力学进展

IMPLICATION OF SCALING HIERARCHY ASSOCIATED WITH NONEQUILIBRIUM: FIELD AND PARTICULATE

2004, 34(2): 145-170. doi: 10.6052/1000-0992-2004-2-J2003-048

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The advent of nanotechnologyhas necessitated a better understanding of how the material microstructurechanges at the atomic level would affect the macroscopic properties thatcontrol the performance. Such a challenge has uncovered many phenomenathat were not previously understood and taken for granted. Among themare the basic foundation of dislocation theories which are now known tobe inadequate. Simplifying assumptions invoked at the macroscale may notbe applicable at micro- and/or nanoscale. There are implications ofscaling hierarchy associated with inhomogeneity and nonequilibrium ofphysical systems. What is taken to be homogeneous and in equilibrium atthe macroscale may not be so when the physical size of the material isreduced to microns. These foundamental issues cannot be dispensed atwill for the sake of convenience because they might alter the outcome ofpredictions. Even more unsatisfying is the lack of consistency inmodeling physical systems. This could be translated to the inability foridentifying the relevant manufacturing parameters and rendering the endproduct unpractical because of high cost. Advanced composite andceramic materials are cases in point.Discussed are potential pitfalls for applying models at both the atomicand continuum levels. No encouragement is made to unravel the truth ofnature. Let it be particulates, a smooth continuum or combinationof both. The present trend of development in scaling tends to seekdifferent characteristic lengths of material microstructure with orwithout the influence of time effects. Much will be learned fromatomistic simulation models to show how results could differ asboundary conditions and scales are changed. Quantum mechanics,continuum and cosmological models provide evidence that no generalapproach is in sight. Of immediate interest is perhaps theestablishment of greater precision in terminology so as to bettercommunicate results involving multiscale physical events.

SURVEY OF EXPERIMENTS FOR DYNAMICS OF FLEXIBLE MULTIBODY SYSTEM

2004, 34(2): 171-181. doi: 10.6052/1000-0992-2004-2-J2002-028

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This paper presents a survey of experiments dedicated to the study of dynamicsof flexible multibody systems. Topics include verification of theories,experimental investigation on dynamics characteristics, and other test work such ascontact-impact experiment. The development of the dynamics of flexible multibody systemsinvolves three stages: Kineto-Elasto Dynamics Method (KED), traditional hybridcoordinates method and non-linear theories taking into account the dynamic stiffening effect. The relatedexperiments used for the verification of these theories are described in detail. Theexperiments on the dynamics characteristics of flexible multibodysystem, such as modalfrequencies and modal shapes and resonance researches, are also discussed. The experimentson the control of manipulator and contact-impact researches are brieflymentioned. Twokey problems in experiments are discussed in detail. One is how to measure the deformation offlexible body undergoing large overall motions, the other is how to deal with the effects ofdamping such as internal damping and air drag forces. Finally, some current and future researchdirections are pointed out. In this paper, some of experiments aredescribed with figures containingthe experiment setup and data plotting.

RECENT DEVELOPMENT ON MODELS AND NONLINEAR DYNAMICS OF PIPES CONVEYING FLUID

2004, 34(2): 182-194. doi: 10.6052/1000-0992-2004-2-J2003-028

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In this paper, various physical and mathematical models ofpipes conveying fluid are summarized. Under some assumptions for the fluidin the pipe, the mathematical models of the beam-pipe are proposed togovern the dynamics of straight or curve pipes with internal radii lessthan their length. The proposed models arediscussed in details. The governing equations of shell-pipe are given forshort and thin pipes subjected to dynamic pressure in the pipes. Then,therecent research development is reviewed on nonlinear vibration,stability, bifurcation and control for pipes conveying fluid. The futuretrends and advances are proposed. From the history ofnonlinear dynamics, one may see that it is very important to choose sometypical systems as models, such as van der Pol, Duffing, Mathieu, Lorenz andso on, for studying low dimensional systems. The motivation of this paperis to represent fluid-reduced vibrations as one of typical nonlinearproblems. It may be considered as a model to investigate nonlinear dynamicsin high dimensional systems since its engineering background is intuitiveand easy to be understood, vibrations of shell and beam are included, itsmathematical model is simple but may present rather rich dynamics, and the results of the mathematical analysis is easy to be explained andapplied. It is expected to establish models of analysis for high-dimensionalsystems and to develop nonlinear dynamics in terms of discussions in this paper.In addition, it may also provide some guidance for establishingthe control theory.

MICROMECHANICS OF HETEROGENEOUS MICROPOLAR MEDIUMS

2004, 34(2): 195-214. doi: 10.6052/1000-0992-2004-2-J2003-007

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Different homogenization schemes are discussed in viewof the order relations for the different length scales. The emphasis is thenplaced on the micro-macro transition from local micropolar mediums to ahomogenized Cauchy medium, suitable for the following order relation of thelength scales $L \gg l \gg A \approx l_m $. The microstructural size effectcan be naturally taken into account in the proposed homogenization scheme.This method is useful for the metal matrix composites, foam matrixcomposites and nanocomposites, in which the microstructural length scales ofthe matrix are important compared to that of the reinforced phase.

PROGRESS OF DAMAGE DETECTION FOR STRUCTURAL HEALTH MONITORING

2004, 34(2): 215-223. doi: 10.6052/1000-0992-2004-2-J2002-111

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This paper discusses the current approaches of structuraldamage detection in structural health monitoring (SHM) and theirrespective features. The damage detection methods are classified into twocategories, one is based on the theory of modal analysis and another isbased on signal processing of the structural dynamic tests. The damage detectionmethod in the first category uses low order vibration modes of structure andrequires dynamic testing on the whole structure, the dynamic responsesof the structure can be calculated from its finite element model. In thesecond category, the damage detection method is usually used to detectdamage of structural components by the damage characteristic parametersextracted from measured dynamic response data without finite elementmodeling of the structure. The concepts of comparative method andnon-comparative method of damage detection are proposed in this paper. Inthe comparative damage detection method, the characteristic parameter of theintact structure is required to serve as the comparing template, while thenon-comparative method determines the damage state directly from themeasured dynamic response of the structure with the help of some physical andengineering knowledge. The problems of signal sensing and processingtechniques and the collocation of sensors used in damage detection are alsodiscussed in this paper. The approach to quantify damage severity and toestimate residual life of the damaged structure by combined activeand passive detecting techniques is proposed.

ON THE MATHEMATICAL SIMULATION OF NON-EQUILIBRIUM HYPERSONIC FLOW AROUND THE FLYING VEHICLE

2004, 34(2): 224-236. doi: 10.6052/1000-0992-2004-2-J2002-101

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The Computational Fluid Dynamics ofhigh-speed flight is developing in parallel with thecomputer technology. In treating the problem macroscopically, the ordinaryway of solving the Euler equations and N-S equations is improved to accountfor the real gas effect, which means including chemical reactions andionization of the gas particles. Microscopically, treating the problem byMonte-Carlo method to simulate the motion of gas particles(DSMC) isalso developed. Although theoretically the DSMC method is applicable to allkinds of flow, the computer time required for computation is enormous,therefore it is only used in special cases and themacroscopic method is mostly used. This paper discusses the hypersonic flightproblems related to the aerodynamic heating, including the choice ofthe mathematical model, the determination of chemical species and theirreactions, the treatment of boundary conditions, the calculation of theheat generated byradiation and so forth. Finally, the proper way of mathematical simulationof hypersonic flight is proposed.

REVIEW ON PLASMA ELECTROLYTIC DEPOSITION

2004, 34(2): 237-250. doi: 10.6052/1000-0992-2004-2-J2003-045

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Plasma electrolytic deposition (PED) is a new technology in surfaceengineering. The paper introduces the main mechanism of PED, as well asitsapplications in different fields such as surface modification of metal,electronic films, medicine films, DLC films and nitrogen-containing carbonfilms etc. The principal mechanism of PED is as follows: when the electrical potentialbetween the anodic and cathode reaches a certain value, the electricalfield strength in the electrode/ electrolyte interface is sufficient toproduce a dielectric breakdown, which is utilized to deposit ceramic layer orto saturate some elements into the substrate. As its applications to thestructuralmaterials, PED is successful in increasing material's anti wearand anti corrosion ability by depositing ceramic layers to light metals suchas aluminum alloy, magnesium alloy and titanium alloy or saturating carbon,nitrogen into steel. Electrolyte containing calcium and phosphorus isutilized to deposit bioactive film on the surface of titanium alloy to formchemical bond with host bone. Appropriate electrolytes are chosen tosynthesize perovskite type electric films such asBaTiO$_{3}$、SrTiO$_{3}$、NaTaO$_3$、SrZrO$_3$ etc. High voltageelectrolysis of organic liquid is utilized to form high performance filmssuch as DLC films and carbon nitride films. The toughening mechanismand some important mechanics problem about PED coatings such as theinfluences of micro defects on macro performance, interface fracturetoughness, residual stress and adhesion strength are discussed and needfurther research work. Ceramic coating deposited with PED on aluminum alloy hasbeen used successfully. Furthermore, PED is also suitable for surfacetreatment for steel, biological active materials and electronic films.

APPROXIMATE THEORITICAL AND EXPERIMENTAL RESEARCH DEVELOPMENT OF CONE PENETRATION RESISTANCE IN STATIC CONE PENETRATION TEST

2004, 34(2): 251-262. doi: 10.6052/1000-0992-2004-2-J2003-055

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Cone resistance plays a very important role in static cone penetrationtests. The studies on thecone resistance in static cone penetration tests are discussedbriefly. Some theoretical methods - bearingcapacity theory, cavity expansion theory, strain path method, movingpoint dislocation method - arereviewed, together with the developments of numerical analysis andexperimental research. At the sametime, the applicabilities of various methods are compared. Bearingcapacity theory is simple, but it cannot be used tosimulate accurately the deep penetration of cone because it ignores the compressibility of soil and theincrease of the initial stress around the shaft. Cavity expansion theory is a simple and more accurate methodof analyzing cone penetration resistance and it considers the influence of compressibility or expansibility ofsoil and the increase of the stress around the shaft in the process of cone penetration on the penetrationresistance. Because cavity expansion theory uses the expansion of cavity to simulate equivalently thepenetration of cone, the results obtained from different simulatingmethods are different. Strain path methodcan solve effectively the undrained penetration problem in saturatedclay, but it is not applicable to sand.Moving point dislocation method considers drainage in part and can predict consolidation coefficient well,but its other applications remain to be tested because it is an analytic approach of linear elasticity. Finite-element method lacks a suitable technique in dealing with the slow penetration of cone and this results insignificant errors and serious difficulties in calculating failure loads. Calibration chamber tests will continueto play an important role in validating and establishing correlations between cone resistance and soilproperties, but the results obtained need to be corrected before they are used in field. Finally, some researchtrends in the field are discussed.

SPATIOTEMPORAL EVOLUTION IN BINARY FLUID MIXTURE CONVECTION WITH THROUGH-FLOW

2004, 34(2): 263-269. doi: 10.6052/1000-0992-2004-2-J2003-005

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Reylaigh-Benard convection in binary fluid mixtures withthrough-flow provides a particular of useful model for the study of patternformation and nonlinear dissipative waves in open flow systems. In thispaper we will introduce some preliminary research results for thissystem. First, wepresent briefly the linear stability analysis and discuss the influence ofthrough-flow on the nonlinear bifurcation of spatial uniform patterns. Then,we focus on our results about the traveling-wave convection of this systemin limited spaces with non-periodic boundary conditions, including existingspatiotemporal states and the dependence of their properties on Rayleighnumber and the aspect rations of the channel. Instead, somefurther studies for this system are outlined.

AERODYNAMICS OF SMALL VEHICLES

2004, 34(2): 270-279. doi: 10.6052/1000-0992-2004-2-J2004-027

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In this review we describe the aerodynamic problems that must beaddressed in order to design a successful small aerial vehicle. The effects of Reynoldsnumber and aspect ratio (AR) on the design and performance of fixed-wing vehicles aredescribed. The boundary-layer behavior on airfoils is especially important in the designof vehicles in this flight regime. The results of a number of experimental boundary-layerstudies, including the influence of laminar separation bubbles, are discussed. Severalexamples of small unmanned aerial vehicles (UAVs) in this regime are described.Also, a brief survey of analytical models for oscillating and flapping-wing propulsionis presented. These range from the earliest examples where quasi-steady, attached flowis assumed, to those that account for the unsteady shed vortex wake as well as flowseparation and aeroelastic behavior of a flapping wing. Experiments that complementedthe analysis and led to the design of a successful ornithopter are also described.

The introduction of application projects on mechanics of 2004

2004, 34(2): 280-280. doi: 10.6052/1000-0992-2004-2-J2004-079

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2004, 34(2): 281-283. doi: 10.6052/1000-0992-2004-2-J2004-080

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A brief introduction of National Microgravity Laboratory, Institute of Mechanics, CAS

2004, 34(2): 284-285. doi: 10.6052/1000-0992-2004-2-J2004-082

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Contents of retrospectives,review articles and spcial issues on applied mechanics reviews,vol.56,2003

2004, 34(2): 286-287. doi: 10.6052/1000-0992-2004-2-J2004-083

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Contents of annual review of Fluid Mechanics

2004, 34(2): 288-288. doi: 10.6052/1000-0992-2004-2-J2004-084

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2004 Vol. 34, No. 2

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