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Title: ANISOTROPY EVOLUTION DUE TO SURFACE TREATMENT ON 3D-PRINTED FUSED DEPOSITION MODELING (FDM) OF ACRYLONITRILE BUTADIENE STYRENE (ABS).
Creator: Lozinski, Blake E, Kassab, Alain, University of Central Florida
Abstract / Description: Purpose: This paper will present insight to the methodology and results of the experimental characterization of Acrylonitrile Butadiene Styrene (ABS) using Fused Deposition Modeling (FDM). The work in this research explored the effects of print orientation, surface treatment, and ultraviolet (UV) light degradation with the utilization of Digital Image Correlation (DIC) on ABS tensile specimens. Design/methodology: ABS specimens were printed at three build orientations (flat (0 degrees), 45...
Show morePurpose: This paper will present insight to the methodology and results of the experimental characterization of Acrylonitrile Butadiene Styrene (ABS) using Fused Deposition Modeling (FDM). The work in this research explored the effects of print orientation, surface treatment, and ultraviolet (UV) light degradation with the utilization of Digital Image Correlation (DIC) on ABS tensile specimens. Design/methodology: ABS specimens were printed at three build orientations (flat (0 degrees), 45 degrees, and up-right (90 degrees)). Each of these specimens were treated with three different surface treatments including a control (acrylic paint, Cyanoacrylate, and Diglycidyl Bisphenol A) followed by exposure to UV light to the respective batches. This experiment design will provide tensile direction properties with the effect of thermoset coatings and UV degradation. Dogbone FDM specimens based on ASTM standard D638 type IV were printed on a Stratasys Dimension SST (Soluble Support Technology) 1200es 3D Printer and loaded into a MTS Landmark Servohydraulic Test Systems. Analysis was preformed on the fracture section of the tensile specimens utilized DIC and comparing Ultimate Tensile Strength (UTS) and Ultimate Fracture Strength (UFS). Findings: From the results UV light did not play a large factor in the strength of the specimens. The print orientation showed the largest anisotropic behavior where some specimens experienced as much as a 54% difference in ultimate tensile strength. Thermoset coated specimens experienced a maximum of 2% increase in strength for the Cyanoacrylate and Diglycidyl Bisphenol A specimens where the acrylic paint and natural did not. Several findings were of value when looking at the stress strain plots. Originality/value: This paper provides knowledge to the limited work on print build orientation, thermoset coatings and, UV light on ABS specimens. Very little to no work has been done on these three properties. This paper can serve as the foundation of future work on external applications on ABS plastics.
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Date Issued: 2017
Identifier: CFH2000269, ucf:45825
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000269

Title: AN INTERACTIVE FRAMEWORK FOR MESHLESS METHODS ANALYSIS IN COMPUTATIONAL MECHANICS AND THERMOFLUIDS.
Creator: Gerace, Salvadore, Kassab, Alain, University of Central Florida
Abstract / Description: In recent history, the area of physics-based engineering simulation has seen rapid increases in both computer workstation performance as well as common model complexity, both driven largely in part by advances in memory density and availability of clusters and multi-core processors. While the increase in computation time due to model complexity has been largely offset by the increased performance of modern workstations, the increase in model setup time due to model complexity has continued to...
Show moreIn recent history, the area of physics-based engineering simulation has seen rapid increases in both computer workstation performance as well as common model complexity, both driven largely in part by advances in memory density and availability of clusters and multi-core processors. While the increase in computation time due to model complexity has been largely offset by the increased performance of modern workstations, the increase in model setup time due to model complexity has continued to rise. As such, the major time requirement for solving an engineering model has transitioned from computation time to problem setup time. This is due to the fact that developing the required mesh for complex geometry can be an extremely complicated and time consuming task. Consequently, new solution techniques which are capable of reducing the required amount of human interaction are desirable. The subject of this thesis is the development of a novel meshless method that promises to eliminate the need for structured meshes, and thus, the need for complicated meshing procedures. Although the savings gain due to eliminating the meshing process would be more than sufficient to warrant further study, the proposed method is also capable of reducing the computation time and memory footprint compared to similar models solved using more traditional finite element, finite difference, finite volume, or boundary element methods. In particular, this thesis will outline the development of an interactive, meshless, physically accurate modeling environment that provides an extensible framework which can be applied to a multitude of governing equations encountered in computational mechanics and thermofluids. Additionally, through the development of tailored preprocessing routines, efficiency and accuracy of the proposed meshless algorithms can be tested in a more realistic and flexible environment. Examples are provided in the areas of elasticity, heat transfer and computational fluid dynamics.
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Date Issued: 2007
Identifier: CFE0001913, ucf:47484
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001913

Title: CHARACTERIZATION OF A HYDROGEN-BASED SYNTHETIC FUEL IN A SHOCK TUBE.
Creator: Flaherty, Troy, Kassab, Alain, University of Central Florida
Abstract / Description: Shock-tube experiments were performed with syngas mixtures near atmospheric pressure with varying equivalence ratios behind reflected shock waves. Pressure and hydroxyl radical (OH*) emission traces were recorded and used to calculate ignition delay time for a single mixture at equivalence ratios of 0.4, 0.7, 1.0, and 2.0 over a range of temperatures from 913 – 1803 K. The syngas mixture was tested at full concentration as well as with 98% dilution in Argon. The full concentration...
Show moreShock-tube experiments were performed with syngas mixtures near atmospheric pressure with varying equivalence ratios behind reflected shock waves. Pressure and hydroxyl radical (OH*) emission traces were recorded and used to calculate ignition delay time for a single mixture at equivalence ratios of 0.4, 0.7, 1.0, and 2.0 over a range of temperatures from 913 – 1803 K. The syngas mixture was tested at full concentration as well as with 98% dilution in Argon. The full concentration mixtures were used to compare ignition delay time measurements with the theoretical calculations obtained through the use of chemical kinetics modeling using the Davis et al. mechanism. The dilute mixtures were used to study the OH* emission profiles compared to those of the kinetics model. The model was in poor agreement with the experimental data especially at lower temperatures with an ignition delay difference of more than an order of magnitude. These ignition delay time data supplement the few existing data and are in relative agreement. The species profile comparison of OH* compared to the model also showed poor agreement, with the worst agreement at the highest temperatures. While the disagreements with ignition delay time and profile comparisons cannot be explained at this time, the data presented support other findings. The data provide additional information towards understanding this disagreement relative to syngas mixtures despite the relatively well known kinetics of the primary constituents Hydrogen and Carbon Monoxide.
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Date Issued: 2009
Identifier: CFE0002552, ucf:47657
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002552

Title: AN INVERSE ALGORITHM TO ESTIMATE THERMAL CONTACT RESISTANCE.
Creator: Gill, Jennifer, Kassab, Alain, University of Central Florida
Abstract / Description: Thermal systems often feature composite regions that are mechanically mated. In general, there exists a significant temperature drop across the interface between such regions which may be composed of similar or different materials. The parameter characterizing this temperature drop is the thermal contact resistance, which is defined as the ratio of the temperature drop to the heat flux normal to the interface. The thermal contact resistance is due to roughness effects between mating surfaces...
Show moreThermal systems often feature composite regions that are mechanically mated. In general, there exists a significant temperature drop across the interface between such regions which may be composed of similar or different materials. The parameter characterizing this temperature drop is the thermal contact resistance, which is defined as the ratio of the temperature drop to the heat flux normal to the interface. The thermal contact resistance is due to roughness effects between mating surfaces which cause certain regions of the mating surfaces to loose contact thereby creating gaps. In these gap regions, the principal modes of heat transfer are conduction across the contacting regions of the interface, conduction or natural convection in the fluid filling the gap regions of the interface, and radiation across the gap surfaces. Moreover, the contact resistance is a function of contact pressure as this can significantly alter the topology of the contact region. The thermal contact resistance is a phenomenologically complex function and can significantly alter prediction of thermal models of complex multi-component structures. Accurate estimates of thermal contact resistances are important in engineering calculations and find application in thermal analysis ranging from relatively simple layered and composite materials to more complex biomaterials. There have been many studies devoted to the theoretical predictions of thermal contact resistance and although general theories have been somewhat successful in predicting thermal contact resistances, most reliable results have been obtained experimentally. This is due to the fact that the nature of thermal contact resistance is quite complex and depends on many parameters including types of mating materials, surface characteristics of the interfacial region such as roughness and hardness, and contact pressure distribution. In experiments, temperatures are measured at a certain number of locations, usually close to the contact surface, and these measurements are used as inputs to a parameter estimation procedure to arrive at the sought-after thermal contact resistance. Most studies seek a single value for the contact resistance, while the resistance may in fact also vary spatially. In this thesis, an inverse problem (IP) is formulated to estimate the spatial variation of the thermal contact resistance along an interface in a two-dimensional configuration. Temperatures measured at discrete locations using embedded sensors appropriately placed in proximity to the interface provide the additional information required to solve the inverse problem. A superposition method serves to determine sensitivity coefficients and provides guidance in the location of the measuring points. Temperature measurements are then used to define a regularized quadratic functional that is minimized to yield the contact resistance between the two mating surfaces. A boundary element method analysis (BEM) provides the temperature field under current estimates of the contact resistance in the solution of the inverse problem when the geometry of interest is not regular, while an analytical solution can be used for regular geometries. Minimization of the IP functional is carried out by the Levenberg-Marquadt method or by a Genetic Algorithm depending on the problem under consideration. The L-curve method of Hansen is used to choose the optimal regularization parameter. A series of numerical examples are provided to demonstrate and validate the approach.
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Date Issued: 2005
Identifier: CFE0000748, ucf:46582
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000748

Title: APPLICATION OF TRAINED POD-RBF TO INTERPOLATION IN HEAT TRANSFER AND FLUID MECHANICS.
Creator: Ashley, Rebecca A, Kassab, Alain, University of Central Florida
Abstract / Description: To accurately model or predict future operating conditions of a system in engineering or applied mechanics, it is necessary to understand its fundamental principles. These may be the material parameters, defining dimensional characteristics, or the boundary conditions. However, there are instances when there is little to no prior knowledge of the system properties or conditions, and consequently, the problem cannot be modeled accurately. It is therefore critical to define a method that can...
Show moreTo accurately model or predict future operating conditions of a system in engineering or applied mechanics, it is necessary to understand its fundamental principles. These may be the material parameters, defining dimensional characteristics, or the boundary conditions. However, there are instances when there is little to no prior knowledge of the system properties or conditions, and consequently, the problem cannot be modeled accurately. It is therefore critical to define a method that can identify the desired characteristics of the current system without accumulating extensive computation time. This thesis formulates an inverse approach using proper orthogonal decomposition (POD) with an accompanying radial basis function (RBF) interpolation network. This method is capable of predicting the desired characteristics of a specimen even with little prior knowledge of the system. This thesis first develops a conductive heat transfer problem, and by using the truncated POD - RBF interpolation network, temperature values are predicted given a varying Biot number. Then, a simple bifurcation problem is modeled and solved for velocity profiles while changing the mass flow rate. This bifurcation problem provides the data and foundation for future research into the left ventricular assist device (LVAD) and implementation of POD - RBF. The trained POD - RBF inverse approach defined in this thesis can be implemented in several applications of engineering and mechanics. It provides model reduction, error filtration, regularization and an improvement over previous analysis utilizing computational fluid dynamics (CFD).
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Date Issued: 2018
Identifier: CFH2000279, ucf:45782
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000279

Title: DESIGN OF A PHYSICAL WINDKESSEL MODEL FOR USE IN IN-VITRO BENCHTOP MODELING.
Creator: Beggs, Kyle, Kassab, Alain, University of Central Florida
Abstract / Description: Despite improved life expectancy compared to medical management alone, Ventricular Assist Device (VAD) recipients show survival rates of 80% at 12 months and 70% at 24 months. A large portion of VAD-associated mortality results from increased risk of stroke with an event frequency reported between 14-47%. Recent concerns have been raised about unprecedented increases of thrombus formation in VAD recipients with subsequent reports pointing towards implantation techniques as a critical...
Show moreDespite improved life expectancy compared to medical management alone, Ventricular Assist Device (VAD) recipients show survival rates of 80% at 12 months and 70% at 24 months. A large portion of VAD-associated mortality results from increased risk of stroke with an event frequency reported between 14-47%. Recent concerns have been raised about unprecedented increases of thrombus formation in VAD recipients with subsequent reports pointing towards implantation techniques as a critical contributor to these events. Thus, the overall prognosis with mechanical support can improve by advancing the surgeon's approach to VAD implantation. Previous studies using Computational Fluid Dynamics (CFD) were aimed at reducing stroke rates by tailoring the VAD outflow graft (VAD-OG) angle to direct any circulating emboli away from the cerebral vessels. In-vitro, or benchtop, models are often developed as computational counterparts. In order to accurately model the hemodynamics in the cardiovascular system, pulsatile flow must be mimicked. This is achieved in the computational domain by what is called a Windkessel model. This project seeks to develop a physical analogy to the Windkessel model for use in the benchtop experiments.
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Date Issued: 2015
Identifier: CFH0004894, ucf:45420
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004894

Title: DEVELOPMENT OF A SET OF FORCE RESPONSE EQUATIONS TO REPRESENT THE MUSCULATURE IN INFANTS TO STUDY DEVELOPMENTAL DYSPLASIA OF THE HIP.
Creator: Jones, Brendan, Kassab, Alain, University of Central Florida
Abstract / Description: This paper describes how a force response equation was created to model muscles, tendons, and ligaments of the hip joint to improve a biomechanical model of an infant hip to study Developmental Dysplasia of the Hip (DDH). DDH is the most common abnormality in newborn infants and is defined as any amount of instability in the hip including complete dislocation. Researchers at our institution are attempting to increase the success rate of treatment methods by creating computer models of the...
Show moreThis paper describes how a force response equation was created to model muscles, tendons, and ligaments of the hip joint to improve a biomechanical model of an infant hip to study Developmental Dysplasia of the Hip (DDH). DDH is the most common abnormality in newborn infants and is defined as any amount of instability in the hip including complete dislocation. Researchers at our institution are attempting to increase the success rate of treatment methods by creating computer models of the biomechanics of infant hip instability and dislocation. The computer model used a scaled adult pelvis, femur, tibia, fibula and foot to match the size of an infant for the bone geometry. The current infant muscle model is an undifferentiated model based on the area of a single infant muscle, for all muscles modeled. This muscle model was able to provide some insight into the nature of the biomechanics. To improve the infant muscle model, a set of equations differentiated by muscle area was developed. The new set of equations uses a ratio of infant over adult muscle area of a single muscle to create a ratio that can be used to scale all adult muscle areas to infant areas. This model will be more physiologically accurate because it will be differentiated based on muscle area.
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Date Issued: 2015
Identifier: CFH0004896, ucf:45421
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004896

Title: UNDERSTANDING AND MODELING PATHWAYS TO THROMBOSIS.
Creator: Seligson, John, Kassab, Alain, University of Central Florida
Abstract / Description: Intra-vessel thrombosis leads to serious problems in patient health. Coagulation can constrict blood flow and induce myocardial infarction or stroke. Hemodynamic factors in blood flow promote and inhibit the coagulation cascade. Mechanically, high shear stress has been shown to promote platelet activation while laminar flow maintains plasma layer separation of platelets and endothelial cells, preventing coagulation. These relationships are studied experimentally, however, physical properties...
Show moreIntra-vessel thrombosis leads to serious problems in patient health. Coagulation can constrict blood flow and induce myocardial infarction or stroke. Hemodynamic factors in blood flow promote and inhibit the coagulation cascade. Mechanically, high shear stress has been shown to promote platelet activation while laminar flow maintains plasma layer separation of platelets and endothelial cells, preventing coagulation. These relationships are studied experimentally, however, physical properties of thrombi, such as density and viscosity, are lacking in data, preventing a comprehensive simulation of thrombus interaction. This study incorporates experimental findings from literature to compile a characteristic mechanical property data set for use in thrombosis simulation. The focus of this study's simulation explored how thrombi interact between other thrombi and vessel walls via Volume of Fluid method. The ability to predict thrombosis under specific hemodynamic conditions was also a feature of the data collection. Using patient specific vessel geometry, the findings in this study can be applied to simulate thrombosis scenarios. The possible applications of such a simulation include a more precise method for estimation of patient myocardial infarction or stroke risk and a possible analysis of vessel geometry modification under surgery.
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Date Issued: 2015
Identifier: CFH0004837, ucf:45440
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004837

Title: MIMICKING BLOOD RHEOLOGY FOR MORE ACCURATE MODELING IN BENCHTOP RESEARCH.
Creator: Webb, Lindsey, Kassab, Alain, University of Central Florida
Abstract / Description: To confirm computer simulations and Computational Fluid Dynamics (CFD) analysis, benchtop experiments are needed with a fluid that mimics blood and its viscoelastic properties. Blood is challenging to use as a working fluid in a laboratory setting because of health and safety concerns. Therefore, a blood analogue is necessary to perform benchtop experiments. Viscosity is an important property of fluids for modeling and experiments. Blood is a shear thinning fluid, so it has a decreasing...
Show moreTo confirm computer simulations and Computational Fluid Dynamics (CFD) analysis, benchtop experiments are needed with a fluid that mimics blood and its viscoelastic properties. Blood is challenging to use as a working fluid in a laboratory setting because of health and safety concerns. Therefore, a blood analogue is necessary to perform benchtop experiments. Viscosity is an important property of fluids for modeling and experiments. Blood is a shear thinning fluid, so it has a decreasing viscosity with higher shear rates. This project seeks to create a blood mimicking fluid for benchtop laboratory use. Numerous fluids with different combinations of water, glycerin, and xanthan gum were created to mimic the shear thinning property of blood at different hematocrit levels. Since the amount of xanthan gum is very small, an analytical balance was used. To mix the solution, an immersion blender and a heat circulator were used. The data were obtained from 10-90 torque percent, which is the range over which the rheometer is accurate, so the exact ranges of shear rate tested depended on the test fluid. The created solutions were compared to blood at the equivalent hematocrit and previously performed tests.The three different equivalent hematocrits all produced results similar to viscosities of blood. The results were similarly representative of blood at different equivalent viscosities for the 0.0075% xanthan gum and the 0.075% xanthan gum by weight. The solutions were able to mimic the shear thinning behavior of blood at different equivalent hematocrits. The fluids with 0.075% xanthan gum and 50% water and 50% glycerin is a better representative than the fluids with 0.075% xanthan gum and 60% water and 40% glycerin.
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Date Issued: 2018
Identifier: CFH2000447, ucf:45701
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000447

Title: COMPUTATIONAL FLUID DYNAMICS INVESTIGATION OF THE ORIENTATION OF A PEDIATRIC LEFT VENTRICLE ASSIST DEVICE CANNULA TO REDUCE STROKE EVENTS.
Creator: Guimond, Stephen, Kassab, Alain, University of Central Florida
Abstract / Description: Ventricle Assist Devices (VADs), which are typically either axial or centrifugal flow pumps implanted on the aortic arch, have been used to support patients who are awaiting cardiac transplantation. Success of the apparatus in the short term has led to long term use. Despite anticoagulation measures, blood clots (thrombi) have been known to form in the device itself or inside of the heart. The Ventricle Assist Devices supply blood flow via a conduit (cannula) implanted on the ascending aorta....
Show moreVentricle Assist Devices (VADs), which are typically either axial or centrifugal flow pumps implanted on the aortic arch, have been used to support patients who are awaiting cardiac transplantation. Success of the apparatus in the short term has led to long term use. Despite anticoagulation measures, blood clots (thrombi) have been known to form in the device itself or inside of the heart. The Ventricle Assist Devices supply blood flow via a conduit (cannula) implanted on the ascending aorta. Currently, the implantation angle of the VAD cannula is not taken into consideration. Since the VADs supply a significant amount of blood flow to the aorta, the implantation angle can greatly affect the trajectory of the formed thrombi as well as the cardiac flow field inside of the aortic arch. This study aims to vary the implantation angle of a pediatric Left Ventricle Assist Device (LVAD) through a series of computational fluid dynamics (CFD) software simulations focusing on the aortic arch and its branching arteries of a 20 kg pediatric patient in order to reduce the occurrence of stroke.
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Date Issued: 2012
Identifier: CFH0004305, ucf:45044
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004305

Title: A COMPUTED TOMOGRAPHY-BASED MODEL OF THE INFANT HIP ANATOMY FOR DYNAMIC FINITE ELEMENT ANALYSIS OF HIP DYSPLASIA BIOMECHANICS.
Creator: Snethen, Kyle, Kassab, Alain, University of Central Florida
Abstract / Description: Newborns diagnosed with hip dysplasia face severe consequences when treatments fail. The Pavlik harness presents the most common worldwide treatment for correcting this medical hip abnormality in newborns, but becomes increasingly ineffective as subluxation increases. A dynamic finite element analysis on the hip joint would yield results that could provide insight to physicians as to how the Pavlik harness could be optimized to increase its success rate and develop patient-specific treatment...
Show moreNewborns diagnosed with hip dysplasia face severe consequences when treatments fail. The Pavlik harness presents the most common worldwide treatment for correcting this medical hip abnormality in newborns, but becomes increasingly ineffective as subluxation increases. A dynamic finite element analysis on the hip joint would yield results that could provide insight to physicians as to how the Pavlik harness could be optimized to increase its success rate and develop patient-specific treatment plans. The study completes the first step in such an analysis by generating a three-dimensional model of an infant hip joint directly derived from computed tomography imaging in order to accurately represent the anatomical locations of muscle origins and insertions points as well as the unique cartilaginous characteristics of a neonate hip and femur. Such models will further enhance findings on the biomechanics of hip dysplasia that resulted from a preliminary study using computer-aided design to recreate the hip joint. In addition to the models, the orientation of the psoas tendon in a dysplastic hip through full range abduction and flexion was analyzed using a cadaveric dissection. It was determined that the psoas tendon was not an obstruction to reduction when the hip was in flexion so long as the tendon was not adherent to the hip capsule, and therefore can be disregarded in a finite element analysis or dynamic simulation that introduces flexion. The work of this thesis will lay the foundation for complex finite element analyses regarding the biomechanics of hip dysplasia in neonates as well as other hip abnormalities relevant to early child development.
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Date Issued: 2013
Identifier: CFH0004423, ucf:45144
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004423

Title: ADDING CEREBRAL AUTOREGULATION TO A LUMPED PARAMETER MODEL OF BLOOD FLOW.
Creator: Gentile, Rusty, Kassab, Alain, University of Central Florida
Abstract / Description: A mathematical model of blood flow in infants with hypoplastic left heart syndrome (HLHS) was improved by adding cerebral autoregulation. This is the process by which blood vessels constrict or dilate to keep blood flow steady in certain organs during pressure changes. The original lumped parameter model transformed the fluid flow into an electrical circuit. Its behavior is described using a system of thirty-three coupled differential equations that are solved numerically using a fourth-order...
Show moreA mathematical model of blood flow in infants with hypoplastic left heart syndrome (HLHS) was improved by adding cerebral autoregulation. This is the process by which blood vessels constrict or dilate to keep blood flow steady in certain organs during pressure changes. The original lumped parameter model transformed the fluid flow into an electrical circuit. Its behavior is described using a system of thirty-three coupled differential equations that are solved numerically using a fourth-order Runge-Kutta method implemented in MATLAB. A literature review that includes a discussion of autoregulation mechanisms and approaches to modeling them is followed by a description of the model created for this paper. The model is based on the baroreceptor or neurogenic theory of autoregulation. According to this theory, nerves in certain places within the cardiovascular system detect changes in blood pressure. The brain then compensates by sending a signal to blood vessels to constrict or dilate. The model of the control system responded fairly well to a pressure drop with a steady state error of about two percent. Running the model with or without the control system activated had little effect on other parameters, notably cardiac output. A more complete model of blood flow control would include autonomic regulation. This would vary more parameters than local autoregulation, including heart rate and contractility. This is suggested as a topic of further research.
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Date Issued: 2012
Identifier: CFH0004214, ucf:44933
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004214

Title: MESHLESS HEMODYNAMICS MODELING AND EVOLUTIONARY SHAPE OPTIMIZATION OF BYPASS GRAFTS ANASTOMOSES.
Creator: El Zahab, Zaher, Kassab, Alain, University of Central Florida
Abstract / Description: Objectives: The main objective of the current dissertation is to establish a formal shape optimization procedure for a given bypass grafts end-to-side distal anastomosis (ETSDA). The motivation behind this dissertation is that most of the previous ETSDA shape optimization research activities cited in the literature relied on direct optimization approaches that do not guaranty accurate optimization results. Three different ETSDA models are considered herein: The conventional, the Miller cuff,...
Show moreObjectives: The main objective of the current dissertation is to establish a formal shape optimization procedure for a given bypass grafts end-to-side distal anastomosis (ETSDA). The motivation behind this dissertation is that most of the previous ETSDA shape optimization research activities cited in the literature relied on direct optimization approaches that do not guaranty accurate optimization results. Three different ETSDA models are considered herein: The conventional, the Miller cuff, and the hood models. Materials and Methods: The ETSDA shape optimization is driven by three computational objects: a localized collocation meshless method (LCMM) solver, an automated geometry pre-processor, and a genetic-algorithm-based optimizer. The usage of the LCMM solver is very convenient to set an autonomous optimization mechanism for the ETSDA models. The task of the automated pre-processor is to randomly distribute solution points in the ETSDA geometries. The task of the optimized is the adjust the ETSDA geometries based on mitigation of the abnormal hemodynamics parameters. Results: The results reported in this dissertation entail the stabilization and validation of the LCMM solver in addition to the shape optimization of the considered ETSDA models. The LCMM stabilization results consists validating a custom-designed upwinding scheme on different one-dimensional and two-dimensional test cases. The LCMM validation is done for incompressible steady and unsteady flow applications in the ETSDA models. The ETSDA shape optimization include single-objective optimization results in steady flow situations and bi-objective optimization results in pulsatile flow situations. Conclusions: The LCMM solver provides verifiably accurate resolution of hemodynamics and is demonstrated to be third order accurate in a comparison to a benchmark analytical solution of the Navier-Stokes. The genetic-algorithm-based shape optimization approach proved to be very effective for the conventional and Miller cuff ETSDA models. The shape optimization results for those two models definitely suggest that the graft caliber should be maximized whereas the anastomotic angle and the cuff height (in the Miller cuff model) should be chosen following a compromise between the wall shear stress spatial and temporal gradients. The shape optimization of the hood ETSDA model did not prove to be advantageous, however it could be meaningful with the inclusion of the suture line cut length as an optimization parameter.
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Date Issued: 2008
Identifier: CFE0002165, ucf:47927
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002165

Title: INVERSE BOUNDARY ELEMENT/GENETIC ALGORITHM METHOD FOR RECONSTRUCTION OF MULTI-DIMENSIONAL HEAT FLUX DISTRIBUTIONS WITH FILM COOLING APPLICATIONS.
Creator: Silieti, Mahmood, Kassab, Alain, University of Central Florida
Abstract / Description: A methodology is formulated for the solution of the inverse problem concerned with the reconstruction of multi-dimensional heat fluxes for film cooling applications. The motivation for this study is the characterization of complex thermal conditions in industrial applications such as those encountered in film cooled turbomachinery components. The heat conduction problem in the metal endwall/shroud is solved using the boundary element method (bem), and the inverse problem is solved using a...
Show moreA methodology is formulated for the solution of the inverse problem concerned with the reconstruction of multi-dimensional heat fluxes for film cooling applications. The motivation for this study is the characterization of complex thermal conditions in industrial applications such as those encountered in film cooled turbomachinery components. The heat conduction problem in the metal endwall/shroud is solved using the boundary element method (bem), and the inverse problem is solved using a genetic algorithm (ga). Thermal conditions are overspecified at exposed surfaces amenable to measurement, while the temperature and surface heat flux distributions are unknown at the film cooling hole/slot walls. The latter are determined in an iterative process by developing two approaches. The first approach, developed for 2d applications, solves an inverse problem whose objective is to adjust the film cooling hole/slot wall temperatures and heat fluxes until the temperature and heat flux at the measurement surfaces are matched in an overall heat conduction solution. The second approach, developed for 2d and 3d applications, is to distribute a set of singularities (sinks) at the vicinity of the cooling slots/holes surface inside a fictitious extension of the physical domain or along cooling hole centerline with a given initial strength distribution. The inverse problem iteratively alters the strength distribution of the singularities (sinks) until the measuring surfaces heat fluxes are matched. The heat flux distributions are determined in a post-processing stage after the inverse problem is solved. The second approach provides a tremendous advantage in solving the inverse problem, particularly in 3d applications, and it is recommended as the method of choice for this class of problems. It can be noted that the ga reconstructed heat flux distributions are robust, yielding accurate results to both exact and error-laden inputs. In all cases in this study, results from experiments are simulated using a full conjugate heat transfer (cht) finite volume models which incorporate the interactions of the external convection in the hot turbulent gas, internal convection within the cooling plena, and the heat conduction in the metal endwall/shroud region. Extensive numerical investigations are undertaken to demonstrate the significant importance of conjugate heat transfer in film cooling applications and to identify the implications of various turbulence models in the prediction of accurate and more realistic surface temperatures and heat fluxes in the cht simulations. These, in turn, are used to provide numerical inputs to the inverse problem. Single and multiple cooling slots, cylindrical cooling holes, and fan-shaped cooling holes are considered in this study. The turbulence closure is modeled using several two-equation approach, the four-equation turbulence model, as well as five and seven moment reynolds stress models. The predicted results, by the different turbulence models, for the cases of adiabatic and conjugate models, are compared to experimental data reported in the open literature. Results show the significant effects of conjugate heat transfer on the temperature field in the film cooling hole region, and the additional heating up of the cooling jet itself. Moreover, results from the detailed numerical studies presented in this study validate the inverse problem approaches and reveal good agreement between the bem/ga reconstructed heat fluxes and the cht simulated heat fluxes along the inaccessible cooling slot/hole walls
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Date Issued: 2004
Identifier: CFE0000166, ucf:52896
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000166

Title: A MULTISCALE MODEL OF THE NEONATAL CIRCULATORY SYSTEM FOLLOWING HYBRID NORWOOD PALLIATION.
Creator: Ceballos, Andres, Kassab, Alain, University of Central Florida
Abstract / Description: Hypoplastic left heart syndrome (HLHS) is a complex cardiac malformation in neonates suffering from congenital heart disease and occurs in nearly 1 per 5000 births. HLHS is uniformly fatal within the first hours or days after birth as the severely malformed anatomies of the left ventricle, mitral and aortic valves, and ascending aorta are not compatible with life. The regularly implemented treatment, the Norwood operation, is a complex open heart procedure that attempts to establish...
Show moreHypoplastic left heart syndrome (HLHS) is a complex cardiac malformation in neonates suffering from congenital heart disease and occurs in nearly 1 per 5000 births. HLHS is uniformly fatal within the first hours or days after birth as the severely malformed anatomies of the left ventricle, mitral and aortic valves, and ascending aorta are not compatible with life. The regularly implemented treatment, the Norwood operation, is a complex open heart procedure that attempts to establish univentricular circulation by removing the atrial septum (communicating the right and left ventricle), reconstructing the malformed aortic arch, and connecting the main pulmonary artery into the reconstructed arch to allow direct perfusion from the right ventricle into the systemic circulation. A relatively new treatment being utilized, the Hybrid Norwood procedure, involves a less invasive strategy to establish univentricular circulation that avoids a cardiopulmonary bypass (heart-lung machine), deliberate cardiac arrest, and circulatory arrest of the patient during the procedure. The resulting systemic-pulmonary circulation is unconventional; blood is pumped simultaneously and in parallel to the systemic and pulmonary arteries after the procedure. Cardiac surgeons are deeply interested in understanding the global and local hemodynamics of this anatomical configuration. To this end, a multiscale model of the entire circulatory system was developed utilizing an electrical lumped parameter model for the peripheral or distal circulation coupled with a 3D Computational Fluid Dynamics (CFD) model to understand the local hemodynamics. The lumped parameter (LP) model is mainly a closed loop circuit comprised of RLC compartments that model cardiac function as well as the viscous drag, flow inertia, and compliance of the different arterial and venous beds in the body. A system of 32 first-order differential equations is formulated and solved for the LP model using a fourth-order adaptive Runge-Kutta solver. The output pressure and flow waveforms obtained from the LP model are imposed as boundary conditions on the CFD model. Coupling of the two models is done through an iterative process where the parameters in the LP model are adjusted to match the CFD solution. The CFD model domain is a representative HLHS anatomy of an infant after undergoing the Hybrid Norwood procedure and is comprised of the neo-aorta, pulmonary roots, aortic arch with branching arteries, and pulmonary arteries. The flow field is solved over several cardiac cycles using an implicit-unsteady RANS equation solver with the k-epsilon turbulence model.
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Date Issued: 2011
Identifier: CFE0004037, ucf:49183
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004037

Title: NUMERICAL MODELING OF THE SHOCK TUBE FLOW FIELDS BEFORE ANDDURING IGNITION DELAY TIME EXPERIMENTS AT PRACTICAL CONDITIONS.
Creator: lamnaouer, mouna, Kassab, Alain, University of Central Florida
Abstract / Description: 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 Ã‚Â–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.
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Date Issued: 2010
Identifier: CFE0003011, ucf:48366
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003011

Title: PARAMETER ESTIMATION IN HEAT TRANSFER AND ELASTICITY USING TRAINED POD-RBF NETWORK INVERSE METHODS.
Creator: Rogers, Craig, Kassab, Alain, University of Central Florida
Abstract / Description: In applied mechanics it is always necessary to understand the fundamental properties of a system in order to generate an accurate numerical model or to predict future operating conditions. These fundamental properties include, but are not limited to, the material parameters of a specimen, the boundary conditions inside of a system, or essential dimensional characteristics that define the system or body. However in certain instances there may be little to no knowledge about the systems...
Show moreIn applied mechanics it is always necessary to understand the fundamental properties of a system in order to generate an accurate numerical model or to predict future operating conditions. These fundamental properties include, but are not limited to, the material parameters of a specimen, the boundary conditions inside of a system, or essential dimensional characteristics that define the system or body. However in certain instances there may be little to no knowledge about the systems conditions or properties; as a result the problem cannot be modeled accurately using standard numerical methods. Consequently, it is critical to define an approach that is capable of identifying such characteristics of the problem at hand. In this thesis, an inverse approach is formulated using proper orthogonal decomposition (POD) with an accompanying radial basis function (RBF) network to estimate the current material parameters of a specimen with little prior knowledge of the system. Specifically conductive heat transfer and linear elasticity problems are developed in this thesis and modeled with a corresponding finite element (FEM) or boundary element (BEM) method. In order to create the truncated POD-RBF network to be utilized in the inverse approach, a series of direct FEM or BEM solutions are used to generate a statistical data set of temperatures or deformations in the system or body, each having a set of various material parameters. The data set is then transformed via POD to generate an orthonormal basis to accurately solve for the desired material characteristics using the Levenberg-Marquardt (LM) algorithm. For now, the LM algorithm can be simply defined as a direct relation to the minimization of the Euclidean norm of the objective Least Squares function(s). The trained POD-RBF inverse technique outlined in this thesis provides a flexible by which this inverse approach can be implemented into various fields of engineering and mechanics. More importantly this approach is designed to offer an inexpensive way to accurately estimate material characteristics or properties using nondestructive techniques. While the POD-RBF inverse approach outlined in this thesis focuses primarily in application to conduction heat transfer, elasticity, and fracture mechanics, this technique is designed to be directly applicable to other realistic conditions and/or industries.
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Date Issued: 2010
Identifier: CFE0003267, ucf:48517
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003267

Title: A MODEL INTEGRATED MESHLESS SOLVER (MIMS) FOR FLUID FLOW AND HEAT TRANSFER.
Creator: Gerace, Salvadore, Kassab, Alain, University of Central Florida
Abstract / Description: Numerical methods for solving partial differential equations are commonplace in the engineering community and their popularity can be attributed to the rapid performance improvement of modern workstations and desktop computers. The ubiquity of computer technology has allowed all areas of engineering to have access to detailed thermal, stress, and fluid flow analysis packages capable of performing complex studies of current and future designs. The rapid pace of computer development, however,...
Show moreNumerical methods for solving partial differential equations are commonplace in the engineering community and their popularity can be attributed to the rapid performance improvement of modern workstations and desktop computers. The ubiquity of computer technology has allowed all areas of engineering to have access to detailed thermal, stress, and fluid flow analysis packages capable of performing complex studies of current and future designs. The rapid pace of computer development, however, has begun to outstrip efforts to reduce analysis overhead. As such, most commercially available software packages are now limited by the human effort required to prepare, develop, and initialize the necessary computational models. Primarily due to the mesh-based analysis methods utilized in these software packages, the dependence on model preparation greatly limits the accessibility of these analysis tools. In response, the so-called meshless or mesh-free methods have seen considerable interest as they promise to greatly reduce the necessary human interaction during model setup. However, despite the success of these methods in areas demanding high degrees of model adaptability (such as crack growth, multi-phase flow, and solid friction), meshless methods have yet to gain notoriety as a viable alternative to more traditional solution approaches in general solution domains. Although this may be due (at least in part) to the relative youth of the techniques, another potential cause is the lack of focus on developing robust methodologies. The failure to approach development from a practical perspective has prevented researchers from obtaining commercially relevant meshless methodologies which reach the full potential of the approach. The primary goal of this research is to present a novel meshless approach called MIMS (Model Integrated Meshless Solver) which establishes the method as a generalized solution technique capable of competing with more traditional PDE methodologies (such as the finite element and finite volume methods). This was accomplished by developing a robust meshless technique as well as a comprehensive model generation procedure. By closely integrating the model generation process into the overall solution methodology, the presented techniques are able to fully exploit the strengths of the meshless approach to achieve levels of automation, stability, and accuracy currently unseen in the area of engineering analysis. Specifically, MIMS implements a blended meshless solution approach which utilizes a variety of shape functions to obtain a stable and accurate iteration process. This solution approach is then integrated with a newly developed, highly adaptive model generation process which employs a quaternary triangular surface discretization for the boundary, a binary-subdivision discretization for the interior, and a unique shadow layer discretization for near-boundary regions. Together, these discretization techniques are able to achieve directionally independent, automatic refinement of the underlying model, allowing the method to generate accurate solutions without need for intermediate human involvement. In addition, by coupling the model generation with the solution process, the presented method is able to address the issue of ill-constructed geometric input (small features, poorly formed faces, etc.) to provide an intuitive, yet powerful approach to solving modern engineering analysis problems.
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Date Issued: 2010
Identifier: CFE0003299, ucf:48489
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003299

Title: Simulating Human Pleura Performance in Medical Training Using Measured Tissue Mechanical Properties.
Creator: Norfleet, Jack, Bai, Yuanli, Kassab, Alain, Metcalf, David, Cendan, Juan, University of Central Florida
Abstract / Description: Medical simulations provide hands-on training at various levels of medical expertise. Yet these simulators fail to accurately mimic the look, feel and behavior of human tissue. Applying measured mechanical properties from human cadaver tissues promises to improve the fidelity of simulated tissue behaviors when subjected to medical procedures. Samples of human parietal pleura were tested under uniaxial tension to failure and measured characteristics were replicated in synthetic pleura. Context...
Show moreMedical simulations provide hands-on training at various levels of medical expertise. Yet these simulators fail to accurately mimic the look, feel and behavior of human tissue. Applying measured mechanical properties from human cadaver tissues promises to improve the fidelity of simulated tissue behaviors when subjected to medical procedures. Samples of human parietal pleura were tested under uniaxial tension to failure and measured characteristics were replicated in synthetic pleura. Context specific parameters were then collected and compared between human pleura and the new synthetics. These comparisons tested the hypothesis; H1 Gaps exist between synthetic and human pleura performance, H2: Human tissue fracture mechanics define desired performance of synthetic tissues, H3: Synthetic and human tissues with similar stress/strain parameters will behave similarly when blunt punctured. The results promote the future development of high fidelity tissue simulants for medical training.The studied tissue is parietal pleura which contributes the critical haptic (")pop(") indicating access to the proper anatomic space during the tube thoracostomy procedure. Once accessed through blunt puncture, tube is then inserted to drain air and fluid from around the lungs.Stress/strain based hyper-elastic and fracture properties calibrated from fresh human cadaver pleura were used to define performance requirements. Synthetic pleura were then prototyped and their mechanical properties were characterized. Commercial pleura simulants were puncture tested and compared to compliant custom and off-the-shelf formulations. A non-compliant but commonly used pleura substitute was also tested. Blunt puncture force and displacement were compared for each of the materials to test the stated hypotheses.
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Date Issued: 2018
Identifier: CFE0007065, ucf:52023
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007065

Title: Compressible Turbulent Flame Speed of Highly Turbulent Standing Flames.
Creator: Sosa, Jonathan, Ahmed, Kareem, Kassab, Alain, Kapat, Jayanta, University of Central Florida
Abstract / Description: This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind...
Show moreThis work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.
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Date Issued: 2018
Identifier: CFE0007102, ucf:51955
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007102

CFD (8)	+ -
Combustion (7)	+ -
combustion (5)	+ -
heat transfer (5)	+ -
Computational Fluid Dynamics (4)	+ -

LVAD (4)	+ -
computational fluid dynamics (4)	+ -
Finite Element Analysis (3)	+ -
Heat Transfer (3)	+ -
Left Ventricular Assist Device (3)	+ -
Pavlik Harness (3)	+ -
Acoustic (2)	+ -
Anisotropy (2)	+ -
Autorotation (2)	+ -
Developmental (2)	+ -
Developmental Dysplasia of the Hip (2)	+ -
Fluid Structure Interaction (2)	+ -
Fused Deposition Modeling (2)	+ -
Ignition Delay Time (2)	+ -
Inverse Problem (2)	+ -
LPM (2)	+ -
Lean (2)	+ -
Lumper Parameter Model (2)	+ -
Meshless Methods (2)	+ -
Methane (2)	+ -
Modeling (2)	+ -
Optimization (2)	+ -
Parameter Estimation (2)	+ -
Premixed Combustion (2)	+ -
Proper Orthogonal Decomposition (2)	+ -

ETD Collection (86)	+ -
Honors Collection (9)	+ -

Kassab, Alain (95)	+ -
University of Central Florida (95)	+ -
Divo, Eduardo (19)	+ -
Kapat, Jayanta (19)	+ -
Vasu Sumathi, Subith (18)	+ -

Mansy, Hansen (14)	+ -
Bai, Yuanli (8)	+ -
Das, Tuhin (8)	+ -
Chow, Louis (6)	+ -
DeCampli, William (6)	+ -
Moslehy, Faissal (6)	+ -
Ahmed, Kareem (5)	+ -
Gordon, Ali (4)	+ -
Ilegbusi, Olusegun (4)	+ -
Ilie, Marcel (4)	+ -
Simaan, Marwan (4)	+ -
Chopra, Manoj (3)	+ -
Deng, Weiwei (3)	+ -
Gou, Jihua (3)	+ -
Kumar, Ranganathan (3)	+ -
Lin, Kuo-Chi (3)	+ -
Orlovskaya, Nina (3)	+ -
Peles, Yoav (3)	+ -
Qu, Zhihua (3)	+ -
Steward, Robert (3)	+ -
Beggs, Kyle (2)	+ -
Bhattacharya, Samik (2)	+ -
Ceballos, Andres (2)	+ -
Gerace, Salvadore (2)	+ -
Guimond, Stephen (2)	+ -

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