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SIMULATION OF SEDIMENT-LADEN FLOW BY DEPTH-AVERAGED MODEL BASED ON UNSTRUCTURED COLLOCATED GRID

Journal of Hydrodynamics 2007年第4期19卷 525-532页

作者： LIU Shi-he LUO Qiu-shi MEI Jun-ya School of Water Resource and Hydropower Wuhan University Wuhan 430072 China

The 2-D depth-averaged mathematical model for sediment-laden flows has been widely used in river control and other related engineering problems, and now it is usually solved on structured grids. Since the natural river is usually very complicated in plane boundary, and unstructured grids are more attractive in solving the problems with complicated domains, the following questions about solving 2-D depth-averaged model were discussed in this article：（1） a modified Bowyer algorithm was suggested to generate unstructured grids for natural rivers, （2） the Finite Volume Method （FVM） is employed to discretize the governing equations of the 2-D depth-averaged model and an implicit scheme was suggested with unstructured collocated grids, （3） the observed hydrological data of the Chenglingji Reach in the Yangtze River are used for verification of the presented method It seems that the suggested numerical scheme works very well, and the simulation results of both hydraulic characteristics and river bed deformation are in good agreement with the observed ones.

关键词： Bowyer algorithm unstructured grid simple algorithm

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Turbulent natural convection in an enclosure with localized heating from below

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INTERNATIONAL JOURNAL OF THERMAL SCIENCES 2007年第12期46卷 1232-1241页

作者： Sharma, Anil Kumar Velusamy, K. Balaji, C. Indian Inst Technol Dept Mech Engn Heat Transfer & Thermal Power Lab Madras 600036 Tamil Nadu India Indira Gandhi Ctr Atom Res Safety Engn Div Safety Grp Dept Atom Energy Kalpakkam 603102 Tamil Nadu India

This study reports the results of a numerical investigation of turbulent natural convection in a square enclosure with localized heating from below and symmetrical cooling from the vertical side walls. The present study simulates the case of an accidental heat generation due to fire in a typical isolated building of a nuclear reactor or electronic components cabin. The source of fire is considered to be centrally located at the bottom wall with different heated widths, which is assumed to be either isothermal or with isoflux. For the purpose of the analysis, the source length is varied from 20 to 80% of the total width of the bottom wall. The top wall and the unheated portion of the bottom wall are considered to be adiabatic, whereas sidewalls are isothermal. Steady as well as transient forms of two-dimensional Reynolds-Averaged-Navier-Stokes equations and conservation equations of mass and energy, coupled with the Boussinesq approximation, are solved by the control volume based discretisation method employing the simple algorithm for pressure-velocity coupling. Turbulence is modeled using the standard k-epsilon model. Rayleigh number, Ra, based on the enclosure height is varied from 10(8) to 10(12). Stream lines and isotherms are presented for various combinations of Ra and the heated width. A double cell flow pattern is observed with marginal loss in symmetry as Ra increases. The results are reported in the form of local and average Nusselt number on the heated floor. Correlations are developed to predict the heat transfer rates from the enclosure as a function of dimensionless heated width of the bottom wall and Ra, by least square linear regression analysis. (C) 2007 Elsevier Masson SAS. All rights reserved.

关键词： turbulent natural convectiom standard k-epsilon turbulence model square enclosure simple algorithm

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Numerical simulation of bubble rising in viscous liquid

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JOURNAL OF COMPUTATIONAL PHYSICS 2007年第2期222卷 769-795页

作者： Hua, Jinsong Lou, Jing Inst High Performance Comp Singapore 117528 Singapore

An improved numerical algorithm for front tracking method is developed to simulate the rising of a bubble in quiescent viscous liquid due to buoyancy. In the new numerical algorithm, volume correction is introduced to conserve the bubble volume while tracking the bubble's rising and deforming, and volume flux conservation based simple algorithm is adopted to solve the Navier-Stokes equation for fluid flow using finite volume method. The new front tracking algorithm is validated systematically by simulating single bubble rising and deforming in quiescent viscous liquid under different flow regimes. The simulation results are compared with the experimental measurement in terms of terminal bubble shape and velocity. The simulation results demonstrate that the new algorithm is robust in the flow regimes with larger ranges of Reynolds number (Re < 200), Bond number (Bo < 200), density ratio (rho(1)/rho(b) < 1000) and viscosity ratio (mu(1)/mu(b) < 500). The new front tracking algorithm is also applied to investigate bubble rising and deforming behaviour in the various flow regimes of "air bubble/water solution" system under effects of Reynolds number, Bond number, density ratio, viscosity ratio as well as the bubble initial shape, which have been explored previously by experiments. The predicted bubble shape and terminal velocity agree well with the experimental results. Hence, the new modelling algorithm expands the conventional front tracking method to more realistic and wider applications. (c) 2006 Elsevier Inc. All rights reserved.

关键词： front tracking method incompressible flow simple algorithm bubble rising two-phase flow computational fluid dynamics

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Thermodynamic instability of siRNA duplex is a prerequisite for dependable prediction of siRNA activities

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NUCLEIC ACIDS RESEARCH 2007年第18期35卷 e123-e123页

作者： Ichihara, Masatoshi Murakumo, Yoshiki Masuda, Akio Matsuura, Toru Asai, Naoya Jijiwa, Mayumi Ishida, Maki Shinmi, Jun Yatsuya, Hiroshi Qiao, Shanlou Takahashi, Masahide Ohno, Kinji Nagoya Univ Grad Sch Med Div Neurogenet & Bioinformat Ctr Neurol Dis & CancShowa Ku Nagoya Aichi 4668550 Japan Chubu Univ Coll Life & Hlth Sci Dept Biomed Sci Kasugai Aichi 4878501 Japan Nagoya Univ Grad Sch Med Dept Pathol Nagoya Aichi 4668550 Japan Nagoya Univ Grad Sch Med Dept Publ Hlth Hlth Informat Dynam Field Social Life SciProgram Hlth & Community Me Nagoya Aichi 4668550 Japan Nagoya Univ Grad Sch Med Div Mol Pathol Ctr Neurol Dis & Canc Nagoya Aichi 4668550 Japan

We developed a simple algorithm, i-Score (inhibitory-Score), to predict active siRNAs by applying a linear regression model to 2431 siRNAs. Our algorithm is exclusively comprised of nucleotide (nt) preferences at each position, and no other parameters are taken into account. Using a validation dataset comprised of 419 siRNAs, we found that the prediction accuracy of i-Score is as good as those of s-Biopredsi, ThermoComposition21 and DSIR, which employ a neural network model or more parameters in a linear regression model. Reynolds and Katoh also predict active siRNAs efficiently, but the numbers of siRNAs predicted to be active are less than one-eighth of that of i-Score. We additionally found that exclusion of thermostable siRNAs, whose whole stacking energy (Delta G) is less than 34.6 kcal/mol, improves the prediction accuracy in i-Score, s-Biopredsi, ThermoComposition21 and DSIR. We also developed a universal target vector, pSELL, with which we can assay an siRNA activity of any sequence in either the sense or antisense direction. We assayed 86 siRNAs in HEK293 cells using pSELL, and validated applicability of i-Score and the whole Delta G value in designing siRNAs.

关键词： .linear regression Neural Network Preferences prediction accuracy simple algorithm siRNA duplex prediction of siRNA predict active siRNAs comprised of siRNAs thermostable siRNAs

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Numerical Oscillatory on the Simulation of Thermoacoustic Waves

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HEAT TRANSFER-ASIAN RESEARCH 2007年第5期36卷 265-275页

作者： Liu Jiping Zhou Zhijie Chong Daotong Yan Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian Peoples R China China Ship Dev & Design Ctr Beijing Peoples R China

The simple algorithm for compressible flows is introduced to predict the thermoacoustic wave in a one-dimensional closed region. The thermoacoustic waves are generated by an impulsive rise of the temperature on the left wall, while the other walls are kept at the initial temperature. Four different schemes are employed to deal with the convection-diffusion terms, i.e., CD, FUD, QUICK, and MUSCL. The calculations and analysis show that numerical oscillation occurs under all four schemes, affected by the intensity of the waves, type of schemes, and other factors. The results are beneficial for the further investigation of the thermoacoustic waves and high efficiency scheme development. (C) 2007 Wiley Periodicals, Inc.

关键词： thermoacoustic convection simple algorithm numerical oscillatory compressible flow

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NUMERICAL SIMULATION OF 2D HORIZONTAL COOLING WATER DISCHARGE IN GENERALIZED CURVILINEAR COORDINATE

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Journal of Hydrodynamics 2006年第1期18卷 91-96页

作者： XIE Zuo-tao ZHANG Xiao-feng TAN Guang-ming YANG Fang-li State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan 430072 China

2D horizontal model is one of the major mathematical methods for the research on cooling water discharge from the power plant. In this paper, the shallow water equations are transformed under the generalized curvilinear coordinate system and the elliptic differential equations are used to generate curvilinear grids, so a model in generalized curviline ar coordinate is presented to simulate 2D horizontal cooling water, Governing equations of the model are discretized by finite volume method, and non-staggered grids and simple algorithm are introduced to simplify the program during the discretization. This model is used to simulate the movement of cooling water in a simplified meandering channel and a natural channel, calculating results indicate this model can correctly reflect the movement rules of cooling water, which verifies the model can be applied in engineering practice.

关键词： cooling water generalized curvilinear coordinate non-staggered grids numerical simulation simple algorithm

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Unsteady laminar buoyant flow through rectangular vents in large enclosures

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2006年第2期20卷 276-284页

作者： Kumar, R Sleiti, A Kapat, J Univ Cent Florida Dept Mech Mat & Aerosp Engn Orlando FL 32816 USA

This computational study concentrates on transient laminar How of air through rectangular vents in horizontal partitions between two large enclosures. For a vent aspect ratio of 1, three flow regimes were identified as the Rayleigh number (Ra) was varied from 1 x 10(3) to 5 x 10(4) based on flow parameters in the vent and corresponding modes of heat transfer through it. The Rayleigh number was found to be the critical control parameter, which determined the flow regimes of conduction, countercurrent, and oscillatory flow regimes. As the effective driving potential decreased with time, flow changed from one regime to the other so that higher-Rayleigh-number results showed all three regimes over time. Circulation patterns within the vent for the conduction regime (Ra < 1500) appeared to follow Chandrasekhar's well-known linear stability results. At higher Ra, sudden bursts of upflow with corresponding downflow have been documented and compared with experimental observations in the literature. The time traces of velocity and temperature fields for this flow regime reveal interesting mechanisms, which have been explained.

关键词： Natural Convection Heat Transfer Correlations Aspect Ratio Thermal Diffusivity Flow Patterns Flow Characteristics Buoyancy Force Hydrostatic Pressure simple algorithm Conservation of Mass

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Numerical simulations of the flow field around the rings of mechanical seals

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JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME 2006年第3期128卷 559-565页

作者： Luan, Zhaogao Khonsari, M. M. Louisiana State Univ Dept Mech Engn Baton Rouge LA 70803 USA

The flow inside a seal chamber as induced by the influx of the flush fluid and the rotation of the primary ring is analyzed. The 3-D flow characteristic around the mating ring and the rotating ring are predicted by solving the Navier-Stokes equations in cylindrical coordinates. For this purpose, the pressure correction method was used in conjunction with the simple algorithm. A series of numerical solutions is presented that show the flow mechanism within the gap between the rings and the gland. The implication of the flow characteristic on the cooling of the rings is discussed.

关键词： mechanical seal flow field CFD simple algorithm pressure correction method

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Introductory computational fluid dynamics model for inertance pulse tube cryocooler 5

Introductory computational fluid dynamics model for inertanc...

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5th South African Conference on Computational and Applied Mechanics

作者： Smith, Gerrit Harms, Thomas Dobson, Robert Univ Stellenbosch Dept Mech & Mechatron Engn Private Bag 11 ZA-7602 Matieland South Africa

Pulse tube cryogenic coolers (cryocoolers) are among the latest innovations of cryogenic coolers. They fall in the same category as the reversed Stirling cycle cryocoolers that have been used for decades to cool infrared detectors in military and space applications. Pulse tube cryocoolers will replace most of the Stirling cryocoolers in future applications, because they have no moving parts at their cold points and therefore are subject to less vibrations, and hence has a longer service life [1]. A schematic of the pulse tube cryocooler is shown in figure 1. [GRAPHIC] A typical pulse tube cryocooler consists of a regenerator, cold and hot heat exchangers, an empty tube (pulse tube), a long neck tube (inertance tube) and a reservoir (surge volume) [2]. The compressor (reciprocator) provides a pressure wave (30-50 Hz) to the cooler. The inertance tube and surge volume work together to provide a phase shift between the mass flow and the pressure wave in the pulse tube. In this paper the pulse tube cryocooler is modeled with a one-dimensional CFD program in FORTRAN. In this program the conservation equations for momentum, continuity, energy and an equation of state were discretized and solved. The reciprocator is presented by an open pressure boundary condition to avoid having a moving boundary in this model for the time being.

关键词： simple algorithm one dimensional staggered mesh fully compressible flow time dependant laminar flow porous media heat transfer variable flow area and ideal gas

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Modeling of aluminum profile extrusion processes using finite volume method

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Suxing Gongcheng Xuebao/Journal of Plasticity Engineering 2006年第4期13卷 34-37+48页

作者： Lou, Shu-Mei Zhao, Guo-Qun Wu, Xiang-Hong Xu, Shu-Bo Wu, Xin Mould and Die Engineering Technology Research Center Shangdong University Jinan 250061 China

Euler equation is discretised by using finite volume method. The mathematic model of aluminum profile extrusion processes was established using simple algorithm and applying the boundary conditions. The key technologies for simulating aluminum profile extrusion processes using finite volume method were studied. A simulation program was developed, The non-isothermal aluminum profile extrusion processes with circular cross-section and I shaped cross-section were simulated. The three-dimensional steady velocity fields and temperature fields were obtained. The equivalent strain rate fields were also computed. The simulation results show that the established finite volume mathematic model for simulating aluminum profile extrusion processes is feasible.

关键词： Aluminum profile extrusion Euler equation Finite volume method Numerical simulation simple algorithm

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