Abstract:With the rapid development of spacecraft rendezvous and proximity operation technology, the problem of orbital pursuit-evasion has gradually become a research hotspot in the aerospace field. From the perspective of dynamics and control, the research status of spacecraft orbital pursuit-evasion was reviewed. General form of the orbital pursuit-evasion problem model based on quantitative differential games was given, and various types of orbital pursuit-evasion problems were systematically sorted out. For the solution of pursuit and escape strategies, the advantages and disadvantages of various methods were analyzed for closed-loop strategy and open-loop strategy. Focusing on the combination of artificial intelligence algorithm and orbital pursuit and escape problem, the research status of orbital pursuit and escape strategy based on deep neural network and reinforcement learning was expounded. Regarding future prospects, development directions has been proposed, including the pursuit-evasion game situation analysis, the multi-spacecraft game control, the game dynamics and control under three-body problem.

Abstract:Aiming at guarding high-orbit high-value targets, a multi-spacecraft cooperative guard strategy based on reachable domain coverage was proposed. The cooperative guard mission was described from the perspective of relative motion, and the multi-pulse reachable domain of the threat was modeled as a convex optimization problem. In the framework of receding optimization, the guard planes and points were designed based on the dynamically updated terminal reachable domain of threat, and a multi-spacecraft cooperative trajectory planning model was constructed with the guard points as terminal position constraints, the corresponding guard trajectories were generated. Simulation results show that the proposed method can quickly calculate the terminal reachable domain of the threat. The cooperative guard strategy can effectively prevent the threat in multiple scenarios, and the guard success rate increases with the enhancement of the maneuvering ability of the guard spacecraft.

Abstract:Given the influence of uncertainty such as measurement errors in the process of spacecraft free-time orbital pursuit-evasion game for rendezvous, a high-efficiency strategy based on receding horizon optimization was proposed as a solution method. The saddle point control strategy of the game was derived according to differential games, and the equivalent transformation of the problem was carried out. By solving open-loop saddle point strategy off-line in advance, the initial states of the problem and the corresponding solutions were taken as samples for neural network training, and the trained network structure can quickly obtain the approximate solution of the corresponding problem. In order to better deal with the measurement noise in the game environment, a receding horizon optimization framework was designed based on the neural network structure. By periodically solving the problem, the rendezvous of the pursuer and evader was finally realized. Numerical simulation shows that the proposed strategy can effectively deal with the uncertainty of measurement noise, and compared with the existing strategy in the literature, the calculation time can be reduced from minutes to several seconds.

Abstract:Spacecraft pursuit-evasion game is currently a research hotspot in the field of aerospace dynamics and control. Qualitative spacecraft pursuit-evasion game was studied in order to provide feasibility support for strategy design, and a situation analysis method for scenarios in close range was proposed by comprehensively using dimension-reduction dynamics and backwards reachability set. A dimension-reduction dynamic model was derived in the line-of-sight rotation coordinate system, and the pursuit-evasion qualitative model of the game system was determined to reduce state space dimension. The backwards reachable set of the target set was used to divide the pursuit-evasion state space and describe the capture zone. A time-dependent HJI (Hamilton-Jacobi-Isaacs) PDE (partial differential equation) was established to describe the evolution of backwards reachable set in the dimension-reduction dynamics, based on level set method, and a WENO-TVD(weighted essentially non-oscillatory-total variation diminishing) solver was designed to numerically calculate the viscous solution of the final value problem of the HJI PDE. These measures achieve the accurate description of pursuit-evasion target set and avoid the possible terminal singularity. The effectiveness of the method was demonstrated by numerical simulations of several pursuit-evasion scenarios with different thrust configurations, and the function of batch processing of initial situations in a single calculation was demonstrated.

Abstract:The development trajectory of the flying-wing aircraft was sorted out, encompassing the early evolutionary history to the current state of research, along with contemplation and forecasts regarding future directions. Meanwhile, several key control challenges associated with flying-wing aircraft were discussed, including attitude control in a wide-speed domain under nonlinear conditions, high-precision autonomous take off and landing control under multiple effect coupling, robust control issues with approximate aerodynamic models and under strong disturbances, as well as control allocation problems arising from multi-surface redundancy. Moreover, the discussion on flow control issues that were currently a focal point in flying-wing aircraft research were discussed in depth. The following research trend of active flow control technology was expounded.

Abstract:In order to address the problem that the dynamic response characteristics of the bolted flange connection structure, which is widely used in aerospace rocket structures, are significantly affected by the magnitude of bolt preload, the static and dynamic response characteristics of the rocket connection structure were studied taking into account the discrepancy of bolt preloads under different conditions. A set of methods for analyzing the dynamic response of rocket body connection structures considering the discrepancy of bolt preloads was proposed based on finite element analysis and knock tests for a specific barrel-shell bolted flange connection structure. By investigating the response characteristics of the connection structure with a loose bolt, a new bolt loosening detection procedure based on the complementary ensemble empirical mode decomposition algorithm is proposed which can quantify the characteristics of the increase of the frequency response amplitude in the middle and high frequency bands of the connection structure when the loosening happens, and can quickly identify the occurrence of loose conditions without damage.

Abstract:Bending and buckling behavior of the macro CNTRCs (carbon nanotubes reinforced composites) beam was studied considering the scale effect of CNTs (carbon nanotubes). Based on the EMT (Eshelby-Mori-Tanaka) method and using nonlocal theory to characterize the scale effect of CNTs, the nonlocal EMT constitutive model was established. According to the Timoshenko beam theory, the static differential equations and boundary conditions of CNTRCs beams were derived through Hamilton principle. Bending response and ultimate buckling load of CNTRCs beams at S-S (simply supported) edges were obtained and compared with the literature to verify the correctness of the proposed model and solution method. Influences of the scale effect parameters and volume fraction of CNTs and the slenderness ratio of composite beams on the bending response and ultimate buckling load of S-S CNTRCs beams were analyzed. Results show that the equivalent stiffness of the CNTRCs beam is weakened by considering the scale effect of CNTs, and the volume fraction of CNTs and the scale effect parameter both have a great impact on the bending response and ultimate buckling load of the CNTRCs beam with a large slenderness ratio.

Abstract:The aerodynamic characteristics of the inflatable reentry decelerator were studied with chemical nonequilibrium numerical simulation using five-species air model. The effects of reentry decelerator′s shape deformation on distributions of flow temperature and pressure , heat flux and pressure along the wall were investigated, and the mole fractions of each species in the flow filed were presented. The modeling results show that the shape deformation of inflatable reentry decelerator has little influence on flow characteristic, and leads an increase of heat flux on the capsule surface. The study of species distribution shows that since N₂ is more difficult to dissociate than O₂, the mole fraction of N is much lower than the mole fraction of O in the flow filed. Under the current calculation conditions, the ration of nitrogen and oxygen along the wall and axis is almost consistent with the incoming flow. The modeling study results are in good agreement with the experiment results, which verify the reliability of the model.

Abstract:The control force can be mismatched on pitch and yaw plane for plane-symmetric launch vehicle, a control method named BTW(bank-to-wind) was proposed to solve the problem, which adjusts the windward side according to rolling program angle to decrease the maximum engine deflection. The off-line method of BTW control was studied, the analytical solution of the theoretical value of BTW control rolling program angle was derived, and it was proved that the deviation of the theoretical value is the same order as the flight attitude deviation. A fitting algorithm based on Fourier series with weights was proposed to modify the rolling program angle, ensuring engineering feasibility. Six-degree-of-freedom flight dynamics simulations were conducted to analyze the impact of BTW control on control forces, aerodynamic loads, and the tracking quality of the program angle, thereby verifying the effectiveness of BTW control. By comparing the simulation results of different fitting base frequencies, it is concluded that excessively high fitting frequencies can affect control quality. From an engineering perspective, the "smoothness" of the rolling program angle is more important than its "fitting accuracy".

Abstract:Wall boundary conditions for the macroscopic equations, i.e. the NSF(Navier-Stokes-Fourier) equations, R13/R26 moment equations, lose their accuracy dramatically and are easy to diverge, especially in the middle and high Knudsen number regimes.To overcome these difficulties, a wall boundary condition for the R13/R26 moment method was proposed at the mesoscopic level. The velocity distribution function was reconstructed and feedback into the Boltzmann model equation in the near-wall region, and the wall boundary condition for the R13/R26 moment method was calculated on the basis of solving the Boltzmann equation with the discrete velocity method. Results indicate that:the proposed wall boundary condition is able to increase the computational accuracy up to 59.84% compared with the classical approach. Meanwhile, it is able to get the steady-state solution for the Knudsen number up to 1.0.

Abstract:In order to improve the flow induced vibration of the adjustable central flap mechanism deployed in the second throat in the working state, a SMA (shape memory alloy) self-resetting vibration damping device which could meet the limited installation space of the central flap mechanism was designed and manufactured according to the biasing two-way driving principle of SMA. The SMA constitutive relation subroutine compiled by UMAT interface was used to realize the numerical analysis of the maximum pressing force of the damping device, and the error between the numerical analysis and the static test results is about 2.58%. A ground vibration reduction test platform was built to test the vibration reduction effect of SMA self-resetting vibration damping device in the separated and closed states. The vibration reduction test results show that the vibration response of the central flap mechanism is significantly reduced with SMA self-resetting damping device activated. An obvious damping effect appear in the frequency band of 0～100 Hz, especially, the damping rate in the range of low frequency to 55 Hz is greater than 50%.

Abstract:The lift of the powered parafoil system is determined by the system′s airspeed, making it susceptible to external wind interference and the primary disturbance factor affecting the accuracy of the parafoil′s altitude tracking. To address this issue, an eight-degree-of-freedom model of the powered parafoil was established based on traditional active disturbance rejection control. An improved disturbance compensation controller was designed based on wind field feedforward compensation. The compensation for external wind disturbance was targeted. The altitude tracking control of the parafoil system was achieved. Based on preliminary verification of the controller through simulation experiments, actual flight experiments of the parafoil system were conducted. In the actual flight environment, the control parameters adjusted in the simulation can be directly applied to the actual flight experiments, and the average altitude tracking error of the paraglider system is within 2.5 m, which proving that the designed controller has some practical application value.

Abstract:Unmanned swarm operation is becoming a new operation style that changes the shape of warfare. In response to the current problem that unmanned equipment experiments are relatively independent and lack of integrated closed-loop design and integrated verification means, a SoS(system-of-system) design, simulation and evaluation method was proposed. The method contains five stages:operational concept modeling and requirement analysis, SoS design concept and SoS design, infield simulation experiment and scheme exploration, SoS prototype development and evaluation optimization, and outfield integrated test and comprehensive decision. It innovates and develops theoretical methods, tool chains, and integrated environment for SoS design, simulation test, and evaluation optimization, which provides certain theoretical and technical support for the systematization intellectualization and actual combat of unmanned swarm.

Abstract:By integrating the working principles of water silencers with the pipeline system and water cabin characteristics of underwater vehicles, a gas-water cabin silencing method was proposed. Air with certain pressure and volume was filled into the water cabin to form an accumulator-type elastic-compressive expansion chamber silencing cavity, and the water cabin of the underwater vehicle was fully utilized to silence the sea pipeline. Experimental studies were conducted on the silencing principles and performance of the gas-water cabin. The results show that the flow and pressure pulsation at the pipeline outlet is effectively suppressed by the gas-water cabin, the noise propagation pathway of the pipeline is blocked and the underwater radiation noise of the pipeline system is reduced. This gas-water cabin provides a usefully approach on underwater radiation noise reduction of underwater vehicle.

Abstract:Latin hypercube design is one of the most commonly used computer experimental design methods, in response to the problem of one-time sampling and difficulty in balancing spatial uniformity and computational efficiency in existing Latin hypercube design methods, an experimental design method of permutation evolution Latin hypercube was proposed. By evolving small-sample designs, inheriting and expanding permutation information, the expansion and optimization of samples were achieved with a relatively small computational effort. In addition, this method gives consideration to the relationship between existing samples and new added samples and realizes the sequence expansion of samples, which is very convenient in the actual approximate modeling process. Through several groups of numerical experiments, the advantages of this method in space filling quality and calculation efficiency were verified.

Abstract:In order to make multiple missiles effectively complete the simultaneous attack of maneuvering targets in the presence of communication delay, a fixed-time convergence distributed cooperative guidance law against communication delay was proposed. Based on the framework of fixed time control technology, the guidance law can stabilize the time boundary independent of the initial state of multiple missile system and improved the control efficiency of multiple missile system. A fast non-singular terminal sliding mode and virtual leader were used to realize the guidance law′s robustness against communication delay. The Lyapunov stability theory was used to prove the consistency in fixed time. Simulation results show that under the condition of communication time delay, multiple missiles can effectively attack the target simultaneously based on the designed distributed cooperative guidance law.

Abstract:In view of the problems in the traditional regular grid digital elevation model terrain feature line extraction method, such as the threshold is difficult to be adjusted quantitatively, the connection mode cannot be adjusted adaptively, and the type of terrain feature line is incomplete, an automatic extraction method of TIN-DDM (triangulated irregular network digital depth model) terrain feature line based on rolling ball transformation model was proposed. Based on the judgment criterion of a quantitative identification for terrain feature points associated with the critical rolling sphere radius, the concept of terrain shape boundary points was introduced, and the automatic extraction model of terrain feature lines based on subdivision unit was established according to the modeling idea of reverse engineering. Combined with the multi-scale expression characteristics of the terrain type judgment criteria and the terrain feature optimization model considering water depth values, an automatic extraction method of terrain feature lines that can be expressed at multiple scales and complete types was proposed. The experimental results show that compared with the classical surface water simulation method, this method can automatically extract complete, continuous, subdivided and multi-scale TIN-DDM terrain feature lines, and the generated terrain feature lines have higher terrain reconstruction accuracy.

Abstract:Aiming at infrared dim and small targets detection in complex background, a new kernel norm estimation method was proposed based on the non-convex tensor low-rank approximation algorithm with asymmetric spatial-temporal total variation regularization, replacing the original estimation method in the algorithm. An adaptive weight tensor based on structure tensor and multi-structure element Top-Hat filtering was proposed to constrain the target tensor, which had enhanced the sparsity and suppressed the remaining strong edge structures of the target tensor. Experimental results show that the proposed improved algorithm can better eliminate the influence of strong edge structure on the detection results, and has a lower false alarm rate than the original algorithm under the condition of ensuring the detection rate.

Abstract:Tracking procedure of DS/FH (direct sequence/frequency hopping) spread spectrum signal is effected by Doppler effect and ionospheric effect seriously, which makes it hard to be used for the anti-interference field of satellite navigation. To solve this issue, a recursive least square based filtering was proposed to improve this stability of DS/FH signal tracking. The carrier Doppler estimation with variable center frequency in different channel was converted to the estimation with the center frequency of the DS/FH signal and filtered, and the numerically controlled oscillator of carrier was revised according to the predicted Doppler frequency as the frequency hops. The total electron content was estimated in real time by observing the carrier phase and code phase mutations, and the carrier phase and code phase was revised as the frequency hops. Simulation experiments demonstrate the proposed method is effective to eliminate the frequency and phase discontinuity of the DS/FH signal tracking, whose tracking accuracy can be the same level as DS signal.

Abstract:A novel high-accuracy microwave frequency measurement based on dual coherent optical frequency combs and stimulated Brillouin scattering was investigated. The unknown microwave signal and the sweep signal were modulated by two dual parallel Mach-Zehnder modulators as the signal optical and the pump signal which were lunched into the dispersion shift fiber. Using dual optical frequency combs and the sweep signal with shifted frequencies, the proposed measurement system could realize the wave-division and time-division multiplexing simultaneously. At the same time, the action of dual optical frequency combs and stimulated Brillouin scattering brought the system a series of stimulated Brillouin scattering. The frequency of the unknown signal was estimated by measuring the output optical power of the multiple channels. Furthermore, in order to improve the frequency measurement accuracy, the measured optical power values were employed to generate an amplitude comparison function which can be utilized for error correction. The effectiveness of the proposed scheme is verified via numerical simulations with a measurement error at ±2.5 MHz.

Abstract:In the case of lack of information, how to improve the reliability of the evaluation of the damage effect of multiple missiles against irregular surface targets is a major difficulty in the research of missile operation. An evaluation model for the damage effect on area targets with given parameters was established using the Monte Carlo method. Belief degree distribution functions were employed to assess the uncertainties in the problem, and the assessment results showed a high level of uncertainty in the damage effect. Based on belief entropy, the influence of the uncertainty in each attribute of the missile on the uncertainty of the damage effect was analyzed. By specifically reducing the uncertainty of attributes with significant impact, the uncertainty of the damage effect was iteratively decreased. Simulation results show that the range of uncertainty for the effective damage rate of the area target is significantly reduced. This research can effectively guide the work of damage assessment and reduce its uncertainty.

Abstract:As a special kind of wideband high-power microwave source, the GNLTL (gyromagnetic nonlinear transmission lines) have drawn much attention due to the characteristics of high center frequency, easily implementation of frequency adjustment, high repetition frequency, etc. In order to clarify the special working mechanism of GNLTL, the differences between GNLTL and the traditional magnetic applications were compared and analyzed. Starting from the microscopic magnetization dynamics, a qualitative explanation was provided for the reasons of microwave generation at GNLTL. A low-power validation experimental setup was built, with a focus on introducing the construction of experimental scenarios and GNLTL design. Microwaves signals are generated in the experiment with a center frequency of 750 MHz, a 3 dB bandwidth of 12% and a peak power of 245 kW, the microwave generation effect of GNLTL is preliminary verified.

Abstract:In order to improve the signal-to-noise ratio of the target axial frequency electric field, a coherent accumulation method combined with AR(autoregressive) model filtering was proposed to process the array electric field signal for the application scenario of using an array of electric field sensors to measure the electric field of a ship. The measured array electric field signal with time delay compensation was accumulated. The ambient electric field signal was AR modeled. By using the parameters of AR model, a filter was constructed to filter the accumulated signal. To verify the effectiveness of the proposed method under low signal-to-noise ratio conditions, the measured array electric field signals were processed. Results show that the proposed method can effectively suppress the noise spectrum and retain the axis frequency line spectrum under the condition of a signal-to-noise ratio of -25.39 dB. After keep the axial frequency line spectrum, the signal-to-noise ratio increased by about 21.92 dB.

Abstract:In order to enhance the security and reliability of the payment system, an intelligent payment system under blockchain technology was designed. This system leverages the decentralized and distributed ledger nature of blockchain to provide a more secure and transparent payment solution. The system combined blockchain technology, state secret algorithm and payment system to provide a more secure guarantee for the traditional internet payment system. The point-to-point characteristics of blockchain technology was used to solve the problems of payment efficiency, data security, etc. With the help of big data technology of internet, credit rating was provided to users and credit services are provided. Using trans-chain technology, the data of different blockchains can be shared to figure out a better solution to the liquidity of funds. Compared with Bitcoin, Ethereum and other electronic money systems, the system has achieved a balanced development in terms of security, transaction throughput and transaction delay, which has improved the performance of all aspects to a certain extent, and can better meet the application needs in the current environment.