Abstract:Based on the Biot’s wave theory and thermoelastic theory for saturated porous medium, three relaxation factors were introduced and the generalized thermoelastic theory for saturated porous medium was developed. Reflection of SV waves on the surface of the plane was used to analyze the influence of relaxation effect on the reflection, and the expressions of the reflection coefficient for the p₁ wave, p₂ wave, T-wave and S-wave were derived. Numerical results were obtained and used to discuss the difference of reflection amplitude for four kinds of reflection waves among the generalized thermoelastic theory G-TE, L-S theory, and G-L theory. The effect of the relaxation time factors was also discussed. It is indicated that there is apparent effect of G-TE, L-S theory, and G-L theory on the results and it is different from p₁ wave,p₂ wave and S-wave. In addition, there is greater effect of relaxation time on p₂ wave, and less effect on p₁ wave, and the effect can be omitted on the S wave.

Abstract:The dynamic overset method and Eulerian approach were applied to solve the unsteady NS function and 6DOF movement function, and to numerically simulate the separation processes of KSR-III rocket’s core and to booster with and without additional forces. Major factors that affect the separation processes were also analyzed. It shows that the numerical results agree with the experimental results, indicating that the dynamic overset assembly method is able to correctly predict the complex flow between the rocket’s core and booster. Furthermore, based on the results of numerical simulations, separation parameters and rules of the booster under different conditions are also obtained.

Abstract:An asteroid rendezvous plan for CHANG′E-2 was put forward and the corresponding mission was designed to maximize the satellite utilization. First, the satellite status of CHANG′E-2 at present was introduced. Based on the constraint of the current CHANG′E-2 orbit and remaining fuel and TT&C (telemetry, track, and command) capacity, the design of optimal transfer trajectory and the selection of rendezvous asteroid were studied. The suitable asteroids for rendezvous were given as a result. Second, the mid-course correction was studied according to two orbit maneuver modes, i.e., the fixed interval mode and the fixed interval mode with a least velocity increment constraint. Finally, the TT&C condition of the asteroid rendezvous mission was briefly analyzed according to the Chinese deep space network. The results show that the fuel remains can support the rendezvous of CHANG′E-2 with Asteroid 1997XF₁₁ and 2005VS. Furthermore, the Chinese deep space network can provide an 8-h daily VLBI (Very Long Baseline Interferometry) tracking at least in the interplanetary course. The velocity increment for mid-course corrections is less than 10 m/s.

Abstract:As for the long-time error propagation problem of the space station rendezvous phasing，a nonlinear covariance analysis method based on the unscented transformation (UTCAM) is presented. The strategy of rendezvous phasing and the computation method of orbit maneuver parameters is proposed，then the principles and flow of UTCAM are introduced. The comparison between UTCAM and the two methods of STK and the Monte-Carlo shows that the relative error of covariance analysis between those methods is under 1.2%, and the computation consumption time is only 1/460 that of Monte-Carlo, so it can accomplish the propagation of mean and covariance rapidly and exactly for nonlinear systems. Finally, the error propagation of a 20-day rendezvous phasing of space station is conducted by using UTCAM, and the results are validated by the Monte-Carlo simulation.

Abstract:The slide mode tracking guidance strategy for hypersonic vehicle that can realize both precise guidance and maneuver flight was investigated. First, the diving trajectory which can satisfy terminal constraints in longitudinal direction and the maneuvering trajectory were designed. Second, with the aid of feedback linearization, the nonlinear motion equations were converted into the linear ones, which can be used to track the designed trajectories. Besides, in order to improve the guidance performance, slide mode tracking guidance law was proposed and the law was converted into nonlinear system to get nonlinear slide mode tracking guidance law. The guidance law is formed from the current motion states completely, therefore, the relative motion information can be decreased enormously. Finally, the results of a CAV-H vehicle guidance test show that the algorithm can realize maneuver flight and high precision guidance under the path constraints even if the outside disturbances exist. Therefore, it can offer references for precision guidance and maneuver penetration for hypersonic vehicle in dive phase.

Abstract:The design of a blockage adjustor at the exit is commonly used in simulating the impacts of backward pressure on the isolator flow field. Numerical simulation was adopted to study the effects of different block modes. Three modes were compared, including installing a flat on the ramp side wall, a flat on the cowl side wall and a wedge in the middle of the flow field. The results show that due to the asymmetric boundary layer on the ramp wall and cowl wall, the shock trains formed by them are all next to the cowl side. The intensity of the shock train generated by the second mode is stronger and the boundary layer separates more evidently, which chocks the isolator more easily and poses difficulty for the study of shock train in experiment. The other two modes can generate similar flow field, but the first one can be realized more easily. 

Abstract:The hypersonic vehicle has a large number of configuration parameters, and its aerodynamic shape design is very complicated. To overcome this difficulty, a lifting body shape parametric design method is proposed. This method is based on class function/shape function transformation (CST) and power function expression, whose design variables are limited to six ones, which makes it very convenient for configuration analysis and design. By means of orthogonal experiment analysis, the influence of the configuration parameters on volume efficiency and lift-drag ratio of the lifting body was studied, and the ones with the great influence were obtained. Meanwhile, the experiment results found that the configuration parameters have conflict influence on the volume efficiency and lift-drag ratio. Thus, to search for the best configuration parameters, a Kriging surrogate model based multi-objective genetic algorithm was applied to design the lifting body shape, in which the volume efficiency and lift-drag ratio were taken as the two conflict objectives under the constraints of the longitudinal stability and vehicle volume. Numerical results show the efficiency of the method and a uniform Pareto front was obtained. The volume efficiency and lift-drag ratio of the typical optimized shape can be increased by 17.31% and 11.94%, respectively, in comparison with the baseline. Differences of the results gained from the Kriging surrogate model and real physical model are less than 4%. Furthermore, the influences of leading edge blunting on aerodynamic character were researched. The results indicate that, the lift-drag ratio of the lifting body decreases significantly with the increase of blunting radius. It is also found that the optimized results can be extrapolated to the leading edge blunting shapes when aerodynamic character is the unique concern.

Abstract:The dynamical interaction of payload brackets and spacecraft frame structure can observably magnify the responses of payloads. Vibration reduction studies usually focus on component-level payload brackets, but in this research, spacecraft frame structure and payload brackets are considered as a whole system (Spacecraft-Bracket System). A certain spacecraft was modeled with finite element method. With structure parameters extracted from this model, a system-level lumped parameter model was built, and the univariate analysis for structure parameters was done. The results indicate that the lumped parameter model can expose the coupling pattern of payload brackets and spacecraft frame structure clearly, and that the sensitivity for responses of payloads related to frequency parameters of both structures are evidently higher than that related to damp and mass parameters. Consequently, for improving the dynamic environment of payloads, the frequency relationship of payload brackets and spacecraft frame structure should be anatomized in spacecraft structure design stage.

Abstract:As is required by sounding rocket utilization, a real-time multi-channel picture capture and compression system applied in sounding rocket is studied and realized in the study, which introduces two key techniques applied in the system. The system bases its architecture on ARM and FPGA, and adopts a dedicated video-compression chip as the core processing unit. By way of improving the reliability of time division multiplexing of cameras and optimizing the control schemes of compression ratio, the system satisfies the requirement of low power consumption and high compression ratio in sounding rockets. It has compact circuit framework, high integration level and great flexibility. Practical tests show that, the system has some good features, such as being light-small, low-power, and low-cost. In the experiment named Space Environment Vertical Exploration, the system shot important scenes, including the separation of rocket head and engine, as well as the deployment of electric field detection boom. By adoption of contour volume evaluation methods, it is concluded that the pictures shot during the flight have sufficient definition for scientific research and engineer application.

Abstract:Global navigation constellation maintenance is an important problem. Firstly, the model of MEO constellation formation was advanced. Then, with consideration of main perturbation forces and orbit ephemeris error, the constellation formation evolvement law was analyzed and asserted with some satellites orbital data. Also, anti-perturbation compensation strategy was put forward, an improved decoupling control method was proposed, and the effect of satellite launch time on anti-perturbation compensation strategy was discussed and analyzed. Finally, some key results were concluded as a summary, which will be helpful for the design of the global navigation constellation with inertial space and its maintenance and control strategies for its rotation around the earth.

Abstract:For the trajectory planning problem in hypersonic glide vehicle, a differential flatness based three-degree-of-freedom trajectory generation approach is proposed. Based on the flatness analysis of the simplified longitudinal motion model, the reference longitudinal trajectory planning problem was mapped into the flat output space to improve the solving efficiency by eliminating the dynamical constraints and reducing the design dimension. Then the initial problem was transformed into a nonlinear programming problem utilizing global polynomial approximations to the flat outputs. To compensate for the effects of the earth rotation and external disturbances, a Proportion-Differentiation control based reference trajectory tracking controller was designed with good convergence capability. By integrating the lateral motion determined by the error corridor of heading angle based bank angle revision, the three-degree-of-freedom gliding trajectory was ultimately generated. Numerical simulations were conducted to validate the feasibility and effectiveness of the approach presented here.

Abstract:When the ground-based pseudolite navigation system is used for vehicle, there will be some bad geometric configuration situations because of the area restriction for pseudolites. If the traditional single positioning algorithm is used with pseudo range only as usual, the precision of positioning for vehicles will be low. In light of this, this study proposed that the inaccurate solution of receiver’s clock error affects the precision of positioning to a great extent. For this situation, an improved approach was suggested to obtain a better precision of positioning through increasing the accurateness of solution of receiver’s clock error. The main idea was to obtain the observation model of the receiver’s clock error and then adding the model to the positioning equations. The simulation results indicate that the approach is feasible and effective.

Abstract:The injection, mixing and atomization characteristics of transverse liquid jet in liquid-fueled scramjet are the determining factors for the efficiency of the combustion chamber. An origin image analysis method, without any threshold choosing section, was developed in house to get the unique unstable boundary of the transverse jet without any manual effects. The lateral extension boundary capturing method, which is based on PIV technique and the corresponding image analysis method, was developed to illustrate the lateral outer boundary of the jets. Results from targeted and comparative experiments indicate that, compared with the single jet case, the penetration heights and lateral extension become larger in the assemble jets cases. A larger distance between the streamwise assembled double injectors contributes to a higher penetration height of the jet.

Abstract:With the growing complexity of VLSI designs, functional verification and debugging has become a resource-intensive bottleneck in modern CAD flows, consuming as much as 60% of the total design cycle. Error localization in circuits is difficult and time-consuming. Therefore an efficient error debugging and localization method is necessary for hardware design. Recently there are many different contributions to research on error localization in circuits. Firstly, the categories and workflow of error debugging method were introduced. The fundamental principles of SAT-based error localization method were described. Then the existing algorithms were introduced and analyzed. Furthermore, the research results about extract unsatisfiable subformulae, which can strongly improve the efficiency and accuracy of error localization, were presented. Finally, the current challenges were discussed, and the future research directions of error localization in circuits were outlined.

Abstract:In view of the large dynamic and fast acquisition requirement of inter-satellite links (ISLs) signal, a capture initial information solution method is presented for ISLs of navigation constellation. This method evaluates time-delay and Doppler frequency based on ephemeris. The analysis shows that this method has a simple realization process, a high speed of restraining and a high precision of evaluation, and can achieve the degree of nanosecond for the time delay through merely two times of iteration, which has greatly reduced the computing difficulty and complexity. This analysis is made upon the model of BeiDou navigation system and can provide reference for our country’s ISLs design.

Abstract:The low angle tracking problem was investigated for shipborne X-band array radar working at frequency diversity mode. Firstly, the receiving array signal model with multi-frequency was established in multi-path environment based on the relation between complex reflection coefficient (CRC) and grazing angle of seawater at X band. Then, the research put forward the MFML (Multi-Frequency Maximal Likelihood) elevation spectrum, in which the elevation ambiguity is alleviated by frequency diversity. The spacing between spectrum peaks was presented. The influence on elevation spectrum of frequency width was analyzed. Lastly, the probability of exact peak selection was proposed to describe the elevation estimation performance. Elevation estimation performance was evaluated by simulation, related to SNR and target elevation. Given target elevation, the minimal SNR was obtained for a certain angular accuracy, which is not strictly monotone downtrend with target elevation.

Abstract:Motivated by the demands of real-time video stabilization, a real-time video stabilization algorithm based on homography trajectory is proposed. For each input frame, our approach regenerates four short homography trajectories by applying inter-frame homography transformations to the four corners of image rectangle. An associate Kalman filter is then performed to smooth these transformational trajectories. Finally, at the stage of image composition, constraints of inclusion and similarity are considered for selecting a visually plausible stabilized video. The proposed method can offer real-time video stabilization and it can remove the delays for caching coming images. In addition, our method does not rely on sophisticated 3D reconstruction or long-range feature tracking and it can effectively relieve the errors introduced by using homography to model the video motion. Experiments show that our approach can offer real-time stabilizing for videos with 2D scenes or the 3D scenes with moderate depth variation. 

Abstract:Enhancing reputation mechanism’s capability of aggregating reputation information effectively is the foundation of a successful reputation system. Current reputation systems based on localized reputation information cannot process such strategic recommendations as correlative and collusive ratings. Furthermore there exists unfairness to blameless peers in these models. Therefore, a Credibility Enhanced Reputation mechanism CERep is presented. In CERep, a peer uses its experiences to compute the direct trust valuation which contains direct trust value and level of confidence about this value, then a reputation-based trust valuation scheme and recommendation credibility computation model is proposed. Moreover, the strategies used for implementing the reputation mechanism are also discussed. Theoretical analysis and simulation show that CERep reputation mechanism proposed can help peers effectively detect dishonest recommendations in a variety of scenarios where more complex malicious strategies are introduced, and achieve a more accurate trust valuation and fair evaluation of recommendations.

Abstract:The traditional object tracking algorithms require manually annotated tracking area, and suffer from the problem of drift. To address these difficulties, the problem of person tracking was focused on, and a new detection-based tracking algorithm was proposed. To reduce failure in tracking, multiple detectors to locate multiple body parts were employed, and then their detection results were mapped to a common body area. To adapt for the quickly moving objects, the KLT tracker and agglomerative clustering for linking the detection windows to form person body trajectories was employed. The experimental results reveal that using multiple detectors improves the tracking performance significantly, and the KLT tracker is adaptable for quickly moving objects. This algorithm is nearly real-time. 

Abstract:The PCRB-GMSPPF algorithm is proposed in order to achieve the computation of posterior Cramer-Rao bound in magnetic target tracking issues. In the proposed method, the GMSPPF algorithm is adopted to perform the sampling toward the actual posterior distribution of target state, hence the Fisher information matrix at each observation time in PCRB computation can be approximated using Monte Carlo integral method. The proposed method overcomes the depletion and degeneracy problem which causes the failure to correctly sample in posterior distribution. The simulation analysis is performed on the basis of the establishment of magnetic target tracking state model and observation model. The proposed PCRB is compared with the mean square error performance of tracking using GMSPPF and PF algorithm to validate correctness of proposed PCRB computation algorithm. The results exhibits that PCRB-GMSPPF outperforms the PCRB-PF in accuracy for magnetic target tracking issues, and can be generalized for general non-linear tracking model analysis for error lower bound.

Abstract:A variable modulator scheme is presented. The hardware system adopting the proposed approach was accomplished based on field programmable gate array (FPGA). The proposed system can deal with signals with bit rate even varying from （13.5～300）Mbps continuously. By splitting the whole rate range into several small parts and filtering the input data with different interpolation times, the correctness of transferring all rates into the dealing range of digital analog convert (DAC) was ensured. The architecture of system was devised and the difficulties in hardware realization were analysed. The ways to solve the pivotal problem were particularly indicated. Realization on FPGA demonstrates the good performance of the proposed idea. The expansibility of system makes it easy to be applied in wider rate bound.

Abstract:Recently spatial pyramid matching (SPM) with scale invariant feature transform (SIFT) descriptor has been successfully used in image classification. Unfortunately, the codebook generation and feature quantization procedures using SIFT feature have the high complexity both in time and space. To address this problem, a feature descriptor called Binary Pattern of Oriented Gradients is presented. Firstly, the input image was densely sampled and divided into small uniform image patches. Secondly, each patch was divided into 2*2 grids uniformly. For all grids the histograms of oriented gradient were computed and all dominant directions of the histograms were coded by binary coding. Then the descriptor was generated by converting the binary number to decimal number. Finally, this descriptor was combined in the spatial pyramid domain. Experiments on popular benchmark dataset demonstrate that the proposed method always significantly outperforms the popular SPM based SIFT descriptor method both in time and classification accuracy.

Abstract:Doppler frequency shift simulation is a key technique in high dynamic satellite navigation signal simulator. Considering the features of field programmable gate array, a mixed-clk third-order direct digital synthesizer (DDS) simulation model was built, and its output phase expression was derived. The calculation method for initial control word for each stage DDS was given and it was pointed out that the same-clk third-order DDS simulation model is only a special case of mixed-clk simulation model. After analyzing the signal phase error caused by mixed-clk, the word length design method for each stage DDS was discussed. Comparison between the same-clk third-order DDS and the mixed-clk third-order DDS can reduce both resource and power consumption. Simulation results indicate that the proposed method can be used to simulate signal Doppler is of high precision.

Abstract:Compressive sensing provides a new way for increasing the ability of information acquisition. Compressive sensing asserts that it is possible to accurately reconstruct signals from sub-Nyquist sampling, provided some additional assumptions (sparse or compressible) are made about the signal in question. The compressive imaging technology, which is based on the compressive sensing theory, integrates the processes of sensing, compression and processing perfectly, avoiding the resource waste caused by a traditional “sample-then-compress” framework. With a review of some of the recent progress in compressive sensing theory from the following three aspects: sparsity, the design of measuring matrix and recovery conditions, the reconstruction algorithms, several optical compressive imaging systems are introduced, and some key challenges in this area have been discussed in the end. 

Abstract:Aiming at applications of small unmanned aerial vehicle (UAV) in earth observations, this research explores the multi-viewpoint image mosaicing problems for roughly planar scenes. When coarse camera poses are known, a method for integrating camera poses and feature correspondences is proposed, in which direct sparse Cholesky factorization algorithm is used to solve the global optimization problems of mosaicing. Global distortions do not exist in the obtained mosaics and local mosaic errors are suppressed effectively. When the camera poses are unknown, a structure-from-motion (SFM) system is used to recover the cameras poses and sparse structure of the scene firstly. Then, the sparse global adjustment is used to refine the transformations. The proposed algorithm is validated using sand table images and real aerial images.

Abstract:The encoding algorithms of the LDPC codes with quasi-cyclic dual-diagonal parity check matrix were studied. It is demonstrated that the matrix decomposition encoding algorithm and the cumulative recursion encoding algorithm are equivalent for implementation. The cumulative recursion encoding algorithm is straightforwardly facilitated to hardware implementation. Besides, a partly parallel encoding architecture for the QC-LDPC codes with dual-diagonal parity check matrix was proposed and a LDPC encoder compatible with IEEE 802.11n standard was designed. FPGA implementation results show that the hardware overhead of the proposed LDPC encoder is low and the throughput is high. The encoding throughput can reach up to 13Gbps with code length 1944-bit and rate 5/6.

Abstract:Target selecting is an important aspect of military operational planning. The Markov Decision Process(MDP) method was used to solve the multi-phase target selecting problem which has complex relations among targets. Firstly, the and-or tree was used to describe the relations among the layers of the target system of system(TSoS), and a Discrete Time Markov Decision Process(DTMDP) method was proposed for modeling target selecting whose objective was to neutralize the TSoS. Secondly, an LRTDP algorithm based heuristic was proposed to give the estimate value of the current state of the TSoS, which was calculated by considering the potential resource consumption and failure probability of the evolution process from the current state to the lapse state of the TSoS, and the heuristic can effectively exclude the intermediate states which cannot be transferred to the lapse state, in order to reduce the huge search space of the model because of the complex relations among targets. Finally, a case was proposed to validate the method. The results show that the method is intuitive and practical, and can facilitate the target selecting decision making when there are complex relations among the targets.

Abstract:Some key issues of real-time interpretation for optical measurement images in test ranges to design were researched and a real-time interpretation and estimation system was realized. Automatic Target capture, tracking and high precision location for interpretation features are the questions under probe. Shape similarity analysis, online region tracking and learning, and iterative contour registration were respectively used to locate multiple interpretation points. Based on the characteristics of real-time processing, such as high efficiency requirement, strong parallelism capability, and rigorous sequence in time, the software architecture design pattern of distributed framework with business process management was adopted to achieve the centralized administration of data and process, multiple sites parallel interpretation, data-driven auto estimation method selection and friendly user interface. Take the aerial launching tests of the air ranges as an example, the feasibility and efficiency of the system was examined by the experiment. The system can be extended to various test ranges to meet the users’ need of weapon test data’s real-time gain and analysis.

Abstract:Ultra-precision single point diamond flycutting is a novel method to manufacture the microstructures with grooves. In the flycutting process, the cutting force is an important physical quantity. It is closely associated with cutting quality and tool wearing. To develop the cutting regularity, a flycutting force model based on the theory of orthogonal microcutting was presented. The cutting force model on rake and flank face is achieved. The shear angle in flycutting process was analyzed based on the kinematical regularity. The value of the shear angle in specific processing parameters technological conditions was achieved by single-turn flycutting experiments. To verify the flycutting force model, overlapping flycutting experiments with variant parameters feed rates were carried out. The validity of the force model is demonstrated with the accordance of experiments and theoretical analysis.

Abstract:On the basis of the giant magnetoimpedance (GMI) effect found in the amorphous wire, and with the utilization of the CoFeBSi amorphous wire as the sensing material, a novel differential-type high sensitively sensor adopting the technology of orthogonal lock-in amplifier was designed. Firstly, the concept of the GMI effect and the magnetic sensing head based on the double-sensing-elements and differential-type structure, were briefly instructed. Secondly, the principle of the conditioning circuit of the sensor based on orthogonal lock-in amplifier was analyzed in detail. Thirdly, based on the impedance magnitude and phase characteristics of the amorphous wire, an approximate algorithm was put forward to calculate the envelope of the output of the orthogonal lock-in amplifier for simplifying the arithmetic circuit. Experiment results show that the sensitivity of the sensor can achieve about 748mV/Oe with the full measurement range of -2.0Oe ～ +2.0Oe, and the linearity error is about 0.98%FS, while the average noise power spectral density is about 0.8nT/Hz^1/2.

Abstract:Taking the spiral bevel gear transmission system of a helicopter tail reducer as research object, a computation model for the temperature field simulation was built, a steady-state temperature field distribution was derived under normal lubrication condition. The spiral bevel gear can be equivalent to the spur gear in basis in equivalent gear theory, and its gear backlash can be reflected at the transverse plane of the equivalent spur gear .The influence of thermal deformation of the spiral bevel gear transmission system on the gear backlash was computed and analyzed under normal lubrication condition using the thermo-elasticity theory. The results provided a theoretical basis for the design correctness of backlash considering thermal deformation, thus ensuring the working accuracy of the spiral bevel gear.

Abstract:The problem of cooperative localization in the situation when an object is detected by robots simultaneously was studied. As each robot has its own relative observation about the object, a mathematical model for comparing the consistency of these relative observations was presented. With that method, a new cooperative localization algorithm based on maximum entropy gaming and Extended Kalman Filter(EKF) was proposed. As the gaming results are different, the EKF equations that can match any gaming result were derived. Several simulation results showing that the proposed algorithm can improve the localization performance and avoid the relative observations conflict problem in cooperative localization in the meantime.