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Aerospace, Volume 9, Issue 6 (June 2022) – 52 articles

Cover Story (view full-size image): The use of EMAs for aeronautical applications promises substantial benefits regarding efficiency and operability. To advance the design of power electronics and secondary power supply, there is a strong need for the ability to swiftly study the effects of mission and operational aspects on actuator energy consumption. Pursuant to this, a generic mission-level flight control surface EMA power consumption simulation framework is presented. The core of the framework comprises physics-based EMA power estimators, linked with a six-degree-of-freedom flight dynamics and control simulation module. The developed framework could aid in the selection of the actuator, as well as in the optimization of airborne electronics and secondary power supply. View this paper
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16 pages, 4014 KiB  
Article
Energy System Optimization and Simulation for Low-Altitude Solar-Powered Unmanned Aerial Vehicles
by Ke Li, Yansen Wu, Abu Bakar, Shaofan Wang, Yuangan Li and Dongsheng Wen
Aerospace 2022, 9(6), 331; https://doi.org/10.3390/aerospace9060331 - 20 Jun 2022
Cited by 8 | Viewed by 2000
Abstract
The accurate calculation of energy system parameters makes a great contribution to the long-term low-altitude flight of solar-powered aircraft. The purpose of this paper is to propose a design method for optimization and management of the low-altitude and long-endurance Unmanned Aerial Vehicles (UAV) [...] Read more.
The accurate calculation of energy system parameters makes a great contribution to the long-term low-altitude flight of solar-powered aircraft. The purpose of this paper is to propose a design method for optimization and management of the low-altitude and long-endurance Unmanned Aerial Vehicles (UAV) energy system. In terms of optimization, the power input and output generated by solar panels and cruise thrust are calculated, and the energy balance of the UAV during flight is analyzed. In addition, in order to meet the energy consumption requirements of UAV during day and night flight, the influence of local environmental conditions (such as morning and evening clouds and night interference) on the aircraft is considered, and the remaining time indicator is designed to ensure long-term flight stability. Battery capacity is also estimated by the remaining time. This paper will describe extended criteria for optimization and extension methods to improve the stability and robustness of aircraft flight performance for multiple consecutive days. In addition, a design method for the UAV has been developed, which simulates and optimizes the parameters of the solar-powered UAV so that it has a wingspan of 5 m and a relative battery mass of 3 kg. The simulation in this paper describes in detail the aircraft taking off from 7 a.m. on the first day to verify the aircraft’s full day and night flight capability, and achieving the aircraft’s long flight on 22 June to meet the mission requirements of multi-day flights. It also analyzed and verified the performance at the edge of the 48 h flight time window on 21 April, which differs from the lighting in August. Finally, a flight experiment was completed on 9 August. The feasibility of the proposed method and process is verified in this paper along with the performance of the designed UAV, which will provide more guidance for future work. Full article
(This article belongs to the Section Aeronautics)
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14 pages, 20956 KiB  
Article
MC-New: A Program to Calculate Newtonian Aerodynamic Coefficients Based on Monte-Carlo Integration
by Michiko Ahn Furudate
Aerospace 2022, 9(6), 330; https://doi.org/10.3390/aerospace9060330 - 20 Jun 2022
Viewed by 2711
Abstract
A computer program, MC-New, to calculate Newtonian aerodynamics is presented. The aerodynamic coefficients of a geometry expressed by an analytic function are calculated in a Monte-Carlo integration manner, in which the local forces on the randomly chosen sample points are summed up. The [...] Read more.
A computer program, MC-New, to calculate Newtonian aerodynamics is presented. The aerodynamic coefficients of a geometry expressed by an analytic function are calculated in a Monte-Carlo integration manner, in which the local forces on the randomly chosen sample points are summed up. The verification study and the accuracy analysis show that the program can provide good approximations of exact solutions. The example results of the parametric study on the Apollo-like entry capsule geometry are presented, showing the potential capability of the MC-New program as an efficient open-source tool for designing hypersonic vehicles. Full article
(This article belongs to the Special Issue Hypersonics: Emerging Research)
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19 pages, 9300 KiB  
Article
Flight Anomaly Detection via a Deep Hybrid Model
by Kun Qin, Qixin Wang, Binbin Lu, Huabo Sun and Ping Shu
Aerospace 2022, 9(6), 329; https://doi.org/10.3390/aerospace9060329 - 19 Jun 2022
Cited by 11 | Viewed by 2500
Abstract
In the civil aviation industry, security risk management has shifted from post-accident investigations and analyses to pre-accident warnings in an attempt to reduce flight risks by identifying currently untracked flight events and their trends and effectively preventing risks before they occur. The use [...] Read more.
In the civil aviation industry, security risk management has shifted from post-accident investigations and analyses to pre-accident warnings in an attempt to reduce flight risks by identifying currently untracked flight events and their trends and effectively preventing risks before they occur. The use of flight monitoring data for flight anomaly detection is effective in discovering unknown and potential flight incidents. In this paper, we propose a time-feature attention mechanism and construct a deep hybrid model for flight anomaly detection. The hybrid model combines a time-feature attention-based convolutional autoencoder with the HDBSCAN clustering algorithm, where the autoencoder is constructed and trained to extract flight features while the HDBSCAN works as an anomaly detector. Quick access record (QAR) flight data containing information of aircraft landing at Kunming Changshui International and Chengdu Shuangliu International airports are used as the experimental data, and the results show that (1) the time-feature-based convolutional autoencoder proposed in this paper can better extract the flight features and further discover the different landing patterns; (2) in the representation space of the flights, anomalous flight objects are better separated from normal objects to provide a quality database for subsequent anomaly detection; and (3) the discovered flight patterns are consistent with those at the airports, resulting in anomalies that could be interpreted with the corresponding pattern. Moreover, several examples of anomalous flights at each airport are presented to analyze the characteristics of anomalies. Full article
(This article belongs to the Collection Air Transportation—Operations and Management)
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23 pages, 6289 KiB  
Article
Effect of Lifting Gas Diffusion on the Station-Keeping Performance of a Near-Space Aerostat
by Jun Li, Linyu Ling, Jun Liao, Zheng Chen and Shibin Luo
Aerospace 2022, 9(6), 328; https://doi.org/10.3390/aerospace9060328 - 18 Jun 2022
Viewed by 1600
Abstract
During the long-endurance flight of a near-space aerostat, the characteristics of lifting gas diffusion have a great influence on the flight altitude adjustment and station-keeping performance. Thus, in this study, a lifting gas diffusion model and a dynamic model that consider thermal effects, [...] Read more.
During the long-endurance flight of a near-space aerostat, the characteristics of lifting gas diffusion have a great influence on the flight altitude adjustment and station-keeping performance. Thus, in this study, a lifting gas diffusion model and a dynamic model that consider thermal effects, which had not been studied in similar models before, were developed. The dynamic model and thermal model were validated by historic flight data, and the calculated lifting gas diffusion results were compared with the experimental data of other researchers. The variations in the flight endurance, flight altitude, lifting gas diffusion rate, and diffusion coefficient of a near-space aerostat were analyzed. The effects of the ratio of porosity to tortuosity and envelope radiation properties on the mass of the lifting gas and flight altitude were considered in detail. To analyze the effect mechanism of the ratio of porosity to tortuosity and the envelope radiation properties, the envelope and gas temperature, as well as the gas pressure, were studied. The results show that the lifting gas diffusion rate and diffusion coefficient are very sensitive to the change in the ratio of porosity to tortuosity and envelope temperature. The results obtained from the analysis of the lifting gas diffusion can lay a solid foundation for improving the flight performance of near-space aerostats and for providing improved design considerations for aerostats. Full article
(This article belongs to the Special Issue Mission Analysis and Design of Lighter-than-Air Flying Vehicles)
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21 pages, 11364 KiB  
Article
Vibro-Acoustic Modelling of Aeronautical Panels Reinforced by Unconventional Stiffeners
by Giovanni Fasulo, Pasquale Vitiello, Luigi Federico and Roberto Citarella
Aerospace 2022, 9(6), 327; https://doi.org/10.3390/aerospace9060327 - 17 Jun 2022
Cited by 3 | Viewed by 2435
Abstract
The purpose of this work is to characterise the vibro-acoustic behaviour of rectangular flat panels reinforced by “unconventional” stiffeners. Such panels are being increasingly employed in the aircraft industry in the case of composite fuselage, so that the assessment of the most efficient [...] Read more.
The purpose of this work is to characterise the vibro-acoustic behaviour of rectangular flat panels reinforced by “unconventional” stiffeners. Such panels are being increasingly employed in the aircraft industry in the case of composite fuselage, so that the assessment of the most efficient and accurate numerical techniques and modelling procedures to correctly predict their dynamic and acoustic behaviour is required. To this end, an analytical method, available from literature, has been initially employed to investigate on the main attributes of sound transmission loss properties of stiffened panels driven by an acoustic diffuse field excitation. Based on existing commercial codes, different numerical techniques have been implemented and deeply examined to assess their potentiality and restrictions. Among them, the Hybrid method has been eventually identified as the best compromise in terms of accuracy and computational effort. The drawbacks of deterministic and even Hybrid numerical approaches for medium–high frequency vibro-acoustic analysis when dealing with large structures, make use of the pure SEA approach compulsory. In particular, a refined tuning of a specific feature made available within the employed SEA analysis environment when dealing with reinforced shells is implemented as a potential solution to overcome the complexity in correctly modelling the examined unconventionally stiffened panels. Full article
(This article belongs to the Special Issue Advances in Aerospace Sciences and Technology III)
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21 pages, 10238 KiB  
Article
Numerical Investigation on the Heat Transfer of n-Decane in a Horizontal Channel with Axially Nonuniform Heat Flux under Supercritical Pressure
by Jin Zhang, Qilin Zhou, Xudong Zhao, Yuguang Jiang and Wei Fan
Aerospace 2022, 9(6), 326; https://doi.org/10.3390/aerospace9060326 - 17 Jun 2022
Cited by 1 | Viewed by 1806
Abstract
Regenerative cooling is considered promising in the thermal protection of hypersonic propulsion devices such as SCRamjet. However, the heat transfer deterioration (HTD) of hydrocarbon fuel is a severe threat to the thermal structure safety, especially under axially nonuniform heat flux caused by the [...] Read more.
Regenerative cooling is considered promising in the thermal protection of hypersonic propulsion devices such as SCRamjet. However, the heat transfer deterioration (HTD) of hydrocarbon fuel is a severe threat to the thermal structure safety, especially under axially nonuniform heat flux caused by the thermal load difference in different components. In this work, the heat transfer of trans-critical n-decane in a mini-horizontal channel is numerically investigated. The influences of the axially nonuniform heat flux on the heat transfer is focused on. Two types of HTD are recognized and analyzed. The first type of HTD is induced by the near-wall flow acceleration and the local thickening of the viscous sublayer. The second type of HTD is closely related to the expansion of the low thermal conductivity λ and specific heat cp region, which is seriously worsened under axially nonuniform heat flux, especially when the heat flux peak locates where TwTpc. The minimum HTC deteriorates by 40.80% and the Tw_max increases from 857 K to 1071 K by 27.5%. The maximum fluctuation in pressure drop is 6.8% in the variation in heat flux distribution with Φ = 2. This work is expected to offer a reference to the proper match of fuel temperature distribution and the engine heat flux boundary in SCRamjet cooling system design. Full article
(This article belongs to the Special Issue Cooling/Heat transfer (Volume II))
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18 pages, 2160 KiB  
Article
Performance Comparison of Control Strategies for a Variable-Thrust Solid-Propellant Rocket Motor
by Jihyoung Cha and Élcio Jeronimo de Oliveira
Aerospace 2022, 9(6), 325; https://doi.org/10.3390/aerospace9060325 - 16 Jun 2022
Cited by 6 | Viewed by 4752
Abstract
This paper deals with a performance comparison of the control algorithm for a variable-thrust solid-propellant rocket motor (VTSRM). To do this, we develop a simulation model of a VTSRM considering characteristic changes in the combustor and design control systems for pressure and thrust. [...] Read more.
This paper deals with a performance comparison of the control algorithm for a variable-thrust solid-propellant rocket motor (VTSRM). To do this, we develop a simulation model of a VTSRM considering characteristic changes in the combustor and design control systems for pressure and thrust. We use three types of control algorithms for the pressure control: classical PID control, feedback linearization control, and fuzzy PID control, and two control algorithms for thrust control: classical PID control and fuzzy PID control. Finally, we compare the performance of each control system through a numerical simulation using step responses. Through this work, we check that feedback linearization is better in pressure control, and fuzzy PID control is more appropriate in thrust control. Especially using fuzzy PID control, we can get fast settling with a small undershoot even if the system is a nonminimum phase system. Full article
(This article belongs to the Collection Space Systems Dynamics)
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20 pages, 3200 KiB  
Review
Progress of Stewart Vibration Platform in Aerospace Micro–Vibration Control
by Zepeng He, Xiangchao Feng, Yeqing Zhu, Zhibo Yu, Zhen Li, Yan Zhang, Yinhang Wang, Pengfei Wang and Liangyu Zhao
Aerospace 2022, 9(6), 324; https://doi.org/10.3390/aerospace9060324 - 15 Jun 2022
Cited by 11 | Viewed by 3321
Abstract
In order to support the development of high–precision spacecraft, the current state of the Stewart vibration isolation platform in the field of aerospace micro–vibration was surveyed. First, based on analyses of the causes and characteristics of spacecraft micro–vibration, the principles, characteristics, advantages and [...] Read more.
In order to support the development of high–precision spacecraft, the current state of the Stewart vibration isolation platform in the field of aerospace micro–vibration was surveyed. First, based on analyses of the causes and characteristics of spacecraft micro–vibration, the principles, characteristics, advantages and disadvantages of four vibration isolation technologies are summarized. Second, the development process of the Stewart vibration isolation platform, from structural proposal and theoretical calculation to application in various fields, is introduced. Then, the current state of kinematics, dynamics and braking control algorithms of the Stewart platform is investigated, and related work on rigid/flexible platforms in the field of aerospace micro–vibration is introduced in detail. Finally, the idea that the Stewart platform can be fabricated by 4D printing technology is proposed. The novel Stewart platform can be combined with artificial intelligence algorithms and advanced control strategies, allowing for further development in the direction of an integrated omnidirectional, full–frequency and multi–function platform with variable stiffness. Full article
(This article belongs to the Section Astronautics & Space Science)
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17 pages, 2060 KiB  
Article
Midcourse Iterative Guidance Method for the Impact Time and Angle Control of Two-Pulse Interceptors
by Yifan Deng, Jinlei Ren, Xu Wang and Yuanli Cai
Aerospace 2022, 9(6), 323; https://doi.org/10.3390/aerospace9060323 - 15 Jun 2022
Cited by 3 | Viewed by 1470
Abstract
To address the need for flexible energy management and impact angle control in the midcourse guidance of modern long-range antiballistic interceptors, an impact time and angle guidance law is designed for the exoatmospheric midcourse flight of antiballistic interceptors, which covers two pulse sections [...] Read more.
To address the need for flexible energy management and impact angle control in the midcourse guidance of modern long-range antiballistic interceptors, an impact time and angle guidance law is designed for the exoatmospheric midcourse flight of antiballistic interceptors, which covers two pulse sections and two coast sections. The problem is described as an optimal control model with discontinuities in the system equations at interior points, and an iterative guidance method is used to efficiently solve the two-point boundary value problem. Simulation results demonstrate the effectiveness of the proposed guidance law; the obtained miss distance accuracy has an order of magnitude of 1 m, and the impact angle accuracy has a 1° order of magnitude while the angle can be achieved. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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14 pages, 1796 KiB  
Article
A Routing Optimization Method for LEO Satellite Networks with Stochastic Link Failure
by Guohong Zhao, Zeyu Kang, Yixin Huang and Shufan Wu
Aerospace 2022, 9(6), 322; https://doi.org/10.3390/aerospace9060322 - 14 Jun 2022
Cited by 2 | Viewed by 2224
Abstract
In this paper, for an Low-Earth Orbit (LEO) satellite network with inter-satellite links, a routing optimization method is developed in the case of stochastic link failure. First, a discrete-time strategy is used for the satellite network to acquire several static topological graphs during [...] Read more.
In this paper, for an Low-Earth Orbit (LEO) satellite network with inter-satellite links, a routing optimization method is developed in the case of stochastic link failure. First, a discrete-time strategy is used for the satellite network to acquire several static topological graphs during a cycle. Based on the static topological graphs regarding stochastic link failure, a constraint model is established that constructs the task revenue, switching times and routing cost as indicators. Then, an improved Genetic Algorithm based on A* is proposed to optimize the topology under the constraint model. In particular, to reduce the cost of computation, a new generation strategy for the initial solution is presented which combines the roulette wheel operator and the A* algorithm. Finally, the effectiveness of the proposed method is illustrated by a group of numerical simulations for the network with stochastic link failure. Full article
(This article belongs to the Section Astronautics & Space Science)
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15 pages, 1768 KiB  
Article
Efficient Modeling of Heat Conduction across Thin Surface Coatings on 3D Anisotropic Substrate
by Yui-Chuin Shiah, Po-Wen Hwang, Mohammad-Rahim Hematiyan and Nguyen Anh Tuan
Aerospace 2022, 9(6), 321; https://doi.org/10.3390/aerospace9060321 - 13 Jun 2022
Cited by 1 | Viewed by 1471
Abstract
In aerospace applications, surface coatings have been widely applied for variouspurposes. One typical example is the use of thermal barrier coating (TBC) applied on anisotropic substrate for enhancing the heat resistance of the substrate under severe operational environments. Numerical modeling of thin coatings [...] Read more.
In aerospace applications, surface coatings have been widely applied for variouspurposes. One typical example is the use of thermal barrier coating (TBC) applied on anisotropic substrate for enhancing the heat resistance of the substrate under severe operational environments. Numerical modeling of thin coatings usually present difficulties for most techniques, due to their dimensional orders being far below that of the substrate. This paper presents a numerical methodology to efficiently model the heat conduction across thin layered coatings on 3D, generally anisotropic, media by the boundary element method (BEM). In the modeling, singularities of the surface-integrals are weakened by using Green’s Second Identity, where a newly introduced function is solved by the finite volume method. Using the proposed approach, the heat conduction problem can be efficiently analyzed, despite the great difference in dimensional orders in comparison with that of the substrate beneath, by simply employing very coarse surface meshes. Such analysis shows great efficiency in calculating the nearly singular boundary integrals for the modeling. Finally, two benchmark examples of thermal barrier coatings are analyzed to illustrate the effectiveness of this approach. Full article
(This article belongs to the Special Issue Recent Advances in Computational Mechanics)
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16 pages, 3558 KiB  
Article
Identification Strategy Design with the Solution of Wavelet Singular Spectral Entropy Algorithm for the Aerodynamic System Instability
by Mingming Zhang, Pan Kong, Anping Hou, Aiguo Xia, Wei Tuo and Yongzhao Lv
Aerospace 2022, 9(6), 320; https://doi.org/10.3390/aerospace9060320 - 13 Jun 2022
Cited by 3 | Viewed by 1573
Abstract
In order to effectively identify the signs of instability in the aerodynamic system of an axial compressor, a wavelet singular spectral entropy algorithm incorporated within the wavelet transform, singular value decomposition and information entropy is proposed to describe the distribution complexity of the [...] Read more.
In order to effectively identify the signs of instability in the aerodynamic system of an axial compressor, a wavelet singular spectral entropy algorithm incorporated within the wavelet transform, singular value decomposition and information entropy is proposed to describe the distribution complexity of the spatial modalities in the flow field. This kind of identification design can accurately distinguish the boundary between the stable and unstable states of the internal flow field from the view of a dynamic system. On the basis of the information entropy algorithm, the wavelet singular spectral entropy algorithm is designed to integrate with the advantages of wavelet transform analysis on the time-frequency localization and singular value decomposition for signal processing and data mining together. So that the quantitative analysis of the definition of rebuilding a system image can be achieved by the solution of wavelet singular spectral entropy. This method can automatically extract the transient information of the space mode in the time-frequency domain. It effectively avoids the shortcoming that the feature extraction on spatial information cannot be accomplished from multiple angles with the single information entropy algorithm. In the data processing of instability signals under different speeds, the wavelet singular spectral entropy algorithm shows a greater advantage in the early warning for compressor stall. The result shows that the value of the wavelet singular spectral shows an obvious mutation when the aerodynamic system approaches the instability boundary. According to the threshold set, the identification hybrid algorithm can detect the stall precursor about 23~96 r in advance. Compared to the single information entropy algorithm, the hybrid wavelet singular spectral entropy algorithm is able to shift to an earlier precursor identification by about 11~82 r. This established hybrid identification algorithm accounts for the nonlinearity of the aerodynamic system, providing a new perspective for the nonlinear system instability identification. Full article
(This article belongs to the Special Issue Advanced Flow Diagnostic Tools)
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81 pages, 12700 KiB  
Review
The Enabling Technologies for a Quasi-Zero Emissions Commuter Aircraft
by Danilo Ciliberti, Pierluigi Della Vecchia, Vittorio Memmolo, Fabrizio Nicolosi, Guido Wortmann and Fabrizio Ricci
Aerospace 2022, 9(6), 319; https://doi.org/10.3390/aerospace9060319 - 12 Jun 2022
Cited by 10 | Viewed by 4763
Abstract
The desire for greener aircraft pushes both academic and industrial research into developing technologies, manufacturing, and operational strategies providing emissions abatement. At time of writing, there are no certified electric aircraft for passengers’ transport. This is due to the requirements of lightness, reliability, [...] Read more.
The desire for greener aircraft pushes both academic and industrial research into developing technologies, manufacturing, and operational strategies providing emissions abatement. At time of writing, there are no certified electric aircraft for passengers’ transport. This is due to the requirements of lightness, reliability, safety, comfort, and operational capability of the fast air transport, which are not completely met by the state-of-the-art technology. Recent studies have shown that new aero-propulsive technologies do not provide significant fuel burn reduction, unless the operational ranges are limited to short regional routes or the electric storage capability is unrealistically high, and that this little advantage comes at increased gross weight and operational costs. Therefore, a significant impact into aviation emissions reduction can only be obtained with a revolutionary design, which integrates disruptive technologies starting from the preliminary design phase. This paper reviews the recent advances in propulsions, aerodynamics, and structures to present the enabling technologies for a low emissions aircraft, with a focus on the commuter category. In fact, it is the opinion of the European Community, which has financed several projects, that advances on the small air transport will be a fundamental step to assess the results and pave the way for large greener airplanes. Full article
(This article belongs to the Section Aeronautics)
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16 pages, 16784 KiB  
Article
Numerical Prediction of Unsteady Aerodynamics of a Ducted Fan Unmanned Aerial Vehicle in Hovering
by Hongming Cai, Zhuoran Zhang and Shuanghou Deng
Aerospace 2022, 9(6), 318; https://doi.org/10.3390/aerospace9060318 - 11 Jun 2022
Cited by 5 | Viewed by 2084
Abstract
Recently, ducted fan unmanned aerial vehicles (UAVs) have attracted considerable attention due to their potential for application in both civil and military missions. Compared with free propellers, the presence of duct can in principle decrease the flow contraction after propeller, and gives the [...] Read more.
Recently, ducted fan unmanned aerial vehicles (UAVs) have attracted considerable attention due to their potential for application in both civil and military missions. Compared with free propellers, the presence of duct can in principle decrease the flow contraction after propeller, and gives the potential to fly efficiently with high security, compact structure, and low noise. In the present study, a ducted fan UAV is designed using the open source code OpenProp. The computational fluid dynamics (CFD) simulation model using sliding mesh technique is established and validated as a reliable tool for highly vortical flows by propeller thrust experiment. The effect of the duct, revolution speed, and distance between propellers on the aerodynamic characteristics of the ducted fan UAV is evaluated in detail. Results show that the unducted coaxial upper and lower propellers generate 3.8%, 4.3% more thrust than the unducted single propellers, respectively, and the unducted upper and lower propellers generate 55.9%, 34.9% more thrust than ducted propellers, respectively. The ducted fan UAV generates 5.7% more thrust and consumes 39.1% less power than the unducted coaxial propellers. The thrust of the ducted fan UAV increases first and then follows with a decreased tendency as the distance between propellers increases. Full article
(This article belongs to the Section Aeronautics)
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21 pages, 4741 KiB  
Article
A New Method for Remote Sensing Satellite Observation Effectiveness Evaluation
by Zhi Li, Yunfeng Dong, Peiyun Li, Hongjue Li and Yingjia Liew
Aerospace 2022, 9(6), 317; https://doi.org/10.3390/aerospace9060317 - 11 Jun 2022
Cited by 7 | Viewed by 1720
Abstract
The number of remote sensing satellites has increased rapidly in parallel with the advancement of space technology and the rising demand in the space industry. Consequently, the observation effectiveness evaluation of remote sensing satellites has received extensive attention. As the core content of [...] Read more.
The number of remote sensing satellites has increased rapidly in parallel with the advancement of space technology and the rising demand in the space industry. Consequently, the observation effectiveness evaluation of remote sensing satellites has received extensive attention. As the core content of the effectiveness evaluation, index systems are usually established and screened using qualitative or quantitative methods. They can hardly satisfy the construction principles such as completeness and independence simultaneously. To address this issue, we propose a new method for remote sensing satellite observation effectiveness evaluation that considers various principles. Firstly, a three-layer evaluation index system structure is constructed. The principle of completeness, hierarchy, and measurability of the index system is ensured by decomposition, clustering, and preliminary screening. Secondly, the principal component contribution rate is obtained through principal component analysis. Finally, we introduce a comprehensive scoring method (ICCLR) based on the combination of independence coefficient and principal component comprehensive loss rate. It realizes the screening of an index system from the index set containing correlation relationships. The validity and optimality of the proposed method are verified through experiments and analysis of three typical tasks. Full article
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21 pages, 5086 KiB  
Article
A Prognostic and Health Management Framework for Aero-Engines Based on a Dynamic Probability Model and LSTM Network
by Yufeng Huang, Jun Tao, Gang Sun, Hao Zhang and Yan Hu
Aerospace 2022, 9(6), 316; https://doi.org/10.3390/aerospace9060316 - 10 Jun 2022
Cited by 7 | Viewed by 9690
Abstract
In this study, a prognostics and health management (PHM) framework is proposed for aero-engines, which combines a dynamic probability (DP) model and a long short-term memory neural network (LSTM). A DP model based on Gaussian mixture model-adaptive density peaks clustering algorithm, which has [...] Read more.
In this study, a prognostics and health management (PHM) framework is proposed for aero-engines, which combines a dynamic probability (DP) model and a long short-term memory neural network (LSTM). A DP model based on Gaussian mixture model-adaptive density peaks clustering algorithm, which has the advantages of an extremely short training time and high enough precision, is employed for modelling engine fault development from the beginning of engine service, and principal component analysis is introduced to convert complex high-dimensional raw data into low-dimensional data. The model can be updated from time to time according to the accumulation of engine data to capture the occurrence and evolution process of engine faults. In order to address the problems with the commonly used data driven methods, the DP + LSTM model is employed to estimate the remaining useful life (RUL) of the engine. Finally, the proposed PHM framework is validated experimentally using NASA’s commercial modular aero-propulsion system simulation dataset, and the results indicate that the DP model has higher stability than the classical artificial neural network method in fault diagnosis, whereas the DP + LSTM model has higher accuracy in RUL estimation than other classical deep learning methods. Full article
(This article belongs to the Special Issue State Monitoring and Health Management of Complex Equipment)
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12 pages, 3057 KiB  
Article
Research on Dual-Arm Control of Lunar Assisted Robot Based on Hierarchical Reinforcement Learning under Unstructured Environment
by Weiyan Ren, Dapeng Han and Zhaokui Wang
Aerospace 2022, 9(6), 315; https://doi.org/10.3390/aerospace9060315 - 10 Jun 2022
Cited by 4 | Viewed by 1864
Abstract
When a lunar assisted robot helps an astronaut turn over or transports the astronaut from the ground, the trajectory of the robot’s dual arms should be automatically planned according to the unstructured environment on the lunar surface. In this paper, a dual-arm control [...] Read more.
When a lunar assisted robot helps an astronaut turn over or transports the astronaut from the ground, the trajectory of the robot’s dual arms should be automatically planned according to the unstructured environment on the lunar surface. In this paper, a dual-arm control strategy model of a lunar assisted robot based on hierarchical reinforcement learning is proposed, and the trajectory planning problem is modeled as a two-layer Markov decision process. In the training process, a reward function design method based on the idea of the artificial potential field method is proposed, and the reward information is fed back in a dense reward method, which significantly reduces the invalid exploration space and improves the learning efficiency. Large-scale tests are carried out in both simulated and physical environments, and the results demonstrate the effectiveness of the method proposed in this paper. This research is of great significance in respect of human–robot interaction, environmental interaction, and intelligent control of robots. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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22 pages, 4687 KiB  
Article
A Preliminary Top-Down Parametric Design of Electromechanical Actuator Position Control
by Jean-Charles Maré
Aerospace 2022, 9(6), 314; https://doi.org/10.3390/aerospace9060314 - 09 Jun 2022
Viewed by 2027
Abstract
A top-down process is proposed and virtually validated for the position control of electromechanical actuators (EMA) that use conventional cascade controllers. It aims at facilitating the early design phases of a project by providing a straightforward mean that requires simple algebraic calculations only, [...] Read more.
A top-down process is proposed and virtually validated for the position control of electromechanical actuators (EMA) that use conventional cascade controllers. It aims at facilitating the early design phases of a project by providing a straightforward mean that requires simple algebraic calculations only, from the specified performance and the top-level EMA design parameters. This makes it possible to include realistic control considerations in the preliminary sizing and optimisation phase. The position, speed and current controllers are addressed in sequence. This top-down process is based on the generation and use of charts that define the optimal position gain, speed loop second-order damping factor and natural frequency with respect to the specified performance of the position loop. For each loop, the control design formally specifies the required dynamics and the digital implementation of the following inner loop. A noncausal flow chart summarises the equations used and the interdependencies between data. This potentially allows changing which ones are used as inputs. The process is virtually validated using the example of a flight control actuator. This is achieved with resort to the simulation of a realistic lumped-parameter model, which includes any significant functional and parasitic effects. The virtual tests are run following a bottom–up approach to highlight the pursuit and rejection performance. Using low-, medium- and high-excitation magnitudes, they show the robustness of the controllers against nonlinearities. Finally, the simulation results confirm the soundness of the proposed process. Full article
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16 pages, 10361 KiB  
Article
Trajectory Tracking Based on Active Disturbance Rejection Control for Compound Unmanned Aircraft
by Bohai Deng and Jinfa Xu
Aerospace 2022, 9(6), 313; https://doi.org/10.3390/aerospace9060313 - 09 Jun 2022
Cited by 3 | Viewed by 1883
Abstract
The compound unmanned aircraft is provided with three primary flight modes, which are helicopter flight mode in low forward speed flight, airplane flight mode in high forward speed flight and transition flight mode in middle forward speed flight. For the different flight modes, [...] Read more.
The compound unmanned aircraft is provided with three primary flight modes, which are helicopter flight mode in low forward speed flight, airplane flight mode in high forward speed flight and transition flight mode in middle forward speed flight. For the different flight modes, an appropriate flight control law is the need to ensure good flying qualities. In this paper, a trajectory tracking control system based on the active disturbance rejection controller (ADRC) for the compound unmanned aircraft is proposed to adapt the full flight modes. A flight dynamics model and a Simulink simulation model of the compound unmanned aircraft are developed. The transition flight control strategy is analyzed and synthesized to meet the requirement of control strategy in the full flight modes. The internal uncertainties and external disturbance of the UAV are estimated with an extended state observer to compensate control input. A genetic algorithm-particle swarm optimization (GA-PSO) algorithm is utilized to optimize the controller parameters. The simulation of route tracking and spiral climb with different flight modes is conducted, which demonstrates the tracking ability, interference rejection, robustness and effectiveness of the developed controller in the full flight modes. Full article
(This article belongs to the Collection Unmanned Aerial Systems)
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18 pages, 2369 KiB  
Article
The ORIGIN Space Instrument for Detecting Biosignatures and Habitability Indicators on a Venus Life Finder Mission
by Niels F. W. Ligterink, Kristina A. Kipfer, Salome Gruchola, Nikita J. Boeren, Peter Keresztes Schmidt, Coenraad P. de Koning, Marek Tulej, Peter Wurz and Andreas Riedo
Aerospace 2022, 9(6), 312; https://doi.org/10.3390/aerospace9060312 - 09 Jun 2022
Cited by 8 | Viewed by 2717
Abstract
Recent and past observations of chemical and physical peculiarities in the atmosphere of Venus have renewed speculations about the existence of life in its clouds. To find signs of Venusian life, a dedicated astrobiological space exploration mission is required, and for this reason [...] Read more.
Recent and past observations of chemical and physical peculiarities in the atmosphere of Venus have renewed speculations about the existence of life in its clouds. To find signs of Venusian life, a dedicated astrobiological space exploration mission is required, and for this reason the Venus Life Finder mission is currently being prepared. A Venus Life Finder mission will require dedicated and specialized instruments to hunt for biosignatures and habitability indicators. In this contribution, we present the ORIGIN space instrument, a laser desorption/laser ablation ionization mass spectrometer. This instrument is designed to detect large, non-volatile molecules, specifically biomolecules such as amino acids and lipids. At the same time, it can also be used in ablation mode for elemental composition analysis. Recent studies with this space prototype instrument of amino acids, polycyclic aromatic hydrocarbons, lipids, salts, metals, sulphur isotopes, and microbial elemental composition are discussed in the context of studies of biosignatures and habitability indicators in Venus’s atmosphere. The implementation of the ORIGIN instrument into a Venus Life Finder mission is discussed, emphasizing the low weight and low power consumption of the instrument. An instrument design and sample handling system are presented that make optimal use of the capabilities of this instrument. ORIGIN is a highly versatile instrument with proven capabilities to investigate and potentially resolve many of the outstanding questions about the atmosphere of Venus and the presence of life in its clouds. Full article
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17 pages, 4975 KiB  
Article
Probabilistic Risk Assessment in Space Launches Using Bayesian Network with Fuzzy Method
by Xing Pan, Song Ding, Wenjin Zhang, Tun Liu, Liqin Wang and Lijing Wang
Aerospace 2022, 9(6), 311; https://doi.org/10.3390/aerospace9060311 - 09 Jun 2022
Cited by 5 | Viewed by 2573
Abstract
Space launch projects are extremely risky, and any equipment failure or human error may lead to disastrous consequences. Probabilistic risk assessment (PRA) is beneficial to qualitative analysis of risk, but it has not been paid enough attention in risk analysis for space launch [...] Read more.
Space launch projects are extremely risky, and any equipment failure or human error may lead to disastrous consequences. Probabilistic risk assessment (PRA) is beneficial to qualitative analysis of risk, but it has not been paid enough attention in risk analysis for space launch systems (SLSs). Compared with most qualitative risk analysis in this field, this paper proposes a risk analysis framework based on Bayesian network (BN) with fuzzy method, which is suitable for probabilistic risk analysis of SLS. This method establishes a risk analysis model of SLS based on statistics and expert experience and reduces the uncertainty of the model by using fuzzy theory. By predicting the system risk probabilities, diagnosing the key risk causes, determining the risk conduction path, and performing a sensitivity analysis, the proposed risk analysis framework is aimed at alleviating this drawback to deal more effectively with the uncertainties in the field of space launches. A case study of space launches demonstrates and verifies the proposed method, and it also provides guidance for similar engineering projects. Full article
(This article belongs to the Section Astronautics & Space Science)
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22 pages, 929 KiB  
Article
Sound-Quality-Based Decision Making in Multiobjective Optimisation of Operations for Sustainable Airport Scenarios
by Umberto Iemma and Francesco Centracchio
Aerospace 2022, 9(6), 310; https://doi.org/10.3390/aerospace9060310 - 08 Jun 2022
Cited by 4 | Viewed by 1578
Abstract
The paper deals with a community-oriented approach to the multiobjective optimisation of sustainable takeoff and landing procedures of commercial aircraft. The objective functions to be minimised are defined as the measure of area surrounding the airport where the Sound Exposure Level (SEL) is [...] Read more.
The paper deals with a community-oriented approach to the multiobjective optimisation of sustainable takeoff and landing procedures of commercial aircraft. The objective functions to be minimised are defined as the measure of area surrounding the airport where the Sound Exposure Level (SEL) is higher than 60 dBA, and the amount of fuel burned during the procedure. The first merit factor is a measure of the number of citizens affected by a potentially harmful noise level, whereas the second is proportional to the chemical emissions. The novelty of the present approach is the use of a criterion based on sound quality for the selection of the optimal procedure from the Pareto front set. The spectrum of the noise produced by each non-dominated solution is compared to a reference spectrum, the target sound. This is synthesised to meet the acceptance requirements that emerged by a campaign of psychometric tests. The rationale underlying the research is tightly linked to the expected transformation of civil aviation, with the advent of new air transport solutions in urban and suburban environments. The breakthrough nature of the emerging scenarios requires a drastic renewal of the approaches used in the management of operations, and the present work represents a contribution to this evolution. The optimisation is attained adopting a global, deterministic method, and numerical results are obtained for single- and twin-aisle aircraft. Full article
(This article belongs to the Special Issue Aircraft Noise)
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16 pages, 897 KiB  
Article
Remaining Useful Life Estimation of Cooling Units via Time-Frequency Health Indicators with Machine Learning
by Raúl Llasag Rosero, Catarina Silva and Bernardete Ribeiro
Aerospace 2022, 9(6), 309; https://doi.org/10.3390/aerospace9060309 - 08 Jun 2022
Cited by 5 | Viewed by 2530
Abstract
Predictive Maintenance (PM) strategies have gained interest in the aviation industry to reduce maintenance costs and Aircraft On Ground (AOG) time. Taking advantage of condition monitoring data from aircraft systems, Prognostics and Health Maintenance (PHM) practitioners have been predicting the life span of [...] Read more.
Predictive Maintenance (PM) strategies have gained interest in the aviation industry to reduce maintenance costs and Aircraft On Ground (AOG) time. Taking advantage of condition monitoring data from aircraft systems, Prognostics and Health Maintenance (PHM) practitioners have been predicting the life span of aircraft components by applying Remaining Useful Life (RUL) concepts. Additionally, in prognostics, the construction of Health Indicators (HIs) plays a significant role when failure advent patterns are strenuous to be discovered directly from data. HIs are typically supported by data-driven models dealing with non-stationary signals, e.g., aircraft sensor time-series, in which data transformations from time and frequency domains are required. In this paper, we build time-frequency HIs based on the construction of the Hilbert spectrum and propose the integration of a physics-based model with a data-driven model to predict the RUL of aircraft cooling units. Using data from a major airline, and considering two health degradation stages, the advent of failures on aircraft systems can be estimated with data-driven Machine Learning models (ML). Specifically, our results reveal that the analyzed cooling units experience a normal degradation stage before an abnormal degradation that emerges within the last flight hours of useful life. Full article
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19 pages, 4856 KiB  
Article
Recognition of the Airspace Affected by the Presence of Volcanic Ash from Popocatepetl Volcano Using Historical Satellite Images
by José Carlos Jiménez-Escalona, José Luis Poom-Medina, Julie Roberge, Ramon S. Aparicio-García, José Eduardo Avila-Razo, Oliver Marcel Huerta-Chavez and Rodrigo Florencio Da Silva
Aerospace 2022, 9(6), 308; https://doi.org/10.3390/aerospace9060308 - 07 Jun 2022
Cited by 2 | Viewed by 2159
Abstract
A volcanic eruption can produce large ash clouds in the atmosphere around a volcano, affecting commercial aviation use of the airspace around the volcano. Encountering these ash clouds can cause severe damage to different parts of the aircraft, mainly the engines. This work [...] Read more.
A volcanic eruption can produce large ash clouds in the atmosphere around a volcano, affecting commercial aviation use of the airspace around the volcano. Encountering these ash clouds can cause severe damage to different parts of the aircraft, mainly the engines. This work seeks to contribute to the development of methods for observing the dispersion of volcanic ash and to complement computational methods that are currently used for the prediction of ash dispersion. The method presented here is based on the frequency of occurrence of the regions of airspace areas affected by ash emission during a volcanic eruption. Popocatepetl volcano, 60 km east of Mexico City is taken as a case study. A temporal wind analysis was carried out at different atmospheric levels, to identify the direction towards which the wind disperses ash at different times of the year. This information showed two different trends, related to seasons in the direction of dispersion: the first from November to May and the second from July to September. To identify the ash cloud and estimate its area, a set of 920 MODIS images that recorded Popocatepetl volcanic activity between 2000 and 2021 was used. These satellite images were subjected to a semi-automatic, digital pre-processing of binarization by thresholds, according to the level of the brightness temperature difference between band 31 (11 µm) and band 32 (12 µm), followed by manual evaluation of each binarized image. With the information obtained by the processing of the MODIS image, an information table was built with the geographical position of each pixel characterized by the presence of ash for each event. With these data, the areas around Popocatepetl volcano with the highest frequency of affectation by ash emissions were identified during the period analyzed. This study seeks to complement the results obtained by numerical models that make forecasts of ash dispersions and that are very important for the prevention of air navigation risks. Full article
(This article belongs to the Special Issue Application of Data Science to Aviation II)
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30 pages, 11806 KiB  
Article
Study on the Characteristics of Boundary Layer Flow under the Influence of Surface Microstructure
by Hongqing Lv, Shan Liu, Jiahao Chen and Baoli Li
Aerospace 2022, 9(6), 307; https://doi.org/10.3390/aerospace9060307 - 03 Jun 2022
Viewed by 1795
Abstract
The energy consumption of a vehicle is closely related to the resistance it receives, and it is of great significance to study the drag reduction of a vehicle to promote energy conservation and emissions reductions. Boundary layer control drag reduction is mainly achieved [...] Read more.
The energy consumption of a vehicle is closely related to the resistance it receives, and it is of great significance to study the drag reduction of a vehicle to promote energy conservation and emissions reductions. Boundary layer control drag reduction is mainly achieved by controlling the coherent structure in turbulence and reducing its burst intensity and frequency. It can be divided into an active control drag reduction and passive control drag reduction. In passive drag reduction, the advantages of the surface groove drag reduction are relatively obvious. In this paper, the large eddy simulation method is used to study the boundary layer flow with triangular groove and rectangular groove plates along the flow direction under subsonic flow, and to explore the influence of a surface micro-groove structure on the boundary layer flow. The simulation results show that the fluid inside the groove can be blocked by the triangular groove which can keep the low-velocity fluid at the bottom of the groove, and that it can increase the thickness of the viscous bottom layer as well as reduce the velocity gradient at the wall. The spanwise stress component of the Reynolds stress in the triangular groove boundary layer and the burst of turbulence on the wall are inhibited, and the spanwise flow in the boundary layer is blocked. In the subsonic range, about 10% shear force can be reduced because there are secondary vortices induced by the upper flow vortices at the top of the groove wall, and these secondary vortices can restrain the rising of the low-speed strip in the groove and reduce the burst of turbulence. The rectangular groove creates a weak blocking effect on the fluid inside the groove, which can only inhibit spanwise pulsation under subsonic speed. The wall shear stress cannot be reduced when the flow velocity is low, and it even increases. Full article
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21 pages, 7893 KiB  
Article
Mars Exploration Using Sailplanes
by Adrien Bouskela, Alexandre Kling, Tristan Schuler, Sergey Shkarayev, Himangshu Kalita and Jekan Thangavelautham
Aerospace 2022, 9(6), 306; https://doi.org/10.3390/aerospace9060306 - 03 Jun 2022
Cited by 2 | Viewed by 13738
Abstract
We present the preliminary design of sailplanes, used for Mars exploration. The sailplanes mitigate the weight and energy storage limitations traditionally associated with powered flight by instead exploiting atmospheric wind gradients for dynamic soaring, and slope/thermal updrafts for static soaring. Equations of motion [...] Read more.
We present the preliminary design of sailplanes, used for Mars exploration. The sailplanes mitigate the weight and energy storage limitations traditionally associated with powered flight by instead exploiting atmospheric wind gradients for dynamic soaring, and slope/thermal updrafts for static soaring. Equations of motion for the sailplanes were combined with wind profiles from the Mars Regional Atmospheric Modeling System (MRAMS) for two representative sites: Jezero crater, Perseverance’s landing site, and over a section of the Valles Marineris canyon. Optimal flight trajectories were obtained from the constrained optimization problem, using the lift coefficient and the roll angle as control parameters. Numerical results for complete dynamic soaring cycles demonstrated that the total sailplane energy at the end of a soaring cycle increases by 6.8–11%. The absence of a propulsion system, allowing for a compact form factor, means the sailplanes can be packaged into CubeSats and deployed as secondary payloads at a relatively low cost; providing scientific data over locations inaccessible by current landers and rovers. Various sailplane deployment methods are considered, including rapid deployment during Entry, Descent, and Landing (EDL) of a Mars Science Laboratory-class (MSL) vehicle and slow deployment using a blimp. Full article
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20 pages, 13785 KiB  
Article
Lifetime Extension of Ultra Low-Altitude Lunar Spacecraft with Low-Thrust Propulsion System
by Jingxi Liu, Bo Xu, Chengzhang Li and Muzi Li
Aerospace 2022, 9(6), 305; https://doi.org/10.3390/aerospace9060305 - 03 Jun 2022
Cited by 2 | Viewed by 1782
Abstract
Due to the non-spherical perturbation of the Moon, the lifetime of ultra low-altitude Lunar spacecraft may be quite short. In this paper, we analyze the lifetime of about 50 km-altitude Lunar spacecraft with different initial orbit. The lifetime in low inclination orbits is [...] Read more.
Due to the non-spherical perturbation of the Moon, the lifetime of ultra low-altitude Lunar spacecraft may be quite short. In this paper, we analyze the lifetime of about 50 km-altitude Lunar spacecraft with different initial orbit. The lifetime in low inclination orbits is much shorter than the ones in the near polar orbits. To extend the lifetime and keep the spacecraft in an appropriate range, an orbit maintenance strategy based on low-thrust propulsion system is proposed. The influence of the orbit initial conditions (e.g., semi-major axis, inclination, right ascension of the ascending node) on lifetime extension are discussed and the effect of the low-thrust magnitude in orbit maintenance is analyzed. According to the numerical simulation results, the lifetime of about 50 km-altitude 100 kg Lunar spacecraft with 10 kg fuel and 20 mN thruster can be extended from 7.958 days to over a 109.1725 days, which demonstrates the effectiveness of the strategy. Furthermore, a global perspective for ultra low-altitude Lunar spacecraft lifetime extension problem is provided in this paper, which can be applied to Moon mission designs extensively. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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15 pages, 2594 KiB  
Article
Fault-Tolerant Control for Hexacopter UAV Using Adaptive Algorithm with Severe Faults
by Ngoc Phi Nguyen, Nguyen Xuan Mung, Le Nhu Ngoc Thanh Ha and Sung Kyung Hong
Aerospace 2022, 9(6), 304; https://doi.org/10.3390/aerospace9060304 - 03 Jun 2022
Cited by 7 | Viewed by 2338
Abstract
In this paper, a fault-tolerant control method is proposed for a hexacopter under uncertainties. The proposed method is based on adaptive-sliding-mode control (ASMC) and a control allocation scheme. First, a mathematical model of the hexacopter is employed with model uncertainties. Next, the control [...] Read more.
In this paper, a fault-tolerant control method is proposed for a hexacopter under uncertainties. The proposed method is based on adaptive-sliding-mode control (ASMC) and a control allocation scheme. First, a mathematical model of the hexacopter is employed with model uncertainties. Next, the control allocation strategy is combined with ASMC to handle actuator faults, which can distribute the virtual control signal to redundant actuators. A modified fault-tolerant control is proposed to overcome this virtual input saturation. Finally, the system stability is validated using the Lyapunov theory. The performance of the proposed method is compared with that of normal ASMC. The simulation results show that the suggested strategy can realize quicker compensation under faulty conditions. Full article
(This article belongs to the Special Issue Applications of Drones)
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25 pages, 6828 KiB  
Article
Attitude Maneuver and Stability Control of Hyper-Agile Satellite Using Reconfigurable Control Moment Gyros
by Zhi Qu, Gaofei Zhang, Ziyang Meng, Kai Xu, Ruiqin Xu and Jiaojiao Di
Aerospace 2022, 9(6), 303; https://doi.org/10.3390/aerospace9060303 - 03 Jun 2022
Cited by 3 | Viewed by 2071
Abstract
Addressing the problems of insurmountable unknown frictional disturbance and balancing the trade-off between high maneuverability and stability during attitude maneuver are important in low-cost miniaturized single control moment gyro clusters (SGCMGs) for hyper-agile satellite. This paper proposes a new concept of reconfigurable octagonal [...] Read more.
Addressing the problems of insurmountable unknown frictional disturbance and balancing the trade-off between high maneuverability and stability during attitude maneuver are important in low-cost miniaturized single control moment gyro clusters (SGCMGs) for hyper-agile satellite. This paper proposes a new concept of reconfigurable octagonal cone-type SGCMGs by considering practical engineering requirements of hyper-agile satellites. Firstly, the momentum characteristics of typical configurations are quantitatively explained, and the evaluation metrics for SGCMGs based on norm L and norm L2 are defined, respectively. Secondly, a reconfiguration design of SGCMGs from octagonal cone-type into pyramid-type is proposed by analyzing the unknown disturbance mechanism based on SGCMGs. When the hyper-agile satellite is supported to perform fast attitude maneuvers, all units of SGCMGs can work together to output rough and large torque. On the other hand, when the maneuvering ends with stable pointing control, gimbles of one pyramid-type SGCMGs are locked down and fine torque is outputted using another pyramid-type SGCMGs. This will greatly reduce the difficulty of controller design and improve the satellite attitude performance indices. The superiority of the control strategy and selection of the proposed actuator is verified by experiments. Full article
(This article belongs to the Special Issue Recent Advances in Spacecraft Dynamics and Control)
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21 pages, 4286 KiB  
Article
Congestion Recognition of the Air Traffic Control Sector Based on Deep Active Learning
by Xianghua Tan, Yushi Sun, Weili Zeng and Zhibin Quan
Aerospace 2022, 9(6), 302; https://doi.org/10.3390/aerospace9060302 - 02 Jun 2022
Cited by 5 | Viewed by 1864
Abstract
The air traffic control sector (ATCS) is the basic unit of the airspace system. If we can identify the congestion of an ATCS, it will help provide decision support for planning and daily operations. However, current methods mainly characterize congestion from the static [...] Read more.
The air traffic control sector (ATCS) is the basic unit of the airspace system. If we can identify the congestion of an ATCS, it will help provide decision support for planning and daily operations. However, current methods mainly characterize congestion from the static structure and the dynamic operational features, resulting in poor generalization and operability. To this end, we propose a deep learning method from the perspective of complex networks. It takes aircraft as nodes to construct an aircraft network and utilizes the complexity indices to characterize it. So, the problem of identifying congestion becomes the complexity of the aircraft network. Inspired by active learning methods, we construct a deep active learning (DAL) model for congestion recognition. It adopts an iterative semi-supervised approach to reduce the number of labeled samples while ensuring recognition performance. To make full use of a large number of unlabeled samples, the sparse autoencoder is employed to characterize all labeled samples and unlabeled samples. The hidden layer of the deep neural network is constructed by stacking. In the process of active learning iteration, minimum confidence, marginal sampling, and information entropy are introduced as measures to select samples from the unlabeled sample set with significantly different features from the labeled sample set. The model is applied to three representative sectors in China’s airspace as cases. Results suggest that DAL can reduce the labeled sample set’s redundancy and achieve the desired performance with the smallest number of samples. Additionally, DAL is superior to the existing mainstream methods in the four objective evaluation indices. Full article
(This article belongs to the Section Air Traffic and Transportation)
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