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... 

Soil liquefaction is a phenomenon in which soil loses much of its strength or stiffness for a generally short time but nevertheless long enough for liquefaction to be the cause of many losses. Thus, many researchers have worked on the factors which affect this phenomenon. Effects of initial static shear stress on liquefaction strength of loose and medium dense Babolsar sand specimens were investigated in this study. Babolsar sand is fine to medium uniform sand classified as SP in USCS. Tests were performed with cyclic simple shear and static triaxial devices. All tests were performed under consolidated undrained conditions. Cyclic simple shear tests were performed under constant vertical... 

Carotid bifurcation is one of the most important bifurcations in human body which has a lot of curvature in some people. The common carotid artery bifurcates into an internal carotid artery (ICA) and an external carotid artery (ECA). The incidence of stenosis in carotid bifurcation and in particular in the internal carotid artery is of special importance. In the United States of America by 2006, nearly 700000 strokes occur each year, with about 160000 deaths and 20 to 30% of strokes are caused by stenotic carotid that cost estimated at $160 billion. The purpose of this thesis is to investigate in hemodynamic factors of blood flow such as velocity variation, vortex patterns, shear stress and... 

The study of the behavior of gravelly soil in undrained condition has been a major topic for researchers for decades. Liquefaction in gravelly soils in recent earthquake has exposed the importance and necessity of investigation on undrained the behavior of gravely soils in earthquakes. In this research, undrained behavior of gravely soils and the effects of initial static shear stress on their behavior have been investigated. In this experimental research a gravelly soil (GP) performed and a triaxial apparatus is used. All tests are performed under consolidated undraiend condition and the specimens are prepared by wet tamping method. The diameter of the specimen was 10 cm and the height was... 

In femoral neck fracture when the non-union happens in the fractured zone, valgus osteotomy is a surgery method to overcome bone non-union. In this method, a wedge osteotomy-with specific depth and angle- at the femoral neck is created. By changing the bone angle at the fracture site and the angle of the wedge osteotomy it is desired to convert the shear stress to the normal stress. Clinically it is believed that this would facilitate bone healing and prevent bone fracture. This surgery method also changes the anatomy of muscles due to changing hip anatomy, joint reaction force , and it’s direction. This procedure while minimizing shear stress it also reduces the blood supply to the area and... 

The transport behavior of water molecules inside a model carbon nanotube is investigated by using nonequilibrium molecular dynamics simulations. The shearing stress between the nanotube wall and the water molecules is identified as a key factor in determining the nanofluidic properties. Due to the effect of nanoscale confinement, the effective shearing stress is not only size sensitive but also strongly dependent on the fluid flow rate. Consequently, the nominal viscosity of the confined water decreases rapidly as the tube radius is reduced or when a faster flow rate is maintained. The effect of ion concentration and temperature rise on fluid flow and shearing stress is also investigated.... 

One of the most useful methods in metal forming is Sheet Metal Forming. Use of Forming limit diagrams (FLD) in designing is a conventional method. Therefore many experimental and theoretical efforts have been carried out in order to investigate the FLDs. Many ways to obtain this FLDs and their effective parameters have been studied. But the stress state at these studies is planar which lead to an untrue model for several metal forming process such as incremental sheet forming. With this technique, the forming limit curve (FLC) appears in a different pattern, revealing an enhanced formability, compared to conventional forming techniques. Therefore, in this study, the effect of through... 

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... 

Study on gravelly soils is one of the topics that Geotechnical Engineering researches have been concentrated on. Although several researches have enlightened the way to understand the behavior of gravelly soils, yet, there are some shortage of information about the dynamic behavior of this kind of soil in undrained condition. In this research, a series of cyclic triaxial tests have been performed using cyclic triaxial apparatus of Advanced Soil Mechanics Laboratory of Sharif University of Technology to study the effect of anisotropic consolidation (initial static shear stress) on dynamic behavior of a kind of gravel. The performed tests were divided into four groups with different initial... 

Initial static shear stress caused by slopes or nearby structures' foundations can affect the behavior of the soil which is concerned many investigators during previous three decade. In this investigation, the effect of initial static shear stress on the liquefaction resistance of Babolsar sand has been probed using cyclic simple shear tests. Three different initial relative densities (Dr0=20%, 40% and 60%) and three different initial normal stresses (σv0= 50, 150 and 250 kPa) were considered in tests and four various initial static shear ratios (α) ranging between 0.0 and 0.3 were applied which leads to more than 190 distinct experiments. All tests were conducted under constant volume and... 

Tack coat is a layer of asphaltic materials, which is used for binding the surface layer to the current asphalt layer. The appropriate interlayer bonding condition will help different layers form a monolithic structure to resist traffic. The lack of proper interlayer bonding result in slippage between pavement layers, decrease the capability for transferring the load to the underlying layers, rutting, crescent cracking and decreasing the life of the Overlay. This study intends to model a pavement system in three dimensions with ABAQUS software in order to evaluate the amount of shear stress at the interface of asphalt layers. In order to prove the validity of the model, the results of the... 

Softening and liquefaction of granular soils due to earthquakes have been a major cause for much destruction in preceding decades. This phenomenon mostly occurs in sandy soils, yet its occurrence has also been reported in gravelly soils in the last three decades. Despite the numerous researches which have investigated the undrained cyclic behavior of gravelly soils during earthquakes, there are still some aspects that need further study.This research investigates the effect of initial static shear stress on undrained cyclic resistance of a well graded, medium dense gravelly soil by conducting a series of cyclic triaxial tests. The 23 performed tests are categorized into 5 groups with... 

An improvement of thermal efficiency of modern gas turbines is achieved by increasing turbine inlet temperatures. One of the methods of turbine cooling is to form a film layer on the external surfaces of the blades, so that they can work at high temperatures. Most of the studies concentrate on flat plate geometries with injection through slots or rows of holes. Turbine blade surfaces usually have curvatures which seem to alter the flow field significantly on the film-cooled surfaces. However, there are few reports which investigate the effect of curvature on three-dimensional jet flow injected into the turbulent boundary layer over a curved surface. The surface curvature and the blowing... 

It is known today that arterial diseases are among the leading cause of death in modern societies. More than 50% of deaths in western countries are mainly occurred as results of these diseases, namely atherosclerosis. In order to study risk factors and to understand the full process of how arterial diseases initiate and progress, many research topics have been introduced and studied. Researchers believe that mechanical factors such as Wall Shear Stress (WSS), Pressure distribution, Cyclic strain, Back flow zones and many other factors are responsible for initiation of atherosclerosis. Different patterns of Wall Shear Stress and Strain are seen in arteries. Among other factors outlined in... 

Morphology and alignment of endothelial cells (ECs) have great influence on plaque formation. These alignments are based on the cyclic strains and wall shear stress (WSS) on the arterial wall. In the present study, cyclic strains and WSS are investigated to predict the secondary plaque locations downstream of the primary stenosis. Therefore, left coronary artery (LCA) with its branches to left anterior descending (LAD) and left circumflex (LCX) are 3D located on a virtual sphere to consider the cardiac motion. Stenoses are placed at the beginning of the bifurcation with varying degrees from 40% to 70% based on diameter reduction. Healthy coronary is also constructed to compare with those of... 

Collapsible soils such as loess, which are naturally nearly dry or unsaturated, are problematic soils that experience significant decrease in volume when they are subjected to increasing moisture under loading. This type of soils are present in some parts of Iran such as province of Golestan. Most of the researches to date has tended to focus on measuring the values of collapse using conventional double oedometer. However, the study of hydromechanical behavior of this type of soils considering the effect of initial shear stress using unsaturated triaxial device has been rarely investigated by the researchers. The study on the unsaturated behavior of collapsible soils has started at Sharif... 

Collapsible soils such as loess, are kinds of problematic soils which are found as the unsaturated state in nature. Due to strong inter-particle bonds, these soils have a high rather shear strength in their low water content. Upon wetting and under existence or absence of external loading these bonds are loose and soils structure undergo to collapse. These type of soils are found in various regions of Iran such as Gorgan plain. Despite previous studies in order to investigate the behavior of collapsible soils, but assessing the effect the anisotropic compression or initial shear stress on the hydromechanical behavior of these soils has been rarely investigated by the researchers. According... 

Due to increased atherosclerosis-caused mortality, identification of its genesis and development is of great importance. Although, key factors of the origin of the disease is still unknown, it is widely believed that cholesterol particle penetration and accumulation in arterial wall is mainly responsible for further wall thickening and decreased rate of blood flow during a gradual progression. To date, various effective components are recognized whose simultaneous consideration would lead to a more accurate approximation of Low Density Lipoprotein (LDL) distribution within the wall. In this research, a multilayer Fluid-Structure Interaction (FSI) model is studied to simulate the penetration... 

Researchers have done a lot of studies about the use of CFS in blood flow modeling in order to improve the supplementary devices or find mechanical factors which cause artery to be diseased. Blood is a complex rheological fluid, blood flow is a pulastile flow, and blood flow field interacts with the deformable vessel wall. Thus, blood flow modeling like other biological phenomena has its own complexities such as anisotropy, vsicoelasticity, and nonlinearity in stress-strain relationship of vessel wall. To explore the role of hemodynamics in the initiation and progression of stenosis in carotid artery bifurcation, a 3D Computational Fluid Dynamics (CFD) technique is applied. The effect of... 

Static culture systems, such as well-plates, T-Flasks and gas-permeable blood bags are restricted by their limited number of hematopoietic stem cells (HSCs) available. Hence, stirred culture systems are alternative options due to their appropriate culture conditions. Ex-vivo expansion of HSCs in suspension bioreactors has been successfully developed in recent years. The purpose of this study is comparing HSCs expansion in bioreactor with reciprocating impeller and static culture, investigation the effect of rotational speed changes in suspension culture on HSCs expansion and comparing the expansion potential of static and suspension cultures with rotational movement.
Expansion of...