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Micro- and nano-mechanics in China： A brief review of recent progress and perspectives

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Science China(Physics,mechanics & Astronomy) 2018年第7期61卷 18-31页

作者： ZhiPing Xu QuanShui Zheng Applied mechanics Laboratory and Center for Nano and Micro mechanics Department of Engineering Mechanics Tsinghua UniversityBeijing 100084 China

The past three decades have witnessed the explosion of nanoscience and technology, where notable research eftbrts have been made in synthesizing nanomaterials and controlling nanostructures of bulk materials. The uncovered mechanical behaviors of structures and materials with reduced sizes and dimensions pose open questions to the community of mechanicians, which expand the framework of continuum mechanics by advancing the theory, as well as modeling and experimental tools. Researchers in China have been actively involved into this exciting area, making remarkable contributions to the understanding of nanoscale mechanical processes, the development of multi-scale, multi-field modeling and experimental techniques to resolve the processing-microstructures-properties relationship of materials, and the interdisciplinary studies that broaden the subjects of mechanics. This article reviews selected progress made by this community, with the aim to clarify the key concepts, methods and applications of micro- and nano-mechanics, and to outline the perspectives in this fast-evolving field.

关键词： micro- and nano-mechanics multi-scale and multi-field methods nanotechnology nanomaterials nanostructurcs

PRELIMINARY PROBE INTO OPTIMIZATION ON PROPULSION IN SHORT DISTANCE COMPETITIVE SWIMMING

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Applied Mathematics and mechanics(English Edition) 2006年第1期27卷 117-124页

作者：王新峰王连泽 department of Engineering mechanics

Based on the modeling of dynamics and energy conversion in competitive swimming, the optimal control theory was used to make an optimization analysis of the distance traveled in a given time. Using the records of the 27th Olympics and the results from previous research, an optimal solution of propulsion was derived using some hypotheses and constraints. Correspondingly, the optimal tactic for velocity and energy was put forward which was in agreement with the practice.

关键词： competitive swimming energy optimization propulsion

Experimental study on spectrum and multi-scale nature of wall pressure and velocity in turbulent boundary layer

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Chinese Physics B 2015年第6期24卷 385-394页

作者：郑小波姜楠 department of mechanics Tianjin University Tianjin Key Laboratory of Modern Engineering mechanics The State Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of Sciences

When using a miniature single sensor boundary layer probe, the time sequences of the stream-wise velocity in the turbulent boundary layer （TBL） are measured by using a hot wire anemometer. Beneath the fully developed TBL, the wall pressure fluctuations are attained by a microphone mechanism with high spatial resolution. Analysis on the statistic and spectrum properties of velocity and wall pressure reveals the relationship between the wall pressure fluctuation and the energy-containing structure in the buffer layer of the TBL. Wavelet transform shows the multi-scale natures of coherent structures contained in both signals of velocity and pressure. The most intermittent wall pressure scale is associated with the coherent structure in the buffer layer. Meanwhile the most energetic scale of velocity fluctuation at y＋ = 14 provides a specific frequency f9 ≈ 147 Hz for wall actuating control with Ret = 996.

关键词： multi-scale coherent structures hot wire anemometry microphone wavelet transform

Analytical solutions for plane problem of functionally graded magnetoelectric cantilever beam

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Applied Mathematics and mechanics(English Edition) 2015年第7期36卷 955-970页

作者： Yanmei YUE Xiaofen YE Kaiyu XU Shanghai Institute of Applied Mathematics and mechanics Shanghai Key Laboratory of Mechanics in Energy EngineeringDepartment of MechanicsShanghai University

In this paper, an exact analytical solution is presented for a transversely isotropic functionally graded magnetomelectro-elastic （FGMEE） cantilever beam, which is subjected to a uniform load on its upper surface, as well as the concentrated force and moment at the free end. This solution can be applied for any form of gradient distribution. For the basic equations of plane problem, all the partial differential equations governing the stress field, electric, and magnetic potentials are derived. Then, the expressions of Airy stress, electric, and magnetic potential functions are assumed as quadratic polynomials of the longitudinal coordinate. Based on all the boundary conditions, the exact expressions of the three functions can be determined. As numerical examples, the material parameters are set as exponential and linear distributions in the thickness direction. The effects of the material parameters on the mechanical, electric, and magnetic fields of the cantilever beam are analyzed in detail.

关键词： functionally graded material (FGM) analytical solution magnetoelectrie(ME) material cantilever beam plane stress problem

Lithiation-enhanced charge transfer and sliding strength at the silicon-graphene interface:A first-principles study

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Acta Mechanica Solida Sinica 2017年第3期30卷 254-262页

作者： Cheng Chang Xiaoyan Li Zhiping Xu Huajian Gao Applied mechanics Laboratory Department of Engineering Mechanics Center for Nano and Micro MechanicsCenter for Advanced Mechanics and Materials Tsinghua University School of Engineering Brown University

The application of silicon as ultrahigh capacity electrodes in lithiumion batteries has been limited by a number of mechanical degradation mechanisms including fracture, delamination and plastic ratcheting, as a result of its large volumetric change during lithiation and delithiation. Graphene coating is one feasible technique to mitigate the mechanical degradation of Si anode and improve its conductivity. In this paper, first-principles calculations are performed to study the atomic structure, charge transfer and sliding strength of the interface between lithiated silicon and graphene. Our results show that Li atoms segre- gate at the （lithiated） Si-graphene interface preferentially, donating electrons to graphene and enhancing the interfacial sliding resistance. Moreover, the interfacial cohesion and sliding strength can be further enhanced by introducing single-vacancy defects into graphene. These findings provide insights that can guide the design of stable and efficient anodes of silicon/graphene hybrids for energy storage applications.

关键词： Lithium-ion batteries Silicon anode Graphene coating Interracial sliding strength First-principles calculations

Stability of focal adhesion enhanced by its inner force fluctuation

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Chinese Physics B 2015年第8期24卷 632-638页

作者：毛志秀陈笑风陈彬 department of Engineering mechanics Zhejiang University

Cells actively sense and respond to mechanical signals from the extracellular matrix through focal adhesions. By representing a single focal adhesion as a cluster of slip bonds, it has been demonstrated that the cluster often became unstable under fluctuated forces. However, an unusual case was also reported, where the stability of the cluster might be substantially enhanced by a fluctuated force with a relatively low fluctuation frequency and high fluctuation *** an observation cannot be explained by the conventional fracture theory of fatigue. Here, we intensively investigate this intriguing observation by carrying out systematic parametric studies. Our intensive simulation results indicate that stability enhancement of this kind is in fact quite robust, which can be affected by the stochastic features of a single bond and the profile of the fluctuated forces such as the average value of bond force. We then suggest that the fluctuation of traction force within a focal adhesion might enhance its stability in a certain way.

关键词： focal adhesion slip bonds stability fluctuated forces

Developing theory of probability density function for stochastic modeling of turbulent gas-particle flows

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Applied Mathematics and mechanics(English Edition) 2018年第7期39卷 1019-1030页

作者： Lixing ZHOU department of Engineering mechanics Tsinghua University

Turbulent gas-particle flows are studied by a kinetic description using a prob- ability density function （PDF）. Unlike other investigators deriving the particle Reynolds stress equations using the PDF equations, the particle PDF transport equations are di- rectly solved either using a finite-difference method for two-dimensional （2D） problems or using a Monte-Carlo （MC） method for three-dimensional （3D） problems. The proposed differential stress model together with the PDF （DSM-PDF） is used to simulate turbulent swirling gas-particle flows. The simulation results are compared with the experimental results and the second-order moment （SOM） two-phase modeling results. All of these simulation results are in agreement with the experimental results, implying that the PDF approach validates the SOM two-phase turbulence modeling. The PDF model with the SOM-MC method is used to simulate evaporating gas-droplet flows, and the simulation results are in good agreement with the experimental results.

关键词： probability density function(PDF)modeling turbulent flow gas-particleflow

THERMOELASTICALLY COUPLED AXISYMMETRIC NONLINEAR VIBRATION OF SHALLOW SPHERICAL AND CONICAL SHELLS

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Applied Mathematics and mechanics(English Edition) 2004年第4期25卷 430-439页

作者：王永岗戴诗亮 department of Applied mechanics China Agricultural University department of Engineering mechanics Tsinghua University

The problem of axisymmetric nonlinear vibration for shallow thin spherical and conical shells when temperature and strain fields are coupled is studied. Based on the large deflection theories of von Krmn and the theory of thermoelasticity, the whole governing equations and their simplified type are derived. The time-spatial variables are separated by Galerkin's technique, thus reducing the governing equations to a system of time-dependent nonlinear ordinary differential equation. By means of regular perturbation method and multiple-scales method, the first-order approximate analytical solution for characteristic relation of frequency vs amplitude parameters along with the decay rate of amplitude are obtained, and the effects of different geometric parameters and coupling factors as well as boundary conditions on thermoelastically coupled nonlinear vibration behaviors are discussed.

关键词： shallow spherical shell shallow conical shell thermoelastically coupled nonlinear vibration perturbation method

Convection and correlation of coherent structure in turbulent boundary layer using tomographic particle image velocimetry

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Chinese Physics B 2014年第10期23卷 323-333页

作者：王维管新蕾姜楠 department of mechanics Tianjin University Tianjin Key Laboratory of Modern Engineering mechanics The State Key Laboratory of Nonlinear mechanics Institute of Mechanics Chinese Academy of Sciences

The present experimental work focuses on a new model for space-time correlation and the scale-dependencies of convection velocity and sweep velocity in turbulent boundary layer over a flat wail. A turbulent boundary layer flow at Reo = 2460 is measured by tomographic particle image velocimetry （tomographic PIV）. It is demonstrated that arch, cane, and hairpin vortices are dominant in the logarithmic layer. Hairpins and hairpin packets are responsible for the elongated low-momentum zones observed in the instantaneous flow field. The conditionally-averaged coherent structures systemically illustrate the key roles of hairpin vortice in the turbulence dynamic events, such as ejection and sweep events and energy transport. The space-time correlations of instantaneous streamwise fluctuation velocity are calculated and confirm the new elliptic model for the space-time correlation instead of Taylor hypothesis. The convection velocities derived from the space-time correlation and conditionally-averaged method both suggest the scaling with the local mean velocity in the logarithmic layer. Convection velocity result based on Fourier decomposition （FD） shows stronger scale- dependency in the spanwise direction than in streamwise direction. Compared with FD, the proper orthogonal decomposition （POD） has a distinct distribution of convection velocity for the large- and small-scales which are separated in light of their contributions of turbulent kinetic energy.

关键词： turbulent boundary layer tomographic particle image velocimetry space-time correlation ellipticmodel