Abstract:To realize precise tracking of test mass in a drag-free satellite, the relative motion between the test mass and the outer satellite is derived and the main disturbance sources in the relative dynamics are analyzed. Based on the analysis, an adaptive controller for the displacement mode of drag-free satellites with single test mass is designed and it is applicable for unknown but constant or slow-varying satellite mass and spatial disturbances. Under the assumption that both the satellite mass and the disturbances are unknown constants, the controller can guarantee global asymptotic convergence of the tracking errors. Simulation results are given to show the efficiency of the controller.

Abstract:The monocular vision-based navigation algorithm for spacecraft is addressed in this paper. Based on dual number, coupled dynamics equations of relative position and attitude are derived, which can describe the coupling effect between the rotational motion and translational motion. The measurement model is proposed on the basis of the projection on the 2-D plane of the line fixed on the target spacecraft. And the Extended Kalman Filtering method is applied to the estimation problem. Numerical simulations are performed to demonstrate that the proposed approaches can provide accurate and fast estimation of relative position and attitude.

Abstract:To deal with the problem that the iteration doesn′t converge well in the maximum principle, a virtual satellite method is proposed to compute a fuel optimal trajectory of Mars probe in the processing of near-center braking. In the virtual satellite method, an optimal trajectory is computed in which the real satellite rendezvous with the virtual satellite so that the real satellite will come into the target orbit. The problem of guessing initial value of co-states is solved by transfer the original co-states, which have no physical meaning, into another one that can be guessed easily and by this way the iteration will converges better. Finally the simulation results prove the efficiency of this method.

Abstract:To solve the problem of noise elimination in fault feature extraction of sensor signal and describing fault propagation under model uncertainty, this article presents a novel fault diagnosis approach based on empirical mode decomposition (EMD) and directed factor graph (DFG). The EMD method is used to decompose the sensor output signal into a number of intrinsic mode function (IMF) components, a block energy criterion based on the signal samples between two adjacent zero-crossings of IMF is proposed to distinguish the useful signal from noise. Directed factor graph is used to model the cause-effect relations between system components, and as the basis for fault diagnosis through probabilistic reasoning under the model uncertainty. A power supply module of a spacecraft power system is provided as case study to show the feasibility and validity of the proposed method.

Abstract:To optimize hydrodynamic layout of ventilated supercavity vehicle, the experiments have been done in a ventilated cavitation tunnel to study the relationship between tail wings and hydrodynamic of ventilated supercavity vehicle. Forming process of ventilated supercavity was recorded and analyzed. The influences of the tail wings and its wedge angle on the hydrodynamic of ventilated supercavity vehicle were obtained. Experimental results show that the tail wings increase drag coefficient and lift coefficient. Drag coefficient and lift coefficient decrease with the decrease of nature cavitation number. When increasing ventilation rate, drag coefficient and lift coefficient first increase a little and then decrease. The smaller drag coefficient and the bigger lift coefficient can be achieved at bigger tail wing wedge angle.

Abstract:Considering the effects of phase-change on the bubble interface, a new cavitation model based on Rayleigh-Plesset Equation is given and the secondary cavitation is successfully modeled. Using the new cavitation model on cavitation flow fields of the 2 d steady axisymmetrical hemispherical cylinder, the model surface is alternately distributed by a higher cavity pressure and lower collapse pressure due to the growth and collapse of the secondary cavity. With the decrease of cavitation number, the main cavity gradually becomes larger, and the secondary cavity zone is gradually moving to the tail of the model and falling off.

Abstract:A major advance of using the quaternion to describe body orientation is that the kinematics equation is linear and the quaternion is also globally nonsingular. However, the algebraic constraint of unit norm needs to be maintained. An improved nonlinear constrained filter algorithm is proposed for the spacecraft attitude estimation problem subject to a unit quaternion norm constraint. First,by comparing the quaternion norm of a priori and a posteriori estimate, it is proved that the Multiplicative Extended Kalman filter can not gain the optimal solution under nonlinear constraint. Then, a generalized quadratically constrained optimization object function is developed by effective combination of QUEST algorithm and Multiplicative Kalman filter. During the predicting state, the attitude and its covariance propagation models are used to modify the cost function. During the measurement update phase, the quaternion normalization is explicitly maintained in a globally optimal manner by solving the eigenvalue-eigenvector problem and therefore the local linearization is avoided. Compared with the Multiplicative Extended Kalman filter, numerical simulation result demonstrates the precision, stability and convergence of the presented algorithm.

Abstract:To solve the identifiability of partial combinational permutation intercomparison in checking angular bias of the regular polygon and the angle dividing table, aiming at prime-sided polygon and composite-sided polygon respectively, the checking series selecting was studied. At first, the prime-sided polygon checking series was studied, the conclusion was drawn that arbitrary two or above series combinatory measurement could identify the angular biases of the regular polygon and the angle dividing table. While aiming at composite-sided polygon, if the difference between the numbers of the two checking series is the factor( or integer times of the factor) of the side number of the polygon, the biases are not identifiable. The multi-series selecting problem was also researched. According to the practical measurement data about 23-sided and 24-sided polygon, checking accuracy appraisal of identified biases was studied. The theoretical standard deviation and the practical calculated standard deviation were given. The results show that only the number of measurement data should be four times greater than the number of the identified bias, the statistic standard deviation will be effective.

Abstract:The bandwidth will get narrow when the size of HF antenna is small. To overcome this problem, a novel miniaturized HF antenna composed of hemispherical wire grids with performance similar to the electric dipole is presented in this paper. The antenna has simple structure and is easy to feed. The largest dimension of this antenna is 3.6 m, which is 3.6％ of its lowest frequency wavelength, and 36％ of its highest frequency wavelength. The antenna is simulated with the help of CST MWS. A 1/5 scale model is manufactured and measured. The results demonstrate that the relative impedance bandwidth is 40％ without loading or external matching networks while maintaining acceptable performance. A method of broadening frequency range by loading lumped elements is further discussed, and simulation and test verification have been done. The designed antenna can be widely used in HF communication system, over-the-horizon radar and so on.

Abstract:Since the performance of cooperative spectrum sensing in cognitive radio (CR) will decrease in the fading channel, a clustering cooperative spectrum sensing algorithm based on the cooperation in cluster and multi-clusters combination is proposed in this paper. In the proposed algorithm, all the CR users are divided into several clusters, and the CR user in each cluster with the shortest distance from the fusion centre is regarded as the cluster head. The cluster head collects the local sensing information from the other CR users in the cluster, obtains the cooperative sensing result of the cluster, and then sends the result to the fusion centre which will combine the results from all the clusters by "OR rule" in order to obtain the final decision on the presence of the primary user. The simulation indicates that when the channels are perfect, the performances of the proposed algorithm and traditional algorithm without clustering are nearly the same, however, when the channels are in deep fading, the performance of the proposed algorithm is improved remarkably, and it can be increased by the decreasing of the number of clusters. 

Abstract:To improve the efficiency of force optimization algorithms, a new method to compute initial grasping force is proposed. A group of grasp forces with respect to external unit forces separately is computed, and an arbitrary external force is decomposed into linear combination of unit forces. The initial force is obtained by linear combination with the same rule. An example indicates that the new method reduces the steps of convergence of force optimization algorithms and is faster than Lagrange dual method and single value optimizing method. The method can be used to provide initial values for the force optimization algorithms in the point contact friction models, and improve efficiency.

Abstract:To deeply study lubrication characteristics of deep cavity hybrid conical bearing, oil film generalized Reynolds’ equation in polar coordinates, energy control equation and the related expressions were deduced with consideration of turbulent fluid, heat effect and axial velocity of fluid film. Finite numerical difference method was used to discretize equations and Patankar’s positive coefficient law was adopted to process coefficients and constant terms of the discrete equation. Results showed that the Patankar’s positive coefficient law efficiently solved reverse-flow at Oil cavity edge. Under circumstances of big eccentricity and high speed, temperature of lubricating oil film gets high and the influence of bearing performance should be taken into account. The flow is proportional to the input pressure and independent of speed. With the increasing of speed, dynamic effects are improved and the bearing eccentricity is small with light loads. Deep cavity hybrid conical bearing shows excellent performances of static pressure up and dynamic lubrication, and the theoretical analysis results are agree well with the experimental tests.

Abstract:Terminal optical module and reflector mount are the important components of laser-driven inertial confinement fusion (ICF) device, having the characteristic of owning much and scattered motion axes. The control system that can achieve the motion control of this device is built upon the thought of distributing control. The system contains Beckhoff embedded PC and bus terminals as underlying controller and EtherCAT as the communication network. Software of the control system is developed under the VC++ and TwinCAT environment. The special functions required by mechanical systems are all be programmed to the PLC function block and work in the clients, such as the function of motor lock when power up and down, the motor’s automatic power-up, certain moving axis’ manual follow, one-way positioning,and so on. Among these functions, one-way poisoning can make sure the repeat location accuracy within 3μrad. The control system has the characteristics of simple construction, low cost and fast communications speed. It can keep stable and reliable in the practical engineering applications.

Abstract:As one of the main bottle necks in Trusted Computing going forward, the technical core of trustworthiness measurement is how to characterize object trustworthiness in accordance with requirement of the trust. This paper states the current state of research and the confronted problems. Firstly, the basic concepts, main tasks and expected objectives of measurement are summarized and presented. Secondly, the framework of measurement, complete measurement process and formal description are described. With considering all factors, in the light of the difference of objects, measurement agents and implementation, some representative model of measurement are discussed. And on that basis, the latest models are classified and summarized respectively, and the directions for continuing research are discussed.

Abstract:To reduce the complexity of program comprehension such as program standardization and program matching, a program comprehension oriented construction algorithm of system dependence graph is proposed. This algorithm can be divided into three stages: program information extraction, control dependence sub-graph construction and data dependence sub-graph construction. Control dependency and data dependency are independently computed. Data flow is directly analyzed based on control dependent sub-graph without extra control flow graph, and computed on demand, which reduces the algorithm complexity. Selection statements and loop statements are uniformly represented, and expressions are represented as abstract syntax trees, which can facilitate program transformation and analysis. The system dependence graph has been used in automatic grading system of student programs and program recognition. Application results show that it can facilitate program comprehension and analysis and reduce the complexity of program comprehension and analysis.

Abstract:To obtain the mechanism of wrinkling behavior of hydroformed torsion beam, numerical simulation and experiments are carried out to analyze the effect of supporting pressure and axle feed on plastic wrinkling behavior during hydroforming process. Stress state and stress locus are gotten by numerical simulation, and they are used to analyze the reason of wrinkling behavior. The results show that the absolute value of axial compressive stress can be reduced by increasing the supporting pressure, and the wrinkling tendency declines. The absolute value of axial compressive stress can be raised by increasing the axle feed, and the wrinkling tendency increases. The wrinkles can appear while the supporting pressure reaches a critical value. To avoid wrinkling, the reasonable load path is that the supporting pressure is 30 MPa and the axle feed is 15 mm for a low carbon steel tube with an outer diameter of 89 mm and a wall thickness of 2.5 mm. 

Abstract:To solve the uncertainty reliability problem of a high reliability structure, a separable Monte Carlo (SMC) method based on crude Monte Carlo (CMC) method and Condition expectation (CE) method is proposed. The method uses different sample size of response and capacity, and replaces the distribution function of CE with empirical distribution function of sample of SMC. Practical example of reliability shows that SMC method not only solves the calculation cost, but also improves the calculation precision, it can be applied to uncertainty reliability problem of structures.

Abstract:To insure the safety of autonomous approaching and capturing of a non-cooperative tumbling target in the on-orbit operating missions, 6 DOF dynamics model of relative translation and rotation is established to describe the relative motion of two spacecrafts in close distance, and the perturbation induced coupling and dynamic coupling existing in the model are presented to make clear what the coupling effect is. Due to the effects of time-varying and nonlinear terms in the model, the systemized integrator backstepping controller is derived after multi-step recursion with regard to the nonlinear high-order terms. The stability of the controller is proved to be global asymptotic stable based on the Lyapunov’s stability theory. With the consideration of rotating characteristic of the target satellite, a linear synchronization rotating approach strategy along the maximum inertial axes is presented to ensure the safety during the final approach. The validity of approach strategy and the effectiveness of controller is verified by the numerical simulation.

Abstract:Aiming at the problem of target recognition in image processing,a novel algorithm based on visual perception with better information processing mechanism was proposed for target recognition, in which the hierarchical information processing mechanism of receptive field were simulated and the lateral inhibition mechanism which was used to filter response of neurons was introduced. Firstly, in receptive field of simple cells, the images are initially processed. Secondly, in receptive field of complex cells, stimulation of receptive field from former layer is further feature extracted, and then a new receptive field is obtained. And finally, the neurons which are strongly responded to the stimulation are found out by lateral inhibition mechanism, and their correspondent content can be output as the standard of aerial target recognition, the recognition rate of algorithm is 95.56％. Experimental results show that this novel algorithm has high efficiency, and can achieve a great number of target recognitions with few samples, and the recognition rate is higher than that of edge detection and image segmentation method.

Abstract:This paper addresses the problem of multi-UUV along given spatial paths with a given forward speed profile while holding a desired formation pattern in three-dimensional space. The decentralized controller is proposed to realize the coordinated path tracking of multi-UUV. In the path tracking control problem of a single UUV, we introduce line of sight navigation algorithm to design path tracking controller, making the tracking error converges to zero asymptotically; introduce graph theory to design coordination controller, making the multi-UUV reach consensus under the provisions formation along the position of desired path and speed, reaching coordination between multi-UUV, without affecting the path tracking performance in spatial domain.

Abstract:To solve the trajectory control problem exactly for Autonomous Underwater Vehicle (AUV) under external marine environment disturbance. Robust H∞ controller is proposed for underactuated AUV trajectory tracking system. The three dimensional trajectory controller was decomposed into the horizontal plane and vertical plane. After that, the dynamic models with the influence of linearization errors, uncertainties and external disturbance were proposed in the horizontal plane and vertical plane respectively. Then the heading controller and pitch controller were designed based on the robust H∞ theory. The simulation result shows that the method can overcome outside disturbance of constant ocean current and ensure the precision track, where the tracking error can converge to zero. The robust H∞ controller designed for AUV is effectively and can be applied to the tracking system.

Abstract:A new interleaving method for adaptive frequency hopping system is proposed, which uses the prime code to control information sequence’s order at the transmitter and change the order back at the receiver. The new interleaving method possesses the features of low correlation coefficient, low interleaving latency, small storage capacity and flexible matrix realization, which reaches the relative optimal performance metrics of interleaving. Monte Carlo simulations show that in an adaptive frequency hopping communication system simulation platform the new interleaving method can improve the performance of anti-consecutive errors beyond the error correction capability of channel coding and has the advantages of easy implementation, low interleaving delay and small calculation amount compared with the block interleaving and pseudo-random interleaving on the premise of meeting the specific error rate performance. Moreover, our new interleaving method has a better anti-jamming performance in the adaptive frequency hopping system. The anti-jamming performance of our interleaving method is better than block interleaving and is a bit worse than pseudo-random interleaving method.

Abstract:Click through rate (CTR) on sponsored search ads determines the search engine’s revenue, thus analysis on users’ ads-clicking intent is one of the fundamental work to improve CTR. Based on the search logs provided by a Chinese search engine, this paper presents statistical analysis of ads clicks, and further proposes two methods to predict ads-clicking intent of query, namely query content match based prediction and Bayesian classification, respectively. Experimental results on large scale real data show the improvements from 3.0％ to 36.8％ in precision and from 0.060 to 0.408 in F-measure on sponsored search ads delivery. The proposed methods are capable of predicting the intent of user queries and enhancing the effect of search engine advertising, and are also applicable for online prediction of advertising click intent of user queries.