Abstract:According to the one-dimension design theory of ejector, cooling the secondary flow before it enters into the mixing chamber can promote the eject efficiency and increase the eject coefficient, but flow loss is brought with the addition of precooler, so the performance evaluation of ejector is necessary. Looking on the eject system with precooler, the effect of precooler on the performance of system was analyzed through the onedimension theory, and the effects of the intensifying effect of precooling and the weakening effect of resistance on eject efficiency were analyzed emphatically. The research results indicate that: the precooler brings intensifying effect of precooling and weakening effect of resistance to eject system, and the cross section area and heat transfer area of the precooler are the dominating factors; cross section area of the precooler has a critical value, when the cross section area is bigger than the critical value, the eject performance improves with the increase of heat transfer area, otherwise it worsens; the eject performance of the equivalent pressure mixing scheme is better than that of the equivalent area mixing scheme, the eject coefficient of the former is 60% higher than the latter; precooling improves the eject performance effectively, especially for the equivalent area mixing scheme, the performance is improved by 35.5%.

Abstract:Space solar power station is a kind of space structure with large size and high flexibility. It is far larger than the previous spacecraft in size, which results in new phenomena and new problems on the study of dynamical characteristics. The kilometerscale dumbbell model was studied. The Hamilton’s dynamical model on orbit was established under the effect of gravity gradient. The symplectic Runge-Kutta method was used with different combinations of parametrical values to obtain dynamical responses. By comparing the simulation results, the quantitative relationships were determined respectively between the size of space structure and the effect of gravity gradient on orbital motion and attitude motion. It is found that: due to the gravity gradient, the coupling phenomenon between attitude motion and elastic vibration occurs; the attitude motion has great influence on the external envelope curve of elastic vibration response, while the period of it is changed by elastic vibration.

Abstract:The basic problem of gliding guidance for hypersonic vehicles was proposed, and the difficulties of complicated multiple constraints, maneuver requirements, and parameter perturbation in the course of gliding guidance were analyzed. The corresponding research status at home and abroad was surveyed, and the problems were also pointed out. On this basis, the key problems required to be solved at present in the research of gliding guidance for hypersonic vehicles were presented, and the research hotspots in the methods of future gliding guidance were also pointed out. 

Abstract:Concentrating on the hypersonic reentry guidance under multiple constraints, a full-state nominal trajectory tracking guidance scheme was proposed by applying the differential transformation approach to the optimal feedback control. In the period of the online closed-loop guidance scheme based on the recedinghorizon control, the nominal trajectory tracking problem was transformed into a state regulator problem of the associated linear time-varying system, and then into a two-point boundary value problem by utilizing the optimal control theory. The differential transformation approach was suggested for the optimal feedback control, avoiding the time-consuming and numerical instabilities of conventional methods. Numerical simulation results validate that the proposed guidance scheme is robust to state dispersions and model uncertainties, providing a reference for engineering design. 

Abstract:The PPP(precise point positioning) algorithm based on the single differencing between satellites and the robust Kalman filter model was studied and analyzed. And then, the global position system, global navigation satellite system and BeiDou navigation satellite system data had been used to analyze to the positioning precision and convergence time of single, double and threesystem PPP. Finally, the conclusion were drawn as follows: the positioning precision or the convergence speed of the three-system PPP technology is optimized, and multiple-system integrated navigation and positioning can improve the precision of navigation and positioning.

Abstract:The analytical model for the output relations of anti-aliasing filtering, sampling, quantization and de-spreading was established. The formulation of de-spreading output SNR (signal to noise ratio) under the influence of three factors was deduced. Analysis and simulation results show that the total SNR loss can be separated to the product of quantization, filtering and sampling loss when the quantization length up to 4 bit; besides, the optimized clipping level coefficient is only related to quantization length. When the quantization length is less than 4 bit, the total SNR loss approximates to the product of the quantization and sampling plus filtering loss. In the condition of the quantization length up to 4 bit, the filter bandwidth up to 5 times of PN (pseudo-random) code rate, the sample rate up to 4 times of PN code rate, increasing the parameters mentioned above cause the SNR loss less than 0.05 dB, thus the despreading performance cannot be increased obviously. Results can be used to optimize the design of the front-end of lowcost global navigation satellite system receiver.

Abstract:In order to achieve the unambiguous and antimultipath reception of the BOC (binary offset carrier) signal, the DPE (double phase estimator) was modified by introducing a strobe waveform in the prompt signal correlation process of the SPLL (subcarrier phase lock loop) integration. The modified DPE possesses multipath error mitigation performance and employs no additional correlator. The theory and the realization of the proposed approach were explained and analyzed, and the performance of the modified DPE was characterized according to the SMEE (subcarrier multipath error envelope) and the tracking jitter. Simulation results show that, compared with the conventional DPE, the proposed algorithm can provide a reduction in the SMEE area of 81.1% for signal BOC(1,1) and 75.1% for signal BOC(14,2). However, the modified DPE experiences a loss of-6 dB in terms of the postcoherent signaltonoise ratio, which impacts its tracking precision. Thus, the selection of waveform parameters involves a tradeoff between the tracking performances obtained under multipath and thermal noise conditions. Above all, the proposed method is applicable to the receiving problems of multipath environment or non weak signal case.

Abstract:The power-inversion adaptive array is very suitable for situations where the desired signals are very weak while the interfering signals are much stronger, thus, it is widely used in the global navigation satellite system. For least mean square based on power-inversion adaptive array which is used in global navigation satellite system receivers, the convergence rate was very slow when sudden change in interference number or interference power occurs. The performance of receiving the satellite signals would be degraded. The cause of this phenomenon was analyzed. Then, an improved least mean square algorithm was proposed to solve this problem. The key novelty of the proposed method was that it monitors the power of the reference antenna output to detect any sudden change in interference number or interference power. Once the interference number or interference power decreases suddenly, the weight vector would be initialized again to improve the rate of convergence. Simulation results show that the improved method outperforms the original algorithm in rate of convergence.

Abstract:Based on the kinetic model of underwater grid fins during the procedure of dynamic expansion, a prediction method was developed, which took the motion parameters at typical expansion points as the design input. The hydrodynamic moment used in the kinetic model was fitted by the values obtained in steady hydrodynamic conditions with specific expansion angles. A modified factor in consideration of the relative velocity was included as well. By comparing with the results obtained by unsteady numerical simulations and the underwater vehicle experiment data, the prediction method is verified, which can provide a design reference for the optimum proposal of the underwater grid fins and the analysis of nonsynchronization expansion.

Abstract:To analyze the supersonic opening performance of the parachute in Mars reentry environment, the coupling dynamic models between compressible fluid and flexible structure of parachute were solved on the basis of the arbitrary Euler-Lagrange penalty function method and the multi-material arbitrary Lagrange Euler algorithm. The evolution of 3D shape of DGB(disk gap band) parachute during supersonic inflation was simulated, and the structural dynamic behaviors of canopy fabric were predicted. The drag area and coefficients were compared with the wind tunnel data, and the inflation performance of parachute and the influence of fore-body were analyzed. Finally, the wake of unsteady fluid and distribution of shock wave around supersonic parachute were investigated. The results show that: the DGB parachute is well inflated without serious collapse; as the increase of Mach numbers, the drag coefficients gradually decrease, along with the increase of the inflation time, which brings into correspondence with the test results, and proves the validity of the proposed method.

Abstract:Aiming at highly reliable microprocessor soft error tolerance design, a new metric, eMWTF (enhanced mean work to failure), was proposed to capture the trade-off among reliability, performance, area and power. A quantitative approach for evaluating eMWTF was also presented. Two control flow checking techniques were quantitatively evaluated in reliability. The experimental results indicate that the control flow checking by compiler signatures and hardware checking achieves better trade-off among reliability, performance, area and power. Because the eMWTF metric takes into consideration performance, area and power overheads, the quantitative reliability evaluation can be more accurate by using this metric and corresponding methodology. Finally, the evaluation results can effectively guild the design exploring and optimization.

Abstract:To break through the limitations of huge memory space and low evolution speed for complex circuits′ evolution, the bitstream relocation and the discrepancy configuration were adopted to improve the efficiency of the evolvable hardware implementation approach based on dynamic partial reconfiguration. Firstly, an evolvable IP core capable of bitstream relocation was customized by using the technology of early stage accession to partial reconfiguration provided by Xilinx. Then the original bitstream files were presynthesized to form a partial bitstreams library stored in the CF memory for the system to call. Next, a self-evolving system based on a programmable chip system was built, in which the soft processor, MicroBlaze, was utilized as the evolution controller. And the discrepancy configuration was adopted for the real-time adjustment of the circuit topology of the evolvable IP core. Finally, the system structure and the self-evolving mechanisms were verified by the online evolution of digital image filters implemented on the Xilinx Virtex-5 FPGA(field programmable gate array) development board ML507. Experimental results show that the proposed evolutionary mechanisms can reduce the storage space of bitstream files and can accelerate the speed of evolution significantly.

Abstract:The FRSHV(friend relationship strength hierarchy vote), a hierarchical model, was proposed to measure the friend relationship strength by user′s daily moving track, semantic positions and the corresponding semantic labels. The daily track similarity was measured by dynamic time warping model using the spatial distance between friends, and the results were then weighed by the entropy of track series. The similarities of friend′s behavior patterns were inferred by latent Dirichlet allocation topic model, respectively using semantic positions and the corresponding semantic labels. Finally, these three similarity results were voted for the ultimate relationship strength. The FRSHV was evaluated by using an open dataset and the results proved the validity of the model in inferring friend′s relationship strength.

Abstract:The news topic discovery model based on multi feature fusion text clustering was proposed fusing multi features of news, such as named entities, news headlines, important paragraphs, text semantics and so on. Based on the multi feature influence of news, a multi feature fusion text clustering method was put forward in this model. In this way, vector space model and similarity algorithm based on feature words, news headlines, important paragraphs were constructed, subject space model and similarity algorithm based on latent Dirichlet allocation were constructed, named entity model and similarity algorithm based on named entities were constructed, and those three similarity algorithms were fused optimally. Based on multi feature fusion text clustering method, the Single-Pass algorithm used in the news topic discovery was improved. Experiments were carried out on the real news data set, and the experimental results show that the model can improve the accuracy rate, recall rate and comprehensive evaluation index of the news topic discovery, and have some ability of self-adaption.

Abstract:Firstly, the MSERs (maximum stable extremal regions) which corresponded to Chinese strokes was extracted. The morphological close operation was used to connect the nearby MSERs. The fused MSER corresponded to Chinese characters. Gray level co-occurrence matric was used to describe the textural characteristics of the fused MSER rectangle. They were the input of CNN (convolutional neural network). The MSER rectangles were classified by CNN in order to filter none Chinese character rectangle. Then, Chinese text candidates were constructed by clustering MSER rectangles based on the features such as the color histogram Bhattacharyya distance of MSER rectangles. CNN was reused to classify Chinese text candidates to filter none Chinese text clusters. Finally, the rectangle of the remaining clusters was the Chinese text regions of natural scene image. Experiment shows that the proposed algorithm is desirable in localizing the Chinese text in natural scene images.

Abstract:To address the problems that the resource is surplus, the resource utilization rate is low and the cost is unreasonably high for virtual machines in the scientific application of DAG(directed acyclic graph), a novel DAG scientific workflow scheduling algorithm based on CPC(critical path cut) was proposed. In the algorithm, the CPC technology was adopted to circularly find the unallocated task which is finished at last; the biggest connected subgraph was found from the graph constructed by the whole unallocated tasks; the critical path of this subgraph was calculated and the task set on the critical path was scheduled to the performance-matched virtual machine to execute. Meanwhile, the isolated tasks were used to fill in the idle slots of the virtual machines, such that the resource utilization could be improved. Experimental results demonstrate that, the proposed CPC algorithm can effectively reduce the execution cost of the scientific workflows while satisfying the deadline constraint in mean time. 

Abstract:A novel sliding control approach based on double power combination function reaching law was proposed. The proposed reaching law has faster convergence speed in comparison with fast power/double power reaching law, and it also has the characteristic of global fixedtime convergence, which means the upper bound of convergence time is independent of the initial value of sliding mode variables. It was proved that for a class of bounded external disturbance, the sliding mode variable can converge to a proposed steady-state error bounds in finite time, and the value of the steadystate error is less than the previous reaching law. Simulation results show that the validity of conclusion is confirmed.

Abstract:For it is not accurate under the condition of low availability, VARI-METRIC model of inventory optimization for multiechelon multi-indenture repairable spares was built. Firstly, the birth and death process of each component was established by the prediction of demand rate and arrival rate of each spares in each site. Then, a computational method of availability was put forward based on the birth and death process. With the constraints of availability and objective of lowest cost, the optimal inventory distribution result was obtained by marginal algorithm and the simulation model was built to evaluate and adjust the result. In an actual example, the analytic model and the VMETRIC were compared and described in aspects of optimization performance, calculation precision and applicability by simulation verification. Results show that both the analytic model and the VMETRIC have certain scope of applicability and the method combined analytic model and simulation has a stronger applicability. 

Abstract:In order to resolve the scheduling difficulty in the control of command system, the resource scheduling problem of a special sensor was studied and the constraint conditions including detected times, the interval between two detections, and the resource restrict of sensor were analyzed. A 0-1 programming model was established and transformed to a 0-1 liner integer model whose objective function is the sum of the importance degree of tracking targets. The optimal solution which can reasonably schedule sensor resource when the workload is saturated was obtained by using the cutting plane algorithm. A corresponding simulated annealing algorithm was proposed to improve the speed of solving and was used to solve some examples. Compared with the cutting plane algorithm and the genetic algorithm in terms of resource utilization and the speed of solving, the validity of the proposed model and the high efficiency of the simulated annealing algorithm were proved.

Abstract:Based on analyses about system effectiveness of the weapon and aiming at application requirements from the weapon type approval tests, a modified ADC(availability-dependability-capability) method was put forward in order to solve the problem that the actual usability of the weapon cannot be presented accurately and entirely by dividing system conditions using the traditional ADC method. Comprehensive modifications were performed, such as putting forward the strategy of adding the medial conditions in the model. As the results showed, functions for integrating the sub-system effectiveness, for describing and computing the conditions, for transfers between conditions, and for capabilities were all improved. A software platform SEEK was developed based on these modifications. System effectiveness evaluation of a main tank was selected as an example for demonstrate feasibility and validity of the method.

Abstract:For the optimization problem of MIMO(multiple input multiple output) radar transmit beampattern under jamming, a new MIMO radar waveform design method based on quadratically spatial and spectral optimization was proposed. Firstly, the proposed method converted the problem of MIMO radar transmit beampattern design into the optimization problem about the covariance matrix of MIMO radar’s transmit spacetime sequences. Based on the fact that MIMO radar transmit beampattern was only decided by the correlation of each element’s transmit waveforms, the computational burden of the spatial optimization of waveforms could be reduced. Furthermore, the nulling towards the jamming direction of the transmit beampattern was broadened by the porder derivative constraint. With the optimized covariance matrix, the randomization method was used to synthesize the actual constant modular waveforms under the criteria of least square to gain on the optimal beampattern. Finally, with the optimized waveforms through spatial optimizing process, a phase flexible diagonal matrix was optimized with the likepower method to achieve the spectral optimization of MIMO radar waveforms based on the fact that MIMO radar transmit beampattern would not be influenced by the change of the initial phase of transmit sequence at a certain moment. And the spectral jamming could be avoided by the spectral optimization of waveforms. Simulation results prove the effectiveness of the proposed method in matching desired beampattern and antijamming.

Abstract:To efficiently utilize the information which can be extracted for target recognition and the character that different polarization channels characterize the same structure signature of a target using different polarization modes to boost recognition performance, a method for full-polarization HRRP recognition based on multitask compressive sensing was proposed. Each singlepolarization HRRP was represented by the atoms adaptively selected from its associated dictionary, and the atoms derived from different dictionaries corresponded to the same index set. Compared with the conventional methods, the proposed method has the significant advantage of exploiting the correlation among single-polarization HRRPs to enhance recognition performance. Experiments were carried out on simulated data, and the results demonstrate the efficiency of the proposed method.

Abstract:Radar coincidence imaging is a high-resolution staring imaging technique without the limitation of relative motion between target and radar. Conventional radar coincidence imaging methods ignore the structure information of complex extended target, which limits its applications in high resolution imaging, thus an adaptive pattern-coupled sparse Bayesian learning algorithm was proposed. To model the extended target, a pattern-coupled hierarchical Gaussian prior model was introduced in sparse Bayesian learning framework, and then the algorithm alternated between steps of target reconstruction and parameter optimization under the variational Bayesian expectation maximization framework. Therefore, the reconstruction of each coefficient involved its immediate neighbors, and the parameter indicating the pattern relevance between the coefficient and its immediate neighbors was updated adaptively during the iterations. Experimental results demonstrate that the proposed algorithm can achieve high resolution imaging effectively for the extended target.

Abstract:Aiming at evaluating radar network detection capabilities, firstly, a multilevel evaluation index system was established by using the fishbone diagram to analyze various complex factors. Secondly, the IAHP-CIM (interval analytic hierarchy process-controlled intervals and memory) model was proposed to evaluate the index system. Specifically, interval analytic hierarchy process was used to solve the problem of quantified fuzzy index, and the interval judgment matrix was obtained; the Shuffled frog leaping algorithm was applied to optimal interval matrix and the certain number matrix with the minimum consistency ration was obtained; the risk probability of indexes were acquired by the controlled intervals and memory model, and synthetically the index system was evaluated. Finally, simulation results demonstrate the feasibility of the proposed evaluation method, and the relatively objectivity of evaluation conclusion are of great significance to optimize arrangement for radar network. 

Abstract:In order to improve the torque-output precision of the magnetically suspended reaction flywheel, compensation methods were proposed respectively to attenuate the undesirable torque ripple caused by nonideal back electromotive force waveform and commutation in classical control of brushless direct current motor. The real-time back electromotive force was estimated according to the rotor position and speed in order to obtain the reference current, the pulse width modulation duty cycle was calculated in the torque controller to compensate the torque ripple caused by the nonideal back electromotive force. The theoretical derivation was analyzed, methods of modulation of the non-commutation phase during low-speed range and modulation of the switching-out phase during high-speed range were presented on the basis of the characteristics respectively. Also, a calculation method of the commutation time was given. The experimental results show that the proposed methods can achieve an effective compensation.

Abstract:Three problems are normally found in the spare parts configuration of phased array antenna, namely, the strong redundancy, the batch delivery maintenance and the multi-echelon maintenance. Aiming at these problems, through analyzing the relations among spare parts cost, repair capacity and inventory strategies, an optimal configuration model was established based on the periodic review strategies. Firstly, the repair circulation process of fault component and the periodic supply process of maintenance spare parts were given, and then the system supply availability model was built by analyzing the relations among spare parts, inventories and repair capacity, and the batch arrival queuing theory was also used. Secondly, an optimal configuration model of spare parts was built, which takes minimum spare parts costs as the object and the system availability as the subject. Next, solution algorithm based on the margin analysis theory to the model was also given. Finally, simulations and analysis of an instance were conducted to verify the proposed model, and results show that the model can solve the spare parts allocation problems of phased array antenna well, and has a high superiority. 

Abstract:In order to investigate the meshing scale of the FE-IE (finite element coupled infinite element) method for a ring stiffened cylindrical shell, the guidance was put forward for the structural wetted surface. Numerical results show that, for ring-stiffened cylindrical shells, the bending wavelength of the main vibration mode can be taken as the reference of meshing scale in FE-IE calculation which is testified with at least two finite elements per distance of stiffeners. There are at least six finite elements per one bending wavelength of the main vibration mode. The bending wavelength of the main vibration mode is used as the reference of meshing scale of FE-IE calculation rather than the shortest wavelength of structural waves. The obtained conclusions are significant to the meshing of structural wetted surface and the controlling of the total number of elements in the interior fluid region.

Abstract:A method for measuring the volume fractions of component material of textile composite by using micro CT experiments was developed. This method can present global, local fiber and yarn volume fractions by micro CT images in different scales, and can also offer solutions to the difficult volume fractions measurement of component materials of some composites which cannot be measured directly by conventional physical experiments. An E-Glass/Epoxy textile composite was used to illustrate the feasibility and reasonability of the method by the comparisons of the measured values among ASTM D3171 Procedure G, scanning electron microscope and micro CT experiments. Corresponding image processing methods for the scanning electron microscope and micro CT images were used to acquire the accurate component material segmentations. The measurement of micro CT experiments can be widely applied to measure the volume fractions of component materials of composite.

Abstract:Based on the theoretical resistance function from dynamic spherical cavity expansion model and the surface splitting mechanism, a prediction model was proposed for oblique penetration depth of rigid projectiles into concrete targets. In the proposed formula, the dimensionless coefficients denoting the projectile nose geometry were introduced to consider the variation of projectile nose geometry and the cratering depth. A prediction model for the decelerationtime history of the projectile with different nose geometries was obtained. The penetration depths and overload curve of the model were in good agreement with the test results. The research results can provide some help for the oblique penetration trajectory analysis and the design of the projectile head.

Abstract:The specific humidity profiles derived from the GPS（global positioning system） RO (radio occultation) of the COSMIC (constellation observing system for meteorology, ionosphere, and climate) with those from low latitude（30°S~30°N）radiosonde and MACC(monitoring atmospheric composition and climate) reanalysis during the NH (north hemisphere) winters (December, January, and February ) from 2006 to 2012 over the layers from 1000 hPa to 200 hPa were verified. Comparison results demonstrate that the impact of water vapor on the COSMIC GPS RO inversion is very large, especially over the tropical and low troposphere. And the COSMIC GPS RO observations below 850 hpa may not be suitable for the assessment of other observations. 