Loading...
Search for:
fluid-modeling
0.005 seconds
Total 22 records
Numerical Modeling of Pulse Tube Refrigerator and Study of Multi-Dimensional Effect
, M.Sc. Thesis Sharif University of Technology ; Saeedi, Mohammad Hassan (Supervisor)
Abstract
Pulse Tube Refrigerator (PTR) has an exceptional feature among all similar refrigerators, because of its unique characteristics such as long lifetime, compact size and no moving parts in low temperature. Despite of all these advantages because of its low efficiency, many researchers are trying to optimize performance of this refrigerator. Most of these efforts are based on one-dimensional simulation of the system. In this thesis, a two-dimensional analysis is performed to study the nature of flow field in an Inertance Tube Pulse Tube Refrigerator (ITPTR). This analysis is based on a numerical modeling of an entire ITPTR. To reach this purpose the two-dimensional form of mass, momentum and...
Scheduling in Communication Networks: Inherent Limitations and Analytical Tools
, Ph.D. Dissertation Sharif University of Technology ; Golestani, Jamaloddin (Supervisor)
Abstract
Scheduling algorithms are responsible for allocation of various types of resources, interference management, and choosing the times and paths through which messages are to be delivered in a communication network. We consider certain fundamental problems in network scheduling. Any scheduling algorithm, to be practical, must have tractable computational complexity and tolerable delay. In the first part of the thesis, we address the following question: “for a given class of networks, does there exist a scheduling algorithm that performs polynomially many computations (in terms of the network dimensions), while keeping the expected delay of the network polynomially bounded (again in terms of the...
Modeling and Simulation of Three-phase Tapered Fluidized Beds
, M.Sc. Thesis Sharif University of Technology ; Molaei Dehkordi, Asghar (Supervisor)
Abstract
Gas–liquid–solid fluidized beds are widely used in the petrochemical, biochemical, biotechnology, and wastewater treatment industries. These beds have the advantage of appropriate mass and heat transfer, better temperature control, and more solid content. In the present work, computational studies have been conducted on two-dimensional tapered fluidized beds to characterize their hydrodynamic behaviour. The presence of two dispersed phases in these beds results in difference in interphase interactions compared to two-phase fluidized beds. Generally, the three phase fluidized beds create a more complex flow pattern than the conventional type of fluidized beds. Three-phase flow in these beds...
Numerical study on water distribution in different layers of direct methanol fuel cells
, Article Journal of the Electrochemical Society ; Vol. 161, issue. 8 , 2014 , pp. E3110-E3124 ; ISSN: 00134651 ; Baghalha, M ; Sharif University of Technology
Abstract
In this paper, a two-dimensional, two-phase, isothermal model is presented to investigate the water transport characteristic and water distribution in a direct methanol fuel cell (DMFC) with emphasis on exploring the water distribution in different layers of DMFC. The liquid-gas two-phase mass transport in the porous anode and cathode is formulated based on multi-fluid model in porous media and water and methanol crossover through the membrane are considered with the effect of diffusion, electro-osmotic drag, and convection. The modeling results agree well with the three different experimental data in an extensive range of operation conditions. A parametric study is also performed to examine...
Numerical investigation on the solid flow pattern in bubbling gas-solid fluidized beds: Effects of particle size and time averaging
, Article Powder Technology ; Vol. 264, issue , September , 2014 , p. 466-476 ; Salehi, M. S ; Molaei Dehkordi, A ; Sharif University of Technology
Abstract
The effects of particle size on the solid flow pattern in gas-solid bubbling fluidized beds were investigated numerically using two-fluid model based on the kinetic theory of granular flow. In this regard, the set of governing equations was solved using finite volume method in two-dimensional Cartesian coordinate system. Glass bead particles with mean sizes of 880. μm, 500. μm, and 351. μm were fluidized by air flow at excess gas velocities of 0.2. m/s and 0.4. m/s. For particle diameters of 880 and 351. μm, the predicted characteristic times for solid dispersion were 0.14. s and 0.15. s, respectively, while characteristic times for solid diffusivity were 1.68. ms and 0.75. ms in the same...
A successive boundary element model for investigation of sloshing frequencies in axisymmetric multi baffled containers
, Article Engineering Analysis with Boundary Elements ; Volume 37, Issue 2 , 2013 , Pages 383-392 ; 09557997 (ISSN) ; Noorian, M. A ; Haddadpour, H ; Sharif University of Technology
2013
Abstract
This study presents a developed successive Boundary Element Method to determine the symmetric and antisymmetric sloshing natural frequencies and mode shapes for multi baffled axisymmetric containers with arbitrary geometries. The developed fluid model is based on the Laplace equation and Green's theorem. The governing equations of fluid dynamic and free surface boundary condition are also applied to proposed model. A zoning method is presented to model arbitrary arrangement of baffles in multi baffled axisymmetric tanks. The influence of each zone on neighboring zones is applied by introducing interface influence matrix which correlates the velocity potential of interfaces to their flux. By...
Temperature tunable random laser using superconducting materials
, Article Optics Communications ; Volume 285, Issue 7 , 2012 , Pages 1900-1904 ; 00304018 (ISSN) ; Hosseini, M ; Bahrampour, A. R ; Mahdavi, S. M ; Sharif University of Technology
2012
Abstract
We propose that spectral intensity of superconductor based random lasers can be made tunable by changing temperature. The two fluid model and wavelength dependent dispersion formula have been employed to describe the optical response of the superconducting materials. Random laser characteristics have been calculated using the one dimensional FDTD method. Our simulation results reveal that the emission spectrum can be manipulated through the ambient temperature of the system. It is observed that transition from metal phase to pure superconducting phase leads to the enhancement of the laser emission. Furthermore, spatial distribution of the fields in one dimensional disordered media is very...
A reduced order model for liquid sloshing in tanks with flexible baffles using boundary element method
, Article International Journal for Numerical Methods in Engineering ; Volume 89, Issue 13 , 2012 , Pages 1652-1664 ; 00295981 (ISSN) ; Firouz Abadi, R. D ; Haddadpour, H ; Sharif University of Technology
2012
Abstract
In order to study the interaction of sloshing and structural vibrations of baffled tanks, a reduced order model based on modal analysis of structure model and boundary element method for fluids motion is developed. For this purpose, the governing equations of elastic structure and incompressible flow are used to derive simple models to simulate both fields. Using the modal analysis technique, the structural motions are applied to the fluid model and on the other hand by using boundary element method, the fluid loads are applied to the structural model. Based on this formulation, a code is developed which is applicable to an arbitrary elastic tank with arbitrary arrangement of baffles. The...
Simulation of 3D freely bubbling gas-solid fluidized beds using various drag models: TFM approach
, Article Chemical Engineering Research and Design ; Volume 100 , 2015 , Pages 377-390 ; 02638762 (ISSN) ; Molaei Dehkordi, A ; Sharif University of Technology
Institution of Chemical Engineers
2015
Abstract
In this article, 3D modeling and simulation of bubbling fluidized beds has been conducted using various drag models, and the model predictions were validated against reported experimental data and 2D simulation results. In this regard, different drag models reported in the literature including Gidaspow, Syamlal-O'Brien, Hill-Koch-Ladd, and Wen-Yu were applied. A standard Two-Fluid Model (TFM) closed by the Kinetic Theory of Granular Flows (KTGF) was used to simulate bubbling gas-solid fluidized beds. Excellent agreements between the simulation results and experimental data, concerning bed expansion ratio, gas volume fraction, and time-averaged particles velocity, were found over a wide range...
Experiment of new laboratory prototyped magneto-rheological dampers on a light commercial vehicle using neuro-fuzzy algorithm
, Article JVC/Journal of Vibration and Control ; Volume 21, Issue 15 , 2015 , Pages 3007-3019 ; 10775463 (ISSN) ; Matbou, F ; Khayyat, A. A. A ; Sharif University of Technology
SAGE Publications Inc
2015
Abstract
Magneto-rheological (MR) fluids consist of magnetic particles in carrying fluid. One of the drawbacks in using MR dampers in laboratory work is their price. At present, there is a compelling need for the production of the laboratory scale of MR fluids to lower their production cost. In this study, to show that the MR fluid is an applicable prototyped laboratory scale of single ended and mono-tube, MR dampers with a prototyped MR fluid are presented. The main features of produced MR fluid and dampers are simplifying in constructing and their low cost. These dampers are useful for laboratory research work. To illustrate the validity of the MR fluids, using this fluid, four MR dampers are made...
Formation and breakup patterns of falling droplets
, Article Numerical Heat Transfer; Part A: Applications ; Volume 68, Issue 9 , Jun , 2015 , Pages 1023-1030 ; 10407782 (ISSN) ; Taeibi Rahni, M ; Azwadi Che Sidik, N ; Sharif University of Technology
Taylor and Francis Ltd
2015
Abstract
Some interface front patterns of falling droplets are studied via direct numerical solution of the full Navier-Stokes equations governing the system of droplets and the ambient surrounding media as a single-fluid model. We focus on the mutual interactions of the effects of characterizing nondimensional parameters on the formation and break-up of large cylindrical droplets. The investigation of droplet cross sections and deformation angles shows that for moderate values of the Atwood number, increasing the Eötvös number explicitly increases the deformation rate in formation and breakup phenomena. Otherwise, increasing the Ohnesorge number basically amplifies the viscous effects
Numerical simulation of orifice cavitating flows using two-fluid and three-fluid cavitation models
, Article Numerical Heat Transfer; Part A: Applications ; Volume 58, Issue 6 , Sep , 2010 , Pages 505-526 ; 10407782 (ISSN) ; Sadeghi, H ; Sharif University of Technology
2010
Abstract
A number of numerical simulations is carried out to study the turbulent cavitating flow through an orifice. We use two different two-fluid (consisting of two interpenetrating liquid and vapor phases) and three-fluid (consisting of three liquid, vapor, and non-condensable gas phases) cavitation models to extend our study. We use the finite-volume method to solve the multiphase flow governing equations, the SIMPLEC algorithm to link the pressure and velocity equations, and the standard k- model to treat the turbulence closure problem. We fix the outlet pressure and change the inlet pressure suitably in our simulations. The discharge coefficient values obtained by the two chosen models are...
Geometry effects in Eulerian/Granular simulation of a turbulent FCC riser with a (kg-g)-KTGF model
, Article International Journal of Chemical Reactor Engineering ; Volume 8 , 2010 ; 15426580 (ISSN) ; Basirat Tabrizi, H ; Farhadpour, F. A ; Sharif University of Technology
Abstract
Three-dimensional, transient turbulent particulate flow in an FCC riser is modeled using an Eulerian/Granular approach. The turbulence in the gas phase is described by a modified realizable (kg-g) closure model and the kinetic theory of granular flow (KTGF) is employed for the particulate phase. Separate simulations are conducted for a rectangular and a cylindrical riser with similar dimensions. The model predictions are validated against experimental data of Sommerfeld et al (2002) and also compared with the previously reported LES-KTGF simulations of Hansen et al (2003) for the rectangular riser. The (kg-g)-KTGF model does not perform as well as the LES-KTGF model for the riser with a...
Analysis of non-newtonian fluids in microchannels with different wall materials
, Article ASME 2009 7th International Conference on Nanochannels, Microchannels, and Minichannels ; 2009 , Pages 697-703 ; 9780791843499 (ISBN) ; Behshad Shafii, M ; Safari Mohsenabad, S ; Sharif University of Technology
Abstract
The behavior of non-Newtonian fluids is considered as an important subject in micro scale and microfluidic flow researches. Because of the complexity and cost in the numerical works and the experimental set-ups in some instances, the analytical approach can be taken into account as a robust alternative tool to solve the non-Newtonian microfluidic flows in some special cases benefiting from a few simplified assumptions. In this work, we analyze the flow of two non-Newtonian fluids including the power-law and grade-fluid models in microchannels. For the grade-fluid, the stress tensors are defined considering the Rivlin-Ericksen tensor definitions. To avoid the complexities in the entrance...
Application of a free volume model in correlating thermodynamic properties of β-lactam, tetracycline, fluoroquinolone and chloramphenicol antibiotic groups in associating fluids
, Article Chemical Engineering Research and Design ; Volume 87, Issue 3 , 2009 , Pages 335-342 ; 02638762 (ISSN) ; Taghikhani, V ; Vossoughi, M ; Alemzadeh, I ; Sharif University of Technology
2009
Abstract
In this work, an expression for the free volume Gibbs energy model based on the local composition concept (LCC) has been proposed in correlating the solubility, the partitioning and the surface tension of β-lactam, tetracycline, fluoroquinolone and chloramphenicol antibiotic groups in water, alcohol, ketone, trihalomethane, ether and ester solvent groups. Similar to the LCC models the proposed model has two combinatorial and residual terms. The extended Guggenheim model is used as combinatorial term and a new local composition-based model, which is the extended local area fraction NRTL-NRF model, is proposed for the residual term. The results obtained from the proposed model have been...
Layers from initial Rayleigh density profiles by directed nonlinear force driven plasma blocks for alternative fast ignition
, Article Laser and Particle Beams ; Volume 27, Issue 1 , 2009 , Pages 149-156 ; 02630346 (ISSN) ; Cang, Y ; Sadighi Bonabi, R ; Hora, H ; Osman, F ; Sharif University of Technology
2009
Abstract
Measurement of extremely new phenomena during the interaction of laser pulses with terawatt and higher power and picoseconds with plasmas arrived at drastically different anomalies in contrast to the usual observations if the laser pulses were very clean with a contrast ratio higher than 108. This was guaranteed by the suppression of prepulses during less than dozens of ps before the arrival of the main pulse resulting in the suppression of relativistic self-focusing. This anomaly was confirmed in many experimental details, and explained and numerically reproduced as a nonlinear force acceleration of skin layers generating quasi-neutral plasma blocks with ion current densities above 1011...
A new multiphase and dynamic asphaltene deposition tool (MAD-ADEPT) to predict the deposition of asphaltene particles on tubing wall
, Article Journal of Petroleum Science and Engineering ; Volume 195 , 2020 ; Jamshidi, S ; Taghikhani, V ; Sharif University of Technology
Elsevier B.V
2020
Abstract
As expounded, the precipitation and deposition of asphaltene particles in pipelines has been proved to be the most challenging flow assurance problem due to its unknown and complex behaviors. In this work, a new multicomponent, multiphase and dynamic tool was developed to model the aggregation and deposition of asphaltene particles in a bulk medium. The multiphase and dynamic asphaltene deposition tool, shortened as MAD-ADEPT is, in fact, a modified version of the previously developed ADEPT. The new tool was developed to make the asphaltene deposition and aggregation concepts in oil production wells more predictable. To tackle the complexity of the asphaltene problem, a bespoke algorithm was...
Fluctuation bounds for the max-weight policy with applications to state space collapse
, Article Stochastic Systems ; Volume 10, Issue 3 , 2020 , Pages 223-250 ; Tsitsiklis, J. N ; Jamaloddin Golestani, S ; Sharif University of Technology
INFORMS Inst.for Operations Res.and the Management Sciences
2020
Abstract
We consider a multihop switched network operating under a max-weight scheduling policy and show that the distance between the queue length process and a fluid solution remains bounded by a constant multiple of the deviation of the cumulative arrival process from its average. We then exploit this result to prove matching upper and lower bounds for the time scale over which additive state space collapse (SSC) takes place. This implies, as two special cases, an additive SSC result in diffusion scaling under nonMarkovian arrivals and, for the case of independent and identically distributed arrivals, an additive SSC result over an exponential time scale. © 2020 The Author(s)
Numerical modeling of die filling of semi-solid A356 aluminum alloy
, Article Semi-Solid Processing of Alloys and Composites 10 - Selected, peer reviewed papers from the 10th International Conference on Semi-Solid Processing of Alloy and Composites, S2P 2008, Aachen, 16 September 2008 through 18 September 2008 ; Volume 141-143 , 2008 , Pages 605-610 ; 10120394 (ISSN); 9771012039401 (ISBN) ; Aashuri, H ; Narimannezhad, A ; Khosravani, A ; Kiani, M ; Sharif University of Technology
Trans Tech Publications Ltd
2008
Abstract
Computer base and simulation technique have been applied for modeling the semi-solid die filling and part of the solidification process of aluminum A356 alloy. A fairly simple one-phase rheological model has been implemented into a fluid flow finite element software Procast, to solve the partial differential equations. This model is purely viscous nature and is implemented in the power law cut-off model of Procast. The constitutive parameters of this model were determined for a rheocast A356 alloy. Using these parameters and comparing the simulation results with experimental data showed good correlation with the model prediction. The designed die for rheocasting was applied for the...
Sensitivity analysis of torque transmission efficiency of a half-toroidal CVT
, Article 2006 SAE World Congress, Detroit, MI, 3 April 2006 through 6 April 2006 ; 2006 ; 01487191 (ISSN) ; Zohoor, H ; Sharif University of Technology
SAE International
2006
Abstract
In this research a computer model based on elasto hydrodynamic fluid film lubrication is developed in order to calculate the torque transmission efficiency of a half-toroidal CVT variator. Validation of this model is verified by comparing the experimental and the model results. Sensitivity of torque transmission efficiency to eleven parameters is investigated. These parameters are: dimensionless roller curvature, aspect ratio, half cone angle, fluid viscosity index, pressure constant for Roelands model, input rotational velocity, absolute viscosity at atmospheric pressure, Young modulus of disks and power rollers, Poisson ratio of disks and power rollers, number of power rollers and variator...