Sharif Digital Repository

In the ongoing research project on tall buildings, the study of wind-induced demands is categorized as: along-wind and crosswind responses. These demands are caused by different mechanisms. Moving along the wind-induced is due to the effects of turbulence impact while the perpendicular component is related to the effects of windstorm. Along-wind response may be of special importance with respect to the comfort criteria. The loading condition on skyscrapers may differ from low-rise buildings due to the number of stories, on structures due to the high number of stories, and the importance of dynamic effects of current loading (wind). On the other hand the effect of wind load on tall structures... 

With the expansion of the use of renewable photovoltaic sources in electricity generation, the problem of uncertainty in predicting the production capacity of these sources has become one of the most important challenges of power networks due to dependence on climatic conditions, which is a random and uncertain phenomenon. Eliminating or reducing the stated problem requires economic policies that hold the producers of these resources accountable for deviating from the promised products in the day-ahead market. This thesis, the first place, proposes a fuzzy-neural prediction method with minimal input information considering the speed and accuracy of the prediction, which reduces the... 

This thesis’s problem is how a manufacturer should select distribution channels and how to interact with the selected ones. The acquired model, analyzes strategies of the manufacturer regarding selecting distribution channels and coordinating contracts for a triple-channel supply chain environment. The aforementioned channels are physical, electronical, and direct. It is assumed that manufacturer is the Stackelberg leader and the physical channel is the electronical’s follower. Four scenarios are introduced to analyze players’ interactions through contracts. Horizontal competition with Stackelberg game is present in first three scenarios. The forth scenario obtains the maximum total profit... 

Primordial black holes have attracted attention because of their possible role in explaining phenomena such as dark matter and gravitational waves. These observations require the primordial black holes to be in different mass ranges. We investigated the inflaton potentials in which the stochastic sequence of sharp step-like features on the slow-roll potential can produce primordial black holes in different mass ranges. To this end, we first studied the cumulative effects of consecutive steps and showed that there is a resonance mechanism that leads to an exponential enhancement of the power spectrum of certain wavelengths.
 

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... 

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,... 

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... 

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... 

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,... 

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... 

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... 

Coronary artery disease (CAD) is characterized by the accumulation of fats, cholesterol, and other substances in the artery walls, leading to thickening and narrowing, commonly referred to as plaque formation. Clinical studies have shown that this process primarily occurs in regions of low wall shear stress. This study numerically investigates the influence of factors such as low-density lipoprotein (LDL) concentration, the role of antioxidants, and specifically the antioxidant effect of high-density lipoprotein (HDL) and the reverse cholesterol transport (RCT) process on plaque formation in a three-dimensional bifurcation geometry of the left main coronary artery (LMCA) using Fluent... 

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... 

Atherosclerosis is a vascular disorder caused by inflammation of the arterial wall. This inflammation leads to the accumulations of low-density lipoprotein (LDL) cholesterol, monocytes, macrophages and fat-laden foam cells at the site of inflammation, often referred to as plaque formation. This work uses a mathematical model for simulating the deposition of atheroma plaque in coronary arteries. In this study, the effect of time average wall shear stress (TAWSS), oscillatory shear index (OSI), non-Newtonian characteristics of blood and variable hematocrit values on the occurrence of atherosclerosis in a three-dimensional coronary artery was numerically investigated. Simulations was conducted...