Advanced Search

2014 Vol. 40, No. 9

  Previous Issue | Next Issue 
Display Method:
Space-time coding in asynchronous dual-satellite MIMO systems
Zhao Danfeng, Wang Yang, Liao Xi
2014, 40(9): 1165-1169. doi: 10.13700/j.bh.1001-5965.2013.0602
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 622
Abstract:
The received signals are asynchronous due to the different transmission delays in the dualsatellite multiple-input multiple-output (MIMO) system. Aiming to solve the asynchronism problem, a time reversal full-rate full-diversity space time coding scheme was proposed. The space-time code words were interleaved and divided into two groups after the transmitting symbols were space time coded. Then the symbol sequence in one group was time reversed and a guard interval was added between groups, which ensured that the full rate and full diversity gain could be achieved in the asynchronous dual-satellite MIMO system. Meanwhile, there was a low-complexity optimal decoding algorithm for the proposed scheme. The simulation results show that the proposed space time coding scheme can achieve better performance compared with the traditional schemes. And the performance gain is more considerable when the high-order modulation is employed or the channel is in the deep shadowing state.
Solution region synthesis theory and method of six-bar linkages with 4-position motion generation
Han Jianyou, Cui Guangzhen, Yang Tong
2014, 40(9): 1170-1175. doi: 10.13700/j.bh.1001-5965.2013.0590
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 590
Abstract:
According to the Stephenson-Ⅱ six-bar linkage with 4-position motion generation, the concept and equation of generalized Burmester curves based on Burmester curve was proposed. The solution region method was given. Firstly, this method required to get solution curves meeting requirements. Then the six-bar linkage with defects was removed from the solution region using the sign of Jacobin determinant value and mechanism motion continuity. Finally, considering the practical engineering requirements, the feasible solution region was obtained. Analysis example demonstrates that the method is practicable and effective. The proposed method is simple and convenient to be realized in programming. Besides that, the method can provide reference for other multi-bar linkages 4-position motion generation.
Rolling element bearing fault diagnosis based on spectral kurtosis and bi-spectrum
Zheng Hong, Zhou Lei, Yang Hao
2014, 40(9): 1176-1182. doi: 10.13700/j.bh.1001-5965.2013.0628
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 681
Abstract:
Aiming to deal with the bearing fault diagnosis problem in the case of strong background noise being contained in the collected vibration signals, a rolling element bearing fault diagnosis method based on spectral kurtosis and bi-spectrum was proposed. Spectral kurtosis was used to indicate the frequency band where the transient occurred and the optimal band-pass filter was adopted to remove the background noise. According to the bandwidth of the band-pass filter, a low-frequency rectangular area was determined, and bi-spectrum of the envelope of the band-pass filtered signal on this rectangular area was computed. The bearing fault was diagnosed according to the bi-spectrum graph. Analysis on simulation signals shows that strong background noise and rolling element slip can give rise to the failure of traditional diagnosis methods (e.g. kurtosis, power spectrum and envelop spectrum); the proposed method can inhibit the noise effectively and diagnose the rolling element bearing fault more accurately. A diagnosis instance of the bearing 6205-2RS JEM SKF was presented to show the effectiveness of the proposed method.
Navigation method using a single detector based on the observation of X-ray pulsar in different time interval
Yang Bo, Zhang Rui, Sun Hui, Xu Fan
2014, 40(9): 1183-1188. doi: 10.13700/j.bh.1001-5965.2013.0568
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 543
Abstract:
Traditional X-ray pulsar navigation system needs to track more than 3 pulsars at the same time, which will increase the effective load quality of the navigation system. Aiming at the phenomenon that the pulsars cannot be seen all the time by vehicles because of the earth shadow and the detector's visual angle, a navigation method using a single detector based on the observation of X-ray pulsar in different time interval was proposed. In consideration of the practical flying condition, visibility of X-ray pulsar with different detection range was analysed, and a single pulsar used for navigation was chosen from the detectable pulsars. The results of the simulations show that the navigation accuracy of this system is similar with that of traditional algorithm. The navigation error is 337 m. This algorithm can provide a possible method of the industrialization of X-ray pulsar-based navigation.
Preparation and atomic oxygen resistance of hybrid polyimide
Zhao Xiaohu, Duan Lingze, Zhao Yizhi
2014, 40(9): 1189-1194. doi: 10.13700/j.bh.1001-5965.2013.0595
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 620
Abstract:
Atomic oxygen (AO), the predominant components and the most active species in low earth orbit atmosphere, can cause the erosion and degradation of spacecraft materials. To improve the AO-resistance of the resin, Tetraethyl orthosilicate (TEOS) was added into the polyimide (PI) matrix, and then the inorganic phases of SiO2 were generated in-situ using sol-gel method and the SiO2/PI hybrid materials were obtained. The ground-based simulation experiments were carried out to evaluate the AO-resistance of the SiO2/PI hybrid materials. The mass, surface morphology and surface composition of the samples were compared before and after the AO experiments. The effects of the adding amount of TEOS and the improving mechanism of the AO-resistance were analyzed. Results show that the AO-resistance of hybrid materials is better than that of the pristine resin and the relative mass loss is 31.6% ~14.8%. There are two essential reasons of the AO-resistance of the hybrid material that the silicones and silica are generated in the resin matrix during sol-gel process and the silica protective coating is formed on the sample surface in AO environment.
Real-time relative orbit determination for formation flying satellites using adaptive filtering
Qin Xianping, Ren Xia, Yang Yuanx
2014, 40(9): 1195-1199. doi: 10.13700/j.bh.1001-5965.2013.0589
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 574
Abstract:
A method of real-time relative orbit determination for formation flying satellites using adaptive filtering was proposed. Real-time relative orbit of two gravity recovery and climate experiment (GRACE) satellites was computed by using the global positioning system (GPS) data observed from December 9 to 10, 2005. The results of the real-time relative orbit determination were independently validated with the orbits of jet propulsion laboratory (JPL) which computed separately. The results of computation show that the information of relative dynamics and observation between formation flying satellites can be balanced finely by adaptive filtering through adaptive factor, and the relative orbit of formation flying satellites computed by adaptive filtering is better than that of Kalman filtering. The results of computation also show that the accuracy of relative orbit is improved for the shorter baseline of satellites based on the adaptive relative orbit determination. The accuracy of the baseline of GRACE satellites is better than 6 cm when using GPS single-frequency pseudoranges and broadcast ephemeris.
Simulation of heating control law of electro-thermal deicing of helicopter rotor blade
Fu Jianping, Zhuang Weiliang, Yang Bo, Chang Shinan
2014, 40(9): 1200-1207. doi: 10.13700/j.bh.1001-5965.2013.0551
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 649
Abstract:
The work mechanism of the electro-thermal anti/deicing system is very complex as it is related to the coupled heat transfer between the electro-thermal and the external heat flux, i.e., the convective heat transfer and phase transition heat transfer, and the data available is extremely limited. In order to explore the mechanism of the heat transfer of the electro-thermal anti/deicing mode, a two-dimensional electro-thermal deicing model was established based on the Messinger model and improved enthalpy method. The heat transfer between the icing surface and air flow, phase changes of melting and icing were coupled in the current model. The control volume method was used to discretize the differential equations, and the methods of TDMA (tri-diagonal matrix algorithm) & ADI (alternating direction implicit) were used to solve the linear equations, and then the temperature distribution on the deicing surface was finally obtained as well as the heat transfer mechanism was presented. The effects of the electric heating method and the heating flux on the temperature distribution were analyzed in different icing conditions. The results show that high efficient utilization of the electro-thermal deicing system and the flight safety guarantee can be achieved by adjusting the heat flux density and distribution and the control law of heating time properly.
Real-time evaluation method for stability of fault prognostic algorithm
Yu Jinsong, Liu Hao, Zhang Ping, Wan Jiuqing
2014, 40(9): 1208-1212. doi: 10.13700/j.bh.1001-5965.2013.0532
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 582
Abstract:
An evaluation method of fault prognostic algorithm from the perspective of stability was proposed for the existing evaluation metrics for fault prognostic algorithm were subjected to the actual remaining useful life. Based on studying upon the health degradation process of the system under test, according to the prognostic value of remaining useful life and the value of consumed life, the performance of fault prognostic algorithm could be assessed by calculating the coefficient of variance of the fictitious life before system failed. To verify the proposed method, the stability of recursive least squares algorithm and particle filtering algorithm was assessed with simulated data generated by the fault progression model of electro-mechanical actuator. Simulation results indicate that the proposed algorithm can arrive at the same evaluation conclusion as the existing methods which need the ideal value of remaining useful life of the system under test.
Extraneous torque analysis of pneumatic load simulator
Wei Qiong, Wu Shuai, Jiao Zongxia, Yu Hao
2014, 40(9): 1213-1218. doi: 10.13700/j.bh.1001-5965.2013.0553
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 541
Abstract:
In order to analyze the formation and influence factors of the extraneous torque of pneumatic load simulator, the working principle, structure diagram and experimental platform of the pneumatic load simulator were introduced and the mathematical model of the pneumatic load simulator was deduced. The model was verified through comparing the result of experiment and simulation. The three influence factors (passive pressure, moment of inertia and friction torque) of the extraneous torque of pneumatic load simulator were analyzed qualitatively by using linearization method. The influence of the three factors on the extraneous torque of pneumatic load simulator was analyzed quantitatively by using nonlinear simulation. The conclusion is that the friction torque is an important factor which comes into the extraneous torque in pneumatic servo loading system.
Equilibrium characteristics and stability analysis of helicopter-slung-load coupling system
Cao Long, Cao Yihua, Li Chunhua
2014, 40(9): 1219-1224. doi: 10.13700/j.bh.1001-5965.2013.0561
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 695
Abstract:
A nonlinear dynamical model of the helicopter-slung-load coupling system was presented, based on single mass-point hypothesis. Under this hypothesis, the consideration of the slung-load brought in extra degrees of freedom and constraints, which made the equations of motion increased by 4 orders, and being a set of implicit differential algebraic equations. By distinguishing the generalized acceleration terms from the quadratic generalized speed terms in the inertia forces, the equations of motion can be turned into a set of explicit ordinary differential equations. For the helicopter model and the helicopter-slung-load model, trim states for zero-side-slipping forward flight were first computed, using direct numerical approach, and the results were compared with flight test data. Then, both of the two models were linearized under small-perturbed conditions, and modal decomposition was performed on these linearized models. Results show that 2 new dynamical modes would be introduced by the single-mass-point slung-load. Motions of the slung-load's 2 degrees of freedom would be coupled with the helicopter's altitude response, and modify the characteristics of helicopter's inherence modes, make some of them worse.
Design and analysis on dynamic characteristic of servo mechanism’s load simulation system
Zhang Peng, Fu Yongling, Guo Yanqing, Qi Xiaoye
2014, 40(9): 1225-1230. doi: 10.13700/j.bh.1001-5965.2013.0571
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 638
Abstract:
In view of a load simulating problem of servo mechanism in launch vehicles, a new load simulator device was present, which could simulate the inertia, friction, elastic, servo mechanism mounting rigidity and flexibility characteristics of engine nozzle by the mechanical structures. The complete mathematical models of servo mechanism and load simulator device were constructed. The influence of inertia, elastic and flexible to multiple degrees of freedom was analyzed by simulation. A sweep frequency test of servo mechanism was made to repeat the dynamic characteristics of servo mechanism in practical work when some loads of load simulator device were adjusted in a certain range. The test results validate the reasonableness of the proposed design, which may be a reference for the design of load simulator device with multiple degrees of freedom property. Besides, the simulator has got an actual application.
Identification method for defect-introducing fine-grained software changes
Yuan Zi, Yu Lili, Liu Chao
2014, 40(9): 1231-1238. doi: 10.13700/j.bh.1001-5965.2013.0576
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 524
Abstract:
Software defects were introduced into software system by software changes in the software development process. A new method to identify defect-introducing fine-grained changes was proposed to improve the efficiency of defect finding and reduce the cost of manual inspection. This method was based on the idea of machine learning classification. It took the fine-grained change as classification instance and constructed feature set from five dimensions, namely time, context, content, purpose and implementer of the change. It built fine-grained change instances automatically by mining software history repositories with the program static analysis and natural language semantic analysis techniques. It trained a classifier by learning change instances in software history, which could identify whether a new fine-grained change introduced any defects or not. Cost-effectiveness analysis was conducted on real software systems to verify the validity of the proposed method. The results indicate that compared with methods for file and transaction level changes, this method can reduce the manual inspection cost significantly.
Simulation of non-Gaussian random vibration
Xu Fei, Li Chuanri, Jiang Tongmin, Rong Shuanglong
2014, 40(9): 1239-1244. doi: 10.13700/j.bh.1001-5965.2013.0579
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 866
Abstract:
Traditionally, only Gaussian signal can be produced by random vibration controller using power spectral density (PSD). However, actual vibration is usually non-Gaussian, which makes random vibration testing unable to simulate the failure mode that products will experience. Simulation of non-Gaussian random vibration with constant root mean square (RMS) and running RMS was performed respectively using two case studies. Case study 1 uses Hermite polynomial to transform Gaussian signal to non-Gaussian signal. The synthesized non-Gaussian signal has constant RMS, desired kurtosis and the same PSD with original Gaussian signal. Case study 2 uses a new method to simulate measured non-Gaussian random vibration which has running RMS. The synthesized non-Gaussian signal has the same PSD, kurtosis and probability density function with the field data.
Improved SST-DES in numerical simulation of mild separation
Wang Xiangyu, Li Dong
2014, 40(9): 1245-1249. doi: 10.13700/j.bh.1001-5965.2013.0587
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 755
Abstract:
In the numerical simulation of mild separation by detached eddy simulation (DES) based on shear stress transport (SST) turbulence model, too large turbulent viscosity may translate from the upstream Reynolds averaged navier stokes (RANS) zone to the downstream large eddy simulation (LES) zone by convection, which could restrain the development of resolved turbulence, delay the instability of shear layer and is known as the grey area. Starting from the standard k-equation sub-grid scale model, an improved SST-DES was put forward by preventing the influence of the mixed dependent variables to turbulent viscosity as a result of the original k-equation-like sub-grid model. The numerical study of flow over AS239 airfoil shows that the improved SST-DES keeps the characteristics of delayed detached eddy simulation (DDES) in the boundary layer and increases the accuracy of resolution in the regions far away from the wall at the same time and gets closer results to the experiment compared with SST-DES and SST-DDES.
Flight envelope quantitative division of hypersonic vehicle based on gap metric
He Chaofan, Yang Lingyu, Li Xin, He Niannian
2014, 40(9): 1250-1255. doi: 10.13700/j.bh.1001-5965.2013.0592
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 618
Abstract:
Considering that the existing flight envelope division methods of hypersonic vehicle were too subjective and complicated, a new division method was introduced based on the theory of gap metric. The theory of gap metric was introduced, and the computing method of gap between linear systems was given. Here the gap metric was taken as the quantitative index to analyze the extent of the model characteristics' variation to confirm the frontier of subrange. Based on the result obtained above, the way of choosing the nominal state point was proposed by analyzing the gap metric of all points within the subrange. With the living example of some hypersonic vehicles, the analysis of amplitude-frequency characteristics for nominal state point and the simulations of closed-loop control system prove that the result of envelope division is reasonable, which indicates the method proposed is effective and able to increase the level of automation of envelope division.
Friction parameter identification and compensation for electro-hydraulic load simulator
Guo Yanqing, Fu Yongling, Zhang Peng, Chen Juan
2014, 40(9): 1256-1262. doi: 10.13700/j.bh.1001-5965.2013.0604
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 643
Abstract:
Due to the interference of friction while controlling the electro-hydraulic load simulator, a new model with the consideration of friction was presented. In this model, the test sample was simplified as retractable rigid rods and LuGre model was used to describe the friction. The friction coefficients of LuGre model could be identified based on two specific working conditions and the accuracy of coefficients can be verified by virtue of the corresponding identification data. In order to validate the feasibility of proposed model, the friction compensation controller was deduced on the basic of structural invariance principle. Then a large number of experiments including displacement servo, torque servo, redundant force et al, were carried out. Experimental results show the friction acting on load simulator can be eliminated with the employment of LuGre model and friction compensation controller.
Simulation of droplet impingement characteristics of spinner based on Eulerian method
Wu Menglong, Chang Shinan, Leng Mengyao, Wang Chao
2014, 40(9): 1263-1267. doi: 10.13700/j.bh.1001-5965.2013.0559
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 720
Abstract:
Based on Eulerian theory, the droplet impingement characteristics of the spinner were simulated. The droplet impingement characteristics of the spinner were achieved by calculating the droplets' flow field with numerical diffusion. The rotate speed impact on the droplet impingement characteristics of spinner was analyzed. Results show that the greater the rotate speed, the smaller the droplet impingement limit. In typical flight conditions and weather conditions, the centrifugal force on the trajectory of droplets is much smaller than the inertial force. The rotate speed has little influence on the droplet impingement characteristics of the spinner.
Task allocation in cooperative air combat based on multi-agent coalition
Diao Xinghua, Fang Yangwang, Xiao Bingsong, Mao Donghui
2014, 40(9): 1268-1275. doi: 10.13700/j.bh.1001-5965.2013.0564
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 781
Abstract:
Multi-agent coalition formation theory was used to analyze the task allocation of multi-aircraft against multi-target in net warfare combat. The process of cooperative air combat task allocating was just the process of coalition formatting. First, the whole striking task to all the targets was separated into a serious of subtasks, then the subtasks were decomposed to some task cells that can be executed by single platform. Second, the models of coalition reward, the ability cost and the communication spending were constructed based on the definition of the coalition characteristic function which was set as the object function of the air combat task allocation. Finally, particle swarm optimization was adopted in the form of binary matrix particle coding to generate the coalition, and the feasibility checking strategy of the particle was designed. Simulation studies were carried out to confirm the rationality and validity of the method in the cooperative air combat task allocation.
Sliding mode adaptive synchronization for a class of fractional-order chaotic systems with uncertainties
Yu Mingzhe, Zhang Youan
2014, 40(9): 1276-1280. doi: 10.13700/j.bh.1001-5965.2013.0614
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 485
Abstract:
A fractional-order sliding mode adaptive control approach was introduced to synchronize chaos of a class of fractional-order chaotic systems with uncertainties. The effects of model uncertainties and external disturbances were fully taken into account. An appropriate robust fractional sliding mode adaptive controller was designed by adopting a fractional sliding surface with strong robustness, and using sliding mode adaptive control theory, Lyapunov stability theory and fractional-order linear systems stability theory. The control law can ensure the occurrence of the sliding motion, and achieve synchronization between the drive system and response system. The upper bound of uncertainties was not needed in the proposed controller. The designed controller is not complicated mathematically and easy to implement. The fractional adaptive sliding mode control approach can be applied to control a broad range of nonlinear fractional-order chaotic systems with uncertainties. Numerical simulation was presented to show the efficiency and applicability of the proposed control strategy.
Trajectory optimization for hypersonic gliding vehicle considering stochastic disturbance
Guo Haifeng, Huang Changqiang, Ding Dali, Xiao Hong
2014, 40(9): 1281-1290. doi: 10.13700/j.bh.1001-5965.2013.0755
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 792
Abstract:
To solve the problem of the reentry trajectory optimization for the hypersonic gliding vehicle with stochastic disturbance, the numerical method of trajectory optimization based on the generalized polynomial chaos was put forward. The sampling space was formed by the sampling of stochastic variable using generalized polynomial chaos. The space of the observations came into being after putting every sampling value into solving the problem of the deterministic trajectory optimization iteratively. The expected value, variance and covariance were computed and the outputs were approximated. The simulation of maximizing the downrange angle of the reentry trajectory optimization for the hypersonic gliding vehicle with stochastic disturbance was carried out based on this method. The results of the simulation indicate that the method could solve the problem of trajectory optimization with stochastic disturbance, and the computational efficiency was improved greatly contrasted with the Monte Carlo method.
Inverse dynamic attitude control for re-entry vehicle based on output redefinition
Shi Linan, Zhang Ran, Li Zhaoying, Li Huifeng
2014, 40(9): 1291-1298. doi: 10.13700/j.bh.1001-5965.2014.0098
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 644
Abstract:
Internal dynamics occurs in the lateral/directional motion of re-entry vehicle with two body flaps under the condition of high angle of attack. A method of inverse dynamic control based on output redefinition technique was presented. The output-redefinition technique was used to locally stabilize the zero dynamics. A pole placement strategy enhanced the robustness of the zero dynamics and then provided feedback linearizes of the output-redefinition system to design the inverse dynamic controller. Simulation results show that the zero dynamics is stable and the tracking performances of attack angle and bank angle are very well while sideslip angle is stabilized to zero. The simulation results compared with reaction control system (RCS) control demonstrate that stable attitude control can be realized only by two aerodynamic control surfaces and the complexity of the vehicle structure can be reduced meanwhile the payload can be incerased.
Effect of buckling mode on performance of post-buckled composite stringer-stiffened panels with debond
Xu Rongzhang, Guan Zhidong, Liu Lu, Zhang Nan
2014, 40(9): 1299-1304. doi: 10.13700/j.bh.1001-5965.2013.0605
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 744
Abstract:
Because of the proximity of first and second buckling load, some specific stringer-stiffened panels will exhibit different buckling modes under uniaxial compression load, which causes their post-buckling behavior strikingly different. Test and numerical calculation was conducted to study this phenomenon. Moiré interferometry and ultrasonic scan were used to monitor the buckling mode and debond. Based on the software of ABAQUS, a finite element was developed. Virtual crack closure technology (VCCT) was used to simulate the interfaces with artificial debond. The initial geometric imperfection was led into model to process the nonlinear post-buckling analysis. By comparing the strain energy release rates of the crack front, the performance of debond propagation in two different modes was determined. The calculated results are coordinated with the tested results very well. The results indicate that the different damaging propagates under two buckling modes will generate that strength of panels with three half waves buckling mode exceeds the panels with two half waves buckling mode.
Landmark fixed high-precision binocular visual navigation method
Zhang Yang, Wang Xinlong
2014, 40(9): 1305-1311. doi: 10.13700/j.bh.1001-5965.2013.0588
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 876
Abstract:
Autonomous navigation is a crucial technology in the field of unmanned aerial vehicle (UAV), intelligent robots and smartcars. To overcome shortages in traditional visual navigation methods, a landmark fixed high-precision binocular visual autonomous navigation method, based on the camera egomotion estimation theory, was put forward. In this method, camera's egomotion parameters, velocity and angular velocity, were measured from the variance between frames of the continuing image sequence, then the position and attitude was calculated by accumulating the velocity and angular velocity. Moreover, by bringing in the absolute positioning information provided by the landmarks, the performance of the method in long time navigation was improved. Combining the absolute positioning information from the landmarks and the relative navigation information from the binocular vision, as well as modeling and decoupling the measurement noise of the binocular vision, the accumulation and increasing of the navigation error was suppressed. Simulation result shows that this method has the advantage of high precision, autonomy and completeness of navigation information.
Bayesian evaluation method for binomial system reliability growth
Yuan Kun, Li Xiaogang
2014, 40(9): 1312-1316. doi: 10.13700/j.bh.1001-5965.2013.0599
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 603
Abstract:
Concerning the multi-stages field information during the process of product development, a Bayes evaluation method based on the new Dirichlet prior distribution was proposed. This method made use of discrete army material system analysis activity (AMSAA) model to describe the dynamic change of reliability at different stage and predicted the reliability at next stage according to the multi-stages field data during the reliability growth test (GRT). Then the new Dirichlet prior distribution was introduced and the parameter estimations were obtained by maximum entropy method. Under the conditions of gaining the field test data, the Bayesian evaluation of product reliability was obtained by the proposed method. Finally, numerical example demonstrates the accuracy of the proposed method with appropriate expert experience compared to the discrete AMSAA model and Beta prior distribution.
Image retrieval algorithm based on SIFT, K-means and LDA
Wang Yulei, Bi Shusheng, Sun Minglei, Cai Yueri
2014, 40(9): 1317-1322. doi: 10.13700/j.bh.1001-5965.2013.0601
Abstract References Relative Articles Resource File Access Statistics iconViews $!{v.htmlCount} iconDownload 756
Abstract:
Image retrieval is a problem in the field of information retrieval. An algorithm was developed for image retrieval based on scale invariant feature transform (SIFT), K-Means and latent dirichlet allocation (LDA). This algorithm was mainly divided into two stages. The preparations obtained the classified image library, the probability distribution of parameters table and the base vocabulary library; the retrieval classified the test image based on the preparations, and looked up the most similar image. Compared with the traditional methods based on text or content, the algorithm classifies automatically all the images in the library before the retrieval, which can replace the process of manual label. Meanwhile, the algorithm is based on image feature fully, which will not introduce artificial disturbances. Experimental results show that the algorithm can classify accurately the test image as the corresponding category, which can increase efficiency of the retrieval.

Copyright © Journal of Beijing University of Aeronautics and Astronautics

Address: Editorial Department of Journal of Beijing University of Aeronautics and Astronautics, 37 Xueyuan Road, Haidian District, Beijing Post Code: 100191 Email: jbuaa@buaa.edu.cn

Supported by: Beijing Renhe Information Technology Co., Ltd.