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2006 Vol. 32, No. 03

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Design and simulation of BTT nonlinear controller for hypersonic vehicle
Li Yang, Chen Wanchun
2006, 32(03): 249-253.
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Aerodynamics effects of hypersonic vehicle are complex than that of common vehicle. Bank-to-turn(BTT) technique can satisfy the demands of hypersonic vehicle for aerodynamics shape, with which brings dynamics system the character of fast time-varying, strong coupling and high nonlinear. Against the character of the hypersonic vehicle bank-to-turn nonlinear controller, a more effective control method for nonlinear system was applied, which was nonlinear dynamic inversion technique. A nonlinear model was built. Then the dynamics controlled were separated into fast and slow variables in terms of singular perturbation theory. Two dynamic inversion control laws were designed for the fast and slow inversion loop. The outputs of outer loops were used as the inputs of inner loops. The above designed control laws were used to simulate according to the given bank-to-turn command in hypersonic flight conditions. The simulation results show that the control system can achieve bank-to-turn motion and guarantee the stability of the hypersonic vehicle.
Human modeling and simulation based on Lagrangian method in weightlessness
Wang Juan, Zhuang Damin
2006, 32(03): 254-257.
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The necessity of computational multi-body dynamics simulating the astronaut extra vehicular activity (EVA) was described. The 4 joints universal human body inverse kinematics model and inverse dynamics model in weightlessness utilizing computational multi-body dynamics were proposed. A typical EVA, an actual large-mass-handling EVA performed on STS-63, was chosen as the instance to simulate. Based on some simplifications, a typical EVA was simulated and calculated using universal human model. Considering the influence of weightlessness on human modeling, the universal model should be amended. The results were analyzed according to energy comparison method. The results showed when hand movement contrail radius and angle velocity minishing, movement time prolonging and hip joint flexion moving, accomplishing task retrenched energy. Human body joint movement comfortable scope could be achieved by energy comparison method. The calculational methods provided the reference value for the astronaut intra and extra vehicular activity simulation and ergonomic analysis.
Trajectory planning for low attitude penetration based on improved ant colony algorithm
Li Dong, Cao Yihua, Su Yuan, Feng Ting
2006, 32(03): 258-262.
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To ensure the mission success rate for low attitude penetration, a trajectory with high survivability and acceptable path length must be planned. As a kind of new emulated evolutional algorithm, ant colony algorithm (ACA) is fit for searching the best way in trajectory planning. The algorithm has several shortages including long searching time, slow convergence rate and limiting to local optimal solution easily. In order to overcome these shortcomings and improve its performance, the improved ant colony algorithm was established, and it introduces the mutation in genetic algorithms (GA) and the adaptive adjustment of the volatilization coefficient. With the establishment of the performance index, the results derived from the equiprobable optimization, the original method and the improved one were compared and analyzed in the example. Base on the comparison of the time expenditure and the performance of the flight paths, the effectiveness of the improved ant colony algorithm was proved.
"Over-under" concept hypersonic turbo-ramjet combined propulsion system
Zhu Daming, Chen Min, Tang Hailong, Zhang Ji
2006, 32(03): 263-266.
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Turbo-ramjet combined propulsion system for a hypersonic transport was examined, which can work steadily and reliably in a wide flying-scope(Ma＝0~5,H=0~30 km). The overall performance simulation of turbo engine and ramjet engine was accomplished. The simulation of turbo/ramjet mode transition and the steady performance of the combined cycle engine along the aero track was nearly achieved. The performance simulation model includes variable geometry and variable cycle. The model had been tested by testing data. Based on the models of turbo and ramjet engine for hypersonic flight, the engine with afterburner was analyzed and compared with the one without afterburner. The influence of the flux matching with engine and inlet for the turbo engine on the engine performance was analyzed at the same time. At the end, it is shown that the calculational performance of turbo/ramjet mode transition for an "over-under" concept, turbo-ramjet combined engine.
Algorithm of trimmed surface triangulation of prepositive disposal in predicting RCS of aircraft
Hu Bifu, Song Yuwang, Zhao Hui, Xi Ping
2006, 32(03): 267-270.
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While computing radar cross section(RCS),surfaces of objects were primarily triangulated, which was called prepositive disposal. The length of the edge of the triangle was generally 0.1 wavelength(in general one wavelength is 3 cm).The shape of aircrafts was complex , aircrafts’ geometric model contained many trimmed surfaces, the relationship between trimmed surfaces was complex. Meanwhile surfaces were triangulated into many triangles with the edge of 3 mm, therefore the number of triangles was huge. All these resulted in difficulties in the prepositive disposal. An algorithm of trimmed surfaces triangulation was put forward. Using the characteristic of aircraft model and satisfying the approach error the surface was dispersed by isoparametric curves, the curves were dispersed into points at the given length and the meshes were composed of points on two adjacent isoparameteric curves. According to the position relation of meshes and the trimmed area meshes which were out of the trimmed area were trimmed. Then meshes on the surfaces boundaries were converted into being consistent. Triangulation of trimmed surfaces can be realized.
Influence of circular angle in symmetric plane to the flowfield characteristics of an axisymmetric parachute
Jiang Chongwen, Cao Yihua, Su Wenhan
2006, 32(03): 271-275.
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According to the characteristics of parachute, the 3-D complex flow problem was transformed into an axisymmetric problem with computational timesaving, based on three assumptions (membrane assumption of canopy, axisymmetric assumption of parachute, and steady assumption of flowfield). After the circular angle in symmetric plane was defined and diameters of parachute bottom and top vent were kept invariable, a series of fluid dynamics computational model were established over circular angle range of 80°~140°. By solving renormalization group(RNG) k-epsilon turbulence N-S equations, the numerical simulation result is in good agreement with the relative experiments. It is found that the influence of circular angle and parachute height is very small. The changes of drag in samples are below ±0.28%. The wake topology structure of axisymmetric parachute is unaltered with the circular angel of symmetric plane changed. There are two saddle points in the axis. With the circular angle in symmetric plane increased, the position of the first saddle point is fixed, and the position of the second saddle point moves wake oriented.
Different structure diaphragm plates in complex passages of turbine blade trailing edge
Ding Shuiting, Liu Liyan, Li Li
2006, 32(03): 276-279.
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The experiment mainly conducted the effect of three different structure diaphragm plates in the complex passages on heat transfer and pressure drop characteristics of turbine blade trailing edge. A thermochromic liquid crystal method was used to measure the detailed heat transfer coefficients on the end wall surfaces. Comparison of end wall heat transfer and pressure drop characteristics was made among three kinds of diaphragm plates: rectangular diaphragm plates, 90° and 120°waved diaphragm plates in the complex passages of turbine blade trailing edge. It is found that two waved diaphragm plates produces higher heat transfer with relatively less press drop rather than the rectangular diaphragm plates, and the 90° waved diaphragm plates has higher heat transfer than the 120° waved diaphragm plates in the first passage. In the second passage the two conditions almost have the same effect, while the 90° diaphragm plates cost a higher pressure drop.
Model for ground starting of turbofan engine
Zhu Zhili, Gao Chao
2006, 32(03): 280-283.
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The simulation model of turbofan engine for ground starting was described. The simulation is based on thermo-aerodynamics relationship, the components’ characteristics, experienced formulas. According to being given known condition and fuel regulation, the starting has been simulated by integral method. In order to show the effect of the simulation, the results of the simulation model calculated have been compared with the testing results. The compared result shows that the simulation model can simulate mixed flow turbofan engine with afterburner for ground starting effectively. These parameters and coefficients have been analyzed, including calculating time interval, the rotation speed of the starter off, experiential coefficient of combustion total pressure recovery coefficient, the environment temperature and pressure, the airport attitude. The results show that these parameters and coefficients have significant effect on ground starting simulation.
Local heat transfer in a rotating U-shaped square channel with three channel orientations
Liu Chuankai, Tao Zhi, Ding Shuiting, Xu Guoqiang
2006, 32(03): 284-287.
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The influence of channel orientation on the local heat transfer coefficient in a rotating, U-shaped, square channel with smooth walls was investigated for rotation number from 0 to 0.26. The three channel orientations were square channel parallel to the rotation axis, square channel twisted at 22.5° to the rotation axis and square channel twisted at 45° to the rotation axis. A change in the channel orientation about the rotating frame causes a change in the secondary flow structure,consequently, the heat transfer coefficient from the individual surfaces of the channel changes. Results show that the Nusselt number difference between leading and trailing surfaces was reduced as the channel twisted to the rotation axis, however, the inner and outer surfaces show an increase in Nusselt number discrepancy over their corresponding parallel channel orientation values. Effect of channel orientation on heat transfer is relatively prominent for high rotation number.
Wake integration method for airfoil drag evaluation using N-S equations
Liu Zhou, Zhu Ziqiang, Wang Xiaolu, Wu Zongcheng
2006, 32(03): 288-292.
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Minimal improved far field method for airfoil drag evaluation——wake integration method was introduced. The position of wake integration and associated integral technics were also discussed. Predicted drag values for a given airfoil(RAE2822 airfoil)were compared and discussed using the surface integration and wake integration methods under both subsonic and supercritical flow conditions. Numerical data show that the results of both methods are the same, which indicates the wake surface integration method is valid. The calculated values agree well with the experimental data. It also indicate that in the wake integration method, the location of wake integration surface should be set in the distance of 0.6~1.0 relative chord length from the trailing edge. In the mean time, the results of wake integration method is independent of the variation of detailed configuration surface. Wake integration method might be more potential for the complex three-dimensional configurations having large curvature variation on the surface compared with surface integration method.
Combined simulated annealing and soft-threshold wavelet de-noising of SAR image
Zhou Yinqing, Zhang Lei, Xu Huaping
2006, 32(03): 293-296.
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A technique of speckle reduction in synthetic aperture radar (SAR) images was presented. Based on the character of wavelet transforms that the approximate coefficients of the transformed image still obey Gibbs distribution, the simulated annealing to the wavelet domain was introduced. The traditional logarithmic transformation was modified to adapt the power SAR images, which can maintain the mean of the SAR image better and achieve a better equivalent-look, then based on multi-resolution analysis theory and wavelet transform theory, an optimal mother wavelet was found to match the specific images. The algorithm of simulated annealing was applied to the coefficient in the scaling subspace and the algorithm of soft-thresholding was applied to the coefficient in the wavelet subspace distinctively. The result of experiments show that the new technique achieves a better smooth result when compared to the traditional wavelet denoising, at the same time it saves much time when compared to the simulated annealing, and it improves the structure and edge preservation with satisfying denoising results.
Multiple moving objects segmentation algorithm in complex traffic scene
Li Juntao, Zhang Hai, Fan Yuezu
2006, 32(03): 297-300.
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To solve multiple moving objects segmentation problem in complex traffic scene outdoors, a new segmentation algorithm of multiple moving objects segmentation in complex traffic scene of outdoors was developed. The presented method consists of two phases. In the motion detection phase, motion-changed regionwas determined using an improved level set algorithm based on Mumford-Shah model of two consecutive frames difference of image sequence, and an simplified clustering algorithm providing initialization evolution curves of level set algorithm. Motion window was generated through detecting motion-changed region. In themotion segmentation phase, regions segmentation using an improved weighted k-means clustering algorithm of moving windows area were merged based on region motion similarity criterion. Computation time was reduced because of avoiding processing of the whole image. Very promising experimental results indicates that the proposed algorithm is effective with strong robustness using real image sequences of complex traffic scene and can resolve occlusions among multiple moving objects.
Internal coupling vibration of Coriolis mass flowmeter
Zheng Dezhi, Fan Shangchun
2006, 32(03): 301-305.
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Resonant Coriolis mass flowmeter (CMF) measures liquid mass flux via the Coriolis theory of the measurement tubes resonant vibration. Actually the external coupling and the internal coupling vibration are widely existent, the operating stability and the measurement precision are directly influenced. The external coupling vibration was resolved by increasing the straight pipelines or strengthening the sensor fixure, but the internal coupling vibration is absence of flawless theoretical guidance and solution. The internal coupling vibration phenomenon and the influence to measurement precision of the sensor were put forward on the basis of the Coriolis mass flowmeter operating mechanism, the comparison experiments of the CMFs with internal coupling vibration and without internal coupling vibration were made by using Polytec laser doppler vibrometer, it was revealed that the internal coupling vibration is tantamount to the additive weight on the main vibration, the additive phase difference was induced. For the special CMF, the additive weight is mostly steady, but the Coriolis force increases with the fluid flux, therefore the influence of internal vibration decreases with the increased fluid flux and the measurement error is decreased.
Auto-focusing algorithm based on cross correlation
Dong Dai, Liu Rong, Sun Minglei, Zong Guanghua
2006, 32(03): 306-310.
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Aiming auto-focusing system, auto-focus algorithm based on cross correlation was brought forward. The limitation of conventional auto-focusing in definition and velocity was analyzed. Correlation principle was introduced, and template correlation algorithm based on cross correlation was defined. Owing to difference of template image selected, the result of experimentation is different, so that auto-focus analysis algorithm is different. Based on different template image and the result of experimentation, two forms of correlation function were presented, including the first template correlation and the second template correlation. If the place of template image is before focusing, the form is named the first form, curve of which changes from small value to big, then to small, if the template image is focusing image, the form is named the second form, curve of which changes from big value to least, then to big. The result which two forms processes image was compared with the result of experimentation of other focus evaluating functions, such as square gradient function, correlation function. By experimentation comparison, it concludes that the auto-focusing algorithm based on cross correlation improves definition and velocity of auto-focusalgorithm. The algorithm has been successfully tested to be effective on micro-fluidic alignment assembly auto-focusing system. It shows that the algorithm has achieved better auto-focus effects.
Novel scheduling algorithm based on packet aggregation effect for optical switches
Xiong Qingxu, Feng Jinxin, Wang Fengzhou
2006, 32(03): 311-315.
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The packet scheduling in optical switches has to be frame based because the configuration consumes much time. The frame size is usually selected to be large enough in order to improve transmission efficiency, leading packet aggregation effect. With consideration of the packet aggregation effect, a novel packet scheduling algorithm called permutation-based longest queue first+hold (p-LQF+Hold) was proposed. A set of permutations were calculated by using of the traffic requirement matrix. The permutation with the largest matched occupancy was used to find the matching on each frame boundary. Simulation was made on a 4×4 virtual output queue(VOQ) optical switch under uniform, nonuniform and diagonal Bernoulli and ON/OFF traffic patterns, respectively. The simulation results show p-LQF+Hold can achieve 100% throughput under any admissible traffic that satisfies the strong law of large numbers, and has close to or even lower average packet delay than the popular LQF+Hold algorithm. p-LQF+Hold can guarantees bandwidth requirement and short-term fairness and efficiently accommodate the dynamical packet arrivals.
Signal detecting technique for Sagnac fiber-optic temperature sensor
Yang Yuanhong, Shen Ming
2006, 32(03): 316-319.
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A temperature sensor based on polarization non-reciprocity (PNR) in fiber-optic Sagnac interferometer (FSI) can measure the temperature of one point in high precision. The phasic subtraction of two light beams was shifted while temperature field around the probe changed. Analyzing the temperature measuring theory of Sagnac fiber optic temperature sensor, a linear output model was established. The all digital signal detection was based on square-wave modulation and demodulation. An all digital signal detecting system using C8051F060 as its core was completed. It can maintain the phase relation of sampling signal and modulating signal. Sampling signal achieved by 16-bit A/D converter was computed in digital method to get the output of measuring temperature. This technique has the advantages of convenient realization and digital operation. The experimental data achieved by temperature experiments agree with theory well. The input and output of system achieve a linearity of 10-3. Discussion shows that this kind of temperature sensor can reach high precision.
Some notes on complete synchronization of the coupled neurons
Wang Haixia, Lu Qishao
2006, 32(03): 320-323.
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Complete synchronization of two mutually coupled identical chaotic Hindmarsh-Rose neurons model with gap junction was studied. Gap junction isalso called electrical coupling, it acts as one of the main communications between neurons in nervous systems, its most important role is to make a large ensembles of neurons emit synchronous firing rhythm patterns.The traditional method to investigate complete synchronization was using numerical simulations, such as the conditional Lyapunov exponents, but it was lack of theoretical foundation and can only offer us a necessary condition to guarantee the occurrence of complete synchronization. Based on the conditional Lyapunov exponents method, synchronization of more coupled neurons is hard to be studied. So two new methods of Lyapunov function method and mode decomposition method here was introduced, and if and only if condition and the sufficient condition will be given. These methods are efficient to deal with more coupled neurons and nonsymmetrical coupling schemes, the validity of them was tested by numerical simulation.
Temperature dynamic characteristics analysis and control of optic-fiber light source
Ma Yingjian, Jian Hongqing, Shi Duo
2006, 32(03): 324-327.
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According to the basic theory of the thermo-electric cooler(TEC),the temperature dynamic characteristics of the optic-fiber light source module was analyzed, and mathematics model was established corresponds to its. In the actual experimental test to light source module, the TEC module was driven by multi-point frequency of working current, and dynamic data of light source core’s temperature was sampled with sensing component, and the dynamic data was calculated and fit with least-squares method, then the result was close to mathematics model, so the parameters of the mathematical model were determined. MAX1978 single-chip temperature controllers for Peltier thermoelectric cooler module was used, and the best proportional-integral-differential(PID)compensating network based on temperature dynamic characteristics mathematical model was designed, then the temperature control system of the optic-fiber light source was achieved, the result shows that TEC temperature control system can control the light source precisely and steadily.
Low-rank adaptive method for sub-optimal channel estimation in OFDM system
Ju Min, Xu Zongze
2006, 32(03): 328-332.
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A sub-optimal channel estimation algorithm in orthogonal frequency division multiplexing (OFDM) system was proposed, to reduce the complexity of traditional minimum mean square error (MMSE) channel estimator, and to alleviate the performance deterioration of MMSE estimator due to the mismatch of the estimator-to-channel statistics. This algorithm utilizes time-average channel correlation matrix in place of exact channel correlation matrix and approximates the MMSE estimator by a low-rank structure. Based on subspace tracking, this algorithm adaptively estimates the noise power and the principal eigenspace of time-average channel correlation matrix, and asymptotically converges to the solution of optimal MMSE estimation. Further theoretical analysis indicates that delay subspace tracking algorithm is a special case of this newly proposed algorithm, and both theoretical analysis and simulation results illustrate that this algorithm can significantly improve channel estimation accuracy at low signal to noise ratio(SNR) with reduced implementation complexity.
Design of delay mapping receiver for GPS remote sensing
Zhang Yiqiang, Zhang Qishan, Yang Dongkai, Li Ziwei
2006, 32(03): 333-336.
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Signals of global positioning system (GPS) can be used for purposes such as navigation and positioning. The utility of scattered GPS signals from rough surfaces brings a new technology for microware remote sensing. Background and advantage of GPS based sea surface wind remote sensing technique and scattered GPS signal measurement technique was introduced. Five main techniques were discussed such as improving the signal noise ratio, dual radio frequency front-end circuit design, calculating the specular point code delay, receiver work mode and the embedded firmware process. Data collection campaigns were done at Tianjin near sea with the receiver mounted on an airplane. Results show that the receiver can simultaneously receive direct and ocean scattered GPS signal, correctly calculate specular point delay, successfully measure the ocean scattered signals correlation power around the specular point, and signal noise ratio is higher than 14.9 dB. Receiver outputs provide basic data sets for ocean wind retrieval. The technique can also be used in land moist sensing, sea ice age sensing, ocean wave height remote sensing.
Remote-rendering based 3D model publishing system
Jin Ping, Zhang Haidong, Qi Yue, Shen Xukun
2006, 32(03): 337-341.
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3D models have been widely used on internet. However, the conventional publishing way which downloads models first and then renders has always been haunted by the limitation of security threat, network bandwidth and low graphic performance of client machines. By combining 3D model simplification and remote rendering technology, a new 3D model publishing system was put forward. The high-resolution models were kept on the rendering server. On the 3D viewer client only low-resolution versions of the 3D models were provided. User can zoom, translate and rotate the low-resolution model on the 3D viewer client. When user stops manipulating, the client sends a rendering request to the rendering server which includes the user’s current viewpoint, direction and lighting information. The rendering server then renders and returns images of high-resolution models according to client requests. This system can effectively guarantee the security of the 3D model and significantly lower the requirements for client machine’s graphical performance and network bandwidth.
Intercluster simulation of UPMA protocol for self-organizing networks
Ding Lijun, Liu Kai, Li Hantao, Zhang Jun
2006, 32(03): 342-346.
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Based on the concept of contention reservation, polling transmission and combining distributed clustering network architecture, an user-dependent perfect-scheduling multiple access (UPMA) protocol for supporting node mobility and multihop architecture in wireless self-organizing networks was described, and its performance of intercluster communication was simulated by OPNET. By clustering algorithms, two-hop cluster architecture for polling mechanism was formed to support multihop network topology. The protocol includes reservation access phase and polling phase in channel period. In the protocol, the nodes with packets to send contend to reserve channel resources during access slots of every frame. If successful, they were polled to transmit their packets in subsequent frames. If not, collision avoidance and resolution process was used for efficient access. The simulation results show that the proposed protocol can greatly improve multihop transmission efficiency, and achieve higher end-to-end channel utilization, lower average end-to-end message delay and less average message dropping rate.
Secure trust negotiation system for grid computing
Zhang Rongqing, Li Jianxin, Huai Jinpeng
2006, 32(03): 347-351.
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Grid technology promotes resource sharing and collaboration over wide area network. However, service providers and requestors are always located in different secure domains in grid environment. How to establish trust between strangers without prior relationship has become a pressing problem. A system named secure trust negotiation system was designed and implemented, which depends on the trust management infrastructure, establishes trust between strangers with iterative disclosure of credentials and access control policies and can protect participants’ private information. A sort of attributed-based authorization credential and access control policy was adopted. A novel algorithm for compliance checker of credentials and access policies was carefully designed, which can be used togenerate all the minimal satisfied sets of credentials, so that the trust relationship exsited in theory can be established automatically. During the process of trust negotiation using this system, secure transmission of credentials disclosed was ensured by other subsystems of CROWN. Through the application in CROWN grid, it shows contributions to the automated trust establishment and privacy protection.
Dynamic inlining scheme improvement in JVM
Zhou Jing, Wang Lei, Liu Zhicheng
2006, 32(03): 352-356.
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In the Java virtual machine(JVM), traditional counter-based hotspot-detecting method usually can not get the caller-callee relationship, therefore, the dynamic compiler which applied this scheme would lose some optimization opportunities, such as method inlining. A dynamic inlining scheme based on online feedback information was proposed. Compared with the algorithms presented, the new method introduced BC Map, it was constructed by the baseline compiler when a method was compiled for the first time. BC Map can identify the index of the bytecode that invoked method M in its caller. With constructing Guarded Rec record, the compiler can get the type of virtual method’s receiver object correctly, and then identify the relationship between caller and callee. The guarded inlining guided by this information can avoid identifying the type of virtual method’s receiver object statically, get the dynamic information more precisely, and then it can increase applications’ performance.
Deformation capability and load-carrying capability of steel plate element under high temperature
Zhu Jianming, Wei Dong, Liu Yinghua
2006, 32(03): 357-360.
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In the plastic design and anti-seismic design of steel structures, It is demanded that the component plates undergo large local deformations for the plastic hinge to develop and the load-carrying capability doesn’t decreasebecause of local buckling of the plates. Based on the basic principles and methods which are used to analyze the deformation capability and load-carrying capability of steel plates under normal temperature condition, the nonlinear finite element method was used to analyze the buckling behaviors of four-edge supported plates under uniform uniaxial compression and high temperature. The width-to-thickness ratio, constraint conditions of boundary and initial geometric imperfections were all considered. The relationships among the width-to-thickness ratio, deformation capability and the load-carrying capability were carefully studied. Furthermore, the formulas and the relationships among width-to-thickness ratio, deformation capability and load-carrying capability were also showed according to the parameter analysis, which can be used to evaluate the ductility of steel plates under high temperature.
Preparing technics and decoloring mechanism analysis of high-grade dispropriated rosin decoloration
Zhu Yuelin, Tang Lini, Guo Hong
2006, 32(03): 361-364.
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Aimed at the over tint problem of disproportionated rosin in present demostic market, SQH-9 was used as a new decloring reagent,in order to deoxidize and refine disproportionated rosin, which was produced by Guangxi Wuzhou Rosin Ltd. The best decloring technic conditions were decided, including temprature,time and the dosage of decloring reagent, and the decoring mechanism was analyzed with UV as well as IR analyzing methods. Experimental results show that under the best decloring technics, SQH-9 decloring reagent can reduce the Garner color of first-class disproportionated rosin from 7 Garner color number to 2,while reducing the superfine disproportionated rosin from 5 Garner color number to 2,and the UV absorbing curves of ethanol solutions of disproportionated rosin declored by SQH-9 are basically superposing with that of the disproportionated rosin imported from Japan.Also SQH-9 is cheap and available in demostic market, it has good applying prospect in rosin industry.
Effects of Si on high temperature oxidation resistance of TiAl alloy
Xiao Weihao, Zhang Liang, Jiang Huiren
2006, 32(03): 365-368.
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The isothermal oxidation of TiAl-Si(atom percent is 0~20%) alloys at 1 173 K, 24 hours on atmosphere were studied by X-ray diffraction,scanning electron microscopy and energy dispersive spectrum. The results reveals that the addition of Si improves the oxidation resistance of TiAl alloys. With increasing of Si content, the thickness of oxidation films and TiO2 content are decreasing, and the content of Al2O3 is increasing. when the addition of Si reaches 10%, the continuous and compacted oxide film of Al2O3 is preferentially formed on the surface of TiAl alloy. During the addition of Si content from 0 to 20%, no any form of oxide of Si appears. The main reason of the improvement of oxidation resistance is attribute to Si combination with Ti, which results in the decrease of the activity of Ti, baffles Ti-ions outward diffusion, therefore relatively enhances the activity of Al, and the compacted oxide film of Al2O3 is preferentially formed on the surface of TiAl alloy.
Bubble transfiguration and moving condition in different channels
Zhao Weijuan, Zhang Zuoguang, Sun Zhijie, Wang Jingmi
2006, 32(03): 369-372.
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Void is one of the most important factors which affects performances of composites. The void problem is generic to most polymer composite process, regardless of whether the matrix is a thermosetting or a thermoplastics matrix. In order to eliminate porosity and promote product quality, it is essential to study the bubble traversing behavior during composites manufacturing. Using the laminate simulation systems, the configuration changing process of bubbles under different traversing channels was investigated preliminarily. Then the main factors affecting bubble traversing behavior were studied respectively, such as the bubble volume, the resin viscosity and the inter-space size. Finally the kinematic conditions for bubble traversing were also proposed. The experimental results showed that the external pressure needed for bubble traversing in the woven layers would increase with the increase in resin viscosity, the decreasing of bubble diameter and the inter-space area. These results will provide experimental bases for the establishment of bubble movement model in hot-compaction process.

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