Abstract:Aeroengine onboard adaptive model can be built by estimating the biases of measurable parameters, so the CA (constant acceleration) model was introduced to establish the measurable variables state-space equations and observation equations, and adaptive Kalman filter algorithm was employed to estimate the measurable variables directly. The bias of measurable variables can be obtained by subtracting standard model computing values from the estimated result of measurable variables. When using the standard Kalman filter algorithm to estimate the measurable parameters, the results will offset prominently because of the great system state-space model error. The principle of standard Kalman filter and the impact of model error to the filter estimate results were analyzed, and the technology of dynamically adjusting the weight of state prediction in the filter estimate results was introduced, then the single factor adaptive Kalman filter estimation principle and the recursion formula were presented, which was aimed to make the estimation more accurate. In order to reduce calculation cost, the sequence filter was applied separately to process different measured parameters. The algorithm and system model were verified using the simulated data. The calculation results show that the designed filter can converge rapidly, and the computing speed is satisfied. The estimate results are better than the standard filter’s. So the adaptive filter algorithm has better estimation precision and have some engineering value. 

Abstract:Radiometer effect and residual gas damping are important interfering forces on the proof mass in purely gravitational orbit, which can affect the construction of the purely gravitational orbit. For spacecrafts in purely gravitational orbit, radiometer effect and residual gas damping describe two different kinds of gas molecules forces caused by temperature gradient and the relative motion of proof mass in the cavity, respectively. These two forces describe gas molecules forces from different views and are both parts of gas molecules forces. However, the coupled model of radiometer effect and residual gas damping can reflect the total force of gas molecules on proof mass. Considering the complex form of the coupled model, the physical parameters in coupled model were analyzed by numerical methods in the Inner-formation Flying System (IFS). These physical parameters contain the relative velocity of the inner-satellite, the inner-satellite radius, the outer-satellite cavity radius, the average temperature and pressure, the temperature difference in the cavity. By fitting a large number of numerical results, an approximate formula for gas molecules forces on the inner-satellite was obtained. Compared with the original results, the fitting errors were less than 20%.

Abstract:By introducing VOF model to simulate the cooling liquid film in small thrust liquid rocket engine, numerical method was performed to calculate and evaluate the effects of the expansion size on combustion efficiency and heat transfer in the chamber. Comparison shows the calculation is reasonable. It has shown that as the dimensionless expansion height H^*increases from 0.111 to 0.222, combustion efficiency and specific impulse increase by 0.35 % and 0.5s. However, the dimensionless expansion length L^*plays a less significant role in the process. As it increases from 1.389 to 1.944, combustion efficiency and specific impulse decrease by 0.11 % and 0.3s respectively. It is evident that the heat transfer characteristics of thrust chamber keep stable in the variation of H^*or L^*. This shows in expansion thrust chamber, the main reason for combustion efficiency loss should be that gaseous MMH adjacent side wall cannot mix with gaseous oxidant efficiently. 

Abstract:The flow and distribution of propellant in the vane-type surface tension tank in microgravity condition was studied. The rewetting process of propellant in tank was calculated by numerical simulation using VOF method, and the liquid management capability of the tank and PMD was tested. The interior corner flow of propellant along the PMD was investigated by analytical solutions, and the length of the meniscus in the tank was calculated, and the results were compared with the numerical simulation results. Inevitably, errors were noticed between numerical simulation and analytical solution due to the complication of the model of spherical tank with PMD, but they were in accordance with the tendency of the flow. The present research can provide useful reference for the study of interior corner flow.

Abstract:The waverider is considered as an important candidate for the configuration of hypersonic glide vehicle (HGV) in terms of its high lift-to-drag ratio. Due to the severe aerodynamic heating, the sharp leading edge of waverider need be blunted, and the flow characteristics and the aerodynamic performance along the trajectory will change. In the current research, the flow characteristic of a HGV was studied based on a reference trajectory, and a numerical simulation was carried out to evaluate the performance of HGV with a blunt leading edge under a typical condition. The result indicates that the flow near the stagnation point exhibits three-dimensionality which cannot be approximated as a flow around a sphere or cylinder; the heat flux can be reduced and the aerodynamic performance of HGV may decrease as well when the leading edge is blunted: under the condition of 2 cm radii, the lift-to-drag ratio reduces by 12.34%, and different thermal protection methods can be used in different places of HGV.

Abstract:In order to investigate the system dynamics of spacecraft propulsion system with complex pressurization pipelines and propellant feed pipelines, the Unified Propulsion System simulator (UPSSim) was developed, which consists of a modular and extensible framework based on AMESim software. The pressurant pipelines were separated into several nodes, with each node using lumped parameter model; while the propellant feed pipelines used distributed parameter model. Heat transfer between components and environment was also taken into account. Simulation of a certain UPS during GEO insertion shows that the UPSSim can obtain the parameter variations accurately, and the results are in good agreement with design parameters and measurements. Simulation result indicates that the method proposed is sufficient for the modeling of complex pipelines and has good application prospect for spacecraft propulsion system dynamic simulation. 

Abstract:To meet the needs of failure reappearance of a certain rocket launching, the present research studied the conceivable failure condition by the method of numerical simulation. Firstly, the conceivable failure reasons were analyzed based on the failure phenomenon and the measure data from rocket. Then, the processes of the atomization and the combustion were numerically modeled and simulated, which was based on the performance of the gas generator. Next, the possible failure conditions were simulated one by one, and the results were compared with the limited data from the rocket. The conclusions are as follows: the numerical model proposed can simulate the rocket launching failure very well; the gas generator involved has some design objection, and needs to be optimized in design; the askew turbulent flow annulus is the most possible failure of this rocket launching.

Abstract:A simplified ‘Spring-Mass’ dynamic model and dynamic analysis were performed to obtain the influence of propellant consuming on the dynamic properties of a large scale satellite structure. Then the finite element modeling and analysis methods, including the beam modeling method, added with the mass method, the ‘RBE3-Mass’ modeling method and the virtual mass method, were given based on MSC.PATRAN/NASTRAN. In the end, the satellite finite element model was established and the dynamic analysis was executed. The analysis results indicate that: (1) the frequencies of main mode shapes will raise with the propellant consuming, while those of local shapes will not change ; (2)The frequency and magnitude of response will raise with the propellant consuming.

Abstract:The evaluation index, such as spray combustion, gas mixing and nozzle non-uniformity of air heater based on the combustor of liquid rocket engine, was studied with numerical simulation. The difference between the injectors with ethanol/liquid oxygen/air and the injectors with ethanol/gaseous oxygen/air in the combustion flow field was discussed and analyzed. Two cases were designed by changing the characteristic length of combustor, and the performance of air heaters were investigated by numerical simulation. The results show that, the flame structure is affected obviously by the phase of oxygen. The length of flame with liquid oxygen is larger than that of gaseous oxygen. More hot gas fills in the recirculation zone in the forepart of combustor with gaseous oxygen case, which increases the gas temperature near the faceplate, and worsens the thermal environment on the faceplate. The high quality flow field on the nozzle exit is obtained with the designed air heater. The characteristic length of air heater with gaseous oxygen is at least a quarter less than that of air heater with liquid oxygen to keep the good uniformity of nozzle exit.

Abstract:The control process for the fast maneuvers of the responsive spacecraft was taken as the research object, and the rapid decoupling of the attitude control problem was investigated. A comprehensive control strategy which integrates time optimal control and tilt switch curve control was proposed based on the decision tree theory. Furthermore, the control time was taken as the cost function, the three-channel time optimal control strategy was obtained. Compared with other methods, the control time of the proposed strategy is reduced by nearly 10 seconds, and the control precision meets the design requirements. Additionally, control results were compared in case of different control cycles for the controller, and the instructional conclusions were provided for selecting and designing of the control cycle.

Abstract:Shock wave focusing can produce higher pressure in the focal region. An underwater shock wave focusing system was set up based on the pulsed discharge in water and the focusing characteristics of ellipsoidal reflector. The focusing of shock wave was studied experimentally; the focusing process of shock wave was analyzed. The pressure-time history and the peak pressure along the axial position were presented, the distributing characteristics of the focusing shock wave were revealed. Negative pressure and cavitation phenomenon was induced by shock wave focusing, and the phenomenon was analyzed based on shock dynamic theory. The experimental results indicate that the focusing effect of the ellipsoidal reflector is remarkable.

Abstract:The tracking, telemetry and command (TT&C) system is a phased mission system. In this research, the constraint conditions and the allocation objective were discussed, and the mission reliability allocation model was built. The mission reliability allocation of TT&C system is a kind of combined optimization problem with complicated constraints, and a velocity controllable particle swarm optimization (VCPSO) was proposed for this problem. In order to overcome the local convergence of particle swarm optimization (PSO), velocity direction controllable regulation and velocity scale controllable regulation were introduced to increase the population diversity. The velocity iterative strategy in PSO was improved based on the two regulations. By simulation, it shows that the VCPSO can reach more optimal results and convergence in solving the mission reliability allocation of spaceflight TT&C system.

Abstract:Using Markov model to evaluate reliability of the tracking, telemetry and command (TT&C) and communication system is very difficult if there are many facilities in system, due to the fact that Markov modeling techniques suffer from the state explosion problem. In light of this, a reliability analysis method based on Krylov subspace is proposed; the main idea of this method is projecting the initial problem to a smaller subspace for the obtaining of an approximating result. Examples prove that the proposed method performs better than Ross method and Forward Euler Method, and it can achieve a good efficiency and accuracy.

Abstract:The tasks of disaster relief campaign within military operations other than war comprise emergency roadway repair and relief distribution; however, there exists interrelationship between the two kinds of tasks, and some other challenges, such as fuzzy stochastic demand and variable network structure, are also confronted in scheduling of this kind of campaign. According to the above situation, a bi-level hierarchy optimization model for emergency resource scheduling in a network with non-deterministic attributes was proposed, and a hybrid intelligent heuristic algorithm which combines fuzzy random simulation with improved genetic algorithm was also designed. At last, a data case was presented to highlight the significance of the proposed model as well as the efficacy of the designed algorithm.

Abstract:The efficiency and the parallelism of parallel discrete event simulation can be improved through simulation cloning. Analysis, comparison and evaluation of what-if can be processed quickly and conveniently. Generalized Multi-Scenario Analysis Simulation (GMSAS) concept was given. Based on the introduction of simulation cloning and the analysis of the deficiency on current simulation cloning, the out-place cloning was proposed to advance the efficiency of GMSAS. It was implemented on checkpoint/recover in dynamic parallel simulation engine. An experiment was carried out by using Phold testing program. The results of experimental research demonstrate that the whole efficiency of GMSAS system is improved through out-place cloning.

Abstract:A method of determining the regularization parameter is proposed in order to solve the image deblurring problems. The main objective is to get the regularization parameter from the deblurring image. The method starts by considering the famous Total Variation methods and the Split Augmented Lagrangian Shrinkage Algorithm (SALSA), and then it deals with the effect of the regularization parameter on the result image. The proposed method proves that the parameter is determined by the noise and the gradient of the image. Results of the recovery of images were compared with different gradient and noise, and they help to reach a conclusion that the proposed method maximizes the improvement in Signal to Noise Ratio (ISNR). The method also removed noise and protected the details of the image in the processing of recovery as much as possible.

Abstract:Algebraic immunity has been considered as one of significant properties for Boolean functions. Two constructions of rotation symmetric Boolean functions (RSBFs) in even-variable with maximum algebraic immunity(MAI) were proposed. Furthermore, the nonlinearity of constructed RSBFs were investigated under special cases of Construction 2. When n≥18, the constructed MAI RSBFs by using Construction 3 have higher nonlinearity than that of all known MAI RSBFs in even-variable.

Abstract:Semantic concept detection in video is a challenge for video semantic content analysis. The performance of semantic concept detection methods depends on modeling and matching the video semantic content exactly. In this research, perception concept and semantic concept were defined to abstract and model video semantic content. Furthermore, the knowledge-assisted framework for semantic concept detection was proposed, in which the context knowledge was modeled using ontology, and the semantic concepts were detected by combining with low-level features and context information. Finally, the linear fusion strategy was used to fuse the matching results and detect the semantic concepts. The proposed method was demonstrated in a news video domain and shows promising results.

Abstract:In order to achieve the software remote updating of the vehicle-mounted intelligent terminal based on the Kylin operating system, a design is proposed. The GPRS technology, IAP method, response mechanism, technique of resume from transfer breakpoint and checkout mechanism were applied to the design to insure the real-time, veracity and reliability of during the updating process. A series of experiments were conducted to simulate the exception during the updating process. The results show that the software of remote updating of the terminal applying the design proposed can still complete exactly in all exceptional experiments.

Abstract:The problem of computing the observing angle of an agile imaging satellite was discussed. Considering the constrains of the earth rotation and the satellite moving on its orbit, the kinematic model based on ellipsoid was established by means of space reference frame transformation. Based on this model, the algorithm for computing observing angle at any given visible time was proposed. The results show the efficiency of our approach. The acquired observing angle supports the task scheduling of agile imaging satellite.

Abstract:An efficient parallel PCA-SIFT algorithm for multi-core processor is proposed, which adopts data-level parallel method to implement parallel key points extraction and matching. The computing tasks were assigned to four DSP cores for parallel processing, which fully develops multi-level parallelism of multi-core processor. The experimental results show that the parallel PCA-SIFT algorithm has good adaptability for various distortion images and the image matching ability is close to the sequential algorithm with the average speedup 3.12.

Abstract:The current trend in processor architecture design adopts the integration of multiple cores on a single processor. The tightly integrated processing cores in one chip with communication latencies substantially lower than those present in conventional clusters provide potential performance improvement especially for the fine-grained PDES. Thus, in the PDES domain, one of the research focuses is on modifying software platforms to efficiently utilize the computation resources of multi-core processors. The current dynamic load balancing technologies for PDES cannot reach the twin goals of good balance and low event-scheduling overhead. By taking advantage of multi-core architecture with shared memory address space and low communication, a global schedule mechanism based on a distributed event queue is proposed. Its specially designed data structures and algorithms reduced the cost of lock operations much. In comparison with the distributed event queue local schedule mechanism, the experiment results show that the distributed queue global schedule mechanism can effectively reduce the rollback rate and balance the workloads at a low event scheduling cost for Time Warp system on multi-core platforms.

Abstract:As parallel computing has become mature and practical, data intensive raster data processing algorithms are desiderating parallel computing technologies to reduce the running time. The objectives of this research focuses on the parallelization of neighborhood-scope algorithms. the sequential/parallel temporal model was developed, the affecting factors of each component of the temporal model were analyzed, and two optimization methods were proposed, which can further promote the parallel performance of neighborhood-scope algorithms: the Parallel I/O method that can reduce the data I/O cost; and the Halo Prediction method that can reduce the data communication cost. Experiments verified the effectiveness and efficiency of the proposed optimization methods, which can further promote the parallel performance by making the parallel algorithmic program fully take advantage of parallel computing resources.

Abstract:Single Channel Blind Signal Separation (SCBSS) is a hot and difficult topic in signal processing field. The feasibility of cyclostationary filtering applied in the single channel signal separation problem for the spectrally overlapping signals was analyzed, and then a separation algorithm based on frequency shift filter and Schmidt orthogonal cancellation was proposed. Firstly a source signal by frequency shift filter was extracted, then another source signal was estimated by subtracting the signal recovered from the mixture based on Schmidt orthogonalization. Simulation results indicate that, compared with the Wiener filtering technique, the proposed algorithm can separate radar and communication signals which are spectrally overlapping effectively and the proposed algorithm estimates the source signals with higher gain about 10dB. 

Abstract:A novel structured dictionary training algorithm is proposed for double sparse image representation. Based on the double sparse image representation model proposed by Rubinstein, the zero-tree structure of wavelet coefficients was introduced, and the new dictionary atoms were constructed by linear combination of wavelet bases in all high-frequency bands of same orientation across different scales. The linear combination coefficients were learned via K-SVD. The image decomposition and reconstruction algorithm was proposed based on the learned dictionary. The M-term approximation and compression of remote sensing images both proved the better effects of the proposed structured dictionary than the existing dictionaries.

Abstract:Urban traffic scene understanding is the basis of traffic monitoring and safety driving assistant system. A novel approach to understanding urban traffic scene captured from a car-mounted camera is proposed based on multi-level Sigmoidal neural network. Five 3D structure features were combined with the appearance features to represent the urban traffic environment and the recognition accuracy of traffic environment was improved by utilizing multi-level Sigmoidal neural network(MSNN) to segment and recognize the input images. Tested by the public CamVid dataset, the experimental results demonstrate the efficiency of the proposed approach.

Abstract:Scattering centers matching is currently the primary technique in SAR Automatic Target Recognition (ATR) using scattering centers. The difficulties in scattering centers matching originate in the inexactness of scattering centers and missing scattering centers. The recently developed Coherent Point Drift (CPD) method solves point pattern matching from the perspective of probability density estimation. In the CPD method, the inexactness of scattering centers and missing scattering centers can be well considered. The CPD method was introduced in this research to solve scattering centers matching. In order to improve the accuracy and stability of scattering center matching, the CPD method was modified to incorporate the prior information of vehicles’ azimuth estimation and scattering centers attributes. Experiments on MSTAR dataset show the validity of the proposed method.

Abstract:Traditional peak detecting method is impossible to detect actual signals when the signal-to-noise ratio (SNR) of the output of a giant magneto-impedance (GMI) probe is less than 0dB. A novel method, therefore, is presented to detect weak signals from the probe, which are directly sent to digital signal processing system after signal conditioning and sampling. In this method, the characteristics of the weak signals are extracted by wavelet transform and the amplitudes determined by the correlation method. The simulation results indicate that the probe’s output signals with SNR=-15dB can even be detected by the hybrid method mentioned above.

Abstract:The research on modeling of reverberation and noise in shallow sea based on symmetry Alpha stable distribution was made. The forming process and non-Gaussian characteristics of shallow sea reverberation were analyzed. The theory of symmetry Alpha stable distribution was used to model the reverberation, and the validity of model was verified by the matchable degree between the probability density distribution of reverberation’s instantaneous scales as well as the envelopes and Alpha stable process. The signal detection methods in the reverberation based on symmetry Alpha stable theory were studied. Three methods for detection were proposed and tested by simulation. The advantages and weakness of the methods were analyzed by their performance, model precision and the effect of model precision to performance validated. 

Abstract:As technology feature scales down, SER (Soft Error Rates) induced in the combinational logic wins increasing attention. A mixed-mode simulation method is proposed for computing SER in combinational logic, which is aimed at solving the slow HSPICE simulation speed and the low precise of traditional methods in treating re-convergence. A Mixed-Mode Analysis Tool for Combinational Logic based on this method was implemented. Re-convergence logic gates were simulated with HSPICE; a fast pulse propagate algorithm was used to simulate others. The simulation results illustrate that the proposed method gains a close precision to HSPICE with a faster speed. Compared with the prevalent SER analysis method, it is found that our proposed method can factually reflect the SER in combinational circuits where there are many re-convergence logic gates.

Abstract:DICE cell is an effective method to mitigate SEU effects. SEU, however, still occur in DICE cell-based SRAMs, due to the weakness of DICE cell during reading and writing, and the weakness in the peripheral circuits. A separated-bit-line structure is proposed to handle the DICE cell’s upset during reading and writing, and a double module redundancy method is presented to resolve the upset in the peripheral circuits. The simulation results show these methods are effective to mitigate SEU from DICE cell based SRAMs.

Abstract:Aimed at the Low-angle Height Finding problem under multi-path environment, a novel low angle height finding algorithm at sub-array level is proposed. First, the whole array was divided into three equal sub-arrays. Then, the orthogonal vector of covariance matrix at sub-array level was calculated accurately, not by Eigen Decomposition. Next, the angle spectrum was presented, whose peak just accords with the DOA of target. Finally, the complex reflection coefficient was estimated after the estimated DOA. How this algorithm relies on the SNR, the target’s elevation and complex reflection coefficient has been explained by simulations. Its efficiency was verified by outdoor data obtained by VHF band radar. The elevation angle error is 1.19 percent of beam width of array. This algorithm is independent on the unknown complex reflection coefficient, and the computation is lowered greatly. It can be applied in ship borne radar and VHF band 3-coordinate radar.