Archive

25 September 2013, Volume 30 Issue 5 Previous Issue    Next Issue

---

For Selected:

Download Citations EndNote Ris BibTeX

Toggle Thumbnails

Select

An Approach of Adaptive Mesh Refinement/Unrefinement Based on Prediction-Correction for Unsteady Flows ZHOU Chunhua 2013, 30(5): 633-641.  Abstract ( )   PDF (1906KB) ( )   An approach for performing mesh adaptation in numerical simulation of two-dimensional unsteady flow is presented. A predictor-corrector step is introduced in the process of "solving flow equations-adjusting mesh". At first, flowfield during an adaptation period is precomputed to produce a posteriori error estimate. Then, an indicator for mesh adaptation in which solution progression is taken into account is constructed. Adaptive mesh is generated through multi-level reflnement/unrefinement. Finally, unsteady flow field is recomputed on the new adaptive mesh. In each adaptation period, mesh is refined in regions where solution evolves and is unrefined in regions where phenomena deviate since the last adaptation. A non-boundary-conforming method named local domain-free discretization is employed to solve flow equations. To validate the method, we simulated unsteady flows over a circular cylinder and a self-propelled swimming fish.

Select

SPH Simulations of Parametric Sloshing in Various Shape Aqueducts WANG Zhuang, LI Yuchun, WANG Lishi 2013, 30(5): 642-648.  Abstract ( )   PDF (2293KB) ( )   Smoothed particle hydrodynamics (SPH) is applied to simulate parametric sloshing in various shape aqueducts. Taking rectangular tank as an example, the first symmetric mode of sloshing were investigated, including free surface elevations and frequency relationship, which confirm characteristic of nonlinear parametric sloshing. And the first two anti-symmetric and symmetric mode of parametric sloshing for U-shaped and circular aqueducts were also studied and presented in detail. These results confirm validity of SPH method for simulations of parametrically excited sloshing motion.

Select

LTS in Shallow Flows with RCM and Multi-wave Approximation XU Renyi, ZHONG Deyu, WU Baosheng 2013, 30(5): 649-658.  Abstract ( )   PDF (2442KB) ( )   Exact Riemann solver and wave propagation method are combined to achieve large time-step scheme (LTS) in shallow water flow. Multi-wave approximation is adapted to solve discontinuity of rarefaction, and a random choice method (RCM) is used to eliminate oscillation in nonlinear hyperbolic systems. Efficiency is increased in LTS scheme with multi-wave approximation and random choice method as large Courant-Fridrichs-Lewy (CFL) number is imposed.

Select

Supersonic Non-equilibrium Flow Simulation Based on Lattice Boltzmann Method ZHUO Changfei, WU Xiaosong, FENG Feng, XIE Aiyuan 2013, 30(5): 659-666.  Abstract ( )   PDF (1831KB) ( )   With ideas of vector splitting method and technique of coordinate rotation, a D1Q4 compressible lattice Boltzmann model is used to construct convection flux solvers of 3D Navier-Stokes equations with chemical reactions. Three-dimensional chemical non-equilibrium flow is solved by finite volume method of Navier-Stokes equations. A time-splitting method is applied to resolve stiff problem in computation of chemical reaction flows. Three classic examples of supersonic chemical non-equilibrium flows are simulated. It shows that:At high Mach numbers, numerical simulation using three-dimensional convection flux solvers based on D1Q4 model has no non-physical solution, and can distinguish physical phenomena such as shock, combustion wave in chemical non-equilibrium flow field. Accuracy and resolution are high,which verifys reliability of the three-dimensional convection flux solver. It broadens application of D1Q4 model, and offers a new method for calculation of hypersonic chemical non-equilibrium flows.

Select

Locally Conservative Galerkin Numerical Simulation for Two-phase Flow in Porous Media ZHANG Na, YAO Jun, HUANG Zhaoqin, WANG Yueying 2013, 30(5): 667-674.  Abstract ( )   PDF (2309KB) ( )   A locally conservative Galerkin (LCG) finite element method is proposed for two-phase flow simulations in heterogeneous porous media. The main idea of it is to use property of local conservation at steady state conditions to define a numerical flux at element boundaries. It provides a way to apply standard Ga/erkin finite element method in two-phase flow simulations in porous media. LCG method has all advantages of standard finite element method while explicitly conserving fluxes over each element. Several problems are solved to demonstrate accuracy of the method. All examples show that the formulation is accurate and robust, while CPU time is significantly less than mixed finite element method.

Select

Effect of Embankment Inclining Angle on Aerodynamic Characteristics of High Speed Train Under Crosswinds LUO Jianbin, HU Yuanyuan, YANG Jianheng, HU Aijun 2013, 30(5): 675-682.  Abstract ( )   PDF (3313KB) ( )   With computational fluid dynamics method, effect of embankment inclining angle on aerodynamic characteristics of high speed train under crosswinds is explored. It shows that as inclining angle of embankment is increased, side force coefficient on head train is increased a little and then decreased. Side force coefficient on middle train is gradually decreased. Side force coefficient on rear train is decreased a little and then increased as the angle reaches 47.5°. Negative lifting force coefficient on middle train is increased and lifting force coefficient on rear train is sensitive to inclining angle of embankment. The flow field around train is transformed as the inclining angle of embankment is changed and aerodynamic force or moment is changed consequently.

Select

Marangoni Effect on Soluble Surfactant Droplet Spreading in Different Spreading Systems YE Xuemin, JIANG Kai, LI Chunxi 2013, 30(5): 683-691.  Abstract ( )   PDF (2912KB) ( )   Surfactant driven flows are simulated with three nonlinear partial differential evolution equations for film thickness, surfactant interracial and bulk concentrations based on lubrication theory via PDECOL program numerically, to investigate influence of Marangoni effect in positive, negative and neutral systems. Instability of droplet evolution in negative system is analyzed with method of transient growth analysis. It shows that Marangoni effect plays a positive role in promoting droplets non-uniform spreading and surfactant diffusion in a positive system. A system under negative Marangoni effect exhibits interfacial instability which resulted in spreading inhibited and violent fluctuations occurrence on droplet surface. Instability tends to be more obvious with strengthened effect. Marangoni stress is main driving force in transverse droplet evolution in both positive and negative systems.

Select

A Molecular Dynamics Simulation of Methane Adsorption in Graphite Slit-pores LIU Bing, SHI Junqin, SHEN Yue, ZHANG Jun 2013, 30(5): 692-699.  Abstract ( )   PDF (2810KB) ( )   Adsorption of methane in graphite slit-pores and effect of slit-pores width and temperature on methane adsorption were studied with molecular dynamics simulation. It indicates that methane molecules have layering phenomenon in graphite slit-pores. Structure of methane in adsorption layers shows similar characteristics of liquid while to those of gas in free layers. And in a methane molecule there always exist two hydrogen atoms in a plane that parallels to slit-pore wall and other two hydrogen atoms in another plane that also parallels to slit-pore wall in the first layer. Potential of mean force between carbon atoms shows that binding capacity of methane is stronger in adsorption layers than in free layers. Adsorption state is one of the main occurrence state of methane in graphite slit-pores. London force and electric field force generated by net charge in adsorption layers are dominating reasons of methane adsorption and layering. Adsorption capacity of methane in graphite slit-pores decreases with increasing pore width or temperature. Methane is persisted only in adsorption state in slit-pore with width of 16.46 Å. Diffusivity of methane is the weakest in the first layer and the strongest in a free layer. Diffusion coefficients of methane increase with increasing pore width or temperature.

Select

Singularity at Tip of a Composite Notch Under Anti-plane Loading CHENG Changzheng, GE Renyu, XUE Weiwei, NIU Zhongrong 2013, 30(5): 700-705.  Abstract ( )   PDF (1269KB) ( )   Based on asymptotic extension of displacement field at a composite notch tip, equilibrium equation for a notch subjected to anti-plane loading is transformed into a characteristic differential equation respects to notch singularity orders. A transformation is applied to convert the equation into a set of characteristic linear ordinary differential equations. Interpolate matrix method is introduced to solve the equations for getting notch singularity orders. A single material notch, a bi-material notch and a notch terminated at bimaterial interface are studied successively. Examples indicate that the method provides all stress singularity orders synchronously. Though singular stress state is not shown with regard to non-singular orders, non-singular stress orders are indispensable parameters as evaluating complete stress field at notch tip region.

Select

Lunar Geophysical Parameters Inversion with PSO ZHONG Zhen, YAN Peng, YE Mao, LI Fei 2013, 30(5): 706-713.  Abstract ( )   PDF (848KB) ( )   With application of particle swarm optimization to lunar geophysical parameters inversion, problems resulted from limitation of lunar seismic network and/or unsuitability of conventional inversion methods are avoided. Parameters investigated include load ratio, crustal thickness, crustal density, subsurface load depth and lithospheric elastic thickness. It indicates that the approach is able to calculate model parameters best fitting observed ones automatically and simultaneously. It performs better in computational speed. It is therefore quite useful in lunar multi-parameters inversion and can be employed in lunar interior precision structure research.

Select

An Evaluation Method for Node Importance Based on Efficiency Matrix FAN Wenli, LIU Zhigang 2013, 30(5): 714-719.  Abstract ( )   PDF (798KB) ( )   In order to evaluate network nodes importance effectively, an evaluation method based on efficiency matrix is proposed. Based on node degree and contribution of network node importance comprehensively, the method uses node degree and efficiency matrix to characterize their importance, and to solve deficiency of node's dependence on adjacent nodes only in the method of node importance contribution matrix. Taking actual network sparsity into account,the algorithm has time complexity of O(n2). Finally, feasibility and validity of the algorithm are demonstrated with numerical example analysis. It shows that the method distinguishes node importance differences more directly, simply and effectively. It obtains ideal computing power for large scale complex networks.

Select

A Fast Numerical Algorithm for Six Degrees of Freedom Electromagnetic Probing XIANG Qian, WANG Shiqing 2013, 30(5): 720-726.  Abstract ( )   PDF (1785KB) ( )   A fast numerical algorithm for six degrees of freedom electromagnetic probing is proposed, to simulate magnetic field inside a space of 500 mm×500 mm×500 mm. Compared with strict algorithm and current-loop approximation algorithm, normalization computing time ratio is 106:70:1. It shows that the algorithm is feasible and reliable. Finally, how to effectively minimize deviation caused by limited length effect of solenoid coil is discussed to further improve the probing precision and stability of the probing system.

Select

Flexoelectric Effect in Response Time of Nematic Liquid Crystal Cell XING Hongyu, YE Wenjiang, ZHOU Xuan, SUN Yubao, ZHANG Zhidong, XUAN Li 2013, 30(5): 727-732.  Abstract ( )   PDF (1769KB) ( )   Based on dynamic theory of liquid crystal and finite-difference iterative method, dynamic response of strong anchoring hybrid aligned nematic (HAN) liquid crystal cell as removing applied voltage was studied. Flexoelectricity of liquid crystal material was considered. Time-dependences of transmittance through a HAN cell were obtained. It indicates that response time decreases with increasing of absolute value of the sum of splay and bend flexoelectric coefficient |e11+e33|. Especially, at |e11+e33|=50 pC·m-1 response time is half shortened relative to the case with no flexoelectric effect.

Select

Effects of Two-temperature Electrons on Sheath of Stationary Plasma ZHAO Xiaoyun, ZHANG Kaiyin, ZHANG Bingkai, LI Shigang 2013, 30(5): 733-738.  Abstract ( )   PDF (1260KB) ( )   A fluid model including two-temperature electrons was constructed for a collisionless plasma sheath. Effects of two-temperature electrons on sheath of stationary plasma were simulated. It is found that as temperature of cold electron is lower or density of cold electron at sheath adge is smaller critical ion Mach number decreases, sheath width becomes narrow and ion energy flow deposited on wall reduces. In addition, it is discussed that sheath thickness and ion energy flow deposited on wall are affected by cold electron in different plasma species.

Select

Influence of Surface Barrier on Electron Escape Probability of Gradient-doping GaN Photocathode WANG Honggang, QIAN Yunsheng, DU Yujie, REN Ling, XU Yuan 2013, 30(5): 739-744.  Abstract ( )   PDF (1757KB) ( )   Influence of surface potential barrier on escape probability of gradient-doping negative electron affinity (NEA) GaN photocathode was studied. Electron energy distribution and escape probability are calculated and compared with those of uniform-doping GaN photocathode. It shows that gradient-doping NEA GaN photocathode can obtain higher electron escape probability. And barrier I has an evident influence on escape probability while barrier Ⅱ has limited influence. Photocurrents of two GaN photocathodes are measured with a multi-information-test system. Experimental results show that gradient-doping GaN photocathode has higher escape probability. Obvious effect on escape probability can be found by barrier I from Cs-activation while barrier Ⅱ from Cs/O-joint-activation has little impact.

Select

Numerical Investigation on Thermal Effects of Field-Induced Explosive Emission Cathode Microprotrusion ZUO Yinghong, WANG Jianguo, FAN Ruyu, ZHU Jinhui, NIU Shengli 2013, 30(5): 745-752.  Abstract ( )   PDF (2364KB) ( )   To study non-linear relations between field emission current density and temperature at top surface of a cathode microprotrusion, thermal effects on cathode microprotrusion are investigated numerically at various applied electric fields. Enhancement factor of electric field at top surface of microprotrusion is different as ratio of top radius to bottom radius is changed. It leads to obvious difference in temperature distribution in microprotrusion when temperature at microprotrusion peak reaches melting point of cathode material. At a given applied electric field, the smaller the ratio of top radius to bottom radius of microprotrusion, the shorter the time delay of explosive emission. Time delay of explosive emission increases exponentially with decrease of applied electric field.

Select

Thermal Management of 3D Integrated Circuits Considering Horizontal Heat Transfer Effect ZHANG Yan, DONG Gang, YANG Yintang, WANG Ning 2013, 30(5): 753-758.  Abstract ( )   PDF (1724KB) ( )   A three-dimensional analytical heat transfer model for stacked chips is developed, which takes into account horizontal heat transfer effect in three-dimensional integrated circuits (3D ICs) with through silicon via (TSV). Effects of horizontal heat transfer is analyzed with number of strata, TSV density, TSV diameter and thickness of BEOL layer under specific process and thermal parameters. It indicated that temperature rise simulated by the model is lower compared with result not considering horizontal heat transfer effect. Difference of temperature rise can be above 10%. Effect of horizontal heat transfer on thermal management of 3D ICs is more obvious with increasing of integrated level. The model conforms to actual situation. It is more accurate in analyzing temperatures of stacked chips in 3D ICs.

Select

Numerical Simulation of Surface Roughness Effect in Large Height-Width Ratio Mini-channel Flows LIU Dong, JIANG Bin, LIU Minghou 2013, 30(5): 759-765.  Abstract ( )   PDF (2750KB) ( )   A PML model based on fixed surface roughness is used in simulation of surface roughness effect on flow in mini-channels. Compared with 3-D simulation, results of pressure drop agree well. With PML model and 3-D model we simulate different flow rates and roughness, it shows that surface roughness results in speed linear flow substrate. Pressure drop and relative roughness follow a secondary power relation as Re number is fixed. Pressure drop increased linearly with Re number as roughness elements is equal.

Select

Density Functional Theory Study of Geometry, Stability and Electronic Properties of BeSin(n=1-12) Clusters ZHANG Shuai, ZHONG Zhiguo, BAO Daixiao, LI Genquan, LU Cheng 2013, 30(5): 766-774.  Abstract ( )   PDF (2458KB) ( )   Geometrical structures, stability, electronic properties, vibrational spectrum and polarizations of BeSin(n=1-12) clusters are investigated with density functional theory (DFT) at B3LYP/6-311G level. It indicates that there are many isomers with extremely close energies near the ground state. The most stable structures of BeSin clusters favor three-dimensional structures as n≥4. At n=1 spin multiplicity of the ground state structure of BeSin cluster is triplet while it is singlet as n≥2. Electronic properties of host clusters change obviously due to encapsulation of Be atom. Doping of Be atom reduce chemical stability of pure Si clusters, n=3, 5, 7 and 9 are magic numbers.

Select

Density Functional Theory Study of Structure and Stabiliky of WmBn(m+n≤7) Clusters ZHANG Xiurong, YIN Lin, LI Weijun, WANG Yangyang, YUAN Aihua 2013, 30(5): 775-782.  Abstract ( )   PDF (1889KB) ( )   Geometric structure of WmBn(m+n≤7) clusters are optimized by using density functional theory at B3LYP/LANL2DZ level. For ground state configurations, average binding energies, second order differential energies, energy gaps and WIB bond orders are analyzed. It shows that ground state structures of WBn clusters are flat structures; as m≥2 and m+n≥4, all clusters are cube structure except W3B cluster. Stability of clusters is getting better and better as W atoms increase. The bonding strength of W-W is significantly higher than those of W-B and B-B key. W atom plays a leading role in stability of clusters. Stability of W2B2 and W3B cluster is the best.

Select

First-Principles Study of Structural, Electronic, and Magnetic Properties of Mn-Doped ZnS(111) Surfaces SONG Dewang, NIU Yuan, XIAO Llou, LI Dan 2013, 30(5): 783-790.  Abstract ( )   PDF (2379KB) ( )   With first-principles method based on density functional theory, we studied structural, electronic, and magnetic properties of ZnS(111) surfaces monodoped and bidoped with Mn atoms. In monodoped configuration, the most energetically favorable location of Mn incorporated into ZnS(111) surfaces is in the first Zn atomic layer. Total magnetic moment depends on local structure of Mn atom. In bidoped configuration, short-range ferromagnetism can be explained with existence of strong p-d hybridization between Mn atom and its nearest neighboring S atoms. A Curie temperature of 469 K higher than room temperature is evaluated. Interaction between doping Mn atoms and host semiconductors is major reason for generation of spin polarization. It shows a prospecting prediction for further study of diluted magnetic semiconductors which may be useful in technological application.