Abstract:Form design of net can help to improve the opening and capturing quality of the space net system. The form optimization design problem of space net was studied based on small elastic modulus method. Internal force distributed in the net was selected as the optimization objective. The maximum stress state was chosen as the research condition and the rope was given minimum modulus elasticity. The iteration analysis was carried out using the results of deformation as the initial condition. Optimization results show that the internal force distribution of the rope net tends to be more uniform with the increase of the iteration steps. Without changing the premise of net topology structure, the established optimization design and method for the space net configuration optimization design and provides a means of reference.

Abstract:The impact angle and the flight time were needed to be controlled simultaneously for a saturation attack. A two-stage guidance strategy with impact angle and flight time was proposed for impact angle and flight time control. In the first stage, the impact time high-precision control guidance law was derived by using a switching surface in pitch channel. The traditional proportional guidance law was used in yaw channel. Then in the second stage, the trajectory shaping optimal guidance with gravity compensation was used for impact angle control, which was an extension of explicit guidance in that gravity compensation was incorporated. The effectiveness of the impact angle and impact time two-stage guidance was validated by simulation. Simulation results show that the proposed two-stage control guidance with impact angle and flight time can achieve the simultaneous control of the impact angle and flight time.

Abstract:The time series of 72 international GPS service core stations were selected to make perform analysis on GPS noise model and uncertainties of the velocity. An improved Akaike information criteria and a Bayesian information criteria model were developed to evaluate different combinations of noise model, so as to establish the best noise model of GPS time series and gain the aureate velocity parameters. Results show that the noise model of GPS time series cannot be described as simple noise, it tends to showing diversity, and can be best described by power-law, generalized Gauss Markov, flicker noise plus white noise model, and its three components exhibit different noise characteristics. With the time span increases, the optimal noise model of time series, GPS station velocity and its uncertainty tends to be convergent and steady. Besides, the proportion of random walk noise is proved to increase as time span increases. The final results show that the time span of more than 10 years is an ideal noise model estimation scale.

Abstract:A space debris impact risk assessment model was developed on the basis of the existing space debris environment model. The framework of the model consists of space debris environment module, spacecraft model module, geometry shading module and impact probability module. The impact risk by space debris for three generic spacecraft geometries were offered by IADC in order to validate different models. The result was proved to be effective by comparing with other models. The space debris impact risk for the spacecraft of cube was assessed and analyzed using the developed risk assessment model, and the effect of orbital altitude, inclination and attitude parameters to the space debris impact risk was presented.

Abstract:To support strong interference signal input under “navigation warfare” scenarios, navigation receivers are requested for increasing dynamic range in analog channels. Under the given constraint condition of signal to noise ratio deterioration, a two-dimensional curve model to offer a method for dynamic range optimizing and stage gain design was put forward by the legacy analysis method. However, this method was only applicable for the AGC(automatic gain control) circuits that the output power was basically stable. A solving model involving the three-dimensional curve based on the extra parameter called the rollback value of the AGC output power was put forward. The model revealed the relationship between the circuit parameters and the dynamic range of analog channel and it is suitable for the AGC circuits with variable output power, which can achieve a larger dynamic range. To reduce the complexity of the parameter calculation in the three-dimensional model, the complex numerical solution to linear equation solution according to the features of pure attenuation network was simplified. This simplification can substantially reduce the design complexity. Test results of dynamic range are in good consistence with the expectation in practical designs, which proves the accuracy of the analysis model.

Abstract:Robust and efficient line extraction algorithm has been widely used in space photogrammetry field such as target pose detection, tracking and skeleton reconstruction. A line segment detector based on local contrast of pixels and global false detection control was proposed. The method consists of four steps. Firstly, the gradient and local contrast of each pixel was calculated. Secondly, the pixels with similar orientations were clustered into the line support region which was approximated by a rectangle. After that the line support region was fitted into a line segment with the above one pixel width and the line parameters were estimated. Finally, the line segment candidates were validated and the false detection was controlled. The experimental results show that the proposed method is much more robust and efficient than the traditional methods in hash conditions, especially in complex illumination.

Abstract:In order to improve the memory access efficiency of the DDR3 memory controller, a data buffering mechanism based on DDR3 memory access burst length was proposed. The application requests were guided into three different queues. The data buffering mechanism can make use of the additional data obtained from DRAM(dynamic random access memory) in one of the former request, thus reducing the actual external DRAM access needed. Experiments on several image and video application show that the proposed mechanism can improve the memory controller by an average 21.3% and a peak by 51.3% at an acceptable hardware cost when compared with the FCFS (first-come-first-serve) baseline DDR3 memory controller.

Abstract:In order to recognize multi-class cervical cells automatically, a hierarchical method with PCA (principal component analysis) feature transformation was proposed and this cell recognition could provide the evidence for cervical cancer diagnosis. The cervical cell recognition was treated as a 4-class classification problem. There were two levels in this hierarchical method. First, one-versus-one strategy was used to train 6 SVM (support vector machine) classifiers to do a 3-class classification. Second, abnormal cells in one type of 3 categories were classified by a 2-class SVM. To optimize the feature combination and reduce the running time, a feature transformation method named PCA was adopted to transform the original feature vector into lowdimension feature space. The experiments show that the proposed hierarchical PCA recognition method is faster than the common hierarchical method at a ratio of 21.31%, and can distinguish 4 cervical cell categories better than 6 other traditional methods and achieve above 90% accuracy.

Abstract:Traditional storage strategy of raster data cannot meet the demands of coarse-grained data processing under the distributed computing environment and has low efficiency when dealing with calculations for gigantic raster data. A storage strategy of raster tile data was presented on the basis of the storage characteristics of distributed file system. It also took the calculation characteristics of spatial analysis operators of map algebra into consideration, which uses raster tile as processing unit during map and reduce stage. The storage strategy was implemented by the following steps. Firstly raster data were divided into raster tiles. Then these tiles were compressed and organized by a special sequence in order to be transferred to Hadoop distributed file system. Finally input and output file interfaces were re-implemented to meet the data access requirements of map and reduce stage. The strategy was tested and verified by the distributed calculation process of local map algebra operators. Theoretical analysis and experimental results show that this strategy can significantly improve the processing speed of space analysis operators.

Abstract:Relaxed encryption framework which extends hash functions of Merkle-Damg?rd construction to a parallel construction can improve Hash performance by multi-core processor. A proving process was given to show that relaxed encryption framework has no property of collision resistance when processing messages of different size. A new parallel extending algorithm was proposed base on the design of relaxed encryption framework, which remedies the security flaws of the relaxed encryption framework, and the security of the new parallel Hash construction was also discussed. The cryptanalysis shows that the property of collision resistance of the new parallel construction is not weaker than the hash function of Merkle-Damg?rd construction. Experimental results indicate that the new Hash construction performs better when processing messages of large size.

Abstract:The main objective of this study was to explore the dynamic response and damage pattern of a clamped square steel plate under the synergy effect of blast and fragments loading. A numerical-simulation tool was used to further study the combined blast and fragments loading effects on a clamped square steel plate. Through finite element program ANSYS/LSDYNA, simulations of the response behavior and damage pattern of the plate subjected to the combined blast and fragments loading were conducted. Large punched hole caused by the dense fragment cluster will form in the intensively impacted area under proper launch distance. As launch distance increases, large deformation is the main failure modes of the plate, combined with numbers of perforation holes but no large punched hole.

Abstract:A SWATH (small waterplane area twin hull) installed with stabilizing fins rolling freely in calm water was investigated by both numerical approach and experimental method. Uncertainty analysis was made to verify and validate the numerical method. Both linear roll damping and nonlinear roll damping were obtained and the contributions of the frictional damping and the stabilizing fins to the roll restoring moment were analyzed. The results illustrate that: the numerical free roll decay curve agrees well with the experiment; under the assumption of linear roll mode, the linear roll damping coefficient sees an upward trend with the increase of initial heel angle; the computed free roll decay curves using nonlinear damping coefficients agree well with the experimental results; the frictional damping and the stabilizing fins make minimal contributions to the roll restoring moment for the free roll decay motion in still water.

Abstract:Starting from the basic principle of modal identification, and the expressions were derived for time frequency response of the excitation force and time response of resonant excitation, and the relationships among the timefrequency domain amplitudes were found. It was concerned that the associated free vibration in the resonant response is difficult to decay in a short time, and it was pointed out that the amplitude of the impulse frequency response spectrum at corresponding frequency is equal to the amplitude of forced vibration under resonant excitation. Based on establishing relationship of response equivalence, the formula of damping ratio was derived by a limited spectral information of impulse response spectrum. The accuracy of response prediction and damping ratio estimation was verified by ship girder model. In addition, the first eight modal damping ratios’ tests of 2 typical ship plate element models of different materials were also completed, and the rapidity and reliability of the method were verified by the numeral calculation binding experimental response frequency spectrum.

Abstract:Aiming at sending the line-of-sight angular rate to a small neighborhood of zero before hitting the target to achieve the interception of the missile to the target to quasiparallel approaching state. Based on the active disturbance rejection control to estimate and compensate the uncertainties, a novel three-dimensional finite time convergence guidance law was presented accounting for the second order dynamics of missile′s autopilot and target′s maneuver. The finite time convergence of system was strictly proved based on the finite time convergence control theory. For the purpose of restraining measurement noise, the traditional tracking differentiator was modified to be applied in the process of designing a novel extended state observer and backstepping control. Simulation results demonstrate that the proposed guidance law can guide missiles to accurately 〖JP2〗intercept a maneuvering target with finite time, even if the autopilot has a lag, modified tracking differentiator has the advantages of high precision, fast response and strong ability of noise restraint, the extended state observer based on the modified tracking differentiator has better estimation effect.

Abstract:Aiming to solve the search problem of geomagnetic multi-component and multiobjective, the multi-objective evolutionary search algorithm based on the magneto-taxis sensitivity was proposed for the autonomous underwater vehicles. Combined with the structure of the evolutionary algorithm, this method utilized the restrictive correlation between the geomagnetic components and the navigation path, and the magneto-taxis sensitivity was expressed as a posteriori assessment criteria to establish the navigation model. The geomagnetic multi-component converged to desired value along with the motion of the vehicle at the same time and place, thus realized the navigation goal. Compared with the hex-path searching algorithm, the effectiveness and advantages of the proposed algorithm were validated by the simulation experiments.

Abstract:In order to reduce the effects of parameter variations and complex environment disturbances on the altitude control of parawing UAVs (unmanned aerial vehicles), an altitude control strategy based on LADRC (linear active disturbance rejection control) was studied. An eight degree of freedom model of a parawing UAV was built, and the wind and rain models were introduced for the accurate simulation of real flight environments. Based on the features of LADRC, the whole control structure was determined. As a result, the internal and external disturbances were estimated by using linear extended state observer and compensated real-timely by the feedback control law. Flight simulation experiments under various disturbance conditions were conducted. Simulation results show that the altitude control method based on LADRC can not only accurately estimate and compensate the internal/external disturbances but also implement precise altitude control. Compared with standard PID controller, the LADRC controller has better robustness and disturbance rejection ability.

Abstract:In order to accelerate convergence rate and promote observation precision of linear ESO (extended state observer), an improved linear ESO used in active disturbance rejection control system was proposed. The improved linear ESO followed error controlling principle and used the errors between the state variables and their observed values as the regulation basis. It is proved that the observation error of this improved secondorder and third-order linear ESO is stable, and its steady state error is greatly reduced when compared with the traditional linear ESO. Simulation results show that the secondorder and third-order improved linear ESO is faster and more accurate than the traditional same order linear and nonlinear ESO. 

Abstract:A second-order distributed collective model with spatial coordinates coupling was established. Analysis results show that: if the topology structure of the system is unchanged, the system graph has a directed spanning tree and the speed parameter is over the critical value, the system will present three flocking patterns with the rotation angle variation of coupling matrix—linear pattern, cylindrical spiral pattern, logarithmic spiral pattern. Some simulations for these three patterns were carried out in the last section.

Abstract:The unanticipated fault diagnosis for complex system is a difficult problem. A general process model was proposed. The model adopted a four-layer structure and included four models, i.e. an anticipated fault detection model, an anticipated fault identification model, an unanticipated fault detection model and an unanticipated fault identification model. Several key problems and the corresponding algorithms in each layer were analyzed, including the establishment of the fault detection statistic, the extraction of the fault character, the design of the fault isolation criterion and the construction of the fault contribution rate. The general process model regularized the diagnosis process of unanticipated fault for complex system and defined the datadriven fault diagnosis framework. The effectiveness of the proposed general process model was validated by a satellite control system. 

Abstract:For evaluating the performance of air traffic management system, a model based on linguistic decision map with multi-subnets was proposed as well as the indexes. The influences among indexes were analyzed by using a multi-subnets strategy, and the initial judgment matrices and influence connective matrices were built by multiple experts using linguistic scales. The proposed approach can achieve global priorities of indexes and evaluation results of alternatives. Finally, the case study illustrates that, in comparison with the independent situation, results of the model can represent priorities of indexes more objectively and comprehensively, and can present the gap among the alternatives more obviously.

Abstract:In order to solve the problem of constrained resource and insufficient calculation ability in airbased backbone network and the problem of not fully considering load balancing and difference in requirement of QoS(quality of service) guarantee in the traditional SOAR(simple opportunistic adaptive routing) algorithm, a new algorithm was proposed to support the QoS named improvedSOAR routing algorithm. The algorithm defined comprehensive expected transmission count to describe the comprehensive state of links on the basis of taking the link congestion control and load balancing into consideration. It can effectively reduce the probability of network congestion. A route selection strategy was designed for QoS based on AHP method, according to the service type difference in transmission network. It can achieve the dynamic matching between the path selection and the different service type. Simulation results show that the improved-SOAR routing algorithm has better performance in the transmission delay, the throughput and the throughput rate than the traditional SOAR routing algorithm under heavy network load. When there are different types of services in the network, the improvedSOAR routing algorithm adaptively selects the best transmission path according to the difference of requirement about the QoS guarantee.

Abstract:Gabor transform and K-means algorithm are two commonly used texture analysis methods. However, the texture feature vector has a high dimension by using Gabor transform, which will influence the operating efficiency. Meanwhile, K-means algorithm is affected by the initial clustering centers, and it may lead to the decrease of classification accuracy. Although, some optimization algorithms like genetic algorithm and particle swarm optimization algorithm could improve the performance of K-means algorithm to some extent, the optimization effect is difficult to guarantee as the increase of dimension. Hence, the Relief algorithm was applied to make a feature selection for Gabor texture feature, and to obtain a suitable texture feature subset. Furthermore, a differential evolution algorithm was used to optimize the clustering center of K-means algorithm, and enhance the accuracy and efficiency of texture recognition. Experimental results demonstrate that the dimension of texture feature vector by using the proposed method is obviously lower than that by using the original feature set, and the recognition accuracy is also apparently improved than the basic K-means algorithm.

Abstract:Negative obstacle sensing is one of the most difficult problems for unmanned ground vehicle in unstructured environments. The regular obstacle sensors, such as stereo vision, infrared detector and ladar, have their limited performances in unconstructed environments. Ultrawideband SAR (synthetic aperture radar) sensors have the ability to operate in all weather, all lighting and foliage covered conditions, which have been received widely. Sensing negative obstacle by ultrawideband SAR for unmanned ground vehicle was an effective way. Image geometry of negative obstacle was expounded. The simulation image of negative obstacle was obtained by simulation based on MATLAB, and the conclusion that the image feature of negative obstacle is the shadow area next to shine area is obtained. Moreover, a real data experiment is presented and the experimental result proves the same conclusion again.

Abstract:In order to enhance the anti-jamming operational capability of cognitive antijamming system based on simultaneous transmitting and receiving in the complex electromagnetic environment, an improved energy detection scheme based on the system was studied and the closed expressions of detection probability, false probability and outage probability of the system under Rayleigh fading channels were derived. The scheme decides the detection threshold by obtaining the result of comparison between the selfinterference channel capacity and the required transmission speed for receiver. Simulation results show that the effect of receiver impacted by selfinterference can be reduced and the outage performance of the system can also be improved by the proposed detection scheme.

Abstract:Digital elevation model with regular grids simplifies the modeling and analyzing processes. However, it fails to adapt to different terrain shapes and it is hard to obtain high surface accuracy and small dataset in the meantime, which limits its application in areas such as vehicle dynamic simulation. To solve this problem, a modeling method with varying data resolution was proposed. The node density varied according to the local surface curvature so that it ensures high data resolution around sharp changing areas and low data resolution around relatively flat area. Then Delaunay gridding method together with cubic interpolation was applied to obtain a digital elevation model with high surface accuracy and small data size using the resulting irregular node set. The proposed method was testified with a complex terrain surface used in rover simulation, and compared with the traditional regular grid model, which verified its advantages in achieving the two major objectives. 

Abstract:The pseudo-satellite is stationary for the reference station receiver, therefore, the distance among reference station receivers is nearly kept constant. On that condition, the error caused by sampling and quantization is not Gaussian variables, which can have impact on the measurement accuracy. In order to solve the problem, the digital signal model of satellite navigation receiver was introduced, and then the effect of sampling and quantization error on measure bias was analyzed. Simulation results are presented to support the conclusion, and the optimization of reference receiver in pseudosatellite system is proposed in the end. 

Abstract:During the transmission process of time synchronization signal in troposcatter channel, the multipath effect and noise of the channel can contribute jitter to time synchronization signal. In order to mitigate this jitter, the EMD (empirical mode decomposition) combined with wavelet threshold model was proposed. In the combined model, the EMD was used to decompose the original signal, the wavelet threshold was adopted to process the decomposed components and then the processed results were utilized to reconstruct the final signal. In order to improve the jitter mitigation effect and the signal authenticity of the combined model, the traditional threshold function in wavelet threshold was perfected by the better coherent and gentler threshold function. Experimental data were used to demonstrate this combined model. Compared with the simplex model and the Kalman model, the combined model has advantage in effect of de-noising as well as authenticity.

Abstract:In order to analyze the complexity of space borne optical remote sensing system and the source of complexity and its forms of optical remote sensing system were determined by analyzing the whole imaging chain, and the mathematical model of this process was built starting with the basic characteristics and rules of complex system. Based on the important parameter, namely MTF (modulation transfer function), the fundamental research pathway of complex system was analyzed by combining mathematical modeling and computing, namely combing principle reductionism with principle holism and combing qualitative analysis with quantitative analysis. Through the contrasting of the mathematical model and the computing result, on the one hand, the relationship between system performance and these key parameters were figured out; on the other hand, the true MTF of the system was obtained by using regularization blind deconvolution method. These analyses can make great contribution to not only the image quality but also the optimization of remote sensing system.

Abstract:A new measuring method for fiber ring eigenfrequency was presented. Different from the common square wave modulating, the new method is based on the sine wave modulation, so the problem of dead zone was solved. The output signal of fiber optic gyroscope was analyzed when using sine wave modulation, quadratic relationship was obtained between second harmonic and modulation frequency, eigenfrequency can be obtained by calculating the parabolic vertex. On the basis of the new method, a test system was developed by updating fiber optic gyroscope system. Test result shows that the measuring precision of 10 ppm can be achieved, which shows that the proposed method is a method with low cost and high precision method for fiber ring eigenfrequency.

Abstract:Ignition experiments of methane and air mixture in low equivalence ratio were carried out in a shock tube. Ignition delay in different working conditions was obtained through transient pressure signal and OH emission measurement. The experiment results were compared with the calculation based on detailed methane oxidation mechanism. Analysis results indicate that: there is a linear relationship between the logarithm of ignition delay and the reciprocal of temperature; ignition delay decreases with the reduction of methane concentration; the apparent activation energy of experiment results agrees well with the simulation of detailed mechanism.