A coupled scattered field fast prediction method based on the radiation source pattern and polarization scattering matrix is proposed for the complex electromagnetic environment in which the target and interfering radiation sources exist simultaneously and affect the scattered field of the target. The near real-time fast prediction of the overall electromagnetic field in the radiation-scattering coupled scenario is made possible by utilizing the radiation source pattern and the scattering data of all directions of the target, which can be independently obtained and loaded in advance. The effects of the radiation-scattering coupling on the scene's echo field are determined through simulations by calculating the changes in the total electric field of the radiation source and scatter at different distances and relative strengths. Calculation of the whole field of the scene doesn't involve electromagnetic calculation methods, which meets the demand for real-time data provision in the complex electromagnetic environment infield simulation test and is engineering applicable.

This article gives a review of the evolution of computer use-mode over the time since the invention of modern computers and presents the challenges and tasks in building the national computing infrastructure. The first section of this article provides a brief overview of how computer use-mode has evolved over the past several decades. Then the design and implementation of China's national high performance computing infrastructure CNGrid are introduced. Following that, the trends and new technical challenges in developing the computing infrastructure under the circumstance of the national strategic project of "East-west Computing Transfer" are discussed. Finally, the perspectives of building the supercomputing eco-system and constructing the new type of computing infrastructure in China are presented.

Without knowing the relationship between the chemical composition and properties of the material, the development of new materials with desired properties based on conventional trial-and-error methods is cost inefficient and sometimes ends fruitlessly. With the development of artificial intelligence and the fourth science paradigm, data-driven science, materials genetic engineering (MGE) has become a new approach for designing novel materials. In this paper, recent advances in high-throughput computation, materials database, and artificial intelligence methods in MGE are reviewed. First, the framework and software for high-throughput computations of materials are introduced. Then, the progress and critical problems of materials databases are presented in terms of types and standard interfaces of materials data. Next, we summarize the applications of artificial intelligence methods in critical issues of materials science. In particular, from the aspects of visualized high-throughput calculation methods, multi-type materials database and visualized machine learning framework, we emphasize an in-house developed platform ALKMIE, featured by multi-scale integration of automatic high-throughput calculation, visualization, and intelligent data management. Finally, we highlight the future directions of MGE.

In the context of the globalization of air traffic control, the ICAO has proposed a new generation of surveillance technology called the automatic dependent broadcast surveillance (ADS-B) system. Compared with land-based systems, the space-based ADS-B system can achieve global airspace coverage, which can enhance the capabilities of the existing air traffic control system and promote the opening of national low-altitude airspace as well as the development of the general aviation industry. Firstly, the origin, concept, and operation principle of space-based ADS-B are introduced. Secondly, a brief overview and history of the domestic and international space-based ADS-B systems are provided. Then, the research status on the space-based ADS-B key technologies are sorted out by both domestic and international scholars, including weak signal demodulation, multi-beam reception, de-interleaving, anti-spoofing, and constellation design, routing algorithm, and surveillance performance evaluation. The research work and Beihang space-based ADS-B technology verification satellite of the Beihang University, is introduced. Finally, the development trend and outlooks of the space-based ADS-B system are summarized by combining the future development of space-based air traffic control technology and application needs.

Accurate prediction of passenger flow of airport express rail is the basis for realizing intelligent, refined and efficient control of airport rail transit system. And it is of great significance to improve airport service levels and operational efficiency. The correct prediction of airport express rail passenger flow is particularly difficult due to the complex interplay of multiple factors that influence passenger flow in complicated ways. In this paper, an airport express passenger flow prediction model based on time and feature cooperative attention mechanism is proposed to accurately capture the influence degree of multi-dimensional factors on express passenger flow in different time series. Based on the actual passenger flow data of Beijing Capital International Airport, the experiment results show that the proposed method is effective.

An Aircraft hydraulic pump provides high-pressure energy for aircraft manipulation, landing gear retraction and braking. Maintaining its reliability and safety is critical. In this paper, we construct a mixed lubrication wear degradation model based on the micro topography for rotor-valve plate friction pairs and axial pump mechanical seals. The unified stochastic process model is used to describe the degradation process of these two degradation performance indicators, Copula functions are used to describe the dependent relationships between two performance indicators. Bayesian Markov chain Monte Carlo method is used to estimate unknown parameters in the degradation model considering two dependent performance indicators. The results of the estimation are then utilized to conduct reliability evaluations for aircraft hydraulic pumps. The proposed theory and method were verified through real degradation test data of return oil flow for hydraulic pumps and friction torque for mechanical seals. The results show that the degradation model considering two dependent performance indicators can increase the accuracy of reliability estimation and lifetime prediction.

This paper proposes a multi-unmanned aerial vehicle (UAV) cooperative target defense method based on exponentially averaged momentum pigeon-inspired optimization (EM-PIO). Firstly, the multi-UAV cooperative target protection system in three-dimensional space is modeled. The surface constraint equation of the UAV-dominated area and the optimal control input of UAVs are obtained. Secondly, in order to address the constrained optimization problem, the multi-level penalty function method is used to generate the objective function of the optimization algorithm. In addition, an EM-PIO algorithm is proposed to solve the optimal point. Comparative experiments with the genetic algorithm (GA) and particle swarm optimization (PSO) are conducted. The simulation results show that the EM-PIO method can solve the multi-UAV cooperative target defense problem more effectively.

Fuel injection technology is one of the key technologies of aviation piston engines. Its structure and characteristics directly affect the integral performance of aircraft piston engines. With the requirements of general aviation for better engine performance, the development of fuel injection technology continues. This paper summarizes the current fuel supply systems used in various heavy fuel aircraft piston engines, sorts out the classic models that are applicable to them, and reviews the advantages and disadvantages of the various fuel supply systems. It expounds some cutting-edge theories, simulation calculations and experimental methods used in the study of heavy oil injection technology, and analyzes some difficulties in heavy fuel atomization, followed by relevant suggestions for the study of heavy fuel injection technology. Finally, this paper puts forward some ideas and key technologies for the future development of heavy fuel aircraft piston engine, with a focus on providing technical guidance for the forward development of heavy fuel aircraft piston engines, thus contributing to the sustainable development of China's general aviation.

The supercritical carbon dioxide (SCO₂) closed Brayton cycle has received considerable attention in the field of energy and power due to its advantages of high thermal efficiency and compactness, economy, and environment friendliness. This study reviews research on the SCO₂ closed Brayton cycle in terms of its operating principle, advantages, and domestic and overseas research progress. Key techniques such as cycle thermodynamics, turbomachinery working with supercritical medium, high-efficiency compact heat exchangers, control strategies, and thermal storage are analyzed. Moreover, difficulties in and challenges of engineering applications are discussed, and future development directions are presented. It is indicated that the low-dimensional performance analysis of components should be involved in the conceptual design of cycle thermodynamics to estimate the attainable performance of components, considering the lifecycle performance, compactness, and economy of the cycle. The dramatic variations of working medium properties would lead to special flow and heat transfer mechanisms in turbomachinery and heat exchanger, respectively, motivating the design methodologies for turbomachinery and compact heat exchanger that fully consider the effect of special properties of working medium. The similarity method constructed by theoretical analysis and deep machine learning could provide theoretical foundations for experimental validation of the aerodynamic performance of SCO₂ turbomachinery. Furthermore, robust and efficient control strategies could control the cycle effectively, and SCO₂ closed Brayton cycles integrated with thermal storage techniques adopting novel thermal medium would provide key technical supports for concentrating solar power at high operation temperature.

In recent years, the water striking aircraft which realizes high-speed maneuvering flight near the water surface by using skipping motion has become one of the hot issues in research, and the solution of high-speed oblique water impact load of three-dimensional structure is the key step of skipping motion numerical simulation. Based on the boundary element method, a time-domain numerical simulation method of water surface skipping of three-dimensional structure considering structural elastic effect is established. The high-speed oblique water impact load is obtained by the boundary element method, and the displacement dynamic response of the structural node is obtained by the direct integration method of the state equation. Moreover, the centroid position and motion speed of the structure are updated by the skipping motion dynamic model. To verify the accuracy of the fluid load solution algorithm of this method, the numerical simulation of high-speed oblique water impact of steel sphere is carried out and compared with the experimental value. The time-domain numerical simulation and variable parameter analysis of skipping motion of three-dimensional rigid spherical crown are carried out. Then, the effects of structural mass, initial height, horizontal throw speed and radius on the skipping motion of the spherical crown are obtained. After considering the elastic effect, the impact load of high-speed oblique water entry decreases, which also has a certain influence on the sliding and jumping motion of the spherical crown.

Time integration methods are a powerful tool for solving transient responses, which have been widely used to solve dynamic problems in aerospace, civil engineering, machinery manufacturing, and other fields. This paper reviews the advances in time integration methods in the past decades. Firstly, some classical methods, such as the series expansion method, the Runge-Kutta method and the Newmark method, are introduced. To solve the drawbacks involved in the classical methods, several time integration methods with more desirable numerical properties, including accuracy, efficiency, dissipation and stability, have been developed. Moreover, the advanced methods, including parameters methods, higher-order unconditionally stable methods, energy-conserving methods, linear multistep methods, composite methods and BN-stable methods, are introduced in this paper. Finally, the numerical properties and application scope of the existing time integration methods are compared, and some issues worthy of attention are given.

Rotational components undergo complex loads which can easily initiate cracks, resulting in fatigue and fracture failures. For thermal-loaded rotational components with cracks, the finite element method (FEM) was applied to the global structure without cracks, thus exerting the advantage of FEM in numerical analysis of large-scale structure; meanwhile, the symmetric Galerkin boundary element method (SGBEM) was employed to the subdomain around the crack, thereby developing the advantage of SGBEM in fracture analysis. The SGBEM super element, which took the influence of the rotational inertia loading and the thermal loading into consideration, was developed in this paper. The stiffness matrix of the obtained SGBEM super element was symmetric and positive semidefinite, where the rotational inertia loading and the thermal loading only influence the equivalent force vector. Thus, the SGBEM super element can be directly assembled with the stiffness matrix and the equivalent force vector of the FEM, and be coupled with the FEM to solve the thermoelastic fracture problem of rotational components. Stress intensity factors of the cracked rotational disk undergoing the thermal loading were computed, which validates the effectiveness of SGBEM super element and FEM coupling method.

Due to the complexity of the scene and the diversity of objects, the objects in the scene of outdoor surveillance video are difficult to detect, which involves such problems like the object is blocked, or the size of object changes. Therefore, the object detection task is still challenging. To improve the accuracy of the object detection algorithm, this paper proposed a method of using motion information to guide the object detection algorithm based on convolutional neural network. Firstly, the motion object detection algorithm is improved to keep the foreground of stationary target in the motion foreground map; secondly, using the feature that the foreground in the motion foreground map can indicate the spatial position of the object, the feature map extracted by the network is fused with the motion information to improve the response value of the possible object area in the feature map; finally, in the detector of the object detection algorithm, a localization branch is introduced. Using the motion foreground map of the video frame, the location reliability of the candidate object is learned, and weighted sum with the classification confidence of the object is used as the final confidence of the object. The detection result is obtained through the non maximum suppression method. Experiments show that the proposed method can improve the accuracy of object detection in the data set collected under the fixed camera.

The automated fiber placement (AFP) process has become a promising solution to the fabrication of composite structures, due to its efficiency and stability. However, the instability of the lay-up process parameters and the performance of the equipment can easily cause such defects as gaps, overlaps, and waviness, which severely affect the overall performance and service life of composite structures. Therefore, automatic identification and evaluation of the defects on the surface or inside the laminates during the AFP process through in-situ monitoring systems are of particular importance. In this paper, the causes and appearance of common defects on the ply during the AFP process and their effects on the overall performance of products are first concluded. Then, the advantages, development, and applications of online monitoring systems based on different detection techniques are systematically reviewed, mainly including laser technology, image recognition technology, thermal imaging technology, and fiber Bragg grating technology. Finally, the limitations in the current online monitoring systems are summarized, and outlooks for their future trends are given.

To achieve peak carbon and carbon neutral goals, the development of electric cars has become strategically important. It is necessary to have precise battery management technology because the lifespan and safety of power batteries change dynamically as they are used. This leads to rapid capacity degradation brought on by the inconsistent performance of single cells and thermal runaway brought on by short board batteries or internal defects. New battery management capabilities have been made possible by the development of the digital twin model, which is now one of the technical trends in the industry. Based on the development trend of battery management technology, the article concentrates on the analysis of basic principles of battery digital twin modeling from the aspects of system modeling to management and control requirements. The article systematically introduces the construction method of multi-dimensional, multi-scale and multi-physical field fusion of digital twin battery. Combined with the previous research of the team, the practical case of the digital twin battery was analyzed. Finally, the application perspective of digital twin battery is discussed in production design, life cycle management and other scenarios, which provided ideas and references for the development of battery management technology.

To evaluate reliability of new products, function-oriented design should comprehensively consider the influence of new structure and technology, multiple design variables, and complex working environments, and reasonably quantify uncertainty effects. This will ensure high reliability from the original design. Based on the belief reliability theory, this study investigates a performance margin-based and function-oriented method for belief reliability design and optimization. The basic procedure of the function-oriented reliability design is proposed for the development of new torsion spring electrical connectors, which includes four steps, i.e., initial value selection of design variables, performance margin modeling, uncertainty quantification, and reliability analysis and optimization. This procedure is exemplified in the design and development of a new type of torsion spring electrical connector. The optimal design of multidimensional discrete-continuous variables under the influence of their uncertainties is realized based on orthogonal experiments, response surface modeling, and simulated annealing heuristic optimization.

In the combustion process of liquid fuels, jet instabilities and atomization are the starting points, which can have significant effects on following processes such as evaporation and combustion. There remain gaps in our under standing of the turbulent jet atomization mechanism despite the extensive prior research. This work aims to reveal the atomization mechanism of turbulent liquid planar jets through the use of flow topology. A high-resolution direct numerical simulation method is used to solve the atomization process of a liquid plane jet in a still air environment. In order to clarify the process by which flow topology affects the atomization of liquid plane jets, the interaction between various topologies in the flow field and the curvature of the gas-liquid interface is analyzed. It is found that all flow topologies contribute to the generation of compressive and extensive strain rate, among which the UFC topology has the greatest effect on the flow field strain rate; the curvature of the liquid volume fraction iso-surface shows a negative correlation with the strain rate under the influence of the flow topology. In addition, the UFC structure mainly generates extensive strain, while the remaining flow topologies mainly generate compressive strain. These results suggest that the jet atomization process is mainly influenced by the UFC topology, which facilitates a large extensive strain at the gas-liquid interface, which in turn promotes the generation of sheet or saddle structures, thus causing liquid jet fragmentation.

To accurately detect the residual thickness of pipeline, a non-contact pipeline thickness detection system based on the electromagnetic ultrasonic shear wave was designed. The system adopts a self-developed electromagnetic ultrasonic high-power excitation source and a transducer to generate shear wave, and the receiver is used to filter and process the echo voltage signal in real-time to obtain the accurate residual thickness of the aluminum pipe. The excitation coil parameters were optimized to improve the small-signal and low signal-to-noise ratio of the receiving signal. On this basis, the beam radiation of shear waves propagating within the pipe was analyzed. Based on the fact that the number of turns of the coil and the width of the coil are the majority influence factors to the peak-to-peak value of the echo signal and the SNR respectively, the transducer is designed and the residual thickness detection accuracy with the error less than 0.2% is achieved.

The electrowetting liquid lens is increasingly favored by researchers due to its tunable focal length, fast response, convenient operation, and low power consumption. It can solve some technical problems such as mechanical jitter and discrete zoom in microscopic imaging systems, thus promoting the intelligence and lightweight of these systems. Firstly, the basic concept of and the research on electrowetting liquid lenses are described. Then, the latest research on the microscopic imaging technology with the electrowetting liquid lens is reviewed. Two microscopic imaging technologies, continuous optical zoom and axial scanning, are introduced in detail. Finally, the prosects and challenges of the microscopic imaging technology with the electrowetting liquid lens are presented.

Drag reduction surfaces have attracted more and more attention due to their great potentiality and wide applications in marine ships, pipeline transportation, aircraft, and national defense and military. Interestingly, animals and plants in nature have evolved many unique shapes or surface structures which show excellent drag reduction performance. In this review, we introduce the recent drag reduction technologies of compliant, microstructural, and superhydrophobic surfaces inspired by dolphin surfaces, shark skins, and lotus leaves, respectively. We summarize the research progress, mechanism and challenges of these technologies, and provide an overview of the current research on bionic drag reduction surfaces, and its future perspectives.

High-temperature proton exchange membrane fuel cells (HT-PEMFC) has fast electrode reaction kinetics, strong resistance to fuel/air impurity poisoning, a wide range of fuel sources (pure hydrogen, methanol-reforming gas, formic acid, etc.), and simple water/thermal management systems due to their high operating temperature (130℃-200℃). They have become one of the important development directions of polymer membrane fuel cells. This paper mainly introduces the research progress of Beihang University in HT-PEMFC key materials-high-temperature membrane, catalytic layer, and membrane electrode assemblies in recent ten years. Aiming at the best balance between proton conductivity and mechanical properties of phosphoric acid (PA) doped high-temperature membrane, the influence mechanism of PA distribution and migration in the catalytic layer on cell performance, and the influence and attenuation mechanism of large-size membrane electrode consistency on stack performance. The molecular design of polyelectrolyte membrane materials, the regulation of ordered catalytic layer structure, and the optimization of large-size membrane electrode stack were reviewed, and the technical challenges faced by HT-PEMFC technology as well as the future development trend are reviewed and prospected.

It is difficult for the traditional quadrotor control method with poor control effect in aggressive flight and low control accuracy to track trajectory with high speed and high acceleration. To solve this problem, a control method is proposed based on incremental nonlinear dynamic inversion(INDI) and differential flatness, as well as the complementary filter. The proposed control method not only improves the tracking accuracy of aggressive trajectories, but also enhances the anti-disturbance ability. Since the angular acceleration, which the proposed method is very sensitive to, cannot be directly obtained, a variety of angular acceleration estimation methods are designed for comparison, and the complementary filtering method with the best performance is selected through the flight test. The experimental results show that the proposed control method using INDI and differential flatness based on complementary filter can control the quadrotor to track aggressive trajectories quickly and accurately, and has strong anti-interference ability.

To explore the effect of helmet on neck injury of pilots in-flight, numerical simulations were carried out on four different helmets during sharp turn and stable hover condition based on the established head-neck multi-body dynamic model. Combining the muscle force, intervertebral force and moment, and the neck injury index N_ij, the neck injury of pilots was evaluated and predicted. The results show that the dynamic responses of the model are in agreement with the experimental results, with fair bio-fidelity. In the same flight condition, the wearing of helmet B shifts the center of head forward and increases the muscle force of the trapezius accordingly. For the same cervical segment, the axial compression force for helmet B and the extension moment for helmet C is maximum respectively. The value of N_ij for all simulated conditions is less than 0.5, which conforms to the safety requirements in aviation. The mass of helmet B and helmet C are close, while the mass center of helmet B is forward compared to helmet C, which indicates the anteroposterior position of helmet has an important effect on neck injury. This study provides insights for the optimization of pilot's helmet and its effect on pilot's neck injury.

With characteristics, such as cross interconnection and multiple connections, cyber-physical systems is susceptible to network attack. Through relevant research on its network architecture and on the characteristics of its network application, a model for multidimensional attack damage assessment is established. Firstly, the cyber-physical systems was divided in three dimensions: the physical layer, the rule layer and the service layer. For each layer, an attribute-based method for assessing the network attack damage was given. Then, through monitoring the network status, the attributes for attack damage assessment were obtained, which include topological stability, connectivity availability, failure controllability, transmission stability, packet loss availability, bit error controllability, response stability, service availability and risk controllability. Finally, the analytic hierarchy process was used to gain the evaluation results of the attack damage in each of the three different layers and the whole network, thus providing support and basis for the security protection of the network. Simulation of the DDoS attack on the cyber-physical systems, along with the application of the proposed method to evaluate the attack damage, verifies the practicability and effectiveness of the model.

Cooperative guidance issue with attack time consensus is an important branch of cooperative guidance issues. The main research results and classification methods of cooperative guidance with attack time consensus for multiple aerial vehicles are summarized. Firstly, the tactical significance of cooperative guidance with attack time consensus is analyzed. Secondly, two categories of issues are researched depending on how the target moves: cooperative guidance for fixed targets and cooperative guidance for moving or maneuvering targets. Furthermore, a review of the main research results of these two types of cooperative guidance problems is provided.The advantages, disadvantages and scenarios of the above cooperative guidance methods are summarized from the level of research methods. Finally, a summary of the related technical challenges of cooperative guidance with attack time consensus is given, along with a prospective direction for future development.