Abstract:HALE(high-altitude long-endurance) solar-powered aircrafts are the research frontiers, they can staying airborne for several months, and can form new application ability named "long-endurance+station-keeping". The three-stage development process of HALE solar-powered aircrafts was systematically summarized, including early exploration stage, rapid development stage and operational capability demonstration stage, and typical development plans aboard were introduced. Key technology challenges were analyzed, including aerodynamic configuration design, energy storage battery, high altitude propulsion, large scale structure and flight control, and the suggestions for research directions were proposed. All those can provide reference for innovation development of HALE solar-powered aircrafts.

Abstract:The flexibility of UAV in structural style and material composition makes it have more space for stealth performance optimization than the manned aircraft, so it was urgent to carry out near-field imaging indoors or outdoors. Based on the imaging geometry model of aircraft turntable, a general signal model of near-field turntable imaging was established, and a near-field frequency-domain imaging algorithm for aircraft electromagnetic scattering feature diagnosis was proposed. Under the constraint of sub aperture imaging setting, the slant plane spectrum was approximately processed as the horizontal plane spectrum; the applicable conditions of the algorithm was analyzed, and simulation data around typical near-field imaging geometry and aircraft size was generated.The completes near-field imaging in the range of 0.6~35 GHz was performed. Good imaging results confirm the correctness of the theoretical analysis and the proposed algorithm.

Abstract:According to the requirements of material delivery platform in the complex terrain area, the research on the structural design of the composite wing of the tail-sitter electric aircraft was carried out. Based on the load analysis, the structural configuration and lay out designs were studied, and the structural design scheme of the composite wing was proposed. The finite element model of the composite wing was developed and the static strength analyses under different operating conditions were completed. The deformation, structural stress, and Tsai-Wu failure factor distribution of the wing structure were obtained. The structural optimal analysis of the composite wing was performed on the basis of the stepwise optimization strategy with the layer thicknesses and angles as design variables. The optimal results show that the structural mass is reduced by 47.77% under the constraints of structural stiffness and strength, which can provide the important reference for the design and development of the tail-sitter electric aircraft structure.

Abstract:For the energy management method for hybrid electric propulsion system was studied, an energy management strategy based on fuzzy logic control was presented. By setting the fuzzy membership function of VTOL(vertical take-off and landing) aircraft′s power requirement, internal-combustion-engine-generator′s output power, and the state of charge of battery, the output power of generator and battery were dynamically optimal allocated. So as to increase the fuel economy and aircraft range effectively. According to the model establishment, the energy system changes of 100 kg scale VTOL aircraft were simulated, and simulation results demonstrate that the algorithm was practical. Results indicate that energy management strategy based on fuzzy logic control can effectively improve the performance of hybrid electric propulsion system, during the 1.2 h flight, ICE(internal combustion engine) can run approximately 1 h with the lowest specific fuel consumption, and can improve the energy efficiency of hybrid electric propulsion system.The conduction provide design thoughts and analysis method for energy control and arrangement of hybrid electric propulsion system.

Abstract:The analysis and design method of the sky-ground scaled similarity of aerodynamic characteristics for stratospheric airship were described in detail. The similarity criteria for the rigid and flexible models to complete the wind tunnel tests were given. Two kind of scaled models and wind tunnel test were completed. By analyzing the wind tunnel experimental data for scaled models, it was found that the aerodynamic characteristics of the stratospheric airship under different inflatable internal pressures were basically same, but the rigid body model was obviously different. The aerodynamic drag coefficient under flexible characteristics was significantly higher than that of rigid body, and even twice as high as that under zero attack angle, which lead to the essential changes of the rolling aerodynamic torque characteristics, such as stability and divergence. It has important engineering application value for evaluating flexible aerodynamic characteristics of stratospheric airship, especially under low pressure state. And it overcomes the disadvantages of using rigid body aerodynamic characteristics data or engineering estimation method in the airship overall design of "dynamic-resistance balance".

Abstract:Considering the deficiency of analytic hierarchy process in evaluation of electro-optical protection combat effectiveness, analytic network process was proposed to evaluate, toke analyze of the independence, correlation and feedback of the interior of the element hierarchy as entry point, putted forward the main index dictionary of electro-optical protection combat effectiveness, setted up the evaluation model, according to setting up the matrix, calculating, obtaining the weights, complete the evaluation. Validate the model by an example obtains evaluation results with high reliability, which provide theory-reference for evaluation of electro-optical protection combat effectiveness.

Abstract:For the transmission design problem in an IRS(intelligent reflecting surface)-enabled network, by jointly designing the transmit beamforming and IRS reflecting coefficient, the goal of this paper was to maximize the weighted sum rate for multiply ground users, subject to the transmit power and the unit modulus constraint. To solve the non-convex objective, we developed an alternating optimization method, where the phase shifter optimization was solved by the RMG(Riemannian manifold gradient) method, and the beamforming was obtained by the bisection search method. Furthermore, an element-wise block coordinate descent-based method was proposed to reduce the complexity of the RMG method. Simulation results verify the effectiveness of the proposed algorithm, and demonstrate that IRS can significantly improve the spectrum efficiency, when the reflecting coefficients are properly optimized.

Abstract:A CJ(cooperative jamming) masked secure communication architecture was proposed for confidential communications when malicious interference and illegal eavesdropping coexist. Thereinto, the FH(frequency-hopping) technology was adopted in the transceiver to avoid malicious interference, and the CJ technology was employed to block illegal eavesdropping. Nevertheless, the proposed architecture employs a wide frequency bandwidth, which will raise nonnegligible IQ(in-phase and quadrature) imbalances at the transceiver oscillators. In view of this, the mathematical modeling was conducted on the signal distortion caused by the imbalance of the receiving and transmitting IQ channels, a mathematical expression for SDNR(the signal to distortion-plus-noise ratio) at the receiver was provided, and a closed-form expression for the system CJSR(CJ suppression ratio) was derived. Simulation results show that the power of the signal distortion raised by transceiver IQ imbalance is much greater than that of the thermal noise. Besides, both the SDNR and CJSR will decline sharply as the transceiver IQ imbalance deteriorates, and when the magnitude and phase imbalance are 0.95 and π/50 respectively, both the SDNR and CJSR performance will deteriorate 47 dB.

Abstract:Due to overlapping frequency bands between frequency-consuming devices, the local transmitter will cause serious collocation interference to the receiver, causing the saturation of receiver antenna interface and failing to work normally. In response to the above problems, a collocation interference suppression method based on auxiliary array was proposed, a collocation interference suppression system model based on auxiliary array was established, the expression of minimum residual interference power was derived, channel conditions that need to be satisfied for collocation interference suppression was proposed. In addition, the location of the auxiliary was analyzed when main-transmitter array was non-cooperative, and the relationship of the locations of arrays was analyzed when the main-transmitter array was cooperative. The theory and simulation results show that the collocation interference suppression method based on auxiliary array can effectively suppress collocation interference at the receiver antenna interface without affecting the transmission efficiency of the local main-transmitter array.

Abstract:Aiming at the problem that the accuracy of the existing modulation signal recognition model was low under the condition of weak supervision with only a small amount of labeled data, a semi supervised learning framework based on generated countermeasure network was proposed. By performing a redundant spatial transformation on the communication signals, the method can adapt to the generative adversarial network model and retain rich signal adjacent features. Through the introduction of Wasserstein generative adversarial network-gradient penalty, a semi-supervised learning framework suitable for electromagnetic signal processing was constructed to realize the effective utilization of unlabeled signal samples. In order to verify the effectiveness of the proposed algorithm, sufficient experiments were conducted on the RADIOML 2016.04C dataset. Experimental results show that the proposed method can train an efficient classifier under semi-supervised conditions and obtain excellent modulation recognition results.

Abstract:Plasma has a unique protective effect against high-power microwave attack. Based on the plasma fluid approximation method, the time dependent evolution of the incident electric field during the interaction between high-power microwaves and columnar plasma arrays was studied by using COMSOL software, and the physical process and mechanism of plasma protection against high-power microwaves were analyzed. The results show that the incident high-power microwave will change the plasma parameters drastically, especially the electron density will increase sharply, so that the plasma will show metal-like electromagnetic properties to the incident high-power microwave, and finally realize the effective protection against the incident high-power microwave. In addition, the plasma protection against high-power microwaves was experimentally verified by using columnar plasma arrays generated by high-frequency glow discharge. Finally, the main problems to be solved for plasma-based high-power microwave protection technology were summarized.

Abstract:Considering the distributed intermittent interference threat faced by global navigation satellite system receiver, the anti-jamming performance of STAP(space-time adaptive processing) based on sample matrix inversion method was comprehensively and accurately analyzed. Based on the performance analysis model, according to the mismatch of sampling covariance matrix caused by intermittent interferences, the performance of STAP under different conditions was comprehensively analyzed through classification evaluation, combing induction and theoretical derivation. The analysis results show that when the sampling length is less than the scintillation period and the pre-sample method is used, the missed sampling of space-time adaptive processor will occur and the interference suppression performance will decrease sharply, and the frequency of missed sampling is the sum of the scintillation frequencies of each interference. Numerical and simulation analyses verify the results of analysis, and based on this, the optimal design of STAP in the face of distributed intermittent interference is discussed.

Abstract:Neural architecture search is a task that aims to automatically search for the optimal neural network structure for different tasks, which is of great importance and inevitability in the joint development of deep learning and computer vision to the current stage. A comprehensive review of the research on neural network search was provided. In specific, the definition and significance of neural architecture search were introduced, and the difficulties and challenges faced in relevant research were deeply analyzed. Based on this, the mainstream search strategies was elaborate and summarize; Finally, the potential problems and possible future research directions were summarized and discussed to promote further development in this field.

Abstract:In order to solve the configuration planning problem for intelligent search and rescue robots with assisted flippers to achieve autonomous obstacle crossing, a novel method for planning robot configuration during obstacle crossing was proposed that can be applied to complex terrains. The core of the proposed method is an adaptable and efficient robot pose prediction algorithm. By representing the terrain as a series of discrete point sets, a mathematical model for predicting the one-sided pose of the tracked robot was established; further, a fast solver for this model was proposed, which can predict 1000~1500 poses per second. Based on this, the evaluation metrics of the robot′s state and action in the obstacle-crossing process were established, and an optimization-based real-time flippers action planner was realized by using the dynamic programming algorithm and rolling optimization. The simulation and real-robot experiments show that the proposed approach enables the robot to control the flippers to cross rough terrains autonomously. It performs more smoothly than the reinforcement-learning method and manual operation when crossing obstacles.

Abstract:In order to improve the reliability of the single-reference-station based relative positioning solutions over short baselines, the multi-reference-station based relative positioning method was explored. A priori baseline information between the reference stations was integrated into the observable model, thus giving the functional and stochastic models of the multi-reference-station based relative positioning. Based on that, the closed-form formula of the ambiguity dilution of precision for the positioning was derived so that the influence of the number of reference stations on the float ambiguity precision was revealed. Then the impacts of the biases in the a priori baseline information on the integer ambiguity resolution were analyzed theoretically. It show that the integer ambiguity resolution could barely be influenced on the condition that the bias is less than 5 cm. The multi-reference-station based relative positioning method was validated with both the simulated and real data sets. The numerical results show that, increasing the number of reference stations not only improves the single-frequency ambiguity resolution success rate and convergence rate, but also restrains the biases in the a priori baseline information. For example, the ambiguity resolution success rate is still larger than 92% even when the biases of the baseline components attain 4 cm in the field tests. This contribution provides the theoretical foundation for the fast and imprecise calibration between the multiple-reference-station in special scenarios.

Abstract:Due to the existence of internal resistance and polarization, there will be a large voltage drop at the discharging moment of the lithium battery, especially the high-rate pulse-discharged lithium battery. The power characteristics of high-rate pulse-discharged lithium battery were studied, as well as the influence rules of temperature, state of charge and aging on battery power performance. The power characteristic curve of lithium battery was defined, a high-rate battery test plat-form was built, and experimental research was carried out from three impedance sensitive factors: temperature, state of charge and aging. The research methods and conclusions are of certain significance for the peak power evaluation and power curve prediction of lithium battery system.

Abstract:Noted the limitation of existing methods to study the delay propagation mechanism in high-speed railway network, the Bayesian network was used to analyze delay dependencies between stations based on high-speed train operation data and schedule data. The percolation theory of complex network was applied to study the evolution of delay propagation clusters. Nanjingnan Railway Station in the largest delay propagation cluster and Changshanan Railway Station in the second largest delay propagation cluster were taken as examples to analyze the network at percolation threshold. Based on core delay propagation clusters, the station delay state prediction model was established. The results show that stations can be divided into 3 categories, namely, delay generator, delay mediator and delay absorber according to their characteristic in the aspect of delay propagation. Delay generator can not only spread the delay to stations close to them, but also spread the delay to the far away stations through delay propagation chain, which makes the network taking part of the delay generator as the center and spreading delay to the delay mediator and the delay absorber in a radiational delay propagation mode.

Abstract:A KL(Kullback-Leibler) divergence multi-block moving window slow feature analysis method was proposed to solve the problems that the variable feature information cannot be fully utilized by the traditional block segmentation method based on experience, the local information is ignored by a single modeling method, and the off-line model cannot adapt to the time-varying characteristics. KL divergence was used to measure the distance between variables in the normal working condition data set, and the minimum error sum criterion was introduced to cluster, which was divided into two sub-blocks with the minimum distance. On this basis, the slow feature analysis method was utilized to model each sub-block, and the optimal model was obtained by updating the sampled data with moving window. Monitoring statistics were calculated respectively, and the fault monitoring results were fused with support vector data description to achieve fault diagnosis. The proposed method was applied to the monitoring of Tennessee Eastman process, and higher fault detection rate and lower false alarm rate are obtained, verify the feasibility and effectiveness of this method.

Abstract:The novel non-volatile MRAM(magnetic random access memory) has the advantages of fast read and write speed, long data retention time and low power consumption, which attracts wide attention from researchers. Its excellent anti-irradiation capabilities are explored in depth, and further applications in aerospace and other fields are expected. The industrial development, technological changes and applications of MRAM were reviewed, the mature MRAM products of recent years were listed, and the advantages and disadvantages of different generations of MRAM were analyzed. The radiation effects of MTJ(magnetic tunnel junction) and read/write circuit based CMOS(complementary metal oxide semiconductor) were discussed. The recent achievements in anti-radiative hardening design for MRAM were summarized. The development prospect of anti-irradiation MRAM in aerospace field and even nuclear energy field was prospected.

Abstract:According to the floating weight balance characteristics and the ideal gas state equation, a method to control the height of the aerostat′s flat flight by gas mixing was explored, and the overall design research of constant-height flight by air-lifting gas mixing was carried out. Considering the importance of thermodynamic characteristics to the ascent process and the flat flight process of the aerostat, combined with the thermophysical properties of mixed gas in engineering thermodynamics, the super-pressure balloon was taken as the research object to analyze the thermal environment during the ascent and flight processes of spheres, and coupled with dynamic models. On this basis, the mechanical simulation of the ascent and flat flight process of the balloon was carried out, and the changes in altitude, speed, gas temperature and pressure during the ascent of the balloon were obtained, so as to verify the feasibility of the theoretical model of constant-height flight by air-lifting gas mixing, and provide guidance for the subsequent aerostat flight test.

Abstract:To enhance the stability of the supercavitating vehicle caused by the nonlinear planing force between the cavitation and the vehicle, a cascade control method for the depth tracking was proposed based on the circle criterion theory and the Nelder-Mead algorithm. The mathematical model of the supercavitating vehicle and the circle criterion theorem were introduced. The cascade error state equation of the supercavitating vehicle was established based on the model, and the absolute stability of the inner-loop was studied using the circle criterion. The inner-loop feedback parameters were further optimized through the Nelder-Mead algorithm. The simulation analysis results show that the control method proposed in this paper is convenient for feedback parameter tuning, and can realize the accurate depth tracking effectively.

Abstract:S-bend inlet leads to obvious flow separation and apparent total pressure distortion in unmanned aerial vehicle. To solve this problems, an active flow control method based on dual synthetic jets was proposed accordingly. The numerical simulation model of S-bend inlet with dual synthetic jets was established. The results show that dual synthetic jets can effectively suppress the boundary layer flow separation near the separation point of S-bend inlet through "blowing" and "suctioning" in the whole jet cycle, and effectively improve the total pressure recovery coefficient. The effects of different jet angles, jet peak velocities and jet frequencies on the flow field control characteristics of S-bend inlet were studied. The results shows that the smaller the angle between the dual synthetic jet and the main stream is, the better the flow separation control effect will be. The larger jet peak velocity will form a "blocking" effect on the main stream, resulting in a decrease in control effect. The closer the jet frequency is to the characteristic frequency of the flow field, the more obvious the control effect will be.

Abstract:Space close-range patrol can be used to carry out close-range observation and monitoring of targets for identifying the target′s types and working states, which is of great significance for military and civilian fields such as in orbit services. The study analyzed the general forms of space close-range patrol tasks. Furthermore, based on the optical observations of close-range patrol, the multifactor observation task effectiveness evaluation models were constructed, including a constraint model for observation, a relative distance evaluation model, an effective observation time evaluation model, and a target observation angle evaluation model. This solved the effectiveness evaluation problem for the complete process of patrol tasks, which can support the design of patrol strategies and patrol trajectories better based on the evaluation results. In addition, based on the numerical simulation analysis and semi-physical experiments, the proposed evaluation model was verified. The result shows that the actual observation effect is consistent with the model evaluation result.

Abstract:In order to estimate the overall life of the existing three gate module of 30 cm diameter ion thruster, the grid gap under thermal equilibrium state and the erosion velocity of different regions of the grids were simulated and calculated by FEM (finite element method) and PIC-MCC (particle-in-cell-Monte Carlo collision) method respectively. The results show that when the thruster reaches the thermal equilibrium, the overall deformation of the decelerator grid presents central area depression characteristics, and the overall deformation of the accelerator grid presents a uniform protruding. In the center area of the grids with the diameter of 0~70 mm, the mean gap between the two grids decreases by 0.057 mm. Meanwhile, in the annular region with the diameter of 70~140 mm, the mean gap between the two grids increases by 0.129 mm. The erosion velocity of the apertures at the edge of the decelerator grid reaches 6.25×10^-14 kg/s within 1500 h, and which of the aperture at 5700 h decreases 15.4% compared with 1500 h. The erosion velocity of the apertures at the center and edge of the accelerator grid, and the apertures at the center of the decelerator grid decreases 8.0%，4.1% and 3.6%, respectively. The results of 5700 h life test show that the erosion of the apertures at the center of the decelerator grid, and the apertures at the center and edge of the accelerator grid are basically linear, and the comparison error between the simulation and test is within 10%.