Sharif Digital Repository

Reservoir flow simulation involves subdivision of the physical domain into a number of gridblocks. This is best accomplished with optimized grid point density and minimized number of gridblocks especially for coarse grid generation from a fine grid geological model. In any coarse grid generation, proper distribution of grid points, which form basis of numerical gridblocks, is a challenging task. We show that this can be effectively achieved by generating a background grid that stores grid point spacing parameter. Spacing (X) can be described by Poisson's equation (∇2 L = G) where the local density of grid points is controlled by a variable source term (G). This source term can be based on... 

In this article, a v2f model is employed to conduct a series of computations of incompressible flow in a periodic array of square cylinders simulating a porous media. A Galerkin/least-squares finite element formulation employing equal order velocity-pressure elements is used to discretize the governing equations. The Reynolds number is varied from 1000 to 84,000 and different values of porosities are considered in the calculations. Results are compared to the available data in the literature. The v2f model exhibits superior accuracy with respect to κ - ε results and is closer to LES calculations. The macroscopic pressure gradients for all porosities studied showed a good agreement with... 

Purpose - The purpose of this paper is to examine the cross-coupled responses of a coupled rotor-fuselage flight dynamic simulation model, including a finite-state inflow aerodynamics and a coupled flap-lag and torsion flexible blade structure. Design/methodology/approach - The methodology is laid out based on model development for an articulated main rotor, using the theories of aeroelastisity, finite element and finite-state inflow formulation. The finite-state inflow formulation is based on a 3D unsteady Euler-based concepts presented in the time domain. The most advantages of the model are the capability of modeling dynamic wake effects, tip losses and skewed wake aerodynamics. This is,... 

Circulation regions always exist in settling tanks. These regions would result in short-circuiting enlargement of the dead zone and high flow mixing problems and avoid optimal particle sedimentation. Therefore, the main objective of the tank design process is to avoid formation of the circulation zone, which is known as dead zone. Experiments show that the tank performance can be improved by altering the geometry of the tank which leads to a different velocity distributions and flow patterns. In this paper, the presence of a baffle and its effect on the hydrodynamics of the flow field has been investigated in a primary settling tank. Hydrodynamics of the flow field in these basins is... 

The dynamics of a two dimensional plane jet injected at the base of a step, parallel to the wall, in backward facing step flow geometry is numerically studied. The objective of this work is to gain insight into the dynamics of the igniter flow field in solid fuel ramjet motors. Solid fuel ramjets operate by ingestion of air and subsequent combustion with a solid fuel grain such as polyethylene. The system of governing equations is solved with a finite volume approach using a structured grid in which the AUSM+ scheme is used to calculate the convective fluxes. The Spalart and Allmaras turbulence model is used in these simulations. Experimental data have been used to validate the flow solver... 

The kinetic-theory-based numerical schemes, such as direct simulation Monte Carlo (DSMC) and information preservation (IP), can be readily used to solve transition flow regimes. However, their high computational cost still promotes the researchers to extend the Navier-Stokes (NS) equations beyond the slip flow and to the transition regime applications. Evidently, a suitable extension would accurately predict both the local velocity profiles and the mass flow rate magnitude as well as the streamwise pressure distribution. The second-order slip velocity model derived from kinetic theory can provide relatively accurate velocity profiles up to a Knudsen (Kn) number of around 0.5; however, its... 

Aiming at improving efficiency in combustion systems, the study on droplet behavior and its trajectory is of crucial importance. Vortex engine is a kind of internal combustion engine which uses swirl flow to achieve higher combustion efficiency. One of the important advantages of designing vortex engine is to reduce the temperature of walls by confining the combustion products in the inner vortex. The scopes of this investigation are to study vortex engine flow field as well as effective parameters on fuel droplet behavior such as droplet diameter, droplet initial velocity and inlet velocity of the flow field. The flow field is simulated using Reynolds Stress Transport Model (RSM). The... 

Load flow problems have always been an important issue in power system analysis and require proper modeling of system components. In this regard Flexible AC Transmission System (FACTS) controllers are modern devices that their modeling specially the series type is a challenging topic. This paper describes a three-phase model for Distributed Static Series Compensator (DSSC) based on extending the Static Synchronous Series Compensator (SSSC) model in Newton power flow. To extend the SSSC model the following two differences must be considered; three completely independent phases and the existence of several modules in a DSSC system. Simulation results on the IEEE 30-bus system and a five bus... 

This paper presents a new combined method for accurate upscaling of two-phase displacements in highly heterogeneous reservoirs. The method has the capability to retain its high performance for various flow regimes, from viscous to gravity dominant displacements, without the need for further modifications and computational steps. Two different grids are incorporated for simulation. The grid on fine scale is used to recognize the complicated physics of flow which depends on dominated driving forces and their interaction with heterogeneity. However, to achieve a fast simulation, the global flow calculation is performed on the coarse scale grid using upscaled equivalent properties. The... 

Heat generation from Very Large-Scale Integrated (VLSI) circuits increases with the development of high-density integrated circuit technology. One of the efficient techniques is liquid cooling by using a microchannel heat sink. Numerical simulations on the microchannel heat sink in the literature are mainly two dimensional. The purpose of the present study is to develop a three-dimensional procedure to investigate flow and conjugate heat transfer in the microchannel heat sink for electronic packaging applications. A finite volume numerical code with a multigrid technique, based on an additive correction multigrid (AC-MG) scheme, which is a high-performance solver, is developed to solve the... 

Overall turbine analysis requires large CPU time and computer memory, even in the present days. As a result, choosing an appropriate computational domain accompanied by a suitable boundary condition can dramatically reduce the time cost of computations. This work compares different geometries for numerical investigation of the 3D flow in the runner of a Francis turbine, and presents an optimum geometry with least computational effort and desirable numerical accuracy. The numerical results are validated with a GAMM Francis Turbine runner, which was used as a test case (GAMM workshop on 3D computation of incompressible internal flows, 1989) in which the geometry and detailed best efficiency... 

This paper presents a novel coarse grid generation technique based on using vorticity as a measure of the impact of heterogeneity on flow. Vorticity is a maximum when the total flow is high and perpendicular to a large permeability gradient. Maps of vorticity were generated from single-phase flow simulations and used to generate coarse simulation grids from finely gridded geological models. The resulting grid was more refined in areas of high vorticity and coarser in areas of low vorticity. The method is first demonstrated on a simple five-layered model before being applied to three, 2D models of geologically realistic heterogeneity. The homogenized model generated from vorticity maps shows... 

Simulation has been shown to be one of the most powerful tools in many areas of the health-care system, a system which attracted the attention of researchers due to its intricacy. The main goal of this study is to evaluate the patients' flow in an emergency department (ED). Discrete event simulation (DES)has been used as the core of this research so that it offers various ways to reduce the length of stay (LOS)of patients in different segments of ED by assessing various scenarios. In particular, a new approach for verification of the simulated model will be discussed. This study reports on the results that extracted from a case study on patient record data in one of the EDs located in Tehran... 

UF6 gas flow in the total regions of a rotor with the radius of 0.1 m and the length of 1 m in axisymmetric and steady states was simulated using a new hybrid CFD-DSMC method in the OpenFOAM framework. Implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in DSMC method. Also, as an initial estimation, the local Knudsen number was applied to determine the interface location between the continuum-rarefied regions (r = 0.0855 m). Then it was modified (r = 0.084 m) to reduce the computational cost. The comparison results of pure CFD and CFD-DSMC methods illustrated that there were large differences between the flow... 

The production routing problem (PRP) merges the lot-sizing problem and the vehicle routing problem, two classical problems that have been the focus of comprehensive studies for over half a century. Solving the PRP is an effort to optimize decisions about the production, inventory, distribution, and routing in an integrated manner. In the literature of the recent decade, due to economic changes and regulatory issues, reverse logistics has become a focal point. Subsequently, the vehicle routing problem with simultaneous pickup and delivery (VRPSPD) has drawn more and more attention for its considerable effect on the reverse logistics problem. In addition, one of the major arguments in supply... 

In this study, silicon microchannel heat sink (MCHS) performance using nanofluids as coolants was analyzed. The nanofluid was a mixture of nanoscale Cu particles and pure water with various volume fractions. Based on theoretical models and experimental correlations, the heat transfer and friction coefficients required in the analysis were used. In the theoretical model, nanofluid was treated as a single-phase fluid. In the experimental correlation, thermal dispersion due to particle random motion was included. The microchannel heat sink performances for a specific geometries with Wch = W fin = 100 μm and Lch =300 μm is examined. In this study, flow in laminar and turbulent regimes using the... 

In this paper, the compressible gas flow through a pipe subjected to wall heat flux in unsteady condition in the entrance region is investigated numerically. The coupled conservation equations governing turbulent compressible viscous flow in the developing region of a pipe are solved numerically under different thermal boundary conditions. The numerical procedure is a finite-volume-based finite-element method applied to unstructured grids. The convection terms are discretized by the well-defined Roe method, whereas the diffusion terms are discretized by a Galerkin finite-element formulation. The temporal terms are evaluated based on an explicit fourth-order Runge-Kutta scheme. The effect of... 

One of the most important challenges in mobile Ad-hoc networks is simulation. The simulation of these networks based on the accessible simulation techniques, which are based on packet, is a demanding and time-consuming task. Moreover, with the complexity of the network and the increase in the numbers of the nodes, it is likely to take a long time. This is because these simulators, one by one, regard the acts of all moving packets in one part of the network, and process these acts as a series of events. Since the number of the events is high in this method, the simulation takes time. Nowadays, in wired networks, several methods have been suggested to lessen the time of simulation; one example... 

In this work, we extend a finite-volume pressure-based incompressible algorithm to solve three-dimensional compressible and incompressible turbulent flow regimes. To achieve a hybrid algorithm capable of solving either compressible or incompressible flows, the mass flux components instead of the primitive velocity components are chosen as the primary dependent variables in a SIMPLE-based algorithm. This choice warrants to reduce the nonlinearities arose in treating the system of conservative equations. The use of a new Favre-averaging like technique plays a key role to render this benefit. The developed formulations indicate that there is less demand to interpolate the fluxes at the cell... 

We derive a new non-linear two dimensional model for melt flows and interface instability in aluminum reduction cells. This model is based on non-linear de St. Venant shallow water equations and contains the main features of an aluminum reduction cell. In this model we consider linear friction terms but in a new way that has not been considered in previous works. Our results are in good agreement with the results of simulation of viscous flow. This model is applicable both in determination of melt flows in molten aluminum and cryolite layers and also in finding the extreme limit for stability of interfacial waves in an aluminum reduction cell