Abstract:Rapid actuation is needed to avoid singularity state in the single-gimbal control moment gyros (SGCMG) steering logic. It consumes significant energy and produces danger for system. A novel control method for attitude maneuver combined trajectory and feedback control is proposed. Firstly, to avoid the singularity state, the pseudospectral method was used to solve the energy optimization issue. Then optimal solution of control acted as reference input, and feedback control method based on the system's limit state was used to consider the effect of uncertainty and disturbances. Feedback control predicted the state based on the numerical integration of reference input, and the error was based on the comparison of the designed state and the predicted state. Numerical simulation was carried out to verify the feasibility of the proposed method, which shows that it can avoid the singularity state, and is valid to overcome the error of the initial velocity of satellite and gimbal angular of SGCMGs. 

Abstract:Control Momentum Gyroscopes Assisting Maneuver (CMGs AM) technique, a new large-angle space station attitude maneuver technique concept, is proposed, which employs both the Control Moment Gyroscopes (CMGs) and the thruster Reaction Control System (RCS) as the actuator. The fuel- optimal control problem of CMGs AM is formulated. With a two-step solving strategy, which utilizes an improved pseudo spectral knotting method, the fuel-optimal solution was obtained, and the results were compared with the fuel-optimal solution and constant-rate eigenaxis maneuver of thrust maneuver technique. It is shown that the CMGs AM technique inherits and further enhances the advantages of thruster maneuver and Zero Propellant Maneuver (ZPM) techniques. It significantly saves more fuel than the thrust maneuver and shortens the maneuver time greatly with greater robustness in comparison with ZPM.

Abstract:The Earth gravity field can be measured with high precision by constructing the purely gravitational orbit of the inner-satellite in Inner- formation Flying System (IFS), which offers a new way to carry out gravity satellite measurement without accelerometers. Since it is difficult to analytically evaluate gravity field measurement performance by IFS, numerical simulation for gravity field measurement was done based on MATLAB parallel programs, and the highest degree of recovered gravity field model and the corresponding geoid and gravity anomaly errors were obtained. Under the condition that IFS orbit altitude is 300km, non gravitational interference on the inner-satellite is 1.0×10^-10m/s², the outer-satellite orbit determination error is 3cm and the measurement error of relative position between the inner- satellite and outer-satellite is 1mm, the highest degree of recovered gravity field model is 72, the corresponding geoid cumulative error is 44cm, and the corresponding gravity anomaly cumulative error is 4.5mGal. It is known that the effective frequency band of gravity field measurement by IFS is at the lower degree.

Abstract:Thermal propulsion system includes solar thermal propulsion and nuclear thermal propulsion, and it is a significant issue to improve the heat transfer efficiency of the thermal thruster. Based on the fluid-solid coupled heat transfer, this study utilized the platelet heat transfer characteristics to simulate the heat transfer and flow field of the platelet passage. A coupled system included both the coupled flow and the heat transfer between fluid and solid parts, in addition to the coupled heat transfer among solid parts. Simulation result shows that the fluid-solid coupled method can solve the steady heat transfer in the platelet structure, and the propellant can be heated to the design temperature of 2300K for the thermal propulsion system. 

Abstract:The pulsar profile, which is the key measurements of the pulsar navigation, is an important physical property of the pulsar. For in-depth study of the theoretical properties of the pulsar profile, the mathematical models of the standard pulsar profile and of the observed pulsar profile were established. The Crab Nebula profile function was fitted using the exponential function and the crab nebula standard pulsar profile was simulated using the profile function. Through the simulation of non-homogeneous Poisson random shooting experiment, the value of the photons TOA (time of arrival) was obtained, and the observed pulsar profile of the Crab Nebula was simulated. The simulation results show that the model can well describe the pulsar profile of the sky survey. The observed pulsar profile which was comprised of the profile and the noise was denoised based on wavelet threshold denoising method. Compared with the wavelet thresholding denoising method, through the numerical analysis, the GCV has a better denoising effect for the observed pulsar profiles.

Abstract:In order to satisfy the demand of ground tests of ramjet, a kerosene heater based on gas heating was designed, and tests were taken to do research on the influence of several factors on the operation performance. The results indicate that the kerosene heater has a strong ability of heating, less responding time, and it can produce supercritical/cracked kerosene online; the main factors that influence operation performance of kerosene heater are temperature, mass flow rate of gas, and mass flow rate of kerosene. The kerosene heater can accommodate temperature of kerosene in a large range through control of temperature and mass flow rate of gas. Then it can satisfy demand of different status of ramjet ground tests.

Abstract:The gas generator is the key equipment of scramjet ground test system. A kind of air/kerosene/water gas generator was designed in order to improve the system security and economy. A series of ignition performances experiments were conducted in the fuel-rich condition with the gas generator. The experimental results indicate that: the lower limit of excess oxidizer coefficient for reliable ignition was 0.51 with the gas generator. The injection of water, which lowered the flame propagation speed and reduced the chemical reaction rate, would make it difficult to ignite and stabilize the flame. The ignition reliability could be improved by increasing excess oxidizer coefficient. Simultaneously, the injection of water would easily cause combustion instability. Low frequency combustion instability can be damped by increasing excess oxidizer coefficient.

Abstract:The attitude control problem of a satellite using small thrusters was investigated. With a simulation example, the drawbacks of control method using slantwise on-off switching line proposed in the relevant reference were discussed. A necessary and sufficient condition for an ideal limit circle was deduced theoretically in the case that the desired attitude precision and the parameters of thrusters and slantwise on-off switching line were known previously. Analysis on the case that the ideal limit circle cannot be formed was also conducted. Based on these analyses, a new control method called "Modified Limit Circle Control" was proposed as well as its design procedure. This study can provide meaningful reference for some relevant engineering applications.

Abstract:Due to the affine least squares matching method is unable to select the matching window adaptively without the initial parameter, an adaptive window least squares matching method based on local shape estimation was proposed. First, LOG (Laplacian of Gaussian)detector was used to detect feature points and characteristic scale; second, the second-order moment matrix in the neighborhood of feature points according to the characteristic scale was calculated; finally, the local shape estimation was applied to the adaptive selection of the initial matching window for affine iterative least squares method. The experiment results show that, the method can accurately select effective matching area under the larger affine deformation, avoiding iterative convergence problem caused by the window content differences. 

Abstract:The quality of F track has a critical influence on the safety and comfort of low speed maglev transportation. Therefore, track geometry must be measured termly. And Appropriate maintenance of F track will be carried out according as the measurement results to keep track all right. In order to maintain maglev guideway efficiently, FMS01 is a F track geometry measurement system made by National Univ. of Defense Technology and the first one in China, and it can be operated to measure track geometry fast and accurately, including vertical deviation, lateral deviation, track gauge and level difference when maglev train travel at 20-100km/h. Vertical and lateral deviation can be measured based on inertial principle. The measurements of the 1.5km long line in Tangshan was carried out using FMS01.The experimental results show that maximum error of vertical deviation is less than ±0.7 mm in reference to fine measurement using level gauge and maximum error of track geometries is less than ±0.2 mm in reference to the average of measurements using FMS01.

Abstract:A two-body rolling wave energy conversion system (WECS) is proposed. The system utilizes the rolling difference between the upper buoy and the lower one. On the basis of the lower buoy’s stability, the rolling of the upper buoy determines the wave energy absorption. The buoy's rolling is determined by its natural frequency, which is mainly affected by the G.C position arrangement. Therefore, numerical simulation is applied. A box-shaped buoy is selected as the upper buoy, and the system working in long crest wave with ten conditions is analyzed, in order to find out how the G.C position arrangement influences the wave energy absorption and the PTO damping selection. The results show that G.C position arrangement does affect the wave energy absorption by changing the natural frequency, and a lower G.C. position can enlarge the frequency range, and can absorb more wave energy.

Abstract:To solve the satellite observation planning problem for emergency tasks with timing limits, the process of satellite observation is analyzed, and a whole cycle mission planning model on satellite observation is proposed. The model integrates four phases of satellite observation, to satisfy the timing limits of satellite observation missions in emergency. A heuristic algorithm was suggested to solve the model, and an optimization adjustment strategy based on conflict queue was also proposed. Simulation results show that the model and algorithm are feasible for mission planning of satellite observation, and improving the mission accomplishment ratio of independent mission planning for each phase.

Abstract:An edge point matching method of SAR image based on the joint similarity is presented. First, the matching similarity criterion and the joint similarity——SSJF(Square Summation Joint Feature) were constructed, based on the grad and direction of each edge point in images. Next, a modified ROEWA edge detector was proposed to get the edge intensity and edge direction with the eight directional templates. Then, parameters of the transform model between the matching SAR images were calculated with the modified GA, which is used to obtain the global optimum solution of the similarity. Finally, the performance of the method was validated with SAR image registration experiments.

Abstract:A ground moving target indication (GMTI) method for spaceborne high resolution wide swath (HRWS) synthetic aperture radar (SAR) systems is presented. First, the space time adaptive processing was adopted for clutter suppression followed by the traditional SAR imaging which yields the ambiguous images. Then all the moving targets including the real one and ghost ones were detected by the CFAR technique, and the real one was distinguished from all the imaging targets based on the space relationship of the ambiguous images. Finally, the moving velocity was obtained according to the azimuth position shift, which could be deduced from the range history of the moving target. The advantages of the method are its low computational burden and high accuracy. The spaceborne simulation data confirms its validity.

Abstract:Due to the restriction characteristics of maritime target movement and formation, point sets matching between the bound formation and the detected one by terminal guidance has become an effective approach in selecting the predetermined target.. But the jamming existing within formation can cause the formation structure to change partially, which results in deterioration of the target selection performance. Based on the target selection need for anti-ship missile, the factors causing the position point sets to be differently distorted are analyzed, which mainly contain the navigation and detection errors of sensor, the bound information error, the formation targets motion and the released jamming. Subsequently, through effectively using the uncontaminated structure information, a predetermined target selection method for maritime formation that integrates geometric hashing and structure weighted mean Hausdorff distance was presented. Theoretical analyses and experimental results show that the method is not affected by the sensor navigation error and formations unitary movement; moreover, this method can effectively improve the target selection capability when there exist dilute jammings.

Abstract:The problem of joint designing the base station (BS) precoder, the relay precoder and user equalizers for TDD MIMO amplifying-and-forwarding relay downlink systems is considered. In practical applications, the channel estimation error and the channel reciprocity delay can result in a serious performance loss of a joint designing based on ideal Channel State Information (CSI). Evolved from the distribution of estimation error and the temporal correlation of reciprocity delay, a joint “estimation error-reciprocity delay” channel model that takes both effects into account was established. Based on this model, a channel SVD-based precoding scheme at BS aiming at the first hop transmission was presented, which avoids the feedback overhead of the second hop CSI. Then a joint optimization problem of the relay precoder and user equalizers, which is based on minimizing the sum mean square error (SMSE) of all users with a constraint on the relay total transmit power, was set up. By using KKT (Karush-Kuhn-Tucker) conditions, a closed-form solution to this problem was achieved. Numerical results verify the robustness and effectiveness of the proposed scheme. 

Abstract:To supply accurate stand time signal, timing receivers were used to acquire high precision time by processing satellite navigation signals. A re-radiating spoofing technique was proposed, which dealt with the target receiver's timing uncertainty by controlling the signal delays and positioning antenna precisely. Once the timing receiver was controlled by the spoofing signals, the host system could be collapsed. Simulation results validate the effectiveness of the proposed spoofing technique.

Abstract:Independent and autonomous running of the entire GNSS system in navigation warfare is one of the most important aims of building inter- satellite links. However, it is inevitable that inter-satellite links will be faced with the threats from jams in navigation warfare, which may result in performance declining, or even breaking down. Therefore, exact evaluation of anti-jamming performance is very important. Ant- jamming performance evaluation of inter-satellite links system is much more difficult than other objects, as it is related to almost every aspect of the system, such as the design of signal system, network, linking strategy, equipment performance, and so on. In order to accurately evaluate the anti-interference performance of the entire inter-satellite links network under the conditions of navigation warfare, this study firstly analyzed a variety of factors which affect the anti-jamming performance of inter-satellite links. On this basis, test scenarios for anti-jamming performance evaluation was modeled and designed. And then an evaluation method for anti-jamming performance of inter-satellite links system based on average availability was proposed, and the index system for availability evaluation was defined, which made accurate and quantitative evaluation of anti-jamming performance of the entire inter-satellite links network possible.

Abstract:The signal generator with DDS-PLL Hybrid structure possesses the advantages of wide bandwidth and high frequency resolution. There are also some drawbacks, such as the serious spurious and harmonics, the increasing of difficulties in design and realization due to the zero phase error tracking of the linearity frequency modulation (LFM) signal, the long acquisition time, and the limitation to frequency modulation (FM) rate. A novel structure by adding sweeping voltage circuitry to the classical DDS-PLL hybrid in order to overcome the shortcomings is proposed. The predistortion was also involved in the study to compensate the static phase error which improves the pulse compression qualities. A test circuitry was designed. The measurements indicate that the acquisition time is reduced to 2.175μs and 1.032μs corresponding to loop bandwidths of 1MHz and 2MHz separately, the total phase error is depressed to be less than 4°, and the pulse compression result is nearly ideal where the main lobe width remains as ideal, PLSR is better than-38dB, the ISLR is better than-9.5dB.

Abstract:In real communication systems, each node has a finite queue due to physical constraints. In this study, the influence of queue resource on data traffic dynamic in scale-free networks with finite queue resource was investigated. And a queue resource reallocation strategy was proposed. In this strategy, the allocation of queue length on node i is based on the betweenness centrality of node i. Simulations show that the capacity of the scale-free network can be improved by using the proposed strategy under the shortest path routing. With finite queue resource, the network traffic capacity was also analyzed theoretically.

Abstract:A dielectric cover is usually needed in waveguide slot arrays for protection or thermal insulation purposes, and it can improve the antenna performance with a proper choice of the cover parameters. In light of this, the properties of a SIW longitudinal slot with a dielectric cover were extensively investigated using equivalent relationship between SIW and conventional waveguide together with Method of Moment, as a first step to the design of a SIW slot array and its integrated radome. The accuracy and efficiency of our method was assessed against Ansoft HFSS. The computational time was significantly reduced by a one-order magnitude with acceptable computational accuracy. Finally, effects of the dielectric-cover were extensively investigated through three typical cover configurations and some instructional conclusions were drawn, which finds further application for the optimization design of the dielectric covers to improve the antenna performances.

Abstract:Spectrum sensing technique for wideband analog signals has been applied widely in cognitive radio. Based on the idea of time-division, this study was conducted with the following steps. Firstly, sampling time was divided into time slices which have fixed length. Secondly, the signal was multiplied by a bank of periodic waveforms which are modulated by pseudorandom number generators, and the product is low-pass filtered and sampled at sub-Nyquist rate. Finally, the samples were used to evaluate frequency support. Compared with the multi-channel structure, the single-channel structure proposed here is much simpler and has the ability to spectrum sensing with low-rate samples. Numerical simulations show that this algorithm can effectively use samples sampling at sub-Nyquist rate to finish the task of spectrum sensing in scenarios that the spectral support is unknown in advance.

Abstract:The performance of ToF (Time of Flight) measurement for ultrasonic wave can be obtained only by numeric calculation in traditional narrow band model. To this problem, a method based on Laguerre model is proposed for CRLB (Cramer-Rao Lower Bound) calculation. The characteristics of Lagueree function and its time derivative were studied, and the time derivative inner matrix was derived, which was applied in Fisher matrix, then the CRLB can be calculated fast and accurately. The simulation on hybrid exponential model polluted by Gaussian white noise testified the well coherence between the variance of ToF and the theoretic CRLB obtained with Laguerre model. The variance of ToF obtained by real data has great difference with the theoretic bound for the impact of narrow band noise and reverberant interference.

Abstract:In order to resolve the gain mismatch issue for the Time-Interleaved ADC in wideband radar RF sampling, a gain estimation method based on least square curve fitting is proposed. Based on the gain fluctuation of ADC, the negative influence of gain mismatch on the output signal spectrum was analyzed. According to the characters of wideband DAR echo, the gain estimation curve was obtained. The concrete implementation steps of this estimation method were also presented. Experimental results prove the validity of the proposed method in the wideband TIADC system.

Abstract:Under the harsh environment in which the number of visual navigation satellites is less than four and traditional navigation solution cannot be completed, the navigation receiver can enter the emergency auxiliary positioning mode by equipping the user with external elevation barometer providing for elevation information, or with internal punctuality module providing for clock bias. The traditional navigation and positioning error propagation model cannot be applied to analyze the error in this emergency assisted positioning mode. To solve this problem, this research focused on the basis of several emergency auxiliary positioning principles, such as three satellites combined with the elevation, three satellites combined with clock bias, two satellites combined with elevation and clock bias, and provided a new error propagation analysis model of emergency auxiliary positioning, verifying the correctness of the model by simulation example. Finally, through the positioning accuracy analysis, it concluded that the present method can quantify the optimal magnitude relations between pseudorange measurements and the accuracy of the auxiliary information with minimum cost to improve positioning accuracy, which can guide the choice of external auxiliary devices for navigation receiver.

Abstract:State-of-the-art cross collections topic models suffer from the serious flaw that it cannot capture the tendency of words to appear in bursts. Based on LDA (Latent Dirichlet Allocation)，a topic model CDCMLDA(Cross-collection Dirichlet compound multinomial Latent Dirichlet Allocation), which models the burstiness phenomena of words using Dirichlet compound multinomial (DCM) distribution, was proposed. A Monte Carlo Expectation Maximization algorithm for model inference was presented. A variety of qualitative and quantitative evaluations of CDCMLDA were performed, which shows that CDCMLDA not only discovers the common and unique aspects on topics, but also improves the model perplexity compared with the two cross-collection topic models. 

Abstract:Mapping matrix operations on SIMD processors brings a large amount of data rearrangement that lowers the system performance. In this study, a customized Multi-Grain Matrix Register File (MMRF), which supports multi-grained parallel row-wise and column-wise access, was proposed to eliminate these data rearrangement and increase the performance of matrix operations. The MMRF could be configured into different parallel access modes, in which one or several sub-matrices can be accessed in parallel. Experimental results show that, compared with the traditional Vector Register File (VRF) and the MRF, the MMRF can respectively achieve about 2.21x and 1.6x average performance improvement, where the area of MMRF increases by 14.3% and 3.7% respectively, and the power of MMRF increases by 14.6% and 2.2% respectively. Compared with TMS320C64x+, the SIMD processor of FT-Matrix can achieve about 5.65x to 7.71x performance improvement by employing the MMRF. By hierarchical customized design technology, the area and critical-path delay of MMRF can be reduced by 17.9% and 39.1% respectively.

Abstract:Based on a triad constant-rate biased RLG system, a mathematic model of the heading-sensitive error induced by calibration parameter variation errors in stationary initial alignment was set up. To tackle the problem that calibration parameters cannot be determined separately, installation misalignments were treated as a whole under the field test conditions, and then the heading-sensitive error coefficient was calibrated on-line using least square algorithm without external references. Utilizing the postulate system, field tests were done to estimate the on-line compensation accuracy of the heading-sensitive error coefficient by the on-line calibration method. The results of the experiments show that the on-line calibration and compensation method can eliminate the heading-sensitive error evidently and improve the yaw angle estimation precision in the initial alignment.

Abstract:A new method is proposed for modeling the news event evolution to precisely present the relationships between events. This method utilized the events timestamp, events content similarity, and events dependence between features to build a new event evolution model, and defined five different event evolution patterns to identify the seminal events, the intermediary and ending events. Ultimately, an event evolution graph model was constructed to present the underlying events relationship. Experiments were conducted, confirming that the proposed method is efficient for detecting event evolution, and improves performance of system.

Abstract:Traditional aircraft scheduling on carrier flight deck relies heavily on human commander decisions. To improve the computer aided decision making, an inverse reinforcement learning method was proposed. Learning from the commander or expert's demonstration, a Markov decision process (MDP) based aircraft scheduling model by analyzing the aircraft operations on deck was proposed. Then, the optimal policy and schedule were generated by using the linear approximating and inverse reinforcement learning method. Simulation results show that our method can learn expert's demonstration well, satisfy the requirement of scheduling optimization, and facilitate the computer aided decision making.

Abstract:This paper develops a non-periodic inspection maintenance model for a gamma deteriorating single-unit system based on regenerative and semi- regenerative process theory. Minimizing the expected average cost per unit time is chosen as the optimization goal. The model uses an inspection scheduling function to arrange the inspection scheme based on the system state. Considering measurement errors make the model more realistic. The preventive maintenance threshold and the inspection scheme are obtained after the optimization. A numerical example is given in the last and proves the effectiveness of the model by the sensitivity analysis of degradation rate and cost parameters. By the comparison with the optimal results without considering measurement errors, it proves that measurement error is not a trivial thing for the maintenance optimization. 

Abstract:Based on the analysis of the features and differences between satellite and UAV in earth observation and scheduling, a mathematical model was presented to formulate the scheduling problem for the multi-platforms collaborative observation, and a multi-platforms cooperative evolutionary planning and scheduling algorithm (MPCCPSA) was proposed to solve this problem. MPCCPSA uses co-evolution framework for solving the different platforms' observing plans generated in a unified manner. Based on the divide-cooperation strategy and different characteristics of platforms, the observed targets were allocated to each platform. On the top-level, crossover and mutation operations ensured the diversity of the various groups, and the underlying divide-cooperation operators ensured the dynamic complementarity between different platforms. Simulation results show that this method can effectively solve the multi space aeronautics collaborative observation tasks scheduling problem.