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2000 Vol. 26, No. 5

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Surface Modification of Metals Irradiated by Intense Nanosecond Pulsed Electron Beam
HAN Li-jun, A She-er, JIANG Xing-liu, KANG Wen
2000, 26(5): 497-500.
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Under irradiation of intense-nanosecond-electron beam with power density of 109 W/cm2,tensnanosecond duration,the metal surfaces with enhancement of hardness, corrosion resistance and other physico chemical behavior improvement have been obtained due to the microstructure changing. Thermal transfer processes of rapid melting and solidification have been analyzed. The micrographies of SEM(Scanning Electron Microscopy) show the variety of morphologies due to rapid cooling of treated areas. In the gas environment of 10 Pa, the effect of magnetic self-pinch leads to high power density of pseudospark electron beams due to charge neutralization. It is expected for wide application of material surface modification for such pulsed electron beams. Much more studies should be done for further understanding of the interaction of beam target.
Microstructures of Multi-phase Materials In-situ Formed in γ-TiAl　Based Alloys
LI Jian-guo, ZHANG Fu-xiang, WANG Li-jun, ZHANG Yong-gang
2000, 26(5): 501-504.
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The phases and microstructures in-situ formed by solid-state reaction were studied after the elements of B, C and Si were single and mixed doped to the TiAl-based alloys. The results showed that, in the Ti-Al-B alloys, the phases of TiAl, Ti3Al, and TiB2 were formed; in the Ti-Al-Si alloys, the phases ofTiAl, Ti3Al and Ti5(Al, Si)3 were formed; in the Ti-Al-C alloys, the phases of TiAl and Ti3AlC were formed; in the Ti-Al-B-Si alloys, the phases of TiAl, Ti3Al, TiB2 and Ti5(Al, Si)3 were formed; in the Ti-Al-B-C alloys, the phases of TiAl, TiB2 and Ti3AlC were formed; Finally, in the Ti-Al-B-C-Si alloys, besides the TiAl phases, the phases of partice TiB2, acicular TiB2, lath Ti3AlC and massive Ti5(Al,Si)3 all appeared, and this microstructure was approximately the same as pre-designed, therefore an optimized property is expected.
Numerical Analysis of Circular Aperture Antennas on Finite Planes
GAO Wen-jun, Lü Shan-wei
2000, 26(5): 505-508.
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The circular aperture antenna which is an open-ended circular waveguide stimulated by TE11 mode is analyzed. The method of moments is employed in conjunction with the equivalent-source technique and the modal expansion theory to analyze the open-ended circular waveguide. No restriction is imposed on the number of modes in the analysis. The problem of radiation from a circular aperture antenna embedded in an infinite ground plane is solved at first. Then expressions which represent the elevation-plane patterns of the antenna embedded in a finite ground plane are derived using GTD(Geometrical Theory of Diffraction). The expressions for the field pattern are obtained by superposing the infinite ground plane solutions, the first-order diffracted field solutions and the axial caustic solutions in their respective regions of validity.
Decoupling Sliding Mode Control in A Nonlinear Spacecraft System
ZHU Min-xiong, SONG Yi, SONG Chao-qing
2000, 26(5): 509-512.
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A control method with sliding mode of nonlinear spacecraft system is provided in this paper, in which the interactive influences among channels of strong nonlinear spacecraft system are decoupled. The decoupled spacecraft with large parameter variations and external disturbances is of good robustness. The numerical simulations of its attitude stability and maneuver control give support to the effectiveness of results in this paper.
Design Method of Fuzzy System to Control Large Maneuver Flight of Aircraft
WANG Pi-hong, GAO Jin-yuan, YANG Ke-ming
2000, 26(5): 513-515.
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There is strong nonlinear in the model of an aircraft because flight parameters may change violently in the case of large maneuver flight within the full flight envelope. The traditional PI controller can not guarantee the good control performance within the full flight envelope. A new kind of fuzzy control method is presented in this paper. The fuzzy control method integrates optimization of fuzzy control function and self-regulation gain of fuzzy control systemadaptively in the control system, which could largely improve qualities and adaptability of control system. The new kind of fuzzy control method has been used in the design of integrated flight/pusher system of aircraft to control large maneuver flight. Considering the nonlinear six-freedom model of the aircraft and big maneuver flight, it is demonstrated by digital simulation that this new fuzzy control method gets good control results.
Application of  H∞ Filtering to Fast Ground Alignment of Inertial Navigation Systems
WANG Yan-dong, FAN Yue-zu
2000, 26(5): 516-518.
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The approach of H∞ filtering is presented, which is applied to alignment of inertial navigation systems. The error model of INS(Inertial Navigation System) is introduced,and the observability of the INS error model is analyzed. H∞ filter is designed to an observable subsystem. The simulation results of alignment are given in the condition of bounded noise variance and unknown noise statistics.The results show that H∞ filtering is robustness and it is less sensitive to uncertainty in the noise signals statistics than Kalman filtering. It is demonstrated that H∞ filtering is efficient to alignment of inertial navigation systems. In order to improve the velocity of alignment, a fast estimation method of the azimuth error angle is proposed for the initial alignment of INS . The simulation results illustrate the efficiency of the method.
New Method of Small Sample Experiment for the Simulation System with Hardware in the Loop for Homing Missile
WANG Xiao-hu, ZHANG Ming-lian, DU Yi-min, YANG Xin
2000, 26(5): 519-522.
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The small sample experiment method of a simulation system with hardware-in-the-loop(HWIL) for radar homing missile is studied due to radar guider's high expenses, and a new method of small sample experiment is proposed based on the sensitivity of the target maneuver to the undershoot errors and maneuver-time distribution function. The theory foundation of the method is given, which proves that the expectation and variance are uniformly convergent in measure space, and the orthogonal function series used to approach the sensitivity function is uniformly convergent. It is proved that the method is very effective compared with great sample experiment. The method can be applied to other small sample experiment of simulation systems with HWIL for homing missile and governable variable systems.
Improvement on the Theoretical Model for Dissipation-rate Budgets in Near-wall Region of a Turbulent Boundary Layer
LU Li-peng, MIAO Ze-chun, CHEN Mao-zhang
2000, 26(5): 523-526.
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A symmetric resonant-triad theoretical model is proposed for the turbulent coherent structures in near-wall region of a turbulent boundary layer,sothe terms of triple-correlation can be analyzed theoretically. In accordance with the new theoretical model, budgets of the dissipation-rate of turbulent kinetic energy are calculated and its production rate, dissipation and transportation are evaluated. The new theoretical results are in better agreements with DNS than those by simple 3-D symmetric wave model. It shows that the theoretical method proposed could correctly embody the physical mechanism of near wall region turbulence and there is a possibility of opening a new way for near-wall turbulence modeling.
Experimental Study of the Dynamic Responses of the ECS-s Bleed System
ZHAO Jing-quan, LIN Gui-ping, YUAN Xiu-gan
2000, 26(5): 527-529.
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The experimental results are reported about the pressure transient responses and temperature transient responses of the bleed system of an aircraft environmental control system when the bleed air flows, pressure and temperature are varied. Results show that the pressure response of the bleed system is quite fast and response time is within 1 second, and on the other hand, the temperature response time is 10~30 seconds.
Analysis of the Accuracy of the Spatial Discretization Schemes for Surface Integrals in Finite Volume Method
MA Liang, LI Ting-he
2000, 26(5): 530-534.
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The order of accuracy of Vertex-Centered finite volume scheme for the unsteady Euler equations is investigated and compared with that of cell-centered and cell-vertex schemes. An error analysis using Taylor series expansion is applied. It shows that the accuracy of the vertex-centered scheme, similar to the cell-vertex scheme, is at least first order on skewed meshes and the error terms can be reduced by a mesh refinement and is suitable for multiblock computation. On smooth grids all three schemes exhibit an accuracy of almost second order. Subsonic internal flow over circular arc and transonic flow around NACA0012 airfoil are calculated by using the three different spatial discretization schemes. Numerical results confirm the technique statement.
Tracing Post-buckling Path of Structures by Interval Newton Method
TONG Zong-kai, WANG Shou-mei, QIU Zhi-ping
2000, 26(5): 535-538.
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Post-buckling analysis was traditionally conducted by arc length method. In view of the feature of global convergence of the interval iteration method in solving nonlinear equation sets, an approach is proposed to apply this method in tracing post-buckling path of structures. An incremental solution scheme is introduced. Smaller interval radius is suggested to avoid excessive number of iterations at low loading levels. When time stepping approaches the critical point, two equilibrium configurations of pre and post-buckling can be detected automatically, which avoids iteration failure resulting from the singularity of stiffness matrix. The rest part of tracing is then conducted based on the later configuration. Validation of the new method is demonstrated by a typical numerical example. It also shows that the method can deal with the phenomenon so called Snap-back problems without additional efforts.
Unit Cell Geometric Model of 4-Step 3-D Braided Composites
CHEN Zuo-rong, ZHU De-chao, LU Meng
2000, 26(5): 539-542.
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After briefly reviewing the proceeding of geometric model of 4-step 3-D (1×1) rectangular braided composites, yarn path in 4-step rectangular braiding process is analyzed. On this basis, a 3-D solid unit cell geometric model is proposed, the characteristics of geometry of 3-D braided composites are studied and yarn-jamming condition is discussed. Compared with conventional geometric models, the identified geometric model reflects the continuity of yarn in 3-D braided composites, which makes each unit cell assembled reasonably, so the structural integrity of 3-D braided composites is assured. The 3-D solid geometric model makes it possible to correctly consider the interactions between yarn and matrix for analysis of effective mechanic behaviors of 3-D braided composites.
Perfect Interface Based Method for Homogenization
CHEN Zuo-rong, ZHU De-chao, LU Meng
2000, 26(5): 543-546.
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Several representative micro-mechanical models for the analysis of the effective elastic properties of unidirectional fiber-reinforced composites and textile composites are briefly reviewed, and their characteristics are pointed out. In view of the limitations of the classical mechanical models for the prediction of the overall elastic behaviors of textile composites, a more generalized method is established. According to the fact that the in-plane components of strain tensor and the out-of-plane components of stress tensor are continuous across a perfect interface, interactions between phases are considered, and the perfect interface based formulas for homogenization are derived. This method has been applied to determine the effective elastic modulus of a unidirectional fiber-reinforced composite, and satisfactory results are obtained.
Changing Tendency of Dimensions of Mixed Type Plane Pilots and Its Human Engineering Significance
WANG Xing-wei, YUAN Xiu-gan, SUN Ming-zhao, WANG Rong-di, PENG Fu-min
2000, 26(5): 547-551.
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In order to study the changing extent and tendency of the pilot dimensions of different times/districts/plane-types,5~13 dimension values were obtained by measuring 656 pilots, and those of the 70s' were as controls, difference between the data of different districts/plane-types was analyzed. It was shown that 12 of the 13 dimension values were significantly different from those of the 70s' (p<0.01); there was no significant difference in stature between each 2 districts of all 6 districts and in body weight in most cases (p>0.05), the body weight of fighter pilots is different from that of other pilots. There have been significant changes in the fighter pilot dimensions, and 70s' data should not be used as bases of the design of aircraft and personal protective and survival equipment. Pilots should do regular exercises and the food should be controlled in order that pilots could maintain their dimensions. New pilot dimension database and anthropometric model should be set up. It is necessary to control some dimensions of volunteers when recruiting pilots in different districts.
Experimental Investigation on Porous Plate Water Sublimator under Constant Heat Flux
WU Zhi-qiang, YUAN Xiu-gan, SHEN Li-ping, HAN Li-jun, LI Tan-qiu
2000, 26(5): 552-555.
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Water sublimator is main heat sink of portable life support system of extravehicular activity (EVA) space suit. Manufacture techniques of porous plates are developed. Breadboard and tester of water sublimator are designed. An experimental study under constant heat flux is carried out on water sublimator with different porous plates. The attention is focused on the effects of heat flux, physical parameters of porous plate, pressure of feed water and placement on performance of sublimator. Breakthrough characteristics of sublimator are discussed. Test results have proved that the basic design concept of sublimator is feasible and that sintered powder porous plates can meet experimental needs of sublimator. Finally, some useful conclusions about further design of sublimator are presented.
Stochastic Crack Growth Approach under Corrosive Environment for Durability Analysis
ZHANG Jian-yu, LIU Ai-min, FEI Bin-jun
2000, 26(5): 556-560.
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In order to analyze the aircraft structural reliability under corrosive environment, stochastic crack growth approach (Cor-SCGA) for durability analysis is established. Assuming the influence of the pre-corrosion in parkand the influence of corrosion in flight are independent, the fatigue quality of structure under corrosive environment has a Weibull distribution. Using a log-normal stochastic variable model to describe crack propagation, an equation for predicting the probability of crack exceedance is established. Compared with the probability fracture mechanics approach under corrosive environment (Cor-PFMA) and probability fracture mechanics approach under normal environment (Nor-PFMA), Cor-SCGA is more efficient. This approach will be better used for durability-based design.
Optimization of Aircraft Structural Economic Maintenance Programme
LIU Xiao-dong, LIU Wen
2000, 26(5): 561-564.
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The aircraft structural economic maintenance is one of the important aspects in the durability design of advanced aircraft.To assure economic life and reliability of aircraft structure,an economic maintenance program is essentially needed.In this paper,the effect of various factors on the determination of aircraft structural economic maintenance programme and the criteria of determining these factors are discussed in detail.From the practical engineering application point of view,an analytical methodology for the optimization of aircraft structural economic maintenance programme based on structure durability analysis is presented.It also accounts for the feature of evaluating the economic life of the repaired structures.A practical structural maintenance programme,as an example,to demonstrate the application of the methodology is given.
Study of the Heat Transfer Characteristics of PhaseofChange Thermal Storage/Radiation Heat Sink
ZHAO Chao-yi, YUAN Xiu-gan, SUN Jin-biao, LI Tan-qiu
2000, 26(5): 565-568.
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Performance studies of a phase change thermal storage/radiation heat sink for extravehicular activity have been undertaken by experimental investigation and numerical simulation. The test specimens of phase change thermal storage were designed and the cooling tests of phase change thermal storage were conducted. The mathematical model of phase change thermal storage with coupled convection and conduction boundary conditions has been established. The effects of convective heat transfer and voids are considered in this model. A computational program has been developed for evaluating the performance of phase change thermal storage. The reliability of the program has been verified based on the experimental results. This program is a useful analysis tool for the design and optimization for a phase change thermal storage.
Stability and Precision Analysis for Precise Integration Method
ZHAO Li-bin, ZHANG Jian-yu, WANG Shou-mei
2000, 26(5): 569-572.
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The precise integration method, one of the direct integration methods for problems in structural dynamics, was analyzed. Several comments were made regarding to its formulation, numerical stability, computational accuracy and cost. The method is conditionally stable and belongs to the category of explicit time-integration methods. The precise integration method is based on the 2N-type algorithm for computation of exponential matrix. It controls the order N to satisfy the accuracy requirement. Its numerical results have excellent correlation. According to the analytic results, the numerical stability, computational accuracy and cost depend to a large degree on the selection of the parameters, time-division, truncation order and order of 2N-type algorithm. Then the optimal formulation of parameters was given. And several points about the precise integration method were illuminated theoretically. Finally, two numerical examples verified the validity of the stability, precision and the optimal formulation.
Study on Electromagnetic Scattering Characteristics for Complex Target Using Shooting and Bouncing Rays
LI Jun, MA Dong-li, WU Zhe
2000, 26(5): 573-576.
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The accurate mathematical externality of the target was established with surface generation method in computer graphics, which was dispersed into triangular facets. Relationships between the geometrical elements were described with topological structure. The method of shooting and bouncing rays was used to simulate the multiple-reflection of ray beam. The divergence factor, magnetic field direction and phase difference were educed. The far-field scattering was solved with physical optics integration at the final reflection point. Summing up the contribution from each ray beam, the value of coupled radar cross section was obtained. In order to reduce the calculation amount in the process of ray shooting and bouncing, an acceleration arithmetic was adopted. The calculation results of a wing-body combination were presented as a specific example.
Exact Solution of Eigenvalue and Eigenvector Derivatives and Its Application in Structural Dynamics
LI Shu, ANG Xiao-gu
2000, 26(5): 577-580.
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To compute eigenvector derivatives with repeated eigenvalues, several extended Nelson's methods have been developed. Some of these methods have been pointed out that they may fail in some cases. To deal with those difficulties under repeated eigenvalues circumstances, we develop formulas to calculate sensitivities and discuss the case where repeated eigenvalues are present in this paper. The exact solution of derivatives of eigenvalue and eigenvector is presented by utilizing the mathematical theorem and new definitions of sensitivities. This algorithm is rigorous mathematically and suits for both distinct and multiple eigenvalues cases. The new technique is powerful, easy to implement and simple in its conception. For practical application, the probability is discussed to determining approximate solution by using lower order eigendata. Example will be presented that demonstrates the algorithm.
Study of Active Nucleation Site Density in Subcooled Nucleate Pool Boiling
WU Yu-ting, YUAN Xiu-gang, YANG Chun-xin, MA Chong-fan
2000, 26(5): 581-583.
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The active nucleation site density is an important parameter of nucleate boiling heat transfer model, but none of those theoretical models made by far has successfully predicted the active site density. A fractal model has recently been proposed by authors to describe the active site density in nucleate boiling. In order to study if the fractal model can be used in subcooled nucleate boiling, the active nucleation site densities of four stainless steel surfaces are predicted using the heat transfer model proposed by Judd and Hwang according to the nucleate boiling experiment data on different subcoolings. The predicted result indicates that the active nucleation site density curve is not affected by subcooling and agrees well with the fractal model by authors. The universality of the model is ulteriorly confirmed.
Mechanical Performances of Piezoelectric Element and Optimal Control
REN Xiu-hua, DING Hua, MAI Han-chao, LU Meng
2000, 26(5): 584-587.
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On the basis of performances of the piezoelectric actuators and sensors,the characteristics of beam with highly distributed piezoelectric sensors and actuators and a feedback conditioning system are analyzed,and the dynamic differential equation is also derived.A finite element model of the intelligent beam has been formulated to derive the differential equation.Having obtained the basic theories of the intelligent beam,both the first mode and the second mode of the cantilever beam and the simple supported beam are analyzed and calculated to determine the appropriate criteria for placing the actuator.Characteristics related to the location for the actuator placement are also developed and illustrated.The choice of actuator location is on the assumption that the actuator and sensor have no length,so the location of actuator that has length is also studied.
Upwind Scheme Used on Two Dimensional Unstructured Adaptive Meshes
WANG Ping, ZHU Zi-qiang, Lü Xiao-bin
2000, 26(5): 588-591.
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The AUSM+ (Advection Upstream Splitting Method) finite-volume scheme, which was developed in structured grids, has been extended to be used on unstructured meshes. The linear reconstruction approach using Green-Gauss gradient estimation is applied in order to obtain second order spatial accuracy. A new gradient estimation based on the weighted average of Barth and Jespersen's three point model limiter is employed to minimize the numerical oscillations around solution discontinuities. An adaptive multigrid method is used to accelerate the convergence. Finally, numerical experiments on supersonic shock reflection flow over flat plane, transonic flow over NACA0012 and RAE 2822 airfoils are calculated to validate the methodology.
Flow Characteristics and Its　Melioration of Swept Wing/Body Interference
ZHANG Hua, Lü Zhi-yong
2000, 26(5): 592-595.
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A flow visualization and pressure distribution measurement test have been performed to understand the flow characteristics of swept wing/body junctions better. Different small strakes have been used to ameliorate the characteristics. The results show that with the increase of the angle of attack and the Reynolds numbers, two or three horseshoe vortex systems may appear. The steady vortex system may be changed into the unsteady vortex system and transferred into turbulent flow. With the increase of the swept angle of the wing, intensity and the size of the horseshoe vortex are decreased. It has been shown that the pressure gradient upstream of the wing/body junctions is the cause of the boundary layer separation. When the swept angle is decreased, the pressure gradient can be also reduced. The small strake is able to decrease the pressure gradient and makes the vortex weaken or even disappear upstream of the interference zone.
Simple Conjugation-Gradient BP Algorithm for Feedforward Neural Networks
LIANG Jiu-zhen, HE Xin-gui, HUANG De-shuang
2000, 26(5): 596-599.
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The high dimension of the learning error function for BP networks and the difficult computation complexity are incestigated. A simple modified conjugation-gradient decent algorithm (MPARTAN) is proposed based on improving the gradient BP algorithm. That the computation complexity of this algorithm is not higher than that of the BP momentum algorithm. Compared with FR conjugation algorithm, this algorithm has better stability and fast speed quality of convergence. It is also investigated that the convergence theorems for this algorithm and comparison of the computing results by two computing examples for the promoted three algorithms: BP momentum algorithm, FR conjugation-gradient algorithm and the novel MPARTAN algorithm.
Certificate System in Secure Distributed Application Frame
LU Yu, JIN Hui-hua
2000, 26(5): 600-603.
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According to the characteristics of distributed certification system, a secure distributed application framework based on client/server computation model is put forward, Which exposes how to combine the distributed certification system into it and to afford security mechanism such as authentication of identity, authorization and access control etc. From the needs of security, the main method of realization is listed. The characteristics and security of the framework are analyzed, then the future research direction and thought is proposed.
Process Modeling of Design of Mechanical Product
HAN Xiao-jian, DENG Jia
2000, 26(5): 604-607.
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Product design is a complicated thinking activity of creation of human.Based on analyzing product design and its process,using a theory and method of aggregating and mapping,models of product design,process of product design ,process of conceptual design of product were constructed,a frame of network arithmetic of a process of conceptual design of product was presented,its flow of decomposition and integration was particularly defined,a good base for modeling and ruling of process of product design was founded.At one time,a useful exploration of development of a computer support implement for process of product design at all life cycle was made.
Existence of Duck Solutions of A Kind of Differential Equations with Small Parameter
LI Cui-ping
2000, 26(5): 608-611.
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A kind of one parameter planar singular perturbation equation is studied by the qualitative theory of ordinary differential equations,asymptotic analysis methods,implicit function theorem and fixed point methods.Some sufficient conditions are given to support the existence of duck solutions and duck cycles when the singular points of the system are in the small neighbourhood of turnning points.It is proved that there exists a value of parameter a=ac(ε) such that for a in a small neighbourhood of ac(ε),the systems have duck cycles.Moreover,the asymptotic estimation of corresponding duck solutions and duck cycles and the rule of changing of the duck cycles with parameter are obtained.The article 1 and 2 are the special cases of this paper.
Matrix Coding in GA and Its Application to Fuzzy Modelling
DAI Ji-yang, MAO Jian-qin, ZHANG Jian-gang
2000, 26(5): 612-615.
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In the practical applications of genetic algorithm(GA), a lot of problems can be described as tree structures. In fuzzy modelling, the structure identification of a fuzzy model is to partition the input domain, which is in essence a process of complicated nonlinear optimization. The partition of the input domain can be expressed as a binary tree by a fuzzy tree model. A matrix coding approach to representing a binary tree is presented, which is simple and suitable for the genetic operations in GA. The partition of the input domain is optimized by GA with matrix coding for tree-structured individuals and theresulting suboptimal fuzzy tree model is obtained, which has higher precision and lower complexity of model. A simulation example is given to validate the proposed method.
Study on Flight Management and Control System for Uninhabited Combat Aerial Vehicles
QIU Xiao, LIAO Fang
2000, 26(5): 616-620.
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The development status of uninhabited combat aerial vehicles(UCAVs) in the world is introduced and evaluated. The requirements and characteristics of the flight management and control system (FMCS) for UCAVs are discussed. The layer constructures of the UCAV FMCS are analyzed with the layer theory of man machine complicated hybrid control system. The core technology ingredients to realize the FMCS such as man machine interface for remote control operators,mission planning and control in real time,and design method of maneuver agility controller are considered and the proposals to solve the technology problems are discussed.

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