Abstract:Flamelet model and hybrid LES/RANS method were used to simulate SCRAMJET with strut for the Chemical Propulsion of the German Aerospace Center (DLR). The effect of reaction on turbulence was discussed, and comparison between 2D and 3D simulation were presented. The results show the following indication: (1) Mixing is controlled by large eddy scales in nonreacting flow,and the shear layer has three effects obviously； In addition, the combination and pairing of large eddy scales can be seen in 2D simulation, while stretching, distorting and breaking up can be seen in 3D simulation；(2) In reacting case, jet penetration decreases and recirculation zone becomes larger, while, owing to heat release, large eddy scales turn up and saturation appears late. (3) Numerical shadow picture displays good agreement with experimental shadow photograph, while velocity and temperature measurements are consistent with experimental data qualitatively and quantitatively, but 3D model is superior to 2D model in result accuracy.

Abstract:The autonomous navigation system based on starlight atmosphere refraction has simple structure and low cost. Using the system, the spacecraft can get high-precision navigation data. But the measurement model has some imprecise atmospheric parameter, which reduces the navigation precision and reliability seriously. The above effects can be avoided by nervous network fitting starlight atmosphere refraction model on line, using satellite navigation data, when the spacecraft is at low orbit. This method can improve the navigation precision based on starlight refraction. Through simulation, the characteristics of the starlight refraction model and the fitting method were researched, and the precision analysis of the fitting models were also made.

Abstract:In the process of SRM (Solid Rocket Motor) grain configuration design, high loading fraction always gives rise to high stress and train in the grain, and the structure integrity of grain turns hard to satisfy. To solve this problem, the integration of GA (Genetic Algorithm) and parameterized modeling method was applied to shape the optimization of the wheel shape grain. Parameterized finite element analysis model was constructed by PCL (Patran Command Language), the secondary development tool of MSC.Patran. Based on the model, the finite element mesh could be established and the maximum strain and loading fraction of grain could be exported when the geometric parameters were given.This made it convenient for GA to call, as a function. A shape optimization of a high loading fraction wheel shape grain was carried out, and the optimal grain was found. The maximum strain of the optimal grain, under low temperature load,was 30% less than the initial grain's. Meanwhile, the loading fraction remained the same. The results show that the method presented is feasible and available,and it can be applied to SRM grain configuration design of all sorts.

Abstract:An air-heater was designed for scramjet ground test. The internal flow field in the air-heater was investigated and the results were compared with the test data. The results show that the air-heater basically corresponds with the structure project and performance, the temperature of faceplate is reduced as a result of the air flow from injector-inlet, and the inner surface of the combustion chamber is protected by air flow from chamber-inlet. The results will be helpful for the optimization of the air-heater design.

Abstract:Based on ducted rocket operating principle, mathematical working model of air inlet, gas generator and secondary chamber was built. The altitude characteristics and velocity characteristics of variable flow ducted rocket were numerically studied. Increasing the flight mach or decreasing the flight altitude can not only help the engine work in a wide range of thrust, but also decrease the thrust coefficient. Decreasing the area of gas regulation valve can increase thrust and thrust coefficient

Abstract:Based on the requirement of broadband radome, by using the transmission line theory, the calculation method of transmission efficiency of single-layer structure was conducted when the frequency varied from 2GHz to 18GHz and the incidence angle changed from 0 to 40°,the dielectric properties were optimally designed. The results suggest that when the dielectric constant is no more than 3.0 and the loss angle tangent value is no more than 0.02, the transmission efficiency of single-layer structure material with the suitable wall thickness is more than 60%. According to the design results, considering the mechanical and thermal properties, the hollow silica fiber reinforced BN-Si₃N₄ matrix composites (SiO_2f/BN-Si₃N₄ composites) are selected as single-layer structure radome material. According to the dielectric properties of the composites (ε=2.8，tanδ=0.005), the structural parameter (thickness) was optimally designed, and the optimal wall thickness was 7mm. The broadband properties of SiO_2f/BN-Si₃N₄ single-layer structure radome material in agreement with the wall thickness requirement were tested. The results suggest that the transmission efficiency for single-layer structure radome material is more than 60% when the frequency is 2～18 GHz.

Abstract:A novel multi-sensor image matching method based on spatial sub-area congruency is proposed. In this method, images were segmented into sub-areas with same size. The structure feature represented by matrix of surrounding similarity was obtained by calculating the similarity of intensity histogram of each pair of adjacent sub-areas, and was used to compute spatial sub-area congruency. Through employing optimized searching algorithm, the matching result was acquired. Experimental results show that the proposed method can match multi-sensor images stably and fast and outperforms conventional methods

Abstract:In order to numerically study the reaction characteristics of magnesium and vapor in broad temperature range, the reaction model based on diffusional and chemical dynamic control respectively was established. The diffusional control model considered the partial condensation of gaseous MgO on the surface of magnesium droplet. The chemical dynamic model of Mg/H₂O reaction was based on the Arrhenius equation. The reaction rate of Mg/H₂O at different conditions was studied numerically. The results show that the calculated results are consistent with the experimental results. The reaction rate is great at high temperature and concentration of vapor, but low at high pressure. The reaction rate of magnesium and vapor is controlled by different factors at different temperature region. The reaction rate is controlled by chemical dynamic below the critical transition temperature, but by diffusional dynamic above the critical transition temperature.

Abstract:Distribution flow pipeline used in cylindrical chemical laser is composed of an annular general pipeline and a limited quantity of branch pipelines that are connected with the inner or outer circular arc of general pipeline. Its structure and flow field characteristics differ from those of linear distribution flow pipeline used in conventional chemical laser. Flow field characteristics of above-mentioned three kinds of distribution flow pipelines were analyzed contrastively based on three-dimension computational fluid dynamics methods. The numerical simulation results demonstrate that total pressure of general pipeline in linear distribution flow pipeline is higher than that in outer-circular-arc annular pipeline, but lower than that in inner-circular-arc annular pipeline. Both distribution flows of branch pipelines and secondary flows produced in annular general pipeline can excite radial velocity on the section plane of general pipeline. These phenomena enable the gas flow of general pipeline to have remarkable three-dimension characteristics. Mass flow rates of branch pipeline outlets are higher and higher along the direction of main gas flow movement. Its trend is contrary to upward tendency of total pressure in general pipeline, but is similar to downward tendency of static pressure in general pipeline. By comparison, Mass flow rate fluctuating amplitude of branch pipeline outlets in outer-circular-arc annular distribution flow pipeline is smaller than that in linear distribution flow pipeline, and the amplitude in inner-circular-arc annular distribution flow pipeline is the biggest of the three. As a result, outer-circular-arc annular distribution flow pipeline is of advantage among the three methods in distributing uniformly gas flow, while inner-circular-arc annular pipeline is the lowest and the linear distribution flow pipeline goes between the other two.

Abstract:The remotely-operated weapon station (ROWS) is a non-linear system with strong backlash, time-varying friction and time-varying moment of inertia. The active disturbance rejection controller (ADRC) was designed to improve the system's performance. Based on ADRC extended state observer to estimate the model uncertainty and external interference of the system, the system's ability of disturbance rejection was greatly improved. Experiment result shows that the system used ADRC technique has good dynamic performance. It takes only 2.62s for a 180° maneuver with no overshoot and no chattering.

Abstract:Community structure is one of the common topological characteristics of complex networks. Community detection has become a fundamental problem in the research field of complex networks. The new progress of current algorithms for community detection was reviewed. The characteristics of these algorithms were discussesed. Finally, future direction of this active area was proposed.

Abstract:A multi-satellite cooperative planning problem model was given considering the characteristics of the task requests and satellite constraints. Then the original performance function of each satellite agent was modified by introducing both the constraint punishing operator and the multi-satellite joint punishing operator. Next, a multi-satellite reinforcement learning algorithm (MUSARLA) was proposed to derive the coordinated task allocation strategy. Furthermore, the interaction among multiple satellites was designed based on blackboard architecture to reduce the communication cost while learning. Finally, simulated experiments are carried out which verified the effectiveness of the proposed algorithm.

Abstract:The random step frequency signal shares the characteristics of the step frequency radar and the wideband noise radar. It not only reduces the instantaneous band-width and data sampling rate, but also has the good characteristics of the low probability of intercept, the electromagnetic compatibility and the radio-frequency immunity. The statistic characteristics of correlation output and ambiguity function like first moment，second moment, and variance were analyzed, and the radio-frequency immunity of the random step frequency signal was compared with linear stepped frequency signal in this paper. The SAR imaging algorithm based on the Correlation-Output and Range-Doppler algorithm was presented and analyzed, and the simulation result verified the validity.

Abstract:Airborne Ultra-Wide Band Synthetic Aperture Radar (UWB SAR) has larger integrated angle and longer synthetic aperture, which gives rise to more complexity in motion errors. In light of this, first the motion model of airborne UWB SAR was derived. Then, the expression of echo spectrum in presence of motion error was deducted. Theoretic analysis on the reason of the motion error impacts on SAR imaging and the influences on SAR images induced by the different motion errors were carried out. Experiment results on simulated data proved the validity of the theory analysis presented in this paper.

Abstract:Multipath error is one of the last obstacles for GNSS performance improvement, and accordingly multipath mitigation techniques are developed rapidly. However, there is a lack of evaluation rules for the multipath mitigation performance. Three evaluation criteria based on the multipath error envelope were proposed; the multipath error formulae for both ELS technique and Double-delta technique were derived for the first time; hence calculation expressions of the multipath mitigation performance evaluation for the above two techniques and narrow correlator technique were presented. This research can be used as a guideline for the parameter design of multipath mitigation techniques in GNSS receiver.

Abstract:For hybrid direction of arrival (DOA) and frequency difference of arrival (FDOA) passive localization, a fast and effective algebraic solution is proposed. This method converts the emitter position nonlinear estimation problem into two weighted linear least-squares minimization, which simplifies the emitter localization process. The proposed means does not have the search procedure, so it has less computational load than traditional search method. Furthermore, it is also more convenient, because it does not need the initial value of the emitter as in the Gauss-Newton iterative method. In structure, the observation equations were first established. And then the Cramér-Rao Lower Bound (CRLB) of the emitter's position estimation was presented. Moreover, the procedures and theoretical performance of the algebraic solution were given. Finally, the simulation was conducted. The results show that the location error of the algebraic solution approaches the CRLB at moderate measurement noise level.

Abstract:Proper dynamic models and estimation methods are crucial factors to achieve a nice tracking performance for a reentry target. First, the dynamic model of maneuver reentry vehicle was chosen for reentry target tracking, and the tracking problem was equivalent to the simultaneous estimation of the state and the parameter. Then, the relativity of the state and the parameter were discussed by numerical examination. Next, for the information lost caused by the assumption of a deterministic input vector in the original dual unscented filter, an improved dual unscented filter based on a random input vector was proposed, and a detail accuracy analysis was achieved in theory. Finally, the accuracy, applicability and ability for processing incomplete data were validated by simulations.

Abstract:To sovle the problem of Non-Data-Aided (NDA) sampling frequency synchronization for orthogonal frequency division multiplex (OFDM) systems, the CRB(Cramér-Rao Bound) of NDA sampling frequency synchronization algorithm was proposed. At first, the Probability Distribution Function (PDF) of received signal was deduced. Then, the CRB of NDA sampling frequency synchronization for OFDM systems was deduced according to its definition. At last, the CRB of NDA sampling frequency synchronization for OFDM systems in different modulation, sampling frequency offset and subcarrier number was presented.

Abstract:A method of calibrating the channel uncertainty and mutual coupling of uniform linear array is presented, which is based on simulated annealing algorithm. It used multiple calibration sources working at different time. According to the principle of signal subspace, the target function was constructed. Then, by using simulated annealing algorithm, the gain and phase error matrix and mutual coupling matrix were estimated. Finally, computer simulation and experiment result demonstrates the efficiency of this method.

Abstract:Adaptive algorithms of antenna arrays usually focus on the optimal performance under stable conditions. If GNSS receivers are mounted on moving subjects (such as bombards, aircrafts, vehicles or ships), the movement or turbulence of the platform can make the “null” direction mismatch the interferer direction. The current researchis paper firstly establisheds an array signal model under platform motion, which wais classified into two types: the first motion type (high frequency turbulence) and the second motion type (stable tilting), Then it developeds the analytic formula of array output Signal-to-Interference-plus-Noise ratio (SINR) under two types of motion models. Simulation results show that the array output SINR is more sensitive to the arriving angle of the interferer than to its power, which is because the antenna usually forms narrow and deep nulls. For a 7-element antenna array with one element at center and other elements in a circle around the center, when the arriving angle of the interferer changes by 3 degrees, the loss of SINR reaches 3.3 dB. Improving weight updating rates and widening the null width are both effective means in improving the robustness of the anti-jamming antenna arrays.

Abstract:A simple method of ion beam figuring was successfully employed for processing rectangular off-axis aspheric mirror. Based on the material removal mechanism, the normal removal characteristic was analyzed. Beam diameter, peak removal rate and volume removal rate are the three factors to evaluate the robustness of removal function with respect to little disturbance of incidence angle. According to the results of analyses and experiments, the method of processing rectangular off-axis aspheric mirror by ion beam figuring was appropriately simplified. To validate the feasibility of this method, an off-axis aspheric ellipsoidal mirror was processed in our IBF system. With three iterations of 200 minutes, the surface error was reduced from 0.294λ RMS to 0.05λ RMS and the total convergence ratio was 10. The experimental results indicate that IBF has inimitable material removal characteristics, can effectively improve surface precision and realize the rapid processing of ultra-precision rectangular off-axis aspheric mirror.

Abstract:Currently, the continuous rotary north-finder is widely discussed for its outstanding performance. However, few researches about the influence of turntable error on the continuous rotary north-finding algorithm can be found. For the north-finder based on rate biased RLG (ring laser gyro), the influence of turntable's periodic angular position errors to the north-finding results was studied. Theoretical analysis shows that, the existence of periodic angular position errors may cause unexpected error in the north-finding process and these errors must be modeled and compensated for in order to increase the north-finding precision. Finally, simulation and experiments were carried out to verify the theoretical conclusion.

Abstract:Speed and position detection system is the basis of propulsion and traction control for high speed maglev train. Compared with traditional railways, high speed maglev trains have some exclusive problems which can affect system proper working, such as levitating fluctuation, joint gap of long stator track and contactless reader for absolute position. To reduce detection error of relative position due to levitating fluctuation, a method utilizing levitation gap to normalize detection output into the one of 8mm levitation gap is proposed. It is found that it can satisfy the precision requirement of 2.8°for relative position detection. To reduce detection error of relative position due to joint gap of track, a switching method between two relative-position detections based on a predictive adaptive filter was adopted. As a result, it can avoid distortion and satisfy the precision requirement of relative position detection. To solve the problem of absolute position reader by contactless method, an equivalent model of electro-magnetic induction reader was analyzed. It is found that the frequency and amplitude of magnetic fields need be increased and the resistor of emit coils need be decreased. As a result, it can satisfy the absolute position detection requirement.

Abstract:With terrorism aggravating, anti-terrorism has been a main task for national military security departments around the world. The current study utilized categorical data visualization, Parallel Sets, to analyze the relations among the multi-categories in Global Terrorism Database, aimed to uncover the implicit information within the data set. To alleviate the deficiency of excessive edge crossing brought by random layout of categorical values, the research proposed a heuristic layout algorithm based on average heuristic with cardinality reduction, which optimized the layout order of categories and the visual clutter is eased so that the cardinality reduction strategies can reduce the numbers of categories involved in computation. The experimental results demonstrate that the improved parallel sets can clearly express the association among the multi-categories in Global Terrorism Database, thereby assist users in analyzing the information of various terrorist organizations, such as the behavior characteristics. Furthermore, the average-based heuristic with cardinality reduction is simple and highly efficient, which is suitable for large data sets with many categorical attributes.

Abstract:Two-stage sequential stopping procedure is used for terminating simulation analysis. It can control precision of result data that is required, but cannot avoid redundancy computation and early stopping. Firstly, the existing stopping procedures of terminating simulation were reviewed; then, the relationship between the quantity estimating of the samples total needed and the current amount of the samples usable was analyzed; finally, a modified method based on parameter steady-state estimate was proposed. This method can improve estimating of n (samples total needed) if the n is biggish, and ensure the validity of the simulation result. It can increase go-aheadism for the procedure actualizing.

Abstract:Aiming at the adaptive optimization problem of command and control (C2) organization decision-layer structure, the mission adaptability measure of decision-layer structure was defined, uncertainty factors that affect C2 organization decision-layer structure were analyzed and the decision-layer structure adaptive optimization model was constructed. In order to reduce the solution uncertainty of the adaptive optimization problem and the change cost of decision-layer structure, a dynamic adaptive optimization approach based on the rolling horizon procedure (RHP) was designed. It is found that it improved the performance of decision-layer structure, and also controlled the change cost of decision-layer structure. The efficiency of RHP is confirmed by the computational experiments.

Abstract:Taking the capabilities and usage restrictions of the electronic reconnaissance satellite (ERS) as well as the scheduling requirement of different tasks into account, a multi-objective mixed integer programming model for ERS cooperative reconnaissance problem (ERSCRP) was presented. Then a hybrid algorithm named MOEA-VNS was put forward. MOEA-VNS made full use of the outstanding global search capability of multi-objective evolutionary algorithm (MOEA) and the local search performance of variable neighborhood search (VNS). Taking advantage of the combination characteristic of multiple reconnaissance windows, the evolutionary operators and the neighborhood search operators were designed, which not only ensured the diversity of the non-dominated solutions acquired by MOEA-VNS, but also made them as close to the Pareto optimal solutions of the ERSCRP as possible. The experiment results show that MOEA-VNS can solve the problem effectively.

Abstract:For effectively manage and schedule remote sensing data processing task, which can improve the utility of processing resources, Petri net was adopted to describe this problem based on its characteristics, and its mathematical model was also presented. An ant colony optimization algorithm was proposed for solving this problem. Finally, experiment results, compared with the results of heuristic algorithm and the very fast simulated annealing algorithm, show the effectiveness of the approach proposed.

Abstract:Armada area defense is a complex work. The long-range programming, tha having System of Systems(SoS) characteristics at strategic level, is very important and difficult for it. It's necessary to use Exploratory Analysis(EA) to help us have a broad understanding about the issue, by quantificationally exploring at a high-level model that specially built for EA, before going deep into details. The Armada area defence issue was analyzed at macro-level view, a software tool-EASim to support EA based on time-sliced influence diagrams was developed, a high-level analysis model was built, and some simple analysis illustrations were given.

Abstract:Electromagnetic detection satellite(EDS) holds a significantly important role in the fields of antiterrorism and salvage. Considering the uncertainties of the electromagnetic detection satellite area search tasks in space-frequency domain, the uncertain factors' quantitative description models of the EDS area search problem(EDSASP) were proposed. So were the decision elements' models. An EDS task scheduling technique based on Bayesian decision-making was put forward, and the EDS scheduling model in uncertain space-frequency domain environments was also established, aiming to optimize the objectives of the information detecting reward and the front interception reward. The simulation instances demonstrate that the technique can effectively deal with the EDS detecting problem and the performance goes on well.