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(1 - 7 of 7)
- Title
- A Multi-Scale CFD Analysis of Patient-Specific Geometries to Tailor LVAD Cannula Implantation Under Pulsatile Flow Conditions: an investigation aimed at reducing stroke incidence in LVADs.
- Creator
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Prather, Ray, Kassab, Alain, Mansy, Hansen, Divo, Eduardo, University of Central Florida
- Abstract / Description
-
A Left Ventricular Assist Device (LVAD) is a mechanical pump that provides temporary circulatory support when used as bridge-to-transplantation and relieves workload demand placed on a failing heart allowing for myocardia recovery when used as destination therapy. Stroke is the most devastating complication after ventricular assist device (VAD) implantation, with an incidence of 14-47% over 3-6 months. This complication due to thrombus formation and subsequent transport through the...
Show moreA Left Ventricular Assist Device (LVAD) is a mechanical pump that provides temporary circulatory support when used as bridge-to-transplantation and relieves workload demand placed on a failing heart allowing for myocardia recovery when used as destination therapy. Stroke is the most devastating complication after ventricular assist device (VAD) implantation, with an incidence of 14-47% over 3-6 months. This complication due to thrombus formation and subsequent transport through the vasculature to cerebral vessels continues to limit the widespread implementation of VAD therapy. Patient-specific computational fluid dynamics (CFD) analysis may elucidate ways to reduce this risk.We employed a multi-scale model of the aortic circulation in order to examine the effects on flow conditions resulting from varying the VAD cannula implantation location and angle of incidence of the anastomosis to the ascending aorta based on a patient-specific geometry obtained from CT scans. The multi-scale computation consists of a 0D lumped parameter model (LPM) of the circulation modeled via a 50 degree of freedom (DOF) electrical circuit analogy that includes an LVAD model coupled to a 3D computational fluid dynamics model of the circulation. An in-house adaptive Runge-Kutta method is utilized to solve the 50 DOF LPM, and the Starccm+ CFD code is utilized to solve the flowfield. This 0D-3D coupling for the flow is accomplished iteratively with the 0D LPM providing the pulsatile boundary conditions that drive the 3D CFD time-accurate computations of the flowfield. Investigated angle configurations include cannula implantations at 30(&)deg;, 60(&)deg; and 90(&)deg; to the right lateral wall of the ascending aorta. We also considered placements of the VAD cannula along the ascending aorta in which distances of the VAD anastomosis is varied relative to the take-off of the innominate artery. We implemented a mixed Eulerian-Lagrangian particle-tracking scheme to quantify the number of stroke-inducing particles reaching cerebral vessel outlets and included flow visualization through streamlines to identify regions of strong vorticity and flow stagnation, which can promote thrombus formation. Thrombi were modeled as spheres with perfectly elastic interactions numerically released randomly in time and space at cannula inlet plane. Based on clinical observation of the range of thrombus sizes encountered in such cases, particle diameters of 2.5mm and 3.5mm were investigated in our numerical computations. Pulsatile flow results for aforementioned angles suggest that a 90(&)deg; cannula implementation causes flow impingement on the left lateral aortic wall and appears to be highly thrombogenic due to large momentum losses and zones of large re-circulation and that shallow and intermediate cannula angles promote more regular flow carrying particles towards the lower body potentially reducing stroke risk. Indications from this pulsatile numerical study suggest that up to a 50% reduction in stroke rate can be achieve with tailoring of cannula implantation. Results are consistent with significant reduction in stroke incidence achieved by tailoring cannula implantation as reported in previous steady flow computations carried out by our group. As such, results of this study suggest that a simple surgical maneuver in the process of VAD implantation may significantly improve patient life.
Show less - Date Issued
- 2015
- Identifier
- CFE0005689, ucf:50129
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005689
- Title
- NUMERICAL MODELING OF THE SHOCK TUBE FLOW FIELDS BEFORE ANDDURING IGNITION DELAY TIME EXPERIMENTS AT PRACTICAL CONDITIONS.
- Creator
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lamnaouer, mouna, Kassab, Alain, University of Central Florida
- Abstract / Description
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An axi-symmetric shock-tube model has been developed to simulate the shock-wave propagation and reflection in both non-reactive and reactive flows. Simulations were performed for the full shock-tube geometry of the high-pressure shock tube facility at Texas A&M University. Computations were carried out in the CFD solver FLUENT based on the finite volume approach and the AUSM+ flux differencing scheme. Adaptive mesh refinement (AMR) algorithm was applied to the time-dependent flow fields to...
Show moreAn axi-symmetric shock-tube model has been developed to simulate the shock-wave propagation and reflection in both non-reactive and reactive flows. Simulations were performed for the full shock-tube geometry of the high-pressure shock tube facility at Texas A&M University. Computations were carried out in the CFD solver FLUENT based on the finite volume approach and the AUSM+ flux differencing scheme. Adaptive mesh refinement (AMR) algorithm was applied to the time-dependent flow fields to accurately capture and resolve the shock and contact discontinuities as well as the very fine scales associated with the viscous and reactive effects. A conjugate heat transfer model has been incorporated which enhanced the credibility of the simulations. The multi-dimensional, time-dependent numerical simulations resolved all of the relevant scales, ranging from the size of the system to the reaction zone scale. The robustness of the numerical model and the accuracy of the simulations were assessed through validation with the analytical ideal shock-tube theory and experimental data. The numerical method is first applied to the problem of axi-symmetric inviscid flow then viscous effects are incorporated through viscous modeling. The non-idealities in the shock tube have been investigated and quantified, notably the non-ideal transient behavior in the shock tube nozzle section, heat transfer effects from the hot gas to the shock tube side walls, the reflected shock/boundary layer interactions or what is known as bifurcation, and the contact surface/bifurcation interaction resulting into driver gas contamination. The non-reactive model is shown to be capable of accurately simulating the shock and expansion wave propagations and reflections as well as the flow non-uniformities behind the reflected shock wave. Both the inviscid and the viscous non-reactive models provided a baseline for the combustion model iii which involves elementary chemical reactions and requires the coupling of the chemistry with the flow fields adding to the complexity of the problem and thereby requiring tremendous computational resources. Combustion modeling focuses on the ignition process behind the reflected shock wave in undiluted and diluted Hydrogen test gas mixtures. Accurate representation of the Shock –tube reactive flow fields is more likely to be achieved by the means of the LES model in conjunction with the EDC model. The shock-tube CFD model developed herein provides valuable information to the interpretation of the shock-tube experimental data and to the understanding of the impact the facility-dependent non-idealities can have on the ignition delay time measurements.
Show less - Date Issued
- 2010
- Identifier
- CFE0003011, ucf:48366
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003011
- Title
- Computational Fluid Dynamics Proof of Concept and Analysis of a Self-Powered Fontan Circulation.
- Creator
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Ni, Marcus, Kassab, Alain, Divo, Eduardo, Chopra, Manoj, University of Central Florida
- Abstract / Description
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The Fontan circulation is a result of the last (third stage) surgical procedure to correct a single ventricle congenital cardiac disorder in children. Although the Fontan circulation has been successfully established in surgeries over the years, it is flawed and can lead in certain cases to pre-mature death. The main cause of this failure is due to increased pulmonary vascular resistance due to loss pulse pressure and blood flow. In healthy circulations, the heart pumps directly to the lungs,...
Show moreThe Fontan circulation is a result of the last (third stage) surgical procedure to correct a single ventricle congenital cardiac disorder in children. Although the Fontan circulation has been successfully established in surgeries over the years, it is flawed and can lead in certain cases to pre-mature death. The main cause of this failure is due to increased pulmonary vascular resistance due to loss pulse pressure and blood flow. In healthy circulations, the heart pumps directly to the lungs, where as (")Single Ventricle(") patients must use a single sided heart to supply blood to the rest of the body before the lungs. Improvements to the Fontan circulation have been proposed, but they require extensive care or external devices. We propose a (")Self-Powered(") Fontan circulation that will inject energy into the pulmonary system by adding an injection jet shunt (IJS) directly from the heart. The IJS will provide the pulse pressure, blood flow, and entrainment that the pulmonary vascular system needs to function at a healthy level. The difference between a healthy and sick Fontan circulation is 3-5[mmHg] in the IVC. The goal of the IJS is to cause this 3-5[mmHg] pressure drop in the IVC. In the analysis of the Fontan, ascertaining energy losses due to flow jet impingements and flow mixing is critical. Moreover, in order to better understand surgical alternatives is it important to have a robust multi-scale 0D-3D CFD analysis tool that permits investigation of surgical alternatives in a virtual physics-based environment. To this end, a lumped parameter model (LPM) is tightly coupled at the time step level with a full 3D computational fluid dynamics (CFD) model. Using this model scheme, the Fontan test section is no longer being modeled by the LPM. Therefore, it is not limited by the 0D nature of the vascular resistance, capacitance, and inertia bed model. The CFD can take over at the area of interest which accounts for flow directionality and momentum transfer that the LPM is unable to capture. To efficiently calculate optimal IJS configurations, a closed loop steady state model was created to solve a simplified Fontan circulation in 3D. Three models were created with several different optimized configurations, a synthetic model (average dimensions of 2-4 year-old Fontan patients), and two patient-specific models (10 and 24-year-old). The model configurations include changes in the IJS nozzle diameter and IJS placement along the pulmonary artery. These configurations are compared to a baseline model with no IJS. All three models suggest that the IJS helps to decrease IVC pressure while increasing pulse pressure and blood flow to the pulmonary system.
Show less - Date Issued
- 2017
- Identifier
- CFE0006630, ucf:51303
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006630
- Title
- Multi-Physics Model of Key Components In High Efficiency Vehicle Drive.
- Creator
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Lin, Shao Hua, Wu, Xinzhang, Sundaram, Kalpathy, Wahid, Parveen, Wei, Lei, Chow, Louis, University of Central Florida
- Abstract / Description
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Hybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs) are crucial technologies for the automotive industry to meet society's demands for cleaner, more energy efficient transportation. Meeting the need to provide power which sustains HEVs and EVs is an immediate area of concern that research and development within the automotive community must address. Electric batteries and electrical motors are the key components in HEV and EV power generation and transmission, and their performance...
Show moreHybrid Electric Vehicles (HEVs) and Electric Vehicles (EVs) are crucial technologies for the automotive industry to meet society's demands for cleaner, more energy efficient transportation. Meeting the need to provide power which sustains HEVs and EVs is an immediate area of concern that research and development within the automotive community must address. Electric batteries and electrical motors are the key components in HEV and EV power generation and transmission, and their performance plays very important role in the overall performance of the modern high efficiency vehicles. Therefore, in this dissertation, we are motivated to study the electric batteries, interior permanent motor (IPM), in the context of modern hybrid electric/electric drive systems, from both multi-physics and system level perspectives. Electrical circuit theory, electromagnetic Finite Element Analysis (FEA), and Computational Fluid Dynamic (CFD) finite volume method will be used primarily in this work. The work has total of five parts, and they are introduced in the following.Firstly, Battery thermal management design is critical in HEV and EV development. Accurate temperature distribution of the battery cells during vehicle operation is required for achieving optimized design. We propose a novel electrical-thermal battery modeling technique that couples a temperature dependent battery circuit model and a physics-based CFD model to meet this need. The electrical circuit model serves as a heat generation mechanism for the CFD model, and the CFD model provides the temperature distribution of the battery cells, which can also impact the heat generation of the electrical battery model. In this part of work, simulation data has been derived from the model respective to electrical performance of the battery as well as the temperature distribution simultaneously in consideration of the physical dimensions, material properties, and cooling conditions. The proposed model is validated against a battery model that couples the same electrical model with a known equivalent thermal model.Secondly, we propose an accurate system level Foster network thermal model. The parameters of the model are extracted from step responses of the CFD battery thermal model. The Foster network model and the CFD model give the same results. The Foster network can couple with battery circuit model to form an electric-thermal battery model for system simulation.Thirdly, IPM electric machines are important in high performance drive systems. During normal operations, irreversible demagnetization can occur due to temperature rise and various loading conditions. We investigate the performance of an IPM using 3d time stepping electromagnetic FEA considering magnet's temperature dependency. Torque, flux linkage, induced voltage, inductance and saliency of the IPM will be studied in details. Finally, we use CFD to predict the non-uniform temperature distribution of the IPM machine and the impact of this distribution on motor performance. Fourthly, we will switch gear to investigate the IPM motor on the system level. A reduced order IPM model is proposed to consider the effect of demagnetization of permanent magnet due to temperature effect. The proposed model is validated by comparing its results to the FEA results.Finally, a HEV is a vehicle that has both conventional mechanical (i.e. internal combustion engine) and electrical propulsion systems. The electrical powertrain is used to work with the conventional powertrain to achieve higher fuel economy and lower emissions. Computer based modeling and simulation techniques are therefore essential to help reduce the design cost and optimize system performance. Due to the complexity of hybrid vehicles, multi-domain modeling ability is preferred for both component modeling and system simulation. We present a HEV library developed using VHDL-AMS.
Show less - Date Issued
- 2013
- Identifier
- CFE0005024, ucf:50016
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005024
- Title
- A COUPLED CFD-LUMPED PARAMETER MODEL OF THE HUMAN CIRCULATION: ELUCIDATING THE HEMODYNAMICS OF THE HYBRID NORWOOD PALLIATIVE TREATMENT AND EFFECTS OF THE REVERSE BLALOCK-TAUSSIG SHUNT PLACEMENT AND DIAMETER.
- Creator
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Ceballos, Andres, Kassab, Alain, Bai, Yuanli, Deng, Weiwei, DeCampli, William, Divo, Eduardo, University of Central Florida
- Abstract / Description
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The Hybrid Norwood (HN) is a relatively new first stage procedure for neonates with Hypoplastic Left Heart Syndrome (HLHS), in which a sustainable univentricular circulation is established in a less invasive manner than with the standard procedure. A computational multiscale model of such HLHS circulation following the HN procedure was used to obtain detailed hemodynamics. Implementation of a reverse-BT shunt (RBTS), a synthetic bypass from the main pulmonary to the innominate artery placed...
Show moreThe Hybrid Norwood (HN) is a relatively new first stage procedure for neonates with Hypoplastic Left Heart Syndrome (HLHS), in which a sustainable univentricular circulation is established in a less invasive manner than with the standard procedure. A computational multiscale model of such HLHS circulation following the HN procedure was used to obtain detailed hemodynamics. Implementation of a reverse-BT shunt (RBTS), a synthetic bypass from the main pulmonary to the innominate artery placed to counteract aortic arch stenosis, and its effects on local and global hemodynamics were studied.A synthetic and a 3D reconstructed, patient derived anatomy after the HN procedure were utilized, with varying degrees of distal arch obstruction, or stenosis, (nominal and 90% reduction in lumen) and varying RBTS diameters (3.0, 3.5, 4.0 mm). A closed lumped parameter model (LPM) for the peripheral or distal circulation coupled to a 3D Computational Fluid Dynamics (CFD) model that allows detailed description of the local hemodynamics was created for each anatomy. The implementation of the RBTS in any of the chosen diameters under severe stenosis resulted in a restoration of arterial perfusion to near-nominal levels. Shunt flow velocity, vorticity, and overall wall shear stress levels are inverse functions of shunt diameter, while shunt perfusion and systemic oxygen delivery correlates positively with diameter. No correlation of shunt diameter with helicity was recorded.In the setting of the hybrid Norwood circulation, our results suggest: (1) the 4.0mm RBTS may be more thrombogenic when implemented in the absence of severe arch stenosis and (2) the 3.0mm and 3.5mm RBTS may be a more suitable alternative, with preference to the latter since it provides similar hemodynamics at lower levels of wall shear stress.
Show less - Date Issued
- 2015
- Identifier
- CFE0005772, ucf:50068
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005772
- Title
- Hybrid Multi-Objective Optimization of Left Ventricular Assist Device Outflow Graft Anastomosis Orientation to Minimize Stroke Rate.
- Creator
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Lozinski, Blake, Kassab, Alain, Mansy, Hansen, DeCampli, William, University of Central Florida
- Abstract / Description
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A Left Ventricular Assist Device (LVAD) is a mechanical pump that is utilized as a bridge to transplantation for patients with a Heart Failure (HF) condition. More recently, LVADs have been also used as destination therapy and have provided an increase in the quality of life for patients with HF. However, despite improvements in VAD design and anticoagulation treatment, there remains a significant problem with VAD therapy, namely drive line infection and thromboembolic events leading to...
Show moreA Left Ventricular Assist Device (LVAD) is a mechanical pump that is utilized as a bridge to transplantation for patients with a Heart Failure (HF) condition. More recently, LVADs have been also used as destination therapy and have provided an increase in the quality of life for patients with HF. However, despite improvements in VAD design and anticoagulation treatment, there remains a significant problem with VAD therapy, namely drive line infection and thromboembolic events leading to stroke. This thesis focuses on a surgical maneuver to address the second of these issues, guided by previous steady flow hemodynamic studies that have shown the potential of tailoring the VAD outflow graft (VAD-OG) implantation in providing up to 50% reduction in embolization rates. In the current study, multi-scale pulsatile hemodynamics of the VAD bed is modeled and integrated in a fully automated multi-objective shape optimization scheme in which the VAD-OG anastomosis along the Ascending Aorta (AA) is optimized to minimize the objective function which include thromboembolic events to the cerebral vessels and wall shear stress (WSS). The model is driven by a time dependent pressure and flow boundary conditions located at the boundaries of the 3D domain through a 50 degree of freedom 0D lumped parameter model (LPM). The model includes a time dependent multi-scale Computational Fluid Dynamics (CFD) analysis of a patient specific geometry. Blood rheology is modeled as using the non-Newtonian Carreua-Yasuda model, while the hemodynamics are that of a laminar and constant density fluid. The pulsatile hemodynamics are resolved using the commercial CFD solver StarCCM+ while a Lagrangian particle tracking scheme is used to track constant density particles modeling thromobi released from the cannula to determine embolization rated of thrombi. The results show that cannula anastomosis orientation plays a large role when minimizing the objective function for patient derived aortic bed geometry used in this study. The scheme determined the optimal location of the cannula is located at 5.5 cm from the aortic root, cannula angle at 90 degrees and coronal angle at 8 degrees along the AA with a peak surface average WSS of 55.97 dy/cm2 and stroke percentile of 12.51%. A Pareto front was generated showing the range of 9.7% to 44.08% for stroke and WSS of 55.97 to 81.47 dy/cm2 ranged over 22 implantation configurations for the specific case studied. These results will further assist in the treatment planning for clinicians when implementing a LVAD.
Show less - Date Issued
- 2019
- Identifier
- CFE0007833, ucf:52827
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007833
- Title
- Surface Measurements and Predictions of Full-Coverage Film Cooling.
- Creator
-
Natsui, Gregory, Kapat, Jayanta, Raghavan, Seetha, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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Full-coverage film cooling is investigated both experimentally and numerically. First,surface measurements local of adiabatic film cooling eeffectiveness and heat transfer augmentation for four different arrays are described. Reported next is a comparison between two very common turbulence models, Realizable k-epsilon and SST k-omega, and their ability to predict local film cooling effectiveness throughout a full-coverage array.The objective of the experimental study is the quantification of...
Show moreFull-coverage film cooling is investigated both experimentally and numerically. First,surface measurements local of adiabatic film cooling eeffectiveness and heat transfer augmentation for four different arrays are described. Reported next is a comparison between two very common turbulence models, Realizable k-epsilon and SST k-omega, and their ability to predict local film cooling effectiveness throughout a full-coverage array.The objective of the experimental study is the quantification of local heat transferaugmentation and adiabatic film cooling effectiveness for four surfaces cooled by large, both in hole count and in non-dimensional spacing, arrays of film cooling holes. The four arrays are of two different hole-to-hole spacings (P=D = X=D = 14.5; 19.8) and two different hole inclination angles (alpha = 30°; 45°), with cylindrical holes compounded relative to the flow(beta = 45°) and arranged in a staggered configuration. Arrays of up to 30 rows are tested so that the superposition effect of the coolant film can be studied. In addition, shortened arrays of up to 20 rows of coolant holes are also tested so that the decay of the coolant film following injection can be studied.Levels of laterally averaged effectiveness reach values as high as η = 0.5, and are not yet at the asymptotic limit even after 20 - 30 rows of injection for all cases studied. Levels of heat transfer augmentation asymptotically approach values of h=h0 ≈ 1.35 rather quickly, only after 10 rows. It is conjectured that the heat transfer augmentation levels off very quickly due to the boundary layer reaching an equilibrium in which the perturbation from additional film rows has reached a balance with the damping effect resulting from viscosity. The levels of laterally averaged adiabatic film cooling effectiveness far exceeding eta = 0.5 aremuch higher than expected. The heat transfer augmentation levels off quickly as opposed tothe film effectiveness which continues to rise (although asymptotically) at large row numbers. This ensures that an increased row count represents coolant well spent.The numerical predictions are carried out in order to test the ability of the two mostcommon turbulence models to properly predict full-coverage film cooling. The two models chosen, Realizable k-epsilon (RKE) and Shear Stress Transport k-omega (SSTKW), areboth two-equation models coupled with Reynolds Averaged governing equations which makeseveral gross physical assumptions and require several empirical values. Hence, the modelsare not expected to provide perfect results. However, very good average values are seen tobe obtained through these simple models. Using RKE in order to model full-coverage filmcooling will yield results with 30% less error than selecting SSTKW.
Show less - Date Issued
- 2012
- Identifier
- CFE0004580, ucf:49221
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004580
