Hover Height Research Articles

Joint optimization of UAV aided covert edge computing via a deep reinforcement learning framework

In this work, we consider an Unmanned Aerial Vehicle (UAV) aided covert edge computing architecture, where multiple sensors are scattered with a certain distance on the ground. The sensor can implement several computation tasks. In an emergency scenario, the computational capabilities of sensors are often limited, as seen in vehicular networks or Internet of Things (IoT) networks. The UAV can be utilized to undertake parts of the computation tasks, i.e., edge computing. While various studies have advanced the performance of UAV-based edge computing systems, the security of wireless transmission in future 6G networks is becoming increasingly crucial due to its inherent broadcast nature, yet it has not received adequate attention. In this paper, we improve the covert performance in a UAV aided edge computing system. Parts of the computation tasks of multiple ground sensors are offloaded to the UAV, where the sensors offload the computing tasks to the UAV, and Willie around detects the transmissions. The transmit power of sensors, the offloading proportions of sensors and the hovering height of the UAV affect the system covert performance, we propose a deep reinforcement learning framework to jointly optimize them. The proposed algorithm minimizes the system average task processing delay while guaranteeing that the transmissions of sensors are not detected by the Willie under the covertness constraint. Extensive simulations are conducted to verify the effectiveness of the proposed algorithm to decrease the average task processing delay with comparison with other algorithms.

Separation of Surface Grafted Microparticles via Light and Temperature

Separation of equally sized particles distinguished solely by interfacial properties remains a highly challenging task. Herein, a particle fractioning method is proposed, which is suitable to differentiate between polymer‐grafted microparticles that are equal in size. The separation relies on the combination of a pressure driven microfluidic flow, together with simultaneous light illumination and temperature control. Heating the solution forces thermo‐responsive surface grafts to undergo a volume phase transition and therefore locally changing the interfacial properties of the microparticles. Light illumination induces the phoretic/osmotic activity of the microparticles and lifts them into a higher plane, where hovering particles experience a different shear stress proportional to the height. The light‐induced hovering height depends on the interfacial properties, and this complex interaction leads to different movements of the microparticles as a function of their surface grafting. The concepts are visualized in experimental studies, where the complex physical principle provides a simple method for fractioning a binary mixture with at least one thermo‐responsive polymer graft.

Analytical and experimental studies on dynamic response of a SES air cushion plenum experiencing forced oscillation

In this study, a series of experiments is conducted in which a plenum experiences forced oscillation. The oscillating system is driven by a periodic force arising from regular volumetric fluctuations analogous to fixed-height water waves entering a surface-effect ship (SES) plenum below a heave deck. An analytical study is then conducted in which a MATLAB Simulink model is created to incorporate the same parameters taken into account during the experiments. The results of both the experiments and the simulation demonstrated that as the frequency associated with the plenum volume's forced oscillations approaches the natural frequency of the mass/plenum system, the vibration magnitude of the heave deck increases as predicted. Resonance is observed in vibrations of the heave deck. The mean hover height of the heave deck increases predictably and remains high at higher frequencies when the forced oscillations' frequency approaches the natural frequency of the mass/plenum system. Higher frequency oscillations lead to air accumulation in the plenum. Since there was a significant difference between the experimentally-measured (and simulated) natural frequency and the theoretical natural frequency of a similar, but rigid-walled plenum, it appeared that the natural frequency of the heave deck above the plenum is reduced by the flexibility of the seals and water surface under a SES.

BIM-modeling for geodetic control of construction

Problem. At each stage of the city's reconstruction, high-resolution three-dimensional photogrammetric or laser models can be superimposed and compared to pre-planned BIM objects. The issue is researching the causes of aerial photography errors and identifying the ways to eliminate them. Goal. The task of experimental research is to determine the hovering height of an unmanned aerial vehicle relative to the earth's surface and to compare the value of the height with the planned parameters of the on-board navigator. Methodology. A Phantom-3 quadrocopter, a TRIMBLE 3305DR electronic total station, and a 3T5KP optical theodolite were used for the experiment. Nivelir 2N10KL marks were pasted on the four sides of the quadcopter and the distance from the bottom of its legs to the mark was measured to guide the grid of sighting tubes of the electronic total station and theodolite. Results. As a result of the experiment, it was found that the deviation in the height of the quadcopter is + 1.22 m and + 1.38 m from the planned one, but these values do not correspond to the accuracy specified by the unmanned aerial vehicles manufacturer, which is ± 0.1 m. Originality. New BIM method creates new possibilities for geodesists on construction sites. Geodesists in their practice on construction sites when performing geodetic works have to quickly adapt to new operational procedures, requirements on spatial determination of objects, new technical equipment, SW instruments and standards exploited in BIM method. The value of geodetic works is also the transformation of the resulting spatial data into territorial information systems in 3D-representation. Practical value. The maximum deviation of the quadcopter in the plan from the starting point was 1.25 m for the planned height of the quadcopter of 20 m, and all other values do not exceed ± 1 m, which corresponds to the accuracy of keeping the quadcopter in the vertical plan. It is expedient to use situational aerial photography with the help of a quadrocopter in the study of destroyed buildings in modern urban development. It is especially necessary to obtain a general photograph of the area on which research is being carried out, when this cannot be done from the ground.

Joint Hovering Height, Power, and Rate Optimization for Air-to-Ground UAV-RSMA Covert Communications

In this paper, we investigate covert communications for an unmanned aerial vehicle (UAV)-aided rate-splitting multiple access (RSMA) system in which the UAV transmits to the covert and public users separately while shielding covert transmissions from a warden. Under the RSMA principles, the messages of the covert and public users are converted to common and private streams for air-to-ground transmissions. Subject to the quality of service (QoS) requirements of the public user and covertness constraint of the UAV-aid RSMA (UAV-RSMA) system, the aim of covert communication design is to maximize the covert rate by jointly optimizing the transmit power allocation, common rate allocation, and UAV hovering height, which each contribute to the uncertainty of the warden’s binary decision and attempts to enhance communication performance. To address the non-convex covert rate maximization problem in addition to the highly coupled system parameters, we decouple the original problem into three subproblems of transmit power allocation, common rate allocation, and UAV hovering height. We derive the optimal solutions for each of the subproblems of the transmit power and rate allocations and formulate a signomial programming problem to tackle UAV hovering height optimization. The simulation results indicate the superior covert rate performance achieved by the proposed AO algorithm and demonstrate that the proposed UAV-RSMA scheme achieves a higher covert rate than the benchmark schemes.

Optimal Hovering Height and Power Allocation for UAV-Aided NOMA Covert Communication System

In this letter, we consider an unmanned aerial vehicle (UAV) aided covert communication system in which the UAV provides downlink transmission to the public user and covert user with non-orthogonal multiple access (NOMA). In the considered system, the covert performance can be effectively enhanced by the mobility of the UAV and the transmission from UAV to the public user. Aiming at improving the covert signal-to-noise ratio (SNR), we jointly optimize the hovering height and power allocation of UAV and formulate a signomial programming (SP) problem. To tackle the nonconvex optimization, we develop a successive geometric programming approximation (SGPA) algorithm. The optimal hovering height and power allocation are provided with numerical results and the outperformance of our design is verified.

Joint 3-D Position Deployment and Traffic Offloading for Caching and Computing-Enabled UAV Under Asymmetric Information

To offload the rapidly increasing video traffic in the Internet of Things (IoT), the caching and computing-enabled unmanned aerial vehicles (UAVs) have become a paradigm in alleviating the pressure of wireless backhauls of the mobile network operator (MNO) and improving the Quality of Service (QoS) of subscribers of content providers (CPs), especially, in the situations where fixedly deployed small-cell base stations (SBSs) are not applicable. However, the resources in the UAV are costly and limited, while rational CPs are reluctant to reveal their willingness of leasing. Taking such asymmetric information into consideration, the problem that how the MNO leases the caching and computing resources to different CPs is formulated into a contract design problem, in which the UAV’s 3-D position deployment is also involved. To find the optimal solutions, the proposed problem is decoupled into two subproblems. In the position deployment subproblem, the 3-D position of the UAV is analyzed, and the hovering height and coverage radius are jointly optimized to maximize the offloading volume during the life of the UAV. With the derived optimal position of the UAV, the individual rationality (IR) and incentive compatibility (IC) constraints in the contract design subproblem are simplified, and a low complexity algorithm based on the alternating direction method of multipliers (ADMMs) is proposed to find the optimal contract. Finally, the effectiveness of the proposed scheme is verified by simulation, and a comparative analysis is carried out in terms of save latency, saved bandwidth and utility.

Hydrodynamics study of standing-and-hovering behavior of dolphins on the water surface

This paper aims to explore the standing-and-hovering (SAH) behavior of dolphins on the water surface and to reveal its hydrodynamic mechanism through numerical simulations. A virtual dolphin-like swimmer is constructed to perform the three-stage locomotion for the SAH procedure. Volume of fluid method is adopted to deal with the free surface of multiphase flow, and the fluid-structure interaction is realized by using user-defined function and dynamic grid technology. The maximum water-exit height, hover height, energy change, efficiency, and stability are chosen to evaluate the SAH performance. The results show that with the increase of swing frequency and swing amplitude, the hover height increases linearly, and the energy obtained and consumed increases exponentially. Especially, as the swing amplitude increases, the efficiency shows a trend of first increasing and then decreasing. Closer inspection reveals that different kinematic parameters of the swimmer may achieve the same hover height, but their energy consumption, efficiency, and hover stability are different. Therefore, according to the predetermined hover height, the optimal kinematic parameters could be obtained to achieve different hover goals. The findings provide an important hydrodynamic basis for the development of novel bionic robots with SAH capabilities that can perform both underwater and surface tasks.

Space Deployment Algorithm for UAV-IRS-Based Systems Using a Ck++ Optimizer

With the popularity of 5G mobile communication services, the number of users has increased dramatically, as well as the nonuniformity of user density distribution; many users are in nonideal channel conditions, so unmanned aerial vehicle (UAV) as a passive relay equipment platform has gradually entered people’s vision. Intelligent reflective surfaces (IRSs) capable of reconfiguring electromagnetic absorption and reflection properties in real-time are offering unprecedented opportunities to enhance wireless communication experience in challenging environments. In this paper, we start from the point of minimizing the energy consumption and nodes of UAV passive relay; the paper proposes to install intelligent reflecting surface (IRS) on UAV as a new passive relay and establish the communication coverage model of UAV-IRS. Then, the main relationship between the coverage radius and hover height of UAV-IRS is verified. In view of different distribution densities of target users, a CK++ (cyclic k -means++) is proposed to solve the spatial deployment problem of UAV-IRS, where the optimal solution of the system is obtained through cyclic clustering. And the algorithm is verified to effectively improve the performance of urban mobile communication and user communication service quality through numerical stimulation.

Minimization of the Worst Case Average Energy Consumption in UAV-Assisted IoT Networks

The Internet of Things (IoT) brings connectivity to a massive number of devices that demand energy-efficient solutions to deal with limited battery capacities, uplink-dominant traffic, and channel impairments. In this work, we explore the use of unmanned aerial vehicles (UAVs) equipped with configurable antennas as a flexible solution for serving low-power IoT networks. We formulate an optimization problem to set the position and antenna beamwidth of the UAV, and the transmit power of the IoT devices subject to average-signal-to-average-interference-plus-noise ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bar {\text {S}}\overline {\text {IN}}\text {R}$ </tex-math></inline-formula> ) Quality-of-Service (QoS) constraints. We minimize the worst case average energy consumption of the latter, thus targeting the fairest allocation of the energy resources. The problem is nonconvex and highly nonlinear; therefore, we reformulate it as a series of three geometric programs that can be solved iteratively. Results reveal the benefits of planning the network compared to a random deployment in terms of reducing the worst case average energy consumption. Furthermore, we show that the target <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\bar {\text {S}}\overline {\text {IN}}\text {R}$ </tex-math></inline-formula> is limited by the number of IoT devices, and highlight the dominant impact of the UAV hovering height when serving wider areas. Our proposed algorithm outperforms other optimization benchmarks in terms of minimizing the average energy consumption at the most energy-demanding IoT device, and convergence time.

A Mutual-Capacitance 3-D Gesture Sensing System Based on 2-D Orthogonal Encoding and an Un-Folding Coordinate Interpolation Schemes

This paper describes the design of a capacitance readout IC for 3-D hover gesture sensing system. The proposed IC adopts a multi-channel driving scheme in both driving and sensing electrodes of a TSP (touch screen panel). The proposed single encoding and summing (ENS) filter in the readout circuit senses all TSP channels at once, thereby reducing the power consumption and chip area. An incorporated correlated double sampler (CDS) performs down-conversion of the capacitance signal and moving average filtering for severe noise interferences with high pass-filtering of the ENS filter. The proposed IC also employs an efficient hovering gesture detection method that is based on an un-folding 1-dimensional coordinate extraction scheme and various triggering events. By employing the cascade driving for hovering detection, the hover frame rate is maintained to be the same as the TSP frame rate while achieving a targeted signal-to-noise ratio (SNR). The proposed readout IC was fabricated on a 130-nm CMOS process. The IC achieves 26-dB SNR at 10-mm hover height and 120-Hz frame rate with $16\times16$ TSP. The front end circuit occupies a chip area of 0.0912-mm2 and supports a supply voltage ranging from 2.7 V to 3.3 V.

High-accuracy, high-resolution downwash flow field measurements of an unmanned helicopter for precision agriculture

Unmanned helicopters are used widely in precision agriculture, especially in East Asia. However, the development of the downwash flow field of unmanned helicopters, which strongly influences the movement of spray droplets in the air, is poorly understood. Therefore, an indoor measurement technique was developed to investigate the downwash flow field of a 1:10 scaled unmanned agricultural helicopter (AF-25B; Copterworks). High-speed particle image velocimetry was employed to obtain the instantaneous and average velocity field of the downwash flow, with a spatial resolution less than 0.005 m and temporal resolution less than 0.001 s. Results showed that radial distance of the point at which downwash flow reached the ground was proportional to the hovering height of the helicopter at a hovering height of z/R < 2.5 (where z is the rotor height above the ground, and R is the rotor radius), whereas the maximum radial velocity near the ground was inversely proportional to the hovering height. In addition, the spatial distribution of the turbulence kinetic energy at different hovering heights was determined. Intense fluctuations were concentrated along the outer edge of the main downwash flow and secondary vortex near the ground, which might result in more uniform droplet distribution. Based on the instantaneous analysis of the downwash flow structures, velocity profile induced by the rotor tip vortex, the moving tracks of the vortices, and decay rate were obtained. A typical burst-type flow structure in the downwash flow field was also observed, which may contribute to droplet drift. These indoor test results were comparable to previous field test results. This study offers high-accuracy indoor test data that can be used as a reference for future simulation studies.

Entrainment of particles and gas induced by draft fan over the particles bed

The draft fan is used to generate a controlled transportation of particles to enhance entrainment of gas and particles from the particles bed. Present investigations show the entrainment behavior of particles induced by an axial 4-blade draft fan hovering over the particles bed. The distributions of velocities and volume fractions of gas and particles are simulated using Euler-Euler two-fluid model (TFM) with kinetic theory of granular flow (KTGF) at different hovering heights and rotational speeds of the draft fan. The dense region with high solids volume fraction and low particles velocity and the dilute region with low solids volume fraction and high particles velocity exist beneath the draft fan along hovering heights. The entrainment of particles increases with the decrease of hovering height and increase of rotational speed of the draft fan. Present numerical simulations confirm that the gas-solid TFM with the kinetic theory of granular flow and multiple reference frame model can be effectively applied to analysis for entrainment of particles induced by draft fan.

Aerodynamic interference test of quad tilt rotor aircraft in wind tunnel

There is an obvious aerodynamic interference problem that occurs for a quad tilt rotor in near-ground hovering or in the conversion operating condition. This paper presents an aerodynamic interference test of the quad tilt rotor in a wind tunnel. A 1:35 scale model of the quad tilt rotor is used in this test. To substitute for the ground, a moveable platform is designed in a low-speed open-loop wind tunnel to simulate different flight altitudes of the quad tilt rotor in hovering or forward flight. A rod six-component force balance is used to measure the loads on the aircraft, and the flow field below the airframe is captured using particle image velocimetry. The experimental results show that the ground effect is significant when the hover height above the ground is less than the rotor diameter of the quad tilt rotor aircraft, and the maximum upload of the airframe is approximately 12% of the total vertical thrust with the appearance of obvious fountain flow. During the conversion operating condition, the upload of the airframe is reduced compared with that in the hovering state, which is affected by rotor wake and incoming flow. The aerodynamic interference test results of the quad tilt rotor aircraft have important reference value in power system selection, control system design, and carrying capacity improvement with the advantage of ground effect.

The computational fluid dynamic modeling of downwash flow field for a six-rotor UAV

The downwash flow field of the multi-rotor unmanned aerial vehicle (UAV), formed by propellers during operation, has a significant influence on the deposition, drift and distribution of droplets as well as the spray width of the UAV for plant protection. To study the general characteristics of the distribution of the downwash airflow and simulate the static wind field of multi-rotor UAVs in hovering state, a 3D full-size physical model of JF01-10 six-rotor plant protection UAV was constructed using SolidWorks. The entire flow field surrounding the UAV and the rotation flow fields around the six rotors were established in UG software. The physical model and flow fields were meshed using unstructured tetrahedral elements in ANSYS software. Finally, the downwash flow field of UAV was simulated. With an increased hovering height, the ground effect was reduced and the minimum current velocity increased initially and then decreased. In addition, the spatial proportion of the turbulence occupied decreased. Furthermore, the appropriate operational hovering height for the JF01-10 is considered to be 3 m. These results can be applied to six-rotor plant protection UAVs employed in pesticide spraying and spray width detection.

Hovering height of a high-temperature body over a water-containing porous plate

The hovering behavior of a high-temperature metal disk brought into proximity with a water-containing porous material plate is investigated experimentally. Vapor produced from the porous plate by the heat transferred from the hot disk flows along the small clearance between two bodies in order to establish a pressure field that acts to repel the hot disk away from the porous plate. The repelling force may just balance gravity, allowing the hot body to hover over the porous plate.In the present paper, heat transfer from a high-temperature solid to the water-containing porous material plate separated by a small gap is analyzed based on a simplified model. The calculated heat fluxes in the system and the resulting vapor production rate are compared with the measured results. An expression for the hovering force is derived as a function of the evaporation mass flux and the related parameters based on the model of the vapor flow dynamics. The hovering height of a high-temperature disk is predicted using an approximate correlation for the evaporation mass fluxes, which can express the dependency of the measured results on the temperature and the magnitude of the clearance, and is compared with the measured results.

Magnetorheological Fluid for Levitation Migration Technology

The dispersed particles of magnetic fluid form stable chain-like clusters under the magnetic field, and shows “the flowing is controllable and the shape is controllable” effect. Based on this characteristic, using migration magnetic acted on the magnetic fluid, the object directional migration can be realize, then the magnetic fluid form ribbon at the same time, has the similar fluctuation behavior. The magnetic fluid aerosol migration principle, the aerosol magnetic circuit design, the magnetic field strength and the magnetic force were separately discussed in this paper. The magnetic fluid hover height using the MSL micrometer dial has determined and aerosol migration feasibility has confirmed using the experiment.

上下動可能なノズルによるSESのクッション圧力変動の抑制

In this paper the variation of cushion pressure is investigated theoretically to achieve comfortable riding of SES. A simpler and practical control method is proposed to control cushion pressure changes arising from pumping phenomenon that appears in SES cruising over the waves. Cushion pressure is controlled by varying the discharge height of the vertical nozzle. In this method the nozzle height (hover height) is kept constant according with the motion of the craft. As the result of investigations, cushion pressures are successfully controlled by the proposed method. In addition, it is shown that the pressure variation depends not only hover height but also on rate of change of cushion volume. Therefore it is also necessary to consider phase difference between the motion of models and the vertical displacement of nozzles.

フィンガースカートを装着した小型ＡＣＶの傾斜時の静安定性について

The static pitch stability of small ACVs fitted with finger-type skirts is investigated. A simple method which predicts the static stability and the cushion stiffness is proposed. It yields rough approximations of quantities needed for the initial design. Numerical results of the analysis are presented. We consider two different operating conditions. In one case the skirt is in contact with the ground. In another case the contact does not occur. In both cases the pitch stability decreases with increasing distance of the center of gravity from the skirt hem line and with increasing hover height. However variation of the skirt inclination angle affects the pitch stability in opposite way in two different operating conditions.

地面の不整がＡＣＶの揚力特性に及ぼす影響 ＩＩＩ

Static characteristics of an ACV (Air Cushion Vehicle) over irregular ground are investigated theoretically and experimentally. The exponential theory is developed for this purpose. Calculations are made for the case of two and three dimensional models, and the results are compared with experimental ones.Theoretical results show good agreement with those of experiments except the particular cases such as the hover height is very low, or the higher portions of ground roughness is close to the peripheral nozzle.The effects of the partition on lift and moment characteristics are also studied. Calculations show that partition equipped on the base affects the lift augmentation ratio especially at large d/D, but there exist little effects on experimental results. On the other hand, moment characteristics calculated agree with the measured values qualitatively.