Abstract:A new nonlinear filter algorithm for micro satellite attitude determination was proposed, which adopted three-axis magnetometer(TAM) and fiber optic gyroscope(FOG) as attitude sensors. In the design of the nonlinear filter, square-root sigma point Kalman filter was modified. Firstly, an augmented state vector was derived by combining the vector part of attitude quaternion, the bias and noises of FOG. Secondly, vector rotational model, optimization model and error quaternion multiplication model were established to guarantee the quaternion normalization constraint in the process of nonlinear filter. The simulation results indicate that attitude determination performance is improved effectively by the presented algorithm. In comparison with EKF, the accuracy and stability of the proposed algorithm is much better, and the convergent speed is faster. In comparison with UKF, the convergence is equivalent, the accuracy is slight better, while the stability and computing efficiency are both higher.

Abstract:Hypersonic vehicle can be designed into blended lift body by using light-weighted materials, which leads to close frequencies between controlled rigid-body motion and the oscillation of the structure. It brings about a huge challenge in the design of guidance and control system. Based on the assumed mode method, the free-free beam structural dynamics model considering variable cross-section effect was built. After comparing the mode shape and frequencies between cross-section and variable cross-section beam, it is found that the later one had a bigger mode shape change, and the frequency of second and three order both decreased. Given the hypersonic vehicle equations, the static and dynamic characteristics of constant cross-section and variable cross-section beam were analyzed in a typical condition. The results indicate that the variable cross-section beam has a larger appended angle of attack, the system is open-loop unstable, and exhibits non-minimum phase behavior in the trim condition.

Abstract:By replacing the typical no-slip boundary conditions with velocity slip and temperature jump boundary conditions, the predicting accuracy of the CFD modeling is improved effectively for high altitudes flow in the slip regime. The numerical iterations usually suffer form divergence when the Maxwell slip boundary conditions are implemented with very great number of grid points by the numerical method, which the velocity slip and temperature jump are evaluated through explicit calculation of the velocity and temperature gradient terms. In the theoretical analysis, it is shown that the explicit calculation of gradient terms displays the time advancement process of the Maxwell slip boundary conditions similar to a Jacobian iteration scheme, hence it must satisfy the condition of convergence. In order to remove the limitation from the condition of convergence, a numerical treatment which is convergent for arbitrary grid density was derived for the slip boundary conditions. Numerical tests were calculated to demonstrate the validity of the derived method. A space shuttle model was studied numerically for hypersonic flow at high altitudes. The results disagreement between the slip and no-slip conditions was compared and the influence of slip effects on vehicle aerodynamic characteristics and aerothermodynamic properties was analyzed. 

Abstract:The guidance precision of the launch vehicle during the flight stage within the atmosphere is greatly affected by the guidance coefficients of perturbation guidance. However, there is no comparable database for the guidance coefficients selection in the argumentation of a new launch vehicle, which cannot meet the demand for rapid calculation using the traditional test method. A real-time calculation method for the guidance coefficient which considers both the real-time status and the follow-up flight trajectory is proposed, based on introducing the concept of remaining flight speed in the standard trajectory. Through the numerical simulation, it is proved that higher guidance precision is achieved by the proposed method in comparison with the traditional method with constant coefficients. Since the guide capacity was predicted by this method, the guidance instruction do not change dramatically, which contributes to easy design for the attitude control system. Meanwhile, a fully analytical method was developed, so there is no additional calculation requirement for the rocket-born computer, giving rise to convenient engineering realization.

Abstract:A cumulative damage model of solid propellant was established based on energy dissipation damage variable defining method and dynamic linear viscoelastic theory. The expression of dissipated energy when destroyed was obtained according to the experimental data of different stretch rates, and the formula of cumulative damage for grain was presented as well. Considering influence of circular stress magnitude and frequency, the rule of cumulative damage varying was researched respectively, and a case of cumulative damage and life prediction for solid rocket motor grain was analyzed finally. The method is beneficial for the storage life prediction of solid rocket motor.

Abstract:The optimum design of midcourse guidance law for air-to-air missiles was researched based on Gauss Pseudospectral Method (GPM). The optimal control model for midcourse guidance law of air-to-air missiles was established, the idea to design optimal midcourse guidance law with GPM was proposed, the solving process was described in detail, and effectivity of the proposed method was verified with simulation cases. Simulation results show that GPM is dominant in performance index, computation accuracy and computation efficiency, compared with the traditional methods, such as proportional navigation and shooting method, and the computation accuracy and computation efficiency of GPM are determined by the number of collocation nodes. The above all can provide theoretical reference for research of midcourse guidance law for air-to-air missiles.

Abstract:Three dimensional turbulent fluid flow and heat transfer in the cooling channels of high enthalpy and pressure air heater were numerically investigated. The liquid water was employed as the coolant, and the materials of combustor and nozzle wall were steel and copper respectively, whose thermo physical properties vary with temperature. The hot-fire tests of the facility were performed to validate the simulation results. The influences of gaseous radiation, the channel configuration and cooling routing on the wall heat transfer were discussed and analyzed. The result shows that the heat transfer of combustor wall is affected obviously by the gaseous radiation which has little effect on the nozzle wall. The result will lead to significant error if the gas radiation is neglected. The heat transfer rate of wall is largest if the number and the width of channel was optimized. The flow mode of coolant has a great effect on the coolant side wall temperature but a little impact on the hot-gas side wall temperature.

Abstract:Traditional depleted shutdown guidance approaches for solid launch vehicle have excessive attitude angle adjustment times, which lead to the difficulties of the control system design. A depleted shutdown guidance method with singular attitude angle adjustment was proposed. The required apparent velocity was used as a reference, the initial and final values of the rocket attitude angle were chosen by computing the apparent velocity, which is to be consumed. The attitude angle was changed from the initial value to the final value with a constant angle rate, and then the attitude was kept constant till depleted shutdown. The simulation results show that the proposed method with singular attitude angle adjustment satisfies the rocket’s terminal velocity constraint and that the percentage of consumed apparent velocity mode is more than 30%, and the singular attitude angle adjustment strategy can benefit the control system design.

Abstract:The steady aerodynamic coefficient and pitching dynamic derivative of blunted conical models in hypersonic flow was validated by using implicit scheme, with the technology of the dual time stepping, rigid rotary grid deformation and least square method. Compared with the results from experiments and engineering method, the influence of the pitching dynamic derivative with different grid, bluntness ratio, angle of attack and the center of the gravity was investigated. Moreover, some of the key differences of the dynamic derivative results were derived from using different schemes, including high-order WENO and WNND schemes. The result shows that the viscid resolution of the scheme is the main source of the difference.

Abstract:The inflation process of large-scale or extra large-scale parachute was investigated. The Arbitrary Lagrangian Eulerian (ALE) Method-a Fluid- Structure Interaction (FSI) model, was used to simulate the inflation process of a main parachute (a ringsail parachute, which was used in manned spacecraft) in an infinite mass situation. The dynamic relationship between canopy shape and flow field was obtained, and the adverse inflation phenomena such as asymmetric inflation and whip were observed in simulation results. The “bottleneck” phenomenon in inflation process was found and verified by physical tests. Based on the analysis of calculation results, it is found that the large canopy area, the complicated canopy structure or high inflation speed can block the air mass into the parachute, which can cause the “bottleneck” phenomenon. But the necessary occurrence conditions of the phenomenon need to be studied in future. The present work is significant for explaining parachute working mechanism and preventing its failure.

Abstract:Task allocation model based on Multi-Agent theory was established according to mission planning problem of agile satellite after analysis of agile satellites characteristics and satellite multi-user demand. Agile satellite dynamic task re-scheduling model was proposed for the failure of satellite resources in the agile satellite mission planning initial program scheduling. For obtaining the optimal solution we presented agile satellite dynamic task allocation algorithm based on the agreement ending contract net, and designed bidding mechanism, contract net protocols and strategy of biding and assessing biding. Finally, agile satellite mission planning scheduling problem was taken as an example, and satisfactory results were obtained through experiments, which showed that the model was reasonable and the algorithm was efficient.

Abstract:In order to study the projection angles in asymmetrical structure, the oblique shock wave theory was used to describe the process of detonation wave shocking on the metal surface. The calculation method of projection angle was obtained after the velocity multiplication law on free surface simplified the shock wave theory to estimate the velocity of particles in metal. The explosion experiments of a D-shaped warhead were done to validate this method. The results show that this method is in good agreement with experimental data; when the incident angle is less than 40°, the projection angle will increase linearly with increasing the incident angle.

Abstract:In GPS modernization, LDPC code is used in L1C signal to enhance the receivers’ performance in weak signal environments. The LDPC codes used in L1C signal do not have cyclic or quasi-cyclic structure, which increases the complexity of decoder. To reduce the implementation complexity of decoder, the structure of parity check matrix of the LDPC code used in GPS L1C signal was analyzed. Based on the analysis, a complexity- reduced decoder was presented. The presented decoder divides the check nodes into two groups and changes the variable nodes updating way, which can reduce the storage and simplify the control logic of the decoder. The decoding results of the presented decoder are validated by simulation.

Abstract:Linear Frequency Modulation (LFM) interference mitigation in received GPS signal by antenna array was studied. The pivotal problem of LFM interference suppression is the instantaneous frequency estimation, With this conception, the cross-term in the time-frequency distribution must be suppressed. Thus the received signal vector was whitened and the Spatial-Time-Frequency Distribution (STFD) matrix was formed by utilizing the whitened signal vector. A decision variable which is different from traditional one was deduced. By using the decision variable, the auto-term in the time-frequency distribution of the LFM signal can be selected clearly. Based on the time-frequency distribution of the auto-terms, the parameters and the instantaneous frequency of the LFM signals can be estimated. According to the instantaneous frequency, corresponding notch filters can be formed, which can mitigate the interferences. Through simulation, it can be viewed that the time-frequency distribution of the received signal which is interfered seriously by the cross-term can be mapped into a clear time-frequency distribution of auto-terms of the signal. Under the condition that the number of snap is enough, the LFM interferences can be suppressed clearly.

Abstract:The problem of time and frequency synchronization is a bottleneck technology for the passive SAR system with spaceborne illuminators. In order to analyze the impact of time and frequency synchronization error to passive SAR imaging, the mechanism of time and frequency synchronization error was studied based on the particular operation mode of passive SAR. Then the error model of time and frequency synchronization was established, and the integrated error transfer model from synchronization error to passive SAR imaging was established. In the end, the correctness of the theoretical analysis was validated by simulation experiment. The theoretical analysis and the simulation result show the accuracy requirement of time and frequency synchronization for such a system. The conclusion can be used as principal guidance for passive SAR system design and synchronization method research.

Abstract:S-box is the only nonlinear components of block cipher algorithm which can provide confounding effect. Its password strength determinates the security strength of the whole cipher algorithms. An S-Box generation algorithm based on the discrete chaos system which uses multi-chaos maps and cross-generation method to generate S-Boxes was proposed. Good characteristics such as bounded, aperiodic and extremely sensitive to initial conditions and parameters of discrete chaos system were combined in the algorithm. Experimental analysis shows that the samples generated by our algorithm have strong key sensitivity and good randomness, thus can satisfy both the high security criteria and features required by the S-Box design. It improves the performance by reducing the computational complexity and has good scalability and low implementation cost. Therefore, the proposed method can serve as a promising choice for designing S-Boxes.

Abstract:A joint detection and tracking algorithm based on Random Finite Sets (RFS) theory was proposed for target detection and tracking in presence of clutters using multiple sensors. First, target states and measurements were described as RFS variables, RFS models of target motion including target birth, target survival and target death, and the multisensor measurements including miss detection and false alarm were constructed. The joint target detection and tracking problem was then modeled as a Bayesian optimal estimation to the target state RFS and the theoretically rigorous recursive formulas for the estimation were derived by using RFS theory. Finally, Sequential Monte Carlo (SMC) implementation was presented to the filter recursion. Simulation results demonstrate the effectiveness of the proposed algorithm and its significant improvement in performance over traditional association-based ones.

Abstract:Parallel program has significant percentage of memory requests that target only private data, which does not need to resolve cache coherence conflicts. Yet traditional coherence protocol does not distinguish between shared and private blocks, which leaves much optimization space. An optimized cache coherence protocol, called PMESI, which dynamically deactivates coherence maintenance for private memory space, was suggested. PMESI achieves two distinguishing features: the reduction of memory access latency and system power consumption. Simulation results on the cycle accurate simulator show that 54% memory references can be efficiently optimized and the program execution time is reduced 9% on average.

Abstract:Video object extraction is a key technology in intelligence surveillance. An object detection algorithm for low-quality video based on Gaussian Mix Model and stochastic resonance was proposed. Firstly, the algorithm generated the object probability gray image from the current frame with the Gaussian Mix Model by the mapping function defined. Then, stochastic resonance was applied to the object probability gray image by adding noise until the defined evaluation function achieved the minimum value. After stochastic resonance, an effectively enhanced object probability gray image could be obtained. Hence the binary image including the interested objects is retrieved by segmentation of the enhanced object probability gray image. The experimental results show that the proposed algorithm combining the Gaussian Mix Model and the stochastic resonance achieved satisfactory subjective and objective performance under the worse environment with dark, foggy and infrared imaging while the classic background subtraction method almost could not detect the interested objects.

Abstract:Existing algorithms of distribution reduct, maximum distribution reduct and assignment reduct for inconsistent decision tables are inefficient, which are not suitable for large data sets. A measurement of attribute importance based on the relative discernibility degree was presented firstly, which overcomes the shortcoming of positive domain in measuring the importance of attributes. Then, in order to simplify the decision table, some kinds of simplified consistent decision tables were defined. In the end, an efficient attribute reduction algorithm was designed based on the relative discernibility degree. Theoretical analysis and experimental results show the effectiveness and practicalbility of this algorithm on the large inconsistent data sets.

Abstract:Content-based lunar image retrieval provides a convenient and efficient way for accessing relevant lunar exploration images by their visual contents. To increase the efficiency, the process of content-based lunar image retrieval was analyzed and modeled using Petri nets, and a parallel mechanism was designed based on the model. A parallel architecture was then proposed for the content based retrieval of lunar exploration images. According to the architecture, an experimental system was implemented. Experiments upon real datasets including Chang’e lunar exploration images confirm that the proposed parallel architecture can effectively improve the constructive and retrieval efficiency.

Abstract:Grid-to-grid routing algorithms for distributed hydrological modeling require large amount of computations which cannot be provided by sequential computation techniques. Parallel programming technology is necessary for large-scale and long-period simulations using grid-to-grid routing algorithms. There is currently little research on the parallelization of implicit finite difference based routing algorithms. A parallel implicit finite difference based grid-to-grid routing algorithm was presented, based on grids layering. In this algorithm, grids in the watershed were divided into different layers according to flow direction. The calculations of grids in a downstream layer cannot be performed until its upstream layers’ calculations were completed. The calculations of grids in the same layer are independent of each other, thus can be performed in parallel. So the parallelization strategy is to assign the calculation tasks of grids in the same layer to different CPU-cores to perform parallel computing. The algorithm was implemented by using the C++ programing language and the Open Multi-processing (OpenMP) Application Programming Interface (API) and was tested in the Qingshuihe watershed of Hebei Province under different amount of input data. The result shows that this parallel algorithm had good speedup and parallel efficiency. In addition, the case study showed that the parallel efficiencies were higher for simulations with large datasets than with small datasets and the up-down layering method had better performances than the down-up layering method.

Abstract:Data granularity is one of the most important issues of parallel computing based on large volume of spatial data. After a comparison with the different types of terrain analysis algorithms, a Geo-Data Granularity Model (GDGM in short) was proposed, which can be used for the quantitative description of data partition granularity in parallel computing process of massive spatial data. In this algorithm, according to the parallel evaluation method, the parallel data granularity was adaptively adjusted and finally an optimized data grain was obtained. The execution time of each parallel computing was recorded for the comparison of computing efficiency values from different data granularities. Furthermore, by means of the comparison, a dynamic algorithm was designed for the dynamic scheduling of different data granularity so that the optimal performance of specific algorithm was achieved. The preliminary experiments show that the algorithm has much better efficiency and portability than the traditional ones so far.

Abstract:Spatial join aggregate (SJA) is a commonly used but time-consuming operation in spatial database. Especially when faced with the deluge of spatial data，SJA is difficult to be implemented on a single machine. Consequentially, how to design efficient distributed SJA algorithms is receiving more and more attention. Constrained by the sequential scan operation assumption, Map-Reduce is usually used to accelerate the non- indexed spatial join query, but none of the previous work can process SJA with both Map-Reduce and R-tree spatial index. Thus, a novel algorithm, R-tree based Spatial Join Aggregate with Map-Reduce (RSJA-MR) was proposed, which is able to return results more efficiently. A distributed R-tree index structure was presented to index the large-scale spatial data. RSJA-MR first made use of distributed R-tree to generate the tasks. Those tasks met independent parallel computation and could easily be expressed in Map-Reduce. An index cache mechanism was provided to support the concurrent access of R-tree index. The experiment results show that, compared with the non-indexed SJA , the time performance of RSJA-MR is improved at least by 8% for spatial intersection join aggregate and by 35% for spatial containment join aggregate.

Abstract:In the development of GMI magnetic sensor, weak magnetic signals are always submerged in the circuit intrinsic noise. Since traditional peak detecting method is impossible to detect GMI sensor’s output when its SNR is lower than 0dB，a new method is presented to detect the GMI probe’s weak signals（SNR<0dB）. The LMS algorithm was applied firstly to extract the characteristic parameters of the weak signals, and then the cross-correlation function between the characteristic parameters and the idea ones was calculated. Finally the maximal correlation values were regarded as weak signals to be detected by means of calibration. The simulating results indicate that this method can not only detect but also measure the magnetic field by the corresponding relationship of magnetic field intensity and the maximal correlation values, even the SNR of GMI magnetic sensor’s output is 10dB.

Abstract:Vibration can influence the frequency stability of crystal oscillators in radar and worsen the working performance of the system deeply. Thus how vibration influences the reference frequency source on remote sensing satellites, brought up the digital compensating technique of acceleration g was analyzed. Some experiment results proved that this method can reduce the acceleration sensitivity of frequency source. This research has wide application potential for reducing the acceleration effects on frequency resource.

Abstract:Several full custom EDA techniques were developed during the design of YHFT-DX processor. Hierarchical functional model extraction, which can convert a transistor-level netlist into an equivalent RTL netlist, were developed for the functional verification of full custom circuits. Hybrid timing analysis was researched for the transistor-level timing analysis. 10x run-time improvements were achieved by the multi-thread parallel optimization. A measurement was developed to get delays from the simulation waveforms, which improves the efficiency of simulation results analysis. Two signal integrity verification tools, PNVisual and NoiseSpy, were developed for IR-Drop and noise analysis of full custom circuits. These techniques have been widely used in the design of YHFT-DX, which greatly improves the efficiency and quality of full custom design.

Abstract:The construction of command post under informationization condition and the change of command behavior and command art are important parts of accelerating the transformation of combat effectiveness model. Command post already has a variety of new interactive devices and interactive tools, but between the “fragmented” sections, not in a unified framework of coordinated use. As a result, a lot of equipment and technology have to be shelved, and it is difficult to integrate into the command and control system. To solve this problem, a command post oriented multimodal interaction framework was put forward. The framework describes in detail the multimodall interactive command space software architecture, the architecture describes various models (command space conceptual model, hierarchical model, process model, component model, integration model) and their mutual relations, while the framework involves some key technical issues in depth. Finally, a comprehensive case studies on the subject were implemented which fully validate the research results.

Abstract:As the fast development of the Internet scale, “data overload” has become one of the most critical problems in computer network analysis. Recommender system has been regarded as the most effective method to solve the problem. But most of existing methods just consider the independent feedback of users without considering the relationship between users, which will inevitably decrease the performance of recommender system. Thus, a friendship prediction algorithm for recommender system was proposed to predict the relationship between different users. Firstly the topological and historical interaction information was taken as the features to judge the existence and relationship type of links. Then the feature combination process based on linear regression algorithm and logistic regression algorithm was implemented. Finally, the experiments based on the real data sets of Epinions and Slashdot were implemented. The experiment results show that our approaches perform very well in link prediction problem.

Abstract:Some problems about the traditional identity authentication model for PKI(Public Key Infrastructure) were analyzed. For example, because certificate status verification service and key verification service depend on different service providers who have not enough trust degree in open network environment, the trust degree of the traditional model decreases and its risk increases. Additionally, there are other problems about cross-CAs and incomplete authentication service in the traditional model. Thus a new open identity authentication model was put forward for PKI, which can solve the above problems. In this model, the above two verification services were both provided by CA, and the service result was applied by providing identity certification file instead of OCSP answer. The trust degree of the traditional model and our model by using the cloud trust model presented by other researchers was calculated. The result of the calculating test shows that our model can improve the trust degree obviously. Finally, the prototype system of our model was completed, and especially the performance of the model was optimized. The test shows that the model has good practical value.

Abstract:Inadequate information under uncertainty is indispensable to multiattribute analysis, which can be well handled by the Evidential Reasoning Approach. The factors which bring about influence on the belief of the inadequacy in the assessment results were studied, including the belief of the inadequacy in the rules as input, the weights and the consistency of the rules. The domain of the inadequacy in the assessment results was determined and a preliminary result was drawn: the belief of the inadequate information in the assessment result can be less than the bigger one of the belief of inadequate information in the rules as input, but may not be more than the smaller one of the belief of inadequate information in the rules as input. The logical and geometry meaning of consistency of the rules was illustrated. The link between the consistency of the rules and the concept of “degree of conflict” was studied. 

Abstract:The impact of satellite reconnaissance information precision on hitting probability of missile hitting maritime floating target was investigated，which is significant for improving the operational efficiency of missile. According to the principle of missile hitting maritime floating target, the operational process was depicted, the impact factors of hitting probability were analyzed, and the calculating model of hitting probability based on satellite reconnaissance information precision was established. The impact of satellite reconnaissance information precision on hitting probability was analyzed by Monte-Carlo method. The results prove that if the satellite reconnaissance information precision is in the acceptable range，the impact is able to be ignored；otherwise，the missile hitting probability descends along with the fall of the information precision.