Abstract:A dual time-step approach was developed for simulation of unsteady supersonic combustion flow. The flow and reaction were separately calculated with a time-splitting method. The flow equations were solved by the dual time-step approach with the inner iteration proceeded by a LU-SGS method. The source equations were solved by 2^ndorder trapezoidal formulas. The influences of the time-splitting scheme and the time step were studied. The results show that the 1st order time-splitting can slightly overestimate the chemical efficiency and a 2^ndorder time-splitting should be implemented. The time step has a significant effect on the results. In order to ensure the computational precision of the uncoupled method, the time step should be kept small enough so that the unsteady behaviors of the large scale vortices, which dominate the transport processes in the flow, can be captured accurately.

Abstract:Analytical and numerical models of influence of docking process on combined spacecraft's initial attitude were developed. Based on the theorem of angular momentum with respect to total centroid, the general expression of numerical model for combined spacecraft's attitude angular velocity was obtained. By combining chase spacecraft's absolute motion with target spacecraft's relative motion equations, numerical model based on docking dynamics was developed. Finally, combined spacecraft's attitude angular velocity was contrasted with analytical and numerical models on different cases of single-error and multi-error. The results show that absolute error is within 0.07°/s and relative error is less than 10 percent between two models. Additionally, applicable phases of two models for engineering missions are presented.

Abstract:In order to realize auto target detection of multi-target image of shooting ranges, the similarity of targets' shape was utilized, and a new method for auto similar target detection based on shape entropy difference was proposed. First, the concept of shape entropy difference was presented, which merged shape information into the calculation of entropy, and the target was detected by searching for the extreme point of entropy difference. Then, an auto target detection method based on shape entropy difference was realized. Finally, the validity and robustness of the algorithm was approved by experiment. Compared with the common algorithms of target detection, the method proposed here has better tolerance capability against noise and illumination variety. The method can be used for target detection of image of shooting ranges and other similar applications.

Abstract:3 kinds of laminate samples reinforced by UD, 0/45/-45, 0/45/90/-45 multi-axial fabric respectively, were manufactured by the vacuum infusion moulding process. Each laminate had 4 types of thickness. Experiment was made to investigate the short-beam shear strength and the failure mode of them. The finite element model of the short-beam shear sample was established, and the interlaminar shear stresses in different positions were calculated. The result shows that the free edge delamination failure is liable to occur with the increment of the off-axis plies which is mainly due to the stress gradient through the width direction. The interlaminar shear strength of the 0/45/-45 laminate is the highest of the 3 kinds of laminate with the same thickness. There are size effects in the short-beam shear strength test, the shear strength decreases while the sample coefficient of variation increases with the thickening of laminate.

Abstract:A ramjet with a center preburner was designed for the purpose of intensifying the ability of ignition and flamehold characteristic at low pressures. The numerical studies were conducted to investigate the spray and combustion characteristics in the simplified model combustion. The result reveals that, with the change of the work conditions, the convergent rear of the preburner has a different impact on the interaction between the inner and the outer flow. The flow at the entrance of the preburner will accelerate due to the increase in the pressure drop and combustion occurring downstream affects the flow characteristics in the preburner.

Abstract:In order to reduce influence on early warning results caused by the system error in the early warning system, the calibration to the instrument must be carried on. So it is necessary to discuss the line of sight measuring error farther. This article theoretically discussed the sight error influence on early warning results, including trajectory launch point, trajectory course, and trajectory falling point, and found that the most important influence factor was frequency change. Based on the constant error, linearity error and periodicity error, the corresponding simulation was given to provide the support for the geometry calibration plan.

Abstract:The absolution navigation based on X-ray pulsar is an entirely new autonomous technology. This paper put forward the basic theory of absolution navigation based on pulsar, and proposed a bettered algorithm of integer cycle ambiguity in the method of absolution navigation. Then the algorithm was analyzed deeply and the theoretical derivation was made. Through the simulation solution of ambiguity and position of spacecraft, it can achieve ideal precision. This cycle ambiguity arithmetic provides a new avenue for absolution navigation based on X-ray pulsar.

Abstract:The effect of pressure and temperature on carbon particle combustion was studied by an improved Moving Flame Front (MFF) model. On the basis of the above discussion, the carbon particle combustion in solid rocket ramjet was analyzed. As a result, the carbon particle combustion mechanism in solid rocket ramjet was achieved. Moreover, numerical results were validated by direct-connect test of solid rocket ramjet. The result shows that most of carbon particle in the secondary combustion chamber burned near the inlet exit.

Abstract:In view of human exploration of Mars, the three-degree-of-freedom dynamic model of aerocapture trajectory was established. The constraints which satisfy the mission requirements were listed, and the entry corridor was obtained. The influence of some parameters on the trajectory shape was analyzed. A pipelining optimization approach of Genetic Algorithm(GA) and Sequential Quadratic Programming(SQP) were introduced to analyze the attainable region of flight through bank angle control. The results indicate that, compared with direct deceleration by retro-rocket, aerocapture mode is highly advantageous in energy requirement, and has good maneuver ability. It is a feasible approach for manned spacecraft to insert into Mars orbit.

Abstract:Scene match arithmetic which has high dependability and precision is the most important factor of image navigation for independent navigation aircraft. The current study has researched into gray distortion of scene match images, and brought forward the emendation method based on the histogram similar transform which can improve the veracity and reliability of scene matching arithmetic. For different external condition and imaging apparatus, there are many gray differences in images participating in scene match, which will affect the scene match robustness seriously. Via adjusting the histogram of scene match images to make them identical, this research eliminated the gray distortion. As a result, the scene match images histogram similar coefficients were all more than 0.95. 10 300 true outfield scene matching orientation experimentations have testified that the pretreatment method for gray images based on histogram can effectively eliminate the gray distortion and decrease the repetitious patterns caused by gray distortion. The success ratio of scene match has reached the level of 99.98%, which has met the high dependability need of projects.

Abstract:Current literature on indexing current and future positions of the moving objects lacks the mechanisms on concurrent access. To solve this problem, the current research proposed an efficient moving object index that supports concurrent access, also called CS²B-tree(Concurrent Space-filling curve enabled Cache Sensitive B⁺-tree). CS²B-tree combines the characteristics of the B^x-tree and CSB⁺-tree, thus it can support querying the predicted future positions of the moving objects and is cache sensitive. Focus was put on studying a concurrent access mechanism to CS²B-tree which resulted in a two-level lock mechanism and particularly a lock memo structure was designed. Based on the concurrent access mechanism, a CS²B-tree concurrent location update algorithm and a concurrent predicted range query algorithm were proposed respectively. Experimental results show that, compared with B^x-tree, the throughput of the CS²B-tree improves by 15.1%, and the response time decreases by 14.9%.

Abstract:Error in the estimation of the ground interferometric phase and that in the forest scattering model will bring about errors of the inversion of the vegetation height. Aiming at this problem, a new inversion method based on the BP neural network was proposed. The new method directly fits the nonlinear mapping relationship between the complex polarimetric correction coefficients and the vegetation height, so it can reduce the error caused by the error in the estimation of the ground interferometric phase, and that caused by the scattering model error. The new method has better performance than the three-stage vegetation height inversion method, and the simulated results validate the superiority of this new method.

Abstract:Network on Chip (NoC) adopts the packages exchanging interconnection framework for communications on chip. The interconnection problem of NoC can be abstracted as a minimal spanning forest problem in Manhattan plane. A new algorithm based on obstacle avoiding rectilinear Steiner minimal tree by changing the edge weights is proposed for the connection, an optimization method for interconnection redundancies removing is also proposed. Experiments show that the total connection length for NoC is minimized. So the traditional bus communication framework's disadvantages, such as long global connect delay, weak signal integrity may be eliminated.

Abstract:Cancellation processing is one kind of classical and feasible idea for the purpose of cancelling clutter. A novel method of clutter cancellation for stepped-frequency radar was proposed. Transmitting the basic stepped-frequency waveform, the radar achieves two high resolution range profiles (HRRP) that were produced by the Inverse Discrete Fourier Transform (IDFT) of two frames of return pulses on a same range cell. The two HRRPs which the number of frame interval was chosen rationally were utilized to cancel the clutter, which can keep the HRRP property of a target. To resolve the problems of the clutter shift and the clutter component change induced by the radar platform movement, a strategy was also brought out. The clutter of two HRRPs was aligned by the clutter correlation and then was cancelled. The simulation results validate the correctness of the method.

Abstract:FDPM and FOOJA, which belong to the low complexity class, are the most efficient algorithms for principal or minor subspace tracking. Reducing computational cost is crucial for guaranteeing the real time implementation. Under lower computational complexity background, it was found that there exist two other simplified methods (FDPM＿1st＿col and FOOJA＿1st＿col) through analysis of FDPM and FOOJA. Under the finite word length condition, the stability and numerical robustness were analyzed and compared with the former two algorithms. Simulation results verified our conclusion.

Abstract:There are abundant mixed data sets with various types of attributes in application fields. However, most multivariate data visualizations are only effective with simplex one data type. As for mixed data sets, the visualizations of them are usually dissatisfied. We present a data transformation technique for mixed data sets involving both numerical and categorical attributes. Firstly, every numerical attribute was categorized by clustering; then, all categorical attribute was quantified by Correspondence Analysis; finally, the transformed mixed data were presented in numerical data visualizations like Star Coordinates. Furthermore, aiming at those mixed data sets that have many attributes or the cardinality which is high, a set of cardinality reduction strategies were proposed to diminish the attributes number involved in computation to improve computational efficiency. Empirical studies show that the visualization of mixed data sets is easily-understandable and propitious for the user to discover the connotative information within; and that cardinality reduction strategies are highly memory-saving and time-efficient.

Abstract:Logical worm propagation model can characterize how the worm-like malicious code spreads in network exactly, which contributes the analysis of worm propagation mechanism in depth to engaging in the study of worm defense, detection and containment. The significance of infection time is often neglected in worm propagation models based on classic epidemic model. By introducing and analyzing infection time, a worm propagation model called SSI is derived using deterministic modeling methods. This model reflects the possible state-transition of vulnerable hosts during worm propagation, and results in a better understanding and modeling of the propagation of Internet worms.

Abstract:Quantum TV algorithm, the result of which only takes values from a finite discrete set(the quanta set), is a kind of quantized TV regularized algorithm. It can find applications mainly in binary image restoration, image quantization and image segmentation. Different part of an image varies differently, thus it needs varied number of quantized levels. Different image histogram also corresponds to different quantized levels. We made improvements to the quantum TV algorithm according to the above statements. Experiments and related data demonstrated that the improved algorithm showed better appliance in image quantization.

Abstract:Active MMW seeker can locate and track the target by emitting high-frequency pulse, and possess satisfying adaptability to suddenly cut-off radar while conical scanning is one of the effective seeker-steering systems. This paper aims to distill from the echo of the target location-related angles via Flourier Transformation, for these angles can be used to revise the attitude and course of the seeker timely, so that the target is kept in sight commendably. Numerical simulations were carried out to verify the satisfying performance of the proposed method.

Abstract:A new timing synchronization method for OFDM systems based on repeated-conjugated-symmetric preamble was proposed. The proposed timing method utilized delayed correlation and symmetric correlation to search the first tap of multipah channel with the fixed threshold after the peak position of timing metric was detected. Theoretic analysis shows that the proposed method can achieve good performance of timing synchronization. Simulation results in static multipath channel and 6-path channel for typical urban show that the proposed method prevents the timing synchronization from moving backward and achieves more accurate timing result than conventional timing synchronization method based on conjugated-symmetric timing metric.

Abstract:The front end RF for radiated radar target simulator was designed and integrated in this paper. This simulator was operated on the L/S/X three bands, and it supported the CW and pulse operation. It generated multi-targets in high precision. The plug module structure design improved the EMC and the extension performance of the RF front end. The measured results of the system are better than the target. Furthermore, this RF front end supports the radar simulator finish the target simulating for the real radar successfully, which verifies the performance of this radar simulator.

Abstract:Unmanned aerial vehicle systems (UAVS) will be an important means of executing information counter, attaining information advantage, and carrying out precision strike in the future. Autonomy is the first technical feature of UAVS, which is different from manned aerial vehicles in nature. To realize autonomous control of UAVS and improve its intelligence degree is an important development trend of UAVS. Autonomous control of UAVS was reviewed in this paper. First development requirement for autonomous control of UAVS was analyzed, and the concept of autonomous control and the autonomy level was introduced. Then the researches in this field were investigated, and the relevant key techniques of autonomous control of UAVS, including the system structure, perception and cognition, planning and control, cooperation and interaction et al, were discussed respectively. Finally, the research areas were proposed to address the development directions.

Abstract:Voronoi diagram is often used for UCAV path planning in SEAD mission. General Voronoi diagram is constructed by connecting the circum-centers of Delaunay triangles, while every vertex of Voronoi diagram is considered as a kind of enemy air defense. But there are a lot of enemy air defenses in the battlefield, and every enemy weapon has its action area, so that the perpendicular bisector of Delaunay among different threats which is the edge of Voronoi diagram is no longer the safe path of UCAV. Firstly, the current study proposed a novel method to modify the general Voronoi diagram so that the generated improved Voronoi diagram could be applicable for the UCAV path planning, and the criteria of constructing the improved Voronoi diagram were presented. Secondly, based on “Delaunay polygon”, it presented all the possible conditions which the improved Voronoi diagram could be constructed. Finally, the simulation demonstrates that the planned path based on the improved Voronoi diagram can increase the survival probability of UCAVs in SEAD mission obviously.

Abstract:The hydrostatic pressure tolerance of spherical-cymbal transducer was investigated. Theoretical Von Mises stress analysis was carried out using finite element method. Effects of cavity geometry and material selection on limits pressure were evaluated. It shows that cavity depth, end-cap thickness and end-cap materials have strong effects on pressure tolerance of spherical-cymbal transducers. The comparison analysis indicates that the pressure tolerance of spherical-cymbal transducers with reference dimensions is higher than that of traditional cymbal transducers.

Abstract:In order to improve the security in pipes inspection for in-pipe robots, the current study developed an electromagnetic clutch, which was aimed to insure the in-pipe robots quitting from pipes where they worked in any conditions. The specific size that is 42mm in diameter and 220mm in length was designed for using in pipes. With this contact structure, it still can transfer a relative large torque and hold a 10mm effective distance. After the structure and work principle of the electromagnetic clutch were introduced, the magnetic circuit was analyzed, and then the heat of coils was calculated. The relationship between the attraction and the air distance was worked out based on the Langrage-Maxwell Equations. To testify the correctness of the theory results obtained above, some simulations were made. The data from the simulation also optimized the length of the stopper. Base on the theory result, a prototype was designed and some related experiments were made.

Abstract:PUFFIN is a block cipher with 64-bit block size and 128-bit key size. For evaluating its security, the balance at bit-level was analyzed. A 5-round integral distinguisher was constructed and then extended to a 6-round one based on the theory of higher order integral. By using the 6-round distinguisher, 8-round attack was performed. For 8-round attack, the data complexity, time complexity and space complexity were, and respectively. The result shows that PUFFIN reduced to 8 rounds is not immune to the integral attack. Besides, the cipher with SPN-structure and permutation-linear layer which at least has 3-round integral distinguisher is proved. The result also indicates the method for finding the distinguisher.

Abstract:A new class of perfect nonlinear binomials was just found by Helleseth et al, which are the first perfect nonlinear binomials composed with two inequivalent monomials. We transformed the class of perfect nonlinear binomials to another form, and gave a concise proof for their perfect nonlinearness. It shows that this family of binomials is equivalent to . Furthermore, the calculation of the count of this family of functions is presented as well.

Abstract:Smoothing splines are well known to be the ideal functions for fitting of discrete data, and also the effective method for smoothing noisy data. Therefore, it is very important to study the construction and computation of smoothing splines. In this paper, the construction and computation of smoothing splines associated with general linear differential operators and linear functionals were discussed. By constructing an appropriate reproducing kernel Hilbert space framework, the proposed splines were expressed as minimum norm problems. Thus the expression and interpolation error of the smoothing spline were obtained via reproducing kernel. Based on this, a new method for computing polynomial smoothing splines was presented.

Abstract:Based on the general singular value decompositions of quaternion matrices, a relationship of the singular values and singular vectors was given between the generalized extended quaternion matrix of symmetric rows or columns and its original quaternion matrix, which extends the existing results. Theoretical predictions and numerical evidences show that, for a class of extended matrices, the singular value decomposition using the original quaternion matrix rather than the generalized extended quaternion matrix can save dramatically the memory and alleviate considerably the computational burden without loss of any numerical precision.

Abstract:A fuzzy reliability growth model was presented on the basis of a Bayesian reliability-growth model based on Dirichlet prior distribution using fuzzy theory. The method for determining prior parameters was studied using Dirichlet prior distribution. A metal/water reaction ramjet's reliability growth test data was analyzed using this distribution. The prior distribution and the posterior distribution at each test stage were presented. And the effect of the parameter related to prior information's variance on posterior reliability was analyzed. Fuzzy variable was introduced in the original model to build a fuzzy reliability growth model. Using the model, the fuzzy reliability at each stage was calculated.