpoint, it is important to obtain sufficiently accurate predictions of flow field variables in a reasonable amount of time so that the design process can be fast and efficient, in particular the subsequent structural and flight mechanics analyses. That is why more or less standard fluid flow models, e.g. Reynolds-averaged Navier—Stokes (RANS) equations solved by the finite volume method (FVM), are constantly being employed and validated. On the other hand, special attention must be given to various flow peculiarities occurring around the blade segments shaped like airfoils since these flows are characterized by small chords (length-scales), low speeds and, therefore, low Reynolds numbers (Re) and pronounced viscous effects. The investigated low-Re flows include both transitional and turbulent zones, laminar separation bubbles (LSBs), flow separation, as well as rotating wakes, which require somewhat specific approaches to flow modeling (advanced turbulence models, fine spatial and temporal scales, etc). Here, the conducted computations (around stationary blade segments as well as rotating rotors), closed by different turbulence models, are presented and explained. Various qualitative and quantitative results are provided, compared and discussed. The main possibilities and obstacles of each computational approach are mentioned. Where possible, numerical results are validated against experimental data. The correspondence between the two sets of results can be considered satisfactory (relative differences for the thrust coefficient amount to 15%, while they are even lower for the torque coefficient). It can be concluded that the choice of turbulence modeling (and/or resolving) greatly affects the final output, even in design operating conditions (at medium angles-of-attack where laminar, attached flow dominates). Distinctive flow phenomena still exist, and in order to be adequately simulated, a comprehensive modeling approach should be adopted

Design of optimal flow concentrator for vertical-axis wind turbines using computational fluid dynamics, artificial neural networks and genetic algorithm

Wind energy extraction is one of the fastest developing engineering branches today. Number of installed wind turbines is constantly increasing. Appropriate solutions for urban environments are quiet, structurally simple and affordable small-scale vertical-axis wind turbines (VAWTs). Due to small efficiency, particularly in low and variable winds, main topic here is development of optimal flow concentrator that locally augments wind velocity, facilitates turbine start and increases generated power. Conceptual design was performed by combining finite volume method and artificial intelligence (AI). Smaller set of computational results (velocity profiles induced by existence of different concentrators in flow field) was used for creation, training and validation of several artificial neural networks. Multi-objective optimization of concentrator geometric parameters was realized through coupling of generated neural networks with genetic algorithm. Final solution from the acquired Pareto set is studied in more detail. Resulting computed velocity field is illustrated. Aerodynamic performances of small-scale VAWT with and without optimal flow concentrator are estimated and compared. The performed research demonstrates that, with use of flow concentrator, average increase in wind speed of 20%-25% can be expected. It also proves that contemporary AI techniques can significantly facilitate and accelerate design processes in the field of wind engineering

Structural analysis of small-scale composite propeller blade

Contemporary, light-weight, unmanned air vehicles almost exclusively imply propeller rotors that enable them to hover, as well as to move vertically and horizontally at acceptable amount of required power (that is usually supplied by electric motors). Rotor main parts are blades − curved, rotational lifting surfaces subject to conjugate aerodynamic, inertial and gravitational loads. Their skin is usually made of composite materials, i.e. glass or carbon fibres (or their combination) immersed in epoxy resin. Additional inner structural elements may include shear webs, spar caps, ribs or foam fillers. The goal of the presented research study is conducting and validating structural analysis of a propeller blade by finite element method. Different structural models (containing just skin, or skin with foam filler), materials (glass or carbon, uni-or biaxial plies), and ply-up sequences (differing in layer numbers and orientations) are considered. The complete blade geometry is modelled, including the root and tip sections. The blade is clamed at the root, while computed aerodynamic, inertial and gravitational forces are distributed along its surface (and volume). Since the blade operates in axisymmetric conditions, it was possible to perform static structural analyses. Obtained results include deflection (and deformation) fields, normal and shear stress distributions along the plies, etc. From the acquired numerical values, it is possible to define an adequate blade structure that will be able to withstand all working loads (multiplied by necessary safety factors) and ensure safe flight of the aircraft. Future research may include modal or fatigue analyses of propeller blades