Abstract:From 2018 to 2019, the BDS-3(BeiDou navigation satellite system phase Ⅲ) has successively launched more than a dozen MEO(medium earth orbit) satellites, gradually completing global networking. The BDS-3 satellites simultaneously broadcast smooth transition signals B1I, B3I and new signals B1C, B2a.The analysis of actual data shows that the civil B1C frequency and B1I frequency of MEO satellites contains obvious pseudorange multipath errors. Due to the orbital characteristics of MEO satellites, this phenomenon is very significant at low altitude angles of satellites. Two algorithms of MHM(multipath hemispherical map) and CNMC(code noise and multipath correction ) were used to correct the pseudorange multipath error. The correction of the pseudorange multipath error by the MHM algorithm was not obvious. The CNMC algorithm can reduce the B1C frequency multipath error from 0.11 m to 0.03 m and reduce the B1I frequency multipath error from 0.074 m to 0.024 m when the altitude angle is greater than 30 degrees. The multipath error of the MEO satellite is reduced by about 60%.

Abstract:The power-enhancement technology of GNSS is one of the effective measures to improve the anti-jamming capability of regional satellite navigation signals. How to select power enhancement sub-constellation which has less satellite quantity and better service performance from global constellation is a problem in urgent need to be solved urgently in the construction of modern navigation system. An optimal design method of power-enhanced sub-constellation based on minimum number of satellites was proposed. The design process, mathematical model and optimal solution search strategy were introduced. Availability level, accuracy level and coverage area were defined to evaluate the performance of the power-enhanced sub-constellation. Taking GPS as an example, the optimal design and performance evaluation of power-enhanced sub-constellation was carried out for the application background of covering point target and regional target. The results of simulation show that power enhancement at any target point worldwide requires 12~17 satellites. 18 satellites are needed to achieve continuous coverage to the coastal area of China. And, covering the entire Asia-Pacific region requires full constellation satellite enhancements to meet continuity and accuracy requirements. In this case, the service range of optimal power enhanced sub-constellation can be extended to the whole world.

Abstract:High-altitude balloon provides a reliable low-cost platform for high altitude scientific experiments. The shape of the balloon is directly adopted as natural-shape or based on natural-shape； however, how to simply and quickly solve the natural-shape equation general-purpose is a difficult problem. The mature solution tool in the field of optimal control—gauss pseudospectral optimization software was used to solve the natural-shape balloon equation which is transformed into the optimal control description. Furthermore, a general algorithm was designed to solve the natural-shape balloon shape with any spherical control factor and any height by analyzing the shape data. Results show that this algorithm can calculate the required natural-shape without adjusting parameters, which is convenient for researchers to quickly obtain a large amount of required spherical data.

Abstract:Region-based detectors with convolutional neural networks tend to learn textural rather structural feature and thus face substantial difficulties in detecting objects with various textures. To tackle this problem, the texture randomization to augment the synthetic training image dataset was employed and a novel method for structure-aware object detection was proposed. The texture-randomized simulation data were generated by rendering 3D model with varied textures using Blender. Experiments on synthetic and real images indicate that the proposed method is capable of robustly detecting texture-varied objects based on structural information.

Abstract:Considering the short circuit fault at DC(direct-current) converter side, the rectifier generator with DC converter can be equivalent to the rectifier generator suddenly applied with RLC(resistance inductance capacitance) load, and its transient current calculation is directly related to DC fault diagnosis and protection. When the RLC load was equivalent from the DC side to the AC(alternating-current) side, the transient current was equivalent to the three-phase short circuit current under the condition of the synchronous generator in series of RLC. Through the expression of the transient current, the analytical expression of the transient current was obtained by calculating the initial value, final value and time constant with the method of analogizing the three-phase short-circuit current′s calculating process of the synchronous generator, and the peak value and peak time of the current were given. Finally, the validity of the analytical expression is verified by simulation,which can be used for the improvement of the diagnosis and the determination of the protection way of DC faults.

Abstract:In order to improve the registration precision and robustness of image splicing, an improved random sampling consensus algorithm based on local pixel matching was proposed. After completing image feature extracting and feature matching with the scale invariant feature transform operator or other operator, using the local pixels that are independent of feature matching points, then the optimal configuration of the four pairs of feature matching points, and the best homography matrix were determined by matching the local pixel of the reference image with the mapped local pixel of the image to be stitched. The experimental results show that, compared with the classical random sampling consensus algorithm, the computation time is close, the homography matrix is more accurate, and the image mosaic is more robust.

Abstract:In a lithium-ion battery energy storage system for electromagnetic launch, the accurate extraction of the battery pack stray inductance is significant for designing a reasonable system solution. To meet this demand, the process of battery pack pulse discharge was modeled and analyzed, and the discharge stage suitable for stray inductance extraction was obtained. The method of solving the numerical differentiation by discrete Fourier transform was changed to the sliding-window recursive form, which was combined with multi-innovation least square algorithm, so a novel stray inductance extraction method was proposed, which can make full use of waveform data. Experimental results show that this method can extract stray inductance more accurately and reliably than the traditional method, and the calculation results are consistent under different discharge currents.

Abstract:In view of the wide application prospect of intelligent ammunition, the development of two-dimensional trajectory correction projectile, main correction mechanism scheme and guidance control technology were summarized. The development process of the two-dimensional trajectory correction projectile was reviewed, aiming to reveal the development principle. Several main correction schemes were discussed, and the function characteristics and research difficulties of each mechanism were analyzed. Based on the requirements of the two-dimensional trajectory correction projectile, the research status of its control technology was summarized from three aspects:aerodynamic identification and state estimation algorithm, parameter optimization algorithm and guidance law. The rapid development of intelligent algorithm in recent years, especially the application of neural network theory in the field of control algorithm was focused on. The main technical difficulties and the future development direction of the control research of the two-dimensional trajectory correction projectile, which provides ideas for the design, were pointed out.

Abstract:The structure and performance evolution of 1 200 ℃ ceramic tile repeated at 1 200 ℃ were studied. Results show that after heat treatment at 1 200 ℃ for 20 times, the ceramic tile with 1 200 ℃ exhibits good macroscopic thermal stability. During the repeated heat treatment, sintering occurs between the fibers, and the bonds are melted. Quartz fiber crystallization and grain growth result in fiber diameter changes, such as neckdown, and 14% shrinkage rate of Z direction, which in turn makes the compressive strength slightly increase, and the thermal insulation performance decrease. After 1 260 ℃ and 11 times of single-sided radiant heating, the Z-direction shrinkage rate was 5.58%, and the thermal insulation effect is reduced by 7.59%. However, the thermal insulation material can maintain the thermal insulation performance of the material after 6 repeated heating.

Abstract:In order to realize the high maneuverability of the electromagnetic catapult and the high power density of the linear catapult motor of the land-based unmanned aerial vehicle, a multi-population genetic algorithm with elite retention (MPGAER) was proposed to optimize the maximum power density of motor. It takes flux density and current density as constraints, and optimizes the structure parameters of the motor with its strong search ability and fast convergence speed, and compares with the initial scheme based on magnetic circuit method and the optimization results of traditional genetic algorithm. The results show that, compared with the initial scheme design, MPGAER can reduce the motor mass by 6.25%, increase the power density by 10%, and improve the dynamic performance of the motor; the motor power density of the MPGAER optimized design is higher than the genetic algorithm design result, which indicates that the proposed method effectively solves the problems of easy convergence to the local best advantage and poor optimization effect in the optimization process.

Abstract:In order to accurately describe the object model, the first-order equivalent circuit transient eddy current analysis method was used to quantitatively calculate the parameter time-varying rule of the moving primary high-speed six-phase linear induction motor under the influence of the dynamic end effect, and the equivalent circuit of the motor was deduced considering the dynamic end effect through the deduce of the induction eddy current loss. On this basis, the performance characteristics of the motor under the influence of the dynamic end effect were analyzed in detail through the calculation of electromagnetic thrust and efficiency evaluation. The correctness of the theoretical analysis and the accuracy of the motor model were verified by the finite element simulation and dynamic experiment under different operating speeds.

Abstract:The rotating high-frequency injection method can estimate the rotor position of the permanent magnet synchronous motor at zero speed and low speed. However, the use of filters in demodulation introduces estimation errors. A virtual current injection method was proposed to compensate the rotor position error on-line. Based on the estimated speed, the method structured a virtual current same frequency as the negative sequence response current. After the same demodulation as the negative sequence current, the method obtained the phase of virtual current. The error between the obtained phase and structured phase was used to compensate the estimated rotor position. Further analysis compared the actual speed fluctuation with that of the estimated speed fluctuation, caused by the rotating voltage and the positive sequence response current respectively. A low-pass filter was advocated to improve the compensation effect. Simulations and experiments verified the effect of the proposed method on rotor position error compensation when the motor was in different states.

Abstract:In order to establish a life prediction method for hull structures considering corrosion factors, based on the analysis of the existing time-varying corrosion damage models of ship hull structures, a time-varying corrosion model considering the factors of action time and maintenance time of corrosion protection system was established according to the actual situation of ship maintenance support. According to the relevant codes, the lifetime standard of hull structure was selected and a prediction method for calculating the lifetime of hull structures was established. The method established the quantitative relationship between the lifetime of hull structure and the factors such as the action time and repair time of corrosion protection system. This method can be used to predict the life of ship structure under uniform corrosion condition, and in turn can be used to guide the selection of design indexes of corrosion protection system and the determination of maintenance strategy of hull structure.

Abstract:Aiming at the shortcomings of the traditional clustering algorithm on the clustering effect of manifold data, and the low real-time performance, the improved CBSCAN (cell-based density spatial clustering of applications with noise) was proposed to solve air combat target grouping issue. By analyzing the air combat situation parameters, the general model of air combat target grouping was established and the target grouping was transformed into clustering problem. Then, the target grouping model based on improved CBSCAN was established by improving the clustering method of CBSCAN algorithm. Through simulation experiments, the clustering accuracy and real-time performance of K-means, expectation maximum algorithm, density peak algorithm, density-based spatial clustering of applications with noise algorithm, CBSCAN algorithm and improved CBSCAN algorithm in 30 combat situations were compared and analyzed. The results show that the improved CBSCAN algorithm can correctly group multi-target formations under the condition of unknown number of formations and target manifold distribution, and the real-time performance was improved by about 30% compared with the original algorithm, which shows the practical application value of the proposed method.

Abstract:The application requirements of UAV (unmanned aerial vehicle) swarm communication payload technology based on FSO (Free Space Optical) were summarized, and the current status of FSO technology and application at home and abroad UAV payloads was discussed. The development prospect of the payload technology of UAV swarm based on FSO communication in high-speed mobile communication environment was also analyzed. Furthermore, a profound analysis on the key technologies in FSO communication links applied to UAV swarm was conducted. Predictably, FSO-based communication payload will be used widely for wide-bandwidth communication networking of UAV swarm in the future.

Abstract:In order to relax the filtering requirements and improve the wideband performance of the all-digital transmitters, a novel multi-level RF-PWM(radio frequency pulse width modulation) method for all-digital transmitters was introduced. This method limits the selective harmonics of RF-PWM signals by controls the pulsewidth of the corresponding subpulses to make the selected harmonics cancel each other out and keep the weighted superposition of fundamental frequency components proportional to input envelope. For the third harmonic elimination, the corresponding 5-level RF-PWM scheme was presented. And the optimal gain index for 5-level RF-PWM scheme was also analyzed and proved. On this basis, the proposed scheme was verified by extensive simulations.

Abstract:In order to solve the beamforming problem of meter-wave OFDM-MIMO (orthogonal frequency division multiplexing-multiple input multiple output) radar, a signal model of frequency division multiplexed MIMO radar array under meter-wave conditions was established, and a theoretical framework for quantitative analysis of multipath characteristics of this system was derived theoretically. The direct-wave and multipath echo models, as well as the closed-form expression of the gain of the joint transmitter-receive bi-directional pattern were derived. A multipath suppression algorithm with range-angle two-dimensional resolution based on the bi-path pattern of a meter-wave OFDM-MIMO radar array was proposed. The proposed method can effectively suppress the multipath echo in the normal direction of the array, and also effectively suppress the periodic loss of the output fresh dryness ratio, and the inhibition ability is further improved with the increase of the frequency offset bandwidth.

Abstract:In order to solve the low recall problem of the region proposals in object detection, the object region proposals algorithm, which combines neural networks and superpixels, was proposed. The edge features, which can be represented clearly by neural networks, were extracted from the images to be detected, and the score of edge information for per sliding window was computed by the strategy of edge clustering and the affinities between the edge groups. The several superpixels of this images were obtained by simple linear iterative clustering algorithm, and the salient object score of a superpixel was calculated using the location, integrity of this superpixel and the contrast with neighbors. The salient objects score of per sliding window was received by these saliency scores of superpixels according to the Euler distance strategy between the sliding window and these superpixels. The region proposals were determined by two components including edge information scores and salient object scores. The comparative experiments were conducted in PASCAL VOC 2007 test set, and the experiment results show that the proposed algorithm can fast generate a set of region proposal with higher localization.

Abstract:In the process of realizing multi-source to multi-target program translation, the dynamic binary translation uses intermediate code to shield the hardware differences between different source platforms, and the memory virtual strategy is adopted to achieve the goal. As a result, it brings about the problem of intermediate code expansion. Traditional intermediate code optimization methods usually use the method of matching and deleting redundant instructions. The intermediate representation rule replacement for special instruction matching was focused on, and an intermediate code optimization method for binary translation based on intermediate representation rule replacement was proposed. This method described the corresponding intermediate representation replacement rules for several typical scenarios of intermediate code expansion, and the register direct mapping strategy used in the back-end code optimization was applied here. By establishing mapping formula, the memory virtual operation was replaced by local register operation, thus reducing the expansion degree of intermediate code. The SPEC CPU2006 test suite was used to carry out the experimental, and the experimental results verify the correctness and effectiveness of this optimization method. The results before and after optimization are consistent, which verifies the correctness of the optimization method, meanwhile, the average reduction rate of intermediate code for each case after optimization is 32.59%, which verifies the effectiveness of the optimization method.

Abstract:The related concept of intelligent unmanned swarm operation was introduced. In order to reflect the autonomous capability and adaptive capability of intelligent unmanned simulation entity, the OODA-L (observe, orient, decide, act and learning) pattern was proposed to make the learning process explicit, and was further extended to Co-OODA-L pattern. In the general description of the intelligent unmanned simulation entity, Markov decision process was adopted to carry out the mathematical abstraction, and a three-domain hierarchical structure of intelligent unmanned Agent was proposed. In order to embody the characteristics of autonomous cooperation and distribution of intelligent unmanned swarm operation, an architecture for cooperative operation modeling of swarm was proposed, which uses an artificial neural network to integrate a variable number of intelligent unmanned Agents into a homogeneous or heterogeneous swarm.