力学进展

The study on dynamics modelling and control of flexible mechanical arms

2001, 31(1): 1-8. doi: 10.6052/1000-0992-2001-1-J1999-027

Abstract(2000)

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Abstract:

In this paper, a review has been made on dynamics modelling and control of flexible mechanical arm, including the rotation algebra method, the method based on Lagrange equation and the method based on model identification in dynamics modelling, the PD control, the feedback control, the adaptive control, the robust control, the predictive control, the nonlinear control and the intelligent control in dynamics control, and the mixed control. The problems to be solved in dynamics modelling and dynamics control of flexible mechanical arms are discussed.

ADVANCES IN THE NUMERICAL METHODS FOR LAGRANGE'S EQUATIONS OF MULTIBODY SYSTEMS

2001, 31(1): 9-17. doi: 10.6052/1000-0992-2001-1-J1999-078

Abstract(2165)

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The Lagrange's method is one of the general methods to derive the dynamic equations for multibody systems, which are in the form of ordinary differential equations or differential-algebraic equations. Numerical analysis is an important way to investigate the behaviors of the dynamics of multibody systems. In this paper, the first kind and the second kind of Lagrange's equations and the modified Lagrange's equations for multibody systems with their canonical forms are introduced, together with the characteristics of their numerical solutions. The advances are reviewed in the following numerical methods, symplectic algorithms and the implicit algorithms for the dynamic equations of multibody systems, as well as other algorithms for dynamic behaviors of multibody systems, such as Poincaré maps and Lyapunov exponents.

DELAYED FEEDBACK CONTROL OF CHAOTIC SYSTEMS AND ITS THEORETICAL AND EXPERIMENTAL RESEARCHES

2001, 31(1): 18-32. doi: 10.6052/1000-0992-2001-1-J1999-093

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This paper summarizes the recent progress in the delayed feedback control (DFC) technique for controlling chaos. The theoretical results on the limitation and controllability of delayed feedback control with respect to the stabilization of unstable fixed point or unstable periodic orbit and the experimental results of the delayed feedback control's applications in controlling chaos in electrical circuits and magneto-elastic beam are summed up. The future research and development trends of the delayed feedback control are discussed.

DEVELOPMENT OF ROLLING CONTACT MECHANICS OF WHEEL/RAIL SYSTEMS

2001, 31(1): 33-46. doi: 10.6052/1000-0992-2001-1-J1999-068

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Rolling contact mechanics of wheel/rail systems mainly involve the study on the performance of wheel/rail in rolling contact. Due to its complexity, the study can be divided into six independent but interconnected parts. They are, respectively, creep theory of wheel/rail in rolling contact, adhesion, corrugation on the contact surfaces of wheel/rail, rolling contact fatigue, derailment and wheel/rail noise. In the paper, a historical introduction to the research fields mentioned above is given. The advantages and disadvantages of some typical creep theoretical models of whell/rail in rolling contact are emphatically discussed because they are widely applied to the dynamics of railway vehicle and track structure and wheel/rail performance. According to many serious problems concerning the performance of wheel/rail system in practical railway engineering, the authors suggest some further researches on the creep theory of wheel/rail in rolling contact, experimental method and important factors on the performance of wheel/rail in rolling contact.

PROGRESS IN NANOSTRUCTURED MATERIALS

2001, 31(1): 47-61. doi: 10.6052/1000-0992-2001-1-J2000-020

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Nanostructured materials are characterized by a typical structural size below 100nm. Due to its unique properties, great attention to nanostructured materials has increased in past years. The recent progress in nanostructured materials, especially their generation and synthesis, microstructure, mechanical and thermodynamic properties, is summarized in this paper. This paper also discusses several research hotspots of nanostructured materials and related molecular dynamics simulations. Several future research topics are also presented.

MECHANICAL PROPERTIES OF NANOCRYSTALLINE METALS

2001, 31(1): 62-69. doi: 10.6052/1000-0992-2001-1-J2000-016

Abstract(1438)

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This paper reviews the progress on studying the mechanical properties of nanocrystalline metals, such as the elastic modui, hardness and Hall-Petch relationship, tensile and compressive properties, creep and fatigue properties.

A REVIEW OF STUDIES ON TURBOMACHINERY TIP GAP LEAKAGE FLOW

2001, 31(1): 70-83. doi: 10.6052/1000-0992-2001-1-J1999-080

Abstract(1992)

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The objective of this paper is to review and assess various models, experiment techniques and numerical methods for the analysis of the fluid mechanism about the tip gap leakage flow within turbomachines. The origins and effects of tip gap leakage flow on the performance of turbomachines are discussed with the emphasis on the physical origins of tip gap leakage flow. Blades are concerned with two types of flows, that is diffusing, or compressor type flows and accelerating, or turbine type flows. A brief review on the tip gap leakage flow of the blades is made as a main content of the paper. It can be found from the review that the major issues at present about the tip leakage flow of turbomachinery are focused on the leakage vortex structure, the leakage flow model, the vorticity, and the shock-leakage vortex interaction, etc. Meanwhile, recommendations are made for future research, including the vorticity in high-speed turbine and compressor, the tip leakage vortex breakdown, the relationship between stall and leakage flow, and the size of blockage region.

ADVANCES IN NUMERICAL SIMULATIONS ON THE HEMODYNAMICS OF INTRACRANIAL ANEURYSMS AND THEIR RUPTURE MECHANISM

2001, 31(1): 84-94. doi: 10.6052/1000-0992-2001-1-J1999-109

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The dependence of the formation, development and rupture of intracranial aneurysms on their hemodynamic parameters has recently been studied numerically by the finite element method. Such studies provide some important guidelines for clinical medicine, especially for interventional therapy. This paper reviews some typical computational models and results concerning the hemodynamics and rupture mechanicsm of intracranial aneurysms.

THE ADVANCE AND REVIEW ON FROZEN SOIL MECHANICS

2001, 31(1): 95-102. doi: 10.6052/1000-0992-2001-1-J2000-007

Abstract(2239)

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The recent advances in frozen soil mechanics are demonstrated and discussed from four aspects: (1) Test studies on the mechanical properties of the frozen soil; (2) Heat conductivity properties of the mixture materials of the freezing soil; (3) Water migration behaviors in the freezing soil; and (4) The Heat-Moisture-Deformation Coupling Models. A discussion on above four areas is made for further researches, and suggestions are offered as follows: (a) The research should be transferred from the deformation and strength properties of the frozen soil to the heat and moisture migration behaviors of the freezing and thawing soil, which is often important in engineering. (b) More attentions should be paid to the field tests with complex water and heat boundaries, instead of the lab tests with very simple boundaries. (c) The structure and grade size distribution of the frozen soil should be considered in the further test studies.

NONHOLONOMIC MECHANICS

2001, 31(1): 103-142. doi: 10.6052/1000-0992-2001-1-J2000-105

Abstract(2057)

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This is a concise review of nonholonomic mechanics. It deals with the fundamental concepts, variational principles, equations of motion, special problems, integration methods, algebraic structure, and the geometrical methods of nonholonomic mechanics. It also points out some problems for future research. There are 90 references.

2001 Vol. 31, No. 1

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