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2011 Vol. 37, No. 3

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Application of super-heterodyne phase-sensitive detector in electromagnetic acoustic testing
Zhou Zhenggan, Huang Fengying, Ni Xiansheng
2011, 37(3): 253-258.
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In order to increase the signal-to-noise ratio of the electromagnetic acoustic received signal,an electromagnetic acoustic inspection system based on super-heterodyne receiver orthogonal phase-sensitive detection technique was designed and applied to inspect samples of aluminum, carbon steel and stainless steels. The received signal after being processed with the orthogonal phase-sensitive detection technology was compared with the received original radio frequency signal. The effects on the testing results of bandwidth settings in the intermediate frequency(IF) amplifier and the low-pass filter of phase-sensitive detector were analyzed. The results show that the application of orthogonal phase-sensitive detection technology in the inspection of aluminum alloy, carbon and stainless steels non-ferromagnetic or ferromagnetic metal materials can denoise from the received signal and increase the signal-to-noise ratio.
Analysis of glint characters of complex coated target
Fang Ning, Wang Gu, Wang Baofa
2011, 37(3): 259-262.
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Appropriate coating material can reduce the back radar cross scatter of air target, at the same time, it may affect the glint of target greatly. To study this affection, first, through physical optics and impedance boundary condition the radar cross section(RCS)was obtained in graphic electromagnetic computing (GRECO) in high frequency region, then using phase gradient method, the glint model of coated target was created. Due to the characters of graphic electromagnetic computation, the computation of glint of coated target has visual, rapid and efficient features. On the basis of this visual method the computation was performed on one two-sphere target and one complex target, respectively. The results show that the coating material can not only reduce radar cross section but also enhance the glint certainly.
Error model analysis of 2-RSSS spatial mechanism
Chen Pei, Wang Xing
2011, 37(3): 263-267.
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The position error sources of a low speed 2-RSSS spatial mechanism were studied. Firstly, error model of this mechanical system was built considering realistic joint characteristics, namely, joints with clearance was presented. A simplified model was built under the assumption of two-force principle, error of the clearance joints was represented by linkages- length. The simplifications not only simplify the process of solving the problem but also maintain the accuracy. Secondly, the error sensitivity matrix of the spatial mechanism derived in parameterization form. The invariants in it were figured out by a series of numerical examples. The analytical expressions were straightforward and numerical computation can provide precise amounts. Thirdly, numerical examples verified the results of the semi-analytical method. Finally, designing guidelines for low speed 2-RSSS spatial mechanism are given.
Threshold setting method for GPS signal acquisition under cross-correlation effect
Liu Yang, Qin Honglei, Jin Tian
2011, 37(3): 268-273.
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Traditional global positioning system(GPS) signal acquisition threshold method suffers from large false alarm ratio in the condition of cross correlation interference, and thus influences weak signal acquisition. This problem was analyzed and signal acquisition detector was improved under the situation of more than one satellites existing with different signal power. Double threshold multiple detection algorithm was introduced based on the coherent correlation and non-coherent accumulation. The statistical model is non-central chi-square distributed due to cross correlation influence. A threshold calculation method was put up in the weak signal detection based on the original fixed false alarm criterion, and this threshold was considered to be the upper threshold. The original threshold was considered to be the lower threshold. An algorithm was put up considering both strong and weak signal coexistence, strong signals were acquired first and then cross correlation interference was eliminated, weak signals were acquired after that. Simulated and real data have been used to test the upper threshold, results were compared with the original method. It is proved that original method can-t detect satellite signals while new threshold works efficiently with high detection possibility and low false alarm ratio.
Dynamic optimization method for valve plate structure of aviation piston pump
Guan Changbin, Jiao Zongxia
2011, 37(3): 274-278.
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Through the discharge area of aviation piston pump was calculated accurately, and the compressibility of oil and leakage of cylinder were considered, the nonlinear mathematical model of instantaneous flow rate was established. A dynamic optimization method of valve plate structure was proposed based on the nonlinear instantaneous flow model. The amplitude of instantaneous flow fluctuation was the objective function of the dynamic optimization method. With rotate-vector method, the structural parameters of valve plate were optimized on line dynamically. The simulation results indicate that the dynamic optimization method is high practical and efficient. This provides the theoretical foundation to the structural optimization of aviation piston pump, and the study of vibration elimination and noise reduction.
Novel calibration method for emissivity measurement of radiometer calibration load
Li Zhiping, Miao Jungang, Bai Ming
2011, 37(3): 279-282.
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A novel bistatic measurement for calibration load used in prelaunch calibration for microwave radiometer carried on the Feng-Yun series satellite was preposed. The pyramidal metal calibration target which has the same structure to the periodic calibration load to be measured was introduced. Based on the three-dimension finite-difference time-domain (FDTD) method with perfectly matched layer (PML), the simulation results indicate that the novel calibration target has similar characteristics with the calibration load, and the power density distribution coupled by the horn antenna with a lens are also similar with each other, therefore using the pyramidal metal array can reduce the error caused by the antenna coupling. For the given calibration load, by taking the pyramidal metal array instead of the metal plane as the calibration target, an improvement of one order of magnitude will be achieved without considering the direct coupling between the transmitting and receiving antennas.
Helicopter rotor tuning based on neural network and particle swarm optimization
Liu Hongmei, Lü Chen, Ouyang Pingchao, Wang Shaoping
2011, 37(3): 283-288.
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Considering the drawbacks of traditional rotor adjustment method without calculating possible nonlinear between rotor adjustments and fuselage vibration signals of the helicopter, a new rotor adjustment method based on the general regression neural network (GRNN) and the particle swarm optimization (PSO) was presented. GRNN network was employed to model the relationship of the rotor adjustment parameters and the fuselage vibrations, whose input parameters are rotor adjustment parameters and whose outputs are acceleration measurements along the three axes of rotor shaft and the fuselage. With the helicopter vibration as an objective function, the PSO was used to make a global optimization to find the suitable rotor adjustments corresponding to the minimum vibrations. Flight test results indicate that the neural networks are easily updated if new data becomes available thus allowing the system to evolve and mature in the course of its use.
Influence of carrier motion on landing safety for carrier-based airplanes
Xu Dongsong, Liu Xingyu, Wang Lixin
2011, 37(3): 289-294.
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The landing safety grading standard was summarized for carrier-based airplanes. The influence of carrier motion such as navigation, wobble and surge due to wave on landing safety was researched and the best carrier navigation velocity cooperated with carrier-based airplane approach velocity was given. The research results indicate that because of the angle between directions of carrier navigation and airplane approach,the pilot must operate aileron and rudder in phase to keep the airplane safe. Pilot operation and landing error increase as the carrier navigates faster. The prediction precision of landing signal officer about carrier motion decreases and the probability of landing failure increases as the sea condition is more severe. To keep carrier-based airplanes safe, the velocity of carrier navigation should be neither too large nor too small and severe sea condition should be avoided during the landing process for carrier-based airplanes.
Numerical simulation on aerodynamics of airfoil flying over wavy water surface
Qin Xuguo, Liu Peiqing, Qu Qiulin
2011, 37(3): 295-299,304.
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Aerodynamic characteristics of an airfoil NACA2410 in flight being close to wavy water surface are investigated numerically. The Reynold average Navier-Stokes(RANS) equation of unsteady incompressible flow, the standard k-ε turbulence model and volume of fluid(VOF) method were solved. Appropriate mesh and time step were used to avoid the distortion of regular cosine wavy surface. The difference of the solid wall of water waves and water surface wave was compared. The results of the solid wall are closer to the cosine curve distribution. The aerodynamic forces of the airfoil are periodic when it flies over cosine-shaped water surface. The variation of the aerodynamic forces in one period is presented. The effect of wavelength and wave amplitude on mean and amplitude values of aerodynamic forces is provided.
Numerical simulation of three dimensional wall temperature of combustor liner based on thermal-fluid-solid coupling method
Gao Jinhai, Wang Jianjun, Ma Yanhong, Hong Jie
2011, 37(3): 300-304.
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It is the premise and basis of thermal structure analysis to determine the temperature distribution of combustor liner. The three dimensional temperature distribution of a combustor liner was captured by the numerical simulation of an annular return-flow combustion chamber with ANSYS/CFX based on the thermal-fluid-solid coupling finite element method (FEM). The calculation analyzes the effect of heat source and heat radiation, the influence of variable flow field on heat exchange parameter, and the change of the parameters of gas, kerosene, solid with temperature were taken into account. The numerical simulation results demonstrate that the interaction between the flow field and solid wall is more sufficient comparing with traditional methods. The complete feature of flow field and temperature field could be reflected, and the distribution of flow field and temperature field and corresponding flow and heat transfer characteristics could be simulated reasonably. The work is significant on the application of structure design of combustor liner.
Mission planning of multiple UCAV based on DTC and GPGP
Zhao Zhenyu, Lu Guangshan, Liao Mo, Chen Zongji
2011, 37(3): 305-310.
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Task analysis, environment modeling, and simulation(TAEMS) was used as task structure model for uninhabited combat aerial vehicle(UCAV). The UCAV task structure model was presented and UCAV mission planning was defined and described based on TAEMS. A mission planning algorithm based on heuristic design to criteria (DTC) method was proposed, which integrated path planning in the process of mission planning. Based on the theory of generalized partial global planning (GPGP), a framework for multi-UCAV coordinated mission planning system was developed to coordinate and control the process of GPGP, which integrated the GPGP coordinated mechanism and synchronization coordinated mechanism. The case study demonstrated feasibility of the proposed mission planning algorithm.
Aerodynamic characteristic of canard rotor/wing aircraft in conversion
Li Yibo, Ma Dongli, Niu Lingyu
2011, 37(3): 311-315.
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The aerodynamic characteristics and mechanism of canard rotor/wing(CRW) aircraft during conversion from rotary to fixed-wing flight was numerically investigated. The variation of forces, moments and aerodynamic center with respect to rotor position are presented, the amplitude of lift, drag and aerodynamic center for this configuration in conversion can reach 10.7%, 3.7% and 0.6 m separately. The investigation shows that the cause of forces and moments variation is the asymmetry flow field in rotary plane and asymmetry interference between rotor and fuselage, the motion of aerodynamic center can be explained by the motion of rotor aerodynamic center and the variation of lift curve slope of rotor and horizontal tail.
Modal tests and properties analysis on truss structure of large scale carbon fiber
Tao Guoquan, Wei Yuchen, Lü mingyun, Wu Zhe
2011, 37(3): 316-319.
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Based on stochastic subspace system identification method,the modal properties of the truss structure of large scale, light weight, high strength, and force bearing type carbon fiber composites were investigated by ambient excitation. On basis of the characteristics of the truss structure itself, three fundamental assumptions were forwarded. In conjunction with the constraint conditions of the truss structure in practical applications, a modal test scheme for the truss of large scale carbon fiber composites was designed. Through detailed analysis of the test results, the characteristics of frequency, damp, and vibration mode were summarized. By hammer impacts test and finite element method, the test results were comparatively analyzed. It is proved that the three fundamental assumptions are reasonable, the test scheme is effective, the analytical results of the test are reliable. The research results are of essential meaning to the design of aerostat structures and their health monitoring.
Flow characteristic and starting method for divergent dual throat nozzle
Eriqitai, Deng Shuangguo, Li Jiajun
2011, 37(3): 320-324.
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The flow characteristic and starting method of two-dimensional divergent dual throat nozzle were studied numerically. The results show that there will be normal shock waves in the divergent zone of the dual throat nozzle, which result in great loss in total pressure and choke at the second throat, thus the nozzle can not start. In the condition of low nozzle pressure ratio, a large separation region, which weakens the shock waves, can be formed by injection in the throat, and the nozzle can start; in the condition of high nozzle pressure ratio, a large separation region will not be formed. A large separation region in the nozzle can be generated by injecting in the divergent, thus the oblique shock is formed instead of the normal shock, the total pressure loss decreases, and the nozzle can start.
Effects of software test efficiency on software reliability demonstration testing effort
Li Qiuying, Li Haifeng, Wang Jian
2011, 37(3): 325-330.
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To solve the problem that in the traditional software reliability demonstration testing(SRDT), software testability was not considered as one of the possible influence factors on test effort, a method which introduced test efficiency to improve the quantity model of minimal sample size in SRDT was put forward. The definition of software testability and its effect on software reliability test suite were analyzed. The concept of test efficiency was proposed. The difference between the numbers of test cases with different test efficiency and whether efficiency is considered were compared. It was demonstrated in detail that the traditional method and the Bayesian method with no prior knowledge are all the conditions where the test efficiency equaled to zero, so both the methods gave the most conservative value. The improved method combined with the test efficiency was recommended. Based on the principle of statistical fault injection, the quantitative estimation method of test efficiency was proposed and the process and the estimation method were shown by a case study.
Support generation design for rapid prototyping of functionally gradient material objects
Wang Su, Hu Haiou, Liu Heng, Zhu Xinxiong
2011, 37(3): 331-336.
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Rapid prototyping technology makes the manufacturing of functionally gradient materials objects come true for its digital concurrent design and manufacturing. The design of supporter generation defines the machining accuracy of functionally gradient material(FGM)parts in the process of rapid prototyping. An algorithm based on sorting by adjacency in layers was adopted a new method of supporter generation which is based on polygon boolean operation in order to solve the problem occurred in digital manufacturing of FGM parts were proposed. The support spaces between layers can adaptively change according to the geometry and material information of FGM objects, which makes the machining accuracy of rapid prototyping increase. Finally, an example of adaptive support is presented to validate the algorithm.
Dynamic performance of three kinds of supply chains based on control theory
Wang Jing, Lü Guoli, Jia Jingdong
2011, 37(3): 337-343.
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Based on the APIOBPCS (automatic pipeline, inventory and order based production control system), three kinds of two-echelon supply chains were established using the discrete control theory: traditional, demand information sharing and vendor managed inventory two-echelon supply chain. It developed the transfer function models of the systems. On this basis, the dynamic responses of the three systems to stepwise customer demand were analyzed by simulation. As the system parameters change, the performance of the three kinds of supply chains were compared, as well as the fluctuations of the system order, works in process and inventory. Simulation result showed that the smaller Tp was, the better the performance of supply chain was. The impact of Ti,Tw and Ta on peak value were different from the impact on settling time. Any system of three kinds of supply chain was not better than the other twos when peak value and settling time were both taken into account. Management decision-making recommendations were given finally.
Design and hydrodynamic experiments on robotic fish with oscillation pectoral fins
Gao Jun, Bi Shushing, Li Ji, Cai Yueri
2011, 37(3): 344-350.
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A robotic fish propelled by a pair of pectoral fin with oscillation motion was proposed, and experiments were carried out to study the hydrodynamic characteristic. Based on the analysis of motion feature and skeletal structure of pectoral fin of cownose ray, a kind of robotic cownose ray actuated by two DC servo-motors is implemented. A measurement device is designed to test the thrust force and efficiency in the low-speed water tunnel, and the relationship of thrust coefficient and efficiency varying with Sr(Strouhal number) was obtained. Both the maximum thrust coefficient and the maximum efficiency are achieved at the same Sr of 0.4, which is in good agreement with the Sr range of swimming or flying animals- propulsion at high efficiency. Finally, an experiment of free swimming was conducted in a swimming pool, and it demonstrated that the maximum speed of 0.64 m/s (1.5 times body-length) was achieved, which was faster than that of other ray-like- robotic fishes. The results indicate that the design method is effective for building a robotic fish propelled by pectoral fins with fast speed, which is meaningful to implement a kind of UUV(unmanned underwater vehicle) by employing the propulsion mode of cownose ray.
Investigation of aviation oxygen regulator
Wan Yuqin, Zhao Jingquan, Zeng Yu
2011, 37(3): 351-354.
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The working principle of the two components(pulmonary-based institutions and air intake body of oxygen regulator) was presented, and the mathematical model was established based on the analysis of the balance of the imposed forces on the kinetic components. The numerical simulation was implemented through MATLAB/simulink with the technical performance and operating conditions of oxygen supply system as the designing and calculating constraints. The selection of the main structural parameters was achieved through the analysis of the characteristic curve attained from the simulation results, and the flow characteristics of the system together with the characteristics of the oxygen percentage on a whole altitude were drawn. The simulation results show that the method are feasible for design and performance improvement for the oxygen regulator.
Simulation platform design for space intercept
Liu Zhe, Dong Changhong, Han Chao
2011, 37(3): 355-359.
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It is important for system simulation to build up a simulation platform. A simulation platform scheme, which was able to integrate varied space intercept missions,easy to extend,and with perfect visualization ability, was presented. The hiberarchy of the platform, main functions of each layer, and relationship between layers were introduced. The platform-s architecture was described in detail. The implementation of visualization and concrete approaches to integrate varied missions were particularly studied. It is demonstrated through practice that this platform is capable of performing multi space intercept tasks, easy enough to extend, and convenient to study space intercept problems due to its powerful visualization.
One sneak circuit analysis method for the switch circuit
Xu Ping, Ma Qishuang, Zou Tao
2011, 37(3): 360-363.
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The switch circuit was modeled by graph theory model. The function edge and the switch edge were two important factors in the sneak circuit analysis. The two states of edge were represented by the edge state variable.The characters of the interface in the circuit were studied and the sneak circuit analysis was simplified. The relationships between the function edge and the switch edge were showed by changing the standard format of the switch function. The number of the system functions and the methods of function realized were obtained. Whether there were sneak circuits which influence the design functions in the system were determined by using the comparison between the numbers in the design circuit and the actual circuit. The position of the sneak circuit can be known by analyzing the actual circuits in different combination of switches. The sneak circuit problem was found when use this method to analyze the typical sneak circuit example. The results show this method can be used to analyze the sneak problem quickly and effectively at engineering analyses.
Prediction of tool VB value based on PCA and BP neural network
Nie Peng, Chen Xin
2011, 37(3): 364-367,373.
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Five layers of wavelet decomposition was applied on acoustic emission signals for extracting the acoustic emission(AE) signals energy value of six bands. Energy value and cutting speed, cutting depth, feed rate, cutting time were turned into state feature vectors of tool wear. The principal component analysis was used to reduce dimension and eliminate the correlation between the feature vectors. The principal components were seen as back propagation(BP) neural network input vector. Improved Levenberg-Marquart (LM) algorithm was used to BP neural network for learning, input vectors were trained for BP neural network. Then, the BP neural network would realize the forecast of tool flank wear VB value. The results indicate that the VB value forecast system based on principal component analysis (PCA) and the improved BP neural network with LM algorithm can accurately predict the tool flank wear VB value within the error range 0.03. The different states of tool wear can be judged according to the VB value.
Supercritical airfoil parameterization method feasible to optimum design
Deng Jinqiu, Feng Renzhong
2011, 37(3): 368-373.
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To reduce the number of design variables in the supercritical airfoil optimization, eliminate the unfairness phenomenon, ensure C2 condition, control the geometric characteristics of the airfoil in the optimization process, a parameterization method for supercritical airfoil based on four rational Bézier curve was presented. In the parametric process to the airfoil data, the Bézier curve approximation algorithm and SPSA(simultaneous perturbation stochastic approximation) algorithm were used and in the Bézier curve approximation algorithm the way to choose the parameter to the data points is different from the common method. Supercritical airfoil shape optimization can be achieved by combining this method with optimization algorithms. It contents 21 design variables, the optimization result is fair and satisfies the C2 condition, the geometric characteristics of the airfoil such as leading edge radius, upper and lower crest location including curvature there, the boattail angle can be controlled in the optimization process by setting the range of the design variables.
Reliability optimization of standby phased mission systems based on desirability function
Yu Jian, Hu Tao, Yang Chunhui
2011, 37(3): 374-378.
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A phased mission system to be a success, the system must successfully operate throughout all of the phases. A reliability computative model of cold-standby phased mission systems was proposed based on the reliability computative model of cold-standby systems, its components have two states and the time to failure of all the components obeys the exponential distribution. Considering some important effect factors of systems- reliability optimization, the sub-desirability functions of system reliability, system volume, system mass and system cost were built, and their effect modulus were determined through analysis hierarchy process method. Synthesizing these effect factors, a reliability redundancy optimization model of cold-standby phased mission systems was established based on the synthesis desirability functions. The particle swarm optimization was used to solve the reliability redundancy optimization model. The proposed solutions are verified and illustrated through a three phased cold standby system. The model-s rationality and the arithmetic-s validity were validated by the experimental results.

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