Sharif Digital Repository

In this paper we will present some approaches on Reynolds stress production by vortex transport phenomena and nonlinear vorticity generation in momentum equation. First of all we represent a history of recent works to describe how fluid particle motions can be associated with Reynolds stress through either displacement or acceleration terms. In the next section we will describe how vortex stretching causes the Reynolds stress production and what is the dominant effect near and far from the boundary where viscous effects have to be considered. On the other hand, some vortex considered methodologies such as those synthesize boundary layer, as a collection of vortical objects seem to be... 

Electroosmosis is the predominant mechanism for flow generation in lab-on-chip devices. Since most biofluids encountered in these devices are considered to be non-Newtonian, it is vital to study the flow characteristics of common non-Newtonian models under electroosmotic body force. In this paper, the hydrodynamically fully developed electroosmotic flow of power-law fluids in rectangular microchannels is analyzed. The electrical potential and momentum equations are numerically solved through a finite difference procedure for a non-uniform grid. A thoroughgoing parametric study reveals that the Poiseuille number is an increasing function of the channel aspect ratio, the zeta potential, the... 

The High-Performance Light Water Reactor (HPLWR) is the European version of the Supercritical-pressure Water Cooled Reactor (SCWR). Light water reactors at supercritical pressure, being currently under design, are the new generation of nuclear reactors. The present article is a thermal-hydraulic analysis of the HPLWR fuel assembly cluster. The existing thermal hydraulic codes are not capable of analyzing and designing the HPLWR fuel assembly. It is necessary to introduce a new thermal-hydraulic code that can incorporate the parameters and specifications of the HPLWR fuel assembly. The governing equations include energy, mass and momentum equations beside thermal-hydraulic equations are... 

In this paper, a linear theory for the analysis of beams based on the micropolar continuum mechanics is developed. Power series expansions for the axial displacement and micro-rotation fields are assumed. The governing equations are derived by integrating the momentum and moment of momentum equations in the micropolar continuum theory. Body couples and couple stresses can be supported in this theory. After some simplifications, this theory can be reduced to the well-known Timoshenko and Euler-Bernoulli beam theories. The nature of flexural and longitudinal waves in the infinite length micropolar beam has been investigated. This theory predicts the existence of micro-rotational waves which... 

At the present research, a new analytical model is developed for the impact of a deformable blunt projectile to metallic targets using the plastic stress wave propagation theory and the momentum equations. At this model, the deformation of the projectile is considered, too. Also, the effects of dishing and plugging phenomena on failure of the target are investigated. All of the obtained results are compared with the experimental and other available analytical results where good agreement has been observed. The other outcome of this research is a new definition for the penetration stages which includes 9 ones. Motion equations are derived for each of these stages, accordingly  

In the present study criterion for local thermal equilibrium assumption is studied. It concerns with the fluid flow and heat transfer between two parallel plates filled with a saturated porous medium under non-equilibrium condition. A two-equation model is utilized to represent the fluid and solid energy transport. Numerical Finite Volume Method has been developed for solving coupled energy equations and the Non-Darcian effects are considered for description of momentum equation. The effects of suitable non dimensional parameters as Peclet number and conductivity ratio has been studied thoroughly. A suitable non dimensional equation proposed in wide range of Peclet number and conductivity... 

The advent of microfluidics as suitable environments for culturing cells is associated with some challenges as shear stresses applied on the cells. Moreover, among all factors needed for cell viability, feeding hepatocytes with adequate oxygen is of great importance due to their high demand for oxygen compared the other cell types. In this paper three kinds of geometries has been studied in order that shear stresses would be in allowed range and provision of hepatocytes with sufficient oxygen concentrations has been ensured as well. In addition to supplying hepatocytes with oxygen, the range of its concentration has been adjusted in physiologic value so that it would be practical for further... 

In this work, Compressible Smooth Particles Hydrodynamics (C-SPH) is applied for numerical simulation of impulsive wave. Properties of linear and angular momentum in SPH formulation are studied. Kernel gradient of viscous term in momentum equation is corrected to ensure preservation of angular momentum. Corrected SPH method is used to simulate solitary Scott Russell wave and applied to simulate impulsive wave generated by two-dimensional under water landslide. In each of test cases, results of corrected SPH are compared with experimental results. The results of the numerical simulations and experimental works are matched and a satisfactory agreement is observed. Furthermore, vorticity... 

The governing equations of two-dimensional steady density currents are solved numerically using a finite volume method. The v2̄-f turbulence model, based on standard k - s model, is used for the turbulence closure. In this method, all Reynolds stress equations are replaced with both a transport equation for v2̄ and an elliptic relaxation equation for f, a parameter closely related to the pressure strain redistribution term. The Simple-C procedure is used for pressure-velocity coupling. In addition, Boussinesq's approximation is used to obtain the momentum equation. The computed height of the progressive density current is compared to the measured data in the literature, resulting in good... 

Changes in thermodynamic properties such as pressure, temperature, and composition may result in asphaltene precipitation and deposition in porous media. In addition, asphaltene deposition can cause wettability alteration, permeability reduction, and ultimately a decrease in the productivity of a reservoir. Natural depletion is one of the most common processes of asphaltene deposition in which pressure changes destabilize the dissolved asphaltene in the oil and settle them onto the rock surface. In this work, natural depletion experiments in consolidated core samples were performed under simulated reservoir conditions to obtain reliable data and analyze the asphaltene deposition mechanisms.... 

Different models have been proposed for deposition of asphaltene on reservoir rocks that due to complexity of asphaltene nature, most of them have not been productive. Here, a reliable model is proposed which despite of previous models, considers the change in asphaltene saturation in the core. The obtained experimental data in the laboratory was used for model validation. In this work, a series of core flooding tests was carried out in presence of connate water at different solvent-oil volume ratios. Pressure drop was measured at three different terminals along the core. The obtained experimental data as well as mass balance equations, momentum equation, asphaltene deposition and... 

A new approach has been presented to solve gas-liquid flow numerically in vertical pipes of air-lift pumps. To improve modelling, a new strategy has been employed with the capability of coupling the continuity and momentum equations and enforcing the role of pressure directly in the continuity equation. This is achieved via applying a novel scheme called the Physical Influence Scheme (PIS). The current finite volume solution is compared with other available numerical solutions. Indeed, they are in fair agreement. However, the present predictions are far superior to those obtained from an existing simple method, which is widely used in airlift pump modelling  

In this article, transient hydrodynamic and heat-transfer behavior of Newtonian fluid flow in vertical parallel-plate channels partially filled with a porous medium has been investigated numerically. In this regard, the influences of macroscopic local inertial term and the viscous heating due to the viscous dissipation were taken into account in the momentum equations of porous region and the thermal energy equations, respectively. Moreover, Forchheimer-Brinkman extended Darcy model was used to model fluid flow in the porous region. In addition, an analytical solution was obtained in the case of negligible Brinkman and Forchheimer number values at the steady-state conditions. The predicted... 

In this paper, the transient motion of a three unit intelligent Pipe Inspection Gauge (PIG) while moving across anomalies and bends inside gas/oil pipeline has been investigated. The pipeline fluid has been considered as isothermal and compressible. In addition, the pipeline itself has also been considered to be flexible. The fluid continuity and momentum equations along with the 3D multi body dynamic equations of motion of the pig comprise a system of coupled dynamic differential equations which have been solved numerically. Pig's position and velocity profiles as well as upstream and downstream fluid's pressure waves are presented as simulation results which provide a better understanding... 

In this paper, the transient motion of an intelligent Pipe Inspection Gauge (PIG) while moving across anomalies inside a typical gas/oil pipeline has been investigated. The pipeline fluid has been considered as isothermal and compressible. In addition, the pipeline itself has also been considered to be flexible. The fluid continuity and momentum equations along with the 3D dynamic equations of motion of the pig comprise a system of coupled dynamic differential equations which have been solved numerically. Pig's position, orientation and velocity profiles as well as upstream and downstream fluid's pressure waves are presented as simulation results which provide a better understanding of the... 

Asphaltene deposition is a problematic challenge for oil production. Changes in key parameters like pressure and fluid composition during natural depletion and different gas injection scenarios may result in asphaltene precipitation and deposition. In this work, a model is developed by application of mass balance equations, momentum equation, asphaltene deposition and permeability reduction models. An algorithm is developed to perform iterative procedure to solve the numerical equations that contains highly coupled variables. Indeed, an equation is introduced to calculate the saturation of the precipitated asphaltene phase. Model parameters were determined by genetic algorithm which is a... 

The influence of variable fluid properties on mixed electroosmotic and pressure driven flow of non-Newtonian fluids is investigated in this paper. The non-linear coupled energy and momentum equations are solved by means of an iterative numerical approach. The results reveal that the temperature dependent effects only become significant at very high values of the Debye-Hückel parameter in case of combined electroosmotic and pressure driven flow and could safely be neglected in other cases. It is observed that the physical properties variation lead to a higher mean velocity in case of pressure assisted flow and a lower mean velocity in case of pressure opposed flow. Furthermore, the... 

Electroosmotic flow of power-law fluids in the presence of pressure gradient through a slit is analyzed. After numerically solving the Poisson-Boltzmann equation, the momentum equation with electroosmotic body force is solved through an iterative numerical procedure for both favorable and adverse pressure gradients. The results reveal that, in case of pressure assisted flow, shear-thinning fluids reach higher velocity magnitudes compared with shear-thickening fluids, whereas the opposite is true when an adverse pressure gradient is applied. The Poiseuille number is found to be an increasing function of the dimensionless Debye-Hückel parameter, the wall zeta potential, and the flow behavior... 

In this work, Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) is applied for numerical simulation of impulsive wave. Properties of linear and angular momentum in WCSPH formulation are studied. Kernel gradient of viscous term in momentum equation is corrected to ensure preservation of angular momentum. Corrected WCSPH method is used to simulate solitary Scott Russell wave and applied to simulate impulsive wave generated by two-dimensional under water landslide. In each of the test cases, results of corrected WCSPH are compared with experimental results. The results of the numerical simulations and experimental works are matched and a satisfactory agreement is observed.... 

The Adomian Decomposition Method is employed in the solution of the two dimensional laminar boundary layer of Falkner-Skan equation for wedge. This work aims at the solution of momentum equation in the case of accelerated flow and decelerated flow with separation. The Adomian Decomposition Method is provided an analytical solution in the form of an infinite power series. The effect of Adomian polynomials terms is considered on accuracy of the results. The velocity profiles in boundary layer are obtained. Results show a good accuracy compared to the exact solution. © 2007 Elsevier B.V. All rights reserved