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2015 Vol. 41, No. 7

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Volume 41 Issue72015
2015 Year 41 Volume 7 Issue E-journal
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Geometric approach for intercontinental formation flight path planning
XU Xiaohao, MENG Linghang, ZHAO Yifei
2015, 41(7): 1155-1164. doi: 10.13700/j.bh.1001-5965.2014.0515
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For intercontinental formation flight path planning problem, a basic model was developed based on the aerodynamic models and spherical metric characteristics of formation flight. The problem was then abstracted as the weighted geodesic Steiner minimum tree (WGSMT) problem in spherical point set due to its topological characteristics. The principles of simplifying WGSMT to a finite geometry planning problem were proposed. We also proved that the connecting points induced by obstacles only changed the topology of their adjacent Steiner points while did not lose the accuracy of solution. Finally, a two stage formation path planning algorithm based on “construct-repair” approach was developed, whose validity was verified by an example. Significance of the study is that the sphere geometric fundamentals of intercontinental formation path planning are built,which therefore makes the complexity of the problem depend on the scale of flight set rather than that of geographic grids, thereby reduces the complexity of the problem dramatically.
Fire protection design in aircraft cabin based on fire evacuation safety index
ZHANG Qingsong, QI Hanpeng, LUO Xingna
2015, 41(7): 1165-1170. doi: 10.13700/j.bh.1001-5965.2014.0489
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In order to study the influence of aircraft cabin design on fire protection performance, a concept of fire evacuation safety index (FESI) was firstly presented. The fire scenario and evacuation procedures in aircraft cabin were simulated via simulation software PyroSim and Pathfinder. FESI at different exits were determined under the scenarios of different internal surface area of cabin, width and height of the exit and population. An analysis was conducted to study the influence of such design factors to cabin fire evacuation performance. The maximum populations of several narrow-body aircrafts were determined using back-propagation (BP) neural network in case to ensure the safe evacuation. And an optimized evacuation program was proposed for B737 aircraft. The results reveal that internal surface area of cabin, width and height of the exits and numbers of seats are the design factors that significantly impact cabin fire protection performance. The maximum population of B737-800 under typical layout is 154. However, it may increase to 175 after optimizing to the evacuation program. The proposed concept of FESI not only performs an assessment for the existing aircrafts against fire protection performance and an optimization for cabin layout and evacuation program, but also provides a basis for fire protection design of domestic large aircraft cabin. In addition, it can also provide a reference for other areas of fire research.
Accessory gearbox temperature field analysis considering fuel injection lubrication
CHEN Yunxia, LIU Wangjia
2015, 41(7): 1171-1176. doi: 10.13700/j.bh.1001-5965.2014.0533
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Accessory gearbox is a major component of aero-engine, and the heat production and heat dissipation problems of accessory gearbox are complex. Previous studies have focused only on solid domains thermal analysis, however oil cooling effect has not been taken full account of. Aiming to complement this, a fluid simulation based on the steady-state temperature field thinking method of analysis was proposed. Firstly, basic rules and characteristics of the heat production and heat dissipation problems of the accessory gearbox were analyzed. Then we applied the k-ε turbulence model to simulation, applied the multiphase flow model to simulate the oil, and used multiple reference coordinate system to simulate heat transfer with gear rotation. Finally, the application of a specific case of accessory gearbox verified the correctness and feasibility of the method, which formed a set of effective models and methods using FLUENT software to simulate accessory gearbox's steady state temperature field. The result plays an important supporting role for subsequent research on accessory gearbox reliability and lifetime analysis.
Spacecraft electrical characteristics identification method based on PCA feature extraction and WPSVM
LI Ke, LIU Yi, DU Shaoyi, SUN Yi, WANG Jun
2015, 41(7): 1177-1182. doi: 10.13700/j.bh.1001-5965.2014.0482
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To solve the problems of large amount of unlabeled test data, high dimension characteristics, slow computing speed and low recognition rate during the spacecraft electrical characteristics identification process of monitoring system, an on-line identification algorithm based on principal component analysis (PCA) feature extraction and weighted proximal support vector machine (WPSVM) was proposed. The principal component analysis is used for feature selection and extraction during complex signal analysis process, to reduce the characteristics dimension and improve the speed of the spacecraft electrical on-line identification. In order to resolve the PCA results selection problem, our team put forward data capture contribution method by using threshold to capture data, effectively guarantee the validity and consistency of the data. The experimental results indicate that this method we proposed can get better spacecraft electrical characteristics data feature, improve the accuracy of identification, and shorten the compute-time with high efficiency at the same time.
Path planning for UAV under three-dimensional real terrain in rescue mission
LIANG Xiao, WANG Honglun, MENG Guanglei, CHEN Xia
2015, 41(7): 1183-1187. doi: 10.13700/j.bh.1001-5965.2014.0479
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Basing on the capability of three-dimensional flight and planning of optimal path, unmanned aerial vehicles (UAVs) can reach the disaster areas within shorter time than ground vehicles, which will improve the efficiency of rescue. Firstly, according to the real geographical environment, terrain is modeled by a mesh uniform method based on UAV constraints. Secondly, a data structure which is suitable for calculation is designed based on the characteristics of terrain data. Finally, the integrative performance function includes the deviation cost, height cost, terrain following/avoidance cost, threat cost and security distance cost. Both methods of waypoints cross and grid search instead of waypoints are engaged in the improved ant colony algorithm to make three-dimensional UAV path planning. The simulation results show that the method can deal with three-dimensional terrain data directly. While maintaining the topography of the premise, it can find the three-dimensional optimal path of UAV and improve the practical value of path planning technology.
Rigid-flexible coupling multibody model for the tethered satellite system based on recursive dynamics algorithm
ZHONG Rui
2015, 41(7): 1188-1195. doi: 10.13700/j.bh.1001-5965.2014.0525
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A multibody dynamics model of hinged flexible rods was established for the spatial tethered satellite system (TSS) based on the recursive dynamics algorithm. The system was consisted of two rigid end-satellites and a flexible tether connecting them. In the model, the tether was discretized into a series of flexible rods connected by spherical hinges and the non-uniform longitude deformations of the rods were considered, whereas the bending and torsion of the tether were simulated by the motion of the spherical hinges. Then, the equation of motion of the rigid-flexible coupling multibody model was derived based on the recursive dynamics algorithm. The simulation results prove the efficiency of the proposed model in simulation spatial motion of the TSS, including tether vibrations and oscillations in different directions. The introduction of the recursive dynamics algorithm effectively decreases the dimension of the discretized model and therefore reduces the computational efforts sharply.
Digital combined measuring technology assisted quality inspection for aircraft assembly
JING Xishuang, ZHANG Pengfei, WANG Zhijia, ZHAO Gang
2015, 41(7): 1196-1201. doi: 10.13700/j.bh.1001-5965.2014.0635
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Aimed at the issues, including that detail features of the large size aircraft panel components couldn't be achieved directly and the low measuring efficiency by using a laser tracker separately in large size aircraft panel shape measurement, a combined measurement method based on the laser tracker and the articulated arm coordinate measuring machine (AACMM) was proposed. Under the premise of the measurement precision, by adding the AACMM to the measurement field of laser tracker, the detailed forming information of large size aircraft panel could be acquired comprehensively. According to the characteristics of the aircraft panel assembly process, some combined measurement tools were developed based on the Spatial Analyzer software, which could process all measurement data from the combined measurement system. Some examples are also given to illustrate the effectiveness and the efficiency of the method.
Subgraph matching algorithm based on graduated nonconvexity and concavity procedure
LI Jing, LIU Chuankai, WANG Yong, GU Nannan, SHI Rui, LI Lin
2015, 41(7): 1202-1207. doi: 10.13700/j.bh.1001-5965.2014.0505
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To achieve robust and efficient matching with outliers is a fundamental problem in the field of graph matching. To tackle this problem, a novel subgraph matching algorithm was proposed, which was based on the recently proposed graduated nonconvexity and concavity procedure (GNCCP). Specifically speaking, the graph matching problem in the existence of outliers was firstly formulated as a quadratic combinatorial optimization problem based on the affinity matrix, which was then optimized by extending the GNCCP. This is a new second-order constraint graph matching algorithm. Compared with the existing algorithms, there are mainly three benefits for the proposed algorithm, which are as follows. Firstly, it has a flexible objective function formulation; secondly, it is effective in graph matching problems with outliers; thirdly, it is applicable on both directed graphs and undirected graphs. Simulations on both synthetic and real world datasets validate the effectiveness of the proposed method.
Gust response analysis of flexible aircraft with aerodynamic nonlinearity
BI Ying, YANG Chao, WU Zhigang
2015, 41(7): 1208-1214. doi: 10.13700/j.bh.1001-5965.2014.0492
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Aiming at the gust response of high aspect ratio flexible aircraft, the unsteady aerodynamic considering the nonlinear effect at high angle of attack (AOA) was calculated in time domain by combining the modified Theodorsen method with the strip theory. Based on the nonlinear aerodynamic in time domain, the aeroelastic model of high aspect ratio flexible aircraft with gust disturbance was established, and a novel method applied to gust response analysis with nonlinear aerodynamic was integrally developed. The method was validated by carrying out numerical simulation and method validation basing on a general flexible aircraft, and the gust induced load at wingtip and center of gravity (CG) were compared between linear and nonlinear cases. Numerical results show that the nonlinear effect of aerodynamic at high AOA obviously influences the gust response of the flexible aircraft, and the gust induced load at wingtip reduces as much as 41.7% compared with linear case. The aerodynamic nonlinear effect cannot be ignored for flexible aircraft.
Acoustic numerical simulation of high frequency combustion instability
CHU Min, XU Xu
2015, 41(7): 1215-1222. doi: 10.13700/j.bh.1001-5965.2014.0527
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High frequency combustion instability is one of the major issues existed in design process of liquid rocket engine. A time domain numerical simulation was used to predict high frequency combustion instability of hypergolic propellant orbit maneuvering engine (OME) by computational aeroacoustics, which was less dispersive and dissipative. The coupling between unsteady heat release and acoustics was realized by Crocco's pressure time lag model. The effects of different parameters of pressure time lag model on stability were analyzed, and the stability map was obtained. The first order transverse mode and the first order radial mode were recognized as the most dominant instable modes, which were consisted with the instable modes recognized from experimental results of ground test. The results show that high frequency combustion instability can be successfully predicted, when acoustic perturbation equations with Crocco's pressure time lag model are solved in the time domain by computational aeroacoustics.
Dynamic parameter estimation of pressure transducer in shock tube calibration test
LI Qiang, WANG Zhongyu, WANG Zhuoran, YAN Hu
2015, 41(7): 1223-1230. doi: 10.13700/j.bh.1001-5965.2014.0549
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Shock tube is the key device in the pressure transducer dynamic calibration. But as the output of pressure transducer often contains strong interference, which makes it difficult to directly use the output to build the dynamic model of calibrated pressure transducer, in addition, the accuracy of the model is hard to be characterized. A parameter estimation method was proposed which could be applied to pressure transducer in shock tube calibration test. Firstly, the operation of information generation was employed to process the output of calibrated pressure transducer under the pressure of step excitation, and then estimated sequences, upper boundary and lower boundary were obtained. Secondly, the processing methods about filtering and modeling were used to deal with the estimated sequences, upper and lower boundary, and then we could obtain the best estimated value model, the upper boundary model and the lower boundary model. Finally, by solving the obtained models, the indicators obtained by the best estimated model was the best characteristic indicator of the calibrated transducer, the indicators obtained by upper and lower boundary model could compose confidence interval of best indicators, it could show the reliability of the best indicators. A calibration test of shock tube is conducted with the piezoresistive pressure transducer of Endevco 200 series type. The relative errors of dynamic indices of time-domain are no more than 8.17%; the relative errors of dynamic indices of frequency-domain are no more than 9.15%. All the obtained indicators fall in the estimated interval with 100% probability of reliability.
Modeling and analysis of dynamic collision region for UAV avoiding aerial intruders
LIU Chang, WANG Honglun, YAO Peng, LEI Yupeng
2015, 41(7): 1231-1238. doi: 10.13700/j.bh.1001-5965.2014.0497
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In view of the existing methods to calculate collision region using certain threshold value of distance or time, an unmanned aerial vehicle (UAV) dynamic collision region model based on maneuver information of both UAV and aerial intruder was presented. Firstly, the no-maneuver collision region was proposed. In this region, UAV and intruder would undergo collision if UAV didn't execute any avoidance maneuver. Using a geometric method, a mathematical model of no-maneuver collision region was formulated utilizing the motion states of UAV and intruder, and minimum safety distance, etc. Secondly, the constraints on the UAV maneuverability were added to calculate the maximum maneuverability collision region, which was the border for UAV to avoid the collision by maximum maneuverability flight. Thirdly, the concept of non-escape region was proposed. Then the safe flight envelope was presented. This safe flight envelope was a boundary line of avoiding a collision with aerial intruder for UAV. Finally, the key factors of the proposed regions were analyzed by theoretical derivation combined with simulation. The results show that the presented collision regions are useful for UAV to select and evaluate the avoidance maneuver, and to decide whether to execute maximum maneuverability flight. The presented collision regions provide a practical guideline for UAV to ensure safe collision avoidance.
Propagation characteristics of Rayleigh wave under gravity based on FDTD method
LIU Ning, LI Min, SUN Jie
2015, 41(7): 1239-1245. doi: 10.13700/j.bh.1001-5965.2014.0503
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R wave is short for Rayleigh wave. R wave, on which the effect of gravity is generally inevitable, has received considerably extensive attention and been widely used in many fields, such as geological exploration, nondestructive test, etc. The effects of gravity on R wave velocity for elastic parameters were further analyzed based on available R wave velocity function, and the applicable range of the approximate one was given as well. Wave propagation through quasi-half-space isotropic linear elastic medium with gravity, under the excitation of differentiated Gaussian pulse (DGP) was studied by finite difference time domain (FDTD) method with staggered grid discretization, and extended boundary conditions were introduced. Velocity values obtained were closer to the theoretical ones. Meanwhile, the influence of gravity on time domain, frequency domain response was discussed. By analyzing the theoretical and numerical results, it is necessary to take the effect of gravity into account in simulation for more accurate prediction.
Parameter identification of magnetic bearing based on rotor unbalance responses
LIU Chao, LIU Gang
2015, 41(7): 1246-1252. doi: 10.13700/j.bh.1001-5965.2014.0516
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The force parameters of magnetic bearing obtained by theoretical design method were usually inaccurate. To solve this problem, an identification method based on rotor unbalance responses was proposed. Making the rotor rotate at high speed, the eccentric effect of the rotor imbalance can be used. The force parameters of magnetic bearing were calculated by measuring the synchronous currents when the rotor was in the null-displacement control mode and the synchronous displacements when the rotor was in the null-current control mode. The null-current controller and the null-displacement controller were designed based on the generalized notch filter theory, and the T matrix was set up to ensure the close loop was stable. The experimental results indicate that the difference rate between experiment identification result and the theoretical design result is within 20%. And it proves that the method is correct and effective to improve the identification precision for the force parameters of the magnetic bearing.
Experiment of air flow behavior and heat transfer characteristics in microchannels with different aspect ratios
LIU Yangpeng, XU Guoqiang, LI Haiwang, TIAN Yitu
2015, 41(7): 1253-1258. doi: 10.13700/j.bh.1001-5965.2014.0524
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Experiments were conducted to investigate the flow behavior and heat transfer characteristics in minichannels with different aspect ratios. The widths of microchannels are constant of 0.4mm. The aspect ratiosof the microchannels are 2/5, 1/2, 2/3 and 1, respectively. All tests were performed with air. The experiments were completed with the Reynolds number in the range of 200 to 1600. Results of experiments show that the aspect ratios of microchannels have a remarkable effect on the performance of flow behavior and heat transfer characteristics. The friction factors decrease with the increase of the Reynolds numbers. The Poiseuille numbers increase when the Reynolds numbers keep rising. Both of the friction factors and Poiseuille numbers drop as the aspect ratios increase. Nusselt numbers increase as Reynolds numbers increase, but decrease with the increase of aspect ratios. The corresponding empiric equations for the flow resistance and heat transfer characteristics in microchannels with different aspect ratios are fitted.
Control method and applications of robust trajectory linearization via nonlinear differentiators
SHAO Xingling, WANG Honglun, ZHANG Huiping, ZHANG Xiaofeng
2015, 41(7): 1259-1268. doi: 10.13700/j.bh.1001-5965.2014.0544
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Considering the lack of enough robustness against uncertainties in conventional trajectory linearization control (TLC) method, an improved robust control method was proposed, based on the design principle of nonlinear differentiators. Firstly, via introducing the concept of second-order linear differentiator (SOLD), it was indicated that peaking phenomenon which was similar with using high-gains in SOLD would emerge during the transient profile of differentiation of the nominal command in the existing TLC. And then, tracking differentiator (TD) was used to produce the nominal command and its derivative, peaking phenomenon was totally eliminated and the ability of adjusting the response speed of closed-loop system under the physical limitations was endowed simultaneously. Secondly, by constructing the desired tracking error dynamics of closed-loop system, the control law of the linear time-varying (LTV) system could be directly obtained, PD-spectrum theorem and real time tuning of the time varying bandwidth (TVB) of TLC were both avoided. Meanwhile, by utilizing the non-perturbation form of hybrid differentiator (HD) as the desired error dynamics of closed-loop system, the robustness of the system was thus enhanced. In addition, the boundedness of the tracking error in interference system was proved by Lyapunov theory. Finally, the proposed method was applied to the attitude tracking problem of hypersonic vehicle. The simulation results demonstrate the proposed method can still exhibit better control performance and anti-interference capability even if there exist large uncertainties in the aerodynamic parameters, thus the effectiveness and robustness of the control scheme is validated.
Measurement method for thermal radiation characteristics of IR window materials
WANG Yahui, WANG Qiang, ZHANG Bochuan, XU Li
2015, 41(7): 1269-1274. doi: 10.13700/j.bh.1001-5965.2014.0553
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When a hypersonic vehicle is flying in the atmosphere, serious aero-thermo-radiation effects can reduce or even destroy the performance of infrared (IR) detection, and high-temperature IR window becomes the main factor of the effects due to the aerodynamic heating. Based on thermal radiation transfer model for IR window, a method was proposed to measure thermal radiation characteristics of IR window materials. And thermal radiation characteristics of a sapphire IR window material applied to mid-wave infrared (MWIR) detection system were measured. The results indicate that thermal radiation characteristics of the sapphire IR window material with thickness of 0.1mm, in the wavelength region 3.7-4.8μm, have an approximate cubic relationship with temperature, changing from 100℃ to 350℃. With the rise of temperature, the transmittance decreases, while the self-radiation increases. The intensive self-radiation can make detector into saturation state easily, of which the influence on the MWIR detection system is bigger than that of transmittance which decreases detecting signal to noise ratio (SNR).
Spacecraft test requirement description and automatic generation method
GAO Shiwei, LYU Jianghua, WUNIRI Qiqige, MENG Xiangxi, MA Shilong
2015, 41(7): 1275-1286. doi: 10.13700/j.bh.1001-5965.2014.0762
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Spacecraft as a typical safety-critical system, its trustworthiness study is very urgent. The evaluation and verification for spacecraft depends on the data obtained from the execution of spacecraft test cases. Moreover, spacecraft test requirement is the important basis for test case generation.In practical application, such complex system of spacecraft is faced with problems of the complexity for the spacecraft test requirement, long preparation period for the test requirement, and difficulty in assuring the adequacy, completeness, and reusability of test requirement using artificial experience. To solve these problems, the spacecraft formalized model was constructed by analyzing the characteristics of the spacecraft structure.The formalization specification of spacecraft static test requirements and dynamic test requirements were given based on spacecraft testing task flow. And the corresponding automatically generation methods for spacecraft testing requirements were proposed. The adequacy and completeness of spacecraft test requirement are ensured, and the reusability of test requirement is enhanced. Compared with the artificial establishment way, the period of the compiled test requirements is shorten. Finally, the application system for spacecraft test requirement generation is designed and implemented, which validates the effectiveness of the proposed method.
Performance comparison of four pre-filters used to prevent pitch categoryⅡPIO
LU Yang, YU Liming, FU Yongling
2015, 41(7): 1287-1293. doi: 10.13700/j.bh.1001-5965.2014.0507
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Category Ⅱ PIO cases are mostly characterized by actuator saturation. FWB, DS, DASA, RLF are four nonlinear pre-filters that have already been used to compensate for the phase lag led by actuator saturation, thus to prevent pilot-induced oscillation (PIO). Different means were used to make comparison among four pre-filters. Dscribing function was used to analyze and compare the phase compensation in open loop analysis by linearizing the nonlinear components of the fourpre-filters. The study mainly focused on pitch attitude PIO, in a pilot-vehicle closed loop system with a neutrally stable pitch bare aircraft that could easily cause PIO, three typical pitch flight simulation tasks were used to make comparison in terms of actuator velocity saturation prevention, pitch output dynamic characters, degree of phase compensation and alleviation of pilot operation burden, measured by pilot input magnitude. DASA turns out to be a better design among the four pre-filters. The result can provide a useful reference for filter design and pitch attitude PIO prevention study.
Effects of solution-aging treatment on microstructure and mechanical properties of a high-strength and high-toughness titanium alloy
XIA Xiaojie, WU Guoqing, HUANG Zheng, LI Zhiyan
2015, 41(7): 1294-1299. doi: 10.13700/j.bh.1001-5965.2014.0517
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Solution-aging treatment was performed to a high-strength and high-toughness titanium alloy. Several microstructural feature including volume fraction of primary α phase, size factor of primary α phase, volume fraction of secondary α phase, αs/β interface density, were quantitatively characterized. By making a statistical analysis of the microstructure characteristics, the relationship between microstructure features and mechanical properties of the high-strength and high-toughness titanium alloy was investigated as solution temperature changed. The results show that with the increase of solution temperature in α+β phase, the volume fraction of primary α phase decreases, the size factor of primary α phase firstly decreases and then increases, volume fraction of secondary α phase increases, and the αs/β interface density increases and then decreases. The elongation, static toughness and crack initiation energy increase with the growth of the volume fraction of primary α phase. And yield strength is positively correlated with the αs/β interface density.
NUIO based actuator fault detection for a UAV
ZHANG He, ZHONG Maiying
2015, 41(7): 1300-1306. doi: 10.13700/j.bh.1001-5965.2014.0522
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The actuator fault detection for an unmanned aerial vehicle (UAV) longitudinal system with unknown atmospheric disturbances and stochastic noise was studied. Based on introducing a nonlinear longitudinal model of the fixed UAV, a residual generation was designed by employing a nonlinear unknown input observer (NUIO) which is based on cubature Kalman filter (CKF). The unknown input observer structure was constructed to decouple the unknown disturbances from residual. At the same time, the CKF was applied to calculate the gain matrix to achieve the requirement of robustness to noise. Finally, the occurrence of fault can be detected based on chi-square test about the residual sequence. The simulation results show that the proposed method can decouple the unknown disturbances from residual effectively and achieve the fast and accurate actuator fault detection.
Probability model for early warning aircraft radar flight test based on probability of detection curve
WANG Han, MA Xiaobing, ZHAO Yu
2015, 41(7): 1307-1312. doi: 10.13700/j.bh.1001-5965.2014.0536
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A novel probability model was proposed to ensure the coverage rate and the accuracy of probability of detection (POD) curve in early warning aircraft radar flight test, which can also provide the distance sampling intervals and boundary conditions of flight routes. Firstly, we derived the optimal number of sampling points used for curve-fitting after the test based on the requirements of the coverage rate and the accuracy of POD curve. Then, an algorithm was proposed based on the empirical distribution function of POD curve, which could calculate the minimum and maximum detection distance of early warning aircraft radar flight test. Simultaneously, the length of distance sampling intervals was obtained on the basis of the algorithm. Finally, we calculated the number of sampling points in distance sampling intervals and the number of flights according to the statistical properties of the detection probability. The proposed model provides a quantitative basis for the design of radar flight test and the performance evaluation of early warning.
Effect of sweep angle on stability and transition in a swept-wing boundary layer
SUN Pengpeng, HUANG Zhangfeng
2015, 41(7): 1313-1321. doi: 10.13700/j.bh.1001-5965.2014.0540
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The stability and transition of swept-wing boundary layers have important reference value to the design and optimization of airfoil. The sweep angle is one of the key parameters to the cross-flow instability of swept-wing boundary layers. Based on the NACA0012 airfoil profile, the mean flow of a swept-wing boundary layer was calculated by numerically solving the three-dimensional compressible Navier-Stokes equation, then the neutral curve and the growth curve of unstable Toumien-Schlisting wave were obtained by solving the Orr-Sommerfeld equation to study the effect of the sweep angle, and the transition position was predicted by applying eN method. Study shows that with the increase of sweep angle, both the strength of the cross-flow and the amplification factor n of the disturbance amplitude increase firstly and then decrease, and the strength of the cross-flow reaches its peak value when the sweep angle is in the range of 40° to 50°. The N factor predicted by eN method is the largest one when the sweep angle is about 50°, implying that with which angle, the induce disturbance with a smaller amplitude can easily lead to the occurrence of transition.
Influence of quantum dots and TiO2 photoanode parameters on electron lifetimes and performance of photonode
QUAN Linlin, LI Weiping, GENG Huifang, LIU Huicong, ZHU Liqun
2015, 41(7): 1322-1329. doi: 10.13700/j.bh.1001-5965.2014.0541
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Effects of film thickness of P25TiO2 photoanode, different types of quantum dots sensitized and method of quantum dots co-sensitization, which are the factors of interest, on P25TiO2 photoanode were analyzed. The relationship between P25TiO2 film thickness and electron lifetimes were investigated by the method of successive ionic layer absorption and reaction (SILAR). Besides, the influence of quantum dots type and method of quantum dots co-sensitization on photoelectrochemical performance of photoanode was studied. Electrochemical impedance spectra (EIS), open circuit voltage decay (OCVD) and UV-Vis absorption spectra were used to measure and analyze the factors which influence the photoelectrochemical performance and electron lifetimes of P25TiO2 photoanode. The results indicate that P25TiO2 with the film thickness of 12μm exhibits the minimum recombination losses and longer electron lifetimes. Furthermore, the short circuit current and power conversion efficiency of co-sensitized photoanode (TiO2/CdS/CdSe/ZnS) increase 34% and 42% respectively compared to those of single sensitized photoanode (TiO2/CdS). Besides, appropriate film thickness of P25TiO2 photoanode and method of co-sensitization are important factors to increase the electron lifetimes of photoanode, the absorption spectrum and intensity of photoanode.
3D light fields based foreground segmentation in static scenes
WEI Wei, LAO Songyang, KANG Lai, BAI Liang
2015, 41(7): 1330-1336. doi: 10.13700/j.bh.1001-5965.2014.0477
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To address the problem of extracting foreground objects from complex scenes, a 3D light field based method for foreground segmentation of static scenes was presented. Firstly, the method relies on densely sampled 3D light field formed by stacking a sequence of images captured at different viewpoints. These viewpoints were equally spaced along a linear path so that object trace was smooth in epipolar plan image (EPI). Secondly, line segment detection (LSD) method was performed to extract edges and compute the corresponding depth in EPI, based on which a depth map of the scene was obtained through a fast local depth interpolation algorithm. Piecewise cubic Hermite interpolating polynomial (PCHIP) algorithm proved to have desirable results in this phase. Finally, the recovered dense depth information was exploited to facilitate foreground segmentation. A threshold approach was used to separate different objects in scenes. Preliminary experimental results show that our method is able to estimate the correct relative spatial relation of multiple objects and our proposed foreground segmentation method reduces over-segmentation effects existed in traditional methods based on region clustering and mathematical morphology.
Image crosstalk correction method of the infrared multispectral camera
CHEN Huiwei, ZHAO Huijie, JIA Guorui
2015, 41(7): 1337-1342. doi: 10.13700/j.bh.1001-5965.2014.0486
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There are two bands in the wavelength of 1.55-2.35μm region for the infrared multispectral camera. Due to the detectors being located on the same focal plane assembly and the design of the readout circuits, one band was found to have crosstalk from other band. Firstly, the crosstalk phenomenon in the infrared multispectral camera image was described and the mechanism of crosstalk phenomenon was investigated. Secondly, based on the aspects of the inner structure of the HgCdTe detector's focal plane array and some important parameters of the detector, it was found that light is reflected and transported by multiple reflections in the focal plane area, which was mechanism of optical and electrical crosstalk phenomenon. Meanwhile, the readout circuits' inaccurate design could also lead to crosstalk phenomenon. Mathematical model was built based on crosstalk phenomenon. The research shows that the crosstalk phenomenon (negative/positive pulse) of B10 is relevant to the step (ascending/descending edge) of B11. At last, the crosstalk math model is validated and relevant correction algorithm is developed.
Algorithm of position-based dynamics and cutting simulation for soft tissue using tetrahedral mesh
BAI Junxuan, PAN Junjun, ZHAO Xin, HAO Aimin
2015, 41(7): 1343-1352. doi: 10.13700/j.bh.1001-5965.2014.0526
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Abstract:
In order to improve the realism and real-time performance of virtual surgery technique, a cutting algorithm for soft tissue using tetrahedral mesh and position-based dynamics was proposed. Firstly, the tetrahedral mesh was chosen as the geometrical model for soft tissue, and position-based dynamics were employed as the physical model. The external surface of soft tissue was formed by the convex hull of the tetrahedral mesh. Secondly, to support the cutting simulation, we also modified the position-based dynamics method to ensure it worked well when the topology of soft tissue model changed. Moreover, the tetrahedral mesh coupled with texture information was applied for the highly-detailed incision exposure. Finally, the haptic rendering was implemented on this dissection algorithm to enhance the realism of the surgery simulation environment. The experimental result shows that the simulator works effectively and stably with this physical model, when deformation and dissection occurs. Moreover, the algorithm has been used in the virtual surgery simulator designed by State Key Laboratory of Virtual Reality Technology and Systems in Beihang University. The laparoscopic surgeons from cooperative hospitals have given a pilot study and high evaluation has been given from the doctors for this simulator.
Lossless intra coding on whole frame for screen content video based on template matching
FENG Lixin, TAO Pin, WEN Jiangtao, YANG Shiqiang
2015, 41(7): 1353-1358. doi: 10.13700/j.bh.1001-5965.2014.0529
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Abstract:
The-state-of-art video compression standards, such as H.264 and high efficiency video coding (HEVC) are mainly designed towards the camera-captured video. However, screen content (SC) video is created by the computer without noise, which needs higher efficiency than the camera-captured video. SC picture contains more structural similarity in contrast to camera-captured picture which could be used to improve the intra-picture compression ratio. A template matching method (TMM) was proposed by exploiting this similarity for SC intra lossless picture. The 21 pixel points template and the high efficiency 24-bits hash table were designed in TMM intra frame coding. For every picture, the first step was to use template matching for every pixel, and then speed up the matching processing by hash function, finally encode the residual picture by entropy coding. Experimental results show that TMM can double the lossless compression ratio compared to HEVC range extensions version 4.1 and reduce the compression time by half.

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