Abstract:It is common to use passive isolator to protect the payload from the platform noise in space applications. The design of a passive isolator involves a trade-off between the resonant peak reduction and the high frequency attenuation. Firstly, the equation of motion and transfer function model for single-stage and two-stage connector model was derived, and then the multiobjective optimization model, in which the objective functions are the resonant peak reduction and the high frequency attenuation, was proposed,. Secondly, the multiobjective optimization design method for the design of the passive isolator was proposed, using the multiobjective evolutionary algorithm based on decomposition (MOEA/D). The simulation result shows that the proposed method is effective for the design process of the passive isolator, and can provide multiple candidate solutions for the designer.

Abstract:The electrode is one of the most important components of the pulsed plasma thruster(PPT), which has great influence on PPT performance. In view of this, the upper limitation of PPT efficiency theoretically was analyzed, and the results showed that the upper limitation of PPT efficiency increases by increasing the flare angle or decreasing the end width of electrodes. And then the impulse bit and the mass bit of different PPTs were measured by varying the flare angle and the end width of electrodes. The experimental results indicated that the flare angle has different effects on mass bit of PPTs for different electrode shapes; effects of flare angle on impulse bit are similar to the effects of flare angle on mass bit for corresponding electrode; the specific impulse increases firstly and then decreases with the increase of flare angle; the influence of electrode shape on the performance of PPTs is different at different flare angles.

Abstract:With the centerline Mach-number distributions provided in advance, a two-dimensional supersonic wave-cancelled channel was designed by the Method of Characteristics. The shock train，wall static pressure distributions and separation region were investigated. The relationship between the shock train and back pressure was also investigated. The flow-field had dual solutions when the head of the shock train was in the vicinity of the channel inflection. When the flow evolved into the single-solution domain from the dual-solution domain，the larger separated zone transferred quickly and the shock-train structure evolved fast.

Abstract:An anti-rendezvous evasion maneuver method is proposed in order to escape from the spacecraft that has autonomous approaching ability. Supposing that a two impulse C-W navigation strategy is used by the approaching spacecraft, first a bearing-only relative navigation model is built. Then, a definition of degree of observability based on state estimation error is proposed so as to quantify observability. By using the degree of observability conception, the evasion maneuver direction is chosen as its gradient, which guarantees that every unit impulse can reduce the system observability mostly. Finally, the numerical simulation is conducted with different maneuver impulse, and the result shows that the method proposed can attenuate the system observability obviously. The method offers a new viewpoint for evasion maneuver research.

Abstract:The test range for launch vehicle is intended for certain launch missions, while land, sea area and airspace are all included. The safety issues of test range are complicated and involve many factors. Before rockets' entry to the outer space, it is forbidden to cross foreign territory or the safety distance have to be guaranteed to the boundary. In addition, falling zones for the re entry are prohibited from being in the foreign region. In China, with the restriction of territory and to meet the requirements of intercontinental rockets’ full-range flight test, particular trajectory schemes are selected, such as “low trajectory”, “high trajectory”, to substitute full range flights. Based on the description of the features of those two trajectories, the range control for rocket flight test was analyzed, focusing on taking suborbital vehicles as payloads, including re-entry and penetration. Based upon suborbital flight inside China's territory, the manners for test range safety control are studied. For the low trajectory flight, controlling the angular velocity of the pitch program is a useful manner of range control. For the high trajectory flight, controlling the angle of the pitch program is a useful manner of range control.

Abstract:For a launch vehicle in erect status, an earthquake may bring severe consequence, such as the toppling failure of the launch vehicle. To ensure the safety of a launch vehicle during earthquake, analysis of earthquake time history response was executed. The distributions of peak moment and peak displacement in longitudinal direction of the launch vehicle were derived. Frequency-domain characteristic of moment response in key positions were researched. Seismic-relieving design was performed on the launch vehicle. Seismic response's influence disciplines of link stiffness between rocket and launcher, stiffness of isolation bearing were analyzed. The results show that: (1) the maximum of moment response occurs in tail of the launch vehicle, and the maximum of displacement response occurs in front of the launch vehicle; (2) the seismic response can be reduced significantly by changing link stiffness between rocket and launcher or equipping the launcher with isolation bearing.

Abstract:Aiming at the reentry guidance of hypersonic gliding vehicle considering multi-constraints, the research proposes an improved predictor-corrector guidance law, which is based on model predictive static programming(MPSP). The initial value generator was founded by using the rapid generation of three dimensional trajectory, which solves the MPSP problem of providing guess history difficultly and refreshing nominal trajectory for the initial perturbation. The kinematic model of the hypersonic gliding vehicle was built based on energy, and the predictor-corrector guidance based on MPSP was deduced. The influence factors from the initial decent phase to the gliding phase were investigated. The digital simulation was carried out in gliding phase considering perturbations of the initial values and aerodynamic parameters. The results turn out that the improved MPSP predictor corrector method have the advantages of precise initial guess values, computational efficiency and strong robustness to the perturbations.

Abstract:Through numerically simulating the hypersonic reentry flow with ablation of carbon-phenolic heat-shield, the effects of ablation and pyrolysis on the thermochemical properties and electron densities of the flowfield were analyzed. 19 chemical species were considered and a two-temperature model was taken to describe the thermal nonequilibrium. The Navier-Stokes equations of thermochemical nonequilibrium flow coupled with the ablating boundary condition were solved to obtain the steady-state solution of the flowfiled. The effects of ablation were shown in comparison with the non-ablating baseline case, which has a non-reacting, non-catalytic wall and equilibrium radiation wall temperature. The method to determine surface chemical composition of the pyrolysis gas was discussed, and the effects of the pyrolysis ratio were investigated. The simulation and analysis performed on RAM-C model at flight speed of 7.65km/s and altitude of 61km or 71km show that, the dominant ablation and pyrolysis species are CO, H₂ and H, and both the ablation species and the effects of ablation are limited to the boundary layer. The mass fractions of atoms and ions decline as a result of ablation and this may result in the decrease of the peak values of electron density when they appear in the boundary layer. Furthermore, the ablation effects become more pronounced as the pyrolysis ratio rises, and the effects extend further into the flowfield with increasing distance from the stagnation point or with higher flight altitude.

Abstract:Since many target characteristics can be extracted from the echoes by wideband inverse synthetic aperture radar (ISAR), the jamming signal on ISAR need to simulate the electromagnetic scattering characteristics and kinematics characteristics with high fidelity. According to the electromagnetic scattering mechanism of missile target, the generation process of jamming signal was analyzed and a scheme for two-dimensional imaging jamming was proposed. Concerning the false target characteristic simulation issues, an algorithm was presented, using high range resolution profile (HRRP) template to synthesize a deception jamming signal via convolution operation with actual ISAR signal. By multiple pulses simulations, the obtained jamming signal is capable of simulating the electromagnetic and kinematic characteristics accurately. In numerical experiments, the imaging results were compared by using dark room measurements and HRRP template data, and it verified the effectiveness of the proposed algorithm, which has guiding significance for the engineering design of two-dimensional imaging jammer.

Abstract:For the navigation signal spoofing signal transmitted with single antenna, a spoofing detection technology based on multi-antenna carrier phase double difference was stuied. Three-antenna array, in which not all antennas are placed in direct line, was proved to be the minimum antenna array which can solve the navigation signal arrival angle without ambiguity. Based on the corresponding antenna array, a method for constructing spoofing test statistic based on multi-antenna carrier phase double difference was proposed, and the detection performance analyzing method was presented. Then, the minimum detection threshold was defined for limiting the decrease of the detection performance. Finally, detection performance of the proposed detection method was simulated by Monte Carlo method, and the results validate the correctness of theory analysis.

Abstract:In satellite navigation channel simulator, the traditional pseudo-range Doppler simulation method has some flaws, such as the low delay accuracy and the large filter resource. A new Doppler simulation method is proposed, using Lagrange interpolation variable fraction delay filter and Farrow structure. Based on analyzing the system architecture of channel simulator, the model of Doppler simulation was established, including the delay calculation module and variable delay filter. Compared with the multi-rate sampling digital delay filter method, the proposed method is just about 0.2% of the former filter resource, and the one parameter is just changed when the delay of filter is changed. Actual measured results with channel simulator indicate that the Doppler accuracy is 0.1 mHz.

Abstract:The statistical properties of mobile cascade channel in amplify-and-forward (AF) two-way relay networks (TWRN) is focused on. Based on the statistical properties of double Gaussian, the mobile cascade channel is divided into transmission and interference processes. In addition, the probability distribution functions (PDF), temporal auto-correlation functions (ACF) and Doppler spectrums of the two processes are derived, respectively. Furthermore, by approximating the PDFs of the cascade channel by the concise Gamma distributions, closed-form and approximated expressions of two critical temporal merits, level-crossing rate (LCR) and average duration of fades (ADF), are provided. Numerical simulation demonstrates the validity of the proposed expressions. 

Abstract:For the parameters estimation of synthetic aperture radar (SAR) raw data, the estimation of Doppler rate is robust with the advantage of high estimation precision and less dependence upon situations. Thus it is widely employed in the autofocus correction. Based on the estimation of Doppler rate, two different error extraction models for the range migration and phase are proposed, respectively. The three dimension (3-D) motion errors are removed by correcting the residual range cell migration and compensating the phase errors, respectively. Real SAR data test shows that the proposed method is feasible to generate high resolution SAR image with only low-accuracy navigation information.

Abstract:According to the IRIG-106 telemetry standard, FQPSK-JR and SOQPSK-TG are two interchangeable signals, which have almost the same power efficiency and bandwidth efficiency. The two signals can be demodulated by the universal receiver of OQPSK. The optimal performance degradation of the symbol by symbol demodulation based on the OQPSK structure can reach 2dB while its optimal demodulation may ignore the two signals' characteristics of memory. The 2dB power loss is crucial in the telemetry link for the limit of equipment size and power. The optimum receivers based on their modulation schemes can improve the power efficiency, but the different system of signal generating will lead to different structure of corresponding optimal receiver. In this research, the FQPSK-JR signal in IRIG-106 standard was approximated by CPM modulation, the SOQPSK-TG signal was truncated for an approximate analysis. The result of simulation showed that the signals demodulated by the CPM-based demodulator and by the OQPSK-based demodulator display the same function of little with incremental loss, and demand no need to do signals recognition. In addition, the implementation complexity was also taken into account.

Abstract:Named Entity Recognition (NER) is a basic task in information extraction, and it is an important research direction in this domain to use the abundant unlabeled corpus to improve the performance of NER system. An approach combining self-training with active learning based on CRF (SACRF) is proposed. It selected samples by setting the threshold of confidence and 2-Gram frequency, and expanded the training set by annotating the unlabeled corpus manually and automatically. The experiments revealed that this approach can not only improve the precision and recall of NER system, but also reduce the manually annotation efforts greatly. 

Abstract:DS-CDMA developed on spread spectrum is a multiple access technology, but it is difficult for such a system to attain a satisfactory performance under overloading conditions. A sparse DS-CDMA system is presented. It is possible to represent the relationship between the chips and the users using a low density Tanner graph. By doing so, each user is only connected to limited non-zero chips, which can minimize the multiuser interference. According to graph theory, a belief propagation algorithm, which is suitable to the case of low density graph, was adopted by the sparse DS-CDMA to perform multiuser detection. Thus the negative effect of channel noisy and interference can be eliminated. Computer simulation was done. The theory analysis and simulation results showed that the sparse DS-CDMA can achieve excellent performance even under serious overloading conditions.

Abstract:Traditional synthetic aperture radar uses wideband signal to achieve range resolution, and uses one-dimensional synthetic aperture to achieve azimuth resolution, thereby forming a two-dimensional image. In the cases of short range imaging, a very high imaging resolution may be required, and it is difficult to achieve such high resolution using signal bandwidth. A two-dimensional synthetic aperture imaging system is proposed; it uses the two-dimensional synthetic aperture to achieve two-dimensional resolution. The resolution depends on the length of the synthetic aperture, and it is no longer limited by the signal bandwidth and can obtain ultra-high resolution. The transmitted signal is single frequency waveform, thus the system can be very simple. The imaging algorithm for the single frequency two-dimensional synthetic aperture imaging system was derived in detail. Simulation results showed that the single frequency two-dimensional synthetic aperture imaging system is an effective technique for high resolution imaging.

Abstract:The research demonstrations on the implementation of the future CSGM satellite gravity mission in China were carried out, based on the preferable selection of satellite tracking modes, the optimal combination of key payloads, the preferred design of orbital parameters, the beforehand execution of simulated studies, and the optimum improvement of gravity recovery methods. Firstly, the Satellite-to-Satellite Tracking in the High-Low/Low-Low mode (SST-HL/LL) was used in the future CSGM satellite gravity mission due to the high-accuracy measurement of the Earth's gravitational field, the lower technical requirements and the successful experiences of the current twin GRACE satellites. Secondly, the space-borne instruments consisting of the interferometric laser intersatellite ranging system, the compound GPS receiver, the drag-free system, the center of mass trim assembly, etc. were developed in advance. Thirdly, the orbital altitude of 300～400 km and the intersatellite range of 100±50 km were designed in the unmeasurable area of the existing gravity satellites. Fourthly, the simulation techniques were applied to the holistic processes of the development and operation for CSGM, including scheme demonstration, system design, parts development, production test, practical application and malfunction analysis. Fifthly, the advantages and disadvantages of the satellite orbital perturbation, dynamic, energy conservation and semi-analytic methods were contrastively analyzed, and the new-type, high precision, high-efficiency and full-frequency satellite gravity recovery methods were investigated. Finally, the expected scientific objectives of the future CSGM satellite gravity mission showed that the cumulative geoid height error is 1～5 cm and the cumulative gravity anomaly error is 1～5 mGal at degree 300.

Abstract:Multi-sensor images matching method based on multi-area histogram of oriented gradient is proposed. Firstly, the images were segmented into some sub-areas. Secondly, histogram of oriented gradient was calculated for every subregion. Then, the histograms similarity was computed with convergence degree as power. In the end, through two-step searching, the histogram with the highest similarity was found and the corresponding image was the matching result. The algorithm was tested using emulational images and real multi-sensor images. Experimental results showed that the new matching algorithm can match multi-sensor images effectively and efficiently. 

Abstract:A visualization method based on dynamic topological graph specific to satellite networks changing over time is proposed. The challenge of dynamical topological graph visualization lies in how to preserve the dynamic stability during visualization process and facilitate the perception of dynamic change of networks for users. Firstly, a continuous dynamical topological graph model was built, based on the analysis of dynamic characteristic of satellite networks. Then, a strategy for preserving dynamic stability of layout was designed and a dynamical topological graph layout algorithm was proposed, based on force-directed. Finally, the Iridium system was taken as a representative instance and the rationality and feasibility of our approach was validated. The experiment illustrated that the visualization results of our approach effectively supports the perception and understanding of dynamic topological of satellite networks.

Abstract:The dimension condition of multilayer cylinder sapphire-loaded-cavity resonator to meet the requirement of Bragg mode was analyzed. The single layer cavity was simulated and designed and the Teflon support was used to fix the sapphire in the inner-silver-plated cavity. A test showed that the Bragg mode is realized at 9.7GHz and the quality value is greater than 200,000. The Bragg mode is being used as band pass filter to build X band oscillator, which includes low noise amplify, filter and mechanical phase shifter. The oscillator realized stabilization by choosing proper insert loss and adjusting phase shifter. A secibd test showed that the oscillator has low phase noise output and is vulnerable to environment temperature. As ultra high quality value sapphire resonator is being used, the oscillator has the potential to be the state-of-art X band frequency standard with lowest phase noise at room temperature.

Abstract:1/f noise is one of the main noise sources of giant magnetoresistance (GMR) and magnetic tunnel junction (MTJ), which can cause intrinsic detection limit at low frequency. Based on this fact, a sort of magnetic field sensor using microelectromechanical system (MEMS) flux concentrator and flux vertical motion modulation is proposed. The frequency of the measurement magnetic field was shifted from low to kHz ranges, which realized the translation of measurement magnetic field from DC to AC, thus 1/f noise of magnetoresistance element was mitigated. A prototype sensor was fabricated using multi-layered GMR element AA002, and the test was done. The results showed that the modulation efficiency achieves the levle of 19.3%, which exceeds the efficiency of most existing sensors with other modulation schemes, and the low frequency magnetic detection ability is improved to 120pT/√Hz, which is enhanced by 40 times compared with that of the GMR element AA002.

Abstract:CFD-DEM model was used to simulate the gas-solid flow in dilute pneumatic conveying with bends. In CFD-DEM, the discrete particle phase was obtained by Discrete Element Method (DEM), and the flow of continuum gas phase was determined by Computational Fluid Dynamics (CFD). In order to consume less simulation time, the effect of the particle solid fraction on the gas phase was not taken into account. The results showed the particle rope formation in the bend and its dispersion in the vertical pipe, and obtained the particle-particle and particle-wall collision information. Comparison of the collision information in the bend, the collision and abrasion seemed more intensive at the bottom of the bend. It was also found that the geometry and parameters have different magnitude effects on the gas-solid flow and collisions in the pipe. The gas velocity was considered to be limited influence on the rope dispersion, but significant effect on the collisions in bend section. With the increase of the solid mass flow, the particle rope seemed stronger and more dispersed at a low rate, and there was a shield formed to impede particle-wall collision at the bend section. The increase of the bend radius ratio also made the particle rope stronger, and the dispersion rate lower.

Abstract:To deal with the lack of information for coordinate measurement of three-dimensional model and the difficulty of quality evaluation of task-specific coordinate measuring results, the computer aided design method for coordinate measuring technology based on the secondary development of CATIA system was presented, according to the new gengration Geometrical Product Specifications (GPS). The XML data structure for integration of CAD and CMM was designed. The extended data model used UML technology for coordinate measurement was established. The scripted description of measurement process meeting the requirements of new generation of GPS was achieved. Some algorithms for measurement data processing were developed. And method and process of measurement uncertainty evaluation based on Monte Carlo simulation were proposed. Based on the above methods, the special software for three dimensional CAD-based computer aided design and assessment was developed and applied in pose measurement for assembly of aircraft parts. The results indicated that the measurement plan generated by the special software meets the requirements of part docking in aircraft flexible assembly, thus the effectiveness of the method was verified. 

Abstract:Based on Virtual Model Control method, the control laws of the single leg for stance phase and swing phase were obtained from the single leg Jacobian of the quadruped robot. In order to realize the full body control, a decomposed method was proposed, which decomposes the body control objectives of the quadruped robot into each standing leg control. The virtual components of each standing leg were set up, and the virtual forces were transformed into desired joint torques to achieve the virtual model control for standing leg. The swing foot trajectories were planned in real time and the virtual components were used to connect the swing foot and the planned trajectories, so that the virtual model control for swing leg was realized. Based on the switching rule of the leg phase sequence, simulations about velocity control and disturbance rejection were studied with a planar quadruped model using trotting gait. The simulation results verified that the proposed control method is effective in height, speed and pitch angle control of the body, can achieve dynamic control of the quadrupedal trotting locomotion, and is robust for disturbance rejection.

Abstract:The configuration and control system of a linear long stroke and high frequency fast axis servo (FAS) is developed for the production of asymmetric optics. The maximum stroke of the FAS is 30mm. The proposed Fast Axis Servo (FAS) utilizes the aerostatic bearings driven by a voice coil actuator, a custom linear current amplifier, a high-resolution encoder and a high-speed control system. The static and dynamic characteristic of air slide with different cross-sectional shapes was studied by the finite element method. A control strategy consists of a proportional, integral and derivative (PID) feedback controller and velocity/acceleration feed forward controller was implemented to accommodate the changed system dynamics. The 0.1mm step response was applied on the FAS, the rise time is 2ms, the over shoot is 0.4%, the settling time is 4ms. An aluminum part with the super precision cutting has a surface finish value 24nm Ra. The experiment results indicate that the FAS displays satisfactory dynamic and cutting performance.

Abstract:It is generally acknowledged that the sound pressure level (SPL) of air-modulated speaker (AMS) will finally reach the level of saturation when the chamber pressure increases to a certain degree. As a new approach to obtain higher SPL output, supersonic flow modulation was discussed in which the flow speed of nozzle exit was increased from sonic to supersonic. Results from the quasi-steady theory proved that, when the chamber pressure is high, the SPL in the supersonic case is higher than that in the sonic case. Larger SPL increments generally appear at smaller nozzle area ratio. The improvement of the source intensity was validated by the comparison of sound measurements between the sonic and supersonic cases in low frequency modulation. But in high frequency modulation, due to the transient flow effect, the SPL in the supersonic case is the same as that in the sonic case while the air jet is considered to be not fully developed or sped up to be supersonic.

Abstract:Aimed at the problem of detecting and characterizing community structure is one of the outstanding issues in the study of complex network, a new community detect algorithm based on Force-directed model was proposed, which categorizes the point to community decided by the force between them. An algorithm named Force-Directed Community Detect, FDCD, and an implementing algorithm using four different Force-directed Models were designed. The experiments show that the algorithms can find community in real social network with high Q Modularity, and each efficiency of algorithm based on LL model reaches the complexity degree of linear computation, which proves fit for the community detection in large network.

Abstract:There are many news events reported daily on the Internet. An innovative method is proposed to mine event-relations between news. Following an adjacent term-combining strategy, this method primarily utilized a so-called term frequency & inverse event frequency (TF-IEF) model to extract key phrases from the corresponding reports set as to a particular event. Then term co-occurrence windows were employed to calculate the associating degree of every single term pair. This degree is indicative in building event key phrase-networks. Further, two matters were correlated to shape the event relation-network model: (I) common key phrases as mediators within event key phrase-network, and (II) the degree of commonness of key phrases within different observed events. An experiment was conducted to examine the performance of proposed method. The results show that the method can accurately extract key phrases and comprehensively mine associations between events.

Abstract:A research on the temporal preference in course-of-action planning is presented, focusing on the scheme to implement planning with inconsistent temporal preference. The difficulties and innovations lie in two aspects. Firstly, considering the representation issue, a unified binary format is established for temporal preference and temporal constraints. Secondly, argumentation is utilized to develop a deduction framework in order to sort out the conflicts inside the constraint/preference set, achieving a subset of constraints/preferences with maximum consistence. A plan generation strategy was then proposed to acquire segments of plan via mapping, and to combine the segments into a complete plan. A case study was done in detail to show the effectiveness of the scheme.

Abstract:This paper describes JavaKBB, an expert systems tool, is described and the central idea of the project is to make an easy-to-use and easy-to-extend tool for building practical expert systems. It can simultaneously represent conceptual knowledge and procedural knowledge of domain; which can run on commercial operating systems such as Windows along with military domestic operating systems such as NeoKylin. This study presents a knowledge representation model of integrating frame with production rule, which defines five levels of abstraction in order to design an expert system, including knowledge primitives, knowledge units, knowledge elements, knowledge base and knowledge systems. Based on this model, JavaKBB was designed and implemented with Java language. Another important feature of JavaKBB is its capability of saving knowledge bases in XML format, thus making them potentially easy to interoperate with other knowledge bases on the Internet. Currently, JavaKBB has been used to build the Chronic Hepatitis Prophylaxis and Treatment Expert System and the Equipment Decision Support System.

Abstract:Based on the notion of duality in convex optimization, a novel online learning algorithmic framework with forgetting property is proposed. The Fenchel conjugate of hinge functions is a key to transfer the basic learning problem from batch to online. New online learning algorithms were derived by different dual ascending procedures: (1) gradient ascent; (2) greedy ascent. Earlier researches were reviewed. Detailed experiments on synthetic and real-world datasets verified the effectiveness of the approaches. An important conclusion is that our derived online learning algorithms can handle the settings where the target hypothesis is not fixed but drifts with the sequence of examples, which paves a way to the design and analysis of online learning algorithms.