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Two-dimensional Numerical Model for Debris Flows in the Jiangjia Gully,Yunnan Province

Journal of Mountain Science 2011年第6期8卷 757-766页

作者： PENG Hong ZHAO Yanxin CUI Peng ZHANG Wanshun CHEN Xuejiao CHEN Xiaoqing College of Water Resources and Hydropower Engineering Wuhan University Wuhan 430072 China School of Resource and Environmental Science Wuhan University Wuhan 43o079 China Institute of Mountain Hazards and Environment Chinese Academy of Sciences Chengdu 610041 China

Debris flows are recurrent natural hazards in many mountainous *** paper presents a numerical study on the propagation of debris flows in natural erodible open channels,in which the bed erosion and sedimentation processes are *** on the Bingham fluid theory,a mathematical model of the two-dimensional non-constant debris flow is *** governing equations include the continuity and momentum conservation equations of debris flow,the sediment convection-diffusion equation,the bed erosion-deposition equation and the bed-sediment size gradation adjustment *** yield stress and shear stress components are included to describe the dynamic rheological *** upwind control-volume Finite Volume Method (FVM) is applied to discretize the convection *** improved simple algorithm with velocity-free-surface coupled correction is developed to solve the equations on non-orthogonal,quadrilateral *** model is applied to simulate a debris flow event in Jiangjia Gully,Yunnan Province and to predict the flow pattern and bed erosion-deposition *** results show the effectiveness of the proposed numercial model in debris flow simulation and potential hazard analysis.

关键词： Debris flow Numerical simulation simple algorithm Finite Volume Method Hazardanalysis Jiangjia Gully

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Fluid dynamical view of pressure checkerboarding problem and smoothing pressure correction on meshes with colocated variables

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2003年第25期46卷 4885-4898页

作者： Date, AW Indian Inst Technol Dept Mech Engn Bombay 400076 Maharashtra India

This paper presents derivation of the pressure correction equation appropriate for colocated grids within the framework of the simple algorithm. It is shown that checkerboard prediction of pressure can be prevented by employing algebraic smoothing pressure correction [Numer. Heat Transfer, Part B 29 (1996) 441] that is very simple to implement on both the structured as well as unstructured grids. The ability of the smoothing correction (which is shown to be independent of transformations of the system of coordinates) in providing the necessary dissipation is explained and the connection of the former with requirements of the Stokes's laws is established. (C) 2003 Elsevier Ltd. All rights reserved.

关键词： simple algorithm smoothing pressure correction structured and unstructured meshes colocated variables Navier-Stokes equations

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Thermosolutal mixed convection of a shear thinning fluid due to partially active mixed zones within a lid-driven cavity

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2017年 106卷 686-707页

作者： Nayak, A. K. Hague, A. Banerjee, A. Indian Inst Technol Roorkee Dept Math Roorkee 247667 Uttar Pradesh India

In this paper, a generalized forced convective flow inside a cubical enclosure filled with a non-Newtonian power-law fluids is carried out numerically. The flow is influenced due to a discrete temperature and mass gradients along its short side walls. The non-Newtonian fluid considered here are described by the power-law model (also known as the Ostwald-de Waele model), which leads to a relationship between the shear stress and shear rate. The fluid is assumed to be laminar, incompressible and suppose to satisfy the Boussinesq approximation. A detailed physical insights into the flow, heat and mass transfer effects due to the different physical parameters such as Reynolds number (0 < Re <= 200), Grashof number (Gr(T) = 100), power law index (0.2 <= n <= 1) and Lewis number (1 <= Le <= 10) are presented. Comparison of the present result with the published results are found to be satisfactory for wide range of physical parameters. The results reveal that the location and length of the heating and cooling zones has a significant contribution on the flow, heat and mass transfer. The rate of heat transfer is found to be maximum on minimizing the heat source length and maximizing the power law index. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Mixed convection Pseudoplastic fluid Lid-driven cavity Discrete active zone Finite Volume Method simple algorithm

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Parameter identification of small distributed hydro generators during excitation system start-up

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IET GENERATION TRANSMISSION & DISTRIBUTION 2022年第15期16卷 3119-3127页

作者： Arastou, Alireza Rabieyan, Hadi Karrari, Hesam Karrari, Mehdi Amirkabir Univ Technol Elect Engn Dept 350 Hafez AveValiasr Sq Tehran Iran

Concerning the penetration of renewable energy resources into the power grid, investigation of the power system dynamics to meet the power demand and maintain stability has gathered momentum recently. On the other hand, evaluating the generator parameters in the distributed generation (DG) units as a subsystem of a large-scale power grid is crucial for control and stability analysis purposes. To this aim, a simple and efficacious algorithm to identify the operational parameters of synchronous generators (SGs) in small hydro DGs is proposed here. The required data for the SG identification using the recommended approach is gathered during excitation system start-up while the DG is disconnected from the grid. Using the proposed test procedure, the adverse impact of magnetic saturation on estimation results can be avoided. Furthermore, a straightforward parameter estimation (PE) procedure is established here to obtain the intended parameters from the recorded data. Finally, the proposed method was applied to a 10 MW hydro DG, and the results are discussed.

关键词： efficacious algorithm parameter estimation hydroelectric generators power demand distributed hydro generators power grids generator parameters power system dynamics test procedure recommended approach operational parameters large-scale power grid renewable energy resources parameter identification SG identification excitation system simple algorithm distributed power generation intended parameters straightforward parameter estimation procedure distributed generation units hydro DGs synchronous generators 10 MW hydro DG

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NUMERICAL MODELING OF A RADIO-FREQUENCY PLASMA IN ARGON

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AIAA JOURNAL 1989年第12期27卷 1779-1784页

作者： RHODES, R KEEFER, D University of Tennessee Space Institute Tullahoma Tennessee

An axisymmetric, two-dimensional mathematical model of a radio frequency gas heater is described and compared with experimental data. The model includes mass, axial momentum, radial momentum, and energy conservation equations along with Maxwell's equation for the circumferential component of the electric vector potential. Buoyancy along the heater axis and radial Lorentz forces are included in the momentum equations. Ohmic heating and radiation losses are included in the energy equation. The radiation loss terms are divided into an optically thin component that leaves the gas directly and an optically thick component that is modeled as a conduction term. Results from the model agree reasonably well with data obtained from a laboratory-scale gas heater using a bluff body to stabilize the plasma. Calculated results at increased mass flow and pressure are shown to indicate the model’s capability in designing larger scale heaters. © 1989 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.

关键词： Numerical Modeling Magnetic Induction Mass Flow Thermal Diffusivity Viscosity Thermal Conductivity Electric Potential Temperature Fields simple algorithm Power Supplies

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A high-order discontinuous Galerkin solver for low Mach number flows

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INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS 2016年第8期81卷 489-520页

作者： Klein, B. Mueller, B. Kummer, F. Oberlack, M. Tech Univ Darmstadt Chair Fluid Dynam Petersenstr 30 D-64287 Darmstadt Germany Tech Univ Darmstadt Grad Sch Computat Engn D-64293 Darmstadt Germany Tech Univ Darmstadt Ctr Smart Interfaces Petersenstr 30 D-64287 Darmstadt Germany

In this work, we present a high-order discontinuous Galerkin method (DGM) for simulating variable density flows at low Mach numbers. The corresponding low Mach number equations are an approximation of the compressible Navier-Stokes equations in the limit of zero Mach number. To the best of the authors'y knowledge, it is the first time that the DGM is applied to the low Mach number equations. The mixed-order formulation is applied for spatial discretization. For steady cases, we apply the semi-implicit method for pressure-linked equation (simple) algorithm to solve the non-linear system in a segregated manner. For unsteady cases, the solver is implicit in time using backward differentiation formulae, and the simple algorithm is applied to solve the non-linear system in each time step. Numerical results for the following three test cases are shown: Couette flow with a vertical temperature gradient, natural convection in a square cavity, and unsteady natural convection in a tall cavity. Considering a fixed number of degrees of freedom, the results demonstrate the benefits of using higher approximation orders. Copyright (c) 2015 John Wiley & Sons, Ltd.

关键词： finite element discontinuous Galerkin Navier-Stokes low Mach variable density flows simple algorithm

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Modeling of aluminum alloy profile extrusion process using finite volume method

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JOURNAL OF MATERIALS PROCESSING TECHNOLOGY 2008年第1-3期206卷 481-490页

作者： Lou, Shumei Zhao, Guoqun Wang, Rui Wu, Xianghong Shandong Univ Engn Res Ctr Mould & Die Technol Jinan 250061 Shandong Peoples R China

The most popular numerical method used for simulating aluminum alloy extrusion process is finite element method (FEM). But aluminum alloy profile extrusion process is a metal forming process with severe and large plastic deformation. If finite element method is used to simulate aluminum profile extrusion process, mesh always distorts quickly and frequent remeshing is needed. In addition, the checks for node-separation-from or node-contact-to die surfaces are also frequently needed. The continuous remeshing and node-separation-contact checks usually decrease the accuracy of FEM-based simulation results and increase the CPU time. In this paper, finite volume method (FVM) based on Euler mesh is used to simulate three-dimensional steady or transient aluminum alloy profile hot extrusion process. Semi-implicit method for pressure-linked equations (simple) algorithm is used to calculate the velocity field and the pressure field of the extrusion process. The dynamic viscosity coefficient of the material mostly dependent on temperature and the effective strain-rate is updated in every simple inner iteration. At every exterior time step, the method of volume of fluid (VOF) is applied to catch the transient free surface of the material. "Moving grids system" is also used to deal with the moving problem of the boundaries of the calculated domain caused by the moving of the extrusion ram. To ensure the stability and efficiency of the simulation, automatic adjustment of the time increment is realized. Two typical extrusion processes are simulated by the FVM model of this paper. Some results are compared with those simulated by FEM. The material flow characteristics from transient state of extrusion process to steady state of extrusion process are also discussed. (C) 2008 Elsevier B.V. All rights reserved.

关键词： aluminum alloy extrusion finite volume method simple algorithm volume of fluid moving grids system

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A study on preconditioning iterative methods and relativity of pressure in the numerical calculation of fluid flow

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NUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS 2004年第5期20卷 789-802页

作者： Hirano, H Yoshida, H Ozoe, H Okamoto, N Okayama Univ Sci Dept Appl Chem Okayama 7000005 Japan Hiroshima Univ Dept Chem Engn Higashihiroshima 7398527 Japan Kyushu Univ Inst Mat Chem & Engn Kasuga Fukuoka 8168580 Japan

This article presents the effect of preconditioning iterative methods on boundary conditions of the pressure-correction in the numerical computation of fluid flow with known velocity components on all boundaries using the simple algorithm. In such computation, a set of solutions of the pressure-correction is indefinite, because only the Neumann condition is imposed on all boundaries. However, solutions become unique if the value of pressure-correction is fixed at least on one boundary point, and the Dirichlet condition is additionally imposed. Though both conditions must give exactly the same velocity and temperature fields, this problem arises from the relativity of the pressure. The mathematical illustration for this problem is provided using the numerical computation of the natural convection in an enclosure. It is concluded that the preconditioner adopted and the condition that only the Neumann condition on all boundaries is given are effective to reduce the number of iterations in solving the linear system of equations of the pressure-correction at the computation of the natural convection. (C) 2004 Wiley Periodicals, Inc.

关键词： Neumann condition Dirichlet condition relativity of pressure simple algorithm

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CONVECTIVE HEAT-TRANSFER IN A CURVED ANNULAR-SECTOR DUCT

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JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 1993年第3期7卷 441-446页

作者： YANG, G EBADIAN, MA Florida International Univ. Miami

A numerical analysis of heat transfer behavior in a curved annular-sector duct is presented in this article. A uniform axial heat flux and constant peripheral wall temperature boundary condition are applied in this study. The effects of three major parameters on the heat transfer process (the axial pressure gradient, the dimensionless radius ratio, and the dimensionless curvature) are systematically studied. The results indicate that completely different temperature distribution patterns are evident among the segmented duct in different locations relative to the symmetrical centerline. The Nusselt number significantly increases as the pressure gradient increases. Furthermore, an increase of the dimensionless curvature will also enhance heat transfer because of a strong secondary now. Finally, the results indicate that heat transfer is improved dramatically as the duct radius ratio decreases, especially when the duct radius ratio is smaller than 0.6.

关键词： Forced Convection Heat transfer Temperature Distribution Wall Temperature Heat Flux Numerical Analysis Vortices Flow Patterns Dean Number Thermal Boundary Layer simple algorithm

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ON COMPUTING THE RANGE OF VALUES

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COMPUTING 1982年第3期28卷 225-237页

作者： ASAITHAMBI, NS ZUHE, S MOORE, RE Computer Science Department University of Wisconsin 1210 West Dayton Street 53706 Madison WI USA

A simple algorithm is given for computing the range of values of a differentiable function over ann-dimensional rectangle.

关键词： Computational Mathematic Differentiable Function simple algorithm

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