Abstract:In order to realize the controllable flight of stratospheric airships during floating, the sliding mode control for lateral trajectory tracking in wind field was researched. The dynamic models of the stratospheric airship during floating were established, and the models were linearized by using linear perturbation theory. The sliding mode controller for lateral trajectory tracking was designed. Considering that this method was insensitive to external perturbation, the trajectory tracking for linear formation and circular was simulated. Simulation results show that the robustness and response characteristic of the trajectory tracking method based on sliding mode control are both satisfactory, and the control accuracy is high in wind field.

Abstract:A novel near-space aerostat based on quasizero wind-layer field for station-keeping was investigated. The working principle and system composition of the aerostat were introduced first. After that, a model comprising of dynamics, altitude control and energy circle was established. The properties of station-keeping and energy circle of the aerostat were studied in two typical working modes: flight speed limitation and north-south displacement limitation. With the weather input of Changsha, it is found that, compared with uncontrolled free-flying mode, the aerostat can achieve long resident in a 100 km diameter range under both working modes. Moreover, the energy consumption of the aerostat with flight speed limitation mode is lower than that of the other mode.

Abstract:The power of airship′s curved solar array is closely related to the position of airship, time of flight, flight of attitude, layout of solar array and so on. Through the analysis of solar radiation model, and combined with the variation of azimuthal angle in the course of stratospheric airship′s flight, the projection was used to calculate the power of curved solar array, thus the dynamical power generation of the airship was calculated. The analysis results show that the projection in horizontal is the main component of curved solar array′s power, which is little influenced by airship′s azimuthal angle; the power of projections in vertical is smaller, which is more easily affected by airship′s azimuthal angle.

Abstract:To satisfy the rigorous constraint of energy balance, near-space solar aircrafts are usually designed with large aspect ratio and lightweight structures, which leads to a very slow airspeed and a bad flight safety in low altitude airspace. For matching the aerodynamic performances at nearspace working point and in low-altitude climbing process, a climbing approach of solar aircraft based on active morphing was proposed. The aerodynamic and propulsion modeling methods were researched. The flight safety and maneuverability of the pitch, roll and yaw attitude channels were analyzed in quantification. As a result, a climb process with the wing gradually stretching was decided, in which the level flight thrust and power costs were checked. Results show that the stability and maneuverability in low altitude flight are effectively improved, and the cost of power is increased by the wing morphing.

Abstract:Scramjet engine is one of the most important components of air-breathing hypersonic vehicles, and the research on flame structures in the combustion chamber of scramjet engines plays a significant role in studying the mechanism of flame stabilization of the supersonic combustion. Two-dimensional distributions of CH were measured at a direct connect test facility using the PLIF (planar laser-induced fluorescence) technique to visualize the flame heat-release structures in a cavity-stabilized scramjet combustor. Verification and optimization of the CH-PLIF technique were conducted in a methane/air premixed lowspeed flame generated by a jet flame burner. Two-dimensional distributions of flame heat-release structures in the scramjet combustor were achieved by using the CH-PLIF technique. OH-PLIF images and CH chemiluminescence images were also performed in the scramjet combustor to compare these images with the CHPLIF images. Experimental results show that the heat-release zones of the low-speed premixed jet flames can become distorted, wrinkled and separated. The heat-release zones are highly wrinkled with the increasing Reynolds numbers. The heat-release zones with a thickness of 0.5~6.5 mm in the cavity-stabilized scramjet combustor become highly distorted and wrinkled, and the separation of the heat-release zones can be observed. It is found that the CH-PLIF technique is able to visualize the heat-release zones in cavity-stabilized scramjet combustors and can play a promising role in understanding cavity stabilization mechanisms of the supersonic combustion.

Abstract:Aiming at the special environment of the air-breathing hypersonic ramjet flight test, especially the booster separation conditions, the multi-body separation of an axisymmetric hypersonic aircraft was studied. Six degrees of freedom solver and local mesh reconstruction based on non-structured mesh method were proposed to simulate the separation process. Results include motion parameters of the booster and the aerodynamic characteristics ranging from 0 ms to 300 ms for the aircraft under the weak perturbance states. Meanwhile, the trajectory curve of separation was demonstrated. Finally, the feasibility of the subsequent scheme was estimated and the optimal conditions for the separation reached requirement of mild interference.

Abstract:In order to explore the application of morphing technology in hypersonic aircraft, a hypersonic morphing aircraft based on telescopic wing was proposed. Then the trajectory of glide phase was optimized through multi-objective optimization method. Firstly, the aerodynamic characteristics of different telescopic morphing phases were offered, the 3- degree of freedom dynamic model of free glide phase and the heat flux model of the leading edge of the wing were built. In the MOP (multi-objective optimization problem), the two optimization objectives were the range of trajectory, and the total heat of the leading edge of the wing. The optimization variables include the Mach numbers when the aircraft was morphing, and the angle of attack of different phases. MOP was solved by using the MOEA/D (multi-objective evolutionary algorithm based on decomposition). Numerical simulation results show that the proposed method can obtain the Pareto Front. Also, compared with the non-morphing aircraft, the aircraft can achieve a larger range and a smaller total heat of the leading edge of the wing.

Abstract:In order to explore the chemical kinetics process of kerosene combustion in scramjet combustor, a detailed chemical reaction model for the combustion of RP-3 surrogate fuel was simplified to obtain a new reduced model (26 species and 89 reactions) based on the sensitivity analysis and reaction path analysis, and the combustion characteristics of supersonic reacting flow field were depicted. The ignition and combustion characteristics of this surrogate fuel under various conditions were simulated by using the reduced reaction model，and the simulation results were compared with the experimental data and the calculated results by the detailed reaction model. Furthermore, numerical simulations were implemented by using a coupled nonequilibrium reaction solver with the proposed reduced model, and the combustion characteristic of a scramjet combustor with single-side cavity was analyzed in detail. The results indicate that the reduced model can represent the ignition and combustion characteristic of the detailed model to some extent. And the proposed reduced chemical kinetic model predicts the myriad details of the reacting flow field accurately, including the distributions of major species, such as alkenes and cycloalkanes. At the same time, the number of species involved in the reduced model is much fewer, and the reduced model can improve the combustion simulation efficiency.

Abstract:High altitude balloon provides a reliable platform for high altitude scientific experiments. The shape of the balloon is directly related to the whole process of making and flying. The multiple-shooting method was combined with the sequence of two quadratic programming method, and the under-expansion shape and optimum-expansion shape were obtained. In addition, the finite element method was used to analyze the stability and stress and strain of the sphere to verify the correctness of the derived sphere. On this basis, the sensitivity analysis and related application of the key parameters affecting the balloon shape were carried out, and the effects of balloon load, flight altitude and temperature difference between day and night on the balloon shape were obtained quantitatively.

Abstract:Since the bandwidth of modernized navigation signal is increasing, the advantages of complex signal sampling have a raising benefit by substantially reducing the sampling rate. Because of the I/Q amplitude and phase response imbalance, the complex signal sampling may introduce error to the pseudo range measurement in the navigation receivers. The analysis model explaining the influence of the non-ideal characteristic of signal channel, I/Q amplitude and phase response imbalance on the zero value measurement in BPSK/QPSK navigation receivers were improved. Based on the model, the pseudo range zero value of BOC signal affected by I/Q imbalance and the nonideal characteristic of signal channel was derived. The zero value shift caused by the two factors in the frequency domain anti-jamming processing was discussed. The proposed theoretical analysis is highly close to the simulation result in software receivers, where the error is within 1.5×10^-4 chip. This result proves the accuracy of the analysis model. The proposed analysis method can be used to provide prior constraint for features of analog channel in high performance navigation receivers, which can meet the requirement of the zero value change in the jamming scenario.

Abstract:The performance of the multibaseline phase unwrapping is directly related to noise level. For instance, the presence of phase noise makes the phase unwrapping method based on the classical Chinese remainder theorem unrobust enough and inapplicable in practical cases. So a method based on a SR-CRT (searchedform robust Chinese remainder theorem) was presented, and the common factor was carried out to build the new system of simultaneous congruence in the method. Theoretical analysis and experimental results prove the effectiveness of the SR-CRT method and demonstrate that selecting reasonable common factor can improve the noise robustness of the SR-CRT method.

Abstract:There are transition zones in the transitions between the chaotic and periodic states while blindly detecting weak BPSK (binary phase shift keying) signal by using Dufffing oscillator. The relationship expression between transition zone time length and forcing frequency of Duffing system was deduced, and the conclusion that higher forcing frequency leads to shorter transition zone time length was drawn. The simulation experiment gave the time-frequency response curve. The detection sensitivity of Duffing system will lower with the increasing of forcing frequency. The equations of output amplitude as dependent variable and the internal frequency as argument were deduced while Duffing system was in periodic state. The simulation experiment gave the amplitude-frequency response curve. Finally, by using S transform to extract the envelope of Duffing system output, the blind detection model of weak BPSK signal with the scale transformation method combined and the detection array was built. The simulation experiment results show the efficiency of the blind detection model.

Abstract:In order to solve the problem that the feature extraction of ship radiated noise in complex ocean environment is difficult, a method for feature extraction and classification of ship radiated noise based on variational mode decomposition, center frequency, complexity and support vector machine was presented. Four kinds of ship radiated noise signals were decomposed into several intrinsic mode functions with variational mode decomposition. In comparison, the center frequency and permutation entropy of intrinsic mode function with the maximum energy were taken as the characteristic parameters. The characteristic parameters acted as the input of support vector machine to distinguish the four kinds of ship. Results show that this method can realize the feature extraction of ship radiated noise, and it has higher recognition rate than the existing methods.

Abstract:Aiming at solving the decline of detection performance under low signalnoise ratio and nonstationary background noise and combining the principle of eigenvalue detection, a combination information cross-correlation detection algorithm based on single vector hydrophone was presented. This algorithm makes an assemble velocity by using electronic rotation angle and velocity information, and obtains a cross-correlation value with pressure. This value satisfies the asymptotic Gaussian distribution under large snapshot without target signal. This value is divided by minimum eigenvalue of analytical velocity covariance matrix to get a detection statistic. Finally, compared with the threshold, the object detection is achieved. The analysis of theory shows this algorithm does not need to know any prior information of background noise, and the detection performance can be improved by adjusting the guiding angle. This algorithm can achieve bearing estimation by using the relationship between detection statistic and guiding angle as to single target. The simulation and real data prove the superiority of the proposed algorithm, compared with the maximum-minimum eigenvalue detection algorithm and the energy detection algorithm.

Abstract:Aiming at the modeling problem of hypersonic gliding missile tracking, a method of aerodynamic parameter model based on the law of guidance variables was studied. The aerodynamic parameters were analyzed and the shortcomings of the traditional modeling method were pointed out. With the assumption that the guidance variables obey the first-order delay process, the aerodynamic parameter model was derived by using the linearized aerodynamic coefficients. By analyzing the variants of model under different flight conditions, the model adaptability for target′s maneuver was proved. The values of unknown parameters were discussed, so as to realize the adaptive matching of model with flight state. Simulation results show that the performance of the proposed model is obviously better than the traditional model when the target is maneuvering. Simultaneously, the simulation under different filter parameters confirms the model′s validity.

Abstract:In view of the LPAR (large phased array radar) system has too much safety factors and it is difficult to evaluate. Firstly，the LPAR safety evaluation index system based on the radar characteristic was analyzed and established. Secondly, a method to determine the comprehensive weight based on the improved FAHP(fuzzy analytic hierarchy process), entropy weigh and Lagrange algorithm was put forward, and the safety fuzzy comprehensive evaluation model was established. Thirdly, taking safety evaluation of the certain LPAR system as an example, the safety comprehensive weight of the LPAR system was determined by the proposed method, the safety evaluation was carried out by the established model. Finally, this method is compared with the traditional AHP method, and the feasibility and rationality of the method are verified.

Abstract:It is now a basic premise to acquire the polarization scattering matrix of radar target accurately before the polarization information processing. Based on a pair of linear frequency modulation signals with opposite slopes and aimed at the simultaneous polarimetric radar adopting the digital dechirp processing, the mathematical model of the influence of the intermediate frequency deviation and sampling frequency deviation on simultaneous polarization measurement was derived. An intermediate frequency deviation and sampling frequency deviation joint estimation and calibration algorithm was proposed. Simulation and real data results show that the radar frequency stability can change the peak position and phase of the simultaneous polarization scattering matrix measurement. The approach proposed can regulate the peak deviation effectively, compensate the phase error and accurately acquire the four elements of polarization scattering matrix.

Abstract:Aiming at the process of executing combat mission, the collision may occur between the UAVs (unmanned aerial vehicles), or between the UAV and the enemy plane. A collision avoidance control algorithm and a control strategy based on the artificial potential field were simultaneously applied for a Multi-UAV collision avoidance control. The three UAVs constituted the triangular formation as the control object, the leader flight path as the expected path, the followers tracked the leader to maintain the triangle formation flight. From the UAV formation encountering the obstacle to the UAV formation system accomplishing the avoidance, the UVA formation experienced three stages, including the merging formation, the splitting formation and the closing rank to the triangle formation, which is the convergence to the steady flight state. The simulation results show that the proposed collision control avoidance strategy can converge to the desired formation and the stability-flight state.

Abstract:In video surveillance, one scene image/frame can be modeled as a superimposition or linear mixture of foreground visual contents and background contents. In the real world, however, the background and foreground are correlated to each other. Therefore, the foreground extraction cannot be well solved by the PCA (principle component analysis) and the ICA (independent component analysis) algorithms. The foreground extraction was modeled as a BSE (blind source extraction) problem. The MSCPE (mean square cross prediction error), one solution of BSE, was generalized to extract desired source signal which was correlated with other source signals. Then MSCPE BSE method was applied to the background subtraction schemes by using the basic model and eigen backgrounds method. Experimental results on artificial video shows the feasibility of MSCPE, and the realworld video experiments demonstrate its effectiveness.

Abstract:Aimed at solving the lack of control of container technology at the network level, a network control architecture for large-scale container clusters was designed. The architecture was researched respectively from three aspects (flexible networking, intelligent adaptation and security isolation) in container cluster network, mainly to solve the key issues of large-scale container clusters deployment in the network adapter and isolation control, etc.. The experimental results show that the designed network control architecture can achieve intelligent network adaptation, network node migration, and accurate isolation control of node-to-node communication in virtual local area network.

Abstract:The cache ubiquity feature in ICN (information-centric networking) causes many problems such as higher data duplication rate, underutilization of cache space, etc. To solve such problems, the benefits of multiple network roles were considered. From the views of user-service provider and network operator, two single-objective optimization models were established respectively, aiming at minimizing the network traffic and the network expense, which were merged into the Pareto model. The proposed cache location selected algorithm was described based on the mathematical programming method of Pareto. Simulation results show that the proposed algorithm outperforms the default cache mechanism of ICN in terms of traffic cost-effective. In terms of network expense, the proposed algorithm is more applicable to ICN when there are a few popular contents. However, when all contents are popular, the default mechanism of “cache everywhere” in ICN is more applicable.

Abstract:For the problem that 6LoWPAN(IPv6 low power wireless personal area network) wireless sensor network has poor scalability in design and application and is incompatible with IPv4 environment, a wireless sensor network based on 6LoWPAN and MQTT(message queuing telemetry transport) was designed and implemented. Among them, the wireless sensor network node works as MQTT client to communicate with MQTT server, and the border router implements communication between wireless sensor network node and IPv4 network through NAT64(network address translation IPv6 to IPv4). Finally, the designed wireless sensor network was applied to the smart home scenario, the performance of wireless sensor network and border router was evaluated, and the implementation of the system function was tested. Results show that the wireless sensor network has good connectivity and stability, the data uploading and command receiving of the wireless sensor node is stable and reliable, the border router works stably, and the system has good performance.

Abstract:According to the operational characteristics of the high-speed network model of nearly polar constellation of micro-satellite, the definition of the high-speed network of constellation was given. The routing protocol adapted to the transmission model was analyzed, its deficiency under the model was illustrated and the calculation method of protocol overhead was deduced. Then the optimized protocol was provided. The high-speed network model of microsatellite constellation was established by using the NS3 network simulation platform, and the key performance indexes of the routing protocol were simulated before and after adopting the optimization strategy. The results show that the optimized routing algorithm reduces the overhead significantly, meanwhile it improves the throughput and packet arrival rate in the high-speed network. The performance of the high-speed network of nano-satellite constellation is optimized.

Abstract:According to the fact that current effectiveness evaluation models lay more emphasis on the static observations of indicators and less on the trend information inherent in sequential observations, a new dynamic evaluation methods for spare parts support effectiveness based on grey clustering-rough set and set pair analysis was proposed. Compared with the subjective and the objective weight-deciding method′s virtue and disadvantage, the weight of every index was decided by using grey clustering-rough set combinational method. By establishing the set of spare parts support effectiveness evaluation set pair, the dynamic variation law of the protection of spare parts was described by definition of set pair equal power balance power and opposite power, Based on Markov chain, the dynamic set pair model was analyzed, The results show that the model can reflect the spare parts support effectiveness dynamic characteristics effectively, giving the decision makers a scientific reference to develop a long-term plan for the support of spare parts.

Abstract:Considering the fact that the community detection algorithm based on label propagation can detect overlapping community structures of complex networks, an overlapping community detection algorithm COPRAPC (community overlap propagation algorithm based on PageRank and clustering coefficient) was proposed. The algorithm used PageRank algorithm to rank the influence of nodes, which can stabilize the community finding results. The parameter of node clustering coefficient was a noderelated parameter, which can be used to modify the parameters of the algorithm and limit the maximum number of labels each node, so as to improve the quality of community mining. Experiments on artificial networks and real-world networks show that the algorithm can effectively detect overlapping communities, and the algorithm has acceptable time efficiency and algorithm complexity.

Abstract:Comprehension of complexity is one of the key challenges in science and technology. Complexity is a very important conception in interdisciplinary systems science, and is significant to researchers. The basic semantic background on system complexity was presented and the various definitions of complexity domestically and overseas were analyzed. On the basis of the classification of ontology and epistemology, a taxonomy of complexity was described on the basis of the state-of-the-art works on complexity definition. Meanwhile, a category of complexity measurements and the corresponding mathematical tools were proposed. Examples were given for the efficiency of complexity classification and measures.

Abstract:The essence of the type selection of the platform for ship repairing and maintenance at far sea is a decision-making with multiple fuzzy related attributies, including of operability, stability, timeliness, safety and economy. In order to reflect the decision-making intention of decision makers and integrate decision information more accurately in the platform selection process, a R-THIOWGA (related triangular hesitate intuitionistic ordered weighted geometric average) operator was built, and a new comparison rule of the triangular hesitate intuitionistic fuzzy number was also presented. A method of the group decision-making for type selection of ship repairing and maintenance at far sea was proposed, based on the R-THIOWGA operator. The application of the method was analyzed on Chinese Navy ship repairing and maintenance practically. The result shows that the R-THIOWGA operator is feasible for multiple fuzzy related attributes decision-making, and the self-propelled semi-submersible repair and maintenance ship is confirmed as the best platform type for China navy.