Abstract:The novel UAV (unmanned aerial vehicle) ground station with advanced control capabilities such as immersive display, intelligent assistance, and naturalized human-computer interaction has become a hot research topic in the field of UAV control. To analyze the technical aspects, the functional points and designs concepts of a series of advanced ground stations for UAVs at home and abroad were systematically compared. The technical system composition from the OODA (observe, orient, decide and act) loop of UAV ground station command and control were summarized and refined. The key techniques such as task environment construction, battlefield situation immersive display, intelligent assisted decision and naturalized human-computer interaction were analyzed and pointed out. The main research methods of various techniques were deeply analyzed, and the current challenges and future development trends of UAV advanced ground stations were also studied and judged. In addition, it provides guidance and reference for the development of novel ground stations.

Abstract:VINS (visual-inertial navigation systems) solve a series of parameters required for state estimation through initialization, such as scale, gravity vector, velocity, inertial measurement unit′s bias, etc., to improve the accuracy of navigation positioning and environmental perception of the system. The initialization methods of VINS can be divided into three categories according to the sensing information fusing mode:joint initialization, disjoint initialization and semi-joint initialization. Based on the existing research work, the current mainstream initialization methods of VINS were reviewed from four aspects:basic theory, development and classification, existing methods, performance evaluation, and the future development trends were summarized, which is helpful to have a general understanding of VINS initialization methods and grasp its development direction.

Abstract:For the tracking performance problem of hypersonic vehicle with actuator constraints of amplitude and rate, a prescribed performance control scheme based on constrained command filter was proposed. In order to improve the transient and steady state performance of the system, a prescribed performance backstepping controller was designed. And a new performance function was designed to reduce the tracking error overshot. A command filter was introduced to solve the problem of difficult derivation in the design of backstepping controller. For the problem of limited input, a constrained command filter was constructed to constrain the control law of the system, which guaranteed that the control input meet the limit requirements of amplitude and rate, and the corresponding theoretical proof was carried out. In addition, the linear extended state observer was used to observe and compensate the system parameter uncertainties and external disturbances. Based on Lyapunov stability theory, it was proved that all tracking errors of the system are ultimately uniformly bounded. The effectiveness of the proposed method was verified by simulation.

Abstract:In order to solve the problem that the capacity of line transformer in AC power network interconnected by conventional bus switch can not be utilized reasonably, a coordinated control strategy for active power of AC power grid on both sides was proposed, which relies on a new type of high-power flexible interconnection equipment composed of back-to-back voltage source converter. The topological structure and basic control principle of the flexible interconnection equipment were introduced, and a method of generating active power reference was developed to realize the reasonable capacity of the transformers on both sides of the line. Moreover, a simulation example was built based on PSCAD/EMTDC to verify the basic control of the flexible interconnection equipment and the proposed coordinated control method of active power cooperation. Simulation results show that when the flexible interconnection equipment adopts the proposed method, the cooperation of active power of AC lines on both sides can be realized, and the problem that the capacity of line transformer can not be allocated reasonably is solved.

Abstract:Aiming at the problem that the traditional hybrid fuzzy test promotion technology focuses more on the use of multiple dynamic and static analysis methods to assist and ignores the performance of concolic execution, a hybrid fuzzing balance-point model was proposed. Based on the model, the popular concolic execution tools were analyzed, including taint-assist fuzzing, hybrid fuzzing and concolic execution, and 6 symbol execution schemes were summarized. Based on the hybrid symbol execution engine Triton, 6 symbol execution schemes were reproduced, and tested and evaluated through 10 typical real programs. Performance comparison and impact factor analysis of each scheme were conducted from three dimensions of efficiency, memory consumption and coverage. Experiment results show that all of the optimization patterns can basically reduce the unnecessary constraints and thus reduce time and space consumption. However, the reduction of constraints can cause information loss and lead to coverage decrease. Based on the analysis of experimental data, the performance sequence of an optimization scheme was proposed, and three optimization schemes for different test requirements were proposed.

Abstract:Crowd profiling of massive transit data is valuable for analyzing the travel characteristics and traffic trends of urban groups, but the processing of the data is time-consuming, low-quality and difficult to interpret. A systematic solution for crowd profiling of massive public transport data was proposed. Based on the PageRank algorithm, the trajectories of people passing through important stations were filtered out, which greatly reduced the trajectory data of the target population. A textual analysis method for trajectories was proposed to improve the interpretability of crowd profiling. And the K-means algorithm based on cosine distance as the clustering algorithm for crowd profiling was analysed and determined. The experiments on 30 million passengers′ transit data show that the proposed algorithm can solve the problem of crowd profiling in massive transit data in a more systematic way, while the K-means algorithm based on cosine distance has the best clustering effect and the accuracy rate is about 80%. The crowd profiling and its trajectory were visually displayed by using Flow Map, and the results are consistent with real-world crowd behavioural characteristics.

Abstract:Aiming at the problem of isolated information of monitoring points and low degree of intelligent decision-making in the current warship fire-fighting system, a node-based fire-fighting system functional logic model was constructed. The intelligent decision algorithm of fire-fighting system damage isolation and reconstruction based on combat damage employment was put forward. And the intelligent monitoring system for fire-fighting was developed. Results of case comparison calculation and system inspection show that the intelligent decision-making algorithm and intelligent monitoring system can effectively improve the speed and accuracy of analysis and decision-making and significantly improve the efficiency of command and control, which provides effective support for the water fire fighting system under combat damage condition.

Abstract:Aiming at the problems of high random fluctuation of urban traffic flow and high noise in data, which leads to the decline of prediction accuracy, a combined traffic flow prediction model based on EEMD (ensemble empirical mode decomposition) and BiGRU (bidirectional gated recurrent unit) was proposed, which can effectively improve the accuracy of short-term traffic flow prediction. EEMD algorithm was used to decompose the original data, and the noise energy map was drawn according to the IMF(intrinsic mode function) component to remove the noise in the component. The denoised IMF components were trained as the input of BiGRU network. And the results of training were reconstructed and added to obtain the final prediction result. The experimental results show that,compared with the EMD+LSTM model, LSTM model and EEMD+LSTM model proposed in references, the mean absolute percentage errors are improved by 42.36%, 61.82% and 30.95% when the IMF components containing noise are not abandoned during reconstruction; after abandoning the IMF component containing noise, the mean absolute percentage error is improved by 56.62% compared with the reconstruction of all IMF components.

Abstract:For the remote communication scenario of UAV(unmanned aerial vehicle) at sea, the received power was measured on the basis of the wireless communication link between UAVs. In terms of large-scale path loss, the logarithmic distance linear model was used to fit the measurement data. The characteristics of remote air-to-air wireless channel at sea were analyzed, and the path loss index was obtained. The ray tracing method was used to simulate and verify the measurement results. Through the simulation of channel impulse response, the reasons for the rapid change of received power were analyzed in terms of multipath delay and power. The analysis results show that the multipath reflection in the nearshore causes the fluctuation of the received power and increases the path loss. Three kinds of distribution functions were used to fit the measured data, and the small-scale distribution characteristics of air-to-air wireless channel under sea surface and inshore communication conditions were analyzed. The analysis of the measurement results shows that the small scale characteristics are significantly affect by the land reflection, showing Gaussian distribution characteristics at the sea surface far from the land, but not typical distribution characteristics near the land.

Abstract:In order to analyze the anti-spoofing performance of the GNSS multi-beam anti-jamming receiver under spoofing interference scenario, a performance metric named deception suppression ratio was put forward. The theoretical formula for the power of the authentic and spoofed signal was deduced considering the anti-jamming receiver using the MVDR (minimum variance distortionless response) algorithm with limited number of snapshots. And the influence of the power of the spoofed signal arriving at the antenna array on the output power of the authentic and spoofed signal was analyzed in detail. The analysis shows that even if the power of the spoofed signal is below the noise level, the multi-beam anti-jamming receiver using the MVDR algorithm can still suppress the spoofing interference. And when the spoofed signal-to-noise ratio is high, the suppression is more effective. The conclusion was verified by simulation and hardware platform test.

Abstract:With the gradual increase of space exploration tasks and the increasing tension of space channel spectrum resources, the traditional Gardner timing synchronization algorithm can no longer meet the demand of high throughput and high reliability of high-speed data transmission system. In order to improve the throughput and increase the correctable error range of Gardner timing synchronization algorithm, a high-speed parallel Gardner algorithm was proposed. To ensure the interpolation accuracy and reduce the multiplier consumption, a parallel piecewise parabolic interpolation filter was designed. To facilitate the parallel pipeline design and optimal sampling point selection, a counting module and a timing cache adjustment module were built. To improve the equivalent throughput rate, the pipelined parallel loop filter structure and the pipelined parallel numerically controlled oscillator structure were reconstructed. Results show that the equivalent throughput rate of the algorithm can reach 1 739.13 Msps, the digital signal processor resource consumption can be reduced by 44%, and the timing error of 2×10^-3 can be corrected.

Abstract:In order to reduce the peak sidelobe level of sparse rectangular array with fixed sparse ratio and fixed aperture, a modified integer genetic algorithm was proposed. On the basis of the integer genetic algorithm, the crossover strategy of equal interval sampling, multi-point mutation strategy and excellent gene recombination strategy were proposed. The crossover strategy of equal interval sampling can effectively exert the advantages of integer coding, which improves the operation efficiency of the algorithm. In order to improve the diversity of the population and avoid falling into the local optimum, the multi-point mutation strategy was adopted. The excellent gene recombination technology was used to accelerate the convergence speed of the algorithm. Simulation results show that, compared with the traditional binary and real coding, the integer coding is more direct and efficient; compared with the related algorithms for sparse rectangular array optimization, the proposed algorithm obtains the better sidelobe level, which proves the effectiveness and superiority of the algorithm.

Abstract:A variety of typical signal processing algorithms and deep learning algorithms were analyzed and modularized from the calculation requirements level. The computing modules, which were suitable for hardware acceleration parallelly in the two types of applications were extracted. A consistent computing model for signal processing and deep learning was proposed, and a hierarchical processing element and arrayed processing structure were proposed based on the consistent computing model in which the control part and computation part were separated. By the software definition of different application computing processes, the consistent hardware-accelerated computation of signal processing and deep learning could be realized flexibly.Based on Zynq computing platform, the consistency computing model and computing structure were verified from two aspects of reconstruction efficiency and computing performance. The validation results indicate that software-defined reconfigurable computing structures based on consistency computing models have high computational performance and reconstruction efficiency.

Abstract:GNSS (global navigation satellite system) vertical time series have the characteristics of non-stationary, non-linear, and noisy. Based on the in-depth study of the Prophet prediction model, and the good predictive effect of Prophet prediction model on trend signals and periodic signals, a “noise reduction-decomposition-prediction” combined prediction method of GNSS vertical time series that introduces EMD (empirical mode decomposition) was proposed. EMD denoising was performed on the original time series, the denoised series were decomposed and predicted, and the predicted signal of each component was reconstructed into the final predicted series. The measured vertical data was used for research, and results show that the average signal-to-noise ratio of the signal after noise reduction is 10.30 dB, and the average energy percentage is 88.75%; using the short-term prediction method, the root-mean-square errors of GNSS vertical time series prediction results are increased by 26.41% and 14.88% on average, respectively; the average percentage errors are increased by 18.92% and 7.91% on average, respectively, and the effectiveness and practicability of the combined forecasting method are verified.

Abstract:In order to scientifically and reasonably select the third-party service organizations of equipment price, the evaluation model was constructed by gray correlation analysis and neural network.The research data was obtained in the form of questionnaire survey. The gray correlation method was used to analyze the correlation between the evaluation index and the comprehensive score. It is found that the two primary evaluation indicators of service attitude and system construction are more important, with a correlation degree of more than 0.74. Using effective secondary indicators and comprehensive scores as input and output data, the evaluation model based on neural network was built. Finally, through the verification and analysis of the rationality of the method, it is found that the prediction accuracy probability of the neural network model is 75% and the probability of meeting the requirements is 25%, which meets the actual user needs and can provide suggestions for the competent departments to select third-party institutions.

Abstract:The effects of initial beam distribution, divergence, energy divergence and geomagnetic field on the spatial transmission of particle beams were comprehensively analyzed, and the numerical modeling and quantitative numerical simulation of electrostatic diffusion and geomagnetic deflection effects were carried out. The simulation result shows that for particle beam with fixed beam energy and beam intensity, the electrostatic diffusion effect of the particle beam can be weakened by increasing the initial radius, and the exact direction of beam can be accurately predicted through accurate measurement of magnetic field. It can be seen that research on self-consistent force of charged particle beam and its interaction with external field is great significant to the study of generation, transport characteristics and engineering application of the particle beam.

Abstract:A three-dimensional intersection localization method for moving target using two vision-based UAVs (unmanned aerial vehicles), which did not rely on the distance information from the target point to the UAV was proposed. An interacting multiple model estimator was adopted to the localization method to solve the problem of not knowing the motion form of the moving target. A modified Sage-Husa adaptive filtering algorithm that synthesized the covariance matching technique and the positive definiteness judgment was used to improve the accuracy of localization. To assess the performance of these approaches, a set of simulations that carried out under realistic conditions were presented. Results show that the method proposed can get the accurate three-dimensional coordinates of the target. The modified Sage-Husa adaptive filtering algorithm can improve the localization accuracy significantly, with the average estimation error reduced from 27.13 m to 14.62 m under the intersection angle of 90°. The influence of the intersection angle on localization was studied in the simulation, which shows that too small intersection angle is not conductive to the improvement of localization accuracy, a larger intersection angle is good for the localization method without filtering, but the effect on the method with the modified Sage-Husa adaptive filtering algorithm is not significant.

Abstract:In order to improve the performance of the rocket-based combined-cycle engine, the influence of the rocket exit area under the ejector mode was studied. Through numerical simulation research, the mass flow of captured air was mainly affected by the entrainment performance under the condition of low flight Mach number. The larger the rocket exit area, the better the entrainment performance. However, with the increase of flight Mach number, the kinetic energy of the entrainment air increases, and there is flow choking in the isolator. The mass flow of captured air was mainly limited by the geometric size of the isolator, independent of the rocket exit area. Under subsonic conditions, the smaller the rocket exit area is, the lower the specific impulse of the engine is, and when the exit dimensionless area is 3.15, the rocket plume will expand and impact the wall, which can cause a sudden reduction in performance. Under supersonic conditions, the smaller the rocket exit area, the higher pressure in the combustor, and the better performance of the rocket-based combined cycle engine.

Abstract:In order to optimize the design of satellite constellations with specific area coverage and intensive revisits, a design scheme of regression orbit and co-subsatellite point trajectory constellation was adopted, and a method to optimally solve the satellite constellation orbit parameters by integrating genetic ant colony algorithm with the weight ranking coverage of key areas in specific area was proposed. The design requirements of the regional coverage constellation were analyzed, a regression orbit coverage area model was established, the optimal orbit root number was calculated by using the genetic ant colony algorithm, and all the constellation parameters were solved through using the co-subsatellite point trajectory constellation solution algorithm. The simulation results show that the optimized constellation meets the coverage time and revisit frequency requirements for the area target, and provides focused coverage and revisits of important locations in order of weight, which verifies the feasibility of the algorithm.

Abstract:As an important uncertainty factor in multidisciplinary optimization design of aerocraft, the statistical characteristics of aloft wind should be acquired accurately. The probability distribution of conditional aloft wind speed is unique, in order to facilitate the use of probability model of aloft wind for uncertainty design and reduce the amount of calculation, an analysis method of difference between probability distribution of conditional aloft wind speed and normal distribution was proposed, and the applicable condition for simplifying the distribution of probability distribution of conditional aloft wind speed to normal distribution was given. Numerical simulation results show that within latitude range of 24.3°N～42.2°N, the difference between condition aloft wind speed probability density and normal distribution probability density in different regions is trumpet-shaped in the range of 2～30 km above sea level, and the conditional aloft wind speed probability density is closest to that of normal distribution nearby the altitude of 15 km, which can be approximately assumed to be normally distributed. Based on the above work, suggestions were given for selecting the method of generating random samples when considering the uncertainty of the conditional aloft wind speed in the uncertainty design of aerocraft.

Abstract:In order to achieve the deterministic transmission of diverse data streams in a short time on the SpaceFibre network, the fine-grained low-latency deterministic scheduling algorithm with classification was proposed. According to the differentiated scheduling strategy, space tasks were divided into three types. For the efficient allocation of resources, the extended time-slot was introduced. The uniform distribution of time-slot without conflict reduced the average delay of data packets. To adapt to aerospace applications where payloads were connected with a network, the method generated scheduling vectors based on the network topology. The simulation model of the SpaceFibre network in OPNET was built to verify the effectiveness of the method. Experimental results show that the scheduling scheme generated by the method has better certainty than the classic scheduling based on priority and conflict-free consecutive scheduling; with the increment of the number of time slots, the average delay and jitter of each traffic are reduced, and the throughput is guaranteed. Therefore, the method has certain practical application value in aerospace engineering.

Abstract:The annular connecting straight cylinder engine has many advantages such as high power density, low inertia force and so on. However, the cylinder rotors always rotate along the circumferential direction of the output shaft during operation, which makes the traditional static gas distribution method no longer applicable. Therefore, it is of great significance to research and design a new type of gas distribution system that meets the intake and exhaust requirements of this type of engine. In view of the unique annular connecting structure and differential velocity motion characteristic of the engine, the volume change law of each rotor cylinder was analyzed, and the relationship between the intake and exhaust phases of each rotor cylinder and the rotor rotation angle was studied. On this basis, an innovative dynamic position gas distribution system with airway reuse feature was designed. According to the gas distribution scheme of two-stroke engine, the parts of the gas distribution system were designed and processed, and the dynamic intake and exhaust process was completed through high-pressure pneumatic test. The experimental results show that the engine can run stably at 200 r/min when the driving air pressure is 0.25 MPa, which effectively verifies the feasibility of the gas distribution system.

Abstract:The penetration performance of the double-arrow negative Poisson′s ratio multicellular structure against bullet penetration was studied by numerical simulation method.The penetration behaviors of bullets and the damage forms of the double-arrow negative Poisson′s ratio structure under the three bullet target conditions of top-edge impact,hinge-point impact and side-impact were compared and analyzed.The results show that the negative Poisson′s ratio effect of the double-arrow negative Poisson′s ratio structure is not significant when the bullet impacts the structure at a high velocity.The bullet directly penetrates the structure at topside impact and hinge point impact,the damage of the cell element is small and the anti-intrusion performance of the double-arrow negative Poisson′s ratio multi-cell structure is poor at this time.The bullet does not penetrate the multi-cell structure at side impact,and the damage of the cell element is large;the double-arrow negative Poisson′s ratio structure relies on its double-Poisson′s ratio structure to deflect the bullet at side impact.The double-arrow negative Poisson′s ratio structure relies on its double triangular structure to deflect and roll the bullet during side impact,which significantly increases its penetration resistance.The effect of the change in the angle of incidence of the bullet during topside impact on the intrusion resistance of the double-arrow negative Poisson′s ratio structure was analyzed. It is found that there is a 30° angle of incidence and a 60° angle of incidence.The double-arrow negative Poisson′s ratio multi-cell structure has some resistance to penetration when the bullet is near these two incidence angles.

Abstract:In order to explore the survival probability of multi-axle special vehicle tire system under battlefield threat and quantitatively characterize the anti-damage capability of tire system, a new method based on isodamage curves was proposed to characterize the battlefield anti-damage capability of the tire system. Aiming at the influence of tire damage on the whole vehicle, the mechanical characteristics of tire system were quantitatively characterized based on vehicle dynamics, and the calculation model of tire system functional damage was established. Based on the damage theory, the collision and quantitative analysis of shock wave overpressure field were carried out, and the calculation model of tire system physical damage was established. According to the position relationship between the burst core and the vehicle, the calculation model of the tire system isometric line was established by using the characteristic line for the vehicle in the whole area. A five-axle special vehicle was taken as an example to verify the characterization method. Results show that this characterization method can be applied to the characterization of the anti-damage capability of the multi-axle special vehicle tire system under battlefield threat, which lays a model foundation for the improvement of maneuvering avoidance and protection ability in the future.