The use of flying platforms such as unmanned aerial vehicles (UAVs), popularly known as drones, is rapidly growing. In particular, with their inherent attributes such as mobility, flexibility, and ...adaptive altitude, UAVs admit several key potential applications in wireless systems. On the one hand, UAVs can be used as aerial base stations to enhance coverage, capacity, reliability, and energy efficiency of wireless networks. On the other hand, UAVs can operate as flying mobile terminals within a cellular network. Such cellular-connected UAVs can enable several applications ranging from real-time video streaming to item delivery. In this paper, a comprehensive tutorial on the potential benefits and applications of UAVs in wireless communications is presented. Moreover, the important challenges and the fundamental tradeoffs in UAV-enabled wireless networks are thoroughly investigated. In particular, the key UAV challenges such as 3D deployment, performance analysis, channel modeling, and energy efficiency are explored along with representative results. Then, open problems and potential research directions pertaining to UAV communications are introduced. Finally, various analytical frameworks and mathematical tools, such as optimization theory, machine learning, stochastic geometry, transport theory, and game theory are described. The use of such tools for addressing unique UAV problems is also presented. In a nutshell, this tutorial provides key guidelines on how to analyze, optimize, and design UAV-based wireless communication systems.
The flow structures at the blade tip in a centrifugal compressor usually have an important impact on compressor performance, especially the TLV, which often plays a dominant role in its performance. ...In order to weaken TLV and improve compressor performance, an unsteady flow control method based on the concept of vortex injection is proposed. The numerical simulation shows that VID method can enlarge the stall margin of the compressor by 8.5%. Meanwhile, the total pressure ratio and efficiency of the compressor can be slightly improved from the design point to the stall point. The maximum efficiency increment and the maximum pressure ratio increment are 0.56% and 0.75%, respectively. A proof experiment on a micro centrifugal compressor shows that the VID can enlarge stall margin of 6.6% and the maximum relative pressure can increase by 2.6%. Therefore, both the simulation and experiment prove that the VID method is effective which utilizes both unsteady excitation and injection of negative circulation to weaken TLV. Finally, enhancing the efficiency of each unsteady jet/suction and separation flow interaction is highly recommended.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Heavier-than-air flight at any scale is energetically expensive. This is greatly exacerbated at small scales and has so far presented an insurmountable obstacle for untethered flight in insect-sized ...(mass less than 500 milligrams and wingspan less than 5 centimetres) robots. These vehicles
thus need to fly tethered to an offboard power supply and signal generator owing to the challenges associated with integrating onboard electronics within a limited payload capacity. Here we address these challenges to demonstrate sustained untethered flight of an insect-sized flapping-wing microscale aerial vehicle. The 90-milligram vehicle uses four wings driven by two alumina-reinforced piezoelectric actuators to increase aerodynamic efficiency (by up to 29 per cent relative to similar two-wing vehicles
) and achieve a peak lift-to-weight ratio of 4.1 to 1, demonstrating greater thrust per muscle mass than typical biological counterparts
. The integrated system of the vehicle together with the electronics required for untethered flight (a photovoltaic array and a signal generator) weighs 259 milligrams, with an additional payload capacity allowing for additional onboard devices. Consuming only 110-120 milliwatts of power, the system matches the thrust efficiency of similarly sized insects such as bees
. This insect-scale aerial vehicle is the lightest thus far to achieve sustained untethered flight (as opposed to impulsive jumping
or liftoff
).
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Drones are rapidly becoming a key part of the toolkit for a range of scientific disciplines, as well as a range of management and commercial applications. This presents challenges in the context of ...how drone use might impact on nearby wildlife, especially birds as they might share the airspace. This paper presents observations (from 97 flight hours) and offers preliminary guidance for drone-monitoring exercises and future research to develop guidelines for safe and effective monitoring with drones. Our study sites spanned a range of arid, semi-arid, dunefield, floodplain, wetland, woodland, forest, coastal heath and urban environments in south-eastern and central Australia. They included a nesting colony of >200 000 Straw-necked Ibis 'Threskiornis spinicollis', the largest drone-based bird-monitoring exercise to date. We particularly focused on behavioural changes towards drones during the breeding season, interactions with raptors, and effects on birds nesting in large colonies - three areas yet to be explored in published literature. Some aggressive behaviour was encountered from solitary breeding birds, but several large breeding bird colonies were surveyed without such issues. With multi-rotor drones, we observed no incidents that posed a threat to birds, but one raptor attacked and took down a fixed-wing drone. In addition to providing observations of interactions with specific bird species, we detail our procedures for flight planning, safe flying and avoidance of birds, and highlight the need for more research into bird-drone interactions, most notably with respect to territorial breeding birds, safety around large raptors, and the effects of drones on the behaviour of birds in large breeding colonies.
In-flight system failure is one of the major safety concerns in the operation of unmanned aerial vehicles (UAVs) in urban environments. To address this concern, a safety framework consisting of ...following three main tasks can be utilized: (1) Monitoring health of the UAV and detecting failures, (2) Finding potential safe landing spots in case a critical failure is detected in step 1, and (3) Steering the UAV to a safe landing spot found in step 2. In this paper, we specifically look at the second task, where we investigate the feasibility of utilizing object detection methods to spot safe landing spots in case the UAV suffers an in-flight failure. Particularly, we investigate different versions of the YOLO objection detection method and compare their performances for the specific application of detecting a safe landing location for a UAV that has suffered an in-flight failure. We compare the performance of YOLOv3, YOLOv4, and YOLOv5l while training them by a large aerial image dataset called DOTA in a Personal Computer (PC) and also a Companion Computer (CC). We plan to use the chosen algorithm on a CC that can be attached to a UAV, and the PC is used to verify the trends that we see between the algorithms on the CC. We confirm the feasibility of utilizing these algorithms for effective emergency landing spot detection and report their accuracy and speed for that specific application. Our investigation also shows that the YOLOv5l algorithm outperforms YOLOv4 and YOLOv3 in terms of accuracy of detection while maintaining a slightly slower inference speed.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The use of automated, unmanned aerial vehicles (drones) to deliver commercial packages is poised to become a new industry, significantly shifting energy use in the freight sector. Here we find the ...current practical range of multi-copters to be about 4 km with current battery technology, requiring a new network of urban warehouses or waystations as support. We show that, although drones consume less energy per package-km than delivery trucks, the additional warehouse energy required and the longer distances traveled by drones per package greatly increase the life-cycle impacts. Still, in most cases examined, the impacts of package delivery by small drone are lower than ground-based delivery. Results suggest that, if carefully deployed, drone-based delivery could reduce greenhouse gas emissions and energy use in the freight sector. To realize the environmental benefits of drone delivery, regulators and firms should focus on minimizing extra warehousing and limiting the size of drones.
With a rewritten chapter on UAS safety evaluation including extra models, this fully updated edition remains a comprehensive examination of the myriad issues surrounding the integration of unmanned ...aircraft systems into the US national airspace system.
Full text
Available for:
FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We determine the efficiency of a delivery system in which an unmanned aerial vehicle (UAV) provides service to customers while making return trips to a truck that is itself moving. In other words, a ...UAV picks up a package from the truck (which continues on its route), and after delivering the package, the UAV returns to the truck to pick up the next package. Although the hardware for such systems already exists, the extent to which such an approach can actually provide a significantly improved quality of service is not yet understood. By combining a theoretical analysis in the Euclidean plane with real-time numerical simulations on a road network, we demonstrate that the improvement in efficiency is proportional to the square root of the ratio of the speeds of the truck and the UAV.
The online supplement is available at
https://doi.org/10.1287/mnsc.2017.2824
.
This paper was accepted by Vishal Gaur, operations management.
Full text
Available for:
CEKLJ, IZUM, KILJ, NUK, PILJ, SAZU, UL, UM, UPUK
PDF
