力学进展

BIOMECHANICS AND GENE ACTIVITIES ------ CELEBRATING THE CENTENNIAL OF PROFESSOR CHOU PEIYUAN

2002, 32(4): 484-494. doi: 10.6052/1000-0992-2002-4-J2002-085

Abstract(2026)

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Abstract:
All biological phenomena involving force and motion are in the realm of biomechanics. Mechanics people, from Galileo on to today, have used the principles of conservation of mass, momentum, and energy to make contributions to human well being. They have added to the scientific understanding of locomotion, circulation, respiration, renal and nervous functions, and artificial internal organs. In recent years, many people, working on tissue engineering, arteriosclerosis, and other health problems, have to focus on the problem of finding out how do living tissues change or remodel themselves under stress. They found that some of the classical conservation laws do notapply, and there is a problem of introducing new axioms to biomechanics. The purpose of the present paper is to discuss these new axioms, then go on to point out that the basic reason for these new axioms is the activity of the genes in our cells. Some of our genes work daily to control our lives. Their functions are not limited to genetics and mutation. This points to a new lead to new thoughts. A new science is waiting to be developed.

ON THE STATISTICAL VORTES STRUCTURE THEORY OF TURBULENCE

2002, 32(4): 505-512. doi: 10.6052/1000-0992-2002-4-J2002-092

Abstract(2046)

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Abstract:
The statistical vortex structure theory of turbulence was put forward by late professor Zhou in the 1950s'. With the efforts of him and his students during the half century, it hasbecome a statistical theory of turbulence with a special feature. Now in order to commemoration of the 100th anniversary of professor Zhou's birthday, this paper gives a summary and anoutline of this theory, which includes the vortex solutions as turbulent elements, the possible vortex structures, the suitable statistical average methods and the statistical rules of turbulence, etc.

COMPARISON AND EVALUATION OF ANALYTICAL APPROACHES TO STRUCTURAL DYNAMIC MODEL CORRECTION

2002, 32(4): 513-525. doi: 10.6052/1000-0992-2002-4-J2001-088

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Considerable discrepancies exist between predictions from a structural dynamic model and experimental results of a laboratory model or actual structure when the two are compared. Updating the existing dynamic model based on modal test data is very important in order to precisely predict actual behaviors of the structure via the structural dynamic model. This paper reviews the procedures for refining a structural dynamic model from modal test data by different approaches which are used effectively, including the modal sensitivity method, neural networks method and Genetic algorithm, together with the recent research advances in this field. Some problems of dynamic model correction encountered in the actual applications such as incomplete modal test data and robustness of correction, as well as the factors affecting the computational efficiency and solution convergence, are discussed. Merits and defects of these proposed methods are also discussed and some current problems needed to be solved in the future are pointed out by comparison of numerical results of a real 5-story-steel-frame model updating from limited modal test data.

CURRENT STUDY, APPLICATION AND DEVELOPMENT TREND OF MESHLESS METHODS

2002, 32(4): 526-534. doi: 10.6052/1000-0992-2002-4-J2001-116

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Meshless methods are a type of new numerical analysis method. As an important complement and development of modern numerical analysis methods, forward processing of some engineering problems and computation analysis of crack extension are simplified greatly by meshless methods. Meshless methods are developed rapidly and have obtainedmuch attention in the field of international computation mechanics recently. The paper summarizes the fundamentals and the features of various kinds of meshless methods,together with some comments on their achievement and latest developments. Some advantages of meshless methods and some problems that have to be solved about meshless methods at present are discussed.

ADVANCES IN REPRODUCING KERNEL PARTICLE METHOD

2002, 32(4): 535-544. doi: 10.6052/1000-0992-2002-4-J2002-001

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The reproducing kernel particle method (RKPM), which utilizes the notions of the convolution theorem, multiresolution analysis and meshless properties, is reviewed. Emphasis is put on the reproducing kernel approximations and implementation of essential boundary conditions for RKPM. An overview of the current application areas of RKPM is given including structural dynamics, large deformation, hyperelasticity, computational fluid mechanics (CFD), damage problems and microelectromechanical systems analysis. Some future research areas, from the point of view of engineering application and futher development of RKPM, are pointed out. These promising research areas may include mould filling simulation, meshless modal analysis, treatment of essential boundary conditions, coupling to finite element method, enhancement of the efficency of RKPM and development ofmeshless environment.

Measurement of mechanical properties of mems materials

2002, 32(4): 545-562. doi: 10.6052/1000-0992-2002-4-J2001-083

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The rapid developments of Microelectromechanical systems (MEMS) promote studies on testing microscale mechanicalproperties for their materials. Firstly, recent methods for testing microscale mechanical properties are summarized, based on four distinct types of tests, nanoindentation/scratch, beam and film bend, tension, and torsion. The integration of the sample and loading system on the microscopic scale is explained in detail. Si, SiO2, Si3N4, Au, Ti, Ni are used in these tests. Experimental results are introduced, including elastic modulus, residual stress, yield strength, fracture strength, fatigue strength, and so on. Finally, a brief discussion on future developments is given.

PROGRESS IN MECHANICAL PROPERTIES OF CARBON NANOTUBE AND CARBON-NANOTUBE-BASED COMPOSITES

2002, 32(4): 563-578. doi: 10.6052/1000-0992-2002-4-J2001-114

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This paper reviews the progress on the mechanical behavior of carbon nanotubes and carbon-nanotube-basedcomposites. Firstly, the structure stability and mechanical properties of carbon nanotubes such as theoretical predictions and experimental results are introduced. Secondly, developments on carbon-nanotube-based composites are summarized, including carbon nanotube-polymer composites, carbon nanotube-metal composites and carbon nanotube-ceramics composites. These composites will benefit from the exceptional mechanical properties of carbon nanotubes, but one must pay attention to the problem of load transfer efficiency. Finally, some future development trends are also presented.

MECHANICAL MODEL AND NUMERICAL SIMULATION OF FRACTUR EPROCESS OF CONCRETE

2002, 32(4): 579-598. doi: 10.6052/1000-0992-2002-4-J2001-001

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Concrete is a typical heterogeneous quasi-brittlematerial used in engineering, and its fracture process is very complex. Main progresses on the study of the fracture and fracture process of concrete are reviewed, a few numerical methods and models used to simulate the fracture process of concrete at macroscopic or mesoscopic level are discussed. At last, the mesomechanical model proposed by authors for simulating the macroscopic fracture process of concrete is briefly introduced.

PLUG-FLOW DENSE PHASE PNEUMATIC CONVEYING

2002, 32(4): 599-612. doi: 10.6052/1000-0992-2002-4-J2001-040

Abstract(2139)

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The experimental equipment of pneumatic conveying is introduced. The pressure drop prediction in horizontal plug-flowpneumatic conveying is reviewed. The calculations of pressure drop used three different method are carring out and are compared withexperimental data. Numerical simulation using the methods ofcharacteristics in a horizonal pipeline, the pressure drop in inclined pipeline, and the long distance plug-flow pneumatic conveying are reviewed. Finally, the development trends of this subject are discussed.

WHY DID THE WORLD TRADE CENTER COLLAPSE?------SIMPLE ANALYSIS

2002, 32(4): 613-624. doi: 10.6052/1000-0992-2002-4-J2002-040

Abstract(2200)

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Abstract:
This paper presents a simplified approximate analysis of the overall collapse of the towers of World Trade Center in New York on September 11, 2001. The analysis shows that if prolonged heating caused the majority of columns of a single floor to lose their load carrying capacity, the whole tower was doomed. Despite optimistic simplifying assumptions, the sturctural resistance is found to be an order of magnitude less than necessary for survival.

2002 Vol. 32, No. 4

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