Sharif Digital Repository

In this research, the developing turbulent swirling flow in the entrance region of a pipe is investigated analytically by using the boundary layer integral method. The governing equations are integrated through the boundary layer and obtained differential equations are solved with forth-order Adams predictor-corrector method. The general tangential velocity is applied at the inlet region to consider both free and forced vortex velocity profiles. The comparison between present model and available experimental data demonstrates the capability of the model in predicting boundary layer parameters (e.g. boundary layer growth, shear rate and swirl intensity decay rate). Analytical results showed... 

Hemodynamic factors, such as Wall Shear Stress (WSS), play a substantial role in arterial diseases. In the larger arteries, such as the carotid artery, interaction between the vessel wall and blood flow affects the distribution of hemodynamic factors. In the present study, both rigid-wall and deformable-wall models are developed in a 3D numerical simulation to assess the effectiveness of arterial rigidity on worsening hemodynamics, especially WSS. Two different rheological models (Newtonian and CarreauYasuda) have been employed to evaluate the influence of blood, non-Newtonian properties, as well. The importance of vessel wall deformability was compared with the rheological model of blood.... 

The F-actin network and cytosol in the lamellipodia of crawling cells flow in a centripetal pattern and spout-like form, respectively. We have numerically studied this two-phase flow in the realistic geometry of a moving keratocyte. Cytosol has been treated as a low viscosity Newtonian fluid flowing through the high viscosity porous medium of F-actin network. Other involved phenomena including myosin activity, adhesion friction, and interphase interaction are also discussed to provide an overall view of this problem. Adopting a two-phase coupled model by myosin concentration, we have found new accurate perspectives of acto-cytosolic flow and pressure fields, myosin distribution, as well as... 

Atherosclerosis is a world-spread and well-known disease. This disease strongly relates to the endothelial cells (ECs) function. Normally, the endothelial cells align in the flow direction in the atheroprotected sites; however, in the case of atheroprone sites these cells orient randomly. The mechanical stimuli such as wall shear stress and strains could determine the morphology and function of the endothelial cells. In the present study, we numerically simulated the left main coronary artery (LCA) and its branches to left anterior descending (LAD) and left circumflex coronary (LCX) artery using fluid-structure interaction (FSI) modeling. The results were presented as longitudinal and... 

In this paper, the structure of a wall jet deflected by a baffle along with the trajectory of particles has been studied. This baffle is used to produce a stable deflected surface jet, thereby deflecting the high-velocity supercritical stream away from the bed to the surface. An elliptic relaxation turbulence model (ν̄2-f model) has been used to simulate this submerged flow. In recent years, the ν̄2- f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proven that the ν̄2- f model is superior to other Reynolds-averaged Navier-Stokes (RANS) methods in many flows where complex flow... 

Generally, the flow in settling tanks is stratified, but the effect of buoyancy force on the flow field depends on the inlet concentration of particles and flow bulk velocity. A common approach for increasing settling tanks performance is to use baffles which can reduce effects of the unfavorable phenomena such as short circuiting between inlet and outlet and density currents in primary and secondary settling tanks, respectively. The suitable position of the baffles is related to the importance of buoyancy force. As a result, effects of inlet Reynolds and Froude numbers on the strength of buoyancy force are studied for a secondary settling tank and the results show that neither Reynolds nor... 

The shape and morphology of endothelial cells (ECs) lining the blood vessels are a good indicator for atheroprone and atheroprotected sites. ECs of blood vessels experience both wall shear stress (WSS) and cyclic stretch (CS). These mechanical stimuli influence the shape and morphology of ECs. A few models have been proposed for predicting the morphology of ECs under WSS or CS. In the present study, a mathematical cell population model is developed to simulate the morphology of ECs under combined WSS and CS conditions. The model considers the cytoskeletal filaments, cell–cell interactions, and cell–extracellular matrix interactions. In addition, the reorientation and polymerization of... 

The function and morphology of Endothelial Cells (ECs) play a key role in atherosclerosis. The mechanical stimuli of ECs, such as Wall Shear Stress (WSS) and arterial wall strain, greatly inuence the function and morphology of these cells. The present article deals with computations of these stimuli for a 3D model of a healthy coronary artery bifurcation. The focus of the study is to propose an accurate method for computations of WSS and strains. Two approaches are considered: Coupled simultaneous simulation of arterial wall and blood flow, called fluid-Structure Interaction (FSI) simulation, and decoupled, which simulates each domain (fluid and solid domain) separately. The study... 

The morphology of endothelial cells (ECs) may be an indication for determining atheroprone sites. Until now, there has been no clinical imaging technique to visualize the morphology of ECs in the arteries. The present study introduces a computational technique for determining the morphology of ECs. This technique is a multiscale simulation consisting of the artery scale and the cell scale. The artery scale is a fluid-structure interaction simulation. The input for the artery scale is the geometry of the coronary artery, that is, the dynamic curvature of the artery due to the cardiac motion, blood flow, blood pressure, heart rate, and the mechanical properties of the blood and the arterial... 

In this study, a new method for the simulation of the time-dependent behavior of actin cytoskeleton during cell shape change is proposed. For this purpose, a three-dimensional model of endothelial cell consisting of cell membrane, nucleus membrane, and main components of cytoskeleton, namely actin filaments, microtubules, and intermediate filaments is utilized. Actin binding proteins, which play a key role in regulating actin cytoskeleton behavior, are also simulated by using a novel technique. The actin cytoskeleton in this model is more dynamic and adoptable during cell deformation in comparison to previous models. The proposed model is subjected to compressive force between parallel micro... 

Interaction between intracellular dynamics and extracellular matrix (ECM) generally occurred into very thin fragment of moving cell, namely lamellipodia, enables all movable cells to crawl on ECM. In fast-moving cells such as fish Keratocytes, Lamellipodia including most cell area finds a fan-like shape during migration, with a variety of aspect ratio function of fish type. In this work, our purpose is to present a novel and more complete two-dimensional continuum mathematical model of actomyosin-cytosolic two-phase flow of a self-deforming Keratocyte with circular spreaded to steady fan-like shape. In the new approach, in addition to the two-phase flow of the F-actin and cytosol, the... 

Through the activation process of T cells, actin filaments move from the cell periphery toward the cell center. The moving filaments engage with T cell receptors and thus contribute to transportation of the signaling molecules. To study the connection between the moving actin filaments and T cell receptors, an experiment available in the literature has measured filaments flow velocity passing over a region of confined clusters of receptors. It shows that flow velocity decreases in the proximity of the receptors, and then regains its normal value after traversing the region, suggesting a dissipative friction-like connection. In this work, we develop a minimal theoretical model to re-examine... 

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... 

Turbidity currents are often the main processes of sediment transport in deep waters and reservoirs. To prevent sedimentation in critical locations, various methods, such as placing solid obstacles in the path of these flows, have been proposed. In the present study, the effect of inlet concentration on the behavior of turbidity currents in the presence of two consecutive triangular obstacles was investigated experimentally. For this purpose, a series of laboratory experiments were conducted with various inlet concentrations. In each experiment, velocity and concentration profiles were measured using an acoustic Doppler velocimeter. The velocity of the current head and local Froude number... 

The effects of an obstacle on the suspended load transport rate of supercritical turbidity currents were investigated experimentally. A Vectrino velocity meter was used to measure velocity and sediment concentration profiles. The effects of important parameters including inlet discharge, mean inlet sediment concentration and obstacle height on suspended load transport rate were investigated. In the upstream velocity profiles, the obstacle generates the reflected and the interface regions in addition to the wall and the jet regions. The average amount of suspended load transport rate downstream of the obstacle decreases to about 92%. This confirms the depositional behaviour of turbidity... 

Turbidity currents are responsible for much of the sedimentation in reservoirs. In order to control these flows, various methods such as placing an obstacle in their path have been proposed. In this study, the effect of inlet sediment concentration and obstacle height on the behaviour of turbidity currents is investigated experimentally. For this purpose, some experiments were carried out with different inlet concentrations and various obstacle heights. Velocity and concentration profiles were measured using an acoustic Doppler velocimeter. To examine the depositional behaviour of turbidity current, suspended sediment flux was calculated using velocity and concentration profiles of the... 

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... 

Interaction between intracellular dynamics and extracellular matrix (ECM) generally occurred into very thin fragment of moving cell, namely lamellipodia, enables all movable cells to crawl on ECM. In fast-moving cells such as fish Keratocytes, Lamellipodia including most cell area finds a fan-like shape during migration, with a variety of aspect ratio function of fish type. In this work, our purpose is to present a novel and more complete two-dimensional continuum mathematical model of actomyosin-cytosolic two-phase flow of a self-deforming Keratocyte with circular spreaded to steady fan-like shape. In the new approach, in addition to the two-phase flow of the F-actin and cytosol, the... 

Hydrostatic pressure is one of the most fundamental and common mechanical stimuli in the body, playing a critical role in the homeostasis of all organ systems. Kidney function is affected by high blood pressure, namely hypertension, by the increased pressure acting on the glomerular capillary walls. This general effect of hypertension is diagnosed as a chronic disease, but underlying mechanistic causes are still not well understood. This paper reports a portable and adaptive device for studying the effects of hydrostatic pressure on a monolayer of cells. The fabricated device fits within a conventional incubation system and microscope. The effects of various pressures and durations were... 

Applying upscaling techniques is an undeniable demand in reservoir simulation, considering the difference between level of details in a geological model and level of details that can be handled by reservoir simulators. Upscaling reservoir model involves first constructing a coarse grid by employing gridding algorithms and then computing average properties for coarse grid blocks. Although various techniques have been proposed for each of these steps, one has to be aware of strengths and weaknesses of each technique before attempting to apply them. In this paper, we focus on different gridding methods and evaluate their performances. Three main grid generation techniques are considered:...