Abstract:Prediction for footprint of incoming hypersonic glide reentry vehicle as a defensive party has such problems as insufficient prior information and high timeliness requirement for solution. A fast prediction method of footprint based on optimal flight hypothesis was proposed:only if the position, velocity and maximum lift-drag ratio of the target at the current time are known (which can be obtained by real-time trajectory estimation based on radar detection data), based on the equilibrium glide hypothesis and the Egers solution of the maximum cross range, the coordinates of the maximum longitudinal range and cross range end points can be obtained respectively; then in the two-dimensional plane of longitude and latitude, the footprint can be approximated as a semi-elliptic area with the intersection of the two maximum cross range end points as the short axis and the distance from the maximum longitudinal range end point to the short axis as the half-long axis. The simulation results show that, compared with the traditional numerical optimization method and the constant bank angle method, the proposed method has the advantages of less prior information, higher accuracy and less computation, and can meet the real-time requirements.

Abstract:Aiming at solving the disturbance problem faced by the mini-missile as well as following practical classic linear frequency-domain design methods, a promoted disturbance estimation and rejection control method based on H_∞synthesis and equivalent-input-disturbance was proposed to apply to the missile longitudinal control system design. The mismatched disturbance problem was resolved by the establishment of equivalent-input-disturbance system. A disturbance filter and a composite controller were designed through H_∞optimization to realize the disturbance estimation and compensation and simultaneously to guarantee the overall stability of the system. The feasibility and effectiveness of the method was validated by numerical simulation and bias comparison with extended state observer based control and disturbance observer based control methods.

Abstract:For payloads with high requirements in time reference precision and public information, the general time data and public telemetry data provided by spacecraft platform is not sufficient. In contrast, some functional payloads have ability to output high-precision time and state measurement information, but their hardware interface resources are limited. To synchronize high-precision clock source of functional payload to other payloads with needs, the IEEE 1588v2 time synchronization protocol can be stacked into an optical fiber FC-AE-1553 network. Measurement information provided by the functional payload, such as location, attitude and orbit data, was then able to be sent to each payload NT terminal nodes distributed in whole network. A protocol was proposed to meet the demand of high precision time and public information of payloads, and also to avoid the resource information interface limitation of functional payloads. Design verification was carried out and the result shows that time data and public information supplied by the functional payload can successfully be sent to each node after the FC-AE-1553 network synchronization. The precision of data accepted by payload is three orders of magnitude higher compared with the information source of spacecraft platform, and the accuracy of UTC(universal time coordinated) time accepted is up to 100 ns.

Abstract:In order to improve the effect of the shape optimization design, the influence of the flight profile with large-airspace and wide speed range for new type of vehicles on aerodynamic shape was studied and a new shape optimization design method based on the aerodynamic and trajectory integrated model was proposed. By this method, the aerodynamic and trajectory integrated model was constructed by using the CST(class/shape function transformation) parametric method, engineering estimation and the Radau pseudospectral method. To implement the efficient global optimization within multi-constraints, an aerodynamic shape optimal design method based on Kriging surrogate model was proposed after clearing the optimization target and constraint condition. The shape optimization design for a type of lifting body vehicles was carried out. It is shown that the aerodynamic and trajectory feature of large-airspace and wide speed range can be better described, and the accuracy and performance of the shape optimization design are improved, which can provide technical support for the conceptual aircraft design.

Abstract:A detection method for intersection points based on gradient-histogram was proposed. The feature descriptor was generated for each image pixel using gradient of neighborhood pixels. The candidate intersection points were taken from all image pixels according to specific constraints. The candidate intersection points were clustered into different categories based on Euclidean distance. The subpixel positions were computed for each intersection points by the weighting method. The proposed method was validated by simulations. The results show that the method can be used to detect the intersection points of crossing angle 65°~90° with the precision of 0.6 pixel and the detection rate exceeds 90%, and the precision and detection rate of proposed method is invariant to image rotating. The method is robust to image noise and can satisfy the need of detecting intersection points on image under normal prospective transformation. It can be applied to the calibration and surface measurement of structure light 3D reconstruction system.

Abstract:In view of the path planning of the unmanned AUV (autonomous underwater vehicle) in the complex sea battlefield environment, the environment model is complex and there are many constraints. A relatively perfect sea battlefield environment model including battlefield shape, enemy threats, obstacles, and sea current field was established. The AUV navigation time and threat time were the shortest as the optimization goal, and an oscillation-based type was given. The AUV global path planning method of the oscillation IWO(invasive weeds optimization) algorithm was compared with other three path planning algorithms, such as the standard IWO algorithm, the full-oscillation IWO algorithm and the PSO (particle swarm optimization) algorithm respectively. Simulation results show that the proposed method which has strong searching ability and excellent robustness, can effectively plan the navigation path which meets the performance requirements for the AUV in the complex sea battlefield environment.

Abstract:It is of great practical significance to study the robustness of networked CPS(cyber physical systems) under cascading failure. A two-tier asymmetric dependency network model was constructed for CPS with one-way dependency and a cascading failure model for asymmetric dependency network which combines the dependency failure with the overload failure was designed. A more practical asymmetric attack method was proposed, and a node capacity allocation method under resource constraints was given. Simulation experiments were carried out on asymmetric dependent networks consisting of scale-free subnets. It is found that the network robustness is positively correlated with the sub-network average, degree exponent, node capacity, etc.; assortative dependency networks and networks with node capacity allocation by degree are more robust; asymmetric dependent networks are vulnerable to attention attacks; when attacking dependent subnets with equal strength, the network is more vulnerable. The constructed model and the law of experimental discovery have certain reference value for studying network robustness and optimizing network design.

Abstract:Taking the lightweight optimization of skinned purlin structure in large-scale launch vehicle as the research background, the post-buckling lightweight optimization of large-diameter and large-loaded skinned purlin structure was carried out. In order to achieve ultimate bearing capacity of the structure, the post-buckling behavior of skinned purlin structure was analyzed based on the parametric model established by Python code. Considering that discrete topology and continuous size variables were involved in the lightweight optimization of skinned purlin structure, sequence approximate optimization method based on the surrogate model and combinatorial optimization algorithm was proposed. What′s more, approximate optimal solution was used to accelerate algorithm convergence, which can obtain the final design scheme of skinned purlin structure. The results of engineering examples show that the sequence approximate optimization method propose in this paper make the weight loss effect of skinned purlin structure obvious, and verifies the effectiveness of the method.

Abstract:NORX is one of the fifteen candidates selected for the third round of the CAESAR (authenticated encryption:security, applicability, and robustness) competition. And its only nonlinear component is made up of XOR, AND and shift operations. The design rationale of the shift parameter of NORX from the perspective of nonlinear approximation and rotational properties were studied. On the one hand, the nonlinear approximation probability of the shift function is theoretically proved to be a three-valued function. When the shift parameter is 1, this function possesses the best nonlinear property. On the other hand, the rotational probability of the shift function is formulated. And it is proved that the maximal rotational probability is the same for all nonzero shift parameters. From the above results, the NORX has the best nonlinear approximation and rotational properties when the shift parameter takes 1. The results can be of reference to the analysis of NORX and can give theoretical guidance when designing similar ciphers.

Abstract:In the OFDM/OQAM system, higher pseudo pilot power means more accurate channel estimation. According to this principle, an effective channel estimation method based on the improved preamble structure with higher pseudo pilot power was proposed. On the basis of the previous preamble structure, the preamble structure with highest power was improved and its channel estimation method was proposed. Because of the lack of enough prior knowledge of receipt signal, the channel is unable to be estimated. The pre-decision method was utilized to solve this problem. The error caused by the pre-decision was reduced through iteration, thus the estimation accuracy was improved. Simulation results prove that the proposed preamble structure shows better channel estimation performance and higher spectral efficiency.

Abstract:Making an optimized and practicable satellite assemble plan, which is closely linked to all the various constraints, is a difficult problem. This issue has attracted wide attention all over the world. In linght of this, the problem′s characteristics were analyzed, the mathematical optimization model was established, and an optimization decision method based on genetic algorithm was proposed. A constraint handling method based on penalty function was introduced to deal with the infeasible solutions generated in the iterative optimization process. In order to alleviate the difficulty of the penalty coefficient setting, a mechanism of penalty coefficient self-adaptive adjustment was designed. Some experiments were conducted to validate the correctness and practicability of the proposed algorithm.

Abstract:The convolutional structure was introduced into the recurrent neural network to construct a convolutional recurrent neural network. Based on this network, a sequence annotation model for joint learning of Chinese word segmentation and entity recognition was constructed. The model relies on the convolutional recurrent neural network to construct feature-encoding layer, which realizes the joint extraction of local spatial features and long-distance time-dependent features of Chinese character sequences; the improved recurrent neural network was relies on the constructing of tag-decoding layer, which realizes the effective modeling of timing-dependent features in the tag sequences; the unified word segmentation and entity recognition annotation mode relies on the achieving of joint learning of word segmentation information and entity information, which avoids the error propagation problem of traditional pipeline methods. Experimental results on the People′s Daily corpus and Microsoft′s annotated corpus show that the framework has significant performance improvement over traditional statistical models and neural network models, especially when identifying entities with multiple characters, and its effect is significantly better than other methods.

Abstract:As one of the key characteristics of vehicle identity, vehicle logo plays an important role in vehicle monitoring and identification. Due to the complexity of the natural scene, it is still a great challenge to identifying the vehicle logo accurately. At present, there are few open databases and there are many limitations, which lead to the lack of credibility and practicability. In this paper, a new dataset for natural scenes which contains 10 324 images with 67 types of vehicle logos in various acquisition environments was established. Based on this dataset, a vehicle logo recognition method based on target detection and deep learning was proposed. The method includes two major steps:regional positioning of vehicle logo and prediction of vehicle logo type. Experiments show that the proposed method has strong adaptability to complex background, and the overall recognition rate reaches 89.0% in the classification task involving 30 kinds of vehicle logos.

Abstract:To improve the localization accuracy of angle of arrival in passive troposcatter surveillance system, an improved particle swarm optimization was employed to arrange distributed nodes. Geometry dilution of precision was deduced and treated as the evaluation index. Chaos theory was adopted to modulate the position parameters for particle swarm optimization. Adaptive inertia weigh and learning factors were introduced to improve the optimization ability. In order to avoid getting stuck at local optimization and enhance the global exploration ability, swarm optimization based on two subgroups was adopted. The crossover operation and mutation operation were carried out based on two subgroups as well. Simulation results demonstrate that the proposed algorithm can obviously improve the location performance of passive troposcatter surveillance system, and the operating time is less than that of the traversal optimization.

Abstract:With the rapid development of urban subway construction, many city subway lines have been networked.Considering the public welfare when making ticket price, most cities in China calculate the ticket price between the two stations of the line network by the shortest path or the least stations now. the traditional Dijkstra algorithm was improved based on the traditional Dijkstra algorithm. The traditional Dijkstra algorithm and the improved Dijkstra algorithm were respectively used to calculate the shortest walking route of Changsha metro line 1~5 network. Results show that the improved Dijkstra algorithm not only effectively improves the efficiency of the algorithm and overcomes the long-time defect of the traditional algorithm, but also partly eliminate the accumulated errors between lines and improve the ductility of the network.

Abstract:Detecting and recognizing targets on the ground is one of the typical tasks of UAVs (unmanned aerial vehicles), but it is limited by the task particularity so that it is often difficult to obtain sufficient data about target samples to achieve highly reliable target recognition. In view of this problem, a small-sample vehicle target recognition method based on the component model was proposed, which combined the cognitive characteristics of human beings to improve the perception ability of ground targets. The possible region of the target was extracted by visual saliency detection and objectness detection, and then the GrabCut segmentation method based on the Graph theory and the maximum between-class variance was used to segment the target and to extract the components from the target. A component recognition method based on a probability map model was used to perform component recognition by sparsely representing a component outline as a conditional random field and performing probabilistic reasoning. The Bayesian-based target recognition method was used to determine whether the target was a vehicle. Verification on real images captured by the UAV showed that the algorithm can detect and identify the vehicle target with high accuracy under the condition of fewer samples, poorer illumination and certain occlusion. At the same time, the recognition method can achieve the effect of certain interpretability.

Abstract:As an important carrier of group intelligence, robot clusters have also received a lot of research and development and more and more applications. Robot cluster path planning technology has also developed rapidly as a core key technology. The technical development status of robot cluster path planning was comprehensively and deeply researched. The basic computing architecture applying to different cluster sizes, scalability requirements, communication requirements, and algorithms of the requirements was innovatively summarized. The basic computing architecture consists of redundant computing architecture, distributed computing architecture, and hierarchical computing architecture. From the perspective of scalability and applicability, the path planning method which takes advantage of the most suitable robot clusters, including bionics, artificial potential field method, geometric method, classical search method and evolutionary learning method, was classified. For the cluster simulation verification research, it provided seven free downloadable or open source robot cluster simulation verification platforms.

Abstract:It is necessary to make the hull potential uniform in order to restrain the characteristics of underwater electric field. A ship hull model in air-sea two-layer medium was established through boundary element method. By changing the number and distribution of sacrificial anodes in passive cathodic protection system, the potential of ship hull and underwater electric field under different protection conditions were calculated quantitatively, and an experiment in laboratory was carried out. Simulation and the experiment results show that the action distance of protection current between anode and corroded area can be shortened by reasonable design of cathodic protection system, which can make share the anticorrosive function of the same area with multiple anodes and can reduce the intensity of protection current output from single anode to improve the uniformity of hull potential, and can restrain the objective of underwater electric field while achieving anticorrosive effect.

Abstract:To improve the scientificalness of equipment maintenance decision-making, an optimal replacement strategy of non-repairable equipment was realized by establishing the optimal maintenance decision model of integrated equipment RUL(remaining useful lifetime) prediction data and uncertain failure threshold. The nonlinear Wiener process was used to establish the degradation model of the equipment and the maximum likelihood estimation was used to determine the parameter estimation of the degradation model. A new estimation method for the distribution coefficient of uncertainty failure threshold based on the EM(expectation maximization) algorithm was proposed. By introducing the virtual failure threshold data, the synchronous iterative update of the distribution coefficient for failure threshold was realized. Based on the concept of the first hitting time, the RUL probability density function of equipment with considering the uncertain failure threshold was derived. The decision model was built on the basis of the renewal-reward theory to determine the optimal replacement occasion. The example analysis shows that the failure threshold of the equipment has an important impact on the result of the maintenance decision. This conclusion fully takes into consideration of the fact that the uncertainty of the equipment failure threshold can not only improve the accuracy of the RUL prediction but also can effectively reduce the life cycle cost of the equipment.

Abstract:Aiming at the characteristics of complex composition of aviation equipment system-of-systems, the fault tree analysis was introduced into the evaluation problem of aviation equipment′s structure contribution rate to system-of-systems, and an evaluation method based on fault tree analysis was proposed. The aviation equipment system-of-systems structure was constructed from the three aspects of operation equipment, information support equipment and support equipment. Furthermore, the fault tree of aviation equipment system-of-systems structure was constructed and the criticality importance index of bottom event was used to calculate the aviation equipment′s structure contribution rate to system-of-systems. And the evaluation model of aviation equipment′s structure contribution rate to system-of-systems based on criticality importance was established. Taking an aviation equipment system-of-systems as an example, the results show that the proposed method can evaluate the aviation equipment′s structure contribution rate to system-of-systems accurately and provide methodological support for short board determination and optimization of aviation equipment system-of-systems structure.