ACCURATE PIPE TOP-ENTRY JUNCTION MODEL FOR STEADY AND UNSTEADY FLOWS

ＡＣＣＵＲＡＴＥ　ＰＩＰＥ　ＴＯＰ－ＥＮＴＲＹ　ＪＵＮＣＴＩＯＮ　ＭＯＤＥＬ　ＦＯＲ　ＳＴＥＡＤＹ　ＡＮＤ　ＵＮＳＴＥＡＤＹ　ＦＬＯＷＳＡＣＣＵＲＡＴＥＰＩＰＥＴＯＰ－ＥＮＴＲＹＪＵＮＣＴＩＯＮＭＯＤＥＬＦＯＲＳＴＥＡＤＹＡＮＤＵＮＳＴＥＡＤＹＦＬＯ...     

FINITE ELEMENT ANALYSIS OF COMPLEX INCOMPRESSIBLE FLOWS

ＦＩＮＩＴＥＥＬＥＭＥＮＴＡＮＡＬＹＳＩＳＯＦＣＯＭＰＬＥＸＩＮＣＯＭＰＲＥＳＳＩＢＬＥＦＬＯＷＳ￥ＪｉｎＳｈｅｎｇ（Ｄｅｐｔ．ＣｉｖｉｌＥｎｇｉｎｅｅｒｉｎｇＤａｌｉａｎＵｎｉｖｅｒｓｉｔｙｏｆＴｅｃｈｎｏｌｏｇｙ，Ｄａｌｉａｎ＇ａｎ，１１６０２３...     

3-D SHALLOW WATER FLOW COMPUTATION BY A SEMIIMPLICIT FINITE ELEMENT METHOD

A simi-implicit finite element method is developed for three-dimensional shallow water flow. By using water depth to scale the vertical coordinate, the governing equation is transformed into fixed computational domain. An efficient generalized conjugate gradient scheme is adopted for the solution of finite element analogy.     

STUDY AND APPLICATION OF STEADY FLOW AND UNSTEADY FLOW MATHEMATICAL MODEL FOR CHANNEL NETWORKS

Based on the Preissmann implicit scheme for the one-dimensional Saint-Venant equation, the mathematical model for one-dimensional river networks and canal networks was developed and the key issues on the model were expatiated particularly in this article. This model applies the method of three-steps solution for channel-junction-channel to simulate the river networks, and the Gauss elimination method was used to calculate the sparse matrix. This model was applied to simulate the tree-type irrigation canal networks, complex looped channel networks and the Lower Columbia Slough networks. The results of water level and discharge agree with the data from the Adlul and field data. The model is proved to be robust for simulating unsteady flows in river networks with various degrees of complex structure. The calculated results show that this model is useful for engineering applications in complicated river networks. Future research was recommended to focus on setting up ecological numerical model of water quality in river networks and canal networks.     

A NEW FINITE DIFFERENCE SCHEME FOR 2-D FLOWS AT LARGE Re

Based on the conventional ADI method and SOR method for solving the Navier-Stokes equations, averaging those linkage terms which also are the terms of vary-ing coefficients of the equations, a new finite difference scheme-Averaging Finite Diffe-rence (AFD) scheme for 2-D flows was proposed. A 2-D driven cavity flow was calculated numerically as an example with the presented scheme at Re= 100, 1000, 2000, 3200, 10000. The results were discussed and compared to those obtained with the conventional methods as well as experimental data. It showed that a slight change of the approximation pattern of the conventional scheme in the terms of varying-coefficients of the governing equations seems to have an obvious influence on the solutions at high Re which will be erro- neous if the conventional schemes was employed.     

A FINITE ELEMENT AND BOUNDARY ELEMENT METHOD OF NUMERICAL SIMULATION OF TWO DIMENSIONAL AND TWO PHASE FLOW

ＡＦＩＮＩＴＥＥＬＥＭＥＮＴＡＮＤＢＯＵＮＤＡＲＹＥＬＥＭＥＮＴＭＥＴＨＯＤＯＦＮＵＭＥＲＩＣＡＬＳＩＭＵＬＡＴＩＯＮＯＦＴＷＯＤＩＭＥＮＳＩＯＮＡＬＡＮＤＴＷＯＰＨＡＳＥＦＬＯＷＦａｎＪｉａｎｇ；ＱｕＤｅ－ｂｉｎ；ＺｈａｎｇＺｉ－ｘｉａｎｇ（Ｑｉｎ...     

2-D CHARACTERISTICS-LIKE MODEL AND OPEN BOUNDARY CONDITION FOR UNSTEADY OPEN CHANNEL FLOW MODELING

1.　ＩＮＴＲＯＤＵＣＴＩＯＮＵｎｓｔｅａｄｙｏｐｅｎｃｈａｎｎｅｌｆｌｏｗｓｗｉｔｈｒａｐｉｄｃｈａｎｇｅｏｆｗａｔｅｒｌｅｖｅｌｏｆｔｅｎｏｃｃｕｒｓｉｎｔｈｅｍａｎｍａｄｅｃｈａｎｎｅｌｓａｎｄｎａｔｕｒａｌｒｉｖｅｒｓ.Ｔｈｅｄａｍｂｒｅａｋｆ?..     

FINITE LAYER MODEL FOR 2-D THERMAL DENSITY FLOW IN A CHANNEL

ＦＩＮＩＴＥＬＡＹＥＲＭＯＤＥＬＦＯＲ２－ＤＴＨＥＲＭＡＬＤＥＮＳＩＴＹＦＬＯＷＩＮＡＣＨＡＮＮＥＬ￥ＺｈａｎｇＢｅｎ－ｚｈａｏ；ＳｈｅｎｇＸｉｎ－ｒｏｎｇ（Ｄｅｐｔ．ｏｆＭｅｃｈａｎｉｃｓ，ＺｈｅｊｉａｎｇＵｎｉｖｅｒｓｉｔｙ，Ｈａｎｇｚｈｏｕ３１...     

ISOPARAMETRIC ELEMENT TRANSFORMATION FOR FINITE ANALYTIC METHOD

The Finite Analytic Method (FAM) is a new numerical method for solvingNavier-Stokes equations. However, on complex geometric domains this method must employ theboundary-fitted coordinate transformation, which becomes very difficult for some flow regions.In this paper, the Isoparametric Element, which has been widely used in the Finite ElementMethod, is incorporated into the FAM. The flow region is subdivided into a number of small ar-bitary quadrilaterals, and each element is transformed into a square element by the shape func-tions of Isoparametric Element. Then the partial differential equations on the square element canbe solved by the FAM. As an example, the flow in tube bundles has been calculated by thismethod.     

RESEARCH ON IMPROVED CUT-OFF NEGATIVE PRESSURE METHOD FOR UNSTEADY SEEPAGE FLOW WITH FREE SURFACE

1.INTRODUCTIONThe analysis of seepage flow with free surfaceis often required in geotechnical engineering andhydraulic engineering.It is complex since the freesurface is unknown prior to analysis,namely thestudy areais unknown before computation.The so-lution of free surface substantially belongs to non-linear and free boundary problem.At present,twokinds of finite element analysis method have beenpresented for solving the problem.One is iterativemethod[1]with mesh changedinstantly andthe…     

TEMPORAL AND SPATIAL DISCRETIZATION ON QUASI-3-D GROUNDWATER FINITE ELEMENT MODELLING TO AVOID SPURIOUS OSCILLATION

In this article, the finite element solution of quasi-three-dimensional (quasi-3-D) groundwater flow was mathematically analyzed. The research shows that the spurious oscillation solution to the Finite Element Model (FEM) is the results choosing the small time step ?t or the large element size L and using the non-diagonal storage matrix. The mechanism for this phenomenon is explained by the negative weighting factor of implicit part in the discretized equations. To avoid spurious oscillation solution, the criteria on the selection of ?t and L for quasi-3-D groundwater flow simulations were identified. An application example of quasi-3-D groundwater flow simulation was presented to verify the criteria. The results indicate that temporal discretization scale has significant impact on the spurious oscillations in the finite-element solutions, and the spurious oscillations can be avoided in solving practical quasi-3-D groundwater flow problems if the criteria are satisfied.     

FINITE ELEMENT ANALYSIS OF VISCOUS FLOW PAST A ROTATING SPHERE

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＶｉｓｃｏｕｓｆｌｏｗｐａｓｔａｂｌｕｆｆｂｏｄｙｈａｓｒｅｃｅｉｖｅｄａｇｒｅａｔｄｅａｌｏｆａｔｔｅｎｔｉｏｎｏｗｉｎｇｔｏｉｔｓｔｈｅｏｒｅｔｉｃａｌａｎｄｐｒａｃｔｉｃａｌｓｉｇｎｉｆｉｃａｎｃｅ .Ｔｈｅｐｒｅｓｅｎｃｅｏｆｖｏｒｔｅｘｓｈｅｄｄｉｎｇ ,ｔｏｇｅｔｈｅｒｗｉｔｈｖｏｒｔｅｘｗａｋｅｓ ,ｉｓｒｅｌａｔｅｄｔｏｔｈｅｐｒｅｓｓｕｒｅｆｌｕｃｔｕａ ｔｉｏｎ ,ｓｔｒｕｃｔｕｒａｌｖｉｂｒａｔｉｏｎ ,ａｎｄｎｏｉｓｅ .Ｔｈｅｂｅｈａｖｉｏｒｏｆｔｈｅｆ…     

A HIGH-ORDER FINITE DIFFERENCE METHOD FOR UNSTEADY CONVECTION-DIFFUSION PROBLEMS WITH SOURCE TERM

1.1NTRODUCTIONTheconvectionanddiffusionarethebasicprocessesinfluidflowandheatormasstransfer.Asafundamentalwaytoimprovethereliabilityofnumericalmedeling,muchat-tentionhasbeendrawntothehigh-accuracynumericalmethodsforsolvingtheconvection-diffusionequations(Rai,l987;RogerandKwak,l99oIYangetal-,199l;Hirsh,l975FDennisandHundson,I989;ChenandYang,199l;Chenetal.,19911Yangetal.,1991;Yangeta1.,l991),suchasthecompactdifferencemethodwithtimesavingandhighaccuracy(Hirsh,1975;DennisandHundson,1989…     

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

A 3-D numerical formulation is proposed on the horizontal Cartesian, vertical sigma-coordinate grid for modeling non-hydrostatic pressure free-surface flows. The pressure decomposition technique and θ 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.     

THE p-VERSION OF FINITE ELEMENT METHODS FOR STEADY VISCOELASTIC FLOWS BETWEEN ECCENTRIC ROTATING CYLINDERS

１．　ＩＮＴＲＯＤＵＣＴＩＯＮＢａｓｉｃａｌｌｙ，ｔｈｅｒｅａｒｅｔｗｏａｐｐｒｏａｃｈｅｓｔｏｉｍｐｒｏｖｅｔｈｅａｃｃｕｒａｃｙｏｆｆｉｎｉｔｅｅｌｅｍｅｎｔｓｏｌｕｔｉｏｎｓ：ｔｈｅｓｏｃａｌｌｅｄｈｖｅｒｓｉｏｎｅｍｐｌｏｙｓｌｏｗｅｒｏｒｄｅｒｉｎｔｅｒｐｏｌａｔｉｏｎｓａｎｄｐｒｏｇｒｅｓｓｉｖｅｌｙｒｅｆｉｎｅｓｔｈｅｍｅｓｈｅｓｗｈｉｌｅｔｈｅｓｏｃｏｌｌｅｄｐｖｅｒｓｉｏｎ（ｓｐｅｃｔｒｕｍｍｅｔｈｏｄ）ｕｓｅｓｌｏｃａｌｈｉｇｈｅｒｏｒｄｅｒｉｎｔｅｒｐｏｌａｔｉｏ…     

A FINITE ELEMENT SIMULATION OF NEW YORK BIGHT TIDES FROM A WAVE EQUATION

A finite element model is used to simulate the tidal circulations in the New YorkBight.In this simulation a generalized wave continuity equation coupled with the primitive mo-mentum equations is used to produce a stable and accurate algorithm.The simulation is carriedout for 30 days to allow for a direct comparison with field measurement.The computed resultsagree well with the observed data.     

A STUDY ON UNSTEADY SEEPAGE FLOW THROUGH DAM

A numerical model is proposed to simulate the unsteady seepage flow through dam,with both saturation and water head as variables to describe the seepage domain.Experiments of seepage flow through dam with unsteady conditions were conducted in laboratory to verify the reliability and the accuracy of the numerical model.The performance of the model is also assessed by comparing with analytical solutions.The examples show that the accuracy and the reliability of the model are adequate to handle seepage flow pr...     

A NEW IMPLICIT SCHEME FOR SOLVING 3-D SHALLOW WATER FLOWS

Based on the improved ADI method, this article proposes an improved implicit finite difference scheme for solving 3-D shallow water flows. The main objective is to design a numerical relation between the horizontal velocity on each layer and the depth-averaged velocity for employing the improved ADI method. With the free surface elevation and the depth-averaged velocity obtained by using essentially 2-D depth-averaged mode, the velocity profiles can be obtained easily and simultaneously. The wind-induced flows, the open channel flows due to the pressure gradient and the tidal flows in coastal waters are simulated, and the results are consistent well with the analytical solution and the field data, which shows that the present implicit scheme is stable and effective, and the established model is practical. Moreover, when only one vertical layer is specified, the present 3-D numerical model is reducea to the 2-D depth-averaged model.     

A NUMERICAL MODEL FOR 3-D FLOW IN OPEN CHANNELS

A 3-D model based on the Reynolds equations with closed k-ε turbulence model ispresented in this paper,which can be used to predict surface water flow in open channels.In-stead of the“rigid lid”approximation,the solution of the free surface equation is implemented inthe velocity-pressure iterative procedure on the basis of the conventional SIMPLE method.Thismodel was used to compute the flow in rectangular channels with trenches dredged across the bot-tom.The velocity,eddy viscosity coefficient,turbulent shear stress,turbulent kinetic energyand elevation of the free surface over the trenches dredged in the main channel,can be obtained.The computed results are in good agreement with existing experimentaing data.     

PENALTY UPWIND FINITE ELEMENT METHOD FOR DIFFUSIVE CONVECTION PROBLEM IN DOUBLE－DIFFUSIVE SYSTEM

ＰＥＮＡＬＴＹＵＰＷＩＮＤＦＩＮＩＴＥＥＬＥＭＥＮＴＭＥＴＨＯＤＦＯＲＤＩＦＦＵＳＩＶＥＣＯＮＶＥＣＴＩＯＮＰＲＯＢＬＥＭＩＮＤＯＵＢＬＥ－ＤＩＦＦＵＳＩＶＥＳＹＳＴＥＭ￥ＺｈａｎｇＤｉ－ｍｉｎｇ；ＣｈｅｎＨｏｎｇ；ＬｉＬｉｎ（Ｄｅｐａｒｔｍｅｎｔｆ...