西南交通大学学报

Theoretical Analysis on Flow-Induced Random Responses of Core Barrel of Nuclear Reactors

YANG Yi-ren, LU Li, TANXiao-hui

2001, 14(6): 557-560.

[Abstract](1665)

Abstract:
The random responses of core barrel of a nuclear reactor excited by a fluctuating flow are discussed in this paper. Fluid dynamic forces are divided into two parts, free vibrating fluid dynamics and fluctuating fluid dynamics. By means of finite element method of structure, a theoretic method is developed to analyze the root of mean square of responses of a core barrel structure in turbulence. It is the focal point to analyze the effects of the mean velocity, the strength of turbulence and the integral measure of turbulence on the root of mean square of structure response.

Stability of Pinned-Pinned Beam in a Rectangular Tube Filled with Incompressible Viscous Fluids

LU Li, YANG Yi-ren

2001, 14(6): 561-564.

[Abstract](1417)

Abstract:
The stability of a pinned plate-type beam in a rigid rectangular tube with incompressible viscous fluids flowing within it is studied. The assumption mode method is utilized to derive the motion equations of the structure. The effects of the thickness of the beam and the gaps between the beam and the tube walls on the stability of the model are discussed. The results show that both the thickness and the gaps have significant influences on the stability of the system and the critical velocity of the system changes remarkably with their variations. In addition, whether the two gaps change at the same time, that is, one changes while the other keeps unchanged, has different effects on the critical velocity of the system.

Nonlinear Finite Element Analysis of Hypervelocity Impact

SONG Shun-cheng, TAN Duo-wang

2001, 14(6): 565-561.

[Abstract](1544)

Abstract:
The geometric frame of finite deformation and Bodner-Parton constitutive equations are introduced into the finite element analysis of hypervelocity impact. The physical parameters of materials are determined by comparison of the one-dimensional calculations with the experimental results. From the comparison of the calculations with the experiments of a tungsten alloy projectile impacting a semi-infinite plate of armor steel, it can be seen that the B-P constitutive equations and the geometric non-linearity introduced by the authors can be used to analysis of hypervelocity impact.

Impact-Induced Martensitic Transformation and Material Constitutive Equations

DING Gui-bao, SONG Shun-cheng

2001, 14(6): 572-574.

[Abstract](830)

Abstract:
This paper presents the quantitative prediction of the volume fraction of martensitic transformation in a austenitic steel that undergoes a impact loading. The coupling relationship between strain, stress, strain rate, transformation rate and transformed fraction was derived from the OTC model and modified B-P equations, where the impact process was considered as an adiabatic and no entropy-increased process (pressure≤20 GPa). One-dimensional results were obtained on 304 stainless steel under Hopkinson impact, which agree well with various experimental results.

Mesomechanics Analysis of Fatigue Damages

DAI Zhen-yu, GAO Qinq, CAIJie

2001, 14(6): 575-577.

[Abstract](1544)

Abstract:
Low cycle fatigue tests were carried out on a number of fatigue specimens of 19Mn6 steel. Multiple small cracks initiated on the surface and their propagation were observed by optical metallography. A parameter,DW, is proposed for quantitative description of local fatigue damages based on local damage concept.DWincreases exponentially with the number of recycles until reaching the critical value, 1. The nonlinear damage factor,m, obtained by correlation of the experimental data is smaller than that by macro-measurement.

Modeling of Saturated Rachetting Strain for Materials under Uniaxial Cyclic Stress Load

CAI Li-xun, LIU Yu-jie, GAO Qing

2001, 14(6): 578-583.

[Abstract](1248)

Abstract:
Based on a series of uniaxial ratchetting tests of 304 stainless steel, the influences of four stresses (mean, amplitude, peak and valley) on saturated ratchetting (SR) strains are investigated. It is discovered that there exists a unique threshold for peak stress and SR strains vary monotonously with peak stresses. Peak stress, therefore, is an essential cause that leads to positive ratchetting deformation of materials. According to this phenomenon, the concepts of ratchetting threshold and ratchetting stress are proposed, and a saturated ratchetting model (SRM) for describing the constitutive relationship between SR strain and ratchetting stress is presented. The experimental results show that the history under previous low cyclic stresses has no effect on SR strains. This leads to the development of a single-specimen method to built SRM, with which a ratchetting test needs only one to three specimens with about ten different levels of peak stresses. The safety factor is between 1 and 1.3 for SRM to predict test results of SR strains for 304 steel specimens under stresses with only one level of peak stress.

Fatigue Reliability Analysis Model for Structural Members under Random Stress-Time Courses

SU Yan-jiang, GAO Qing, WANG Guang-qin

2001, 14(6): 584-587.

[Abstract](1503)

Abstract:
A model for fatigue reliability analysis of structural members under random stress-time courses is proposed. Two kinds of random stresses are taken into consideration. The fatigue reliability of the members under constant amplitude stresses are analyzed based on thep-S-Ncurve of material and the random factors affecting fatigue strength to obtain thep-S-Ncurve of the members. Then the fatigue reliability of the members under random stress-time courses is calculated by using Miner s rule and thep-S-Ncurve of the members.

Elastic-Plastic Analysis of Contact Problems of Wheel/Rail with Surface Micro-Roughness

JIANG Xiao-yu, JINXue-song

2001, 14(6): 588-590.

[Abstract](1376)

Abstract:
The contact element method and original stress method were used to analyze the elastic- plastic contact problem of wheel/rail with measured surface micro-roughness. The distribution of surface contact pressure on the rail was obtained. The results show that the peak value of contact pressure on the contact area for the surface with micro-roughness was much larger than that for smooth surfaces, and the rough surface went into plasticity. It is therefore necessary to conduct elastic-plastic analysis for wheel/rail contact problems when micro-roughness is considered.

Damping Property and Its Micromechanism of ZA27 High Damping Alloy

ZHAO Yu-zhen, GAO Qing, DAI Zhen-yu

2001, 14(6): 591-594.

[Abstract](1224)

Abstract:
ZA27 is zinc alloy which is modified by adding rear earth and Ti, solid-solution and naturally aging. The damping properties of ZA27 and its mechanism are studied. The effect of modification, solid solution and natural aging treatment on damping properties is analyzed. Compare with cast alloy, the damping properties of ZA27 alloy treated by modification, solid-solution and natural aging gets obvious improvement. It is because of microstructure refinement, an increase in boundaries and dislocation multiplication.

Analytical Solution of the Resonance Length for Ultrasonic Torsional Fatigue Samples

WANG Hong, GAO Qing

2001, 14(6): 595-598.

[Abstract](1275)

Abstract:
A method for analytical calculation of the resonance length for ultrasonic torsional fatigue samples is recommended. The angular displacement amplitude and torsional stress/strain amplitude on the surface of samples are derived. Analysis for the stress magnification factor of sample with various cross-sections shows that when the ratio of the minimum section radius to the maximum section radius is 0.5, there is the maximum stress magnification. The sample profile defined by the analytical solution may be approximated by a circular profile, with the error in the frequency and stress being neglectable.

Continuum Theory of Mixture for Freezing and Thawing of Water-Saturated Porous Media

LUHong-lun

2001, 14(6): 599-513.

[Abstract](1226)

Abstract:
With the application of continuum theory of mixture, a mathematical model for the coupled seepage, stress and temperature for freezing and thawing of water-saturated porous media has been established. The conservation equation of water mass, the equilibrium equation of total stress and the conservation equation of total energy are described with the skeleton displacement, water head and temperature. The model contains the equation of the non-freezing zone where the porous medium is saturated by liquid water. The coupled model of two fields such as seepage- elasticity, thermal-elasticity and thermal-seepage, and the model of single field such as seepage, elasticity and thermal conduction, all are special examples of the paper.

Coefficient Matrices of Evolution Equation and the Dissipation Effect of Viscoelastic Medium

DAI Guang-ze, XIA Yan, ARAKI Shigetoshi

2001, 14(6): 604-608.

[Abstract](1267)

Abstract:
It is obvious that the exact solutions of the evolution equation, which is derived by regarding the deformation process of viscoelastic materials as an irreversible themodynamic process, depend very much on the properties of their coefficient matrices. These matrices are usually affected by the nature of the generalized thermodynamic coordinates, say, the number and location of the neutrally stable equilibrium coordinates and those participating in the entropy production of the isolated system. These provide us a ground to distinguish the ideal viscoelastic solid state and the ideal viscoelastic fluid state in creep or stress relaxation behaviour.

Dynamic Stability Analysis of Viscoelastic Cables with Small Sag

LI Ying-hui, GAO Qing, YINXue-gang

2001, 14(6): 609-611.

[Abstract](1579)

Abstract:
Based on the one-dimensional constitutive equation of Relvon materials and the motion equation of cables, the governing equations of the viscoelastic cables in the vertical plane are derived. By using the variable separation method, a linear ordinary equation is obtained, which is expressed by modal coordinates and has periodic coefficients. The dynamic stability criteria of the viscoelastic cables subjected to periodic axial loads are obtained. The regions of stability and instability are plotted for various sag to span ratios.

Study on Wind-Induced Loads of Train-Bridge System by Wind Tunnel Test

GE Yu-mei, LI Yong-le, HE Xiang-dong

2001, 14(6): 612-616.

[Abstract](1717)

Abstract:
The aerodynamic parameters of Wuhu Bridge over the Yangtze River and a high speed running on it were measured respectively by wind tunnel tests. The natural wind loads acting on the train and the bridge were simulated. The calculated wind loads are added into the dynamic equations of train and bridge to calculate dynamic effects of wind loads on train and bridge.

Analysis of Shear Lag Effect of Long-Span Continuous Rigid-Frame Box-Beam Bridges

TANG Huai-ping, TANG Da-pei

2001, 14(6): 617-619.

[Abstract](1323)

Abstract:
The equivalent load resolution method was used in the study. The mechanism of shear lag effect of long-span continuous rigid-frame induced by vertical loads are discussed. The shear flow equilibrium equations of the box-beam are derived by use of three-rod analogous procedure. The shear-lag coefficients of the main controlling cross-sections of the continuous rigid-frame of Luzhou Second Bridge over the Yangzi River are obtained based on static loads measured on site.

Optimality Criterion of the Significant Failure Modes of Engineering Structures

LIU Chang-hong, CHEN Qiu

2001, 14(6): 620-623.

[Abstract](1294)

Abstract:
Based on the enumerate significant failure modes on general reliability of structure static strength, using the entropy concept, a relationship between a random-fuzzy parameter and an equivalent random parameter is presented. With the relationship, it can be made good result on the failure models of the random-fuzzy structures, and an example is given to show the availability and advance of the new method. Finally, after discussed the steps of the optimality criterion, it is pointed out that if combined with the parallel computation, the algorithm will be more efficiently.

Hopf Bifurcation of Flywheel Governor with Feedback Control Device

DING Wang-cai

2001, 14(6): 624-628.

[Abstract](1470)

Abstract:
The mathematical model of the flywheel governor with a feedback device is proposed. Results show that there existsHopf bifurcation in the system. The bifurcation problem can be solved with a center manifold-normal forms theorem. A controllable condition of the system is presented. It was revealed by numerical simulation that the parameters need somehow away from bifurcation point to guarantee a quick convergence to the equilibrium point.

Chaotic Motions in Nonlinear Vibration Systems

YEJian-jun, CHEN Qiu

2001, 14(6): 629-632.

[Abstract](1447)

Abstract:
In this paper, the chaotic motions of non-linear vibration systems are studied. Some non- linear dynamic equations with second-and third-degree variables are discussed, subharmonic orbits, heteroclinic orbits are obtained, and the conditions for chaos to occur are presented.

Forced Torsional Double-Resonance for a Hydro-Generator under Unsymmetrical Operation

CHEN Gui-qing, YANG Yi-ren

2001, 14(6): 633-636.

[Abstract](1435)

Abstract:
The forced double-frequency resonance of a large hydro-generator unit is studied. The resonance is composed of torsional resonance of whole rotor system and 100 Hz resonance excited by inverted-sequence electricity under short-circle between two phases. By applying energy method, the torsional resonance equations of the rotor system are derived. The study results show that compared with the vibrating amplitudes of single-resonance, double-frequency resonance is much larger, the resonance area gets wider and dynamic shear stresses increase greatly.

Analysis of Dynamic Behavior of an Air Compressor Rotor and Contact Strength of the Keys of the Blades

SHENHuo-ming, TANG Wei

2001, 14(6): 637-640.

[Abstract](1400)

Abstract:
Detailed analysis was conducted on the strength of the gear keys of an air compressor rotor. The distribution of stresses in the key and the pressure stresses on the touching surface was obtained by taking the most unfavorable condition that there is only one key touches the keyslot into consideration. Also analyzed was the vibration characteristics of the blades of the rotor turning at high speed. The results show that the distribution of the maximum equivalent stresses is dependent on what sections of the key touch the keyslot. Nevertheless the dynamic characteristics of vibrations is normal regardless of the touching conditions.

Vibration Characteristics of a 3-Dimensional Beam-Pier-Pile System

QU Ai-ping, GAO Shu-ying

2001, 14(6): 641-644.

[Abstract](1587)

Abstract:
A mechanical model for a 3-dimensional beam-pier-pile system is proposed with finite element methods for a continuous rigid-frame bridge to analyze its vibration characteristics. The pile-soil system is simplified to build the space model and to calculate the dynamic behaviors of the system. Then the dynamic analysis model for the rigid-frame bridge is set up. The dynamic behaviors of the rigid-frame bridge are calculated and compared with different models, including that without considering the pile, that with pile base but without considering the effects of soil properties on vibration of the pile, and that with the interaction of the soil and the pile considered. The results show that the main factor affecting the third order frequencies are the properties of piles, but the properties of pile bases have not significant effects on the vibration characteristics of the beam-pier- pile system..

Predication of Efficiency of Railway Anti-Noise Barriers with Statistical Energy Analysis Method

WANG Shao-jia, GAO Shu-ying

2001, 14(6): 645-647.

[Abstract](1233)

Abstract:
Statistical energy analysis (SEA) is used to predict the efficiency of railway anti-noise barriers. An analytical model is proposed, which consists of two sub constructions. The result obtained with the proposed model is similar to that with conventional empirical method.

Application of BP Networks in the Stability Analysis of Slopes

ZHANG Ji-ping, CHEN Qiu

2001, 14(6): 648-650.

[Abstract](1523)

Abstract:
A method is introduced to apply the artificial neural networks on the analysis of slopes. The slope stability coefficient is analyzed by considering natural factors and making use of the nonlinear mapping ability of BP networks. Taking the data of the slopes in a loessial area as an example, the calculating results testify that this method is simple and practical and can meet the requirements of slope stability analysis in engineering.

Backstepping Design in Synchronizing Nonlinear Systems

TANXiao-hui, ZHANG Ji-ye, YANG Yi-ren

2001, 14(6): 651-654.

[Abstract](1364)

Abstract:
Backstepping design is a recursive procedure that combines the choice of a Lyapunov function with the design of feedback control. In this paper, a practical backstepping design scheme is proposed for synchronizing nonlinear systems. In the scheme, only one feedback control is required regardless of the order of the system. It can be applied not only to ordinary nonlinear systems, but also to a variety of chaotic systems, such as van der Pol system and Duffing system with external excitation, Chua s circuit and system,etc. It is easy to be carried out since its feedback control has no derivatives. Examples of van der Pol system and Chua s circuit designs are presented.

Research on FEM Metacomputing Environment DPFEM

YUAN Feng, CHEN Qiu

2001, 14(6): 655-658.

[Abstract](1732)

Abstract:
The mutual operation between different network platforms is realized by deliberate combination of Java and CORBA (Common Object Request Broker Architecture), packing the existing FEM software with Java and packing the packed FEM software into distributed calculating components with CORBA. A skeleton model of distributed parallel finite element method is proposed, and and two examples of metacomputing are presented.

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2001 Vol. 14, No. 6