Abstract:Numerical investigation of the vertex flow characteristics on double-delta wing was presented. The flows over the 76/40-deg double-delta wing were computed with complete laminar when attack angles varies from 5-deg to 30-deg. The flow structures were exhibited in different angles and the analysis of the aero-dynamic characteristics was presented. The investigation shows that vortexes on the double-delta wing surface may fiercely interact with each other and the burst of vortexes caused by large attack angle will exert great influence on the aero-dynamic characteristics of double-delta wing.

Abstract:By the use of linear interpolation and accommodate parameter, a heat transfer bridging relation in transitional region is proposed in this paper, aiming to fix the accommodate parameter for cylinder whose edge surface is windward. The results of the bridging relation were validated by using DSMC method and compared with the results of other bridging relations. The validation shows that the bridging relation can be used to calculate the heat flux at the stagnation point with Mach number larger than 10.

Abstract:Theoretical analysis of heat and mass transfer is developed for the unsteady evaporation of a moving droplet which is suddenly placed into the gas circumstances. A mathematical model is proposed for the unsteady evaporation process of a droplet at the first moment and is solved by numerical method. The results indicate that the evaporation rate is very high for a moving droplet suddenly placed into the gas circumstance at the initial moment, which can make the temperature of droplet surface decline. The scope of the temperature decline is concerned with the initial temperature of the droplet, gas circumstances, and the initial velocity of the moving droplet as well.

Abstract:Two-dimension coupled implicit Navier-Stokes equations and standard k-εviscid model are introduced to simulate the inner and outer flow field of hypersonic vehicle, and the equations are discretized by the second order upwind scheme. When angle of attack is changing from -10°to 7°, the effects of viscosity on the lift, drag force and pitching moment characteristics of hypersonic vehicle in three working conditions including inlet closed, inlet open but unfired, inlet open and fired were discussed. Result shows that the influence is prominent when hypersonic vehicle works under inlet open but unfired、inlet open and fired conditions. especially This case will occur when the drag force characteristic, viscous drag force exceeds 50% of total drag force.

Abstract:VIMP (Vacuum Infusion Molding process) is widely used because it has many advantages, such as low cost, environmental protection and suitable for holistic mould of large composite structures. Curing reaction and rheological behavior of a low viscosity epoxy resin system were studied by DSC and viscosity experiments and an optimum curing temperature was found for the resin system. Based on Dual-Arrhenius equation, a rheological model of the resin system was established, and predicted viscosity values of the resins were in good agreement with the results of the experimental results. The low viscosity processing window for the VIMP was determined by the rheological model. A GFRP laminate was fabricated by the VIMP, and the fiber volume content and mechanical strength of the laminate composites were investigated.

Abstract:Benzoxazine resin is used to fabricate quartz fiber reinforced composites by RTM process in the paper. The processing properties and mechanical performances of benzoxazine resin are studied systematically, and quartz/benzoxazine resin composites are manufactured by RTM to test their mechanical performances and ablation properties. Some properties are compared with those of barium-phenolic resin and its quartz fiber composites. The results show that benzoxazine resin maintains low-viscosity less than 800mPa.s in the range from 85℃ to 145℃, and has a wide low-viscosity temperature window and a long low-viscosity keeping time. The interlaminar shear strength(ILSS) of quartz/benzoxazine resin composites reaches 61.5MPa, the tensile strength and the flexural strength are more excellent than those of quartz/barium-phenolic resin composites. The mass ablation rate and line ablation rate of quartz/benzoxazine composites reach 0.0510g(s^-1and 0.032mm(s^-1 , respectively. Quartz/benzoxazine resin composites can be used as ablative materials and fabricated by RTM process.

Abstract:Bis(4-tertbutylphenyl)hydroxyketone and bis(1,2-di(4-tertbutylphenyl)-1,2-ethylenedithiolato) nickel complex (DYE-02) were synthesized and characterized by elemental analysis, 1H NMR and infrared spectra. The photostabilization of DYE-02 and its photostability to cyanine dye(Cy7) were studied. The results show that DYE-02 has a bathochromic shift absorbing in near infrared at 855nm. In addition, DYE-02 has better self photostabilization and better photostability to Cy7 than bis(1,2-diphenyl-1,2-ethylene dithiolato) nickel complex (DYE-01).

Abstract:Polarimetric characteristic of scattering light was used in the polarization remote sensing to identify targets. It is a new method of detection with several advantages compared with traditional radiant intensity remote sensing. To study the effect of polarization stealth, polarimetric characteristics of camouflage net and images of polarization degree were measured under different conditions. The results indicate that polarimetric characteristics of camouflage net were influenced by several factors, such as conditions of illumination, detection and characteristics of materials. The variation of polarization degree was represented as reverse ratio to the reflectance of surface and direct ratio to the incidence angle. Compared with that of meadow, the polarization degree of camouflage net was much higher and could be identified clearly. Camouflage net meeting the request of multi-spectral remote sensing has little effect when it comes to polarization remote sensing. Thus, polarization remote sensing brings new challenges to camouflage technique.

Abstract:The wide-band LFM pulse de-chirp return signals model of maneuvering target is studied. Based on the spectral expansion characteristics of the velocity and acceleration's frequency modulation, a novel linear frequency modulation(FM) return signals model of wide-band range profile of maneuvering target is proposed. Linear parameter estimation and compensation of range profile via Radon-ambiguity transform (RAT) is presented, and the measurement errors of range and velocity are analyzed. The simulation results validate linear compensation model via RAT, indicating that this method can resolve the range profile spectral expansion of maneuvering target unknown motion parameters.

Abstract:Wideband full-polarization measurement for radar target is of important application in the research fields of radar imaging and target recognition. Based on orthogonal frequency division and full-polarization instantaneous measuring method, a new waveform vector was designed to get full-polarization information simultaneously under wideband condition. Firstly, the models of emitting and receiving signals were given, and full-polarization datum in frequency could be gathered, and then target full-polarization range profiles were obtained after IDFT. Finally, the validity of this measuring method was verified by simulation, using simulated datum and real measured datum.

Abstract:In high precision PN code ranging systems, HPA is an important component. However HPA introduces nonlinear distortion. As a result, it decreases the ranging performance. The PN code ranging error caused by the nonlinearity of HPA is studied, by means of theoretical deduction and numerical simulation. Quantitative relation of ranging error and HPA type, HPA output back-off, code chip waveform parameter is employed. The research result provides important suggestion for the choice of HPA type, the reservation of HPA power and the design of PN code waveform.

Abstract:Polarization estimation of interference signal is crucial for adaptive polarization filters. The filtering effect is restricted by the precision of polarization estimator. Based on the antenna's spatial polarization characteristics of single polarization radar, a new method for polarization state estimation of receiving wave is presented in this paper. Firstly, the principle of the estimation algorithm is introduced. Its performance is analyzed theoretically. Then, corresponding simulation experiment is made to discuss the main factors influencing the algorithm performance and the main approach to improving the performance is given. The validity of this method is demonstrated by theoretical derivation and computer simulation result.

Abstract:The range walk correction (RWC) in time domain can resolve range walk problem in high squint SAR imaging. However, the limit of focus depth exists. By analyzing the residual phase error after wave number decoupling and Doppler rate error caused by RWC, a refined azimuth non-linear chirp scaling (ANCS) algorithm is proposed. Phase error caused by the third order range migration is corrected and a nonlinear CS function is applied to equalize the targets Doppler rates before azimuth compression. Simulation results show that the refined ANCS algorithm has good performance.

Abstract:Owing to the complexity of the electromagnetic scattering characteristics of man-made targets, it is difficult for traditional extraction methods to discriminate all potential targets from polarimetric synthetic aperture radar (POLSAR) images. To overcome this shortcoming, a novel scheme based on scattering mechanism identification and azimuthal symmetry decision is proposed in this paper. The novel scheme is implemented based on the difference between man-made target,and natural clutter on scattering mechanism type and the property of azimuthal symmetry. Compared with traditional methods, our scheme has the advantage of obtaining a more successful result, and targets exhibiting different types of polarimetric characteristics can all be well extracted. The validity of the novel scheme is verified by fully polarimetric SAR data.

Abstract:A robust target tracking algorithm with fast convergence is very important in single observer passive target tracking system which has inherent disadvantage of weak observability and large initial error. Considering the characteristics of single observer passive target tracking systems via spatial-frequency domain information, a robust improved UKF algorithm is proposed in this paper. Robustness of this algorithm is enhanced by using radial velocity as a state variable and limiting its initial estimating error in a certain bound. A re-sampling process is added to replace the state variables extending of conventional UKF, thus making less computation amount and easier realization. Compared with usual algorithms used in single observer passive target trackings, such as EKF and UKF, the new algorithm is more robust and has faster convergence velocity, lower tracking error. The correctness and validity of the algorithm are comfirmed by the numerical simulation results.

Abstract:With an analysis of the types and formation mechanism of interferences in the vehicle-mounted ultra-wideband synthetic aperture radar (UWB SAR) detection system, a novel adaptive method is presented for the interferences suppression in the image domain based on the iterative technique. It can overcome the limitations and drawbacks of a batch processing method proposed by Tsaipei Wang. By exploiting the constant false alarm rate (CFAR) detector with weibull distribution, the new method can improve the accuracy of interference estimation. Then the parameters estimation and updating can be realized by using the iterative operation, and the adaptive interference suppression can be achieved on line. The processing results of real data show that the proposed method can effectively suppress the self-signature interference and is prone to real-time processing in structure. It can meet the needs of real-time preprocessing in the vehicle-mounted UWB SAR detection system.

Abstract:A compact two-dimensional(2-D) finite-difference frequency-domain method is used to analyze propagation characteristics of generalized ridge waveguides for the first time. Only four transverse field components are involved in the final resulting eigenvalue problem, so the required CPU time is reduced considerably as compared to the approaches by which six field components are comprised. Additionally, the feature of finding the phase constant for a given frequency is more pertinent in practical applications. To deal with the generalized ridge waveguides, we divide complex structure into several regular sub-regions, and apply the compact 2-D FDFD method respectively in every sub-region only by setting boundary conditions accordingly. Finally, the calculated numerical results in the current study show good agreement with the published ones in this field.

Abstract:The fractional Fourier transform (FRFT) is a generalization of the Fourier transform. To the linear frequency modulation (LFM) signal, the FRFT is a good way for signal accumulation. Aiming at the linear frequency modulation characteristic of the anti-radiation missile (ARM) echo signal, an improved method for ARM detection based on FRFT is proposed. The areas of peak search were reduced and the detection efficiency was improved when the FRFT was localized. The simulation experiments show that the reliable detection of ARM signal can be achieved with this method under the Gauss or non-Gauss clutter environment.

Abstract:Knowledge reduction is one of the important topics in the research on rough set theory, and rough decision rules are inevitably provided with uncertainty. In this paper, a family of focal sets is constructed within the framework of evidence theory on the basis of variable precision rough set theory. Accordingly, the function of basic probability assignment is defined, and then the total information entropy is calculated for evidence theory, namely the evidence entropy. Uncertainty measure for the decision table is determined by that entropy. Based on the measure, the heuristic algorithm is proposed for decision table reduction. Finally, the experimental results show the validity of the methodology.

Abstract:Magnesium Fluoride crystal processed under high temperature and high pressure, one of the infrared optic material, has been used in many areas. Magnetorheological finishing (MRF) is becoming an ultra-precision finshing technology because of its excellencies of high polishing efficiency, no wear and certain polishing. In this paper, at the first, the polishing characteristics are obtained by using traditional polishing method; and then, a new magnetorheological fluid suitable to finishing Magnesium Fluoride is developed. Compared to traditional polishing method, the method proposed here can yield higher surface quality and higher polishing efficiency.

Abstract:Because of the aliasing of the received waves and the sparse structure of the reflection signals, the temporal resolution is not good in acoustic detection of buried objects with low frequency waves. Thus, the problem of resolving the reflection position is notoriously ill-posed. In this paper, a maximum a posteriori estimator is presented to regularize the ill-posed problem, and an algorithm of particle swarm optimization is proposed to improve temporal resolution and reduce execution time. The results from research show that the method is efficient for using practical data in detecting objects buried in sand.

Abstract:The efficiency and the parallelism of discrete event simulation can be improved through simulation cloning. Analysis, comparison and evaluation of what-if can be processed quickly and conveniently. Based on detailed introduction of simulation cloning and the analysis of the deficiency on encapsuled simulation cloning middleware, an articulated simulation cloning middleware of performing concurrent multiple scenarios is proposed and designed. The architecture of federate based on articulated simulation cloning middleware is discussed. Time delay of the federate based on articulated simulation cloning middleware is measured in experiment. The results demonstrate that the time delay caused by the decoupled federate architecture is limited and stabilized, indicating the feasibility of the method proposed.

Abstract:A measurement matrix optimization approach for the linear time-invariant system of which the cyclic index is bigger than 1 (some different Jordan blocks of its Jordan canonical form have the same eigenvalue) was studied. Based on the proving of some cyclic subspace theories and relative properties of root vector chain, the relationship of measurement vectors' linear combination and the system observability was obtained. An approach which can achieve the minimum test cost and assure the system observability at the same time is presented. As the computation example shows, this approach is promising in engineering application as it is simple and straightforward.

Abstract:HLA can facilitate the interoperability and reuse of all types of simulation systems; however, several drawbacks have affected its wide application in commercial communities, such as binding of interface specification to programming languages, and insufficient integration with commercial technologies. Web service has some attractive features on platform/vendor independence, and hence Web service enabling of HLA-based distributed simulation is promising for adding value to HLA. Based on the analysis of HLA's drawbacks and Web service's advantages, Web service enabling of HLA is introduced, interoperability on those two contexts is compared, and three levels of realizing Web service enabling of HLA are analyzed. Then, related research is surveyed, and key issues and their solutions to realizing a Web enabled RTI are discussed; Finally a prototype is designed, and experiments show that it can primarily implement Web service enabling of RTI.

Abstract:This paper presents a parameter-adaptation sliding control algorithm based on the analysis of zero-order switching sliding mode control algorithm for the non-linear control model of Antilock-Braking System (ABS). The algorithm, which combines sliding mode control, adaptive control and ABS, weakens the influence of chattering on braking process. The closed loop emulated system of ABS, on which ideal and half practical simulation are completed, is designed and constructed. The results of simulation verify that the adaptive sliding algorithm has the advantage of less the brake torque chattering and smoothening fluctuation of wheel speed signals compared with pure sliding control algorithm.

Abstract:Credibility is the key factor for system simulation. The HLA simulation system based on BOM can promote the reusability and interoperability on the simulation model level. To insure the credibility of this simulation system, it is very necessary to study VV&A in modeling and simulation of all the life cycle. Firstly, the FEDEP (Federation Development and Execution Process) model of HLA simulation system based on BOM is introduced, and the VV&A process is put forward briefly. Then the research of V&V for user model, simulation model component and federate are made. Finally the approach is applied in the anti-ship missile's penetration federation. The result shows that the VV&A process is feasible, which can ensure the credibility of the simulation system.

Abstract:Dimension reducing is very important in VSM based text classification system. Feature selection is more suitable for text data because of its efficiency. A new feature selection algorithm is proposed in this paper on the basis of Fisher linear discriminant model, which converts the solution process to feature optimization problem and avoids the complex matrix operations. The experiment shows that the new algorithm has good performance and is better than IG and CHI method.