Abstract:Through combining an experiment and a numerical simulation, a study was carried out on supersonic mixing layer with splitters of different geometric configurations, which is under the condition of Ma₁=1.5，Ma₂=2.5，T_0,1=300K，T_0,2=1200K，and matched pressure p₁=p₂=86kPa.In the experiment, it was discovered that the thickness of mixing layer in the flow field with splitters in which a cavity is mounted grows as the ratio of the length to the depth of the cavity becomes larger; Splitters with sawtooth trail show great effect of mixing enhancement and making the flow field highly unsteady. In the numerical study, it was demonstrated that the mixing-enhancement effect of splitters with cavity is due to the cavity shear layer’s reattachment to the trail of the splitter, and splitters with sawtooth trail due to induced large-scale streamwise vortexes. 

Abstract:A new application based on the parameter modeling method of MSC.Patran and generation algorithm was proposed to design the clamp band joint. First, finite element techniques for 2-dimension axisymmetric analysis of clamp band joints were developed, including the modeling of V-clamp, strap pre-tension and loads, and the optimizing constrains and objectives were also introduced. Then a clamp band joint with the diameter being 3m was designed via the presented method. Finally, a 3-dimension finite element model of the designed clamp band joint was established and analyzed. It indicates that the method is applicable to the design of clamp band joints, that the connective stiffness is strengthened by increasing the length and height of the inner ring of the interface rings, and that the modeling method is proved to be valid by the agreements of the finite element analysis results of 2-D model and 3-D model.

Abstract:The combustion process of pulverized magnesium particle cloud in powdered fuel ramjet preburner was studied and a one-dimension premixed laminar combustion model of pulverized magnesium particle cloud was established. The study shows that the laminar flame propagation of pulverized magnesium particle cloud is very stable, and the flame structure is almost invariable in the combustion process; the combustion zone thickness is very thin and the preheat zone thickness is about 2-3 times as much as the former. The magnesium particles vaporization and the homogeneous reaction of magnesium vapor and oxygen in particle cloud is the direct cause of flame and the key of flame propagation that; the preheat zone gas temperature rising depends mainly on the thermal conductivity of the combustion zone and the reaction heat of magnesium vapor which diffuses from combustion zone and oxygen while the preheat zone particle temperature rise depends on the convective heat transfer from gas phase to particle phase mostly. The effects of the interior parameters on the combustion of the magnesium particle cloud were analyzed. The effect of particle relative concentration on combustion of particle cloud is complex. When the particle relative concentration is low, increasing particle relative concentration is helpful for speeding up the particle cloud combustion process; when the particle relative concentration is high, increasing particle relative concentration is adverse to speeding up the particle cloud combustion process. With the increase of the particle size, the flame propagation speed is reduced, the flame temperature increases, and the thickness of preheat zone increases as well. With the increase of the initial temperature of particle cloud, flame propagation speed and flame temperature display linear growth, and the preheat zone thickness shows parabolic growth. The tendencies obtained by numerical simulation coincide well with those of the experimental results from the previous literature.

Abstract:The traditional fault diagnosis method is generally based on the measuring signal, without considering the actual physical connection characteristics, but these characteristics affect the diagnosis results. With the wide application of professional electric system design software, system designers can easily obtain the physical connection characteristics and logical connection characteristics. By analyzing the signals of product layer or system layer, physical connection and its interconnected relationship, a set of logical physical synthetically (LPS) model, which unifies the abstract signal and the physical connection, was presented to study the LPS model instantiation method based on wire table and net table, and a set of intelligent fault detection software was developed. An example for validation was demonstrated: the fault diagnosis method based on LPS model can isolate the fault to the specified product level, with great value of engineering application.

Abstract:One mission of on-orbit servicing can be fulfilled in many ways, and proper mission assignment must be guaranteed. In light of this, first, the reachable domain of service spacecraft was resolved and the target spacecraft which satisfies the reachable domain was filtered. Then the assignment of servicing based on the optimization of multi-objective, including time, fuel consumption and priority, was studied. The best plan was achieved by building the model of 0-1 integer programming and taking the NSGA-Ⅱ algorithm with the constraint of time and fuel consumption. Finally two examples of simulation were given, one demonstrating the general results of the above method, either compared with another algorithm. The simulation results indicate that the above method is effective in solving the problem of mission assignment for on-orbit servicing.

Abstract:Feasibility of Space-based Tracking Telemetry and Command System (TT&C) based on single satellite was analyzed. A new orbit determination method based on constringent estimation was proposed according to the mode of single satellite observation. In the process of the orbit determination, the law matrix was availably transformed by the constringent estimation to restrain error of singularity cased by law matrix. It was proved that the precision of constringent estimation is higher than the traditional method under the given conditions. Then the error transmitting coefficient (ETC) of observation was proposed, on the basis of the special characteristics of the single satellite observation, and the algorithm of orbit determination was designed. Finally the new method of constringent estimation was proved to be able to improve the precision of orbit determination in the mode of single satellite observation.

Abstract:A methodology is proposed to evaluate the mission reliability of TT&C scenarios by modeling and analyzing space tracking, telemetry and command (TT&C) system using extended object-oriented Petri nets (EOOPN). The formal definition, operational rules and the modeling approach were given. It can embody the object-oriented idea by introducing the concepts of public place, message arc and message handle function into the model, and it has good hierarchical structure and modularity. The EOOPN model can completely describe the TT&C system composite and mission process and reflect the dynamic stochastic factors in system operation. After simulating the EOOPN model, the case study reveals that the simulation results have a good convergence, and the errors are controlled within one percent compared with the analytical result of Markov models, proving the effectiveness of the model.

Abstract:Satellite weekly task scheduling is an important procedure for the Satellite Run and Management System, and it exerts influence on the effectiveness of satellite system. Different from the function and the characteristics of daily task scheduling, weekly task scheduling includes not only the technology problem but also the management problem. This study mainly expounds three aspects of work: firstly, analyzing the demand and the characteristic of weekly task scheduling, explaining four main functions of weekly scheduling, and constructing a hierarchical scheduling framework; secondly, summarizing optimization objects and constraint conditions, and building the weekly task scheduling model with considering the task overloading factor; thirdly, combing the Gene Algorithm and the Simulated Annealing Search to solve the model, while instigating the heuristic rules and introducing distributed parallel computing strategy.

Abstract:Stealthy approach method of fighter was researched for the requirement of concealment counterwork in air combat. Detection threat model for radar was constructed based on dynamic trait for Radar Cross Section (RCS). Guidance model was constructed based on parameters for situation description in air combat. An optimal control was formulated for stealthy approach problem of fighter, in which performance index is built by minimizing detection probability and threat restriction is given by critical exposed distance under given detection probability. Receding Horizon Control (RHC) was introduced for online optimization and Gauss Pseudo-spectral Method (GPM) was adopted for numerical solution to assure the real-time resolution requirement. Simulation result shows that stealthy approach ability is greatly enhanced for fighter by adopting both path restriction and performance index restriction, and the model resolution time can satisfy the real-time requirement for fighter control.

Abstract:According to the heat transfer theory and the thermal network method, and taking the spiral bevel gear transmission system of a helicopter tail reducer as research object, the calculation model of the temperature field Simulink simulation was established. Based on the model, the steady-state temperature field of the transmission system was calculated in the normal lubrication. Taking it as the initial condition, the transient temperature field of the transmission system was calculated and analyzed in the condition of loss of lubrication. It provides the theoretical foundation of predicting the survivability of the gear transmission system in the condition of loss of lubrication.

Abstract:Considering the effect of magnetic field on the plasma plume, a hybrid particle-fluid model combining DSMC and PIC methods was developed to study the plume characteristics of a pulsed plasma thruster. By incorporating a magnetohydrodynamic code to provide inlet conditions, this model was applied to simulate the three-dimensional plume field. The calculation results were validated by an experiment based on triple Langmuir probes. Investigations show that there are substantial differences between the expansion dynamics of various species. It is indicated that the oscillation of discharge current will lead to the generation of a population of low-velocity ions, together with the aggravation of backflow of ions. Electromagnetic acceleration is demonstrated to be the primary mechanism of plasma acceleration, and the magnetic field plays an important role in the diffusion of the thruster plume.

Abstract:Quaternion algebra has been widely applied to many subjects such as quantum mechanics, control theory and inertial navigation, and it has won attention from many scholars in the field of effectively obtaining the roots of a quaternionic polynomial. Recently, Janovska and Opfer have theoretically provided a method of finding all zeros of a simple quaternionic polynomial of degree n. Furthermore, Feng and Zhao have given a formula of finding all zeros of a general simple quaternionic polynomial of degree n in terms of solving polynomials over the field of complex numbers. Based on the results given by Feng and Zhao in this paper, the roots of a quaternionic one-sided polynomial with degree 2 were discussed and classified, and a quadratic formula for quaternions with the help of the Ferrari's quadratic formula over the field of complex numbers was produced. Compared with the results in literature, the formula built in this paper displays its advantages in many aspects.

Abstract:Territoriality-based collaboration is one of the ways to realize situation awareness in tabletop collaboration. Thus the implementation pattern of territoriality-based collaboration was proposed, and three territorialities i.e. storage territory, private territory, public territory, were described. The realization mechanism of territoriality-based collaboration was given afterwards, including multi-touch points management, display management and conflict processing mechanism. Finally, situation awareness platform using territoriality-based collaboration was implemented, whose performance was verified through user testing experiments. 

Abstract:Recently, goalmouth detection has become the basis of highlight summarization and a hot topic in high-level semantic concept detection, as the appearance of goalmouth indicates a high likelihood of exciting action in field-ball game video. In addition, machine learning for object detection is a promising research frontier. A robust method is proposed to detect the presence of goalmouth frame in field-ball game video based on fuzzy decision trees. Balance process was added in training procedure. The experimental results show that our algorithm (F-measure>95%) can improve the classification performance in comparison with the threshold-based algorithm and the decision tree-based algorithm. Fuzzy rules can also be easily deduced from the constructed tree to interpret the classification model.

Abstract:A low computation complexity, which is a very efficient representation of image for visual classification tasks, is presented. The collaborative representation was combined with discriminative ingredient in a unified framework, which is an extended version of collaborative representation-based classification. The coefficients of collaborative representation of test samples are sparse and robust to occlusion or other disguises based on redundant and over-complete dictionary. Besides, the discriminative information was exploited by minimizing the within-class scatter and maximizing the between-class scatter, which is very helpful for visual classification tasks. Experimental results on some widely used benchmark datasets indicate that the proposed method can achieve competitive performance with other existing works.

Abstract:The spread of public opinion across the Internet in China was proposed by constructing a two-player symmetric evolutionary game model with incomplete information, since most of the players have limited knowledge about the spread and exact nature of public opinion. The two-player symmetric game model was presented to decide the strategic choice of players, and the replicated dynamic equation was built to explain the evolution directions of different strategic groups. The memory length of players, updates views and memory list were introduced according to the interaction rules. The simulation result shows that it is easy for players to follow trends under such circumstances, leading to herd behavior and a world in which most players adopt the same view. Furthermore, herd behavior is affected by a series of factors: most notably analysis-strategy based interactive interests, cost coefficients, and memory length. This research offers insights for practical application on how to analyze and guide the spread of public opinion on the internet.

Abstract:A human action recognition method based on a probabilistic topic model is proposed. Firstly, the method extracts space-time interest points to describe human motion. Then the slow feature analysis algorithm was proposed to calculate the invariant optimal solution of the gradient information of space time points. Lastly human actions were recognized with the probabilistic latent semantic analysis(pLSA). The invariant optimal solution of the gradient information can express the inherent characteristics of STIP, and it can also reflect the space and time information of STIP discriminatively. For solving the problem of latent topics that are not guaranteed in pLSA, the topics obtained in supervised fashion correspond to action labels one by one. Action recognition results were presented on KTH human motion data set and Weizmann human action data set. Our results show that the action recognition rates of the tow dataset are respectively more than 91.50% and 97%. 

Abstract:How to improve the transmission efficiency is one of the most important problems in complex networks. Thus the traffic dynamic for scale-free networks with heterogeneous node capacity is studied, and a global dynamic routing strategy based on capacity utilization ratio (CUR routing) is proposed to improve the networks' transportation performance. The CUR routing strategy chooses the route according to the minimum value of the cost function which is based on the utilization ratio of node capacity. Simulation results show that, compared with the classic shortest path routing strategy, the CUR routing strategy can enhance the network capacity several times than the at the cost of a slightly growth in the average path-length. Moreover, the comparison with the efficient routing strategy also reveals the prominent performance of the CUR routing strategy.

Abstract:SpaceWire is the new space bus standard proposed by ESA, which has been successfully applied in many projects. Delay jitter is the key parameter to reflect the network transmission performance, which measures the difference between the maximum transmission delay and the minimum transmission delay from end to end. Through theoretical calculations and modeling simulations, a quantitative analysis and research for the delay jitter of the SpaceWire under specific application scenarios was carried out. Theoretical calculations obtained the delay jitter under particular scenarios by theoretical derivation. Modeling simulations, on the other hand, established simulation model by Opnet, and obtained the maximum transmission delay and minimum transmission delay by simulation. In this way, the delay jitter was calculated both qualitatively and quantitatively, and the parameters which have key impact on delay jitter were obtained. Recommendations and methods to improve the delay jitter were given by analyzing the conclusions. The research results of this article can provide a reference for the SpaceWire design to build a low delay jitter SpaceWire network.

Abstract:Mutual authentication between the user and the cloud is an essential requirement for the user to access the public cloud in cloud computing. In order to solve the problems of password-based identity authentication scheme in the cloud computing environment and to improve the efficiency of authentication in the environments of mass users, a fair equality-determination protocol was presented by developing an equality-determination protocol of constant complexity. The protocol proposed can compare the passwords between the user and the cloud fairly and secretly. Based on the protocol, a two-party privacy-protected identity authentication scheme based on semantically secure algorithm-Bresson algorithm was further presented. Finally, the correctness of the scheme was proved and its security was analyzed.

Abstract:The hypervelocity impact studied in numerical simulation way was discussed. Damage mechanism, the process of the debris cloud forming and its expanding were simulated with the SPH method of ANSYS/AUTODYN code when spherical projectile hypervelocity impacts thin shield. Tungsten alloy, RHA(Rolled Homogeneous Armor) and aluminum material models and parameters were given, using the modeling methods, material models and parameters of the numerical simulation results in good agreement with the experimental results. The debris cloud parameters such as Vx,max,Vy,max and the half-angle of maximum radial extension(θ₁) were obtained with numerical simulation, and the above parameters with the variation of the initial impact conditions were also studied. The empirical equations which relate these parameters to impact parameters, such as velocity, material parameters of projectile and target and plate thickness, were obtained based on dimensional analysis.

Abstract:Defect mode can be created by introducing point defect in the one-dimensional crystal containing Helmholtz resonators. Based on the acoustic transfer matrix method and finite element method, the relationship among the defect mode, the geometrical parameters of the defect cell, and the acoustic field distribution in the structure at the frequency of the defect mode was studied. The results show that the defect mode moves to the edges of the local resonant forbidden band with the increase of the coupling effect between the defect cell and the perfect cells. In addition, acoustic energy localization is also observed due to the existence of the defect state. The research result will be of help for designing new acoustic filters and energy concentrators.

Abstract:The inductance gradient is the most important parameter for coilgun design. By establishing a two-dimensional finite element model, effects of four shield materials with different dimensions and distance between coils and shield on inductance gradient were investigated. The coil's current distribution and magnetic field distribution under different shields were presented. Analysis shows that the inductance gradient is affected both by material conductivity and permeability. The conductivity determines the induced eddy current in the shield. The permeability determines the degree of strengthening the main magnetic field. By reducing the distance between driving coils and shield, the magnetic materials enhance the magnetic flux better, but more eddy currents are induced in the shield conductor. By increasing the thickness of the shield, the magnetic materials enhance the magnetic flux better, but more eddy currents are induced in the conductive materials due to the decreasing resistance. In order to achieve the maximum inductance gradient, high permeability silicon steel sheets can be used as the shield, the distance between coils and shield should be reduced, and the thickness of silicon steel sheets should be as small as possible to reduce eddy current effects.

Abstract:A novel generation method of 2-D ISAR group targets is presented based on Intermittent-Sampling Repeater Jamming (ISRJ). Escort free-flight jammer was used to intermittently sample and repeater target echoes, which can generate vivid 2-D group targets in ISAR. By adjusting jammer and target’s relative space position, 2-D group targets are able to simulate target’s attitude angle dynamically. After the theory of ISRJ was expounded, the principle of escort free-flight jamming was introduced. A theoretical study was carried out to determine the requirement for power and position. Then the theoretical reason of 2-D group targets was emphatically analyzed. The key factor of false targets distribution and attitude angle was explored. Finally, the simulation demonstrates that the above method is effective. The results obtained from this research will help to provide better guidance for the design and engineering application of ISAR jammer.

Abstract:In order to track target accurately during a long term in complicated environment, an adaptive scale feature compressed tracking algorithm is presented. A number of scanning windows with different scales and positions were obtained by construction constraint sampling. To reduce the feature dimension and improve the processing speed, the sparse random perceived matrices of different scales which can be easily computed offline were adopted to extract the features of different sampling image patches with relevant scales online. The sampling patch having a maximal classification score was regarded as the new tracking result by classifying the compressing feature via a naive bayes classifier and updating the parameters through online learning, which can realize the adaptive update of tracking location and scales. Experimental results show that the algorithm can adapt itself to the basic attitude and scale change, which is robust and does not depend on the scale selection of the initial tracking area.

Abstract:The array manifold matrix was constructed as a redundant dictionary in which the array receiving signals were sparse through the appropriate spatial sparse division, and the corresponding L₁-analysis sparse recovery model was established to reconstruct the array output data. The core of this paper is to prove that the manifold matrix is a tight frame and can satisfy the condition which guarantees the accurate recovery of signals through L₁-analysis sparse recovery so that it is reasonable enough to use L₁-analysis sparseness optimization to reconstruct the array output data. The upper bound of reconstruction error was given. The effectiveness of this presented method for improving the performance of DOA estimation with low SNR was verified by the experiments using the actual measurement data received in microwave darkroom through MUSIC algorithm.

Abstract:Spaceborne SAR imaging at lower frequencies such as P/UHF/VHF band is severely affected by ionospheric irregularities induced signal scintillation. Mutual coherence function of signals penetrating through the ionosphere was deduced. Electron density in the ionosphere was modeled by Rino's power density function. Patterns were studied that how spaceborne P band SAR image performances varies with parameters of ionospheric irregularities. The study shows that irregularities in ionospheric will defocus the image, causing considerable gain loss of the imaging. Increases in irregularity strength parameter CkL, outer scale Lo, and index of the power density function will further degrade the image. The study is validated by numerical simulation based on phase screen technique.

Abstract:Aimed to the problem of unified resource optimized allocation in executing multi-virtual network embedding synchronously, a multi-objective particle swarm optimization based virtual network embedding method is proposed to increase the performance of resource utilization and global load balance of the substrate network resource. A multi-objective optimization model for virtual network embedding was put forward, on the basis of which the single virtual network embedding is considered as a swarm and the information exchange among different swarms so as to evolve corporately by employing multi-swarm coordination optimization method, and finally the increase of the performance of global resource allocation was achieved. The simulation results show that the proposed method maintains the best performance of the substrate network resource utilization ratio and virtual network request acceptance ratio compared with typical methods. 

Abstract:Based on the LDO regulator DC offset failure mechanism under electromagnetic interference (EMI) study, the immunity modeling and simulation methods are proposed. A test chip was designed with novel on-chip voltage sensor which is implemented to test the EMI propagation inner LDO regulator. In the immunity modeling process, an equivalent circuit model dedicated to susceptibility prediction was built and validated by DC functional and Z parameter impedance measurements. In the simulation flow, the key sub-circuits and parasitic elements were analyzed to reveal the weight contributions on immunity issues in frequency domain. The DPI measurement results show a good fit with prediction from the model up to 1 GHz.

Abstract:Multi-view point cloud scenes mosaic is an effective method to solve the incomplete object data problem while self-occlusion and occlusion happened in laser 3D imaging process. The mosaic method directly affects the object detection and recognition. In this research, a particle swarm optimization(PSO)based mosaic algorithm is proposed. The projective distribution entropy to construct the scene's coordinate was used, and the transformation between point cloud scenes by the coordinates was estimated. Based on this, the objective function for the mosaic was constructed, and the PSO for optimization was used. In the optimization process, the minimum miscarriage of justice method was used for searching the correspondence. In this way, the optimal transformation was found, and the fine mosaic was realized. Experimental results demonstrate the effectiveness and feasibility of the proposed algorithm.

Abstract:Aimed at the issue about the targets detection and classification in target monitoring system based on WSN, the study proposed a multi-sensor data fusion method based on intuitionistic fuzzy reasoning (IFR). The property functions of two status variables were designed according to the method of fuzzy reasoning. The study constructed the inference rules of the system after acoustic energy attenuation model and the variety of magnetic field model were built, and the rationality of constructed rules was checked. The comparison between theoretical analysis and simulation result show that intuitionistic fuzzy reasoning can classify targets uncomplicatedly and effectively. Because of its less calculation, the method can apply to WSN node, in which the calculation capacity is weak.

Abstract:A grey particle filter (GPF) that incorporates the grey prediction algorithm and wavelet transform into the particle filter (PF) is presented. The GPF self-estimates the depth of maneuvering autonomous underwater vehicle (AUV) using the data measured by sensors equipped in the AUV under the condition that the prior maneuvering information is unknown and the measurement noise is time-varying. To implement the proposed method, the particles were sampled by standard sampling and grey prediction to insure the particles contain enough information about the true state of the maneuvering AUV. In addition, the measurement noise covariance was modified by wavelet transform in real time. Therefore, the GPF can effectively correct the prior distribution and likelihood function of the particles and then alleviate the sample degeneracy problem which is common in the particle filter. A high accuracy depth trajectory, which tracks by the outside position sensor as the true depth of the maneuvering AUV, was employed. Then the performance of the EKF, MMPF and GPF was evaluated through the experimental data. The results show the effectiveness and robustness of the GPF.