Abstract:In order to further improve the communication quality of the extremely-low-frequency communication further, based on the traditional improved generalized sidelobe cancellation, a new interference suppression algorithm in the field of extremely-low-frequency communication called generative sidelobe cancellation algorithm was proposed. Generative adversarial nets as one of the hot research topics in artificial intelligence was introduced into generalized sidelobe cancellation, the network structure and relevant hyperparameters of the generative model were designed and optimized, addressing the problem of the residual desired signal existing into the original algorithm effectively, providing more relevant reference information about the interference components in the main channel for the next-stage filtering algorithm of sidelobe cancellation channel, thereby enhancing the estimation accuracy of the interference components in the main channel. In order to validate the effectiveness of the optimized generative model and the suppression ability of the proposed algorithm on different types of interferences, an experimental platform was set up under the laboratory environment and multiple sets of controlled experiments were designed. The experimental results show that the optimized generative model has better generative ability, better robustness and relatively lower computational complexity. Compared with the traditional improved algorithm, the proposed algorithm can further improve the signal-to-interference-plus-noise ratio within the signal bandwidth further.

Abstract:In the IRCS(integrated radar and communication system), which uses OFDM(orthogonal frequency division multiplexing) signals, the CP(cyclic prefix) and pilots can cause the problem of high peak to side lobe level in autocorrelation operation, which deteriorates the radar detection performance seriously. To solve this problem, a new RadCom signal based on TDS-OFDM(time domain synchronization OFDM) was proposed. The TDS-OFDM adopts TS(training sequence) for guard interval, as well as synchronization and channel estimation, so that the CP and pilots can be avoided. First, the ambiguity function of TDS-OFDM RadCom signal was analyzed. And then, TS was optimized to suppress the range side lobe of TDS-OFDM signal and maintain the autocorrelation properties of TS simultaneously. Theoretical derivation and simulation results show that TDS-OFDM signals are more suitable than CP-OFDM signals for IRCS.

Abstract:The Traditional LMS(least mean square) adaptive filtering algorithm is always in a contradiction state because it has a fixed step size and resolves the relationship between steady-state error and convergence. Based on the analysis of the filtering algorithm, according to the step-size adjustment principle of the variable-step LMS adaptive filter algorithm, a segmented variable step size LMS adaptive filtering algorithm based on the normal distribution curve was proposed by constructing the nonlinear function of the step-size factor and the error signal, and the influence of the parameter value on the performance of the algorithm was analyzed. Aiming at the problem of difficult selection of reference signal in actual signal processing, a method of reference signal selection based on the splitting array was proposed. The theoretical and sea trial data analysis results show that the convergence speed and steady-state error of the proposed algorithm are obviously better than the fixed-step LMS adaptive filtering algorithm and the variable step size LMS adaptive filtering algorithm based on the Sigmoid function.

Abstract:In the existing software-defined satellite network, the storage space of ternary content addressable memory occupied by the flow table is increasing, and the complex flow entry lookup and matching processes will bring about reduced route forwarding efficiency, which cannot meet the requirements of diverse application requirements. A neural network-based software-defined satellite network intelligent routing framework was proposed. The controller acquired the transmission mode of the data flow by training the neural network, and replaced the flow table with the trained neural network. Based on this framework, an intelligent routing strategy based on Chebyshev neural network was proposed. The switch predicts the forwarding path of data flow according to the service type of data flow to meet the quality of service requirements of satellite network applications. The simulation results show that the proposed routing strategy significantly reduces the occupied storage space of ternary content addressable memory and improves the routing efficiency.

Abstract:For the problem of the pattern synthesis for planar array with large elements spacing, a planar array pattern synthesis method of wideband real time delay based on particle swarm optimization algorithm was proposed. In this method, according to the characteristics of the main lobe orientation and the grating lobes orientation under the condition of real time delay, the wideband real time delay was adopted to suppress the grating lobe of pattern. Then, the structure of array was optimized by particle swarm optimization algorithm and the pattern with higher main-side-ratio was obtained. The effectiveness of the proposed method was indicated by the simulation for 8×8 rectangular planar array. Furthermore, the relationship between the grating lobe suppression performance and the signal bandwidth was studied through the simulation.

Abstract:In order to improve the efficiency of conventional DOA (directional-of-arrival) estimation methods based on the sparse representation of array covariance, an efficient DOA estimation method relying on the direct 2D sparse reconstruction was proposed. The 2D sparse reconstruction model was constructed by using the array covariance matrix. The noise power can be estimated and the influence of noise on DOA estimation can thus be reduced by applying the eigenvalue decomposition. In solving the 2D sparse reconstruction problem, the 2D-SL0 (2D smoothed L0 norm) algorithm was used, which can deal with the 2D data directly, free of matrix vectorization operation. Simulation results show that the efficiency of the proposed method can be improved significantly, and the performance of the proposed method is better than traditional methods under the conditions of low snapshot, low SNR and sparse array sensors, etc.

Abstract:Electric field measurements in seawater will affect the target electric field. In order to improve the accuracy of the electric field measurement, the influence factors of the object on distribution of the electric field in seawater were studied by the finite element method, and the distribution law of the distortion electric field was determined. The simulation results show that the magnitude of the distortion peak and the distortion area are affected by the conductivity and shape of the object. When the conductivity of the object is smaller or larger than that of the seawater, the effect on the electric field distribution is on the opposite:the larger the curvature of the object is, but the larger the peak value of the distortion is, but the smaller the distortion area is.

Abstract:Traditional planar nearfield acoustic holography places the hologram inside the jet. In order to reduce the adverse effect of window effect and wraparound error on reconstruction accuracy, it is generally required that the hologram size is twice more than that of the sound source, while larger microphone array placed inside the jet will interfere with the stability of the jet. To solve this problem, it was proposed to place the entire hologram outside the jet. According to the classical shear layer correction theory, the changes of path and amplitude of sound wave propagating from sound source to hologram were analyzed. Then the modified sound field propagation formula was derived. Finally, the theoretical model of planar nearfield acoustic holography under the combined action of moving fluid medium with the Mach number below 0.3 and shear layer was established. Numerical simulations show that the improved planar nearfield acoustic holography leads to reconstructed acoustic fields of high resolution, with high localization accuracy of aerodynamic noise source and certain anti-interference ability.

Abstract:In order to investigate the creep performance of multi-barrel rocket weapon launch canister under long-term storage, uniaxial tensile creep test was carried out on composite laminate and the creep constitutive model parameters of single layer in the main directions were obtained. The finite element method and the user-defined material subroutine were used to establish long-term storage numerical analysis model of launch canister. Creep deformation of the bottom launch canister after 15 years storage was predicted. Taking the stored launch canister as initial state, the dynamic simulation model of rocket-tube coupling was built, and the influence of creep on rocket launching process was further investigated. Simulation results show that the change of the parallelism of the director and the flatness of the bottom surface of launch canister caused by creep are smaller than the specified values of technical indicators. The maximum residual deformation of director bundle is saddle-shaped in three-dimensional space, and the deformations of the middle position directors for upper and lower rows are largest, while that of the middle position directors for left and right columns are smallest. Creep deformation of the director reduces the clearance between rocket and director, increases the dynamic contact collision force and lessens the off-track velocity of rocket.

Abstract:Improvement for the adhesive property of the DLC (diamond-like carbon) film on the protected substrate has obvious value in the actual application, and the reason for the validity of the Cu-based multi-layer DLC film designed in our former research was analyzed in the view of the micro-theory. Then, in order to optimize the structure of the multi-layer film and improve its performance in the practical application, the influences of the thickness ratio between the DLC layer and SiC layer in the periodic layer on the adhesion property, nano-hardness and wear property were studied. The results of the nano-scratch and nano-indentation tests show that the adhesive property and nano-hardness of the Cu-based multi-layer DLC film decreased and its nano-hardness increased, respectively, while the thickness ratio was maintained in the increasing state. Critical load of the multi-layer DLC film on the Cu substrate could approach that of the single-layer DLC film with the thickness of 400 nm on the Si substrate, when the thickness ratio was below 2.3. Meanwhile, the wear property of the Cu-based multi-layer DLC film was approximately close to that of the pure DLC film.

Abstract:In order to investigate the damage modes and energy absorption mechanism of the filament wound composite core cylinder under high strain rate impact compression load, the numerical simulation analysis and experimental test verification were carried out by using the ABAQUS finite element software and the Hopkinson bar testing machine. The analysis of the mechanical response characteristics and damage modes show that the energy absorbing element has typical elastic-plastic response characteristics under the high rate impact compression loading. The inner core material mainly produces compression plastic damage, while the surface composite material produces tensile fracture damage along the hoop direction. The study results show that this type of energy absorbing element has excellent compression and energy absorption characteristics, and can achieve the impact protection and buoyancy reserve requirements of the underwater structure platform.

Abstract:Starting from the basic principle of the vertical configuration of the receiving and transmitting coils of torpedo electromagnetic fuze, the ambiguity of operating range caused by the double receiving coils located on the torpedo axis and deviating from the torpedo axis were analyzed respectively. For the first case, the modulo operation of the double receiving coils was proposed to eliminate the ambiguity of the operating distance; for the second case, a pair of coils was appended to the symmetrical position and the output signal of the symmetrical position coil was averaged, then the modulo operation was taken to eliminate the ambiguity of the operating range. Simulation results show that the method can effectively eliminate the ambiguity of the operating range and improve the operating range of the electromagnetic fuze.

Abstract:In order to realize the directed radiating of Ku-band HPM (high-power microwave), a RL-CTSA (radial line continuous transverse stub antenna) was proposed. The antenna was fed by circularly polarized coaxial TE₁₁ mode and radiated by a concentric CTS (continuous transverse stub) array after the wave propagation through a double-layered radial line waveguide. The interspace between adjacent stubs along radial direction was equal to one guide wavelength, a shorting pin was located at the end of the upper radial line waveguide and the space between the pin′s surface and the innermost CTS radiator′s center was half a guide wavelength. As a result, the HPM-RL-CTSA works on standing wave. An antenna prototype with a height of 80 mm and an aperture radius of 285 mm operating at 14.25 GHz has been designed, which has a gain of 35.3 dBi, reaching an aperture efficiency of 47%. The reflectance of this antenna is less than -25 dB and the radiation efficiency is more than 99.0%. The simulated results indicate that this antenna has a power handing capacity of more than 1 GW.

Abstract:During the electromagnetic launch process, the temperature of the rail is affected by many factors and it is difficult to analyze some factors accurately. Based on this, the gray system was used to study the temperature of the electromagnetic launcher. In order to obtain the experimental data needed for the gray model, the electromagnetic launcher data collection system was built, and such data as the current, the rail temperature, the launch speed and other factors concerned were collected. Due to the limitations of measuring instruments, the ANSYS finite-element simulation was adopted to correct the measured rail temperature data to obtain the inner surface temperature of the rail. Based on the classical GM(1,N) and Simpson formula, an improved gray model was proposed, and the rail temperature was studied by this method. The same energy level test was conducted to discuss the contribution of temperature rise of various factors at different locations. The conclusion provides a reference and basis for further research on the temperature of the rail.

Abstract:Aiming at the problem that the navigation accuracy of integrated navigation system of aircraft decreases due to uncertain faults in high dynamic environment, a fault-tolerant federated filtering algorithm based on vector information assignment was proposed. The fault detection function in vector form was designed to determine the fault degree of each observation, which overcomes the disadvantage of isolating all the observations of the fault subsystem at the same time. According to whether the observations were abnormal, the variable measurement noise matrix and information distribution vector coefficient were reconstructed to distribute the information among the state variables of the sub-filter. While isolating the abnormal observation of the fault subsystem, the correct observation information was utilized to the maximum extent. Simulation results show that the algorithm can give full play to the advantages of each navigation subsystem, greatly improve the utilization rate of navigation subsystem information, and have high accuracy and fault tolerance.

Abstract:Strapdown inertial navigation system has been the main navigation and positioning method for long voyage and long-endurance underwater navigation. In order to solve the problem that velocity information provided by Doppler velocity log and position information provided by acoustic single transponder are easily contaminated by non-Gaussian noise, a federated robust Kalman filter algorithm was proposed. In the proposed method, the Mahalanobis distance algorithm was used to introduce a inflated factor to inflate the measurement noise covariance, which can improve the robustness of integrated navigation system. At the same time, the information distribution coefficient was adaptively tuned based on the performance of the sub-filter, which can guarantee the accuracy of integrated navigation system. The semi-physical simulation test for underwater integrated navigation was carried out by the federated robust Kalman filter algorithm and traditional federated Kalman filter algorithm based on measured data of the river test. The experiment results demonstrate that the federated robust Kalman filter algorithm has better performance in underwater integrated navigation compared with the traditional federated Kalman filter algorithm under the non-Gaussian condition and it can meet the requirements of fault tolerance and robustness for underwater integrated navigation system.

Abstract:The trajectory characteristics of the near-space hypersonic glide vehicle are mainly under the influence of the initial state of glide segment and control law of the vehicle. Therefore, the influence of glide segment initial state on trajectory characteristics of hypersonic glide vehicle was studied under the condition that the control law of vehicle is determined. According to the different forms of glide trajectory, under the condition of longitudinal equilibrium glide, the analytical formula of the vehicle state variable was derived theoretically, and the uniqueness of initial state of the equilibrium glide trajectory was analyzed in combination with the equilibrium glide condition. Under the condition of longitudinal skip glide, the evaluation indices of trajectory performance were constructed, and the initial state of glide segment with optimal trajectory performance was found by using the group intelligence algorithm. Through the single factor sensitivity analysis, the sensitivity analysis of the initial states of two forms of glide trajectory was carried out, and the initial velocity of initial state has the greatest influence on the trajectory characteristics. The analysis of the uniqueness and optimality of initial state can be used for reference in the trajectory design, trajectory tracking, trajectory prediction and trajectory optimization of hypersonic glide vehicle.

Abstract:Aiming at the shortage and backlog of equipment maintenance material, and the inefficiency of equipment distribution system in the current equipment supply system, the integrated optimization of production, inventory and distribution operational links is a critical need. In order to reflect each decision link, the problem was formulated as a MILP with multivariable and multiple constraints. A two-level mathematical-programming-based heuristic was developed to solve it. In an actual example, the proposed model was validated; the algorithm and the CPLEX solver and a similar algorithm were compared and described in aspects of solution quality and computation time. Results show that the proposed model is feasible, and the algorithm exhibits extraordinary performance in solving different scales of instances.

Abstract:A high-quality scheduling scheme can not only satisfy users′ demands but also provide a basis for scientific decision-making of tracking and data relay satellites system. Aiming at the increasingly diversified users′ demands, a novel application paradigm for tracking and data relay satellites system, in which users can submit multiple service time windows that can slide within a certain period, was adopted. To handle this application paradigm, by considering the flexibility of task scheduling and the conflicts among tasks, a mathematical programming model for relay satellite schedule was developed and a scheduling algorithm based on stochastic search strategy was designed. The proposed algorithm includes five operators, i.e., resource matching and neighborhood construction, actual service time windows generation, conflict evaluation, local search and conflict resolution, and solution update. The proposed algorithm was verified by comparing with the heuristic algorithm based on time freedom degree according to extensive simulation experiments.

Abstract:In the context of the increasing maturity of on-orbit service and the growing application requirements, taking the on-orbit servicing spacecraft as research object, the satellite-oriented on-orbit servicing mission planning problem was studied, and the way how to rationally arrange and deploy on-orbit servicing resources was discussed. The problem was decomposed into two sub-problems, namely on-orbit service resource allocation and on-orbit service path planning, and the corresponding bi-level mathematical models were established. An on-orbit service mission planning method was designed, including chaotic genetic algorithm based on multi-group parallel evolution and NSGA-Ⅱ+GSDE algorithm based on global coordinate transformation. The feasibility and effectiveness of the algorithm were verified through comparative analysis of simulation results.