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numerical model and experimental observation for distribution of SiC_p in electromagnetic-centrifugally cast composites

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Transactions of Nonferrous Metals Society of China 2010年第5期20卷 870-876页

作者：张伟强娄长胜 School of Materials Science and Engineering Shen yang Ligong University

A two-phase numerical model coupled with heat transfer was presented to describe the radial distribution of SiC particles on centrifugally-cast metal matrix composite,and a transverse static magnetic field was concurrently imposed to induce electromagnetic stirring of the melt as it revolved with the ***,experimental observations were also carried out to examine the radial distribution of SiC particles in pure *** effects of the imposed magnetic field,particle size and the matrix metals were *** computational results show that the particles tend to be congregated by the centrifugal force,and both increasing the imposed magnetic field and decreasing the particle size tend to result in even distribution of the *** the magnetic field varying from 0 to 1 T and the particle size from 550 to 180 μm,a uniform distribution of the particles in the aluminum matrix can be obtained among the computational *** matrix metal can also influence the particle distributions due to the difference in physical properties of *** observation shows similar tendency of particle distributions in aluminum matrix influenced by magnetic field and particle ***,the chilling effect from the mold wall results in an outer particle-free zone,which is not involved in the numerical model.

关键词： electromagnetic centrifugal casting numerical model particle distribution composite

numerical model for the Characterization of Retro-reflective Materials Behavior in an Urban Street Canyon

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Journal of Thermal Science 2018年第5期27卷 456-462页

作者： VALLATI Andrea MAURI Luca COLUCCI Chiara DE LIETO VOLLARO Roberto Department of DIAEE Sapienza University of Rome Department of Mechanical Engineering University of Roma Tre

In this work, a preliminary numerical model of the behavior of retro-reflective materials used as envelope coatings on street canyon buildings facades has been tested. Retro-reflective materials have a surface finish that allows to reflect the solar radiation back in the same direction of the incident radiation. In the last years this kind of materials has been studied as buildings envelope coating for their potentials in the reduction of the UHI effect. As a matter of fact, the angular dependence of their optical-radiative response would help to mitigate the phenomenon of radiative entrapment due to the urban fabric environment. For this reason, an urban canyon was selected as the most common urban architecture to perform the analysis. A virtual retroreflective material has been simulated considering its response as almost diffusive but in the same direction of the incident radiation. The assessment of the energy advantages of the adoption of a virtual retro-reflective material as envelope coating is investigated by means of a numerical model developed in MATLAB and based on the Gebhart factors theory. The final purpose of the numerical model is the evaluation of the surfaces solar loads by a comparison between perfectly diffusive materials and RR materials used as fa？ades coating.

关键词： retro-reflective materials numerical model Gebhart factors radiative trapping urban street canyon

numerical model of soft ground improvement by vertical drain combined with vacuum preloading

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Journal of Central South University 2013年第7期20卷 2066-2071页

作者：吴辉胡黎明 State Key Laboratory of Hydro-science and Engineering (Department of Hydraulic Engineering Tsinghua University)

The rapid development of high-speed transportation infrastructure such as highway and high-speed railway has resulted in the advancement of soft soil improvement techniques. Vacuum preloading combined with vertical drains has been proved to be an effective method in the treatment of soft foundation. A three-dimensional numerical analysis of the coupled methods was presented, in which the smear zone and the well resistance were taken into account. The variations of the basic soil parameters including the permeability coefficient and the coefficient of volume compressibility were considered in the numerical model. The result of the numerical model was then compared to the measured value. The results indicate that the decrease of coefficient of volume compressibility accelerates the consolidation of the soil while the influence of hydraulic conductivity is insignificant. A cube drain presents the closest result to the real situation compared to the other equivalent methods of prefabricated vertical drain (PVD). The case study indicates that the numerical model with variation of soil parameters is closer to the measured value than the numerical model without variation of soil parameters.

关键词： vacuum preloading prefabricated vertical drain (PVD) parameter variation numerical model

A numerical model for Natural Backfill of Pipeline Trenches Subjected to Unidirectional/Oscillatory Flows

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China Ocean Engineering 2005年第2期19卷 269-286页

作者： Kervin YEOW School of Civil and Resource Engineering The University of Western AustraliaCrawley WA6009 Australia

A numerical model for the self-burial of a pipeline trench is developed. Morphological evolutions of a pipeline trench under steady-current or oscillatory-flow conditions are simulated with/without a pipeline inside the trench. The oscillatory flow in this study represents the action of waves. The two-dimensional Reynolds-averaged continuity and Navier-Stokes equations with the standard k-ε turbulence closure, as well as the sediment transport equations, are solved with the finite difference method in a curvilinear coordinate system. Both bed and suspended loads of sediment transport are included in the morphological model. Because of the lack of experimental data on the backfilling of pipeline trenches, the numerical model is firstly verified against three closely-relevant experiments available in literature. A detailed measurement of the channel migration phenomenon under steady currents is employed for the assessment of the integral performance of the model. The two experimental results from U-tube tests are used to validate the model's ability in predicting oscillatory flows. Different time-marching schemes are employed for the morphological computation under unidirectional and oscillatory conditions. It is found that vortex motions within the trench play an important role in the trench development.

关键词： numerical model backfill sediment transport offshore pipeline trench oscillatary flow

numerical model of Internal Solitary Wave Evolution on ImpermeableVariable Seabed in A Stratified Two-Layer Fluid System

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China Ocean Engineering 2006年第2期20卷 303-313页

作者： Chen-Yuan CHEN John Rong-Chung HSU Cheng-Wu CHEN Ming-Hung CHENG Department of Madne Envirorunent and Engineering National Sun Yat-sen University Kaohsiung 80424 Taiwan China School of Civil and Resource Engineering University of Western Australia WA 6009 Australia Department of Logistics Management Shu-Te University Kaohsiung 82445 Taiwan China

In the present study a numerical model developed by Lynett and Liu （2002） is modified to include density difference in a stratified two-layer fluid in a three-dimensional internal wave domain. The internal solitary wave （ISW） in the model is assumed to be weakly nonlinear and weakly dispersive, and the viscosity effects at all boundaries are ignored. The governing equations based on the Navier-Stokes and Euler equations are solved for internal solitary wave propagation over variable seabed topography. Theoretical formulations are established, from which analytical solutions are obtained, in addition to numerical results. Wave profiles from previous experimental studies are compared with the numerical results from the present analytical solutions. numerical models developed on the basis of the present analytical solutions are better than those developed by Lynett and Liu （2002）. The results of numerical modeling agree well with the experimental data.

关键词： Navier-Stokes equation nonlinearity frequency dispersion internal solitary wave numerical model

numerical model of tandem organic light-emitting diodes based on a transition metal oxide interconnector layer

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Journal of Semiconductors 2014年第4期35卷 68-76页

作者：路飞平彭应全邢永忠 College of Physics and Information Science Tianshui Normal University Institute of Microelectronics School of Physical Science and Technology Lanzhou University

By utilizing a two-step process to express the charge generation and separation mechanism of the transition metal oxides （TMOs） interconnector layer, a numerical model was proposed for tandem organic light emitting diodes （OLEDs） with a TMOs thin film as the interconnector layer. This model is valid not only for an n-type TMOs interconnector layer, but also for a p-type TMOs interconnector layer. Based on this model, the influences of different carrier injection barriers at the interface of the electrode/organic layer on the charge generation ability of interconnector layers were studied. In addition, the distribution characteristics of carrier concentration, electric field intensity and potential in the device under different carrier injection barriers were studied. The results show that when keeping one carrier injection barrier as a constant while increasing another carrier injection barrier, carri- ers injected into the device were gradually decreased, the carrier generation ability of the interconnector layer was gradually reduced, the electric field intensity at the interface of the organic/electrode was gradually enhanced, and the electric field distribution became nearly linear： the voltage drops in two light units gradually became the same. Meanwhile, the carrier injection ability decreased as another carrier injection barrier increased. The simulation re- sults agree with the experimental data. The obtained results can provide us with a deep understanding of the work mechanism of TMOs-based tandem OLEDs.

关键词： tandem organic light-emitting diodes numerical model interconnector layer transition metal oxide

A SEMI-IMPLICIT 3-D numerical model USING SIGAM-COORDINATE FOR NON-HYDROSTATIC PRESSURE FREE-SURFACE FLOWS

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Journal of Hydrodynamics 2011年第2期23卷 212-223页

作者： HU De-chao FAN Bei-lin WANG Guang-qian ZHANG Hong-wu State Key Laboratory of Hydroscience and Engineering Tsinghua University Beijing 100084 China Yangtze River Scientific Research Institute Wuhan 430010 China

A 3-D numerical formulation is proposed on the horizontal Cartesian, vertical sigma-coordinate grid for modeling non-hydrostatic pressure flee-surface flows. The pressure decomposition technique and 0 semi-implicit method are used, with the solution procedure being split into two steps. First, with the implicit parts of non-hydrostatic pressures excluded, the provisional velocity field and free surface are obtained by solving a 2-D Poisson equation. Second, the theory of the differential operator is employed to derive the 3-D Poisson equation for non-hydrostatic pressures, which is solved to obtain the non-hydrostatic pressures and to update the provisional velocity field. When the non-orthogonal sigma-coordinate transformation is introduced, additional terms come into being, resulting in a 15-diagonal, diagonally dominant but unsymmetric linear system in the 3-D Poisson equation for non-hydrostatic pressures. The Biconjugate Gradient Stabilized （BiCGstab） method is used to solve the resulting 3-D unsymmetric linear system instead of the conjugate gradient method, which can only be used for symmetric, positive-definite linear systems. Three test cases are used for validations. The successful simulations of the small-amplitude wave, a supercritical flow over a ramp and a turbulent flow in the open channel indicate that the new model can simulate well non-hydrostatic flows, supercritical flows and turbulent flows.

关键词： 3-D numerical model non-hydrostatic sigma-coordinate semi-implicit pressure-splitting

A numerical model for air concentration distribution in self-aerated open channel flows

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Journal of Hydrodynamics 2015年第3期27卷 394-402页

作者：卫望汝邓军张法星田忠 State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University

The self-aeration in open channel flows, called white waters, is a phenomenon seen in spillways and steep chutes. The air distribution in the flow is always an important and fundamental issue. The present study develops a numerical model to predict the air concentration distribution in self-aerated open channel flows, by taking the air-water flow as consisting of a low flow region and an upper flow region. On the interface between the two regions, the air concentration is 0.5. In the low flow region where air concentration is lower than 0.5, air bubbles diffuse in the water flow by turbulent transport fluctuations, and in the upper region where air concentration is higher than 0.5, water droplets and free surface roughness diffuse in the air. The air concentration distributions obtained from the diffusion model are in good agreement with measured data both in the uniform equilibrium region and in the self-aerated developing region. It is demonstrated that the numerical model provides a reasonable description of the self-aeration region in open channel flows.

关键词： self-aeration air concentration open channel flows turbulence diffusion numerical model

An Axisymmetric numerical model for Simulating Kinetically-Limited Growth of a Cylindrical Rod in 3D Laser-induced Chemical Vapor Deposition

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Journal of Materials Science & Technology 2002年第2期18卷 127-132页

作者： R.Nassa, W.Z.Dai and Q.ChenMathematics & Statistics, College of Engineering & Science, Louisiana Tech. University, Ruston, LA 71272, USA [ Manuscript received January 8, 2002] Math. and Statistics Coll. of Eng. and Sci. Louisiana Tech. Univ. Ruston LA 71272 United States

Laser-induced chemical vapor deposition (LCVD) is an important process for freeform microfabrication of high aspect ratio prototypes. The system consists of a laser beam focused onto a movable substrate in a vacuum chamber. Heat from the laser at or near the focal spot of the beam causes gas in the chamber to react. As a result, solid-phase reaction products are deposited on the substrate to form the microstructure. In this paper, we develop a numerical model for simulating growth of an axisymmetric cylindrical rod by pre-specifying the surface temperatures required for growing the rod and then by solving for the laser power that satisfies the pre-specified temperatures. The solution using least squares is obtained by minimizing the sum of square deviations between the pre-specified surface temperatures and the calculated temperatures from the heat equation with a given laser power as a heat source. model predictions of the laser power over growth time helped in optimizing the growth process. Rods grown based on the predicted laser power from the numerical model were very close to being cylindrical in shape. Ways to further improve the model are being investigated.

关键词： numerical model LCVD Cylindrical rod growth Least squares optimization