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Abstract: Abstract To meet the needs of the airborne dispenser to disperse large-mass bullets, the dispersal system of large-size gasbag with multiple inlet nozzles was designed and built. The rationality and feasibility of the dispersal system were verified by the experimental study of the interior ballistic process. On this basis, the fluid–structure interaction method was used to simulate and analyze the process of the gasbag propelling the bullet when the number of inlet nozzles is different. The calculation results show that the final shape of the expanded gasbag is pillow shaped, and wrinkles appear at the ends of the long side and in the middle of the short side of the gasbag. The stress at the wrinkles is relatively large, and the stress on the wall of the gasbag with three inlet nozzles is greater than that on the wall of the gasbag with two inlet nozzles. Affected by the changes of flow field in the gasbag and the deformation of the gasbag, the process of the gasbag propelling the bullet is divided into two stages, and there are also two large fluctuation peaks during the change of the acceleration of the bullet. Moreover, the expansion process of gasbag with two inlet nozzles lags behind that of the gasbag with three inlet nozzles, and the maximum acceleration and separation velocity of the bullet are also relatively reduced by 2% and 3%, respectively. PubDate: 2023-09-26
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract This paper investigates the control direction reversal issue for the attitude control design for hypersonic reentry vehicles, and proposes a novel sliding mode control law which addresses the control direction switching and strong robustness requirement simultaneously. Firstly, the disturbance observer is introduced to estimate the unmatched uncertainties in the attitude model of hypersonic reentry vehicles, and then a periodic function-involved sliding mode control is presented and the bounded stability of the closed-loop system is guaranteed via Lyapunov stability theory. The merits of the proposed method lie in that the closed-loop system is stable even under the unknown control direction reversal, and the unmatched uncertainties can be addressed by the disturbance observer. Finally, the simulation verifies the effectiveness and superiority of the proposed control . PubDate: 2023-09-07
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Abstract: Abstract There have been many civil aircraft fuel tank deflagration accidents under warm weather conditions around the world. To ensure flight safety, the International Aviation Authorities have established quantitative standard limit indicators for the flammability exposure time of fuel tanks of civil transport aircraft on the ground and during climb stages under warm weather conditions above 26.7 °C (80°F). However, in the practice of airworthiness certification of a certain civil aircraft, people found that the smooth development of airworthiness certification work has been restricted due to the lack of in-depth research on the calculation method, influencing factors, and preventive measures of fuel tank flammability exposure time under warm weather conditions. Accordingly, this paper establishes a simulation model based on the physical structure of the fuel system of a civil aircraft, discusses the variation law of the flammability of the fuel tank under warm weather conditions based on MIL-STD-210A hot-weather atmosphere, and analyzes the influence of factors, such as ground temperature, flight phase, cruising time, and fuel type on the flammability of the fuel tank. The results show that compared with normal climate conditions, warm weather conditions will increase the exposure time of fuel tank flammability; at the same time, factors, such as short range, climbing stage, and low-flash point fuel, have more significant effects on fuel tank flammability in warm climates. The research results have a guiding significance for the proposal of fuel flammability airworthiness compliance method under warm weather conditions. PubDate: 2023-09-04
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Abstract: Abstract Reproducing the orbit–attitude–vibration coupling dynamic behaviors of the complex flexible spatial structure provides the basis on the orbit design, the attitude adjustment and the vibration control of the structure. In this paper, the tug–tether–debris system is simplified as a spatial particle–spring–beam physical model, in which, the non-smooth stiffness coefficient of the spring is assumed to describe the tension/loose state switching of the tether. Based on the variational principle, the coupling dynamic equations are deduced for the spatial particle–spring–beam model. To investigate the energy evolution and the energy transfer characteristics of the model, the structure-preserving iteration method is developed focusing on the non-smooth stiffness coefficient of the spring. In the structure-preserving iteration method, the symplectic Runge–Kutta method is employed to solve the ordinary differential equations mainly controlling the plane motion of the system and the multi-symplectic method is employed to solve the transverse vibration of the beam in the model. The structure-preserving characteristics of the iteration method result from the symplectic structure contained in the symplectic Runge–Kutta method and the multi-symplectic structure contained in the multi-symplectic method. In the stages when the spring is in a complete loose or a complete tension state, the total energy of system is a conservative quantity that is preserved by the structure-preserving iteration method in the simulation. In addition, the energy transfer laws of the system in the tension process of the spring are revealed numerically, which gives some guidance on the active flexible space debris removal strategy design directly. PubDate: 2023-09-04
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Abstract: Abstract This study explores an integrated navigation technique using multiple AC magnetic fields to provide stable navigation performance of a vehicle in an unstructured indoor environment. The unstructured indoor environment assumes conditions with limited detection performance of optical and radio sensors due to factors, such as fog, optical scattering, human bodies, and water droplets. In this paper, first, a space representation vector of a magnetic field is modeled to derive the navigation results of 6-Degree of Freedom (DoF) that estimate three-dimensional position and attitude. Furthermore, a sensor fusion technique integrating inertial sensors and range sensors is newly proposed to improve the degraded performance of three-dimensional navigation due to indoor magnetic field noise and distortion characteristics. In particular, the geometric model of range measurement depending on the vehicle’s attitude and the surrounding environment is induced and reflected in the integrated filter to reduce the pose estimation error. To verify the performance of the proposed scheme, the in-house magnetic transmitters, integrated sensor module, and onboard processing computer were implemented, and ground experiments were performed. Finally, it was confirmed that the performance of vertical-axis estimation was greatly improved by the proposed correction technique, which successfully suppressed the environmental magnetic distortion. PubDate: 2023-09-02
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Abstract: Abstract As far as the aerodynamic characterization of a flying vehicle is concerned, flight testing is probably the most accurate approach as it perfectly resembles the real flight environment. Flight data are obtained by tracking the vehicle via radars if modifying the vehicle design is not recommended/attainable. In the open literature, different techniques are used to analyze radar data; the key issue is the computational demands of each technique and the quality of the resulting aerodynamic characteristics. In this paper, three techniques are considered namely, Least-Square (LS), Maximum-Likelihood Estimation (MLE), and Stepwise Regression (SR), with focus on the prediction of the drag coefficient of a case study vehicle. Features for each technique are addressed based on brief previous published data. A new variant of the MLE method is proposed based on the physical segmentation of the available dataset. Predicted point-mass trajectories are compared with own comprehensive flight test to assess the techniques in concern. It is concluded that Stepwise-regression outperforms with a large dataset, while Maximum-Likelihood Estimation is more feasible considering the lack of data. The proposed variant of the MLE method yields more accurate drag prediction compared to the basic one. PubDate: 2023-08-29
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Abstract: Abstract Internal damage to carbon fibre-reinforced plastic (CFRP) laminated plates was detected and visualized. This internal damage was generated via low-velocity impact testing. Prior to the experiment, the impact velocity was established through finite element analysis based on LS-DYNA. The damage size, determined through this analysis and subsequent experiment, presented a maximum error of 17%. Piezoelectric sensors were used to detect and visualize the internal damage. This damage was identified using a diagnostic approach, along with a novel signal separation method. The signal separation method was employed because the distance between the plate edge and the sensor was smaller than the distance between the two sensors on the CFRP-laminated plates. The visualized damage was verified though a comparison with the low-velocity impact experimental results. Both the location and size of damage could be detected with an error of approximately 9.7% and 10%, respectively. PubDate: 2023-08-25
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Abstract: Abstract This paper presents the application of manifolds for space mission design in the Circular Restricted Three Body Problem, Bi-Circular Restricted Four Body Problem, and Patched-Planar Circular Restricted Three Body Problem. We tackle these three types of missions by defining each mission’s manifold-based transfer roadmap/sequence. The transfer to Sun–Earth L4 and L5 planar Lyapunov orbits utilizing the electric-propulsion-system-assisted artificial stable manifolds and the Sun–Earth system’s L1 and L2 stable and unstable manifolds are designed utilizing the circular restricted three-body problem. We also design the weak stability boundary transfers to Earth–Moon’s L1 and L2 utilizing Earth–Moon’s stable manifold and Sun–Earth’s L1 and L2 unstable manifolds utilizing the Bi-Circular Restricted Four Body Problem. We present a manifold projection method to quickly assess manifold reachability for multiple-moon tour analysis utilizing the patched-planar circular restricted three-body problem. A new filter is used during the Poincaré section analysis to determine optimal sets of stable and unstable manifolds for several types of missions. The multiple-point differential corrector is utilized with optimal manifolds to determine a continuous smooth trajectory for spacecraft with impulsive burn maneuvers. PubDate: 2023-08-17
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Abstract: Abstract Uncontrolled spacecraft will disintegrate and generate a large amount of debris in the reentry process. Ablative debris may cause potential risks to the safety of human life and property on the ground. Therefore, predicting the landing points of spacecraft debris and forecasting the degree of risk of waste to human life and property is very important. In view that it is difficult to predict the reentry process and the reentry point in advance, the debris generated from reentry disintegration may cause ground damage for the uncontrolled space vehicle on the expiration of service. In this paper, we adopt the object-oriented approach to consider the spacecraft and its disintegrated components as consisting of simple basic geometric models and introduce three machine learning models: the support vector regression (SVR), decision tree regression (DTR), and multilayer perceptron (MLP) to predict the velocity, longitude, and latitude of spacecraft debris landing points for the first time. Then, we compare the prediction accuracy of the three models. Furthermore, we define the reentry risk and the degree of danger, and we calculate the risk level for each spacecraft debris and make warnings accordingly. The experimental results show that the proposed method can obtain high-accuracy prediction results in at least 10 s and make safety-level warning more real-time. PubDate: 2023-08-17
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Abstract: Abstract For drone using a three-phase motor, it is practically difficult to achieve hardware redundancy due to space constraints. To solve this problem, horizontal separation (HS) dual motor design is proposed. The HS dual motor embeds the physical characteristics of two motors into a single fault tolerant one. On the other hand, the efficiency decreases as motor height increases. The loss is minimized by optimizing the up–down air gap to solve this problem. Moreover, by optimizing the slot shape, efficiency increases. The up–down airgap design variables and slot shape have high-order and nonlinear characteristics with multiple local maxima. The nonlinear problems are handled using polynomial regression-based modeling as a fitness function to maximize efficiency using a genetic algorithm as a global optimization technique and its efficiency is experimentally compared. PubDate: 2023-08-14
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Abstract: Abstract A method for suppressing the pressure oscillation of supersonic parachutes is proposed in this study. This method placed a ring with a triangular or circular cross section in front of the canopy of a parachute. A rigid metal canopy was used in supersonic wind tunnel tests. Hard piano wires with a diameter of 0.8 mm were used as suspension lines and a riser to connect a fore body and the canopy. In the wind tunnel test without a ring, pressure oscillation with the accompanying time variation of the shock wave structure was observed at Mach 3.0. A detached shock wave oscillated back and forth because it interfered with the boundary layer developed on the suspension lines. A large-amplitude pressure oscillation was observed with the pressure sensor placed at the center of the canopy. The large pressure oscillation was suppressed using a ring. The time variation of the shockwave structure suppressed. The amplitude of the pressure with the sensor reduced to 1/2 of that without a ring. We also found that the location and cross-sectional shape of the ring affects the flow around the canopy. PubDate: 2023-08-09
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Abstract: Abstract This paper investigates an integrated guidance and control (IGC) strategy for reentry vehicles equipped with a strapdown seeker subject to the body line-of-sight (BLOS) angle constraint. A novel explicit reference governor-based IGC scheme is proposed to deal with BLOS angle constraint caused by strapdown mechanism. Taking the symmetric constraint interval as an example, the explicit reference governor is constructed for the positive and negative half intervals, respectively. The adaptive terminal sliding mode control (ATSMC) is subsequently designed for the IGC model to ensure that the closed-loop system tracks the commands of the explicit reference governor (ERG), thereby guaranteeing compliance with BLOS angle constraint. The stability of the closed-loop system is rigorously analyzed according to the Lyapunov stability theory. The numerical simulation results demonstrate the effectiveness of the proposed approach. PubDate: 2023-08-04
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Please help us test our new pre-print finding feature by giving the pre-print link a rating. A 5 star rating indicates the linked pre-print has the exact same content as the published article.
Abstract: Abstract Structural coupling (i.e., aeroservoelasticity) between the flight control system with multiple motion sensor feedbacks and the aeroelastic modes of the flexible airframe can be a serious problem in high-performance aircraft. In a military specification document, MIL-STD-9490D, adequate stability margin requirement is required to be complied with for all frequencies at or beyond the first aeroelastic mode in all flight conditions. To minimize the structural coupling effect to satisfy the stability margin requirement in flying qualities aspects, various design methods are adopted during the aircraft development stage as follows: to reinforce aircraft’s structure on which sensor is mounted, to minimize weight/inertia of control surfaces, to select the optimal sensor position, to optimize control gains, to design notch filters for minimizing phase lag in low-frequency band, to design phase advance filters, to apply additional active control technique, and so on. In this paper, we identify major design considerations which have been applied to the production fighter aircraft to minimize the structural coupling. The reviews regarding the prospects on design technologies would be most helpful to the structure and flight control law engineers. PubDate: 2023-08-02
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Abstract: Abstract In this paper, new methods have been proposed that can be applied to the existing terrain scan data generation (TSDG) algorithm. The algorithm is to acquire terrain scan data (TSD) by radiating multiple radar beams at various elevations while maintaining a constant azimuth. The TSDG algorithm consists of the following steps, including calculating the beam direction and the number of beams to be radiated after receiving the terrain scan command, generating measured terrain data from each beam, and merging the measured terrain data into TSD. However, the existing TSDG algorithm still needs practical improvements in acquiring TSD under specific conditions. To address these issues, new methods have been proposed for acquiring terrain data inside the beam and visibility analysis. Through simulation, it has been verified that a new TSDG algorithm combined with the proposed methods improved the existing TSDG algorithm and can be applied to the terrain following (TF) simulator. PubDate: 2023-08-02
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Abstract: Abstract The utilization of deep learning methods for the detection of space targets and components has received significant attention due to the continuous development of space missions. Effective detection and recognition of space target and components utilizing space-based electro-optical sensors is crucial for the intelligent perception and fine control of autonomous spacecraft. From an engineering application perspective, this article systematically reviews the current research status of space target detection and segmentation algorithms. This paper first summarizes the principle and characteristics of electro-optical sensors in space tasks and their application scenarios, and describes the common synthetic methods utilized for space target datasets. A summary of recent research on space target detection and component segmentation is given. Based on the research summary, we discuss several major issues for space target detection and segmentation. Research suggestions and future development directions are finally proposed. PubDate: 2023-08-02
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Abstract: Abstract The aim of this paper is to develop a new numerical program aiming to calculate the stress effect of the successive addition of the vertical spars on the reduction of the maximum tangential and normal stress due to the various internal forces, in multi-box thin-walled airfoils sections. The comparison is made with the single box airfoil without spar. The airfoil is given by tabulated values. An interpolation by cubic spline is necessary to obtain an analytical function for the upper and the lower surfaces. The calculation is based on the computation of the geometrical characteristics of the thin-walled section with different spars number. The method consists of scanning the position of the first spar along the airfoil chord, and calculating the maximum of the tangential and the normal stress, giving at the end the optimal spar position with the smallest stress values. The calculation is be repeated for the second spar based on the first optimal spar position. The insertion of a third spar is made on the optimum position of the first two spars. The calculation will be repeated each time an additional spar is inserted. The optimum spars position is not the same for the two types of torsional and normal stress. The diagrams of the internal forces are necessary to locate the dangerous section stressed by the maximum internal forces. The application is made up to five spars as an improvement to the current applications for 1 and 2 spars. Six airfoils are used for comparison. PubDate: 2023-08-01
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Abstract: Abstract The optimization of air-breathing hypersonic propulsion system designs is crucial for ensuring the viability of aircraft in extreme thermal environments. Integrating a reliable heat transfer model of regenerative cooling systems is important in this optimization process. This study focuses on enhancing the heat transfer model for the cooling channels of scramjet engines operating at Mach 5, with a combustor operating pressure of 3 MPa. The study investigates the thermal properties and phenomena associated with the supercritical state of n-dodecane, as well as heat transfer deterioration (HTD). By improving the modified Bae-Kim (m-BK) heat transfer model, we propose an efficient model to enhance the design of scramjet propulsion systems. Our enhanced one-dimensional heat transfer model successfully integrates the heat transfer phenomenon in the cooling channels. The model accurately represents the supercritical characteristics of n-dodecane considering the three-dimensional aspects of the cooling channel. PubDate: 2023-08-01
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