Abstract:Rendezvous control of spacecraft formation based on cyclic pursuit algorithm is researched. The mathematical model of cyclic pursuit algorithm was established and deduced, and a new control law for spacecraft formation rendezvous was proposed, in which planar cyclic pursuit algorithm and normal proportional derivative method were combined. A rendezvous control for a formation by three spacecrafts adopting linear and nonlinear cyclic pursuit algorithm respectively is simulated. Simulation results show that, the proposed control law based on cyclic pursuit can meet the rendezvous requirement of spacecraft, spacecrafts rendezvous at the reference center determined by their initial position along clockwise trajectories, changing process of relative distance and relative velocity between them is consistent, and consumption of velocity gain is lesser. All this can provide theoretical reference for research of formation control for spacecrafts.

Abstract:A compressible flow heterogeneous parallel solver based on MPI+CUDA on CPU/GPU heterogeneous system was established. Then different parallel computing models and optimizing methods of compressible flow parallel computing algorithm were discussed. This solver runs different codes with difference resources: the codes which are complex or have low computing density are run on CPU, while the codes which are simple or have high computing density are run on GPU. The heterogeneous systems’ computing results and the efficiencies with homogeneous systems were compared through several problems. Finally, the heterogeneous algorithm was applied to the hypersonic flow. The result shows that the algorithm is robust and the computing efficiency is improved ten times more than that of the homogeneous algorithm.

Abstract:The equilibrium condition of hypersonic vehicle during cruise phase is modeled, under which the vehicle can maintain constant speed and altitude. It analyzed the equilibrium conditions that the vehicle can satisfy. Based on the conditions, a guidance law with multiple constraints and terminal course angular constraint is proposed, and the analytic solution is concluded. The method is adaptive since the guidance command is obtained through the analytic expressions in real time. In the end, simulations under different deviations have proved the method is effective.

Abstract:For aircraft navigation in unknown environments, a velocity and height estimation method based on vision/inertial integrated navigation is proposed. An extended inertial navigation state equation was formulated, which contains several aircraft’s positions at latest several imaging times, and a linear vision measurement equation based on two view epipolar geometry constraints was adapted to correct inertial velocity error using a Kalman filter. And then, the coordinates of ground features were estimated by the stereo vision method, which was used to estimate the height of the aircraft. Simulation has been implemented by using the typical cruise trajectory of the aircraft, and the result shows that our method works well for correcting the velocity and height errors, which enables the velocity and height not to drift with time. As a result, it can also suppress the position error of the aircraft.

Abstract:Approaching observation is a new way of space-based inspection. Precisely steering the flight vehicle to the observing point near the target is one of the key technologies. An optimal terminal guidance is presented for the terminal approaching. Firstly, the process of approaching observation is transformed to an optimal control problem by founding equations of relative motion in inertial coordinate systems and performance index which synthesizes the fight time and fuel consuming. Then optimal thrust direction, nozzle working hours, and time-to-go are derived, based on which a scheme of optimal guidance is designed. Finally, simulations are conducted and results demonstrate that the guidance algorithm can meet the requirements of approaching observation mission with the high precision. The study herein also is helpful to deep space exploration, rendezvous and docking.

Abstract:The disturbance, aroused by sun-tracking drive of solar array, has become one of the major barriers for improving the performance of high-precision spacecraft. With the aim to obtain the regular characteristics of this disturbance, the solar array and the drive assembly were considered as a couping system and an electromechanical integration model and a dynamic simulation program are presented based on the major aspects of main driving steps and the Simulink software platform.. The correctness was verified by comparing the experiment results, and the effects of solar array rigid-flexible coupling and the centroid bias to disturbance characteristics were analyzed. The results indicate that the rotation speed fluctuation can activate low order torsion modes of solar array, and disturbance spectrums include both frequency characteristics of motor driving and structure vibration, but torsion vibration has little effect on rotation angle. The centroid bias of solar array can motivate translational-rotational coupling vibration, activate out-of-plane bending modes, change the distribution of disturbance spectrum, and increase the amplitude of disturbance.

Abstract:For the least-square solutions of two positioning models in single-point position, the equivalence proving of position estimation and its precision is given. The basic positioning model and single-difference positioning model were described respectively, then the single-difference positioning model was arranged into three cases, and the least-square solution of each case was proved equal to that of basic positioning model. Finally, the equivalence of the two models was proved by processing the experiment data, and the efficiency of least-square arithmetic for the two models was compared with each other.

Abstract:A novel method based on motion synthesis is proposed for low-thrust trajectory design and optimization. Firstly, the representation of the low-thrust trajectory was obtained by using the motion synthesis technique. In this representation, the equations of motion was decomposed into three independent motions and the analytical expressions of the three motions were deduced separately. Then the approximate analytical expression of the low-thrust trajectory was obtained by synthesizing of the three motions. Secondly, based on this representation, the original problem was converted into a nonlinear programming problem. Finally, the method was applied to three rendezvous missions: from the Earth to the asteroid 1989ML, to the Mars, and to the Venus respectively. It is shown that the transfer orbits satisfy the mission constraints. Numeral results fully validate the availability and the high efficiency of the method.

Abstract:The problem of “burn-coast-burn-coast” deorbit trajectory guidance with finite thrust is studied. The entry interface conditions are transformed into indices of energy and angular momentum, based on which the critical geocentric distance of “burn-coast” deorbit problem is derived and the relationship between entry interface conditions and deorbit strategy is analyzed. Then, the relative changing law of energy and the angular momentum of spacecraft in the burn arc are derived, and the guidance equation is derived by the idea that the energy and angular momentum decrease synchronously in the same relatively rate. According to the entry interface conditions, the trajectory is supposed to be a “burn-coast-burn-coast” style. The first burn needs no guidance, and the direction of the thrust is opposite to the velocity direction. The second burn uses the guidance law. Simulations of different altitude and different entry interface conditions are implemented. The results indicate that the method can effectively solve the deorbit guidance problem that the single “burn-coast” method fails, and the computational effort is not large.

Abstract:Single fiber and fiber bundle tensile strengths of Chinese-made carbon fiber were tested and its average single fiber tensile strength was described by the Weibull statistical method. The carbon fiber reinforced composite core was made by pultrusion process with the Chinese-made carbon fiber. The bending and shearing properties of the composite core were studied. Results show that, compared with the Toray T300 carbon fiber from Japan, domestic carbon fiber has almost the same average single fiber tensile strength, lower discrete property and a little lower average fiber bundle tensile strength. The aggregation property of the domestic carbon fiber is not good enough. Carbon fiber yarns were nipped and fluffed when being drawn out. No significant difference can be found from the mechanical properties of the composite cores made with the domestic carbon fiber and the Toray T700 carbon fiber from Japan.

Abstract:Influence of array errors of azimuth multiple-phase-center (AMPC) synthetic aperture radar (SAR) on signal reconstruction performance is investigated. The array errors were modeled as stochastic process. In combination with least-square (LS) algorithm, the analytical expression of the reconstruction error power spectrum was derived. Then, the analytical expressions of signal to noise ratio (SNR) and azimuth ambiguity to signal ratio (AASR) were obtained. Experiment results confirm the validity of the theoretical analyses. Analytical results indicate that the image quality of AMPC SAR can be improved by decreasing the reconstruction coefficient when the pulse repetition frequency (PRF) increases. The approaches and results are helpful to the system design and the image quality evaluation of AMPC SAR. 

Abstract:The present polling time division duplex (PTDD) ranging hierarchy of GPS inter-satellite links (ISL) demands being optimized for satellite orbit determination. An improved ranging hierarchy named grouping time division duplex (GTDD) is presented. Satellite orbit determination precision based on inter-satellite and satellite-to-station ranges is able to be improved by the novel ranging hierarchy in respect of ISL ranging links increasing by grouping ranging of the whole constellation. Aiming at the optimal satellite orbit determination precision, a two-steps algorithm is presented to optimize the satellite grouping. Firstly, the optimal satellite groupings were obtained to achieve the most inter-satellite ranging links. Secondly, the ranging DOP was made the least in each satellite group. Simulation results show that the satellite orbit determination precision can be improved greatly from the two-steps algorithm.

Abstract:The transmission delay and the number of hops in path are the two main factors which should be considered in designing a routing algorithm for a specific network. The paths generated by different routing strategs are called least delay path (LDP) and least hop path (LHP). In satellite network, the algorithm for LHP is much simpler, but there are limited research achievements for the rationality of LHP. A detailed theoretical analysis, in this research, was made for the differences between LDP and LHP in polar circular LEO satellite network. Based on the results of our analysis, a simplified LHP path selecting strategy with an idea of horizontal transmitting priority (HTP) by using the features of horizontal link length was proposed. The simulation results prove that our path selecting strategy can quickly find out the shortest path among all the LHP between every two nodes. It provides a foundation for the research of routing algorithms in LEO satellite network.

Abstract:Multiple false-target images deception is the thorny point in the jamming against broad-band imaging radars. A jamming approach of applying pulse separation is proposed and the retransmission the usual LFM signal of imaging radar is presented. Combined with the scatter-wave jamming model, the imaging of the jamming signal was expounded, and the ways to achieve a train false-target images along the down-range were analyzed. Based on the divided number and the retransmitted order, the number and the resolution of false-target images were described. Finally, the simulation results are presented and addressed. This work is helpful to the deception jamming against imaging radars.

Abstract:The orbital inclination of 5°coordinate rotation is required in the GEO ephemeris algorithm for users. Aimed at this step, an improved method that the BeiDou GEO satellite position is calculated directly by using the classical broadcast ephemeris algorithm for user was presented, and meanwhile the corresponding broadcast ephemeris fitting algorithm based on the second class of non singularity orbit elements was given. In this method, the classical orbit elements were replaced by the second class of non-singular orbit elements, which solves the problem that the coefficient matrix is non-positive in the process of the classical broadcast ephemeris fitting algorithm because of the small inclination angle. This avoids the orbital inclination of 5°coordinate rotation process, decreases the calculating steps time and enhances the GEO ephemeris algorithmic efficiency. The simulation results show that the accuracy of the improved method is as much as the original algorithm in the satellite orbit fitting process and is reduced slightly in the satellite orbit extrapolation process. But it can still meet the requirement of navigation and position for users. Finally, the validity of the improved algorithm is verified by using orbital data of the actual BeDou GEO broadcast ephemeris. 〖WTHZ〗Key words： 〖WTBZ〗BeiDou satellite navigation system; GEO satellite; broadcast ephemeris fitting; the second class of non singularity orbit elements

Abstract:The cascade channel estimation of Amplify-and-Forward (AF) relay system was dealt with by using Bayesian framework. According to the maximum a posteriori (MAP) and the minimum mean of square error (MMSE) rules, two estimators were derived combining the received training signal with the probability distribution function (PDF) knowledge that cascade channel comprises two independent Rayleigh channels. Due to the intractability of exact Bayesian Cramer-Rao Bound (CRB), alternatively, the approximated Bayesian one was obtained based on the principle of maximum entropy to compare with the CRB of MLE. The numeral simulation demonstrates that the new MAP estimator can bring about significantly improved performance, especially in the low signal-to-noise ratio regime.

Abstract:In stepped-frequency high resolution ISAR imaging radar, target motions produce the range-Doppler coupling which has a serious effect on the ISAR image. Consequently, a novel motion-parameters estimation method based on the image contrast optimization is proposed. Firstly, the effect of radical velocity and acceleration on Doppler profile contrast function was analyzed. Secondly, after constructing phase compensation term, the radical acceleration was estimated by the Doppler profile contrast function. After the radical acceleration compensation, the radical velocity was estimated by the range profile contrast function. Finally, after motion compensation and range-Doppler algorithm, the high resolution ISAR image was obtained. This method has some advantages of high accuracy and fast computation speed. The experimental results demonstrate the effectiveness of the proposed method. 

Abstract:In order to ship model the Shaft-ELFE in shallow sea, the basic simulation unit-time-harmonic horizontal electric dipole was taken for example, the Hertz vector potential was solved based on the uniqueness principle combined with boundary conditions. The electromagnetic field in shallow seawater was derived from the relational expression between Hertz vector potential and electromagnetic field. The electromagnetic field distribution of DC dipole in three media was solved. The simulated results show that the horizontal electric cell can be used to compute the harmonic cell at sufficiently low frequencies between 1Hz and 7Hz. The conclusion was further confirmed in laboratory, utilizing the horizontal electric cell and the horizontal harmonic electric cell source in man made seawater. Finally, the shallow marine environment and horizontal time-harmonic electric dipole were simulated in the laboratory, the electric field distributions of time-harmonic electric dipole and DC dipole were compared. The results show that the time-harmonic electric dipole electric field distribution was consistent with the theoretical calculation, which proved that the derivation and analytical expression are correct; the horizontal time-harmonic current model can be replaced by horizontal DC dipole when the envelop of shaft-ELFE is simulated, and has a higher accuracy and practicability.

Abstract:Variation modeling is one of the most important tools for assembly variation analysis. Considering dimension and geometric precision, and part situation precision, the deviation source that affects assembly accuracy is clustered into two types: deviation of geometric location and orientation, variation of geometric form. And these different types of variation or deviation were unified by Virtual Fixture. So a 3D rigid assembly state space modeling technique was developed for stream of variation analysis (SOVA) in multi-station processes. A missile-cabin-assembly process was analyzed in this model. It enhances the applicability in modeling complex assemblies. The developed methodology outperforms the techniques based on other simulations in computation efficiency. It is more powerful not only in forward analysis of complex assembly systems, but also in backward analysis. The model is validated by using Monte Carloseries simulations.

Abstract:Dual-rotor piston engine (DRPE) is a new type of differential rotary engine, with the pistons moving in a circle rather than linearly. Compared with the conventional engines, the complex valve systems can be omitted, and its power density is higher. In order to study the major performance indicators of DRPE, Matlab/simulink was used to simulate the zero-dimension model of its thermodynamic process. With regard to the characteristics of DRPE’s working process, the differential equations were established. Taking into account various period features, the equations were simplified. The ways to solve the major boundary conditions were found. Values of the mass, pressure and temperate were calculated according to different shaft angles. Then DRPE’s indicated mean effective pressure and power to weight ratio were calculated. Compared with some conventional internal combustion engines, the volume of DRPE’s chamber is used more efficiently, and its integral structure is more compact.

Abstract:According to the insufficiencies of inability to adjust supporting radius and control cutting precision and shape of cutting blade in existing high-speed and dynamic cutting device of bar, the mathematical model between supporting radius, cutting error and cutting parameters such as cutting mode, number of blades and so on were established based on the analysis of cutting principle, and new adjustable support device was designed using slider-crank mechanism. The curvilinear equation between the shape of cutting blade and grinding parameters such as cutting diameter and installing angle of grinding wheel was built by means of homogeneous coordinate transformation, then a new adjustable grinding device was designed. The speed of cutter, cutting error and other parameters were selected as optimization objects, the nonlinear multi-objective optimization of parameters of the two-blade and two-cutting cigarette cutting device was achieved by using the Matlab optimization toolbox. The project of new high-speed and dynamic following cutting device of bar was proposed, and the new device adopts the cut mode of four-blade and two-cutting. It is found that it has better cutting performance and cutting quality when the cutting efficiency is constant, and the device proves possible after simulation.

Abstract:With the development of information technology, the increase of system information brings new problems to the military system effectiveness evaluation. Aiming at nonlinear, high dimension and strong coupling data of system effectiveness analysis, a data yard based system effectiveness evaluation and decision support method was proposed. Data recovery, subtraction, refinement and reconstruction operations were applied to the simulation data processing, then a data yard cube was built up to meet the multiple demands for system analysis of different levels and data dependency were reduced. Taking task-oriented networked fire control system for example, its system effectiveness evaluation, timeliness evaluation and indices analysis were carried out, and practicability and validity of the method were verified in three levels.Applying data mining technology to the simulation system effectiveness evaluation decision-making,makes it get more extensive application.

Abstract:A special uniform circular array (SUCA) was fixed on the underwater monitoring system’s floater system; SUCA’s model was created based on SUCA’s particularity. Then half-power beamwidth and unambiguous condition of SUCA were reseabased by theory of mode-space. Results show that half-power beamwidth and unambiguous condition’s scope of SUCA is wider than UCA, and SUCA is practicable in engineering application.

Abstract:In order to solve the contradiction between high guidance accuracy and fast real-time solving in traditional predictive guidance method, a neural network predictive guidance method is presented, based on the pattern of optimal guidance. The method predicts trajectory based on high believable simulation of kinematic aircraft model, and uses optimization theory to iterative solution of guide variable, so as to generate off-line sample data. By means of choosing multi-modal neural network, training neural network based on dispatching management, to complete the design of the neural network prediction guidance controller. CAV as an example to design, results show that: The method is less real time calculation, fast real-time solution and high guidance accuracy, of which the comprehensive performance is far better than the traditional predictive guidance method.

Abstract:Recently, with the improvement of non-integer order calculus theory, fractional order calculus receives more and more attentions in the application of controlling. Especially, the fractional order PI^λD^μ controlling is applied in many fields. For the traditional PD controller which is usually used in motion control system, a kind of designing and tuning method of PD^μ controller is proposed. Since there is explicit corresponding relation between phase margin and overshoot of the designed system, by designing the rate of change of phase the system’s phase can be made stable around cut off frequency and the influence of open loop gain’s variations on the overshoot can be reduced. Cut-off frequency ω_c and phase margin γ_m given are considered as design specifications in this method. PD^μ’s derivation order μ and derivation coefficient K_d can be derived from system’s phase equation and rate of change equation. Proportional coefficient K_p can be obtained from the magnitude equation on the cut off frequency. Finally, this method is applied to a linear motion control experiment platform. By simulations and experiments comparing with integer order ITAE-optimal method, the effectiveness and excellence of this method is verified. From the results, it can be noticed that the controlling system designed in this method has a good inhibition effect on the overshoot variations caused by the fluctuations of the system parameters on the premise of meeting the design specifications. 

Abstract:Path plan recognition has been a kind of online recognition using positions as inputs. To allow CGF to recognize opponents’paths and destinations in simulation, a recognition framework of Abstract Hidden Markov Model is introduced following analyzing the hierarchy of path plan. Since it is difficult to recognize the path plans using standard model when destinations are changed and plans are executed from top to bottom, the Abstract Hidden Markov Model with Changeable Top-level Policy is proposed. The initial distribution and termination variables of top policy were given and the relations between policy termination variables were adjusted to allow the lower policy for a forced termination. The modified DBN structure was presented, and the approximate inference was realized by deducing processes of updating conditional probability and sampling RB variables as well. Simulation experiments show that different kinds of typical paths in specific environment can be recognized efficiently with this method. The modified model not only confirms good recognition accuracy compared with the standard model under the circumstance when destination is not changing, but also performs well in solving destination changing path plan recognition problems with sufficient observation data provided.

Abstract:Gaussian Process (GP) is characterized by the non-linear property, which leads to too high training time complexity for a large sample, And the hyper-parameters directly affect the prediction accuracy of Gaussian Process. The method of improved GP optimized by the artificial bee colony (ABC) algorithm is proposed to reduce the time complexity and to improve the prediction accuracy. Improved GP constructs the model by selecting a sub-sample of training samples to reduce training time. ABC optimizes the hyper-parameters of improved GP to improve prediction accuracy. Firstly, the improved GPR model is constructed by selecting a sub-sample of training samples; then it is followed by ABC algorithm searching the optimal hyper-parameters of improved GPR; finally the test sample is used to predict and output the prediction accuracy. The model is applied to solve maritime long-range precision sea strike (LPSS) system-of-systems operational effectiveness evaluation issues, and the MATLAB simulation experiments verify the validity of the model compared with other evolutional algorithms.

Abstract:Energy consumption and latency are two major problems that are primarily considered in the design of medium access control (MAC) protocols in wireless sensor networks (WSNs). A new low-latency, energy-efficient and receiver-initiated asynchronous MAC protocol in WSNs is proposed. By precisely predicting the receiver’s wakeup time, THO-MAC protocol can schedule the sender to listen to the channel, such that it can reduce the sender’s energy waste of idle listening. On the other hand, in order to reduce packet delivery latency, THO-MAC protocol chooses the forwarders in the sender’s two-hop forwarders set to minimize the two-hop forwarding latency. The performance of THO-MAC protocol in terms of detailed NS2 simulation is evaluated. The simulation results show that the THO-MAC protocol reduces 35.5% and 18% packet delivery latency, while saving 23.5% and 15.5% sensor energy consumption, compared with RI-MAC and Any-MAC, the two state-of-the-art MAC protocols.

Abstract:With the current access control model, a reasonable unified control over confidentiality, integrity and availability cannot be achieved; especially the dynamic random access request control is far from perfect, not only always leaving some weak points open to possible attacks, but also bringing some unavoidable security problems caused by user errors in practical applications. A kind of confidentiality and integrity access control model based on the pre-authorization mechanisms is put forward. By combining BLP model and Biba model, and introducing the pre-authorization mechanisms, the reasonable control can be achieved over the dynamic random accesses activities. By making use of the condition control, the authority of subject performing the task is monitored timely, and granted or canceled dynamically. So the system’s confidentiality and integrity can both be realized, while guaranteeing its high availability, which is advantageous to the two-way flow of information. Finally, the application example of the model is given and its security is proved. 

Abstract:Aiming at the problem of current scheduling algorithm for multi-core which fails to consider that the nodes on the critical path have a major impact on the ending time of tasks, leading to the delay of the task completion time; a scheduling algorithm based on critical path and task duplication (CPTD) is proposed. Firstly, the fork-nodes were duplicated to change the task graph into products processing tree, then the critical path in the processing tree were found, and the father nodes of the nodes on critical path were made to work at the earliest time. These operations can advance the start time of nodes on critical path. The purpose of the above operation is to shorten the implementation of the mandate of the total time. Theoretical analysis shows that the algorithm can achieve a single task fully parallel processing on multi-core, and also can shorten the completion time of the tasks.

Abstract:As the process of operational support on the antimissile guided missile is complicated, it is very hard to configure and optimize the operational support equipment. The model of configuring and optimizing the operational support equipment was created in this study, based on the requirement of the mission and the character of use support. The model is a NP-hard problem, so the improved particle swarm optimization (PSO) was adopted to solve the problem. In the algorithm proposed, the way of swarm moved was changed from liner mode to non-liner mode so that the algorithm is more efficient. The shift vector representation was first used to code the solution and a new heuristic algorithm to repair the swarm was designed, which makes it simpler to solve the model. Finally, an instance was given and the comparative experiments were designed. The results show that the method proposed can solve the problem of configuring and optimizing the operational support equipment of the antimissile guided missile. Furthermore, it is valuable to solve the other problem of optimizing the resource.

Abstract:The research is focused on the modeling technology of cyber war system. A new idea is proposed for cyber war simulation, based on which an integrated logical evolving network model of cyber war system is proposed. The model regards all of the entities which belong to different forces as components of a whole system, and represents them with verticals of the network, all kinds of interactive behaviors between distinct entities which include the cooperative behaviors, parallel behaviors and confrontational behaviors are represented with edges of the network uniformly. An entity description model based on ontology and a behavior description model based on OO-LAMBDA language are built to describe the verticals and the edges respectively. Finally, a simulation experiment is conducted by using a scenario of a real operation, the results of the experiment validate that our methods are validity and advantage.