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2004 Vol. 30, No. 08

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Investigation of separation mechanism for airfoil leading edge flow at low Reynolds number
Ye Jian, Zou Zhengping, Lu Lipeng, Yang Lin
2004, 30(08): 693-697.
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A direct numerical simulation (DNS) around a 2-D airfoil was carried out through high order finite difference scheme, the Reynolds number based on chord is 1.0×104, the angle of attack is 3°. Via analyzing the quasi-periodic numerical solutions, the separation mechanism of leading edge flow at low Reynolds number is investigated, and the rules of vortices interaction are summarized. Numerical results indicate that there exists suction spike on airfoil near elliptical leading edge, separation occurs on the effect of strongly adverse pressure gradient of suction spike. Vortices structure including primary vortex, shed vortex and secondary vortex forms on the airfoil surface, its scale varies with time and it is absolutely unsteady. Surface pressure distribution can be used to describe the airfoil boundary layer flow well.
X-ray flat-panel-detector-based digital radiography and its image calibration
Zhou Zhenggan, Teng Shenghua, Jiang Wei, An Zhengang
2004, 30(08): 698-701.
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To improve imaging quality of X-ray digital radiography system, an X-ray flat-panel-detector-based digital radiography system was investigated. Four factors of flat panel detector which degrade image quality, such as random noise, offset, response nonuniformity and defective pixels, were introduced. How they occur and influence imaging quality was analyzed. Corresponding methods for image calibration were put forward to minish and eliminate the influences on image quality. Experimental results indicate that, with the image calibration methods, the influences of above mentioned factors can be removed effectively and the quality of image from flat panel detector can be improved greatly, which has founded a good foundation for succedent image identifying.
Analysis of vibration error in digital closed-loop fiber optic gyroscope
Song Ningfang, Zhang Chunxi, Li Lijing, Lin Heng
2004, 30(08): 702-704.
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Vibration error of fiber optic gyro affect its application performance directly. In order to solve the problem, the main causes of vibration error were analyzed. The expression between the closed-loop gyro output and optical power was conducted, The conclusion is that The inner stress of the fiber coil and the device pigtail caused by vibration leads to the variation of the polarization mode and optical power of propagating light. The vibration status of gyro mechanical structure, especially the resonance feature was analyzed with the method of finite element analysis (FEA) and verified by tests. So from the view of design and technique, some effective measures to improve the dynamic performance are put forward, included disposal of fiber coil and optical device pigtail, resonance free with reasonable structure design and improvement of closed-loop control. The result shows that the methods are valid. In vibration condition, the dynamic precision of fiber optic gyro is near static performance and satisfied application need.
Research on the pneumatic position servo system for climbing robot
Zhang Houxiang, Liu Rong, Wang Wei, Zong Guanghua
2004, 30(08): 705-708.
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To meet the requirements of glass-wall cleaning for high-rise buildings, a pneumatically actuated climbing robot has been developed. However, the characteristics of low-stiffness and nonlinearity in pneumatic system make accuratecylinder position control difficulty. To solve this problem, a new bang-bang control method was proposed. The whole control process is segmented into several bang-bang periods according to the piston position and velocity of cylinder. Withthis method, when the piston of cylinder is far from set position it can move quickly towards the target, and when the piston is near the set point it will reach the target accurately. Testing results show that this control method can effectively improve the control quality.
Aeroservoelastic stability on roll loop of a missile
Wang Jingyan, Yang Chao, Wu Zhigang
2004, 30(08): 709-712.
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Flexible air vehicles may encounter aeroservoelastic instability which is induced by the adverse coupling between structure, aerodynamics and controllers. Aeroservoelastic stability on roll loop of a missile with differential rudders and control system is analyzed. The generalized unsteady aerodynamics is calculated by the aerodynamics derivative method which is based on the quasi-steady aerodynamics theories. And the rigid-body roll and the first elastic torsion mode of missile body are concerned in the equations of dynamics. The open-loop transfer function of the roll loop is solved from the equation of dynamics, and the aeroservoelastic stability of the system is analyzed by using the Nyquist method. The results of a missile show that, the closed-loop aeroservoelastic system may be unstable when encounters ill-suited control design. So the elastic modes and frequencies of missile body should not be overlooked in missile design.
Experimental investigations on improvement of AO-resistant of epoxy resin by filled with superfine cenospheres
Wang Mingzhu, Zhao Xiaohu, Shen Zhigang, Xing Yushan
2004, 30(08): 713-717.
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A new method of improving AO-resistant characteristics of spacecraft resins is proposed. The superfine particles, which are stable in AO environment, are filled in the spacecraft resin in order to improve the AO-resistant characteristics of the composite. The emphasis of this paper is filling superfine cenospheres in the spacecraft epoxy resin to produce the AO-resistant composite. Cenospheres/epoxy resin composites were prepared and the AO exposure test was conducted in ground-based AO effects simulation facility. It was found that the filling of cenospheres effectually protected the epoxy resin against AO erosion. In addition, the surface characters of cenospheres affected the AO-resistant characteristics of the composites, and the modification of cenospheres can obviously improve the AO-resistant characteristics of the composites.
Auto-correlation function based estimation of the fractal dimension of natural texture images
Wang Hua, Wang Qi, Sun Jinwei
2004, 30(08): 718-722.
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A novel method for estimating the fractal dimension has been proposed and the method has been applied to estimate the fractal dimension in natural texture images. Fractal dimension is an important parameter to characterize roughness in an image. Extending the basic theory of fractional Brownian motion to the discrete case, the characteristics of auto-correlation function of fractional Gauss noise has been studied. Based on the characteristics, an auto-correlation function method is obtained to estimate fractal dimension. Both synthesis images of fractal and natural texture images are used to test the proposed method. The method is compared with the box-counting method and the results show that the auto-correlation function method is accurate and efficient.
Research on integrated control and supervision of engineering vehicles based on Agent
Yuan Haibin, Li Yunhua, Yang Liman
2004, 30(08): 723-726.
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An Agent-based distributed network control system was proposed, aiming at the requirement of control and supervision for undertaking complex and mission-critic workload in engineering vehicles and construct machinery. The system architecture, component, functionality of Agent-based integrated intelligent control and supervision in the engineering vehicles were studied. The entire system cooperation and information collaboration were accomplished by adopting hierarchical network control system and multi Agent system(MAS), so that the motion control, task plan and collaboration, condition monitoring and maintenance, fault diagnosis and tolerance can be fulfilled. The entire system is characterized by cooperation and collaboration of each Agent. The proposed system architecture was fulfilled in heavy-duty construct machinery and engineering vehicles.
Visco-plastic constitutive modeling of inelastic deformation of Udimet 720 Li at high temperature
Shi Duoqi, Yang Xiaoguang, Wang Yanrong
2004, 30(08): 727-731.
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The mechanical deformations of a Nickel-based superalloy Udimet 720 Li was modeled simultaneously by the Chaboche unified viscoplastic constitutive theory under tensile, cyclic and creep loading conditions at 700℃. To describing the phenomena of cyclic relaxation of mean stress under strain controlled cyclic loading and fast isotropic softening during unloading, the equations of internal variables of the theory were modified. A program code of parameter optimization was compiled with 1-dimentional Chaboche model by Levenberg-Marquadt nonlinear algorithm. A global strategy for model parameters optimization was proposed, which produced good results. The numerical simulations showed that this modified Chaboche model has sufficient capability of modeling various mechanical behaviors under complex loading conditions.
Performance of smart antenna when coupling and excitation error are considered
Li Miao, Lü Shanwei, Xue Minghua, Zhang Lei
2004, 30(08): 732-734.
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The performance of smart antenna in DS/CDMA(direct sequence/code division multiple access) systems is investigated when there are mutual coupling and/or excitation error which is compared with that in ideal situations. As an example, it is shown from the simulation that for adaptive arrays with half-wavelength spaced elements even there exist mutual coupling and/or excitation error, the radiation pattern's main beam can still point to the arrival direction of the desired signal. However, the interference cancellation ability decreases in some degrees and the effect of mutual coupling between array elements on the beamforming performance of adaptive arrays is more serious. So the mutual coupling should be taken into account in order to improve the performance.
Fuzzy adaptive Kalman filtering for spacecraft celestial navigation
Zhang Yu, Fang Jiancheng
2004, 30(08): 735-738.
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High positioning precision can be obtained by autonomous navigation method based on indirectly sensing horizon by stellar atmospheric refraction. Because of the limited resolution of the atmosphere density model, large instantaneous error would occur in the horizon sensed by this method. In this case, the performance of the navigation filter would be degraded, even divergent. A fuzzy inference system was applied to autonomous celestial navigation and a fuzzy adaptive algorithm based on the Unscented Kalman filter was presented to resolve the problem above. Stronger adaptive ability of navigation filter can be obtained by this adaptive algorithm when the observation is abnormal. The computer simulation results demonstrate the validity of this method.
Experimental study on single-phase flow and heat transfer for FC-72 in rectangular microchannels
Xie Yongqi, Yu Jianzu, Zhao Zenghui, Qin Yan
2004, 30(08): 739-743.
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The microchannel heat sink provides an efficient method to solve thermal control problems of the aviation electronic components. The experiment of single-phaseflow and forced convective heat transfer was carried out with FC-72 which was agood prospective electronic cooling fluid. Four rectangular microchannel heat sinks were used which had different structural parameters. The influences of liquid velocity, supercooling temperature and microchannel structures were analyzed. The correlations of single-phase flow resistance and forced convective heat transfer were given, and the uncertainty for experiment data was evaluated. The results show that the single-phase forced convective heat transfer characteristic of FC-72, flowing in rectangular microchannel heat sinks, can satisfy the heat dissipation requirements of middle or high flux for electronic devices.
Error block performance analysis for SDH based on background noise or impulse disturbing
Liu Xingchun, Li Zheng
2004, 30(08): 744-747.
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The error code performance is one of the most important transmission performances for optical fiber digital transmission system. And for synchronous digital hierarchy(SDH), the error block performance is usually used to describe error code performance. The error block performance under the inference of background noise which is usually described by Poisson distribution and impulse disturbing which is usually described by Neyman-A contagious distribution were discussed for SDH system. The general relationship of error block ratio on Poisson distribution and Neyman-A contagious distribution was derived.
Multi-model Kalman filter algorism based on GA
Wang Ziliang, Fang Jiancheng, Quan Wei
2004, 30(08): 748-752.
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A multi-model Kalman filter based on GA(genetic algorism) was designed. When the parameter is imprecise, estimation results of Kalman filter are false.Method used in this paper can estimate the best parameters on line,so as to get true estimation results.At the end of this paper the application to integrated navigation system was studied with simulation. The results of simulation show that as compared with single-model algorithm, this method not only can improve accuracy and reliability of integrated navigation system greatly,but also can identify the noise statistical models of inertial elements in the integrated navigation system relatively well.
Evaluation of fatigue lives for civil aircraft structures under corrosive condition
Liu Wen, Yang Hongyuan, He Xiaofan
2004, 30(08): 753-756.
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A method evaluating fatigue lives for civil aircraft structures under corrosive environment was presented. The service process of civil aircraft structures was simplified to two independent parts: pre-corrosion on the ground and in the air environment, corrosion fatigue in the air. All these effect factors were synthesized then the curve of corrosion influence factor(C) versus time(T) could be built up. Then evaluation of civil aircraft structures fatigue lives under corrosive environment could perform effectively by correcting fatigue life under common environment.
Application of predictive Fuzzy-PID in center air adjusting control system
Pang Liping, Wang Jun, Liu Wangkai
2004, 30(08): 757-761.
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The electrical heating element is often used in center air adjusting system. It is installed in the end of air supply duct system and can improve the control precision of temperature by combining with other elements in center air adjusting system. The temperature control method of electrical heating was presented, which adopted predictive Fuzzy-PID control arithmetic and realized steadytemperature control. The smith predictor, Fuzzy controller and PID controller were integrated into the new control method. The predictive Fuzzy-PID controllingto temperature in center air adjusting system was simulated in MATLAB. Its results indicate that the control method, whose control precision reaches ±0.1℃, can improve the temperature stability and reduce the energy consume. This control method could be used in other similar instance with electrical heating element.
Study on GPS timing and frequency calibration method and the test results
Zhao Junxiang, Li Jianhui, Chang Qing, Zhang Qishan
2004, 30(08): 762-766.
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To solve the problem of time synchronization and frequency calibration among different stations in an integrated multi-target tracking system, two methods using global positioning system(GPS) through observing one or more GPS satellites in common view are put forward. Calculation formulas are derived, the impacts on time synchronization of error sources such as ephemeris error, satellite clock error, ionospheric error, tropospheric error, multi-path effects and receiver’s hardware delay are analyzed. To validate time synchronization and frequency calibration precision, some related tests were got. Comparing with Cesium clock, it shows that nanosecond level time synchronization can be obtained and the precision of frequency calibration is better than 5.0×10-11 using GPS. More precise time synchronization and frequency calibration can be achieved by using multi-satellites in common view than using single satellite.
Application of boundary-tracing and Freeman code in quantitative metallography
Yu Yang, Liu Erli, Zhou Tietao, Liu Peiying
2004, 30(08): 767-770.
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The grainy second phase of multi-phase alloy was processed by various image pretreatments according to different conditions to obtain binary image of the discreet multi-object. These image pretreatments include two-value transformation, grain segmentation, hole-filling and filtering. To analyze the multi-object, a boundary tracing algorithm for multi-object was presented. With the algorithm, the Freeman code of every grain's boundary was produced by 8 direction boundary tracing, thus the second phase characteristic parameters, such as volume fraction, perimeter, area, shape factor, mean free path etc, were obtained. The experiment results show that the algorithm is effective for discreet multi-object analysis by having done the above-mentioned pretreatments.
Ecological organizational model on workflow system
Wan Liangjun, Huai Jinpeng
2004, 30(08): 771-776.
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In order to solve the problem of lacking structure flexibility and changing initiative in traditional organizational models, the weaknesses in existing researching works was summarized and an ecological organizational model was put forward. Essential factors of ecological organizational model was introduced and they embodied environmental relevance and entity changing features. A meta-model and formal definitions were described. The research methodology that described and forecasted relevancy level and changing aptitude for the organization entities on workflow system ecological environment was presented. Ordering method was regarded as a mathematical tool for organizational situation analysis, and a series of situation parameters were designed for displaying entity changing aptitude. These concepts, model description and methodologies are implemented and verified in an open workflow system-ABCflow.
Research of new conceptive rotated ramjet
Wang Yun, Zhao Xiaolu, Xu Jianzhong, Ang Haisong
2004, 30(08): 777-782.
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To solve the problems which the performance and cost of the gas turbine are restricted by structure and material and the ramjet can not be used independently and can be used on ground, a new conceptive rotated ramjet based on the ram-compressed technology was presented by analyzed the structures of the turbine and ramjet and inter-combustion engine. The engine's main body structure is an internal-combustion rotor, which has no blade and no piston but has an internal revolved stream combustor. This rotor has the functions of compressing air and combusting and doing work by exhausting. The general scheme and principle and performance of the engine were discussed. The results show that the configuration of the engine is simple, and the engine will be designed with high efficiency but low cost and large power but small volume. The engine can be use to aviation power and other power on ground.
Effects of defects on the tensile strength of rigid polyurethane foamed plastics
Lu Zixing, Shi Shanglu, Wang Jianhua
2004, 30(08): 783-786.
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The tensile tests have been done for different densities polyurethane rigid foam (PURF) specimens with and without defects. On the basis of experiments, the strength of PURF is investigated and the effects of defect with different kind and different size on the ultimate strength of PURF are discussed at the same time. The result of experiments shows that the tensile strengths of PURF specimens stored in a long time (about 6 years) have not been changed and they are proportional to the square of relative densities of PURF. It also found that the form of defects has significant effects on the tensile strength of PURF and if the defects of specimens have the shape of an arc, they have significant size effect of defects on their tensile strengths.
Study on the simulation of the temperature field of sintering complex ceramics parts
Wang Su, Chen Jia, Li Jianming
2004, 30(08): 787-790.
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As the applied fields of ceramics enlarged, the quality of the ceramics parts was needed higher and higher. However, the designing and the manufacturing of the ceramics parts were separated, and the designing resolution had to be amended many times before it became the final resolution. In order to solve the problem that designing ceramics parts has to depend on experience, to save the cost and to shorten the manufacturing time, the simulation software on the temperature field of sintering complex ceramics parts was developed. First, the formula of temperature field was founded on the basis of the diathermanous theory. Second, the Finite Difference Method was used to deal with the formula of temperature field and make the core code of this software for calculating, thus the simulation of the temperature field of sintering complex ceramics parts and combined component was realized.
Synthesizing algorithm for mining composite-frequent item sets
Li Guohe, Zhao Qinping, Wang Xi
2004, 30(08): 791-796.
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It is very important to get the frequent item set in the associate rule mining. In order to fast obtain the frequent item set from a database that includes multiple values, the definition of transaction database was extended. And then by the tree concept, a special tree was built in which every node is formed by item and item’s count. At last, on the foundation of Apriori Algorithm and Artificial Intelligent Search, FABCTA(fast algorithm by candidate transaction tree and apriori) was presented to solve the frequent item set in small branches of tree. By the test on real data, FABCTA is more efficient than Apriori algorithm.
Process model for software testing based on game theory
Cui Xiaole, Wang Yichen, Ruan Lian
2004, 30(08): 797-802.
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To analysis the dynamic process of software testing and the relationship of relevant factors in it, a new method on modeling and analysis of software testing process with the game theory was provided. A game model of software testing process was established and a series of analysis were made on decision and equilibrium conditions of the game model. The conclusions are helpful for analyzing and solving the problems such as "selection on the software testing strategy" and "when to stop testing" theoretically. It can deduce a better explanation on the activities in the software testing process comparing with the theory of software testing cybernetics because it takes all participants’ interests and their possible actions into consideration. This model has founded a theoretical basis for designing the rules of the software testing, which could make the process more manageable.

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