Table of Content

31 October 2016, Volume 22 Issue 5

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Dual boundary integral equations and numerical solutions for particles and cracks in full space

MA Hang1, PAN Meng2

2016, 22(5):  533-544.  doi:10.3969/j.issn.1007-2861.2015.02.020

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As elastic solids contain particles and cracks, a computational model is proposed for the analysis of particles and cracks in full space using dual boundary integral equations in the displacement discontinuity formulation. The method avoids the difficulty of loading the objects under study in full space. Numerical analysis is carried out for some typical cases with a few particles and cracks using a discrete form of boundary integral equations. A boundary point method and Gauss collocation are used for discretization of the particle boundary or interface, and the crack surface, respectively. The stress intensity factors of cracks are computed. Mutual effects between particles and cracks are investigated and compared with those in the literature, verifying correctness and reliability of the proposed computational model and the program.

Beam splitter in optical waveguides designed by shortcuts to adiabaticity

PU Junhui, SHI Jielong, WU Renhua, CHEN Xi

2016, 22(5):  545-551.  doi:10.3969/j.issn.1007-2861.2015.02.007

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Shortcuts to adiabaticity have been proposed to accelerate “slow” adiabatic processes with the applications in atom, molecular and optical physics. Based on the quantum optical analogy of coupled waveguide, the coupling coefficient and propagating constant are designed by using shortcuts to adiabaticity, to realize optical beam splitters in short length. Compared with resonant and adiabatic couplers by numerical simulation, the designed waveguide is demonstrated its advantages on shorter length and high stability.

Cell reprogramming based on hierarchical networks and feedback mechanism

LIU Shijin, LIU Yanwei, WANG Ruiqi

2016, 22(5):  552-559.  doi:10.3969/j.issn.1007-2861.2016.01.017

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The process that pluripotent cells differentiate and finally commit to certain cell lineages originates from stem cells. It is performed with a series of cellfate decisions driven by pluripotent progenitors. Reprogramming of pluripotent cells can occur in this process. Focusing on the cell differentiation and presenting a hierarchical network with double negative feedbacks, the reprogramming strategy in the pathways of cell differentiation can be induced by integrated influence of a hierarchical network and the feedback regulatory mechanisms.

Dissipative particle dynamics simulation of nanoparticles droplet

SHEN Shiyuan, ZHOU Zhewei

2016, 22(5):  560-572.  doi:10.3969/j.issn.1007-2861.2015.02.015

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Mesoscale dissipative particle dynamics was used to model a nanofluid system considering electrostatic interaction. The effects on the droplet static contact angle of the concentration and charge quantity of the nanoparticles were investigated. Computational results were qualitatively agreed with experiments.

Dynamics modeling and analysis of offshore wind turbines under complicated loads

WANG Qingzhan, ZHAO Jianzhong, GUO Xingming

2016, 22(5):  573-585.  doi:10.3969/j.issn.1007-2861.2015.02.016

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By analyzing the structure and complexity of offshore wind turbines (OWTs), a beam model with free end carrying a concentrated mass body was built to analyze dynamical characteristics of OWTs subject to adverse working environment loads. Factors including vertical excitation, self-weight, rotary inertia and variety of stiffness were considered to study the effect on offshore wind turbines. A general and uniform governing equation was built by taking advantages of the Heaviside step function and Dirac delta function. Based on the Galerkin truncation and the Runge-Kutta time discretization, numerical solutions of the kinematic governing equation were obtained. By comparing with the analytical solution under specified conditions, validity of the method was checked. The time history of the beam’s free end was chosen to represent motion of the beam. Based on the steady time history of the beam, a Poincar´e map was constructed to study its periodic motion. Furthermore, an amplitude-frequency curve was given to find the dangerous frequency range where OWTs exist.

Particles diffusion mechanism in turbulent separation flow

QIU Xiao, DING Jue, WANG Zhongjie, WENG Peifen

2016, 22(5):  586-596.  doi:10.3969/j.issn.1007-2861.2015.03.002

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Back-facing step flow contains important characteristics of a separation flow. Based on this, a numerical simulation on particles diffusion mechanism in turbulent separation flow was conducted by Euler-Lagrangian coupled method. The gas phase governing equations were solved by large eddy simulation method and the subscale grid model was solved by Smagorinsky model. The particle phase was tracked with Lagrangian method. The accuracy of the solver was tested by comparing the simulation results with the experiment data. Based on this solver, the characteristics of the two phase flow, and the developing and evolutional process of vortex were numerically analyzed. The results showed that the diffusion of particles was related to particle’s diameter, the interaction time between particles and vortex structures. The structure of vortex changed when an obstacle was added to the flow field. The number of vortex increased at a certain distance away from the obstacle. The particles concentrate at the edge of the vortex and the distribution of particles were nonuniform in the flow field.

Effect of lateral stimuli on vibration of clamped-hinged pipeline with fluid-structure interaction

ZHU Weiping, ZHOU Chujian, DI Qinfeng

2016, 22(5):  597-605.  doi:10.3969/j.issn.1007-2861.2014.05.023

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The fluid-structure interaction vibration equation of a clamped-hinged pipeline under steady flow, liquid pressure and lateral stimulating force is derived based on the Hamilton principle. A new mode function suitable for the Galerkin method is used to solve the equation. Expressions of the first five orders of natural frequencies of the system are derived and validated. Next, deflection, bending moment, and transverse force exerted on the cross-section of the clamped-hinged pipeline are expressed with the first-order approximation of the mode function. The effects of liquid pressure, flow velocity, and stimulating frequency on the middle-point deflection, maximal bending moment throughout the clamped-hinged pipeline are discussed. The results show that the natural frequencies of the clamped-hinged pipeline are easy to calculate and with high accuracy using the method. Their values depend on the liquid pressure and flow velocity in the pipe. The phenomenon that resonance occurs when the natural frequency is close to the stimulating frequency also exists in fluid-structure interaction.

Design of liquefied natural gas submerged pump guide vane based on CFD

QIAN Tao, CHEN Hongxun, LIANG Chengpeng

2016, 22(5):  606-615.  doi:10.3969/j.issn.1007-2861.2015.01.016

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Liquefied natural gas (LNG) submerged pump is designed to immerse its canned motor and pump body into cryogenic liquid. To reduce radial and axial sizes, special guide vanes with different structures from popular ones are used. By analyzing the LNG pump structure, two key geometric parameters, inlet width and turning angle, were investigated to see how they affect pump hydraulic performance in the design. LNG pump guide vanes with different inlet widths and turning angles were designed to assemble the same impeller. Three-dimensional turbulent flows of different models were then numerically simulated using a standard k-ε turbulence model with ANSYS CFX. The comparative study revealed that optimum value of inlet width exited, and was larger than experience-based values. Inlet width had great influence on the pump performance, while turning angle was much less important. Therefore, designing an LNG pump guide vane, inlet width should be given high priority, and turning angle should be adjustable for structural design.

Temperature field of microbubble ultrasonic contrast agent in cube and closely-packed cube configurations

YANG Qing1, XU Kaiyu1,2, FENG Jiangtao1,2

2016, 22(5):  616-623.  doi:10.3969/j.issn.1007-2861.2015.02.014

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This paper studies the temperature field in blood by calculating viscous energy dissipation of phospholipid membrane based ultrasonic contrast agent under the sound pressure excitation. According to the experimental observation, a cube model with a red blood cell as center and eight microbubbles as vertices is proposed. Temperature rise of the center is also calculated. Furthermore, considering the condition of high microbubble concentration and its adhesion to the surface of organizations, a cube model of closelypacked structure is also built. Temperature field in a rectangular region and the peak temperature is obtained though this model. Safety is analyzed in detail to demonstrate feasibility and effectiveness of the proposed model.

Analysis of one-dimensional consolidation characteristics in unsaturated soil under line loads

QIN Aifang, GE Hang

2016, 22(5):  624-636.  doi:10.3969/j.issn.1007-2861.2015.01.002

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Semi-analytical solutions of excess pore-air pressure, excess pore-water pressure and degree of consolidation are obtained based on the Fredlund’s one-dimensional consolidation theory for unsaturated soil. The research object is a layer of unsaturated soil whose top surface is penetrable, and the bottom surface impenetrable to water and air. With a typical example, rules of excess pore-air pressure, excess pore-water pressure and degree of consolidation changing with time in different soil depth and ratio of permeability coefficient of air and water are analyzed. The linear elastic and viscoelastic situations are calculated, analyzed and compared. The conclusions are useful in the research of unsaturated soil consolidation characteristics and practical engineering problems about consolidation under line loads.

Direct shear behavior of reinforcement soil interface in different geosynthetics

LIU Feiyu1, SHEN Chunchun1, WANG Jun2,3, WANG Pan1

2016, 22(5):  637-647.  doi:10.3969/j.issn.1007-2861.2016.01.016

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To investigate the reinforcement soil interface cyclic and post-cyclic shear behavior in different geosynthetic materials (woven geotextile, nonwoven geotextile, geomembrane), a series of direct shear tests, cyclic shear tests and post-cyclic direct shear tests were performed through a large-scale direct shear device. Comparison and analysis were made between the results from direct shear tests and post-cyclic direct shear tests. In the direct shear tests, the interface shear stress-displacement curve presented large difference due to different material mechanical properties and structural characteristics. More evident deformation was observed in higher vertical stress. Cyclic shear stress degradation was observed in both woven and nonwoven geotextile-sand interfaces, whereas hardening  phenomenon appeared in the geomembrane-sand interface.

Predicting shear strength of unsaturated clay using soil-water characteristic curve

LI Wanshuang, SUN Dean, GAO You

2016, 22(5):  648-655.  doi:10.3969/j.issn.1007-2861.2015.01.015

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The pressure plate method and filter paper method were used to measure the soil-water characteristic curve (SWCC) of clay with almost the same initial void ratio. Shear strength were obtained by performing a series of direct shear tests on the clay under different unsaturated conditions. SWCCs of the silty clay obtained with the pressure plate and filter paper methods were nearly the same. With the same pressure, shear strength increased with a decreasing degree of saturation, and decreases at a very low degree of saturation. The degree of saturation had great influence on cohesion and little influence on the internal friction angle. Shear strength of unsaturated clay was predicted using SWCC. To precisely predict shear strength, a concept of effective degree of saturation was introduced to modify the traditional strength formula of unsaturated clay. The modified formula could better predict tested data.

Strength property and interaction mechanism of sand reinforced with hemispherical inclusions

YANG Lei1, ZHANG Mengxi1, PENG Jimin2, SUN Zhou1, GAO Ang1

2016, 22(5):  656-664.  doi:10.3969/j.issn.1007-2861.2015.02.019

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A series of triaxial tests were carried out to study strength property of sand reinforced by hemispherical inclusions of rubber. The behavior of reinforced sand was studied in terms of shear strength of sand, stress-strain relation and the failure modes of specimen. Influences of confining pressures, number of hemispheres and number of reinforced layers on reinforced sand strength were discussed. The interaction mechanism between the hemispherical rubber and sand were also discussed. It was shown that shear strength is improved significantly under lower confining pressures. In addition, the reinforcing effect of hemispherical inclusions was increased with the number of reinforced layers increasing. Compared with sand reinforced with horizontal inclusions, the soil reinforced with hemispherical inclusions was bound more strongly, shear strength of reinforced soil was more improved, and the cohesion and friction angle of reinforced sand were improved more significantly with the number of hemisphere increasing.

Non-axisymmetrical dynamic response of saturated soil and lining system with deeply embedded circular tunnel under step concentrated load

LU Jianjun, YANG Xiao

2016, 22(5):  665-679.  doi:10.3969/j.issn.1007-2861.2015.01.003

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Considering the interaction between soil and lining in a deeply embedded circular tunnel, the non-axisymmetrical dynamic response of a saturated soil-lining coupled system under step concentrated load was investigated. Based on the Biot’s theory and elasticity, using the Laplace transform and Fourier series, analytical expressions of displacements, stresses and pore water pressure of the saturated soil-lining system subject to step concentrated load were obtained in the Laplace transform domain under the boundary conditions of the lining and the continuity conditions on the interface between the saturated soil and lining. Numerical solutions of the dynamic responses of the saturated soil and lining system were obtained with a Crump method of the inverse Laplace transform. The influences of mechanical and geometric parameters of the soil and lining on the dynamic response of the system were analyzed. It was shown that dynamic response of the soil in a distance from the tunnel center more than 5 times of the radius was much less than that of the soil in the vicinity of tunnel. Influences of stiffness and thickness on displacements and stresses of the soil were significant, while the influences on pore water pressure were trivial. Furthermore, compressibility of pore water had stronger influence on the amplitude of the stress than that of the displacement of the soil.

Surrounding environment impacts caused by high-frequency vibration pile-driving

ZHANG Zhimei1, HUANG Haitao1, ZHANG Jihong2

2016, 22(5):  680-690.  doi:10.3969/j.issn.1007-2861.2015.02.001

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Considering a vibrating pile hammer, a pile and the soil conditions, the mechanism of influences of high frequency vibration pile construction on surrounding environment were analyzed. A three-dimensional finite element model of vibratory piling was established to reproduce the pile-driving process. Having confirmed validity of the model, variable parameters were investigated. The study showed that influences on the surrounding environment decrease with the frequency of pile hammer, and increase with static load of pile hammer and pile diameter. A sandy soil field was more easily affected by vibratory pile driving as compared to a clay soil field. Moreover, the harder the soil, the more serious environmental impact would be. To reduce the effects of pile construction, measures should be taken based on the analysis.