Sharif Digital Repository

Dense underflows are continuous currents, caused by interaction of two or more fluids of different density. Density currents move down-slope due their density being heavier than that of the ambient water. In this work, entrainment in 3-D density currents in a straight channel was investigated by a set of experimental studies and Theoretical calculations. Velocity components were measured using Acoustic Doppler Velocimetry (ADV). First of all, the bed shear stress was calculated by the velocity profile method and Reynolds stress method as well and showed a good agreement. By increasing the Richardson number, the bed shear stress decreases. On the other hand, the interface shear stress was... 

Density currents are occurred as a result of the intrusion of a dense fluid into a fluid with a different density. Density difference is the main agent of current’s movement. These currents are observed in nature numerously and they are one of the main reasons of the erosion and transportation of deposition in oceans, seas and rivers. Investigation of these currents is of great importance especially in dams’ reservoir as major cause of deposition and reduction of reservoir’s efficency. Density differences are typically caused by the difference in temperature, existence of solution or insoluble material and suspended solids. In this work, density current is studied experimentally. Density... 

Flows which density difference in a gravity field is their driven force are called Density Currents. Such flows are present in both nature and man made environments. Due to their importance, there have been large efforts to analyse them in both experimental and numerical way. In the present thesis, Smoothed Particle Hydrodynamics (SPH) is introduced as a new tool to simulate such flows. As the method is Lagrangian and particle based, simulation of Density Currents with particles can be addressed more naturally that can be accounted as the method preference to traditional mesh based methods. SPH projection method is incorporated to impose incompressibility. To precisely simulate Density... 

The results of numerical simulation of underground flows are greatly affected not only by the discretization method of flow equations, but also by the way that the geological domain is upscaled. Including the detailed knowledge of heterogeneous permeability distribution is mostly neither feasible nor computationally efficient. So it is important to develop efficient grid generation and upscaling methods to simplify the fine-scale flow model while still including the impact of the heterogeneities as far as possible. Thus regions where parameters of interest have larger values or higher changes require finer grid blocks and regions with lower values or minor changes should have coarser grid... 

The advent of microfluidics as suitable environments for culturing cells is associated with some challenges such as shear stresses applied on the cells. In fact, hepatocytes lose their function as exposed to high shear stresses similar to other cell types. 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 cells. In this thesis, different types of cultures including 2D and 3D has been used 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... 

Advanced reservoir characterization methods can yield geological models at a very fine resolution, containing 1011-1018 cells while the common reservoir simulators can handle much fewer numbers of cells due to computer hardware limitations. The process of coarsening the fine-scale model to simulation models is known as upscaling. There are three fundamental steps in the procedure of upscaling, i.e. defining the coarse grid geometry, calculating the average properties for the generated coarse grid and simulation of the two-phase flow equations on the generated coarse-scale model. In this thesis, the focus will be on investigating the applicability of optimization in the context of coarse grid... 

Density currents are occurred as a result of the intrusion of a dense fluid into a fluid with a different density. Density differences are typically caused by the difference in temperature, existence of solution or insoluble material and suspended solids. A special kind of density current is called a turbidity current which is a sediment-laden density current. This is a kind of flow which is driven by the force of gravity on suspended sediment particles that causes an excess fractional density with respect to the surrounding ambient fluid. In this work, the 2-D sediment-laden density current on a sloping surface of the channel is investigated through experiments. The channel is 12 m long,... 

Dense underflows are continuous currents which move down slope due to the fact that their density is heavier than ambient water. Driven by density differences between the inflow and clear water in the reservoirs, the density current plunges the clear water and moves on the bed. While density currents flowing on a sloping bed, the vertical spreading due to water entrainment plays an important role in determining the propagation rate in the longitudinal direction. These currents are similar to wall-jet currents according to structure of the flows but are complicated relative to wall-jet currents due to the existence of density difference. Characteristics of the density current sometimes are... 

Atherosclerosis is one of the most important factors for mortality and morbidity in the world. Coronary artery bypass graft (CABG) is applied for treatment of this disease which in this surgery, the patient vessels, such as internal thoracic artery and saphenous vein, are harvested and grafted to the coronary arteries. The graft success and its performance in short and long-term are depended on the much factors e.g. the severity of stenosis in the coronary artery. It should be noted that the low level of stenosis in the coronary artery causes the creation of undesirable phenomenon of competitive flow in the grafts after the surgery which this phenomenon has been reported as a cause of graft... 

Sedimentation tanks are channels designed for sedimentation of suspended solids in water. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of water treatment plants. Therefore, researchers have tried to find better designs of sedimentation tanks. Among several design methods have been presented, modification of the geometry of tanks by installing baffles is one of the most effective and economic methods. According to the importance of performance improvement of industrial sedimentation tanks as well as the diversity in reported results, development and completion of previous studies seem to be necessary. In... 

Endothelial derived nitric oxide (NO) and its role in regulating the physiological conditions of blood vessels is one of the favorite topics among researchers. The majority of previous studies have focused on nitric oxide transport in blood vessels, less attention has been paid to its vasodilative effects in blood vessels. The main aim of this study is to propose an integrated model to study the effects of endothelial-derived nitric oxide on hemodynamic conditions of blood vessels. Nitric oxide is produced by endothelial cells upon exposure to mechanical forces such as hemodynamic shear stress. The synthesized nitric oxide then diffuses into the neighboring vascular smooth cells, where it... 

Atherosclerosis, due to the penetration of low-density lipoprotein particles (LDL) into the arterial wall, is one of the most common and death-leading diseases in today's world. Due to its importance, extensive research has been conducted on the factors that affect this disease. In this thesis, a numerical study of the effects of Wall Shear Stress (WSS), non-Newtonian behavior of blood, different hematocrit values, and blood pressure on LDL permeation through the artery wall layers are investigated in a 4-layer wall model of a coronary bifurcation. To obtain the velocity and concentration fields in the domain, momentum, Brinkman, and mass transport equations are solved in the lumen and wall... 

In recent years, the incidence rate of liver cancer has increased sharply and nowadays liver cancer is known as the second leading cause of cancer death in the world. Surgical resection is usually used to treat malignant hepatic tumors. However, in some cases, surgical resection is not possible because of some reasons, such as tumor size and location. In these cases, other minimally invasive ablation methods such as radio-frequency ablation, microwave ablation, and high intensity focused ultrasound (HIFU) can be used. HIFU has some advantages such as noninvasiveness, high penetration depth, and low cost in comparison to the other ablation techniques such as radiofrequency ablation. In HIFU... 

Endothelial cells that cover the inner wall of blood cells and are sensitive to receiving mechanical signals play important role in regulating many vital activities of the human body especially the function of the cardiovascular system. One of the factors affecting the mechanical functions of these cells is the shear stress applied to them. Due to blood velocity increasing or decreasing the endothelial cells shear stress change and leads to some chemical reactions and finally releasing biochemical substances including Nitrogen-Monoxide and Calcium-ion. Nitrogen-Monoxide produced by endothelial cells by affecting the smooth muscle cells in the vessel wall causes dilating of the vessel wall,... 

This thesis introduces a fast and accurate two-phase reservoir flow simulation procedure. The speed up is achieved by an upscaling technique where coarsening is applied to the detailed geological reservoir descriptions. This process results to two major error sources affecting the simulation accuracy significantly. The homogenization error is appeared when coarse scale data, such as equivalent permeability, is calculated from the available fine grid model information. It is shown that the error can be reduced adjusting coarse grid (non-uniform Cartesian) distribution. For the first time in this study, the grid distribution optimization is done based on “vorticity” map. In particular, the... 

A large number of desalination plants have been established to overcome the drinkable water scarcity in the world. These plants produce saline water as effluent, which is often discharged into local sea water. One of the applicable methods to dispose these kinds of effluents is to install an inclined nozzle below the water’s surface. Hence, an inclined negatively buoyant jet (INBJ) forms which is often fully turbulent due to the high discharge velocity. Local environmental characteristics affect the dynamics and mixing behavior of INBJs. One of these characteristics is the sea bed slope, on which the present study has been focused. Large eddy simulations (LES) are performed in the present... 

Today, due to the decline of drinkable water, many desalination plants have been established and operated around the world. Disposal of these brines, which have higher density and temperature than receiving water, causes many environmental impacts. Industrial power plants discharge these effluents into the seawater body mostly as submerged jets due to their higher effectiveness. Many experimental researches have been done on the negative and positive buoyant jet that discharged form desalination plants. But a few numerical studies have been done with investigating the full Navior-Stokes equations and they have been flawed in modeling. For example, some of these models have been able to... 

More than 80% of desalination units in the Persian Gulf use multi-stage flash (MSF) technology. The discharge of effluent from these units sometimes causes severe impacts to the marine environment due to the increase in temperature and salinity around the discharge point. In the current thesis, the geometrical, mixing and turbulence characteristics of the discharge of thermal-saline inclined jets under the water surface, similar to the effluent of MSF units, are numerically investigated by developing the buoyantBoussinesqPimpleFoam solver in the OpenFoam open-source software, using the LES turbulence model and the dynamic Smagorinsky subgrid scale and the UNESCO equation of state. The... 

In this thesis, the effect of heart dynamic motion and pulsatile inflow on blood hemodynamics and LDL permeation into the arterial wall in a 3-D coronary artery bifurcation was investigated. To determine the effect of each factor alone and simultaneous effect of both factors i.e. heart dynamic motion and pulsatile inflow, flow simulations were performed in four cases i.e. steady-static, steady-dynamic, pulsatile-static, and pulsatile-dynamic. The results of flow simulations showed that dynamic geometry and pulsatile inflow have considerable impact on temporal variations of wall shear stress (WSS), even though the effect of pulsatile inflow on WSS variation dominates over the effect of... 

Nowadays, cardiovascular diseases are among the most prevalent cause of death worldwide. Besides, atherosclerosis is a cardiovascular disease happening with the continuous narrowing of vessels, especially medium and large-sized arteries. Moreover, the human aorta is vulnerable to this phenomenon. Atherosclerosis happens when the excess LDL in the blood flow penetrates the arterial wall. Then, the LDL is oxidized, thereby recruiting monocytes as the response against oxidized LDL. After monocytes enter the arterial wall, they differentiate and become macrophages. Macrophages then transform into foam cells by ingesting the oxidized LDL. The fatty foam cells are eventually responsible for the...