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2011 Vol. 37, No. 12

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Assessing step-down stress accelerated degradation data via nonlinear accelerated model
Yao Jun, Zhong Weiqiang
2011, 37(12): 1475-1478.
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A segmented nonlinear accelerated degradation model (SNADM) was introduced based on the equivalent method of accumulative damage theory, which tackles the problem that product life is difficult to determine with degradation rate being a function of the variable of time. A segmented expression of the function of overall accumulative degradation was derived and combined with nonlinear function and accelerated degradation function, from which a expression of SNADM was obtained. The parameters of the SNADM were identified by numerical iteration; further the statistical function of degradation track was extrapolated. The reliability function was determined through the type of random process of the degradation distribution. Then an evaluation to product storage life was undertaken by combining the statistical function of degradation track, reliability function and failure threshold value. An example of a missile refrigerator undergoes a step-down stress accelerated degradation test while test data were evaluated with SNADM. The technology introduced is validated with the resultant coincidence of both evaluated and field storage lives.
Novel method of multiple-satellite faults exclusion for global navigation satellite system
Chen Canhui, Zhang Xiaolin
2011, 37(12): 1479-1483.
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In global navigation satellite system (GNSS), with the increase in the number of observational satellites comes an increase in the probability of simultaneous multiple-satellite faults. Therefore, the multiple-satellite faults should be taken into account in receiver autonomous integrity monitoring (RAIM). The approach of fault detection is simpler than that of fault exclusion and the fault detection rate (FDR) is higher than the fault exclusion rate (FER), considering the features of satellite navigation system, a novel multiple-satellite faults exclusion method was proposed based on fault detection, named random search method (RSM). The binary code for observational satellites was employed in the new method. Firstly, the initial fault free constellation was obtained by random initialization in RSM. And the final fault free constellation with the largest number of observational satellites was obtained by the search of unselected satellites gradually based on the initialization result. And so, the function of fault exclusion was realized. Simulation results show that, in most cases, the FER of RSM is more than 99%. And the new method has the capable of fault exclusion either for single satellite fault or for simultaneous multiple-satellite faults, and it can effectively meet the requirement of autonomous integrity of GNSS.
Dynamic buckling failure analysis of rod with uncertain initial geometrical imperfection
Wang Xiaojun, Wang Lei, Ma Lihong, Qiu Zhiping
2011, 37(12): 1484-1489,1509.
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It can be found from some data that the buckling load of structure may decrease by 70 percent due to the existence of initial geometric imperfection.The initial geometric imperfection may be uncertain due to the manufacture errors and so on, so this will lead to the uncertainty of the buckling load or the dynamic buckling response of structure. The problem of dynamic buckling failure of rod with uncertain initial geometrical imperfection under the axial dynamic loading was studied. The safety factor was defined based on the integral deflection. The uncertain initial geometrical imperfection was described by interval analysis and convex models respectively, and then the least favorable estimation on the dynamic buckling safety factor of rod was evaluated based on the integral displacements. The results are significant for judging the dynamic buckling failure analysis of rod with uncertain initial geometrical imperfection.
Scene matching semi-physical simulation system based on 6 degree of freedom manipulator
Zhao Long, Li Tiejun
2011, 37(12): 1490-1493.
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In order to overcome the limitations of traditional scene matching semi-physical simulation system, a new scheme of the semi-physical simulation system was proposed for airborne scene matching. The aircraft motion state has been simulated by using motion of 6 degree of freedom manipulator and large screen projection system, the process of real-time image obtained was simulated by captured real-time image for large-screen simulation. Information synchronization of the multiple subsystems was realized by using multi-threaded control and network control. The relative and absolute positioning was completed by using high-precision calibration field. The system has good scalability which can shorten development cycles, reduce development cost for scene matching system. More than 10 million RMB is saved after the system was applied.
Turbine blade DR images fusion based on bi-energy X-ray radiography
Yang Min, Wu Meijin, Wei Dongbo, Li Xingdong
2011, 37(12): 1494-1497.
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In order to increase the single frame digital radiography(DR) image information of the turbine blade, two DR images were captured at different X-ray energy so as to get the turbine blade quality information at different thickness region firstly. Secondly, the two original DR images were decomposed by wavelet transform, and the maximal local variance role was used to carry out the low sub-frequenced image fusion, and the active factors based on local gradients were calculated to carry out the high sub-frequenced image fusion. Finally, through inverse wavelet transform the output image can be obtained. The experimental results show that the single frame fused turbine blade DR image brings more detailed information, so it is useful to the fast and accurate quality judgements of the turbine blade.
Validation of two-dimensional axisymmetric plume model for ion thruster
Ren Junxue, Wang Yan, Qiu Qian, Tang Haibin
2011, 37(12): 1498-1503.
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In order to understand the distribution and flow characteristic of ion plume especially the charge-exchange (CEX) ions, the ion thruster plume model was established and a numerical simulation using the particle-in-cell method was adopted to obtain CEX ions distribution in the plume. The calculation results were compared with the experimental results for the plume fields of two ion thrusters. It agrees well between calculation results and experimental results of CEX ions density distribution, magnitude of electrical potential, position of maximum electrical potential grads, CEX ion flow angle. Structures of electrical potential have somewhat differences because the experimental result is influenced by the vacuum tank wall. The ion thruster plume model and calculation results help for experimental and numerical simulation study of plume.
Novel rapid acquisition algorithm for hybrid DS/FH spread spectrum systems
Wen Xiaojie, Zhang Yanzhong, Shao Dingrong, Li Shujian
2011, 37(12): 1504-1509.
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To improve the mean acquisition time performance of hybrid DS/FH spread spectrum systems, a rapid acquisition algorithm based on alterable frequency hopping rate was proposed. The unaligned states frequencies were excluded to fast decrease mean acquisition time, while the acquisition was declared after adequate verification to decrease false alarm probability. The closed form expression of the mean acquisition time was obtained with the state diagram in additive Gaussian noise channel and typical jamming environment, and the probabilities of detection, missing, and false alarm were derived. The simulation results show that, in the circumstance of additive Gaussian noise channel, the mean acquisition time with the optimal threshold is decreased almost 1/4 of the one using the tradition fast scanning method and the new algorithm is more robust under jamming.
Time series prediction using neuron-expanding regularized extreme learning machine
Zhang Xian, Wang Hongli
2011, 37(12): 1510-1514.
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A new algorithm called neuron-expanding regularized extreme learning machine (NERELM) was proposed and applied to time series prediction. In order to enhance the generalization performance of NERELM, the empirical risk and the structural risk were balanced on the basis of structural risk minimization theory. The output weights of NERELM were analytically determined at extremely fast learning speed instead of using gradient-based learning algorithm, and the optimal network structure of NERELM was automatically determined by expanding its hidden neuron nodes iteratively. Experiments on time series prediction indicate that NERELM has better performance in training computation cost and prediction accuracy in comparison with conventional gradient-based neural networks.
Experiments of aluminum migration of power silicon transistor using planar process
Lü Weimin, Hu Dong, Xie Jinsong, Weng Lu
2011, 37(12): 1515-1518.
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Experiments have been carried out on to study a phenomenon of aluminum migration across a 50 micron semi-insulation gap on the die surface of a power silicon transistor under a high-intensity electric field, which is manufactured using a typical planar process with aluminum as the metallization material. After physical observation and analysis by opening cap, testing at low temperature and validation by drying and analysis and comparison of composition in the migration, the chemical composition of the substances involved in the migration process was verified. Then the correlation between the migration process and environmental conditions of temperature and humidity, contaminants on the die surface as well as local structure of transistor were identified respectively. Based on the experiment results obtained in this study, a hypothesis was made on the mechanism of this migration phenomenon. The analysis provides direction for verification and quantization of the migration mechanism under different induced conditions.
Multi-target detecting and positioning approach of mobile robot based on ultrasonic sensors
Wang Guofu, Gao Feng, Yang Xinhong, Cui Ying
2011, 37(12): 1519-1523.
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To make mobile robot detect and locate scattered multi-targets accurately, a new intelligence measurement approach based on ultrasonic sensors was proposed. An array of three ultrasonic transceivers was employed to transmit approximate plane acoustic beam, and space coordinates were built. Three sensors sent timing ultrasonic pulses, while the digital signal processor sampled and analyzed the received echoes based on designed algorithm to complete the clutter filter, the recognition and extraction of characteristic signal data from the head wave echo, second echo and third echo etc. After detecting time-of-flight of the echoes of each channel correctly, the accurate location of the measured targets was calculated. Rods were adopted as the measured objects in the experiments, which coordinate value was calculated based on high-speed echo data acquisition and processing. Compared the calculated data with the actually measured data of the rod positions, results confirm the feasibility and validity of the method.
Conversion relation of detail fatigue rating based on different fatigue life distribution
Dong Yanmin, He Xiaofan, Liu Wenting
2011, 37(12): 1524-1528.
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Due to the difference of usage, loading, structure, reliability requirement, and so on, the definition of military aircraft structure detail fatigue rating is different from civil aircraft structure which mainly varies in the fatigue life distribution functions and basic structure. The number of details in different basic structure was corrected by structure component fatigue rating coefficient and estimates of median life was supposed to be the same by log-normal distribution and Weibull distribution. The conversion relation of detail fatigue rating based on different fatigue life distribution was acquired. It is showed that the conversion relation depends on the basic value of DFR and the types of material. An approach was presented for determining military aircraft structure DFR value by the similar structure of civil aircraft and an example was given in the end.
High order accurate methods in numerical simulation of hypersonic heat transfer
Jiang Zhenhua, Yan Chao
2011, 37(12): 1529-1533.
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Influencing factors of hypersonic heat transfer simulation were studied with the blunt cone model. The connection between heat transfer computation and wall-normal grid Renolds number was established. Stable and accurate heat transfer result was acquired with high-order interpolation methods. A variety of schemes and limiters were evaluated to research the influence of numerical diffusion on heat transfer calculation. Five-order weighted essentially non-oscillatory(WENO) scheme was employed in heat transfer computation and high-order accurate methods for hypersonic heat transfer prediction were established. It shows that high-order scheme can not only broaden the grid Reynolds number range but also reduce the dependence on space discretization methods in heat transfer computation.
Applicability of shrinkage porosity prediction for casting with Niyama criterion
Pan Liwen, Zheng Lijing, Zhang Hu, Gao Wenli
2011, 37(12): 1534-1540.
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The macroscopic shrinkage cavity and porosity of the TiAl alloy crisscross and clintheriform casting was predicted by the finite element casting simulation software ProCAST with Niyama criterion. The prediction results were tested by experiment. The results show that for the Ti-47Al-2Cr-2Nb alloy crisscross and clintheriform casting, the Niyama criterion values are mainly affected by the casting section thickness (cooling rate). The criterion values increase with the augment of the casting section thickness. The region that the most serious of the macro shrinkage and porosity is not the region that the minimum of the criterion value. While the region that the minimum of the criterion value has only the microporosity but no macro shrinkage and porosity, so it cannot confirm the location and bulk of the macro shrinkage and porosity on the basis of the criterion values. Analyzing makes clear that Niyama criterion is founded on interdendritic microporosity, and its function values are well applied to assessing the tendentiousness of microporosity. It can well predict the microporosity. Because the formation mechanism of macro shrinkage and porosity is different from microporosity, it isn't suitable for predicting the macro shrinkage and porosity of complex castings with great disparity in casting section thickness.
Genetic algorithm based optimal design for dual-redundancy brushless DC motor
Wu Zhiyong, Guo Hong, Lü Zhenhua, Qian Hao
2011, 37(12): 1541-1545,1568.
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A genetic algorithm (GA) based global optimization for a dual-redundancy brushless DC motor (DR-BLDCM) used in aviation actuators was presented. The aim of the optimal design is to reduce the weight of the motor. First, the objective function was established based on the electromagnetic and thermal models. The electromagnetic models include the flux density and the back-electromotive force coefficient expressed by the analytical method. The thermal models were established by the thermal circuit method, in which an accurate estimation for the iron loss was considered. Then the structural parameters of the dual-redundancy brushless DC motor were optimized by using the GA and taking account of the electromagnetic and thermal characteristic constrains. The result of the optimization shows that the weight of the motor had been reduced by 13.3%. This method can be used as a reference for other motor optimal design.
Security evaluation of nose wheel steering systems based on GSPN methods
Zhao Zhe, Jia Yuhong, Zheng Xin, Zhou Yutian
2011, 37(12): 1546-1551.
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To solve the problem of how to evaluate the safety of a system without relative statistical data, the generalized stochastic petri nets(GSPN) and classical evaluating method were hung together. Taking a certain type of airplane's nose wheel steering system, which was still at the stage of design, as an example, the failure modes and effects analysis (FMEA) list was set up by analyzing system's function structure figure. The failure rate, maintenance rate, the mean time between failure and the mean time of the maintenance were calculated by the experiential formula. According to these parameters and the nose wheel steering system's GSPN model, the steady failure probabilities were calculated by the TimeNET software package. The safety of the nose wheel steering system was evaluated with the experiential formula and the risk matrix. After the evaluation, this nose wheel steering system conforms to the design demands.
Dual-stage pressure control and efficiency analysis of motor-pump-valve coordinated control actuation system
Fu Yongling, Zhang Weiwei, Ji Youzhe
2011, 37(12): 1552-1556,1584.
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Based on the low efficiency and the significant heat loss of the aircraft actuating system, the relationship of pressure and efficiency was analyzed in the motor-pump-valve coordinated control actuation system. The method of the dual-stage pressure energy-saving control was proposed, that was, the different maximum pressures were set in the motor-pump and valve unit, and the control unit was determined by the requirement of the actuator system. The simulation and analysis were down by the AMESim software. The results indicate that the heat generated by the dual-stage pressure control system is only 27.9% and 34.1% of that generated by the high pressure valve control unit and the motor-pump separately. This method can obviously reduce the temperature increasing and heat losses of the system, the efficiency of the system can be improved, and consequently increase system life and maintain the security and reliability of the system.
Knowledge representation for CNC equipment fault diagnosis system based on CBR
Chen Youdong, Han Meihua, Ye Jinjun
2011, 37(12): 1557-1561.
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As the computer number control (CNC) become more and more complexity, there is a great demand for fault diagnosis and maintenance system to improve the efficiency of failure diagnostics and maintenance. The case-based reasoning (CBR) has been broadly applied in fault diagnosis. However the case base is increasingly large with the incremental learning which results in low solution retrieval efficiency and weak performance. To improve the accuracy of retrieval cases and reduce retrieval time, a method that searches the cases with stratified indexing and feature retrieval was presented in terms of the structure of CNC, and a frame of knowledge representation was detailed by this method. A prototype system was built with the search method and knowledge representation. The experimental results show that this method is effective.
General model for PMS reliability
Yang Chunhui, Yang Jianjun, Yao Lu
2011, 37(12): 1562-1568.
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The hypothesis of reliability model of phased mission systems (PMS) was summed up, and then the shortcoming was also presented that analytical model of PMS is difficult to describe and calculate the complex system, at the same time the simulation model is also hard to be set up. By using the colored Petri net(CPN) Tools, the general model for PMS reliability was set up. The model includes 3 levels: the top control model, which turns the fault trees of PMS into the input parameters of CPN model; the single phase model, whose output is the state of the top event by the input parameters of the top control model; the bottom event model, which produces fault events by comparing rand number to the probability of fault. The general simulation model is robust which can keep the stable model structure for different PMS and the modeling process. The case contrasts the results of the general CPN model with analytical solution, which shows the CPN model is correct and more efficient.
Object-driving software testability measurement
Fu Jianping, Liu Bin
2011, 37(12): 1569-1574.
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To reduce the difficulty and cost of software testability measurement, an object-driving method was proposed to measure the testability of various programs by a unified manner. It is based on a software testability metrics framework that consists of the testability metric, testable characteristics metrics, testability factors metrics and their relations. First, the measurement object was analyzed to determine the object type, the software type and test conditions. Then suited elements were chose from the metrics framework according to the software type and test conditions to construct a special software testability metrics framework. Finally advantage of the elements in the special metrics framework was taken to calculate the testability factors, testable characteristics or testability according to the object type. The application indicates this method can get the quantitative value of software testability and help the software testing by predicting the test resources.
Fuzzy comprehensive evaluation in FMECA of electro-hydraulic servo valve
Dai Chengguo, Wang Xiaohong, Zhang Xin, Wang Lizhi
2011, 37(12): 1575-1578.
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According to the limited analysis of the whole system or product and the unreasonable weight distribution of the failure risk, occurrence probability and detective difficulty, the fuzzy comprehensive evaluation was proposed to optimize the failure modes, effect and criticality analysis(FMECA) of the electro-hydraulic servo valve. The evaluation result was obtained after the factor set, the evaluation set, the weight set and other parameters determined. The level of the risk degree of every single failure mode to the whole servo valve system was also given. In the application of the fuzzy evaluation results, the order of the failure modes was determined by the relative risk level. And the risk level of the whole electro-hydraulic servo valve would be obtained. These results have a positive meaning to the further improvement of reliability and the maintenance of the electro-hydraulic servo valve and other products.
Design of radiometer for thermal control coatings in situ measurement
Xing Hui, Zhao Huijie, Zhang Ying, Zhang Qingxiang
2011, 37(12): 1579-1584.
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To solve the problem of thermal control coatings degradation in space environment, it is necessary to study coatings degradation law in simulated space environment, thus a radiometer design based on calorimetry was proposed for in situ measurement of thermal control coatings solar absorptance. The radiometer structure was designed according to the requirement of in situ measurement. By conducting thermal analysis on radiometer, the heat transfer equations were built and a calculation model based on transient thermal equilibrium was established by energy conservation principle. An SR107 thermal control coating was tested in isoperibol. The experiment result shows a within 2% relative error between the solar absorptance of SR107 and the coating calibration value, with a 6.3% measurement uncertainty. The result validates the effectiveness of the experiment.
Method of realtime hill-shading in digital earth system
Yang Hailin, Wang Jiaxin
2011, 37(12): 1585-1588.
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Hill-shading terrain effects, which are high precision and real-time dynamic, were achieved on global terrain in the digital earth simulation system developed. It was realized by using the normal map mode without increasing the number of terrain grid. The elevation data was processed to level of detail chunked and create normal map of all levels by calculating normal. Lighting effects of normal map were calculated by pixel shader and the texture was pasted onto corresponding layered terrain meshes. By the direction of incidence of the light source's incidence direction, hue, saturation and brightness, the vertex's ambient light, diffuse light and specular light was calculated. At low-precision terrain grid, obvious changes effect of light and shadow as high-precision terrain grid was reached.
Mahalanobis distance-based semi-supervised discriminant analysis for face recognition
Shi Jun, Chen Caikou
2011, 37(12): 1589-1593.
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To address the problems that there is often no sufficient class-label information of face samples in face recognition application and some relativity also exist among face sample features, a semi-supervised discriminant analysis based on Mahalanobis distance was presented. The method makes use of the Mahalanobis distance to perform marginal fisher analysis (MFA) for labeled samples in the data set, which is on the basis of the graph embedding framework, so that it not only preserves the intraclass compactness and the interclass separability, but also extracts the discriminant characteristics for effective classification, and simultaneously the unlabeled samples were utilized to characterize the geometric structure of the data set, and thus the local neighborhood information among samples was well preserved. Compared with the traditional feature extraction methods, the proposed method has better recognition performance, and the experiments on ORL, YALE and AR face databases demonstrate the effectiveness of this method.
Analysis of oversteer/understeer characteristics of aircraft ground steering
Zhu D, an
2011, 37(12): 1594-1598.
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A lower-order equivalent aircraft steering system model with time-varying parameters was developed to analyze oversteer/understeer characteristics of aircraft steering and improve handling characteristics of nose wheel steering system after touchdown. Combining system stability analysis with flight data, it is found that the curve of oversteer/understeer characteristics rapidly approaches to the critical speed stability boundary in a certain speed range, which is caused by yaw rate command bandwidth decreasing nearly to zero. It results in a sharp deterioration in ground-handling characteristics. Then a stability augmentation design with self-tuning controllers was proposed, using a yaw-rate feedback as the cue of adjusting. The analysis and simulation indicate that the model proposed simplifies the related analysis which would be a complex problem in high-order models and it could be used as a complement to high-order, detailed model analysis. And the stability augmentation design could set yaw rate command bandwidth in a desired range and ameliorate the rudder pedal sensitivity, greatly improving the ground-handling characteristics.

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