No description available.

Deploying unmanned aerial vehicles (UAVs) as aerial base stations (BSs) in order to assist terrestrial connectivity, has drawn significant attention in recent years. UAV-BSs can take over quickly as service providers during natural disasters and many other emergency situations when ground BSs fail in an unanticipated manner. UAV-BSs can also provide cost-effective Internet connection to users who are out of infrastructure. UAV-BSs benefit from their mobility nature that enables them to change their 3D locations if the demand of ground users changes. In order to effectively make use of the mobility of UAV-BSs in a dynamic network and maximize the performance, the 3D location of UAV-BSs should be continuously optimized. However, solving the location optimization problem of UAV-BSs is NP-hard with no optimal solution in polynomial time for which near optimal solutions have to be exploited. Besides the conventional solutions, i.e. heuristic solutions, machine learning (ML), specifically reinforcement learning (RL), has emerged as a promising solution for tackling the positioning problem of UAV-BSs. The common practice for optimizing the 3D location of UAV-BSs using RL algorithms is assuming fixed location of ground users (i.e., UEs) in addition to defining discrete and limited action space for the agent of RL. In this thesis, we focus on improving the location optimization of UAV-BSs in two ways: 1-Taking into account the mobility of users in the design of RL algorithm, 2-Extending the action space of RL to a continuous action space so that the UAV-BS agent can flexibly change its location by any distance (limited by the maximum speed of UAV-BS). Three types of RL algorithms, i.e. Q-learning (QL), deep Q-learning (DQL) and actor-critic deep Q-learning (ACDQL) have been employed in this thesis to step-by-step improve the performance results of a UAV-assisted cellular network. QL is the first type of RL algorithm we use for the autonomous movement of the UAV-BS in the presence of mobile users. As a solution to the limitations of QL, we next propose a DQL-based strategy for the location optimization of the UAV-BS which largely improves the performance results of the network compared to the QL-based model. Third, we propose an ACDQL-based solution for autonomously moving the UAV-BS in a continuous action space wherein the performance results significantly outperforms both QL and DQL strategies.

No description available.

Spring dead spot (SDS) is the most destructive disease of bermudagrass (Cynodon spp.) in Virginia. SDS infects bermudagrass in the fall with symptoms appearing in the spring when dormancy breaks. Patches are sporadically distributed but generally reoccur in the same location. Chemical control options are expensive with inconsistent results. Our objectives were to develop SDS incidence maps, investigate methods to analyze these maps, and evaluate suppression efficacy of incidence-map-based chemical applications. Methods were developed to build SDS incidence maps in 2016 and 2017. 2016 SDS incidence maps were compared for spatial accuracy to Digital Orthophoto Quarter Quadrangle (DOQQ), ground-validated differential GPS coordinates, and to 2017 SDS incidence maps, with average deviations of 1.3 m, 1.6 m, and 0.1 m, respectively. Digital Image Analysis (DIA) of aerial maps was compared to a point-intersect method for validation with a significant linear relationship (r2 = 0.77, P ≤ 0.0001). In the fall of 2016 and 2017, a site-specific penthiopyrad (SSP) treatment was evaluated against blanket, full-coverage applications of penthiopyrad (BP) and tebuconazole (BT), and an untreated control. Treatments were compared using DIA, post-treatment SDS patch count (PC), and SDS patch reduction (PR). Across all three metrics, the penthiopyrad treatments were statistically superior to both the tebuconazole and untreated. SSP compared favorably to BP for DIA, but BP had 2.57 fewer PC (LSD = 2.05) and a greater PR by 2.58 (LSD = 2.55). SSP using SDS incidence maps required 51% less fungicides in 2016 and 65% less in 2017 when compared to BP. / Master of Science in Life Sciences

In this thesis the problem of autonomous landing of an unmanned aerial vehicle named AE-2 is addressed. The guidance and control technique is developed and demonstrated through numerical simulation results. The complete work includes Mathematical modeling, Control design, Guidance and State estimation for AE-2, which is a fixed wing vehicle with 2m wing span and 6kg weight. The aerodynamic data for AE-2 is available from static wind tunnel tests. Functional fit is done on the wind tunnel data with least squares method to find static aerodynamic coefficients. The aerodynamic forces and moment coefficients are highly nonlinear some of them are partitioned in two zones based on the angle of attack. The dynamic derivatives are found with Athena Vortex Lattice software. For the validation of vortex lattice method the static derivatives obtained by the wind tunnel tests and vortex lattice method, are compared before finding dynamic derivatives. The dynamics of the servo actuators for the aerodynamic control surfaces is incorporated in the simulation. The nonlinear dynamic inversion technique has been used for the guidance and control design. The control is structured in two loops, outer and inner loop. The goal of outer loop is to track the guidance commands of altitude, roll angle and yaw angle by converting them into body rate commands through dynamic inversion. The inner loop than tracks these commanded roll rate, pitch rate and yaw rate by finding the required deflection of control surfaces. The forward velocity of the vehicle is controlled by varying the throttle. A controller for actuator is also designed to reduce the lag. The guidance for landing consists of three phases approach, glideslope and flare. During approach the vehicle is aligned with the runway and guided to a specified height from where the glideslope can begin. The glideslope is straight line path specified by a flight path angle which is restricted between 3 to 4 degree. At the end of glideslope which is marked by flare altitude the flare maneuver begins which is an exponential curve. The problem of transition between the glideslope and flare has addressed by ensuring continuity and smoothness at transition. The exponential curve of flare is designed to end below the ground so that it intersects the ground at a prespecified point. The sink rate at touchdown is also controlled along with the location of touchdown point. The state estimation has been done with Extended Kalman Filter in continuous discrete formulation. The external disturbances like wind shear and wind gust are accounted by appending them in state variables. Further the control design with guidance is tested from various initial conditions, in presence of wind disturbances. The designed filter has also been tested for parameter uncertainty.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / Brigham Young University recently introduced a project for undergraduates in which a miniature unmanned aerial vehicle system is constructed. The system is capable of autonomous flight, takeoff, landing, and navigation through a planned path. In addition, through the use of video and telemetry collected by the vehicle, accurate geolocation of specified targets is performed. This paper outlines our approach and successes in facilitating this accomplishment at the undergraduate level.

ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / This paper describes a psychophysical experiment to measure visibility thresholds (VT) for quantization distortion in JPEG2000 and an associated quantization algorithm for visually lossless coding of color aerial images. The visibility thresholds are obtained from a quantization distortion model based on the statistical characteristics of wavelet coefficients and the deadzone quantizer of JPEG2000, and the resulting visibility thresholds are presented for the luminance component (Y) and two chrominance components (Cb and Cr). Using the thresholds, we have achieved visually lossless coding for 24-bit color aerial images at an average bitrate of 4.17 bits/pixels, which is approximately 30% of the bitrate required for numerically lossless coding.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Unmanned aerial vehicles with vertical take-off and landing capabilities have received extensive attention worldwide in the last decade. Their low detectability, high manoeuvrability in confined spaces, and their capability for out-of-sight operations make them practical solutions for an array of military and civilian missions. The main advantage of shrouded rotors in hover and low speed conditions is the decreased blade tip induced drag when the tip gap is small enough. A well-designed shroud augments the rotor thrust in hover and low axial flight conditions. It also provides noise reduction and safety. A contra-rotating rotor system eliminates the need for separate anti-torque devices, thus producing a smaller footprint and a more compact vehicle. In this study a more efficient coaxial rotor for the ducted coaxial rotor system as published by (Lee 2010) was developed. The first phase of the design process consisted of the selection and numerical analysis of the best suited parent airfoils for the rotors by using XFOIL and XFLR 5. The second phase dealt with the design of a counter-rotating rotor system for the existing cambered shroud as published by (Lee, 2010), using the DFDC-070ES2a two dimensional code, specifically written for ducted rotor optimization. The final phase of the study dealt with the Computational Fluid Dynamic (CFD) verification of the design in ANSYS-CFX 15.07. A comparison between the CFX predictions of the newly designed rotor system and the reference design indicates a 33% improvement in hover thrust at the design power input. / AFRIKAANSE OPSOMMING: Onbemande lugvaartuie met vertikale opstyg en landings vermoëns het uitgebreide aandag wêreldwyd in die laaste dekade geniet. Hul lae waarneembaarheid, hoë beweegbaarheid in beperkte ruimtes, en hul vermoë om buite-sig operasies uit te voer maak dat hulle praktiese oplossings vir 'n verskeidenheid van militêre en burgerlike missies is. Die grootste voordeel van gehulde rotors in hangvlug en lae spoed omstandighede is die afname in die lem punt sleepkrag wanneer die lem punt gaping klein genoeg is. 'n Goed ontwerpde omhulsel dra by tot die rotor stukrag in hangvlug en lae aksiale vlug omstandighede. Dit bied ook geraasreduksie en veiligheid. 'n Kontra-roterende rotorstelsel skakel die vereiste van afsonderlike anti-wringkrag toestelle uit, wat lei tot 'n kleiner voetspoor en 'n meer kompakte voertuig. In hierdie studie is 'n meer doeltreffende koaksiale rotor vir die gehulde koaksiale rotor stelsel soos gepubliseer deur (Lee 2010) ontwikkel. Die eerste fase van die ontwerp-proses het bestaan uit die seleksie en numeriese analise van die mees geskikte lemprofiele vir die rotors deur die gebruik van XFOIL en XFLR 5. Fase twee het die ontwerp van 'n teen-roterende rotor stelsel vir die bestaande omhulsel soos gebruik in (Lee, 2010) se publikasie behels. Die ontwerp is met behulp van DFDC-070ES2a, ‘n twee dimensionele kode wat spesifiek vir gehul-rotor optimering geskryf is, gedoen. Die verifikasie van die nuwe ontwerp is in die finale fase met behulp van die berekeings vloeidinamika sagteware, ANSYS-CFX 15.07 gedoen. ‘n Vergelyking tussen die CFX prestasie voorspelling vir die nuwe rotorstelsel en die gepubliseerde data van (Lee, 2010) toon ‘n 33% toename in hangvlug stukrag by die ontwerpsdrywing.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / This paper describes the development and test results of a Frequency Modulated Continuous Wave (FMCW) L-Band radar testbed designed to detect obstacles in the proximity of an Unmanned Aerial Vehicle (UAV). From laboratory loopback tests, it was calculated that with pulse compression and a transmit power of 150 mW (22 dBm), the radar is capable of detecting an object with a 0.014-m2 radar cross-sectional area at ranges between 500 ft to 1 mi. Analysis shows that post processing of the collected data would reveal information about the obstacle such as its range and location relative to the aircraft. Design and testing procedures are discussed.

Performance of inflatable wings was investigated through laboratory, wind tunnel and flight-testing. Three airfoils were investigated, an inflatable-rigidazable wing, an inflatable polyurethane wing and a fabric wing restraint with a polyurethane bladder. The inflatable wings developed and used within this research had a unique outer airfoil profile. The airfoil surface consisted of a series of chord-wise \bumps.andamp;quot; The effect of the bumps or \surface perturbationsandamp;quot; on the performance of the wings was of concern and was investigated through smoke-wire flow visualization. Aerodynamic measurements and predictions were made to determine the performance of the wings at varying chord based Reynolds Numbers and angles of attack. The inflatable baffes were found to introduce turbulence into the free-stream boundary layer, which delayed separation and improved performance. Another area of concern was aeroelasticity. The wings contain no solid structural members and thus rely exclusively on inflation pressure for stiffness. Inflation pressure was varied below the design pressure in order to examine the effect on wingtip twist and bending. This lead to investigations into wing deformation due to aerodynamic loading and an investigation of wing flutter. Photogrammetry and laser displacement sensors were used to determine the wing deflections. The inflatable wings exhibited wash-in deformation behavior. Alternately, as the wings do not contain structural members, the relationship between stiffness and inflation pressure was exploited to actively manipulate wing through wing warping. Several warping techniques were developed and employed within this re-search. The goal was to actively influence the shape of the inflatable wings to affect the flight dynamics of the vehicle employing them. Researchers have developed inflatable beam theory and models to analyze torsion and bending of inflatable beams and other inflatable structures. This research was used to model the inflatable wings to predict the performance of the inflatable wings during flight. Design elements of inflatable wings incorporated on the UAVs used within this research are also discussed. Finally, damage resistance of the inflatable wings is shown from results of flight tests.