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COMPUTATIONAL ACCESS FLOW REDUCTION EFFECT ON WALL SHEAR STRESS IN BRACHIOCEPHALIC FISTULAE
Title
COMPUTATIONAL ACCESS FLOW REDUCTION EFFECT ON WALL SHEAR STRESS IN BRACHIOCEPHALIC FISTULAE
Creator
Wlodarczyk, Marta P.
Date
2017, 2017-05
Description
The population of patients with end stage renal disease (ESRD) is growing at a rate higher than the global population. The only viable...
Show moreThe population of patients with end stage renal disease (ESRD) is growing at a rate higher than the global population. The only viable treatment for these patients is a kidney transplant. However, in the absence of a suitable kidney donor, renal patients are left with hemodialysis as a renal replacement therapy. Hemodialysis is facilitated through arteriovenous fistula (AVF), and the particular interest in this investigation is brachiocephalic fistula (BCF). The survival of dialysis patients depends on maintaining patency of fistula over a prolonged period of time. The extreme hemodynamic environment that is created by BCF triggers the onset of neointimal hyperplasia (NH) in most renal dialysis patients, which leads to access failure via stenosis. This is because the hemodynamics in AVF are well outside the normal physiological range. Computational fluid dynamics (CFD) along with shape optimization allows for the study of the hemodynamic parameters such as wall shear stress that have been shown to be detrimental in the future occurrence of cephalic arch stenosis. In this study, CFD modeling and identification of hemodynamic patterns was possible in three dimensions due to advanced post processing of IVUS patient-specific geometries. A method utilizing 3D CFD and shape optimization has been developed to implement Miller’s banding method used in clinical practice to evaluate its impact on WSS and onset of neointimal hyperplasia. The level of banding represented by a constriction is in fact a patient specific value and is not a trivial solution of minimum flow rate necessary to conduct hemodialysis; hence suggesting that even restoring the inlet velocity to the velocity pre-fistula creation might not reduce incidence of cephalic arch stenosis. The findings of this study support the previous hypothesis that non-homeostatic WSS distributions trigger neointimal hyperplasia and resulting venous stenosis. The important outcome is that the presented computational framework allows for evaluation of Miller's banding method for reducing the blood flow rate via surgical constriction and identification of a patient-specific banding level that restores the WSS to the normal physiological range.
M.S. in Mechanical and Aerospace Engineering, May 2017
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THERMAL ANALYSIS OF PM MACHINES FOR HIGH PERFORMANCE ELECTRIC VEHICLES
Title
THERMAL ANALYSIS OF PM MACHINES FOR HIGH PERFORMANCE ELECTRIC VEHICLES
Creator
La Marca, Frank
Date
2016, 2016-07
Description
As demand grows for electrification of the automotive industry, the need for a traction motor becomes imperative. There has been considerable...
Show moreAs demand grows for electrification of the automotive industry, the need for a traction motor becomes imperative. There has been considerable effort by electric machine manufacturers to develop and build a traction motor that meets the speci- fications of the automobile industry. One of the limiting factors in the design of an electric automobile is the thermal performance of a traction motor. This thesis focuses on thermal analysis of an electric machine with a major focus on a machine that operates in an automotive environment. Thermal analysis of the electric machine will be focus on the analysis of an electric machine that is used in a FSAE electric racecar. Theory behind various thermal extraction methods are reviewed, including heat transfer and the fluid dynamics of an electric machine. Thermal modeling methods are also investigated, including analytical methods and numerical methods such as finite element analysis and computational fluid dynamics. The importance of thermal modeling of an electric machine is to understand the heat transfer occurring in the machine. In high performance electric machines the limiting factor of the machine the temperature rise when torque is applied. In- vestigation of the heat transfer of a machine can identify the hot spot of the machine and methods of reduction. This will allow for more current applied and more torque which will give a higher density machine.
M.S. in Electrical Engineering, July 2016
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DEVELOPMENT OF A PREDICIlVE FRAMEWORK TO FORECAST VENOUS STENOSIS
Title
DEVELOPMENT OF A PREDICIlVE FRAMEWORK TO FORECAST VENOUS STENOSIS
Creator
Mahmoudzadeh Akherat, S.m. Javid
Date
2016, 2016-12
Description
The end stage renal disease (ESRD) patient population is growing at a troubling rate, calling for a focused attention to investigate the...
Show moreThe end stage renal disease (ESRD) patient population is growing at a troubling rate, calling for a focused attention to investigate the chronic kidney diseases, their characteristics and our lines of defense against them. One major medical treatment for ESRD patients is hemodialysis which is facilitated through vascular access (VA). The vascular access of particular interest in this investigation as well as the medical community is the brachiocephalic fistula (BCF), which is a form of arteriovenous fistula (AVF), created surgically by connecting the brachial artery and the cephalic vein. It is commonly used for elderly patients and for those with poor circulation systems, e.g. diabetics. The extreme hemodynamic environment that BCF creates triggers the onset of neointimal hyperplasia (NH) in most of these patients which leads to access failure and a high morbidity and mortality rate. This process happens in a matter of months, providing an excellent translational medicine experimental stage to observe as the vessel walls react and adapt to the new hemodynamically violent conditions. Through extensive analysis of the venous deformation and subsequent hemodynamics of a patient cohort of 160, a prognosticative framework to predict the vein deformation in these patients prior to the occurrence of the failure has been developed. The obtained results are the consequence of the integration of clinical practice and computational science. The proposed method was first based on our hypothesis which roots the NH in non-physiological wall shear stresses (WSS), and was then improved and modified using rigorous optimization and numerical approaches. This finding is essential to the modification of the current VA techniques to increase the patency of the AVFs, to prevent the diminishing functionality of the access, and to increase the life expectancy of ESRD patients. Moreover, this finding will further assist us in comprehension of the human vasculature growth and remodeling (G&R) through bypassing the analysis of unknown biological phenomena, as it is achieved purely by juxtaposing well-defined mathematical, physical, and medical concepts.
Ph.D. in Mechanical and Aerospace Engineering, December 2016
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THE SPATIAL BLOCK: NATURAL VENTILATION IN HOT AND DRY CLIMATES OF TURKEY
Title
THE SPATIAL BLOCK: NATURAL VENTILATION IN HOT AND DRY CLIMATES OF TURKEY
Creator
BAY, EZGI
Date
2020
Description
The housing deficit is a global problem. In Turkey, solutions to remedy scarce, unaffordable, and low-grade housing are being proposed by TOKI...
Show moreThe housing deficit is a global problem. In Turkey, solutions to remedy scarce, unaffordable, and low-grade housing are being proposed by TOKI, the governmental mass housing administration. Its residential projects based on ‘standard regulations’ and ‘high-rise typologies’ have been widely criticized. The ‘one size fits all’ approach is known for its limited exploration of contemporary needs of this society. Low quality urban and architectural conditions in TOKI projects are believed to marginalize the living standards of the residents. Sprawling rapidly throughout different regions around the country, a permanent complaint of TOKI residents is related to outdoor and indoor thermal conditions. As consequence of this ‘homogenization effect’, overheated and underheated conditions are experienced in these ‘naturally ventilated buildings’ designed with few considerations regarding the surrounding environment. Minimal research has been done on how TOKI towers perform under extreme seasonal conditions and what other building forms could be used in consonance with localized Turkish climates. Most TOKI projects have been developed for ‘hot and dry climates’ that also correspond to areas with larger urban growth from recent migrations. Through post-occupancy evaluations, this dissertation investigates a TOKI built in this climatic context. At the same time, this study brings new ‘typological’ alternatives analyzed through energy simulations and computer fluid dynamics (CFD). These methods are intended to bring clarity about the dynamic of thermal stress inside this project, and how renewable sources, such as prevailing winds, could be used to alleviate thermal related problems in consonance with ‘building forms’ derived from ‘vernacular architecture’ in this region.Inputs from residents illustrate the dynamics of thermal stress and reliance on natural ventilation in summer conditions. It is confirmed through results of the Predicted Percentage Dissatisfied (PPD) and the Air Changes per Hour (ACH) obtained from Simulations in the IES-VE software. The relationship between human thermal comfort and indoor microclimate in TOKI housing can be improved through the reformulation of its residential typologies. The ‘Spatial Block’ approach presented in this dissertation brings the idea of how urban and architectural decisions in addition to improving indoor climatic conditions and thermal satisfaction or residents, brings them improved social integration.
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