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Showing papers by "Beihang University published in 2001"


Journal ArticleDOI
Wei-Hong Zhong1, Fan Li1, Zuoguang Zhang1, Lulu Song1, Zhimin Li2 
TL;DR: In this article, a short fiber reinforced composite used in rapid prototyping and manufacturing (RP&M) was modified by incorporating several different property modifiers including the short glass fiber, plasticizer, and compatibilizer.
Abstract: Addressed in this paper are critical material property issues related to the short fiber reinforced composite used in rapid prototyping and manufacturing (RP&M). Acrylonitrile–butadiene–styrene (ABS) copolymer has been a popular choice of material used in fused deposition modeling (FDM), a commonly used RP&M process. However, conventional ABS polymers in the filamentary form for FDM are known to be of low strength and hardness. In order to overcome this deficiency, ABS was modified by incorporating several different property modifiers including the short glass fiber, plasticizer, and compatibilizer. Glass fibers were found to significantly improve the strength of an ABS filament at the expense of reduced flexibility and handleability. The latter two properties of glass fiber reinforced ABS filaments were improved by adding a small amount of plasticizer and compatibilizer. The resulting composite filament, prepared by extrusion, was found to work well with a FDM machine.

557 citations


Journal ArticleDOI
TL;DR: The significance of recycling of waste rubber in protecting the environment and conserving energy is discussed in this article, where various kinds of recycling approaches to waste rubber are summed up, such as reclaiming energy as fuel, reuse of the products of thermal decomposition, cleaning of leaking oil, reuse after simple modification, regenerative rubber and powdered rubber (PR).

190 citations


Journal ArticleDOI
Liu Qihou1
TL;DR: Ghosh and Debnath as mentioned in this paper proved sufficient and necessary conditions for Ishikawa iterative sequences of asymptotically quasi-nonexpansive mappings to converge to fixed points.

159 citations


Journal ArticleDOI
TL;DR: The neural network approach is more appropriate for handling datasets with `smooth' trends than for Handling datasets with large fluctuations, and the training results are much better than the prediction results in general.

152 citations



Journal ArticleDOI
Yi-Tian Gao1, Bo Tian1
TL;DR: Based on computerized symbolic computation, a generalized hyperbolic function method and its algorithm are proposed for the nonlinear equations of mathematical physics in this paper, which could be widely applicable, including (a) the non-traveling solitonic features, (b) the multi-hyperbolic functions, and (c) the coefficient functions.

140 citations


Journal ArticleDOI
TL;DR: In this article, a new method of moving force identification is developed by making use of the dynamic programming technique to overcome the weakness of having large fluctuations in the identified results, and results from the simulation studies and laboratory work show great improvements over existing methods in the accuracy of identification.

106 citations


Journal ArticleDOI
TL;DR: A kind of hybrid heuristic GA is proposed for problem n/m/G/Cmax, where the scheduling rules are integrated into the process of genetic evolution and the neighborhood search technique is adopted as an auxiliary procedure to improve the solution performance.

104 citations


Journal ArticleDOI
22 Jun 2001-Vacuum
TL;DR: In this article, the dc magnetron reactive sputtering method using Ar and O 2 as working gases was used to construct transparent and colourless nanostructured titanium dioxide thin films with anatase phase.

100 citations


Journal ArticleDOI
TL;DR: An embedded simulator is employed to implement the heuristic rules, which greatly enhances the flexibility of the algorithm and shows that the hybrid approach is superior when compared to recently published existing methods for the same problem.
Abstract: The importance of job shop scheduling as a practical problem has attracted the attention of many researchers. However, most research has focused on special cases such as single machine, parallel machine, and flowshop environments due to the “hardness” of general job shop problems. In this paper, a hybrid algorithm based on an integration of a genetic algorithm and heuristic rules is proposed for a general job shop scheduling problem with sequence-dependent setups (Jm|sjk|Cmax ). An embedded simulator is employed to implement the heuristic rules, which greatly enhances the flexibility of the algorithm. Knowledge relevant to the problem is inherent in the heuristic rules making the genetic algorithm more efficient, while the optimization procedure provided by the genetic algorithm makes the heuristic rules more effective. Extensive numerical experiments have been conducted and the results have shown that the hybrid approach is superior when compared to recently published existing methods for the same problem.

93 citations


Journal ArticleDOI
TL;DR: It is concluded that ANN-based fault diagnostic method is of great potential for future use and can also serve as an instant trend detector which greatly improves the current smoothing methods in trend detection.
Abstract: Application of artificial neural network (ANN)-based method to perform engine condition monitoring and fault diagnosis is evaluated. Back-propagation, feedforward neural nets are employed for constructing engine diagnostic networks. Noise-contained training and testing data are generated using an influence coefficient matrix and the data scatters. The results indicate that under high-level noise conditions ANN fault diagnosis can only achieve a 50-60 percent success rate. For situations where sensor scatters are comparable to those of the normal engine operation, the success rates for both four-input and eight-input ANN diagnoses achieve high scores which satisfy the minimum 90 percent requirement. It is surprising to find that the success rate of the four-input diagnosis is almost as good as that of the eight-input. Although the ANN-based method possesses certain capability in resisting the influence of input noise, it is found that a preprocessor that can perform sensor data validation is of paramount importance. Autoassociative neural network (AANN) is introduced to reduce the noise level contained. It is shown that the noise can be greatly filtered to result in a higher success rate of diagnosis. This AANN data validation preprocessor can also serve as an instant trend detector which greatly improves the current smoothing methods in trend detection. It is concluded that ANN-based fault diagnostic method is of great potential for future use. However, further investigations using actual engine data have to be done to validate the present findings.

Journal ArticleDOI
TL;DR: In this paper, a linearized potential flow model is developed to study the effect of grazing flow on the acoustic behavior of an orifice, which uses the particle velocity continuity boundary condition rather than the widely used displacement to match the flow-fields separated by the shear layer over the orifice.
Abstract: A linearized potential flow model is developed to study the effect of grazing flow on the acoustic behavior of an orifice. In accordance with the previous flow visualization and measurements, this model uses the particle velocity continuity boundary condition rather than the widely used displacement to match the flow-fields separated by the shear layer over the orifice. An experiment is also carried out to validate the present theory in the case of circular or rectangular orifices. The theory agrees well with the experiment. In addition, further comparison is made between the present and two existing impedance models. One major objective of the present investigation is to make a tentative judgement on the two boundary conditions for a sound wave transmitting through a turbulent boundary layer over an orifice. It is found that, compared to the particle displacement continuity boundary condition, the use of the particle velocity continuity boundary condition results in a much better agreement between the theoretical predictions and the experimental data. Finally, there is a discussion on the influence of plate thickness on orifice impedance in the presence of grazing flow.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the formation of the exit defects in carbon fiber-reinforced plates and characterised their features in terms of drilling conditions and found that spalling and fuzzing are the major mechanisms of exit defects.
Abstract: This paper investigates the formation of the exit defects in carbon fibre-reinforced plates and characterizes their features in terms of drilling conditions. It was found that spalling and fuzzing are the major mechanisms of exit defects. The spalling, consisting of a main region and a secondary region, is caused by chisel and cutting edge actions, in which the former plays a key role. The fuzzing, however, exists in the cutting region where the included angle between the fibre direction of the surface layer and that of the cutting speed is acute. A severer spalling damage corresponds to a high spindle speed, a large feed rate and a great thrust force. Some empirical relationships, including a dimensionless formula, were developed for assessing the characteristic dimension of the spalling damage based on the known drilling conditions.

Journal ArticleDOI
TL;DR: In this paper, a three-phase piezoelectric cylinder model is proposed and an exact solution is obtained for the model under a far-field antiplane mechanical load and a farfield inplane electrical load.

Journal ArticleDOI
TL;DR: In this article, the dissipative mechanism in the shock capturing schemes, where exact or approximate Riemann solvers are used in the flux evaluation, is analyzed, from which some pathological phenomena from the FVS scheme and the Godunov method will be explained.
Abstract: This paper concerns the dissipative mechanism in the shock capturing schemes, where exact or approximate Riemann solvers are used in the flux evaluation. More specifically, we are going to analyze the dissipation in the flux vector splitting (FVS) scheme and the Godunov method, from which some pathological phenomena from the FVS scheme and the Godunov method will be explained, such as the artificial dissipation and the shock instability. Copyright © 2001 John Wiley & Sons, Ltd.

Journal ArticleDOI
TL;DR: It is proved that the chained form is linearizable via nonregular feedback control, thus enable us to design feedback control laws using standard techniques for linear systems.

Journal ArticleDOI
TL;DR: In this paper, a neural network is trained to create a rapid RTM process model and genetic algorithms are applied to this model to search for the optimum solution to the problem of tooling design.
Abstract: Resin transfer molding (RTM) is a promising fabrication method for low to medium volume, high-performance polymer composite structures. Yet there exist several technical issues which impede a wide application base. One of these issues is tooling design. In the RTM process, the arrangement of injection gates and vents of the mold has a significant impact on product quality and process efficiency. In this paper, a systematic approach for optimum design of RTM tooling is introduced. This approach is built upon an RTM virtual manufacturing (simulation) model coupled with a neural network–genetic algorithm optimization procedure. The simulation model is employed to predict resin flow patterns (i.e. potential quality problems) and processing efficiency (mold filling time). With the simulation results, a neural network is trained to create a rapid RTM process model. Genetic algorithms are applied to this rapid RTM process model to search for the optimum solution to RTM process design. This tooling design scheme enables the engineer to determine the optimum locations of injection gates and vents for the best processing performance, i.e. short filling time and high quality level (minimum defects). The approach is illustrated with an example.

Journal ArticleDOI
TL;DR: In this paper, a generalized selfconsistent method is developed for predicting the relevant effective electroelastic moduli of piezoelectric fiber reinforced composite, accounting for variations in fiber section shapes and randomness in distribution and orientation.

Journal ArticleDOI
TL;DR: The result revealed the sequence of firing patterns near the Hopf bifurcation point and indicated that ASR was probably the cause of the generation of the integer multiple spiking in the experiment.

Journal ArticleDOI
TL;DR: In this paper, a random fractal model is proposed to simulate the drop size and spatial distribution in dropwise condensation and the boundary conditions of heat conduction through the condensing wall surface are then established using the heat transfer model through a single drop proposed by J.W. Rose.

Journal ArticleDOI
S. L. Lan1, Mao Sun1
TL;DR: In this paper, the aerodynamic forces and flow structures of a wing of relatively small aspect ratio in some unsteady rotational motions at low Reynolds number (Re=100) are studied by numerically solving the Navier-Stokes equations.
Abstract: The aerodynamic forces and flow structures of a wing of relatively small aspect ratio in some unsteady rotational motions at low Reynolds number (Re=100) are studied by numerically solving the Navier-Stokes equations. These motions include a wing in constant-speed rotation after a fast start, wing accelerating and decelerating from one rotational speed to another, and wing rapidly pitching-up in constant speed rotation. When a wing performs a constant-speed rotation at small Reynolds number after started from rest at large angle of attack (α=35°), a large lift coefficient can be maintained. The mechanism for the large lift coefficient is that for a rotating wing: the variation of the relative velocity along the wing-span causes a pressure gradient and hence a spanwise flow which can prevent the dynamic stall vortex from shedding. When a wing is rapidly accelerating or decelerating from one rotational speed to another, or rapidly pitching-up during constant speed rotation, even if the aspect ratio of the wing is small and the flow Reynolds number is low, a large aerodynamic force can be obtained. During these rapid unsteady motions, new layers of strong vorticity are formed near the wing surfaces in very short time, resulting in a large time rate of change of the fluid impulse which is responsible for the generation of the large aerodynamic force.

Journal ArticleDOI
Wusheng Yin1, Jun Li2, Yongming Li2, Jingpin Wu2, Tiren Gu2 
TL;DR: In this article, a polypyrrole/crosslinked cellulose conductive composite films were prepared by vapor-phase polymerization of pyrrole on the silicon cross linked cellulose network using anhydrous ferric chloride as oxidant.
Abstract: Polypyrrole/crosslinked cellulose conductive composite films were prepared by vapor-phase polymerization of pyrrole on the silicon crosslinked cellulose network using anhydrous ferric chloride as oxidant. The properties of the composite film depend on their synthetic conditions such as the amount of ferric chloride and tetraethyl orthosilicate crosslinker, the reaction time, the solvent, etc. Interestingly, it was found that the conductivity was strongly affected by the nature of the solvents and their amount in pyrrole solution. When the weight ratio of methanol/pyrrole is 1 : 1, the conductivity was as high as 1.1 S/cm, increased by two orders of magnitude compared to that without solvent, and the mechanical properties was good. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1368–1373, 2001

Journal ArticleDOI
TL;DR: An account of the design of a low-cost Internet-based teleoperation system implemented on China's Internet, using a multimedia-rich human-computer interface, combining predictive displays and graphical overlays is presented.

Journal ArticleDOI
TL;DR: In this paper, the high temperature oxidation behavior of TiAl alloys coated with TiAl-Cr alloys using magnetron sputtering method was studied and the results showed that TiAl−Cr coatings improved the oxidation resistance of all the alloys.
Abstract: The high temperature oxidation behavior of TiAl alloys coated with Ti–Al–Cr alloys using magnetron sputtering method was studied. The results showed that Ti–Al–Cr coatings improved the oxidation resistance of TiAl alloys. The weight gains at 950°C for Ti–Al–Cr coatings are more than those at 1000°C. Oxide formed on the surface of Ti–50Al–15Cr coating after oxidation consisted of Al2O3, whereas oxide formed on the surface of Ti–50Al–10Cr coating after oxidation is composed of a mixture of a large portion of Al2O3 and a small portion of TiO2. The effect of Ti–Al–Cr coatings on the improvement of oxidation resistance of TiAl alloys results from thermodynamic and kinetics factors contributing to Cr effect.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the atomic oxygen (AO) erosion effects in a plasma-type ground-based AO effects simulation facility and concluded that neutral AO is the major cause of material erosion and mass loss and that collision of energetic ions may accelerate the oxidation reaction.
Abstract: Kapton, a commonly used spacecraft material, is studied to investigate the atomic oxygen (AO) erosion effects in a plasma-type ground-based AO effects simulation facility. The samples before and after the experiments are compared in aspect, mass and surface morphology. The reaction characteristics of the material in the facility are obtained. The contribution of AO and ionic oxygen to mass loss in the sample and the reaction mechanism between the different particles and samples are analysed. It is concluded that neutral AO is the major cause of material erosion and mass loss and that the collision of energetic ions may accelerate the oxidation reaction.

Journal ArticleDOI
TL;DR: A two-step, component-wise TVD scheme for nonlinear, hyperbolic conservation laws, which is obtained by combining the schemes of Mac Cormack and Warming-Beam and is found to be two times faster in computation than the usual TVD schemes based on field-by-field decomposition limiting.

Journal ArticleDOI
TL;DR: The comparison of the Lagrange multiplier method with the convex model extension method for evaluating the region of static displacements of structures with uncertain-but-bounded parameters shows that the width of the upper and lower bounds on the static displacement yielded by the Lag Range multiplier method of convex models is tighter than those produced by the conveX model extension.
Abstract: Anti-optimization technique, on the one hand, represents an alternative and complement to traditional probabilistic methods, and on the other hand, it is a generalization of the mathematical theory of interval analysis. In this study, in terms of interval analysis or interval mathematics, the arithmetic operations and the partial order relation of anti-optimization technique can be defined, and the convex model variables and the convex model extension function of convex models can also be introduced. The comparison of the Lagrange multiplier method with the convex model extension method for evaluating the region of static displacements of structures with uncertain-but-bounded parameters shows that the width of the upper and lower bounds on the static displacement yielded by the Lagrange multiplier method of convex models is tighter than those produced by the convex model extension.

Journal ArticleDOI
兰世隆1, 孙茂1
TL;DR: In this paper, the Navier-Stokes equations of two airfoils in a tandem configuration in flapping motions are studied, by solving the NST equations in moving overset grids.
Abstract: Aerodynamic force and flow structures of two airfoils in a tandem configuration in flapping motions are studied, by solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between the fore- and aftairfoil flapping cycles are considered. It is shown that: (1) in the case of no interaction (single airfoil), the time average of the vertical force coefficient over the downstroke is 2.74, which is about 3 times as large as the maximum steady-state lift coefficient of a dragonfly wing; the time average of the horizontal force coefficient is 1.97, which is also large. The reasons for the large force coefficients are the acceleration at the beginning of a stroke, the delayed stall and the “pitching-up” motion near the end of the stroke. (2) In the cases of two-airfoils, the time-variations of the force and moment coefficients on each airfoil are broadly similar to that of the single airfoil in that the vertical force is mainly produced in downstroke and the horizontal force in upstroke, but very large differences exist due to the interaction. (3) For in-phase stroking, the major differences caused by the interaction are that the vertical force on FA in downstroke is increased and the horizontal force on FA in upstroke decreased. As a result, the magnitude of the resultant force is almost unchanged but it inclines less forward. (4) For counter stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased. As a result, the magnitude of the resultant force is decreased by about 20 percent but its direction is almost unchanged. (5) For 90°-phase-difference stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased greatly and the horizontal force on AA in upstroke increased. As a result, the magnitude of the resultant force is decreased by about 28% and it inclines more forward. (6) Among the three cases of phase angles, inphase flapping produces the largest vertical force (also the largest resultant force); the 90°-phase-difference flapping results in the largest horizontal force, but the smallest resultant force.

01 Jan 2001
TL;DR: In this paper, the connotation, architecture and its key technologies for Virtual Prototyping are studied and presented and its details are introduced to facilitate the practice and development for virtual prototyping technology in this country.
Abstract: In this paper, the connotation, architecture and its key technologies for Virtual Prototyping are studied and presented A given Virtual Prototype development supporting environment for complex system composed with some subsystems including mechanical subsystem, electronic subsystem, software subsystem and control subsystem consists of VP development environment, standard data interchange formats and distributed product model database, and its details are also introduced to facilitate the practice and development for virtual prototyping technology in our country

Journal ArticleDOI
TL;DR: In this article, the microstructure and composition distribution of the gradient coating were studied by SEM with EDS, and constituent phases identified by XRD, and it was found that the gradient structure significantly increased the lifetime of the coating.
Abstract: Gradient thermal barrier coatings (GTBCs) have been produced by co-deposition of a tablet of mixtures of Al-Al2O3-ZrO2-8wt.%Y2O3 and an ZrO2-8wt.%Y2O3 ingot onto NiCoCrAlY bond coat by means of EB-PVD. Thermal cycling tests at 1323 K were conducted to evaluate the hot-fatigue behaviors of the coating. The microstructure and composition distribution of the coating- was studied by SEM with EDS, and constituent phases identified by XRD. It was found that the gradient structure significantly increased the lifetime of the coating. Due to the selective oxidation of Al in the NiCoCrAlY bond coat and a Ni3Al film on the surface of the bond coat, an Al2O3 layer was developed between the bond coat and the transition layer. Failure of the gradient coating eventually occurred by cracking near the interface between the Al2O3 and transition layer. In addition, Compared with that before the test, the gradient coating after thermal cycling tests becoming softer than that before the test. (C) 2001 Elsevier Science B.V. All rights reserved.