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shear-stress
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Scour hole influence on turbulent flow field around complex bridge piers
, Article Flow, Turbulence and Combustion ; Volume 97, Issue 2 , 2016 , Pages 451-474 ; 13866184 (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
Springer Netherlands
Abstract
Experimental results of detailed flow measurements using an Acoustic-Doppler Velocimeter (ADV) around a complex bridge pier (CBP) are presented. The pier consists of a column, a pile cap (PC) and a 2×4 pile group. The time-averaged velocities, turbulence intensities, and Reynolds stresses are studied and presented at different horizontal and vertical planes. Streamlines obtained from the velocity fields are used to show the complexity of the flow around the pier. It is shown that the main feature of the flow responsible for the entrainment of the bed sediments is a contracted (pressurized) flow below the PC toward the piles. A deflected flow around the PC and a strong down-flow along its...
Numerical investigation of supercritical combustion of H2-O2
, Article Energy and Fuels ; Volume 32, Issue 3 , 2018 , Pages 3851-3868 ; 08870624 (ISSN) ; Barani, E ; Sharif University of Technology
American Chemical Society
2018
Abstract
This study investigates GH2/LOX coaxial jet flame at trans- and supercritical conditions using the Reynolds averaged Navier-Stokes approach. Four two-equation-turbulence models, three real equation of states, two chemical mechanisms, and three different chamber pressures are examined. Predictions show good agreement with measurements qualitatively and quantitatively. Based on the results, the predictions of the Soave-Redlich-Kwong equation of state (EOS) are closer to the experiment, while the Aungier-Redlich-Kwong EOS has more deviation than the others. Moreover, the k-ω shear stress transport model has better performance than the other turbulence models. It is also found that the flow...
Fluid-structure interaction simulation of blood flow and cerebral aneurysm: effect of partly blocked vessel
, Article Journal of Vascular Research ; Volume 56, Issue 6 , 2019 , Pages 296-307 ; 10181172 (ISSN) ; Shamloo, A ; Mohammadi, A ; Sharif University of Technology
S. Karger AG
2019
Abstract
In this study, using fluid-structure interaction (FSI), 3-dimensional blood flow in an aneurysm in the circle of Willis-which is located in the middle cerebral artery (MCA)-has been simulated. The purpose of this study is to evaluate the effect of a partly blocked vessel on an aneurysm. To achieve this purpose, two cases have been investigated using the FSI method: in the first case, an ideal geometry of aneurysm in the MCA has been simulated; in the second case, modeling is performed for an ideal geometry of the aneurysm in the MCA with a partly blocked vessel. All boundary conditions, properties and modeling methods were considered the same for both cases. The only difference between the...
Primary stenosis progression versus secondary stenosis formation in the left coronary bifurcation: a mechanical point of view
, Article Biocybernetics and Biomedical Engineering ; Volume 39, Issue 1 , 2019 , Pages 188-198 ; 02085216 (ISSN) ; Pakravan, H. A ; Saidi, M. S ; Firoozabadi, B ; Sharif University of Technology
Elsevier Sp. z o.o
2019
Abstract
Biomechanical forces and hemodynamic factors influence the blood flow and the endothelial cells (ECs) morphology. These factors behave differently beyond the coronary artery stenosis. In the present study, unsteady blood flow in the left coronary artery (LCA) and its atherosclerotic bifurcating vessels, left anterior descending (LAD) and left circumflex (LCX) arteries, were numerically simulated to investigate the risk of plaque length development and secondary plaque formation in the post-stenotic areas. Using fluid–structure interaction (FSI) model, compliance of arterial wall and vessel curvature variations due to cardiac motion were considered. The arteries included plaques at the...
Primary stenosis progression versus secondary stenosis formation in the left coronary bifurcation: a mechanical point of view
, Article Biocybernetics and Biomedical Engineering ; Volume 39, Issue 1 , 2019 , Pages 188-198 ; 02085216 (ISSN) ; Pakravan, H. A ; Saidi, M. S ; Firoozabadi, B ; Sharif University of Technology
Elsevier Sp. z o.o
2019
Abstract
Biomechanical forces and hemodynamic factors influence the blood flow and the endothelial cells (ECs) morphology. These factors behave differently beyond the coronary artery stenosis. In the present study, unsteady blood flow in the left coronary artery (LCA) and its atherosclerotic bifurcating vessels, left anterior descending (LAD) and left circumflex (LCX) arteries, were numerically simulated to investigate the risk of plaque length development and secondary plaque formation in the post-stenotic areas. Using fluid–structure interaction (FSI) model, compliance of arterial wall and vessel curvature variations due to cardiac motion were considered. The arteries included plaques at the...
Computational investigation of stenosis in curvature of coronary artery within both dynamic and static models
, Article Computer Methods and Programs in Biomedicine ; Volume 185 , 2020 ; Momeni Larimi, M ; Hassanzadeh Afrouzi, H ; Moshfegh, A ; Toghraie, D ; Javadzadegan, A ; Rostami, S ; Sharif University of Technology
Elsevier Ireland Ltd
2020
Abstract
Background and Objective: Blood flow variation during cardiac cycle is the main mechanism of atherosclerotic development which is dependent on. Methods: The present work mainly tends to investigate stenosis effect in dynamic curvature of coronary artery. This paper presents numerical investigations on wall shear stress profiles in three-dimensional pulsatile flow through curved stenotic coronary arteries for both static and dynamic model. In order to do so, three-dimensional models related to the curved arteries with two degrees of stenosis (30% and 50%). Results: Lower amount of wall shear stress is found near the inner wall of artery distal to the plaque region (stenosis) and in both...
Finite element optimization of sample geometry for measuring the torsional shear strength of glass/metal joints
, Article Ceramics International ; Volume 46, Issue 4 , 2020 , Pages 4857-4863 ; Malzbender, J ; Groß Barsnick, S. M ; Abdoli, H ; Kokabi, A. H ; Faghihi Sani, M. A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Assessment of mechanical properties of glass/metal joints is a challenging process, especially when the application relevant conditions of the joints have to be considered in the test design. In this study, a finite element method (FEM) is implemented to analyze a torsional shear strength test designed for glass-ceramic/steel joints aiming towards solid oxide fuel/electrolysis cells application. Deviations from axial symmetry of the square flanges (ends) of respective hourglass-shaped specimens and also supporting and loading sockets of the test set-up are included in the model to simulate conditions close to reality. Undesirable tensile stress and also shear stress concentration appear at...
An analytical method for spiral-wound heat exchanger: design and cost estimation considering temperature-dependent fluid properties
, Article International Journal of Numerical Methods for Heat and Fluid Flow ; 2020 ; Mostafazade Abolmaali, A ; Afshin, H ; Sharif University of Technology
Emerald Group Publishing Ltd
2020
Abstract
Purpose: Spiral-wound heat exchangers (SWHEs) are widely used in different industries. In special applications, such as cryogenic (HEs), fluid properties may significantly depend on fluid temperature. This paper aims to present an analytical method for design and rating of SWHEs considering variable fluid properties with consistent shell geometry and single-phase fluid. Design/methodology/approach: To consider variations of fluid properties, the HE is divided into identical segments, and the fluid properties are assumed to be constant in each segment. Validation of the analytical method is accomplished by using three-dimensional numerical simulation with shear stress transport k-ω model, and...
An analytical method for spiral-wound heat exchanger: design and cost estimation considering temperature-dependent fluid properties
, Article International Journal of Numerical Methods for Heat and Fluid Flow ; Volume 31, Issue 1 , 2021 , Pages 471-496 ; 09615539 (ISSN) ; Mostafazade Abolmaali, A ; Afshin, H ; Sharif University of Technology
Emerald Group Holdings Ltd
2021
Abstract
Purpose: Spiral-wound heat exchangers (SWHEs) are widely used in different industries. In special applications, such as cryogenic (HEs), fluid properties may significantly depend on fluid temperature. This paper aims to present an analytical method for design and rating of SWHEs considering variable fluid properties with consistent shell geometry and single-phase fluid. Design/methodology/approach: To consider variations of fluid properties, the HE is divided into identical segments, and the fluid properties are assumed to be constant in each segment. Validation of the analytical method is accomplished by using three-dimensional numerical simulation with shear stress transport k-ω model, and...
A stability-based model of a growing spine with adolescent idiopathic scoliosis: A combination of musculoskeletal and finite element approaches
, Article Medical Engineering and Physics ; Volume 64 , 2019 , Pages 46-55 ; 13504533 (ISSN) ; Rouhi, G ; Arjmand, N ; Adeeb, S ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Using a combined musculoskeletal and finite element (FE) approach, this study aimed to evaluate stability-based muscle forces in a spine with adolescent idiopathic scoliosis (AIS) as compared to a normal spine; and subsequently, determine the effects of stress distribution on the growth plates (GPs) of the growing spine. For this purpose a nonlinear 3D FE model of one normal and one scoliotic thoracolumbar spine, consisting of GPs attached to rigid L1 to L4 vertebrae, were developed using computed tomography images coupled with a growth modulation using the Stokes’ model. Corresponding well with recent in-vivo and in-vitro studies, results of the models predicted intradiscal pressures at the...
Effects of Static Shear Stress on Liquefaction Strength of Babolsar Sand Investigated under Cyclic Simple Shear and Static Triaxial Tests
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
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...
Effect of Initial Static Shear Stress on Cyclic Resistance and Undrained Behavior of Gravelly Soils under Low Confining Pressures Using Cyclic Triaxial Apparatus
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
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...
Effect of Initial Static Shear Stress on Undrained Cyclic Resistance of Well Graded, Medium Dense Gravelly Soils by Cyclic Triaxial Tests
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
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...
Study the Effect of Considering two Layered wall for Carotid Artery Bifurcation on Distribution of Hemodynamic and Non-Hemodynamic Parameters using a Fluid-Structure Interaction Method
, M.Sc. Thesis Sharif University of Technology ; Dehghan Firoozabadi, Bahar (Supervisor) ; Saidi, Mohammad Said (Supervisor)
Abstract
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...
Simulation of the Blood Flow in a Stenotic Left Coronary Bifurcation to Study the Effects on the Endothelial Cells
, M.Sc. Thesis Sharif University of Technology ; Saeedi, Mohammad Saeed (Supervisor)
Abstract
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...
Development of Unsaturated Triaxial Device in Order to Conduct Stress-Controlled Tests and Study of the Hydromechanical Behavior of Collapsible Soils under Anisotropic Consolidation Case Study: Loess of Gorgan
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
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...
Assessment of Initial Shear Stress Effect on Unsaturated Behavior of Reconstituted Collapsible Soils (A Case Study of the Gorgan Loess)
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
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...
Simulation of LDL Permeation into Multilayer Coronary Arterial Wall: Interactive Effects of Wall Shear Stress and Fluid-Structure Interaction in Hypertension
, M.Sc. Thesis Sharif University of Technology ; Dehghan Firoozabadi, Bahar (Supervisor)
Abstract
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...
Simulation of the Influence of Hypertension on Low Density Lipoprotein (Ldl) Permeation into Multilayer Coronary Bifurcation
, M.Sc. Thesis Sharif University of Technology ; Firoozabadi, Bahar (Supervisor)
Abstract
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...
Numerical Investigation of Hypertension in Plaque Formation and Growth in Human Aorta
, M.Sc. Thesis Sharif University of Technology ; Firoozabadi, Bahar (Supervisor)
Abstract
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...