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Aerospace, Volume 10, Issue 12 (December 2023) – 61 articles

Cover Story (view full-size image): Civil aircraft engine design trends are currently focused on improving the overall efficiency by increasing the operating pressure ratio (OPR) and the turbine inlet temperature (TIT). This reduces the amount of fuel burn, and, hence, CO2 emissions, but increases NOx and non-volatile particulate (nvPM) emissions. This study investigates the overall impact of engine core design trends on the climate, considering the effects of CO2, NOx, nvPM, and water vapor. A subset of A320 flights over Europe and North America was selected. The analysis shows an increasing climate impact trend (namely, an increasing average temperature response over 100 years) with an increase in the OPR. The impact is dominated by contrails, due to the flights’ geographical location and altitude. View this paper
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23 pages, 8697 KiB  
Article
The Effect of Torsional and Bending Stiffness on the Aerodynamic Performance of Flapping Wing
Aerospace 2023, 10(12), 1035; https://doi.org/10.3390/aerospace10121035 - 15 Dec 2023
Cited by 1 | Viewed by 879
Abstract
For large bird-like flapping wing aircraft, the fluid–structure coupling problem is very important. Through the passive torsional deformation of the wing, sufficient thrust is generated and propulsion efficiency is ensured. Moreover, spanwise bending deformation will affect lift and thrust. The flow field on [...] Read more.
For large bird-like flapping wing aircraft, the fluid–structure coupling problem is very important. Through the passive torsional deformation of the wing, sufficient thrust is generated and propulsion efficiency is ensured. Moreover, spanwise bending deformation will affect lift and thrust. The flow field on the surface of the wing and the geometric nonlinearity caused by the large deformation of the wing should be considered during the design process. Existing research methods do not solve this problem accurately and efficiently. This paper provides a method to analyze the fluid–structure coupling problem of the flapping wing which adopts the three-dimensional unsteady panel method to solve the aerodynamic force, and adopts the linear beam element model combined with the corotational formulation method to consider the geometric nonlinear deformation of the wing beam. This article compares the performance of the flapping wing with different torsional and bending stiffness, and analyzes the airfoil surface pressure coefficients at different portions of the wing during the period. The results show that torsional stiffness has a large influence on the lift coefficient, thrust coefficient and propulsion efficiency. Meanwhile, the torsional stiffness of the wing beam and the initial geometric twist angle of the wing need to be well coordinated to achieve high efficiency. Moreover, appropriate bending stiffness of the wing is conducive to improving propulsion efficiency. Full article
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23 pages, 8756 KiB  
Article
The Solar Particle Acceleration Radiation and Kinetics (SPARK) Mission Concept
Aerospace 2023, 10(12), 1034; https://doi.org/10.3390/aerospace10121034 - 15 Dec 2023
Cited by 1 | Viewed by 1146
Abstract
Particle acceleration is a fundamental process arising in many astrophysical objects, including active galactic nuclei, black holes, neutron stars, gamma-ray bursts, accretion disks, solar and stellar coronae, and planetary magnetospheres. Its ubiquity means energetic particles permeate the Universe and influence the conditions for [...] Read more.
Particle acceleration is a fundamental process arising in many astrophysical objects, including active galactic nuclei, black holes, neutron stars, gamma-ray bursts, accretion disks, solar and stellar coronae, and planetary magnetospheres. Its ubiquity means energetic particles permeate the Universe and influence the conditions for the emergence and continuation of life. In our solar system, the Sun is the most energetic particle accelerator, and its proximity makes it a unique laboratory in which to explore astrophysical particle acceleration. However, despite its importance, the physics underlying solar particle acceleration remain poorly understood. The SPARK mission will reveal new discoveries about particle acceleration through a uniquely powerful and complete combination of γ-ray, X-ray, and EUV imaging and spectroscopy at high spectral, spatial, and temporal resolutions. SPARK’s instruments will provide a step change in observational capability, enabling fundamental breakthroughs in our understanding of solar particle acceleration and the phenomena associated with it, such as the evolution of solar eruptive events. By providing essential diagnostics of the processes that drive the onset and evolution of solar flares and coronal mass ejections, SPARK will elucidate the underlying physics of space weather events that can damage satellites and power grids, disrupt telecommunications and GPS navigation, and endanger astronauts in space. The prediction of such events and the mitigation of their potential impacts are crucial in protecting our terrestrial and space-based infrastructure. Full article
(This article belongs to the Special Issue Space Telescopes & Payloads)
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23 pages, 8145 KiB  
Article
Numerical Investigation of Transverse-Jet-Assisted Initiation of Oblique Detonation Waves in a Combustor
Aerospace 2023, 10(12), 1033; https://doi.org/10.3390/aerospace10121033 - 14 Dec 2023
Viewed by 801
Abstract
Detonation initiation is a prerequisite to normal operations of an oblique detonation engine (ODE), and initiation-assistant measures are imperative in cases of initiation failure that occur in a length-limited combustor under wide-range flight conditions. This study numerically investigates the initiation characteristics of oblique [...] Read more.
Detonation initiation is a prerequisite to normal operations of an oblique detonation engine (ODE), and initiation-assistant measures are imperative in cases of initiation failure that occur in a length-limited combustor under wide-range flight conditions. This study numerically investigates the initiation characteristics of oblique detonation waves (ODWs) in H2-fueled ODE combustors at wide-range flight Mach numbers Maf or flight altitudes Hf. Failures of ODW initiation are observed at both low Maf and high Hf if no measure is taken to assist initiation. Through analyses of the flow fields and theoretical predictions of the ignition induction length Lind, the data reveal that the detonation failure at low Maf is raised by the significant decrease in the post-shock temperature due to insufficient shock compression, leading to a significant increase in Lind. The detonation failure at high Hf is caused by the rapid decrease in the combustor inflow pressure as Hf increases, which also results in an increase in Lind. With further identifications of the key flow structures crucial to detonation initiation, an initiation-assistant concept employing a transverse H2 jet is proposed. The simulation results show that through an interaction between the incident oblique shock wave and the jet shock wave, the transverse jet helps to initiate an ODW in the combustor at a low Maf, and the initiation location is relatively fixed and determined by the jet location. At high Hf, a Mach reflection pattern is formed in the combustor under the effects of the transverse jet, and detonative combustion is achieved by the generated Mach stem and its reflected shock waves. The proposed concept of using transverse jets to assist detonation initiation provides a practical reference for future development of ODEs that are expected to operate under wide-range flight conditions. Full article
(This article belongs to the Special Issue Advances in Detonative Propulsion)
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17 pages, 1740 KiB  
Article
Makespan-Minimizing Heterogeneous Task Allocation under Temporal Constraints
Aerospace 2023, 10(12), 1032; https://doi.org/10.3390/aerospace10121032 - 14 Dec 2023
Viewed by 710
Abstract
Task allocation is an essential element for determining the capability of multi-UAV systems to perform various tasks. This paper presents a procedure called a “rebalancing algorithm” for generating task-performing routes in heterogeneous multi-UAV systems. The algorithm adopts a greedy-based heuristic approach to find [...] Read more.
Task allocation is an essential element for determining the capability of multi-UAV systems to perform various tasks. This paper presents a procedure called a “rebalancing algorithm” for generating task-performing routes in heterogeneous multi-UAV systems. The algorithm adopts a greedy-based heuristic approach to find solutions efficiently in dynamically changing environments. A novel variable named “loitering” is introduced to satisfy temporal constraints, resulting in improved performance compared to heuristic algorithms: a sequential greedy algorithm, a genetic algorithm, and simulated annealing. The rebalancing algorithm is divided into two phases to minimize the makespan, i.e., the initial allocation and reallocation phases. Simulation results demonstrate the proposed algorithm’s effectiveness in highly constrained conditions and its suitability for heterogeneous systems. Additionally, the results show a reduction in calculation time and improved performance compared to the heuristic algorithms. Full article
(This article belongs to the Collection Unmanned Aerial Systems)
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26 pages, 2404 KiB  
Article
Integrating Flight Scheduling, Fleet Assignment, and Aircraft Routing Problems with Codesharing Agreements under Stochastic Environment
Aerospace 2023, 10(12), 1031; https://doi.org/10.3390/aerospace10121031 - 14 Dec 2023
Viewed by 733
Abstract
Airlines face the imperative of resource management to curtail costs, necessitating the solution of several optimization problems such as flight planning, fleet assignment, aircraft routing, and crew scheduling. These problems present some challenges. The first pertains to the common practice of addressing these [...] Read more.
Airlines face the imperative of resource management to curtail costs, necessitating the solution of several optimization problems such as flight planning, fleet assignment, aircraft routing, and crew scheduling. These problems present some challenges. The first pertains to the common practice of addressing these problems independently, potentially leading to locally optimal outcomes due to their interconnected nature. The second challenge lies in the inherent uncertainty associated with parameters like demand and non-cruise time. On the other hand, airlines can employ a strategy known as codesharing, wherein they operate shared flights, in order to minimize these challenges. In this study, we introduce a novel mathematical model designed to optimize flight planning, fleet assignment, and aircraft routing decisions concurrently, while accommodating for codesharing. This model is formulated as a three-stage non-linear mixed-integer problem, with stochastic parameters representing the demand and non-cruise time. For smaller-scale problems, optimization software can effectively solve the model. However, as the number of flights increases, conventional software becomes inadequate. Moreover, considering a wide array of scenarios for stochastic parameters leads to more robust results; however, it is not enabled because of the limitations of optimization software. In this work, we introduce two new simulation-based metaheuristic algorithms for solving large-dimensional problems, collectively called “simheuristic.” These algorithms integrate the Monte Carlo simulation technique into Simulated Annealing and Cuckoo Search. We have applied these simheuristic algorithms to various problem samples of different flight sizes and scenarios. The results demonstrate the efficacy of our proposed modeling and solution approaches in efficiently addressing flight scheduling, fleet assignment, and aircraft routing problems within acceptable timeframes. Full article
(This article belongs to the Collection Air Transportation—Operations and Management)
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22 pages, 6248 KiB  
Article
Design of a Mars Ascent Vehicle Using HyImpulse’s Hybrid Propulsion
Aerospace 2023, 10(12), 1030; https://doi.org/10.3390/aerospace10121030 - 14 Dec 2023
Viewed by 849
Abstract
The recent growth in maturity of paraffin-based hybrid propulsion systems reassesses the possibility to design an alternative Mars Ascent Vehicle (MAV) propelled by a European hybrid motor. As part of the Mars Sample Return (MSR) campaign, a Hybrid MAV would present potential advantages [...] Read more.
The recent growth in maturity of paraffin-based hybrid propulsion systems reassesses the possibility to design an alternative Mars Ascent Vehicle (MAV) propelled by a European hybrid motor. As part of the Mars Sample Return (MSR) campaign, a Hybrid MAV would present potential advantages over the existent solid concept funded by NASA through offering increased performance, higher thermal resilience, and lower Gross Lift-Off Mass (GLOM). This study looks at the preliminary design of a two-stage European MAV equipped with HyImpulse’s hybrid engine called the Hyplox10. This Hybrid MAV utilizes the advantages inherent to this type of propulsion to propose an alternative MAV concept. After a careful analysis of previous MAV architectures from the literature, the vehicle is sized with all its components such as the propellant tanks and nozzle, and the configuration of the rocket is established. A detailed design of the primary structure is addressed. This is followed by a Finite Element Analysis (FEA), evaluating the structural integrity under the challenging conditions of Entry, Descent, and Landing (EDL) on Mars, considering both static and dynamic analyses. The outcome is a Hybrid MAV design that demonstrates feasibility and resilience in the harsh Martian environment, boasting a GLOM of less than 300 kg. Full article
(This article belongs to the Special Issue Space Systems Preliminary Design)
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21 pages, 8451 KiB  
Article
Prediction of Transonic Flow over Cascades via Graph Embedding Methods on Large-Scale Point Clouds
Aerospace 2023, 10(12), 1029; https://doi.org/10.3390/aerospace10121029 - 14 Dec 2023
Viewed by 712
Abstract
In this research, we introduce a deep-learning-based framework designed for the prediction of transonic flow through a linear cascade utilizing large-scale point-cloud data. In our experimental cases, the predictions demonstrate a nearly four-fold speed improvement compared to traditional CFD calculations while maintaining a [...] Read more.
In this research, we introduce a deep-learning-based framework designed for the prediction of transonic flow through a linear cascade utilizing large-scale point-cloud data. In our experimental cases, the predictions demonstrate a nearly four-fold speed improvement compared to traditional CFD calculations while maintaining a commendable level of accuracy. Taking advantage of a multilayer graph structure, the framework can extract both global and local information from the cascade flow field simultaneously and present prediction over unstructured data. In line with the results obtained from the test datasets, we conducted an in-depth analysis of the geometric attributes of the cascades reconstructed using our framework, considering adjustments made to the geometric information of the point cloud. We fine-tuned the input using 1603 data points and quantified the contribution of each point. The outcomes reveal that variations in the suction side of the cascade have a significantly more substantial influence on the field results compared to the pressure side and explain the way graph neural networks work for cascade flow-field prediction, enhancing the comprehension of graph-based flow-field prediction among developers and proves the potential of graph neural networks in flow-field prediction on large-scale point clouds and design. Full article
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13 pages, 1422 KiB  
Article
Optical Design of a Miniaturised Solar Magnetograph for Space Applications
Aerospace 2023, 10(12), 1028; https://doi.org/10.3390/aerospace10121028 - 13 Dec 2023
Viewed by 833
Abstract
Measuring the Sun’s magnetic field is a key component of monitoring solar activity and forecasting space weather. The main goal of the research presented in this paper is to investigate the possibility of reducing the dimensions and weight of a solar magnetograph while [...] Read more.
Measuring the Sun’s magnetic field is a key component of monitoring solar activity and forecasting space weather. The main goal of the research presented in this paper is to investigate the possibility of reducing the dimensions and weight of a solar magnetograph while preserving its optical quality. This article presents a range of different designs, along with their advantages and disadvantages, and an analysis of the optical performance of each. All proposed designs are based on the magneto-optical filter (MOF) technique. As a result of the design study, a miniaturised solar magnetograph is proposed with an ultra-compact layout. The dimensions are 345 mm × 54 mm × 54 mm, and the optical quality is almost at the diffraction limit. The design has an entrance focal ratio of F/17.65, with a plate scale of 83.58 arcsec/mm at the telescope image focal plane, and produces a magnification of 0.79. The field of view is 1920 arcsec in diameter, equivalent to ±0.27 degrees, sufficient to cover the entire solar disk. Full article
(This article belongs to the Special Issue Space Telescopes & Payloads)
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21 pages, 1286 KiB  
Article
Simplified Maneuvering Strategies for Rendezvous in Near-Circular Earth Orbits
Aerospace 2023, 10(12), 1027; https://doi.org/10.3390/aerospace10121027 - 12 Dec 2023
Viewed by 765
Abstract
The development of autonomous guidance control and navigation systems for spacecraft would greatly benefit applications such as debris removals or on-orbit servicing, where human intervention is not practical. Within this context, inspired by Autonomous Vision Approach Navigation and Target Identification (AVANTI) demonstration, this [...] Read more.
The development of autonomous guidance control and navigation systems for spacecraft would greatly benefit applications such as debris removals or on-orbit servicing, where human intervention is not practical. Within this context, inspired by Autonomous Vision Approach Navigation and Target Identification (AVANTI) demonstration, this work presents new guidance algorithms for rendezvous and proximity operations missions. Analytical laws are adopted and preferred over numerical methods, and mean relative orbital elements are chosen as state variables. Application times, magnitudes and directions of impulsive controls are sought to minimize propellant consumption for the planar reconfiguration of the relative motion between a passive target spacecraft and an active chaser one. In addition, simple and effective algorithms to evaluate the benefit of combining in-plane and out-of-plane maneuvers are introduced to deal with 3D problems. The proposed new strategies focus on maneuvers with a dominant change in the relative mean longitude (rarely addressed in the literature), but they can also deal with transfers where other relative orbital elements exhibit the most significant variations. A comprehensive parametric analysis compares the proposed new strategies with those employed in AVANTI and with the global optimum, numerically found for each test case. Results are similar to the AVANTI solutions when variations of the relative eccentricity vector dominate. Instead, in scenarios requiring predominant changes in the relative mean longitude, the required ΔV exhibits a 49.88% reduction (on average) when compared to the original methods. In all the test cases, the proposed solutions are within 3.5% of the global optimum in terms of ΔV. The practical accuracy of the presented guidance algorithms is also tested with numerical integration of equations of motion with J2 perturbation. Full article
(This article belongs to the Special Issue Space Trajectory Planning)
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17 pages, 7879 KiB  
Article
A Dual Perspective on Geostationary Satellite Monitoring Using DSLR RGB and sCMOS Sloan Filters
Aerospace 2023, 10(12), 1026; https://doi.org/10.3390/aerospace10121026 - 12 Dec 2023
Viewed by 783
Abstract
This paper outlines a multi-system approach for ground-based optical observations and the characterization of satellites in geostationary orbit. This multi-system approach is based on an in-depth analysis of the key factors to consider for light curve analysis of Earth’s orbiting satellites. Light curves [...] Read more.
This paper outlines a multi-system approach for ground-based optical observations and the characterization of satellites in geostationary orbit. This multi-system approach is based on an in-depth analysis of the key factors to consider for light curve analysis of Earth’s orbiting satellites. Light curves have been observed in different spectral bands using two different systems. The first system is specialized for astronomical observations and consists of a telescope equipped with an sCMOS camera and Sloan photometric filters. In contrast, the second system is a more cost-effective solution designed for professional non-astronomical applications, incorporating DSLR cameras equipped with RGB channels associated with a Bayer mask and photographic lenses. This comparative analysis aims to highlight the differences and advantages provided by each system, stressing their respective performance characteristics. The observed light curves will be presented as a function of the phase angle, which depends on the relative positions of the observer, the object, and the Sun. This angle plays an important role in optimizing the visibility of Earth’s orbiting satellites. Finally, multiband observations of different satellites will be compared to seek an associated spectral signature, which may allow the identification of structurally similar objects through optical observations. Full article
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51 pages, 4160 KiB  
Review
On Topology Optimisation Methods and Additive Manufacture for Satellite Structures: A Review
Aerospace 2023, 10(12), 1025; https://doi.org/10.3390/aerospace10121025 - 11 Dec 2023
Cited by 1 | Viewed by 1316
Abstract
Launching satellites into the Earth’s orbit is a critical area of research, and very demanding satellite services increase exponentially as modern society takes shape. At the same time, the costs of developing and launching satellite missions with shorter development times increase the requirements [...] Read more.
Launching satellites into the Earth’s orbit is a critical area of research, and very demanding satellite services increase exponentially as modern society takes shape. At the same time, the costs of developing and launching satellite missions with shorter development times increase the requirements of novel approaches in the several engineering areas required to build, test, launch, and operate satellites in the Earth’s orbit, as well as in orbits around other celestial bodies. One area with the potential to save launching costs is that of the structural integrity of satellites, particularly in the launching phase where the largest vibrations due to the rocket motion and subsequent stresses could impact the survival ability of the satellite. To address this problem, two important areas of engineering join together to provide novel, complete, and competitive solutions: topology optimisation methods and additive manufacturing. On one side, topology optimisation methods are mathematical methods that allow iteratively optimising structures (usually by decreasing mass) while improving some structural properties depending on the application (load capacity, for instance), through the maximisation or minimisation of a uni- or multi-objective function and multiple types of algorithms. This area has been widely active in general for the last 30 years and has two main core types of algorithms: continuum methods that modify continuous parameters such as density, and discrete methods that work by adding and deleting material elements in a meshing context. On the other side, additive manufacturing techniques are more recent manufacturing processes aimed at revolutionising manufacturing and supply chains. The main exponents of additive manufacturing are Selective Laser Melting (SLM) (3D printing) as well as Electron Beam Melting (EBM). Recent trends show that topology-optimised structures built with novel materials through additive manufacturing processes may provide cheaper state-of-the-art structures that are fully optimised to better perform in the outer-space environment, particularly as part of the structure subsystem of novel satellite systems. This work aims to present an extended review of the main methods of structural topology optimisation as well as additive manufacture in the aerospace field, with a particular focus on satellite structures, which may set the arena for the development of future satellite structures in the next five to ten years. Full article
(This article belongs to the Special Issue Space Systems Preliminary Design)
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14 pages, 2533 KiB  
Article
An Improved Fault Detection and Isolation Method for Airborne Inertial Navigation System/Attitude and Heading Reference System Redundant System
Aerospace 2023, 10(12), 1024; https://doi.org/10.3390/aerospace10121024 - 11 Dec 2023
Viewed by 1011
Abstract
The integrity of airborne inertial navigation systems (INSs) is the key to ensuring the safe flight of civil aircraft. The airborne attitude and heading reference system (AHRS) is introduced into the construction of a redundant inertial navigation system. As a backup system for [...] Read more.
The integrity of airborne inertial navigation systems (INSs) is the key to ensuring the safe flight of civil aircraft. The airborne attitude and heading reference system (AHRS) is introduced into the construction of a redundant inertial navigation system. As a backup system for an airborne INS, the AHRS exhibits a different device performance. A sequential weighted generalized likelihood ratio test (SWGLT) method, based on a principal component parity vector (PPV), is proposed. The PPV method improves the adaptability of the detection threshold to the inertial sensors’ noise and improves the probability of correct detection. At the same time, the multiscale problem of a heterogeneous redundant system error is solved by sequential weighting, and the false alarm rate is reduced. Simulation experiments show that the proposed method can improve fault detection sensitivity, reduce false alarm rates, and ensure the integrity of civil aircraft navigation systems. Full article
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21 pages, 14886 KiB  
Article
Bayesian Optimization for Fine-Tuning EKF Parameters in UAV Attitude and Heading Reference System Estimation
Aerospace 2023, 10(12), 1023; https://doi.org/10.3390/aerospace10121023 - 09 Dec 2023
Viewed by 1027
Abstract
In various applications, the extended Kalman filter (EKF) has been vital in estimating a vehicle’s translational and angular motion in 3-dimensional (3D) space. It is also essential for the fusion of data from multiple sensors. However, for the EKF to perform effectively, the [...] Read more.
In various applications, the extended Kalman filter (EKF) has been vital in estimating a vehicle’s translational and angular motion in 3-dimensional (3D) space. It is also essential for the fusion of data from multiple sensors. However, for the EKF to perform effectively, the optimal process noise covariance matrix (Q) and measurement noise covariance matrix (R) must be chosen correctly. The use of EKF has been challenging due to the need for an easy mechanism to select Q and R values. As a result, this research focused on developing an algorithm that can be easily applied to determine Q and R, allowing us to harness the full potential of EKF. Accordingly, an EKF innovation consistency statistics-driven Bayesian optimization algorithm was employed to achieve this goal. Q and R values were tuned until the expected result met the performance requirement for minimum error through improved measurement innovation consistency. The comprehensive results demonstrate that when the optimum Q and R, as tuned by the suggested technique, were used, the performance of the EKF significantly improved. Full article
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20 pages, 4787 KiB  
Article
Aerodynamic Uncertainty Quantification of a Low-Pressure Turbine Cascade by an Adaptive Gaussian Process
Aerospace 2023, 10(12), 1022; https://doi.org/10.3390/aerospace10121022 - 09 Dec 2023
Viewed by 783
Abstract
Stochastic variations of the operation conditions and the resultant variations of the aerodynamic performance in Low-Pressure Turbine (LPT) can often be found. This paper studies the aerodynamic performance impact of the uncertain variations of flow parameters, including inlet total pressure, inlet flow angle, [...] Read more.
Stochastic variations of the operation conditions and the resultant variations of the aerodynamic performance in Low-Pressure Turbine (LPT) can often be found. This paper studies the aerodynamic performance impact of the uncertain variations of flow parameters, including inlet total pressure, inlet flow angle, and turbulence intensity for an LPT cascade. Flow simulations by solving the Reynolds-averaged Navier–Stokes equations, the SST turbulence model, and γRe˜θt transition model equations are first carried out. Then, a Gaussian process (GP) based on an adaptive sampling technique is introduced. The accuracy of adaptive GP (ADGP) is proven to be high through a function experiment. Using ADGP, the uncertainty propagation models between the performance parameters, including total pressure-loss coefficient, outlet flow angle, Zweifel number, and the uncertain inlet flow parameters, are established. Finally, using the propagation models, uncertainty quantifications of the performance changes are conducted. The results demonstrate that the total pressure-loss coefficient and Zweifel number are sensitive to uncertainties, while the outlet flow angle is almost insensitive. Statistical analysis of the flow field by direct Monte Carlo simulation (MCS) shows that flow transition on the suction side and viscous shear stress are rather sensitive to uncertainties. Moreover, Sobol sensitivity analysis is carried out to specify the influence of each uncertainty on the performance changes in the turbine cascade. Full article
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20 pages, 17494 KiB  
Article
Transient Flow Evolution of a Hypersonic Inlet/Isolator with Incoming Windshear
Aerospace 2023, 10(12), 1021; https://doi.org/10.3390/aerospace10121021 - 09 Dec 2023
Viewed by 801
Abstract
In this paper, a novel flow perturbation model meant to investigate the effects of incoming wind shear on a hypersonic inlet/isolator is presented. This research focuses on the transient shock/boundary layer interaction and shock train flow evolution in a hypersonic inlet/isolator with an [...] Read more.
In this paper, a novel flow perturbation model meant to investigate the effects of incoming wind shear on a hypersonic inlet/isolator is presented. This research focuses on the transient shock/boundary layer interaction and shock train flow evolution in a hypersonic inlet/isolator with an on-design Mach number of 6.0 under incoming wind shear at high altitudes, precisely at an altitude of 30 km with a magnitude speed of 80 m/s. Despite the low intensity of wind shear at high altitudes, the results reveal that wind shear significantly disrupts the inlet/isolator flowfield, affecting the shock wave/boundary layer interaction in the unthrottled state, which drives the separation bubble at the throat to move downstream and then upstream. Moreover, the flowfield behaves as a hysteresis phenomenon under the effect of wind shear, and the total pressure recovery coefficients at the throat and exit of the inlet/isolator increase by approximately 10% to 12%. Furthermore, this research focuses on investigating the impact of wind shear on the behavior of the shock train. Once the inlet/isolator is in a throttled state, wind shear severely impacts the motion of the shock train. When the downstream backpressure is 135 times the incoming pressure (p0), the shock train first moves upstream and gradually couples with a cowl shock wave/boundary layer interaction, resulting in a more significant separation at the throat, and then moves downstream and decouples from the separation bubble at the throat. However, if the downstream backpressure increases to 140 p0, the shock train enlarges the separation bubble, forcing the inlet/isolator to fall into the unstart state, and it cannot be restarted. These findings emphasize the need to consider wind shear effects in the design and operation of hypersonic inlet/isolator. Full article
(This article belongs to the Special Issue Shock-Dominated Flow)
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16 pages, 15882 KiB  
Article
The Application of a Laser-Printed Miniature Five-Hole Probe in the End-Wall Flow Measurement of a Multistage Axial Compressor
Aerospace 2023, 10(12), 1020; https://doi.org/10.3390/aerospace10121020 - 08 Dec 2023
Viewed by 660
Abstract
To make measurement of end-wall flow between blade rows in a compact multistage configuration possible, a miniature L-shaped five-hole probe was employed in this paper. This compact tip structure, realized by laser-printing instead of the conventional machining technique, reduces the blockage effect of [...] Read more.
To make measurement of end-wall flow between blade rows in a compact multistage configuration possible, a miniature L-shaped five-hole probe was employed in this paper. This compact tip structure, realized by laser-printing instead of the conventional machining technique, reduces the blockage effect of this intrusive measurement on the flow and ensures high spatial resolution. The zonal method is introduced to extend the usable flow angle range up to 60 degrees. A local least-squares interpolation technique is utilized to acquire flow angle and static/total pressure. In order to improve accuracy for the points located at the sector boundary, the overlap region method is included in the interpolation. Additional test data indicate that the maximum error in flow angle is nearly within 1 degree, and the maximum errors of total pressure and static pressure are 0.56% and 1.9% respectively. The application in a low-speed multistage axial compressor indicates that the zonal method can decrease the number of points exceeding the measurable flow range and is of great significance for the end-wall flow measurement, especially for the near-stall condition. Compared with the traditional method, the proportion of available data for the near-stall state measurement was increased by 18% by using the zonal method. Full article
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14 pages, 6614 KiB  
Article
Design and Structure Optimization of Arresting Gear Based on Magnetorheological Damper
Aerospace 2023, 10(12), 1019; https://doi.org/10.3390/aerospace10121019 - 08 Dec 2023
Viewed by 823
Abstract
The UAV cluster combat puts forward higher requirements for short-distance arresting gears for multitype aircraft. Based on magnetorheological technology, an arresting gear was designed, and the structural parameters of the MR damper were optimized. An iterative optimization method of structural parameters via a [...] Read more.
The UAV cluster combat puts forward higher requirements for short-distance arresting gears for multitype aircraft. Based on magnetorheological technology, an arresting gear was designed, and the structural parameters of the MR damper were optimized. An iterative optimization method of structural parameters via a genetic algorithm combined with parametric modeling and magnetic field simulation was proposed. The optimization method was applied to optimize the structure of both a single-coil and double-coil damper. The performance of the optimized arresting gear was studied. The results show that, under the same zero field damping upper limit, the variation range of the damping force of the double coil increases by 10.2% compared with that of the single coil. Comparing the peak overload of UAV before and after the optimization, when the UAV mass increases from 4000 kg to 10,000 kg, the reduction in the peak acceleration is increased from 19.8% to 25.4%. Compared with traditional hydraulic arresting gear, the new arresting gear has good adaptability to UAVs with various qualities and has higher arresting efficiency. This arresting gear has a certain advanced nature. Full article
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16 pages, 354 KiB  
Article
Assessing Space Tourism Propensity: A New Questionnaire for Future Space Tourists
Aerospace 2023, 10(12), 1018; https://doi.org/10.3390/aerospace10121018 - 06 Dec 2023
Viewed by 817
Abstract
(1) Background: Space tourism (ST) is an emerging frontier in tourism, attracting considerable stakeholders in the era of the New Space Economy. Thus, understanding the intentions and the characteristics of future space travelers is crucial. (2) Methods: Here, we validated the brief 11-item [...] Read more.
(1) Background: Space tourism (ST) is an emerging frontier in tourism, attracting considerable stakeholders in the era of the New Space Economy. Thus, understanding the intentions and the characteristics of future space travelers is crucial. (2) Methods: Here, we validated the brief 11-item Space Tourism Propensity Questionnaire (STP-Q) and administered it, along with sociodemographic and psychological questionnaires, to 333 undergraduates in order to explore ST propensity and predictive factors. (3) Results: Linear regression analysis revealed that STP-Q scores are influenced by personality traits, particularly sensation seeking, social distance, and conscientiousness. Sensation seeking predicts the intention to engage in future space travel, while trait anxiety negatively impacts it. Surprisingly, neither sociodemographic features nor pro-environmental behaviors predict ST propensity, as expected. (4) Conclusions: The STP-Q is a cost-effective self-report for assessing ST propensity and can contribute to the evolving field of space tourism when used in combination with other questionnaires. Full article
(This article belongs to the Section Astronautics & Space Science)
24 pages, 1763 KiB  
Article
Empirical Assessment of Non-Intrusive Polynomial Chaos Expansions for High-Dimensional Stochastic CFD Problems
Aerospace 2023, 10(12), 1017; https://doi.org/10.3390/aerospace10121017 - 06 Dec 2023
Viewed by 905
Abstract
Uncertainties in the atmosphere and flight conditions can drastically impact the performance of an aircraft and result in certification delays. However, uncertainty propagation in high-fidelity simulations, which have become integral to the design process, can pose intractably high computational costs. This study presents [...] Read more.
Uncertainties in the atmosphere and flight conditions can drastically impact the performance of an aircraft and result in certification delays. However, uncertainty propagation in high-fidelity simulations, which have become integral to the design process, can pose intractably high computational costs. This study presents a non-intrusive, parametric reduced order modeling (ROM) method to enable the prediction of uncertain fields with thousands of random variables and nonlinear features under limited sampling budgets. The methodology combines linear dimensionality reduction with sparse polynomial chaos expansions and is assessed in a variety of CFD-based test cases, including 3D supersonic flow over a passenger aircraft with uncertain flight conditions. Each problem has strong nonlinearities, such as shocks, to investigate the effectiveness of models in real-world aerodynamic simulations that may arise during conceptual or preliminary design. The performance is assessed by comparing the uncertain mean, variance, point predictions, and integrated quantities of interest obtained using the ROMs to Monte Carlo simulations. It is observed that if the flow is entirely supersonic or subsonic, then the method can predict the pressure field accurately and rapidly. Moreover, it is also seen that statistical moments can be efficiently obtained using closed-form analytical expressions and closely match Monte Carlo results. Full article
(This article belongs to the Special Issue Machine Learning for Aeronautics)
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17 pages, 9180 KiB  
Article
Experimental Investigation on the Control of Hypersonic Shock Wave/Boundary Layer Interaction Using Surface Arc Plasma Actuators at Double Compression Corner
Aerospace 2023, 10(12), 1016; https://doi.org/10.3390/aerospace10121016 - 06 Dec 2023
Viewed by 822
Abstract
Compression corner shock wave/boundary layer interaction (SWBLI) is a typical shock wave/boundary layer interaction (SWBLI) problem in supersonic/hypersonic flows. In previous studies, the separation flow is usually caused by a single shock wave. However, in the actual aircraft surface configuration, two-stage compression or [...] Read more.
Compression corner shock wave/boundary layer interaction (SWBLI) is a typical shock wave/boundary layer interaction (SWBLI) problem in supersonic/hypersonic flows. In previous studies, the separation flow is usually caused by a single shock wave. However, in the actual aircraft surface configuration, two-stage compression or even multistage compression will produce more complex SWBLI problems. The multi-channel shock structure makes the flow field structure more complicated and also puts forward higher requirements for the flow control scheme. In order to explore a flow control method for the double compression corner shock wave/boundary layer interaction problem, an experimental study is carried out to control the double compression corner shock wave/boundary layer interaction with a high-energy flow pulsed arc discharge array under the condition that the incoming flow velocity Ma 6.0 has both noise flow fields and quiet flow fields. The results show that when UDC = 0.5 kV actuation is applied, the influence range of the hot gas mass flow direction is about 65 mm, which can weaken the shock wave intensity to a certain extent. When UDC = 1 kV actuation is applied, the influence range of the hot gas mass flow direction extends to 85 mm, and the actuation has a significant control effect on the flow field. Through spatio-temporal evolution analysis and spatial gradient threshold processing of high-speed schlieren images of actuated flow fields, the feasibility of controlling the hypersonic double compression corner shock wave/boundary layer interaction by using a high-energy flow pulsed arc discharge array is verified. The control law of a high-energy flow pulsed arc discharge array acting on the double compression corner shock wave/boundary layer interaction is revealed. Full article
(This article belongs to the Special Issue Shock-Dominated Flow)
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13 pages, 9635 KiB  
Article
Numerical and Experimental Investigations to Assess the Impact of an Oil Jet Nozzle with Double Orifices on the Oil Capture Performance of a Radial Oil Scoop
Aerospace 2023, 10(12), 1015; https://doi.org/10.3390/aerospace10121015 - 05 Dec 2023
Viewed by 878
Abstract
To study the influence of orifice spacing on the oil–air two-phase flow and the oil capture efficiency of an oil scoop in an under-race lubrication system, an experimental platform for under-race lubrication was built, and a calculation model for the oil–air two-phase flow [...] Read more.
To study the influence of orifice spacing on the oil–air two-phase flow and the oil capture efficiency of an oil scoop in an under-race lubrication system, an experimental platform for under-race lubrication was built, and a calculation model for the oil–air two-phase flow field was established. The rationality of the experiment and the validity of the numerical model were verified by comparing the experimental and numerical results. The results showed that under the same oil supply pressure, the captured oil mass flow rate of the double-orifice structure was much higher than that of the single-orifice structure, though it was still less than twice that of the single-orifice structure. When applying a tandem layout structure of double orifices to an under-race lubrication system, the orifice spacing of the tandem layout structure should be determined based on a full evaluation of the influence of the orifice spacing and working condition parameters on the oil capture performance. Otherwise, it may lead to a decrease in oil capture efficiency, with the maximum reduction even reaching 12%. Full article
(This article belongs to the Special Issue Jet Flows)
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24 pages, 22921 KiB  
Article
Numerical Simulation of Supersonic Turbulent Separated Flows Based on k–ω Turbulence Models with Different Compressibility Corrections
Aerospace 2023, 10(12), 1014; https://doi.org/10.3390/aerospace10121014 - 04 Dec 2023
Viewed by 777
Abstract
The accurate prediction of supersonic turbulent separated flows involved in aerospace vehicles is a great challenge for current numerical simulations. Based on the k–ω equations, several different compressibility corrections are incorporated in turbulence models to improve their prediction capabilities. Two benchmark test cases, [...] Read more.
The accurate prediction of supersonic turbulent separated flows involved in aerospace vehicles is a great challenge for current numerical simulations. Based on the k–ω equations, several different compressibility corrections are incorporated in turbulence models to improve their prediction capabilities. Two benchmark test cases, namely the ramped cavity and the compression corner, are adopted for the numerical validation. Detailed comparisons between simulations and experiments are conducted to evaluate the effect of compressibility corrections on turbulence models. The computed results indicate that compressibility corrections have a significant impact on turbulence model performance. The compressibility correction, considering the effects of both dilatation dissipation and pressure dilatation, is suitable for the prediction of compressible free shear layers, but it may have a negative impact on the prediction of low-speed flows in the near-wall region due to the severe underprediction of the wall skin friction coefficient. In comparison, the compressibility correction only considering the effects of dilatation dissipation is conservative, with decreased predictability of free shear layers in supersonic flows, although it improves the predictions of the original models without corrections. Full article
(This article belongs to the Special Issue High Speed Flows: Measurements & Simulations)
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26 pages, 4655 KiB  
Article
Performance Improvement of Human Centrifuge Systems through Multi-Objective Configurational Design Optimisation
Aerospace 2023, 10(12), 1013; https://doi.org/10.3390/aerospace10121013 - 02 Dec 2023
Viewed by 851
Abstract
Human Centrifuge Systems (HCSs) are an effective training tool to improve the G-acceleration and Spatial Disorientation (SD) tolerance of aircrew. Though highly capable HCSs are available, their structure and performance are yet to be fully optimised to efficiently recreate the G-vectors produced using [...] Read more.
Human Centrifuge Systems (HCSs) are an effective training tool to improve the G-acceleration and Spatial Disorientation (SD) tolerance of aircrew. Though highly capable HCSs are available, their structure and performance are yet to be fully optimised to efficiently recreate the G-vectors produced using Aircraft Combat Manoeuvres (ACMs). To achieve this improvement, the relationship between configurational design and HCS performance should be profoundly investigated. This work proposes a framework for identifying the optimal configurational design of an active four Degree-of-Freedom (DoF) HCS. The relationship between configurational design parameters and objective criteria is established using inverse kinematics and dynamics. Then, a multi-objective evolutionary optimiser is used to identify the optimum arm length and seat position, minimising the Coriolis effect, relative acceleration ratio, and cost. The results of the work show that the applied optimisation step can significantly contribute to (1) efficiently replicating the aircraft motion, (2) minimising the detrimental effects generated during HCS motion, and (3) reducing the overall cost of the system. The applied methodology can be adapted to HCSs with different structures and DoFs. Full article
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18 pages, 5427 KiB  
Article
Initial Identification of Thrust and Orbit Elements for Continuous Thrust Spacecraft in Circular Orbit
Aerospace 2023, 10(12), 1012; https://doi.org/10.3390/aerospace10121012 - 01 Dec 2023
Cited by 1 | Viewed by 802
Abstract
Continuous thrust spacecraft in circular orbits have had a great influence on the identification and cataloging of space targets. Gaussian-type orbital element variational equations are simplified and approximated. Ground-based radar observation datasets are transformed into orbit elements datasets. The initial thrust and orbit [...] Read more.
Continuous thrust spacecraft in circular orbits have had a great influence on the identification and cataloging of space targets. Gaussian-type orbital element variational equations are simplified and approximated. Ground-based radar observation datasets are transformed into orbit elements datasets. The initial thrust and orbit elements are obtained by optimally solving the spatial parameter error sum of squares minimization problem with the Levenberg–Marquardt method. The simulation analysis is carried out under the high-precision orbit model, and the solution error of tangential acceleration is around 5 × 10−7 m/s2, and that of normal acceleration is around 3 × 10−6 m/s2; the accuracy of the semi-major axis is 350 m, and the accuracy of inclination is 0.095°. The method is applicable to the preliminary identification of thrust and orbit elements for circular orbit continuous thrust spacecraft and can provide reliable initial values for the subsequent precision orbit determination of such spacecraft. Full article
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12 pages, 3156 KiB  
Article
Time-of-Flight Measurements in the Jet of a High-Current Vacuum Arc Thruster
Aerospace 2023, 10(12), 1011; https://doi.org/10.3390/aerospace10121011 - 30 Nov 2023
Viewed by 803
Abstract
Measurements of ion speed in the plume of a pulsed high-current vacuum arc thruster were performed by means of electrostatic probes. The probes were designed to provide direct speed measurements with minimum disturbance on the plasma jet. Typical mean values of vi [...] Read more.
Measurements of ion speed in the plume of a pulsed high-current vacuum arc thruster were performed by means of electrostatic probes. The probes were designed to provide direct speed measurements with minimum disturbance on the plasma jet. Typical mean values of vi for Ti and Cu cathodes are determined at different locations downstream of the electrodes, in the far field region. From one VAT discharge to another, the mean ion speed strongly varies which leads to a large statistical dispersion. Single-shot analysis allows the observation of the plume anisotropy and its high divergence as well as the existence of several ion groups of different speeds throughout a discharge. Full article
(This article belongs to the Special Issue Space Electric Propulsion Technology)
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27 pages, 7763 KiB  
Article
Dynamic Modeling and Vibration Suppression of a Rotating Flexible Beam with Segmented Active Constrained Layer Damping Treatment
Aerospace 2023, 10(12), 1010; https://doi.org/10.3390/aerospace10121010 - 30 Nov 2023
Viewed by 732
Abstract
This paper uses high-order approximate coupling (HOAC) dynamics equations for the hub–beam system with segmented active constrained layer damping treatment (SACLD). To improve the damping characteristics of traditional active constrained layer damping (ACLD), the viscoelastic damping layer, and the piezoelectric constraining layer are [...] Read more.
This paper uses high-order approximate coupling (HOAC) dynamics equations for the hub–beam system with segmented active constrained layer damping treatment (SACLD). To improve the damping characteristics of traditional active constrained layer damping (ACLD), the viscoelastic damping layer, and the piezoelectric constraining layer are cut at the same position. The damping characteristics of the structure are enhanced by increasing the shear strain of the viscoelastic damping layer. The finite element method is used to discretize the SACLD beam. The discontinuity of the SACLD beam element-to-element displacement achieves the notch. Based on the theory of rigid–flexible coupling dynamics, the dynamic responses of the SACLD rotating beam under different cases are studied. The results show that the segmentation method is not always effective. A SACLD beam provides better vibration suppression than an ACLD beam only when appropriate material and dimensional parameters are used. The influences of base-layer thickness, piezoelectric constraining layer thickness, viscoelastic damping-layer thickness, angular velocity, the viscoelastic damping-layer loss factor, and control gains on the vibration of the rotating flexible beam with SACLD treatment are also discussed. Full article
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25 pages, 37391 KiB  
Article
Modular Multifunctional Composite Structure for CubeSat Applications: Embedded Battery Prototype Modal Analysis
Aerospace 2023, 10(12), 1009; https://doi.org/10.3390/aerospace10121009 - 30 Nov 2023
Viewed by 858
Abstract
Current CubeSats usually exhibit a low structural mass efficiency and a low internal volume for their payloads. The present work aims to propose an advanced structural architecture for CubeSats that addresses the issues of low structural mass efficiency and payload volume. The starting [...] Read more.
Current CubeSats usually exhibit a low structural mass efficiency and a low internal volume for their payloads. The present work aims to propose an advanced structural architecture for CubeSats that addresses the issues of low structural mass efficiency and payload volume. The starting concept is the smart tiles architecture for satellites developed for the ARAMIS (an Italian acronym for a highly modular architecture for satellite infrastructures) CubeSat project. By introducing multifunctional structures and lightweight, composite materials in the design of smart tiles, the volumetric and structural mass efficiency of the entire CubeSat are enhanced. The advantages of the chosen approach are preliminarily analyzed in terms of the volumetric efficiency and amplitude of the payload design space. A 1U battery tile design is then selected to investigate the multifunctional structures design aspects in the project of space structures. A battery tile prototype is designed, produced, and tested. The CubeSat volumetric increment and the payload volume gain with respect to the traditional architecture is shown to reach a maximum of 37%. The CubeSat structural mass ratio can be reduced to 16.7%. Full article
(This article belongs to the Special Issue Advanced Method and Technology for Miniaturized Space Application)
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18 pages, 3890 KiB  
Article
An Intelligent Autonomous Morphing Decision Approach for Hypersonic Boost-Glide Vehicles Based on DNNs
Aerospace 2023, 10(12), 1008; https://doi.org/10.3390/aerospace10121008 - 30 Nov 2023
Viewed by 801
Abstract
In addressing the morphing problem in vehicle flight, some scholars have primarily employed reinforcement learning methods to make morphing decisions based on task. However, they have not considered the constraints associated with the task process. The innovation of this article is that it [...] Read more.
In addressing the morphing problem in vehicle flight, some scholars have primarily employed reinforcement learning methods to make morphing decisions based on task. However, they have not considered the constraints associated with the task process. The innovation of this article is that it proposes an intelligent morphing decision method based on deep neural networks (DNNs) for the autonomous morphing decision problem of hypersonic boost-glide morphing vehicles under process constraints. Firstly, we established a dynamic model of a hypersonic boost-glide morphing vehicle with a continuously variable sweep angle. Then, in order to address the decision optimality problem considering errors and the heat flux density constraint problem during the gliding process, interference was introduced to the datum trajectory in segments. Subsequently, re-optimization was performed to generate a trajectory sample library, which was used to train an intelligent decision-maker using a DNN. The simulation results demonstrated that, compared with the conventional programmatic morphing approach, the intelligent morphing decision maker could dynamically determine the sweep angle based on the current flight state, leading to improved range while still adhering to the heat flux density constraint. This validates the effectiveness and robustness of the proposed intelligent decision-maker. Full article
(This article belongs to the Section Astronautics & Space Science)
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28 pages, 80578 KiB  
Article
Free Vibrations of a New Three-Phase Composite Cylindrical Shell
Aerospace 2023, 10(12), 1007; https://doi.org/10.3390/aerospace10121007 - 29 Nov 2023
Cited by 2 | Viewed by 820
Abstract
The novel concept of a functionally graded three-phase composite structure is derived from the urgent need to improve the mechanical properties of traditional two-phase composite structures in aviation. In this paper, we study the free vibrations of a new functionally graded three-phase composite [...] Read more.
The novel concept of a functionally graded three-phase composite structure is derived from the urgent need to improve the mechanical properties of traditional two-phase composite structures in aviation. In this paper, we study the free vibrations of a new functionally graded three-phase composite cylindrical shell reinforced synergistically with graphene platelets and carbon fibers. We calculate the equivalent elastic properties of the new three-phase composite cylindrical shell using the Halpin-Tsai and Mori-Tanaka models. The governing equations of this three-phase composite cylindrical shell are derived by using first-order shear deformation theory and Hamilton’s principle. We obtain the natural frequencies and mode shapes of the new functionally graded three-phase composite cylindrical shell under artificial boundary conditions. By comparing the results of this paper with the numerical results of finite element software, the calculation method is verified. The effects of the boundary spring stiffness, GPL mass fraction, GPL functionally graded distributions, carbon fiber content, and the carbon fiber layup angle on the free vibrations of the functionally graded three-phase composite cylindrical shell are analyzed in depth. The conclusions provide a certain guiding significance for the future application of this new three-phase composite structure in the aerospace and engineering fields. Full article
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26 pages, 14635 KiB  
Article
Training Sample Pattern Optimization Based on a Swarm Intelligence Algorithm for Tiltrotor Flight Dynamics Model Approximation
Aerospace 2023, 10(12), 1006; https://doi.org/10.3390/aerospace10121006 - 29 Nov 2023
Viewed by 758
Abstract
Neural networks have been widely used as compensational models for aircraft control designs and as surrogate models for other optimizations. In the case of tiltrotor aircraft, the total number of aircraft states and controls is much greater than that of both traditional fixed-wings [...] Read more.
Neural networks have been widely used as compensational models for aircraft control designs and as surrogate models for other optimizations. In the case of tiltrotor aircraft, the total number of aircraft states and controls is much greater than that of both traditional fixed-wings and helicopters. This requires, in general, a huge amount of training data for the network to reach a satisfactory approximation precision and makes the network size rise considerably. To solve the practical problem of reducing the size of the approximating network, efforts have to be made in the efficient utilization of the limited amount of training data. This work presents the methodology of optimizing the sample pattern of the training data set by adopting the metaheuristic algorithm of the particle swarm optimizer improved by the fourth-order Runge–Kutta algorithm. A 6-degree-of-freedom nonlinear flight dynamics model of the tiltrotor aircraft is derived, along with its approximation radial basis function neural network. An example case of approximating a highly nonlinear function is studied to illustrate the principle and main parameters of the optimizer, and the approximation performance of the time-domain response of the unstable nonlinear system is revealed by the study of a Van der Pol oscillator. Then, the presented method is applied to the modeled tiltrotor aircraft for its early and late conversion modes. The optimization scheme shows great improvement in both cases, as the function approximation error is reduced significantly. Full article
(This article belongs to the Section Aeronautics)
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