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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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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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Modeling and Optimization of Embedded Active Flow Control Systems
Title
Modeling and Optimization of Embedded Active Flow Control Systems
Creator
Henry, James M.
Date
2024
Description
This thesis presents research focused on the aerodynamic performance of circulation control on two-dimensional and quasi-two-dimensional wings...
Show moreThis thesis presents research focused on the aerodynamic performance of circulation control on two-dimensional and quasi-two-dimensional wings. Aerodynamic loads, namely lift, drag, and moment coefficients, are measured through Reynolds Averaged Navier Stokes (RANS) modeling and wind tunnel experiment. A simplified and parameterized RANS model is presented as a rapidly iterable approach to estimating the performance of trailing-edge circulation control on two dimensional airfoils, with the hypothesis that an optimized airfoil shape can be found which maximizes the lift coefficient increment generated by circulation control, through modification of the wing profile. The simplified modeling setup is compared with more conventional approaches to numerical simulation of circulation control. The performance of the simplified modeling scheme is then compared with wind tunnel studies, for both steady-state and dynamic performance, as functions of both momentum coefficient dCμ and chord-based Reynolds number Re_c. The dynamic performance for the model is studied to find an analog to the theoretical unsteady models of Wagner and Theodorsen. An adjoint optimization framework is used to find an optimal airfoil profile for circulation control. The optimized profile is then compared in both a simulation and a wind tunnel test study against a NACA0015 airfoil. In simulation, improvement between 12% and 15% is seen for the lift control authority for all values of dCμ and Re_c tested. In experiment, the optimized profile demonstrated improvements of up to 28% in lift control authority, dCL/dCμfor values of Cμ, and decreased performance for higher values of Cμ.
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Modeling and Optimization of Embedded Active Flow Control Systems
Title
Modeling and Optimization of Embedded Active Flow Control Systems
Creator
Henry, James M.
Date
2024
Description
This thesis presents research focused on the aerodynamic performance of circulation control on two-dimensional and quasi-two-dimensional wings...
Show moreThis thesis presents research focused on the aerodynamic performance of circulation control on two-dimensional and quasi-two-dimensional wings. Aerodynamic loads, namely lift, drag, and moment coefficients, are measured through Reynolds Averaged Navier Stokes (RANS) modeling and wind tunnel experiment. A simplified and parameterized RANS model is presented as a rapidly iterable approach to estimating the performance of trailing-edge circulation control on two dimensional airfoils, with the hypothesis that an optimized airfoil shape can be found which maximizes the lift coefficient increment generated by circulation control, through modification of the wing profile. The simplified modeling setup is compared with more conventional approaches to numerical simulation of circulation control. The performance of the simplified modeling scheme is then compared with wind tunnel studies, for both steady-state and dynamic performance, as functions of both momentum coefficient dCμ and chord-based Reynolds number Re_c. The dynamic performance for the model is studied to find an analog to the theoretical unsteady models of Wagner and Theodorsen. An adjoint optimization framework is used to find an optimal airfoil profile for circulation control. The optimized profile is then compared in both a simulation and a wind tunnel test study against a NACA0015 airfoil. In simulation, improvement between 12% and 15% is seen for the lift control authority for all values of dCμ and Re_c tested. In experiment, the optimized profile demonstrated improvements of up to 28% in lift control authority, dCL/dCμfor values of Cμ, and decreased performance for higher values of Cμ.
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