Abstract:Considering the two different cavity arrangement schemes, a series of direct-connected combustion tests were conducted with vaporized RP-3 under the simulated Mach 6.0 flight condition. Effects of cavity arrangement on characteristics of supersonic combustion of vaporized kerosene were investigated by comparing with the high-speed flame luminosity images, static pressure distributions along the combustor wall, and the thrust increments. The results show that the cavity arrangement and equivalence ratios affect the flame distribution, the heat release characteristic and the combustor performance significantly. For the parallel-cavity-equipped combustor, the flame distribution and heat release are concentrated near cavities, and the fuel specific impulse shows low sensitivity to the equivalence ratio. While the single-cavity-equipped combustor has a dispersive flame distribution and heat release, and the fuel specific impulse increases with the equivalence ratio.

Abstract:In order to satisfy the demand of scramjet ground test, a gas generator was designed. Tests were taken to study the stability characteristics of combustion using the statistical approach. Results indicate that the proportion of unsteady combustion accounts for 32.7%. All unsteady combustion occurred belongs to low frequency oscillation. There are two kinds of oscillation forms. One has dominant frequency crest, which has low frequency combustion instability or chuffing. For the other one, there is no dominant frequency crest，namely rough combustion. The probability that rough combustion occurs is relatively high and it is related to the excess oxidizer coefficient, while the low frequency combustion instability occurs with lower probability. Result shows that the energy distribution of the two unsteady combustions is different. 

Abstract:To study the combustion characteristics of a rocket engine under continuous throttling, a continuous throttling experiment was conducted by using GOX(gaseous oxygen)/kerosene as propellants. Mass flow rate of kerosene was continuously throttled by a throttleable cavitation Venturi nozzle. Successful ignition under fuel rich condition (mixture ratio ranged from 0.405 to 0.690) and the continuous throttling of mixture ratio and combustion gas flow rate were achieved. Results show that chamber pressure increases with the decrease of kerosene flow when the mixture ratio is less than 0.535 but decreases when the mixture ratio is greater than 0.535. Meanwhile, characteristic velocity and combustion efficiency increase with the increasing mixture ratio, but the increasing ratio is bigger when the mixture ratio is less than 0.535 than that when the mixture ratio is greater than 0.535. The results indicate that the mass flow rate of propellants and combustion efficiency simultaneously affect the chamber pressure. Combustion efficiency dominates the chamber pressure when the mixture ratio is less than 0.535 while mass flow rate of propellants dominates when the mixture ratio is greater than 0.535.

Abstract:A new structure, the platelet heatpipecooled leading edge, was proposed for hypersonic vehicle thermal protection. In order to avoid the challenge of modeling two-phase conjugate heat and mass transfer, an approach of modeling the vapor core as a solid thermal conductor with high conductivity was adopted and the effective vapor thermal conductivity was deduced mathematically. Its effectiveness was validated by comparing the wall temperature against experimental date for a conventional heat pipe. The research result indicates that the nickel based alloy IN718, with sodium as the working fluid, is a feasible combination form Mach 7 with a 15 mm leading edge radius.

Abstract:In order to analyze the feasibility of MHD (magnetohydrodynamic) heat shield system for the nose cone of hypersonic vehicles, a normal columned solenoid-based MHD thermal protection system model was built. By using the low magneto-Reynolds MHD model, a set of numerical simulations for hypersonic nose cone with external magnetic field were performed; the feasible range of magnetic induction intensity of normal solenoid-based MHD heat shield system was obtained; the requirements of the solenoid's geometric parameters were drawn to meet the limit of coil current density. Results show that, considering the saturation effect and the current density limit existing in the process of MHD thermal protection, the system works better when the stagnation magnetic induction intensity B₀ is in the range of 0.05～0.20 T. When B₀ is equal to 0.20 T, the stagnation heat flux density and total wall heat flux is reduced by 31.3% and 56.6% respectively, indicating the effectiveness of thermal protection. However, the required coil mass is so heavy that its structure must be optimized to be actually utilized.

Abstract:Method of inviscid flow field simulation of the outer edge boundary layer for hypersonic vehicle was created, which was faster than the numerical method and more accurate than the engineering method. And the curve of specific heat and the specific heat ratio changed with temperature were matched, which deduced the law of air attribute on different temperatures. Based on the law, the model of parameters of the outer edge boundary layer for hypersonic vehicle was built, and the comparisons of the results of the proposed method and the engineering method as well as the viscid method of blunt double-cone model were analyzed. Result shows that at the 0° angle of attack, compared with the viscid method, the maximum differences of the pressures between engineering method and viscid method are about 1.19% and 2.39% respectively, while at the 10°angle of attack, they are about 5% and 50% respectively. And the proposed inviscid numerical method obtained higher accuracy is superior to the engineering method, which lays the foundation for the thermal environment calculation of hypersonic-glide vehicle.

Abstract:Side wall shock wave was introduced in supersonic combustor based on cavity. In order to study the internal flow characteristics of the combustor, nanoparticle planer laser scattering and particle image velocimetry technologies were employed to observe internal flow field of combustor model made by glass. Gray images and average velocity distributions of non-reaction flow field in side view and top view were caught by experimental facilities. Observation results reveal that: speed and density of fluid inside cavity are low in the region far away from the side wall; mass and momentum exchange is enhanced in the region near the side wall on condition of side wall shock wave with high speed and density; boundary layer of combustor bottom wall becomes nonuniform due to side wall shock waves, and large scale of low speed region generates at the rear of cavity with obvious three-dimensional characteristics.

Abstract:An integrated thermoelectric generation thermal management system for a regenerative cooling scramjet was proposed. Thermoelectric power generators were integrated in the scramjet structure. The integrated thermoelectric generation thermal management system reduces the fuel flux for cooling, through converting part of the energy by heat conduction on the scramjet structure to electric power. The heat that must be taken away by fuel is decreased and the fuel cooling capacity is indirectly increased. At the same time, high temperature and high pressure fuel also has the capacity for doing work. It flows through a turbine and get additional power output for the use of hypersonic vehicle. A parametric study of the integrated thermoelectric generation thermal management system for scramjet was performed. It is known through performance analysis that the integrated thermoelectric generation thermal management system has excellent potential performance over the conventional regenerative cooling. The fuel flux is reduced while the integrated thermoelectric generation thermal management system gives power output.

Abstract:Numerical studies on a spatially developing supersonic mixing layer were performed by means of large-eddy simulation. Focusing on the effect of transverse forcing on the passive scalar mixing characteristic of mixing layer. The results for the baseline case without external forcing are in agreement with the analytical evidence. Afterwards, the effect of transverse forcing on the scalar structure, scalar thickness and volumetric entrainment ratio of mixing layer were analyzed. Results indicate that the frequency and amplitude of transverse forcing alter the growth rate and entrainment ratio of the passive scalar mixing significantly. High-frequency forcing magnifies the scalar thickness and volumetric entrainment ratio in the near field of mixing layer. However, the growth rate in the far field is increased by the low-frequency forcing. The entrainment ratio is, to be a large extent, dominated by the large-scale eddy entrainment process. The multiple-frequency forcing seems to validly enhance the scalar mixing in supersonic mixing layer.

Abstract:In order to develop a high-order finite volume scheme, which can perform with high fidelity in smooth regions, capture the discontinuities without oscillation, and overcome the difficulty in choosing stencils, a high-order finite volume scheme on structure meshes was developed on the basis of dimension-by-dimension reconstruction method. The scheme was also extended to the three-dimensional curvilinear coordinate system, which was suitable for the computation under relatively complex configurations. In order to validate the numerical scheme, some test cases were used. In the cases of the isentropic vortex and two-dimensional channel flow, it was found that the designed order of accuracy could be achieved. In the double Mach problem, it was proved that the scheme could well capture the discontinuities. The test cases show that the scheme has high numerical accuracy and robust capturing ability on curvilinear meshes and high efficiency in the simulations of the computational fluids dynamics.

Abstract:The existing integrated methods are mainly aimed at the layer of database system. In view of the shortage of those methods, the integration method in the application layer was focused on. According to a new perspective of access control for the database application system, the access control layer was separated from the application layer. A new method called as “fusion” access control was put forward. Based on the method, a simplified integration method of heterogeneous database application system was proposed. An example was shown about how to apply the simplified integration method to achieve the integration of heterogeneous database application system, and the advantages of the new method were verified by a comparison analysis.

Abstract:A novel method based on generative model was proposed for human behavior recognition. The behavior was represented by using a set of descriptors computed from key point trajectories, which included the orientationmagnitude descriptor, the trajectory shape descriptor and the appearance descriptor. In order to reduce feature dimensions, the agglomerative information bottleneck approach was used for vocabulary compression. The semi-supervised learning method for behavior recognition based on generative model was proposed to solve the problem of small sample in recognition, which made use of both the labeled and unlabeled samples. Compared with other state-of-the-art methods in both UCF sports database and YouTube database, results show that the proposed method has higher recognition accuracy.

Abstract:In order to execute graph pattern matching quickly in distributed large-scale graphs, an effective distributed algorithm using partial evaluation, namely disGPM-PE was proposed. Firstly, partial matching was performed locally at each computer nodes in parallel. Secondly, a coordinator node assembled the partial matching results, evaluated and sent the matching conditions of boundary nodes to corresponding computer nodes. Thirdly, each computer nodes determines the matching conditions of the nodes connected to the boundary nodes. Finally, the maximum matching set was collected at the coordinator node. Experiment results show that the disGPM-PE algorithm can avoid the impact of the dependent relations between data fragments on the execution time. Compared with the previous distributed graph pattern matching algorithms, the disGPM-PE algorithm can reduce the execution time of graph pattern matching while do not increase the network traffic obviously. 

Abstract:With the increasing of clock frequency and the decreasing of supply voltage, power integrity becomes a critical issue. The effect of the transition time of load currents was taken into account, and a more realistic worst-case noise prediction was obtained. In addition, a dynamic programming algorithm is introduced for the time-domain impulse response of the power distribution system, and a modified Knuth-Yao quadrangle inequality speedup method is developed which reduces the time complexity of the algorithm from O(n₂m) to O(mnlogn).

Abstract:Beam forming processing of adaptive antenna introduces the change of antenna phase center. In order to solve this problem, an evaluation method of adaptive antenna phase center on the basis of available beam was proposed. The method achieved the purpose in three steps: setting the available beam threshold; obtaining phase pattern set in available beam areas when the direction of interference signal distributed uniformly; fitting the phase pattern set to get the average phase center variations of adaptive antenna by using least square method. The method was validated by simulation under four typical four-elements-arrays. The analysis of simulated results indicates that the proposed method can be used to evaluate the phase center characters of adaptive antenna conveniently. What’s more, in order to fulfill the performance of high precision for adaptive antenna array, a choice is to reduce the available beam threshold. The research can be used as a guideline for choice of distributions of antenna elements in high-precision GNSS.

Abstract:There exist several problems in the maintenance of phased array antenna, such as high maintenance costs, unsure maintenance chance, complicated model simulation and arithmetical operation. Considering these problems, a maintenance optimal model was put forth on the basis of regional quantification. A regional quantification model was given, and then the maintenance problems of phased array antenna were turned into the maintenance optimal of a k/n system, which consists of different regional array elements. A maintenance optimal model for the antenna was built, which chooses minimum maintenance costs per unit time as the object and the operational availability as the subject. Simulations and analysis of one instance were conducted to verify the validity of the proposed model. The results show that the proposed model could solve the maintenance problems of the asymmetrical array antenna well. 

Abstract:To tackle the inherent high nonlinearity of motion equation and observation equation of radiation source, a GS (Gaussian-sum) based 5CKF (5th-order cubature Kalman filter) tracking algorithm, referred to as GS-5CKF, was proposed. It consists of multiple parallel 5CKFs, which were initialized through partitioning the candidate source positions determined by the time difference of arrival measurement at the beginning of the tracking process with respect to the source latitude. The linear combination of filter outputs was conducted to estimate the motion state of radiation source. A new nonlinearity measure was advocated, on the basis of which a filtering splitting and merging procedure was developed to further enhance the performance of GS-5CKF while keeping its computational complexity fixed. Simulation results show that: compared with the tracking algorithms using the single 5CKF and the GS-3CKF, the newly proposed GS-5CKF technique exhibits higher source geolocation accuracy.

Abstract:The hop timing estimates derived from existing methods are coarse and unreliable, therefore, a novel method for estimating hop timing for frequency-hopping signals precisely was proposed based on an improved orthogonal matching pursuit algorithm. The sparse representation model for hop timing estimation was established according to the principle of frequency-hopping signals. Then, the improved orthogonal matching pursuit algorithm was used to solute the model and get hop timing finally. The theoretical analysis and simulation results verified that the method is capable of obtaining precise hop timing, and is better than current methods.

Abstract:The modulation with different power of data and pilot channels will be used in the next generation of global navigation satellite systems. However, the traditional acquisition algorithms are mostly designed with equal-weighted coefficient of data and pilot channels. When the power of data and pilot channels is not equal, the traditional algorithms are not suitable for optimizing the performance. A power-weighted combining acquisition algorithm, which uses the different weighted coefficients for data and pilot channels, was proposed. The Least-Square fitting method was used to optimize the coefficients. The detection and false-alarm probabilities were derived with characteristic function of decision variable. The simulations prove that the acquisition threshold of the algorithm is improved by 0.4 dB when the power ratio of data and pilot channels is 1 ∶3, and the detection and false-alarm probabilities are 0.8 and 10^-3 respectively.

Abstract:An online prediction model for the energetic electron flux at the geostationary orbit was built based on the PSO (particle swarm optimization) algorithm and the LSSVM (least squares support vector machines) method. To overcome the premature convergence problem in PSO, a new diversity measure was put forward. The improved PSO was utilized to optimize the LSSVM′s parameters. Through a sliding time window strategy, a variable selection invoking threshold and a model re-training mechanism, the online characteristic of the model was realized. 1～3 day ahead prediction experiments were done on the basis of the electron flux data, solar wind parameters and geomagnetic parameters in 2000, and the analysis results show that the proposed online PSO-LSSVM model works well and has practicable value for prediction.

Abstract:There is non-zero bias for the receiver due to the anti-jamming filter in non-ideal channel. Furthermore, since the tap weights of the adaptive transversal filter varies based on jamming pattern, the bias will also vary. This problem of code tracking bias has been a significant hurdle to achieving interference suppression capabilities in precision global navigation satellite system applications. Aiming at this problem, using the symmetrical characteristic of non-ideal analog receiver channel, a new technique called zero bias anti-jamming filter was presented. The proposed method could be easy implement in engineering. Theoretical analysis and simulative results show that the proposed method is capable of reducing the bias to less than 0.2 ns, which is significantly smaller than the traditional adaptive anti-jamming filter.

Abstract:At present, studies in spares allotment optimization area mainly focus on the conditions that there is only qualitative or quantitative constraint. Nevertheless, the mix-conditions have not been reported to the best of our knowledge from the literatures. The researches usually concern the single warship, but fewer show concern about the warship formation. In view of this problem, the mission preparation of warship formation before sailing was taken as a research background; the warship formation support cost, warship storage space, warship carrying ability and crew maintenance ability were adopted as the mixed-constraints conditions; the spare parts support probability was served as the objective function. A normal reverse distribution cloud model, the marginal effect and the Lagrange multiplier methods (CML model) were used to solve such warship formation spare parts allotment problem. A method was proposed for the determination and dynamical updating of system resource constraint factors, meanwhile, the selecting methods and calculating process of the model was optimized. The reliability of the method which can provide a new trial for the problem of warship formation spare parts allotment under the mixed constraints condition was proved by an actual case.

Abstract:In order to exploit horizontal time-harmonic electric dipoles to model shaft rate electric field of practical vessels, the magnitude and location of equivalent source need to be determined. Aimed at vessels mounting the impressed current cathode protection system, the fact that the equivalent source is superimposition of two directionally opposite horizontal time-harmonic electric dipoles is clarified by analyzing the underlying physical mechanism of shaft rate electric field. On the basis of the former conclusion, a practical calculation method of equivalent source magnitude of shaft rate electric field was proposed, which means that the magnitude can be obtained by combining source magnitude of static electric dipole inverted from measured static electric field with the ratio coefficient between the maximum value of shaft rate signal envelope and that of static electric field signal. Besides, the location of equivalent source is identical to that of static electric dipole. The effectiveness of the proposed method is validated by the vessel model test. 

Abstract:The optimal allocation of labor is of great significance to improve the efficiency of equipment manufacturing. For the shortcoming of traditional Hungary algorithm could not solve the resource scheduling problem with parallel links, an improved Hungary algorithm was proposed. The improved algorithm converted the problem into a typical assignment problem by replacing parallel link jobs with virtual jobs, and optimized it with classical Hungary algorithm and determined the realizability of the virtual jobs based on the results. Finally, the optimal scheme was obtained through iterative searching. In addition, an example of multi-skilled labor allocation system is introduced to verify the effectiveness of the proposed algorithm.

Abstract:In order to identify vulnerable points in complex system roundly and assess its vulnerability scientifically, to improve the insufficiency of the pure topological methods, an analysis method integrated complex network theories and effectiveness assessment technologies was proposed, which considers both the topological and non-topological factors of vulnerability. Based on centricity measurements of complex network, a generalized indicators method was used for topological vulnerability analysis. Referring to the probability risk assessment theory, non-topological vulnerability was analyzed from susceptibility and brittleness. Then the final vulnerability results were integrated from the former two results. The demonstration results show that there is an intersection set but also some differences between topological and non-topological analysis. These two aspects of vulnerability are correlative and complementary close, they both contribute to the screening of critical points and links in a complex system, and compared to purely topological study, conclusions from integrated analysis were more comprehensive.

Abstract:The curing properties and chemorheological behaviors of the three heat resistant glyceramine epoxy resin systems for the injection repairing were measured by the isothermal differential scanning calorimetry and the rotational rheometer to investigate the curing cycle and the chemorheological characteristics of the resin systems. The MF-4101/ZH110/DMP-30 resin systems were proved to be the most suitable formulation for injection repairing by comparing the curing conditions and viscosities of the three resin systems. The Daul Arrhenius model and the highorder exponential fitting model were established to analyze the isothermal viscositytime curves of the resin system. Results show that the accuracy and the applicability of the high-order exponential fitting model for viscosity predicting are superior to the Daul Arrhenius model. The predicted results of the high-order exponential fitting model are in good agreement with the experimental data. This phenomenological formula based on the above model can be used to predict the processing windows of injection repairing resin systems. 

Abstract:For the problem of uneven distribution of gas hydrate synthesized in porous media, a new method for obtaining hydrate samples in porous media by microwave heating was proposed and a microwave heating apparatus was designed for this method. Based on the electromagnetic theory and the influencing factors of microwave heating uniformity, the adjustable multi-feeding microwave heating system was created. Numerical simulation and relevant heating test were made to analyze the effects of relative positions of the waveguides and specimen on apparatus heating uniformity, by which the feasibility of the apparatus to prepare gas hydrate synthesis was discussed. The results show that the heating uniformity is greatly affected by the variation of distance between the waveguides and specimen and it gets better with distance significantly. The consequence of numerical simulation is consistent with the result of experiment. The heating uniformity of the apparatus is less affected by heating time and the apparatus can meet the requirement of hydrates synthesis in uniformity，and its design may provide certain reference significance for the design of testing devices with some requirements in heating uniformity.

Abstract:In order to accurately estimate the tropospheric slant delay of the two-way troposphere time transfer system, the Hopfield zenith delay model and the CFA2.2 mapping function model which can estimate the tropospheric slant delay of satellite signals were analyzed and modified, and was accepted by the accurate estimation of slant delay caused by tropospheric scatter. The meteorologic data of three observation stations from 35°N to 37°N in 2010—2012 were selected to verify that the precision range of Hopfield model was less than 35 mm. Then, in order to calculate the tropospheric delay under different angle of incidence through modified model, three observation stations were distinguished by different baseline distance and the meteorologic data of those stations in 2012 were used. The day of year and the incident angle under maximum slant delay were also obtained. Results suggest that the max delay is 21.82 m to 35.45 m in a single way time transfer. In two-way time transfer, when the delay is counteracted by 90% or 95%, the time delay is 7.3 ns～11.7 ns or 3.6 ns～5.9 ns. 

Abstract:During the floating flight, the complex radiation-convection environment remarkably affects the flight performance and security of the stratospheric airship. The forced convection around the stratospheric airship plays an important role in the thermal behavior of the airship. Based on the hypothesis of pure heat conduction inside the airship, a three dimensional CFD model of stratospheric airships was developed and the thermal characteristics of the forced convective heat transfer of the airship were investigated. The distributions of the temperature of skins of the airship and the average temperature of the inner gas were calculated with the variation of the angle of the sun, the wind velocity and the angle of attack. Simulation results can be referenced for the accurate prediction of the thermal behavior of stratospheric airships.

Abstract:In order to reduce the underwater radiated noise of WCS (water-filled cylindrical shell) excited by an interior point acoustic source, a gas-bag was coated on the outer surface to form the gas-bag coated cylindrical shell. In order to give instructions on the design of GCWCS (gas-bag coated water-filled cylindrical shell), the bare and the gas-bag coated WCS were respectively simplified into the single-leaf and the double-leaf partitions. By comparing the wave impedances of the partition, gas and water, the influences of the sound velocity and thickness of gas on the low frequency radiation of double-leaf partition with plane incidence sound wave were analyzed. Analysis results show that gases with smaller sound velocity and proper thickness have better radiation noise reduction effect. The acoustic infinite element method was employed to calculate the underwater acoustic radiation of GCWCS, whose results are in good accordance with those of the partition analysis. The underwater radiated sound power and the far-field radiation sound pressure of the optimized CO₂-bag coated WCS are much lower than the bare one.