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2005 Vol. 31, No. 10

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Pulsed phase thermography and its application in the NDT of composite materials
Guo Xingwang, Liu Yingtao, Guo Guangping, Yang Danggang
2005, 31(10): 1049-1053.
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To suppress various interference and increase the detection capability of pulsed thermography for defect inspection of composite materials, PPT (pulsed phase thermography) based on FFT(fast Fourier transform) for the time history of each pixel and its application to composite structures were studied. The principle of PPT for processing pulsed thermographic data was described; the problems of frequency domain aliasing and frequency spectrum leakage in the signal processing were discussed. A PPT experiment was made on a carbon fibre reinforced plastic sample, and the image processing effects were quantitatively compared by the signal-to-noise ratio. The experimental results show that PPT not only has the advantages of rapid image acquisition, less sensitivity to inhomogeneities of surface heating, non-necessity to know a prior position of a sound area, but also has good robustness to random noise and greater signal-to-noise ratio, so it is an effective method for NDT & E (nondestructive testing and evaluation) of composite structures.
Anti-aliasing technique for surface reconstruction of confocal data
Xue Bindang, Jiang Zhiguo, Zhou Xiaokuan
2005, 31(10): 1054-1057.
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There might exists missing holes and aliasing on the projected image by way of representing object surface with boundary voxels and projecting boundary voxels to the screen as points to render the shading image of the object. An anti-aliasing technique for surface reconstruction is proposed. Firstly, the boundary voxel sets is generated by dividing cubes; Secondly, the values of the center point of the boundary voxel sets is obtained to form the surface point sets; Then, a footprint function is chosen to calculate the effect region of the surface point on the pixel on the screen, and the result value is used as the weight of the pixel. This processing is just like splatting, so the missing holes is eliminated and the display quality is improved. Experimental results show that both the surface reconstruction and the display performance of the technique are satisfactory.
Research on colliding and cushioning of wall-suspension robot
Zhang Zhaojun, Yan Ning, Zong Guanghua
2005, 31(10): 1058-1062.
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Based on the requirement of automatically getting on wall and cushioning, the form mechanism of pull force of robot, cause and process of touch wall were analyzed. Utilized the principle of aerodynamics, calculating method of the pulling force was given and the result was verified through experiment on the robot physical prototype. The robot closes to the wall under the effect of pulling force and collides at the same time. In the colliding process, cushion device which is composed of skirt edge and support mechanism undertakes absorption of impulsive energy. The former also guarantees sealing after the robot closing to the wall, its rigidity cannot become too strong. The later also guarantees that the robot walks steadily on the wall, so its rigidity cannot become too weak. The method of defining cushion rigidity was proposed. The criterions of assigning cushion rigidity to skirt edge and the support mechanism were given. This method could be used to engineering analysis of wall-suspension robot.
Motion compensation processing for airborne SAR data based on real sensing data of IMU/GPS
Ye Shaohua, Zhou Yinqing
2005, 31(10): 1063-1065.
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The motion compensation technique for airborne stripmap mode SAR(synthetic aperture radar) was briefly analyzed, the strong motion errors with small aircraft Y12 were evident through analyzing the position parameters offered by an IMU/GPS(inertial measurement units/global positioning system) unit with laser gyros, then the motion compensation processing, which combined with range-Doppler image formation algorithm, was tested based on the high precision APC(antenna phase center) position parameters provided by the laser IMU/GPS unit. The results showed that high quality SAR images could be obtained directly from SAR raw data with serious motion errors through motion compensation procedure, so any kind of autofocus procedures with heavy computation load does not needed to correct the residual motion errors.
Error analysis of prediction orbit determined by GLONASS ephemeris
Ma Jun, Jiao Wenhai, Xiao Yelun
2005, 31(10): 1066-1070.
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The equation of satellite orbital motion was derived in the conventional terrestrial coordinate system. By analyzing the fitting precision of satellite prediction orbit determined by GLONASS(global navigation satellite system) broadcast ephemeris,it is pointed out that the simplified models of perturbation force, the choice of numerical integration methods and the neglect of the polar motion are main factors causing the orbit fitting error, among which the simplified models of perturbation force is the most effective one. Through integrating the equation of orbital motion of satellite for 30 min, it can be found that the orbit fitting error due to the simplified force model, the numerical integration method and the neglect of the polar motion are respectively 0.827 m, 0.224 m and 0.025 m. Therefore controlling the precision loss of orbital prediction cased by the simplification of models of perturbation force, especially by the truncation of high order terms of Earth gravitational perturbation and simplification of models of Sun and lunar gravitational fields can improve the fitting precision of prediction orbit.
Influence of applied stress on cracking and apalling of oxide film in room temperature
Wang Jingru, Zhu Liqun, Zhang Zheng, Zhong Qunpeng
2005, 31(10): 1071-1075.
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　The cracking and spalling behavior of the oxide film under applied stress in room temperature was studied. The critical applied stress of oxide film cracking and spalling was calculated. By dynamic tension experiments of oxide film on A3 steel and LY12CZ aluminium alloy, the existence of critical applied stress of oxide film cracking and spalling was proved. The different cracking and spalling behavior of two kinds of oxide film was also compared. The electrochemical behavior of oxide film cracking and spalling in 3%NaCl solution was studied, according to the variety of open circuit potential of two kinds of materials under applied stress. The sharp drop in the open circuit potential proved the existence of applied stress too. Finally electrochemical impedance spectroscopy(EIS) measurement of oxide film with and without cracks was carried out.
Analysis and improvements of a remote authentication scheme
Zhang Lihua, Lü Shanwei
2005, 31(10): 1076-1079.
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Password authentication scheme is a very promising and practical solution to remote user authentication.The security of a proposed password authentication scheme using smart cards is analyzed. The scheme has some weaknesses: it cannot resist parallel session attack, an intruder without knowing users' password can masquerade as a legal user by creating a valid login message from the eavesdropped communication, then passes the authentication phase and gains the authority of the legitimate user; it is also vulnerable to changing timestamps attack, an intruder can masquerade as a legal user or impersonate a valid authentication system by changing timestamps of the messages from eavesdropped communication. Furthermore, an enhanced password authentication scheme using smart cards with better security strength by using login counter and different keys via cards is proposed. The scheme has many merits as following: it lets users freely choose and change their passwords at their own will; it provides mutual authentication between two entities; it resists message replaying attack and insider attack; it has strong security reparability by using extended identities and smart cards; it also withstands parallel session attack and changing timestamps attack.
Production of streamwise vortexes in a turbulent boundary layer
Liu Kai, Zhang Nan, Lu Lipeng
2005, 31(10): 1080-1083.
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The whole process of the production and the development of the streamwise vortexes are studied. By using the method of direct numerical simulation, the production of the streamwise vortexes and the process from quasi-2-dimensional coherent structures to 3-dimensional coherent structures in the wall region of a turbulent boundary layer are simulated. The initial values of the quasi-2-dimensional coherent structures in the wall region are obtained on the basis of the idea of resonant triad in the theory of hydrodynamic stability. The results show that due to the nonlinear interaction, the quasi 2-dimensional structures gradually grow to 3-dimensional structures; the streamwise vortexes and the hair-pin vortexes are produced in this process. And the results of the simulation agree well with the experimental results. The affects of the adverse gradient on the generation and the development of streamwise vortexes are also studied. With the adverse pressure gradient, the streamwise vortexes generates earlier, rise faster, the amplitude of the coherent structures grows faster, and the structures becomes more complicated, which means that adverse pressure gradient can actuate the coherent structure and the development of the streamwise vortexes.
Lyapunov adaptive filtering and its application in INS/SMNS integrated navigation system
Zhao Long, Chen Zhe
2005, 31(10): 1084-1086.
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In order to overcome the shortcomings that traditional least square algorithm tends to become divergence with the increase of matching points INS/SMNS (inertial navigation system/scene matching navigation system) integrated navigation system, an improved LAF(Lyapunov adaptive filtering), based on MIMO (multi-input-multi-output) system, is presented. On the basis of the information of observation formula in the algorithm, the recursive formula of LAF is obtained by the definition of filtering error and priori estimation error of LAF. The stability and convergence of LAF are proved by Lyapunov stability theory. LAF is applied to INS/SMNS integrated navigation system, and the simulation results demonstrate that compared with RLS( recursive least square) algorithm, LAF is simpler and more reliable, and its filtering performance is better.
Control response character of the rotorcraft with slung load in forward flight
Guo Guangli, Gao Zheng, Sun Chuanwei
2005, 31(10): 1087-1091.
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A rotorcraft with slung-load model was built for the general real-time flight simulation program. A general dynamic, distortional wake model based on the nonlinear and unsteady Peters-He inflow model was investigated and applied to the real-time wake model, it was an important part in the forward acceleration flight because the wake distortion effect and the blade unsteady aerodynamics relation to the whole aerodynamic force. The steady part of blade circulated airload was calculated by the full angle wind test data for all airfoils of the blade, but the unsteady part of the blade load was just a classical ONERA thin airfoil theory with dynamic stall. A six freedom slung load with a soft cable model was used to simulate the slung and also the helicopter motion. The control response character was analyzed in forward flight simulation under the step inputs of the collective pitch and push/pull stick control.
Integral method for ultimate load analysis of concrete-filled steel tubular columns
Tu Yongqing, Li Cong
2005, 31(10): 1092-1095.
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Based on the synthesis method for calculating elastic-plastic ultimate load of concrete-filled steel tubular columns, a new numerical method is put forward. Hypotheses in the calculation only include the cross-section plane hypothesis and the stress-strain relation of steel and concrete with a consideration of the interaction effect between the steel tube and the core concrete, and the assumption on the deformation curve of the original synthesis method is removed. As in this new approach, the elements are divided not only on the cross-section but also along the column length, the balance conditions of multiple cross-sections can be taken into consideration simultaneously. Comparing the original method, the current method is suitable for calculating the ultimate load of not only axial compression columns and eccentrically loaded columns with equal eccentricity, but also eccentrically loaded columns with unequal eccentricity. The ultimate loads of some axial compression columns, eccentrically loaded columns with equal eccentricity and eccentrically loaded columns with unequal eccentricity are computed using the program. And the results show that the present results agree well with experimental and theoretical results in literature.
Effect of low profile additives on the shrinkage and mechanical properties of unsaturated polyester
Sun Zhijie, Xue Zhongmin, Yang Bo, Zhang Zuoguang
2005, 31(10): 1096-1100.
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In order to reduce the high shrinkage ratio and great brittleness of UPR(unsaturated polyester resin), two kinds of LPA(low profile additives), which are LPA-4016 of polyvinyl acetate and LPA-7301 of polystyrene, are added into UPR cast separately. The effects of LPA on the shrinkage rate and mechanical properties of UPR cast are studied, and then the phase structure transitions of these two systems and their different control mechanisms of low shrinkage rate are analyzed. For LPA-4016, it is by formatting amounts of uniform and disperse voids around the LPA phase to buck the shrinkage during resin cure; while for LPA-7310, this is realized primarily by the sufficient expansion of LPA itself. The results show that there exists an optimal quantity for LPA-4016 to reduce shrinkage rate of UPR, and it can improve the brittleness of UPR and increase its impact strength in contrast with LPA-7310. But both of them tend to reduce the tensile strength of UPR.
Noise robust ICA feature extraction algorithm for hyperspectral image
Du Peng, Zhao Huijie
2005, 31(10): 1101-1105.
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Feature extraction is important to hyperspectral imagery processing in that it can distinguish special featured object from background clutter and remove redundant information. An ICA(independent component analysis) based on the feature extraction algorithm for hyperspectral remote sensing data is proposed. In order to handle the over-sensitivity of ICA to noise and data imperfection, the MNF(maximum noise fraction) is adopted as the replacement of conventional principal component analysis. The UICA(undercomplete ICA) led by the MNF not only raises the time efficiency, but also maintains the extracting ability of ICA. The performance of the algorithm is verified by the results of HYIDCE and PHI experiments.
Adaptive sliding mode control using RBF network
Luo Tingting, Liu Jinkun
2005, 31(10): 1106-1109.
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Like most practical systems, high precision simulator is sensitive to nonlinearities, external disturbances and parameter perturbations. To solve such control problems, an adaptive sliding-mode controller based on RBF network was adopted. The proposed controller was divided into two parts: a nominal feedback controller and a sliding mode disturbance compensator. The feedback controller used pole configuration to stabilize the nominal system. The disturbance compensator used an adaptive RBF network to recognize the upper bound of the uncertainties on line. The result of computer simulation demonstrates the robustness and the effectiveness of the proposed algorithm.
Effect of channel mismatch and mutual coupling on GPS adaptive array
Lu Yan, Tan Zhanzhong, Ding Ziming
2005, 31(10): 1110-1115.
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In order to ascertain the specification of the main modules of an anti-jamming GPS receivers, it is necessary to analyze the effect of channel mismatch and antenna mutual coupling on SINR(signal interference noise ratio) and ICR(interference cancellation ratio). In term of the signal environment of GPS, the expressions of SINR and ICR are conducted in existence of the deviation and the perturbation of the HF channel amplitude/phase (A/P), I/Q imbalance and the antenna mutual coupling by using the orthogonality of weight vector and the jammer space. It is proved that ICR is mainly determined by the HF channel A/P perturbation and the I/Q imbalance, but almost independent of the HF channel A/P deviation and the mutual coupling, and the calibrations for the deviation aren’t always increase the SINR and the correction for mutual coupling can get the benefit of SINR just proportional to the maximal singular value of Scattering matrix. The simulation results on the aspect of the above are given.
Experiment study on magnet sensitivity of fiber optic gyro
Wang Xiaxiao, Song Ningfang, Zhang Chunxi, Ma Zongfen
2005, 31(10): 1116-1120.
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Fiber coil is the sense element of FOG(fiber optical gyroscopes). Except Sagnac effect, magneto-optic Faraday effect is one of the main non-reciprocity effect of FOG. Magneto-optic Faraday effect is caused by fiber twist and residual birefringence during fiber producing and fiber coil winding. It can add one bias in the output of FOG. Based on the finite element analysis,the magnetic model of FOG’s fiber coil is given by using the Jones matrices formalism. The experiment verification is made by using the Helmholtz coil. The result shows that a existing fixed magnet sensitivity axis represents the magnet sensitivity of FOG and the direction of magnet sensitivity axis can be confirmed.And the ways to suppressing the magnetic field effects are discussed.
Wave properties of a traffic flow model for freeways with two lanes
Tang Tieqiao, Huang Haijun
2005, 31(10): 1121-1124.
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A new continuum traffic flow dynamics model for freeways with two lanes where the faster vehicles are allowed to travel on both lanes while the slower vehicles are allowed to travel on the slower lane only, is developed through applying the speed gradient-based momentum equation for each lane. Some non-equilibrium phenomena of traffic flow such as small disturbance instability and stop-and-go waves can be reproduced by the new continuum model. The wave properties of the new model, which include shock waves, rarefaction waves and first order wave of the two lanes, are respectively studied. The numerical results show that the model respectively reflects the shock waves and rarefaction waves of the two lanes, and the figures about first order wave speeds of the two lanes respectively describe the stop-and-go traffic on both lanes. This study can further help understand the complicated driving behavior and the nonlinear properties of traffic flow dynamics on multilane freeways, and then improve the traffic control and management.
Migration from object-oriented legacy system to component-based system
Liu Dongyi, Li Hu, Jin Maozhong, Liu Chao
2005, 31(10): 1125-1129.
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In order to reduce costs, increase productivity, researchers and practitioners make massive research on software reuse. To create reusable assets and reengineer legacy systems, identifying, extracting and reengineering software component that implement abstractions within systems is one of the most cost-effective ways. A reengineering methodology is proposed for migrating from an object-oriented legacy system to a component-based system. This methodology is divided into three parts. Part one extracts component based on component contract. Part two reconstructs cross-cutting component in terms of some rules, which conform to component reusability, lower coupling between components and higher cohesion within a component. Part three refactors component according to component contract. This methodology has successfully been applied to restructure a legacy system.
Research on software architecture of embedded software simulation testing environment
Zhong Deming, Liu Bin, Ruan Lian
2005, 31(10): 1130-1134.
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It is an acknowledged and effective method to test real-time embedded software with ESSTE(embedded software simulation testing environment). The software architecture of ESSTE is described systematically based on UML and "4+1" views model. The contents in different views can coordinate with each other and particularly the software of ESSTE is divided into two system-level components in design view: real-time component and non-real-time component,which are organized by the pipe-filter architectural pattern. Configuration tool class is the key class for non-real-time component and model class, real-time variables class, scheduler class for the real-time component. Designed and implemented hereby, ESSTE-Basic reflects excellent quality characteristics, such as changeability, portability and so on. It has successfully been used for system-testing of several softwares, finding out a great of software faults effectively, through which both the correctness and the effectiveness of the software architecture of ESSTE are validated.
Non-linear least square estimation of geometrical parameters for cone-beam three dimensional computed tomography
Yang Min, Lu Hongnian, Kong Fanqin, Zhang Quanhong
2005, 31(10): 1135-1139.
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The accuracy of reconstructing geometrical parameters is precisely controlled in three-dimensional computed tomography. Because in practical X-ray imaging system, they can’t be measured through direct methods, how to ensure their accuracy becomes the spiny problem. The non-linear least square estimation of three-dimensional reconstructing geometrical parameters based onFeldkamp-type algorithm is introduced. According to the rule that the projection address of a particle in imaging space is as the same as the centroids of its projection. The parameters’ optimal value is estimated through calculating centroids of the measured projections of a point source (or an object close to a point source) and solving non-linear equation sets. Computer simulation proves that when the initial value of the parameters are close to their true value, the estimating results are satisfying and of good repetition. In addition, the parameters’ optimal value of the practical testing system estimated by this method is applied to image reconstruction, and the satisfying results are also obtained.
Method of EEG signals classification based on wavelet transform and neural networks
Mao Xia, Meng Qingyu
2005, 31(10): 1140-1144.
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Electroencephalography (EEG) signals of alcoholic subjects and control subjects were classified by combination of wavelet transforms and neural networks. Classification features were discovered through the EEG data analysis. The frequency bands of EEG signals including classification features were extracted by 1-D wavelet transforms. The decomposed coefficients of wavelet transforms were remained as signals characters to accomplish the length compression of data sequences. Three learning vector quantization (LVQ) networks with same structure corresponding to three kinds of stimulations were built for the predictive classification of the EEG signals. The final classification results were acquired by judge rules. The classification accuracy of experiment EEG signals reach 89%.
Numerical simulation of the flowfield around helicopter engine inlet
Cao Yihua, Yuan Kungang, Li Xiaoyong, Yin Wanli
2005, 31(10): 1145-1148.
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To obverse the flow field of a helicopter engine inlet, the finite volume method was adopted and Navier-Stokes (N-S) equation was solved by generating the body-fitted structural grid. The low speed and hovering flight of MI-171 helicopter were numerically simulated, and the flow field characteristic around engine inlet of this helicopter was calculated. Following this, beginning with the prescribed wake model, a semi-empirical correction for the vortex core effect on rotor wake was made and a free wake model was adopted, this method was also used to calculate the flow field characteristic around the engine inlet of this helicopter. From the calculated results paralleling to the engine line and verticalizing to it on engine inlet showed that these two different methods can predict the vortex wake flow field distribution around the helicopter engine inlet.
Dynamic traffic assignment model based on fuzzy travel time
Wang Li, Wang Chuanjiu, Shen Xiaorong, Fan Yuezu
2005, 31(10): 1149-1152.
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A new fuzzy dynamic traffic assignment (FDTA) model was proposed. Firstly, the fuzzy theory was used to describe the real-time link travel time and path travel time. Secondly, fuzzy shortest path sets were found based on h-level sets, and then their membership functions were calculated. Thirdly, the C-LOGIT model was used for network loading. At last, FDTA model was compared with classical stochastic dynamic traffic assignment (SDTA) model using a small traffic simulation network. The simulation results show that FDTA model can achieve more reasonable network traffic flow, and theoretically resolve the problem of traffic network dynamic traffic flow modeling as the congestion, traffic incidents or construction happened. Further, when the traffic network becomes complex, by changing the value of h, the number of fuzzy shortest paths could be decreased and the computation efficiency could be improved greatly.
Modified RBAC model and its application on content management system
Cao Yonggang, Jin Maozhong, Liu Chao
2005, 31(10): 1153-1158.
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Focusing on the large scale characteristic of content, users and permissions in content management system (CMS), a modified role based access control(RBAC) model, RBAC0.5, is formally defined. In contrast with the four models defined by RBAC96, the RBAC0.5 is formed as a new model between the basic model (RBAC0) and the enhanced model (RBAC1). It covers RBAC0 and alters the hierarchical relations among roles in RBAC1 to flat mapping by introducing the middle layer--user group. By using RBAC0.5, set operation can be performed with the relational database back-end. In addition, the partition and hierarchy category are formally defined for the arrangement of content in CMS by their media type and their semantic. Based on those definitions, the multi-layer permission sets are defined on partitions and categories for the multi-grained access control. According to such models, the implementation of the access control in the CMS uses short circulating operation, garbage collection and caching technology for performance optimization. Pseudo codes of the algorithms are also given.

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