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Analysis of sand particles’ lift-off and incident velocities in wind-blown sand flux

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Acta Mechanica Sinica 2013年第2期29卷 158-165页

作者： Tian-Li Bo Xiao-Jing Zheng Shao-Zhen Duan Yi-Rui Liang key laboratory of mechanics on western disaster and environment Department of MechanicsLanzhou University

In the research of windblown sand movement,the lift-off and incident velocities of saltating sand particles play a significant role in bridging the spatial and temporal scales from single sand particle＇s motion to windblown sand *** this paper,we achieved wind tunnel measurements of the movement of sand particles near sand bed through improving the wind tunnel experimental scheme of paticle image velocimetry（PIV） and data processing *** then the influence of observation height on the probability distributions of lift-off and incident velocities of sand particles was *** results demonstrate that the observation height has no obvious influence on the distribution pattern of the lift-off and incident velocities of sand particles,i.e.,the probability distribution of horizontal and vertical velocities of lift-off and incident sand particles follow a Gaussian distribution and a negative exponential distribution,***,it influences the center of the Gaussian distribution,the decay constant and the amplitude of the negative exponential distribution.

关键词： Probability distribution·Sand particles' horizontal velocities·Sand particles' vertical velocities·Center of the Gaussian distribution·Decay constant of the negative exponential distribution

Stretching strongly confined semiflexible polymer chain

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Applied Mathematics and mechanics(English Edition) 2014年第10期35卷 1233-1238页

作者：王记增李润华 key laboratory of mechanics on disaster and environment in western China the Ministry of Education College of Civil Engineering and Mechanics Lanzhou University

By the so-called wormlike chain （WLC） model in polymer physics envision- ing an isotropic rod that is continuously flexible, the force-extension relations of semi- flexible polymer chains strongly constrained by various confinements are theoretically investigated, including a slab-like confinement where the polymer chains are sandwiched between two parallel impenetrable walls, and a capped nanochannel confinement with a circular or rectangular cross-section where the chains are bounded in three directions. The Brownian dynamics （BD） simulations based on the generalized bead-rod （GBR） model are performed to verify the theoretical predictions.

关键词： semiflexible polymer chain confinement wormlike chain (WLC) model,Brownian dynamics (BD) simulation

Temperature Effects on Unsaturated Hydraulic Property of Bentonite-Sand Buffer Backfilling Mixtures

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Journal of Wuhan University of Technology(Materials Science) 2013年第3期28卷 487-493页

作者：张明张虎元 ZHOU Lang JIA Lingyan key laboratory of mechanics on disaster and environment in western China Lanzhou University

The influence of temperature on the engineered properties of bentonite-sand mixtures （B/S） is of major concern in the design of engineered barriers in underground repositories for high-level radioactive waste disposal. We experimentally studied the influence of temperature on soil unsaturated hydraulic properties related to water holding capacity and permeability of GMZ B/S in China. The vapor equilibrium method and water infiltration apparatus were used to measure the soil water characteristic curve （SWCC） and unsaturated hydraulic conductivity （k）. The results show that the SWCC under different temperatures from 20℃ to 60 ℃ tends to be the same. Temperature influence on unsaturated permeability is more relevant at low suctions, no clear effect is detected below a degree of saturation of 74%, and experimental data show that temperature dependence on unsaturated permeability is small.

关键词： high-level radioactive waste disposal engineered barrier temperature soil water characteristic curve unsaturated hydraulic conductivity

Probability of rebound and eject of sand particles in wind-blown sand movement

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Acta Mechanica Sinica 2007年第5期23卷 471-475页

作者： Li Xie Xiaojing Zheng key laboratory of mechanics on western disaster and environment Lanzhou University Lanzhou 730000 China

When incident particles impact into a sand bed in wind-blown sand movement, rebound of the incident particles and eject of the sand particles by the incident particles affect directly the development of wind sand flux. In order to obtain rebound and eject lift-off probability of the sand particles, we apply the particle-bed stochastic collision model presented in our pervious works to derive analytic solutions of velocities of the incident and impacted particles in the postcollision bed. In order to describe randomness inherent in the real particle-bed collision, we take the incident angle, the impact position and the direction of resultant action of sand particles in sand bed on the impacted sand particle as ran- dom variables, and calculate the rebound and eject velocities, angles and coefficients （ratio of rebound and eject velocity to incident velocity）. Numerical results are found in accordance with current experimental results. The rebound and eject liftoff probabilities versus the incident and creeping velocities are predicted.

关键词： Wind-blown sand movement Rebound andeject coefficient Rebound and eject lift-off probability

Power law creep and relaxation with the atomic force microscope:Determining viscoelastic property of living cells

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Science China(Technological Sciences) 2019年第5期62卷 781-786页

作者： BU Yang LI Long WANG JiZeng key laboratory of mechanics on disaster and environment in western China Ministry of Education College of Civil Engineering and Mechanics Lanzhou University

We have proposed a method to determine the deformation creep and stress relaxation of living cells by using the atomic force microscope(AFM). Based on this method, we have measured the creep and relaxation trajectories of the undifferentiated(HGC-27) and poorly differentiated(AGS) human gastric cancer cells, which were then used to determine their linear viscoelastic properties. We found that the AGS cells are linear viscoelastic materials with the power law creep compliance and relaxation modulus. In contrast, the HGC-27 cells are nonlinear since their measured creep and relaxation behaviours fail to satisfy a verification relation derived based on the linear viscoelastic theory. This fact implies that most traditional methods are not appropriate in determining viscoelastic properties of living cells by simply assuming linear constitutive relation and using classical model of linear springs and dashpots. The combination of suggested power law expression and AFM indentation measurements on the creep compliance and relaxation modulus provides a unique way in determining the viscoelastic properties of living cells.

关键词： atomic force microscope linear viscoelasticity creep relaxation power law living cells

A simultaneous space-time wavelet method for nonlinear initial boundary value problems

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Applied Mathematics and mechanics(English Edition) 2018年第11期39卷 1547-1566页

作者： Jizeng WANG Lei ZHANG Youhe ZHOU key laboratory of mechanics on disaster and environment in western China the Ministry of Education College of Civil Engineering and Mechanics Lanzhou University

A high-precision and space-time fully decoupled numerical method is developed for a class of nonlinear initial boundary value problems. It is established based on a proposed Coiflet-based approximation scheme with an adjustable high order for the functions over a bounded interval, which allows the expansion coefficients to be explicitly expressed by the function values at a series of single points. When the solution method is used, the nonlinear initial boundary value problems are first spatially discretized into a series of nonlinear initial value problems by combining the proposed wavelet approximation and the conventional Galerkin method, and a novel high-order step-by-step time integrating approach is then developed for the resulting nonlinear initial value problems with the same function approximation scheme based on the wavelet theory. The solution method is shown to have the N th-order accuracy, as long as the Coiflet with [0, 3 N-1]compact support is adopted, where N can be any positive even number. Typical examples in mechanics are considered to justify the accuracy and efficiency of the method.

关键词： nonlinear initial boundary value problem Coiflet numerical method

DPTM simulation of aeolian sand ripple

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Science China(Physics,mechanics & Astronomy) 2008年第3期51卷 328-336页

作者： ZHENG XiaoJing BO TianLi XIE Li key laboratory of mechanics on western disaster and environment Lanzhou UniversityLanzhou 730000China

Aeolian sand ripple and its time evolution are simulated by the discrete particle tracing method (DPTM) presented in this paper. The difference between this method and the current methods is that the former can consider the three main factors relevant to the formation of natural aeolian sand ripples,which are the wind-blown sand flux above the sand bed formed by lots of sand particles with different di-ameters,the particle-bed collision and after it the rebound and ejection of sand particles in the sand bed,the saltation of high-speed sand particles and the creep of low-speed sand particles,respectively. The simulated aeolian sand ripple is close to the natural sand ripple not only in basic shape and characteristic,particle size segregation and stratigraphy,but also in formation stages. In addition,three important speeds can be obtained by this method,which are the propagation speed of the saturated aeolian sand ripple and the critical frictional wind speeds of emergence and disappearance of sand ripple.

关键词： wind-blown sand flux aeolian sand ripple discrete particle tracing method (DPTM) mixed-particle-size creep

Thermoelastic stress analysis of multilayered films in a micro-thermoelectric cooling device

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Acta Mechanica Sinica 2012年第6期28卷 1644-1650页

作者： Yu-Mei Yang Xing-Zhe Wang Wen-Jie Zhang key laboratory of mechanics on environment and disaster in western China The Ministry of Education of China College of Civil Engineering and Mechanics Lanzhou University

This paper presents an analytical solution for the thermoelastic stress in a typical in-plane＇s thin-film micro- thermoelectric cooling device under different operating con- ditions. The distributions of the permissible temperature fields in multilayered thin-films are analytically obtained, and the characteristics, including maximum temperature dif- ference and maximum refrigerating output of the thermo- electric device, are discussed for two operating conditions. Analytical expressions of the thermoelastic stresses in the layered thermoelectric thin-films induced by the tempera- ture difference are formulated based on the theory of mul- tilayer system. The results demonstrate that, the geometric dimension is a significant factor which remarkably affects the thermoelastic stresses. The stress distributions in layers of semiconductor thermoelements, insulating and support- ing membrane show distinctly different features. The present work may profitably guide the optimization design of high- efficiency micro-thermoelectric cooling devices.

关键词： Thermoelectric cooling device Multilayeredthin-film Thermoelastic stress - Analytical solution

Degradation of critical current in Bi2212 composite wire under compression load

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Applied Mathematics and mechanics(English Edition) 2017年第12期38卷 1773-1784页

作者： Zhiyang WANG Huadong YONG Youhe ZHOU key laboratory of mechanics on environment and disaster in western China College of Civil Engineering and MechanicsLanzhou UniversityLanzhon 730000China

Since Bi2Sr2Ca1Cu2O8＋x（Bi2212） wires are subject to mechanical loadings, degradation of critical current will occur. The effect of compressive loadings on the critical current of Bi2212 wire is studied by considering micro-buckling of filament. A Bi2212 wire is regarded as a unidirectional filament-reinforced composite in the theoretical analysis. By considering the influence of inclusion, the micro-buckling wavelength can be derived by using a two-dimensional model. Based on the experimental results, the critical current is fitted as a function of buckling wavelength. It is found that the decrease of the critical current is directly proportional to the reciprocal of square of the buckling wavelength. Change of micro-buckling wavelength with material parameters is discussed. A critical strain in the wire with a filament bridge is analyzed using the finite element method.

关键词： micro-buckling Bi2Sr2Ca1Cu2O8+x(Bi2212) wire wavelength critical current