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Title: Effect of Load Path and Failure Modes on Seismic Response of Regular Bridges.
Creator: Darwash, Haider, Mackie, Kevin, Chopra, Manoj, Makris, Nicos, Bai, Yuanli, University of Central Florida
Abstract / Description: Bridges are essential infrastructure constituents that have been studied for centuries. Typically,seismic bridge design and assessment utilize simplified modeling and analysis techniques basedon one-dimensional spine elements and zero-length springs/hinges. The geometry of the elementsand calibration of parameters are based on assumptions for the lateral load path and failure modes,e.g., sacrificial backwall and shear keys, neglecting wing walls, and strength based on backfillalone. These...
Show moreBridges are essential infrastructure constituents that have been studied for centuries. Typically,seismic bridge design and assessment utilize simplified modeling and analysis techniques basedon one-dimensional spine elements and zero-length springs/hinges. The geometry of the elementsand calibration of parameters are based on assumptions for the lateral load path and failure modes,e.g., sacrificial backwall and shear keys, neglecting wing walls, and strength based on backfillalone. These assumptions have led to observations of underestimated resistance, overestimateddisplacement demands, and unpredicted damage and failure mode. The focus of the study is onordinary standard bridges with continuous reinforced concrete box girder superstructures and seattypeabutments.A bridge component calibration study was conducted first using simplified (spine models with 1Delements and springs) and three-dimensional nonlinear continuum finite element models (FEM).Model responses were compared with experimental results to identify the drawbacks in the simplifiedmodels and verify the adequacy of the material nonlinearities and analysis procedures. Thecomponents include a T-girder, abutment backfill, abutment shear key, elastomeric bearing pad,and a bridge pier. Results show the simplified models do not capture damage propagation andfailure mode in the shear key case, nonlinear behaviors in beams with high aspect ratios (or deepbeam action), and underestimate the strength and overestimate the stiffness for the backfill case.The component models (both simplified and continuum) were then used in studying the nonlinearstatic behaviors of key bridge lateral-load resisting substructures, namely abutments and bents.For the abutment subsystem, cases with and without backfill and several back wall constructionjoint configurations for the longitudinal direction, with monolithic shear key and shear key withconstruction joint for the transverse direction, and boundary conditions in the transverse direction were considered. Abutment subsystem results showed simplified models underestimate the resistanceby 10-60%, neglect back wall and wing wall structural contributions, and localize damagein the back fill relative to the continuum models. For the bent subsystem, a full bridge systemthat considers material nonlinearity and damage in the bent segment only was adopted to determinethe effect of the finite bent cap or superstructure-to-column connection. Inelastic behaviorand damage was included in the columns, bent cap, and a superstructure segment with a lengththat correspond to the dead load moment inflection point. The other superstructure segments andthe pile cap were modeled as elastic. Bent subsystem results showed simplified models overestimatethe stiffness, induce excessive flexibility and deformation in the cap beam, and overestimatecolumns' deformations.Due to the differences observed in the abutment subsystem, and the potential impact of the abutmentbehavior on the seismic response of the whole bridge system, dynamic studies on the bridgesystem were conducted using four abutment parameters: abutment stiffness and strength in eachof the longitudinal and transverse directions. Two models were developed to conduct nonlineartime history analysis: an equivalent single-degree-of-freedom (SDOF) model for each of the longitudinaland transverse directions, and a 3D spine bridge model. Constant ductility analyses wereconducted using the SDOF systems, while standard probabilistic seismic demand analysis wasused on the spine systems.Results revealed that, besides the columns yielding, the abutment has an early and significant contributionto the behavior. The SDOF system results showed that increasing the abutment stiffnessor strength reduces the system displacement demand and increases the system forces. The consequenceof such increase in the forces is mobilizing significant amount of force in the abutments,causing inelastic response. The full bridge study also confirmed the SDOF results and showedthat the abutment forces are more than 200% of the columns forces that would result in the sameaftereffect observed in the SDOF system.
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Date Issued: 2017
Identifier: CFE0006869, ucf:51759
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006869

Title: REAL-TIME TREE SIMULATION USING VERLET INTEGRATION.
Creator: Manavi, Bobak, Kincaid, J. Peter, University of Central Florida
Abstract / Description: One of the most important challenges in real-time simulation of large trees and vegetation is the vast number of calculations required to simulate the interactions between all the branches in the tree when external forces are applied to it. This paper will propose the use of algorithms employed by applications like cloth and soft body simulations, where objects can be represented by a finite system of particles connected via spring-like constraints, for the structural representation and...
Show moreOne of the most important challenges in real-time simulation of large trees and vegetation is the vast number of calculations required to simulate the interactions between all the branches in the tree when external forces are applied to it. This paper will propose the use of algorithms employed by applications like cloth and soft body simulations, where objects can be represented by a finite system of particles connected via spring-like constraints, for the structural representation and manipulation of trees in real-time. We will then derive and show the use of Verlet integration and the constraint configuration used for simulating trees while constructing the necessary data structures that encapsulate the procedural creation of these objects. Furthermore, we will utilize this system to simulate branch breakage due to accumulated external and internal pressure.
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Date Issued: 2007
Identifier: CFE0001802, ucf:47381
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001802

Title: MODELING OF LIQUID CRYSTAL DISPLAY AND PHOTONIC DEVICES.
Creator: Ge, Zhibing, Wu, Shin-Tson, University of Central Florida
Abstract / Description: Liquid crystal (LC) materials have been widely applied in electro-optical devices, among which display is the most successful playground and numerous new applications in photonic areas (such as laser beam steering devices) are also emerging. To well guide the device design for optimum performance, accurate modeling is of prior and practical importance. Generally, the modeling of LC devices includes two parts in sequence: accurate LC molecule deformation extraction under external electric...
Show moreLiquid crystal (LC) materials have been widely applied in electro-optical devices, among which display is the most successful playground and numerous new applications in photonic areas (such as laser beam steering devices) are also emerging. To well guide the device design for optimum performance, accurate modeling is of prior and practical importance. Generally, the modeling of LC devices includes two parts in sequence: accurate LC molecule deformation extraction under external electric fields and optical calculation thereafter for the corresponding electro-optical behaviors. In this dissertation, first, hybrid finite element method and finite difference method are developed to minimize the free energy of the LC systems. In this part of study, with computer-aided derivation, the full forms of the LC free energy equations without any simplification can be obtained. Besides, Galerkin's method and weak form technique are further introduced to successfully degrade the high order nonlinear derivative terms associated with the free energy equations into ones that can be treated by first order interpolation functions for high accuracy. The developed modeling methods for LC deformation are further employed to study display structures, such as 2D and 3D in-plane switching LC cells, and provides accurate results. Followed is the optical modeling using extended Jones matrix and beam propagation method to calculate the electro-optical performances of different devices, according to their amplitude modulation property or diffractive one. The developed methods are further taken to assist the understanding, development, and optimization of the display and photonic devices. For their application in the display area, sunlight readable transflective LCDs for mobile devices and the related optical films for wide viewing angle are developed and studied. New cell structure using vertically aligned liquid crystal mode is developed and studied to obtain a single cell gap, high light efficiency transflective LCD that can be driven by one gray scale control circuit for both transmissive and reflective modes. And employing an internal wire grid polarizer into a fringe field switching cell produces a single cell gap and wide viewing angle display with workable reflective mode under merely two linear polarizers. To solve the limited viewing angle of conventional circular polarizers, Poincaré sphere as an effective tool is taken to trace and understand the polarization change of the incident light throughout the whole LC system. This study further guides the design of high performance circular polarizers that can consist of purely uniaxial plates or a combination of uniaxial and biaxial plates. The developed circular polarizers greatly enhance the viewing angle of transflective LCDs. Especially, the circular polarizer design using a biaxial film can even provide comparable wide viewing angle performance for the same vertically aligned cell as it is used between merely two linear polarizers, while using circular polarizers can greatly boost the display brightness. As for the beam steering device modeling, the developed LC deformation method is taken to accurately calculate the associated LC director distribution in the spatial light modulator, while beam propagation method and Fourier transformation technique are combined to calculate the near and far fields from such devices. The modeling helps to better understand the origins and formations of the disclinations associated with the fringe fields, which further result in reduced steering efficiency and output asymmetric polarizations between positive and negative diffractions. Optimization in both voltage profile and driving methods is conducted to well tune the LC deformation under strong fringe fields and improve the light efficiency.
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Date Issued: 2007
Identifier: CFE0001908, ucf:47481
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001908

Title: A HIGH-RESOLUTION STORM SURGE MODEL FOR THE PASCAGOULA REGION, MISSISSIPPI.
Creator: Takahashi, Naeko, Hagen, Scott, University of Central Florida
Abstract / Description: The city of Pascagoula and its coastal areas along the United States Gulf Coast have experienced many catastrophic hurricanes and were devastated by high storm surges caused by Hurricane Katrina (August 23 to 30, 2005). The National Hurricane Center reported high water marks exceeding 6 meters near the port of Pascagoula with a near 10-meter high water mark recorded near the Hurricane Katrina landfall location in Waveland, MS. Although the Pascagoula River is located 105 km east of the...
Show moreThe city of Pascagoula and its coastal areas along the United States Gulf Coast have experienced many catastrophic hurricanes and were devastated by high storm surges caused by Hurricane Katrina (August 23 to 30, 2005). The National Hurricane Center reported high water marks exceeding 6 meters near the port of Pascagoula with a near 10-meter high water mark recorded near the Hurricane Katrina landfall location in Waveland, MS. Although the Pascagoula River is located 105 km east of the landfall location of Hurricane Katrina, the area was devastated by storm surge-induced inundation because of its low elevation. Building on a preliminary finite element mesh for the Pascagoula River, the work presented herein is aimed at incorporating the marsh areas lying adjacent to the Lower Pascagoula and Escatawpa Rivers for the purpose of simulating the inland inundation which occurred during Hurricane Katrina. ADCIRC-2DDI (ADvanced CIRCulation Model for Shelves, Coasts and Estuaries, Two-Dimensional Depth Integrated) is employed as the hydrodynamic circulation code. The simulations performed in this study apply high-resolution winds and pressures over the 7-day period associated with Hurricane Katrina. The high resolution of the meteorological inputs to the problem coupled with the highly detailed description of the adjacent inundation areas will provide an appropriate modeling tool for studying storm surge dynamics within the Pascagoula River. All simulation results discussed herein are directed towards providing for a full accounting of the hydrodynamics within the Pascagoula River in support of ongoing flood/river forecasting efforts. In order to better understand the hydrodynamics within the Pascagoula River when driven by an extreme storm surge event, the following tasks were completed as a part of this study: 1) Develop an inlet-based floodplain DEM (Digital Elevation Model) for the Pascagoula River. The model employs topography up to the 1.5-meter contour extracted from the Southern Louisiana Gulf Coast Mesh (SL15 Mesh) developed by the Federal Emergency Management Agency (FEMA). 2) Incorporate the inlet-based floodplain model into the Western North Atlantic Tidal (WNAT) model domain, which consists of the Gulf of Mexico, the Caribbean Sea, and the entire portion of the North Atlantic Ocean found west of the 60 degree West meridian, in order to more fully account for the storm surge dynamics occurring within the Pascagoula River. This large-scale modeling approach will utilize high-resolution wind and pressure fields associated with Hurricane Katrina, so that storm surge hydrographs (elevation variance) at the open-ocean boundary locations associated with the localized domain can be adequately obtained. 3) Understand the importance of the various meteorological forcings that are attributable to the storm surge dynamics that are setup within the Pascagoula River. Different implementations of the two model domains (large-scale, including the WNAT model domain; localized, with its focus concentrated solely on the Pascagoula River) will involve the application of tides, storm surge hydrographs and meteorological forcing (winds and pressures) in isolation (i.e., as the single forcing mechanism) and collectively (i.e., together in combination). The following conclusions are drawn from the research presented in this thesis: 1) Incorporating the marsh areas into the preliminary in-bank mesh provides for significant improvement in the astronomic tide simulation; 2) the large-scale modeling approach (i.e., the localized floodplain mesh incorporated into the WNAT model domain) is shown to be most adequate towards simulating storm surge dynamics within the Pascagoula River. Further, we demonstrate the utility of the large-scale model domain towards providing storm surge hydrographs for the open-ocean boundary of the localized domain. Only when the localized domain is forced with the storm surge hydrograph (generated by the large-scale model domain) does it most adequately capture the full behavior of the storm surge. Finally, we discover that while the floodplain description up to the 1.5-m contour greatly improves the model response by allowing for the overtopping of the river banks, a true recreation of the water levels caused by Hurricane Katrina will require a floodplain description up to the 5-m contour.
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Date Issued: 2008
Identifier: CFE0002476, ucf:47719
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002476

Title: Quantifying Ultra-high Performance Concrete Flexural System Mechanical Response.
Creator: Xiao, Yulin, Mackie, Kevin, Catbas, Necati, Chopra, Manoj, Gordon, Ali, University of Central Florida
Abstract / Description: The research and application of Ultra-high Performance Concrete (UHPC) has been developedsignificantly within the last 1-2 decades. Due to the specific property of high strength capacity, it is potential to be used in bridge deck system without shear reinforcement so that it provides even lighter self-weight of the deck. However, one of the shear component, dowel action, has not beenadequately investigated in the past. In this dissertation, a particular test was designed and carried out to...
Show moreThe research and application of Ultra-high Performance Concrete (UHPC) has been developedsignificantly within the last 1-2 decades. Due to the specific property of high strength capacity, it is potential to be used in bridge deck system without shear reinforcement so that it provides even lighter self-weight of the deck. However, one of the shear component, dowel action, has not beenadequately investigated in the past. In this dissertation, a particular test was designed and carried out to fully investigate the dowel action response, especially its contribution to shear resistance. In addition, research on serviceability and fatigue behaviors were expanded as well to delete the concern on other factors that may influence the application to the deck system. Both experimental and analytical methods including finite element modeling, OpenSees modeling and other extension studies were presented throughout the entire dissertation where required.
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Date Issued: 2014
Identifier: CFE0005563, ucf:50288
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005563

Title: OPTIMIZATION OF AN UNSTRUCTURED FINITE ELEMENT MESH FOR TIDE AND STORM SURGE MODELING APPLICATIONS IN THE WESTERN NORTH ATLANTIC OCEAN.
Creator: Kojima, Satoshi, Hagen, Scott, University of Central Florida
Abstract / Description: Recently, a highly resolved, finite element mesh was developed for the purpose of performing hydrodynamic calculations in the Western North Atlantic Tidal (WNAT) model domain. The WNAT model domain consists of the Gulf of Mexico, the Caribbean Sea, and the entire portion of the North Atlantic Ocean found west of the 60° W meridian. This high resolution mesh (333K) employs 332,582 computational nodes and 647,018 triangular elements to provide approximately 1.0 to 25 km node spacing. In the...
Show moreRecently, a highly resolved, finite element mesh was developed for the purpose of performing hydrodynamic calculations in the Western North Atlantic Tidal (WNAT) model domain. The WNAT model domain consists of the Gulf of Mexico, the Caribbean Sea, and the entire portion of the North Atlantic Ocean found west of the 60° W meridian. This high resolution mesh (333K) employs 332,582 computational nodes and 647,018 triangular elements to provide approximately 1.0 to 25 km node spacing. In the previous work, the 333K mesh was applied in a Localized Truncation Error Analysis (LTEA) to produce nodal density requirements for the WNAT model domain. The goal of the work herein is to use these LTEA-based element sizing guidelines in order to obtain a more optimal finite element mesh for the WNAT model domain, where optimal refers to minimizing nodes (to enhance computational efficiency) while maintaining model accuracy, through an automated procedure. Initially, three finite element meshes are constructed: 95K, 60K, and 53K. The 95K mesh consists of 95,062 computational nodes and 182,941 triangular elements providing about 0.5 to 120 km node spacing. The 60K mesh contains 60,487 computational nodes and 108,987 triangular elements. It has roughly 0.5 to 185 km node spacing. The 53K mesh includes 52,774 computational nodes and 98,365 triangular elements. This is a particularly coarse mesh, consisting of approximately 0.5 to 160 km node spacing. It is important to note that these three finite element meshes were produced automatically, with each employing the bathymetry and coastline (of various levels of resolution) of the 333K mesh, thereby enabling progress towards an optimal finite element mesh. Tidal simulations are then performed for the WNAT model domain by solving the shallow water equations in a time marching manner for the deviation from mean sea level and depth-integrated velocities at each computational node of the different finite element meshes. In order to verify the model output and compare the performance of the various finite element mesh applications, historical tidal constituent data from 150 tidal stations located within the WNAT model domain are collected and examined. These historical harmonic data are applied in two types of comparative analyses to evaluate the accuracy of the simulation results. First, qualitative comparisons are based on visual sense by utilizing plots of resynthesized model output and historical tidal constituents. Second, quantitative comparisons are performed via a statistical analysis of the errors between model response and historical data. The latter method elicits average phase errors and goodness of average amplitude fits in terms of numerical values, thus providing a quantifiable way to present model error. The error analysis establishes the 53K finite element mesh as optimal when compared to the 333K, 95K, and 60K meshes. However, its required time step of less than ten seconds constrains its application. Therefore, the 53K mesh is manually edited to uphold accurate simulation results and to produce a more computationally efficient mesh, by increasing its time step, so that it can be applied to forecast tide and storm surge in the Western North Atlantic Ocean on a real-time basis.
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Date Issued: 2005
Identifier: CFE0000565, ucf:46421
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000565

Title: ANALYSIS, MODELING, AND SIMULATION OF THE TIDES IN THE LOXAHATCHEE RIVER ESTUARY (SOUTHEASTERN FLORIDA).
Creator: Bacopoulos, Peter, Hagen, Scott, University of Central Florida
Abstract / Description: Recent cooperative efforts between the University of Central Florida, the Florida Department of Environmental Protection, and the South Florida Water Management District explore the development of a two-dimensional, depth-integrated tidal model for the Loxahatchee River estuary (Southeastern Florida). Employing a large-domain approach (i.e., the Western North Atlantic Tidal model domain), two-dimensional tidal flows within the Loxahatchee River estuary are reproduced to provide: 1)...
Show moreRecent cooperative efforts between the University of Central Florida, the Florida Department of Environmental Protection, and the South Florida Water Management District explore the development of a two-dimensional, depth-integrated tidal model for the Loxahatchee River estuary (Southeastern Florida). Employing a large-domain approach (i.e., the Western North Atlantic Tidal model domain), two-dimensional tidal flows within the Loxahatchee River estuary are reproduced to provide: 1) recommendations for the domain extent of an integrated, surface/groundwater, three-dimensional model; 2) nearshore, harmonically decomposed, tidal elevation boundary conditions. Tidal simulations are performed using a two-dimensional, depth-integrated, finite element-based code for coastal and ocean circulation, ADCIRC-2DDI. Multiple variations of an unstructured, finite element mesh are applied to encompass the Loxahatchee River estuary and different spatial extents of the Atlantic Intracoastal Waterway (AIW). Phase and amplitude errors between model output and historical data are quantified at five locations within the Loxahatchee River estuary to emphasize the importance of including the AIW in the computational domain. In addition, velocity residuals are computed globally to reveal significantly different net circulation patterns within the Loxahatchee River estuary, as depending on the spatial coverage of the AIW.
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Date Issued: 2006
Identifier: CFE0000925, ucf:46755
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000925

Title: Shape Recovery Behavior of Carbon Nanopaper Shape Memory Polymer Composite.
Creator: Ozdemir, Veli Bugra, Kwok, Kawai, Gou, Jihua, Ghosh, Ranajay, University of Central Florida
Abstract / Description: This thesis presents analytical, experimental and modeling studies of the shape recovery behavior of electrically activated Carbon Nanopaper (CNP) Shape Memory Polymer (SMP)composite. The composite structure studied consists of a CNP layer sandwiched by two SMP layers where the CNP layer acts as a ?exible electrical heater when a voltage difference is applied. The behavior of CNP/SMP composite presents a coupled electrical - thermal - structural problem. The governing equations for the...
Show moreThis thesis presents analytical, experimental and modeling studies of the shape recovery behavior of electrically activated Carbon Nanopaper (CNP) Shape Memory Polymer (SMP)composite. The composite structure studied consists of a CNP layer sandwiched by two SMP layers where the CNP layer acts as a ?exible electrical heater when a voltage difference is applied. The behavior of CNP/SMP composite presents a coupled electrical - thermal - structural problem. The governing equations for the multiphysics behavior are derived. Derived parameters as a result of multiphysics analysis and effects of these parameters on the shape recovery behavior are investigated. The mechanical properties of the carbon nanopaper and viscoelastic properties of the shape memory polymer are characterized. A nonlinear, fully coupled electrical -thermal-structural ?nite element model is developed, and shape recovery experiments are carried out to validate multiphysics analysis and ?nite element model of the shape recovery of the CNP/SMP composite. Finite element model captures the general behavior of shape recovery, but overpredicts shape ?xity and shape recovery rate.
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Date Issued: 2019
Identifier: CFE0007700, ucf:52417
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007700

Title: The Characterization of the Effects of Stress Concentrations on the Mechanical Behavior of a Micronic Woven Wire Mesh.
Creator: Kraft, Steven, Gordon, Ali, Bai, Yuanli, Gou, Jihua, University of Central Florida
Abstract / Description: Woven structures are steadily emerging as excellent reinforcing components in dual-phase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, significant gaps in mechanical behavior classification remain. This thesis works to address the mechanics of material...
Show moreWoven structures are steadily emerging as excellent reinforcing components in dual-phase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, significant gaps in mechanical behavior classification remain. This thesis works to address the mechanics of material knowledge gap that exists for characterizing the behavior of a metallic woven structure, composed of stainless steel wires on the order of 25 microns in diameter, and subjected to various loading conditions and stress risers. Uniaxial and biaxial tensile experiments, employing Digital Image Correlation (DIC) as a strain measurement tool, are conducted on woven wire mesh specimens incised in various material orientations, and with various notch geometries. Experimental results, supported by an ample analytic modeling effort, indicate that an orthotropic elastic constitutive model is reasonably capable of governing the macro-scale elasticity of the subject material. Also, the Stress Concentration Factor (SCF) associated with various notch geometries is documented experimentally and analytically, and it is shown that the degree of stress concentration is dependent on both notch and material orientation. The Finite Element Method (FEM) is employed on the macro-scale to expand the experimental test matrix, and to judge the effects of a homogenization assumption when modeling metallic woven structures. Additionally, plasticity of the stainless steel woven wire mesh is considered through experimental determination of the yield surface, and a thorough analytic modeling effort resulting in a modified form of the Hill yield criterion. Finally, meso-scale plasticity of the woven structure is considered, and the form of a multi-scale failure criterion is proposed and exercised numerically.
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Date Issued: 2013
Identifier: CFE0004707, ucf:49825
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004707

Title: Biomechanical Models of Human Upper and Tracheal Airway Functionality.
Creator: Kuruppumullage, Don Nadun, Ilegbusi, Olusegun, Kassab, Alain, Moslehy, Faissal, Santhanam, Anand, Mansy, Hansen, Hoffman Ruddy, Bari, University of Central Florida
Abstract / Description: The respiratory tract, in other words, the airway, is the primary airflow path for several physiological activities such as coughing, breathing, and sneezing. Diseases can impact airway functionality through various means including cancer of the head and neck, Neurological disorders such as Parkinson's disease, and sleep disorders and all of which are considered in this study. In this dissertation, numerical modeling techniques were used to simulate three distinct airway diseases: a weak...
Show moreThe respiratory tract, in other words, the airway, is the primary airflow path for several physiological activities such as coughing, breathing, and sneezing. Diseases can impact airway functionality through various means including cancer of the head and neck, Neurological disorders such as Parkinson's disease, and sleep disorders and all of which are considered in this study. In this dissertation, numerical modeling techniques were used to simulate three distinct airway diseases: a weak cough leading to aspiration, upper airway patency in obstructive sleep apnea, and tongue cancer in swallow disorders. The work described in this dissertation, therefore, divided into three biomechanical models, of which fluid and particulate dynamics model of cough is the first. Cough is an airway protective mechanism, which results from a coordinated series of respiratory, laryngeal, and pharyngeal muscle activity. Patients with diminished upper airway protection often exhibit cough impairment resulting in aspiration pneumonia. Computational Fluid Dynamics (CFD) technique was used to simulate airflow and penetrant behavior in the airway geometry reconstructed from Computed Tomography (CT) images acquired from participants. The second study describes Obstructive Sleep Apnea (OSA) and the effects of dilator muscular activation on the human retro-lingual airway in OSA. Computations were performed for the inspiration stage of the breathing cycle, utilizing a fluid-structure interaction (FSI) method to couple structural deformation with airflow dynamics. The spatiotemporal deformation of the structures surrounding the airway wall was predicted and found to be in general agreement with observed changes in luminal opening and the distribution of airflow from upright to supine posture. The third study describes the effects of cancer of the tongue base on tongue motion during swallow. A three-dimensional biomechanical model was developed and used to calculate the spatiotemporal deformation of the tongue under a sequence of movements which simulate the oral stage of swallow.
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Date Issued: 2018
Identifier: CFE0007034, ucf:51986
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007034

Title: TARGET ELEMENT SIZES FOR FINITE ELEMENT TIDAL MODELS FROM A DOMAIN-WIDE, LOCALIZED TRUNCATION ERROR ANALYSIS INCORPORATING BOTTOM STRESS AND CORIOLIS FORCE.
Creator: Parrish, Denwood, Hagen, Scott C., University of Central Florida
Abstract / Description: A new methodology for the determination of target element sizes for the construction of finite element meshes applicable to the simulation of tidal flow in coastal and oceanic domains is developed and tested. The methodology is consistent with the discrete physics of tidal flow, and includes the effects of bottom stress. The method enables the estimation of the localized truncation error of the nonconservative momentum equations throughout a triangulated data set of water surface elevation...
Show moreA new methodology for the determination of target element sizes for the construction of finite element meshes applicable to the simulation of tidal flow in coastal and oceanic domains is developed and tested. The methodology is consistent with the discrete physics of tidal flow, and includes the effects of bottom stress. The method enables the estimation of the localized truncation error of the nonconservative momentum equations throughout a triangulated data set of water surface elevation and flow velocity. The method's domain-wide applicability is due in part to the formulation of a new localized truncation error estimator in terms of complex derivatives. More conventional criteria that are often used to determine target element sizes are limited to certain bathymetric conditions. The methodology developed herein is applicable over a broad range of bathymetric conditions, and can be implemented efficiently. Since the methodology permits the determination of target element size at points up to and including the coastal boundary, it is amenable to coastal domain applications including estuaries, embayments, and riverine systems. These applications require consideration of spatially varying bottom stress and advective terms, addressed herein. The new method, called LTEA-CD (localized truncation error analysis with complex derivatives), is applied to model solutions over the Western North Atlantic Tidal model domain (the bodies of water lying west of the 60° W meridian). The convergence properties of LTEACD are also analyzed. It is found that LTEA-CD may be used to build a series of meshes that produce converging solutions of the shallow water equations. An enhanced version of the new methodology, LTEA+CD (which accounts for locally variable bottom stress and Coriolis terms) is used to generate a mesh of the WNAT model domain having 25% fewer nodes and elements than an existing mesh upon which it is based; performance of the two meshes, in an average sense, is indistinguishable when considering elevation tidal signals. Finally, LTEA+CD is applied to the development of a mesh for the Loxahatchee River estuary; it is found that application of LTEA+CD provides a target element size distribution that, when implemented, outperforms a high-resolution semi-uniform mesh as well as a manually constructed, existing, documented mesh.
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Date Issued: 2007
Identifier: CFE0001738, ucf:52860
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001738

Title: Biomechanical Factors Influencing Treatment of Developmental Dysplasia of the Hip (DDH) with the Pavlik Harness.
Creator: Ardila, Orlando, Kassab, Alain, Moslehy, Faissal, Divo, Eduardo, University of Central Florida
Abstract / Description: Biomechanical factors influencing the reduction of dislocated hips with the Pavlik harness in patients of Developmental Dysplasia of the Hip (DDH) were studied using a simplified three-dimensional computer model simulating hip reduction dynamics in (1) subluxated, and (2) fully dislocated hip joints. The CT-scans of a 6 month-old female infant were used to measure the geometrical features of the hip joint including acetabular and femoral head diameter, acetabular depth, and geometry of the...
Show moreBiomechanical factors influencing the reduction of dislocated hips with the Pavlik harness in patients of Developmental Dysplasia of the Hip (DDH) were studied using a simplified three-dimensional computer model simulating hip reduction dynamics in (1) subluxated, and (2) fully dislocated hip joints. The CT-scans of a 6 month-old female infant were used to measure the geometrical features of the hip joint including acetabular and femoral head diameter, acetabular depth, and geometry of the acetabular labrum, using the medical segmentation software Mimics. The lower extremity was modeled by three segments: thigh, leg, and foot. The mass and the location of the center of gravity of each segment were calculated using anthropometry, based on the total body mass of a 6-month old female infant at the 50th length-for-age percentile. A calibrated nonlinear stress-strain model was used to simulate muscle responses. The simplified 3D model consists of the pubis, ischium, acetabulum with labrum, and femoral head, neck, and shaft. It is capable of simulating dislocated as well as reduced hips in abduction and flexion.Five hip adductor muscles were identified as key mediators of DDH prognosis, and the non-dimensional force contribution of each in the direction necessary to achieve concentric hip reductions was determined. Results point to the adductor muscles as mediators of subluxated hip reductions, as their mechanical action is a function of the degree of hip dislocation. For subluxated hips in abduction and flexion, the Pectineus, Adductor Brevis, Adductor Longus, and proximal Adductor Magnus muscles contribute positively to reduction, while the rest of the Adductor Magnus contributes negatively. In full dislocations all muscles contribute detrimentally to reduction, elucidating the need for traction to reduce Graf IV type dislocations. Reduction of dysplastic hips was found to occur in two distinct phases: (a) release phase and (b) reduction phase.To expand the range of DDH-related problems that can be studied, an improved three-dimensional anatomical computer model was generated by combining CT-scan and muscle positional data belonging to four human subjects. This model consists of the hip bone and femora of a 10-week old female infant. It was segmented to encompass the distinct cartilaginous regions of infant anatomy, as well as the different regions of cortical and cancellous bone; these properties were retrieved from the literature. This engineering computer model of an infant anatomy is being employed for (1) the development of a complete finite element and dynamics computer model for simulations of hip dysplasia reductions using novel treatment approaches, (2) the determination of a path of least resistance in reductions of hip dysplasia based on a minimum potential energy approach, (3) the study of the mechanics of hyperflexion of the hip as alternative treatment for late-presenting cases of hip dysplasia, and (4) a comprehensive investigation of the effects of femoral anteversion angle (AV) variations in reductions of hip dysplasia. This thesis thus reports on an interdisciplinary effort between orthopedic surgeons and mechanical engineers to apply engineering fundamentals to solve medical problems. The results of this research are clinically relevant in pediatric orthopaedics.
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Date Issued: 2013
Identifier: CFE0004646, ucf:49907
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004646

Title: SELF-ASSEMBLED LIPID TUBULES: STRUCTURES, MECHANICAL PROPERTIES, AND APPLICATIONS.
Creator: Zhao, Yue, Fang, Jiyu, University of Central Florida
Abstract / Description: Self-assembled lipid tubules are particularly attractive for inorganic synthesis and drug delivery because they have hollow cylindrical shapes and relatively rigid mechanical properties. In this thesis work, we have synthesized lipid tubules of 1,2-bis(tricosa-10,12-dinoyl)-sn-glycero-3-phosphocholine (DC8,9PC) by self-assembly and polymerization in solutions. We demonstrate for the first time that both uniform and modulated molecular tilt orderings exist in the tubule walls, which have been...
Show moreSelf-assembled lipid tubules are particularly attractive for inorganic synthesis and drug delivery because they have hollow cylindrical shapes and relatively rigid mechanical properties. In this thesis work, we have synthesized lipid tubules of 1,2-bis(tricosa-10,12-dinoyl)-sn-glycero-3-phosphocholine (DC8,9PC) by self-assembly and polymerization in solutions. We demonstrate for the first time that both uniform and modulated molecular tilt orderings exist in the tubule walls, which have been predicted by current theories, and therefore provide valuable supporting evidences for self-assembly mechanisms of chiral molecules. Two novel methods are developed for studying the axial and radial deformations of DC8,9PC lipid tubules. Mechanical properties of DC8,9PC tubules are systematically studied in terms of persistence length, bending rigidity, strain energy, axial and radial elastic moduli, and critical force for collapse. Mechanisms of recovery and surface stiffening are discussed. Due to the high aspect ratio of lipid tubules, the hierarchical assembly of lipid tubules into ordered arrays and desired architectures is critical in developing their applications. Two efficient methods for fabricating ordered arrays of lipid tubules on solid substrates have been developed. Ordered arrays of hybrid silica-lipid tubes are synthesized by tubule array-templated sol-gel reactions. Ordered arrays of optical anisotropic fibers with tunable shapes and refractive indexes are fabricated. This thesis work provides a paradigm for molecularly engineered structures.
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Date Issued: 2007
Identifier: CFE0001918, ucf:47486
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001918

Title: Influence of Topographic Elevation Error On Modeled Storm Surge.
Creator: Bilskie, Matthew, Hagen, Scott, Wang, Dingbao, Chopra, Manoj, University of Central Florida
Abstract / Description: The following presents a method for determining topographic elevation error for overland unstructured finite element meshes derived from bare earth LiDAR for use in a shallow water equations model. This thesis investigates the development of an optimal interpolation method to produce minimal error for a given element size. In hydrodynamic studies, it is vital to represent the floodplain as accurately as possible since terrain is a critical factor that influences water flow. An essential step...
Show moreThe following presents a method for determining topographic elevation error for overland unstructured finite element meshes derived from bare earth LiDAR for use in a shallow water equations model. This thesis investigates the development of an optimal interpolation method to produce minimal error for a given element size. In hydrodynamic studies, it is vital to represent the floodplain as accurately as possible since terrain is a critical factor that influences water flow. An essential step in the development of a coastal inundation model is processing and resampling dense bare earth LiDAR to a DEM and ultimately to the mesh nodes; however, it is crucial that the correct DEM grid size and interpolation method be employed for an accurate representation of the terrain. The following research serves two purposes: 1) to assess the resolution and interpolation scheme of bare earth LiDAR data points in terms of its ability to describe the bare earth topography and its subsequent performance during relevant tide and storm surge simulations.
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Date Issued: 2012
Identifier: CFE0004520, ucf:49265
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004520

Title: Structural Identification through Monitoring, Modeling and Predictive Analysis under Uncertainty.
Creator: Gokce, Hasan, Catbas, Fikret, Chopra, Manoj, Mackie, Kevin, Yun, Hae-Bum, DeMara, Ronald, University of Central Florida
Abstract / Description: Bridges are critical components of highway networks, which provide mobility and economical vitality to a nation. Ensuring the safety and regular operation as well as accurate structural assessment of bridges is essential. Structural Identification (St-Id) can be utilized for better assessment of structures by integrating experimental and analytical technologies in support of decision-making. St-Id is defined as creating parametric or nonparametric models to characterize structural behavior...
Show moreBridges are critical components of highway networks, which provide mobility and economical vitality to a nation. Ensuring the safety and regular operation as well as accurate structural assessment of bridges is essential. Structural Identification (St-Id) can be utilized for better assessment of structures by integrating experimental and analytical technologies in support of decision-making. St-Id is defined as creating parametric or nonparametric models to characterize structural behavior based on structural health monitoring (SHM) data. In a recent study by the ASCE St-Id Committee, St-Id framework is given in six steps, including modeling, experimentation and ultimately decision making for estimating the performance and vulnerability of structural systems reliably through the improved simulations using monitoring data. In some St-Id applications, there can be challenges and considerations related to this six-step framework. For instance not all of the steps can be employed; thereby a subset of the six steps can be adapted for some cases based on the various limitations. In addition, each step has its own characteristics, challenges, and uncertainties due to the considerations such as time varying nature of civil structures, modeling and measurements. It is often discussed that even a calibrated model has limitations in fully representing an existing structure; therefore, a family of models may be well suited to represent the structure's response and performance in a probabilistic manner.The principle objective of this dissertation is to investigate nonparametric and parametric St-Id approaches by considering uncertainties coming from different sources to better assess the structural condition for decision making. In the first part of the dissertation, a nonparametric St-Id approach is employed without the use of an analytical model. The new methodology, which is successfully demonstrated on both lab and real-life structures, can identify and locate the damage by tracking correlation coefficients between strain time histories and can locate the damage from the generated correlation matrices of different strain time histories. This methodology is found to be load independent, computationally efficient, easy to use, especially for handling large amounts of monitoring data, and capable of identifying the effectiveness of the maintenance. In the second part, a parametric St-Id approach is introduced by developing a family of models using Monte Carlo simulations and finite element analyses to explore the uncertainty effects on performance predictions in terms of load rating and structural reliability. The family of models is developed from a parent model, which is calibrated using monitoring data. In this dissertation, the calibration is carried out using artificial neural networks (ANNs) and the approach and results are demonstrated on a laboratory structure and a real-life movable bridge, where predictive analyses are carried out for performance decrease due to deterioration, damage, and traffic increase over time. In addition, a long-span bridge is investigated using the same approach when the bridge is retrofitted. The family of models for these structures is employed to determine the component and system reliability, as well as the load rating, with a distribution that incorporates various uncertainties that were defined and characterized. It is observed that the uncertainties play a considerable role even when compared to calibrated model-based predictions for reliability and load rating, especially when the structure is complex, deteriorated and aged, and subjected to variable environmental and operational conditions. It is recommended that a family-of-models approach is suitable for structures that have less redundancy, high operational importance, are deteriorated, and are performing under close capacity and demand levels.
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Date Issued: 2012
Identifier: CFE0004232, ucf:48997
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004232

Title: STRUCTURAL CONDITION ASSESSMENT OF PRESTRESSED CONCRETE TRANSIT GUIDEWAYS.
Creator: Shmerling, Robert, Catbas, F. Necati, University of Central Florida
Abstract / Description: Objective condition assessment is essential to make better decisions for safety and serviceability of existing civil infrastructure systems. This study explores the condition of an existing transit guideway system that has been in service for thirty-five years. The structural system is composed of six-span continuous prestressed concrete bridge segments. The overall transit system incorporates a number of continuous bridges which share common design details, geometries, and loading conditions...
Show moreObjective condition assessment is essential to make better decisions for safety and serviceability of existing civil infrastructure systems. This study explores the condition of an existing transit guideway system that has been in service for thirty-five years. The structural system is composed of six-span continuous prestressed concrete bridge segments. The overall transit system incorporates a number of continuous bridges which share common design details, geometries, and loading conditions. The original analysis is based on certain simplifying assumptions such as rigid behavior over supports and simplified tendon/concrete/steel plate interaction. The current objective is to conduct a representative study for a more accurate understanding of the structural system and its behavior. The scope of the study is to generate finite element models (FEMs) to be used in static and dynamic parameter sensitivity studies, as well load rating and reliability analysis of the structure. The FEMs are used for eigenvalue analysis and simulations. Parameter sensitivity studies consider the effect of changing critical parameters, including material properties, prestress loss, and boundary and continuity conditions, on the static and dynamic structural response. Load ratings are developed using an American Association for State Highway Transportation Officials Load and Resistance Factor Rating (AASHTO LRFR) approach. The reliability of the structural system is evaluated based on the data obtained from various finite element models. Recommendations for experimental validation of the FEM are presented. This study is expected to provide information to make better decisions for operations, maintenance and safety requirements; to be a benchmark for future studies, to establish a procedure and methodology for structural condition assessment, and to contribute to the general research body of knowledge in condition assessment and structural health monitoring.
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Date Issued: 2005
Identifier: CFE0000658, ucf:46520
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000658

$A modeling framework of brittle and ductile fractures coexistence in composites$

Title: A modeling framework of brittle and ductile fractures coexistence in composites.
Creator: Qiao, Yangyang, Bai, Yuanli, Gou, Jihua, Kassab, Alain, Gordon, Ali, An, Linan, University of Central Florida
Abstract / Description: In order to reduce the weight of automobiles and aircrafts, lightweight materials, such as aluminum alloy, advanced high strength steel, composite materials, are widely used to replace the traditional materials like mild steel. Composite materials are complicated in material mechanical properties and less investigated compared to metallic materials. Engineering composites can be categorized into polymer matrix composites (PMCs), metal matrix composites (MMCs) and ceramic matrix composites ...
Show moreIn order to reduce the weight of automobiles and aircrafts, lightweight materials, such as aluminum alloy, advanced high strength steel, composite materials, are widely used to replace the traditional materials like mild steel. Composite materials are complicated in material mechanical properties and less investigated compared to metallic materials. Engineering composites can be categorized into polymer matrix composites (PMCs), metal matrix composites (MMCs) and ceramic matrix composites (CMCs) according to their matrix materials.A set of mechanical experiments ranging from micro scale (single fiber composite and thin film composite) to macro scale (PMCs and MMCs) were conducted to fully understand the material behavior of composite materials. Loading conditions investigated includes uniaxial tension, three-point bending, uniaxial compression, simple shear, tension combined with shear, and compression combined with shear.For single fiber composite and thin-film composite, details of each composition are modelled. For the PMCs and MMCs which have plenty of reinforcements like fibers and particles, the details of the composition of structures cannot be modelled due to the current limitations of computing power. A mechanics framework of composite materials including elasticity, plasticity, failure initiation and post failure softening is proposed and applied to two types of composite materials.Uniaxial tension loading is applied to several single fiber composites and thin film composites. A surprising phenomenon, controllable and sequential fragmentation of the brittle fiber to produce uniformly sized rods along meters of polymer cladding, rather than the expected random or chaotic fragmentation, is observed with a necking propagation process. A combination of necking propagation model, fiber cracking model and interfacial model are proposed and applied to the finite element simulations. Good predictions of necking propagation and uniform fragmentation phenomenon are achieved. This modeling method of the micro-scale phenomenon reveals the physics inside composites in micro scale and helps the understanding of the process of nano fragmentation.Unidirectional carbon fiber composites were tested under multi-axial loading conditions including tensile/compression/shear loadings along and perpendicular to the fiber direction. Compression dominated tests showed a brittle fracture mode like local kicking/buckling, while tension dominated tests showed a fracture mode like delamination and fiber breakage. Simple shear tests with displacement control showed matrix material hardening and softening before total failure. The proposed modeling framework is successfully applied to the PMCs. A new parameter ? was introduced to represent different loading conditions of PMCs. Numerical simulations using finite element method well duplicated the anisotropic elasticity and plasticity of this material. Failure features like delamination was simulated using cohesive surface feature. It is also applied to carbon fiber composite laminates to further validate the proposed model.A round of experimental study on high volume fraction of metallic matrix nano composites was conducted, including uniaxial tension, uniaxial compression, and three-point bending. The example materials were two magnesium matrix composites reinforced with 10 and 15% vol. SiC particles (50nm size). Brittle fracture mode was exhibited under uniaxial tension and three-point bending, while shear dominated ductile fracture mode (up to 12% fracture strain) was observed under uniaxial compression. Transferring the Modified Mohr Coulomb (MMC) ductile fracture model to the stress based MMC model (sMMC), the proposed modeling framework is applied to this material. This model has been demonstrated to be capable of predicting the coexistence of brittle and ductile fracture modes under different loading conditions for MMCs. Numerical simulations using finite element method well duplicated the material strength, fracture initiation sites and crack propagation modes of the Mg/SiC nano composites with a good accuracy.
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Date Issued: 2018
Identifier: CFE0007078, ucf:51977
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007078

Title: Ultra-Efficient Cascaded Buck-Boost Converter.
Creator: Ashok Pise, Anirudh, Batarseh, Issa, Mikhael, Wasfy, Sun, Wei, Kutkut, Nasser, University of Central Florida
Abstract / Description: This thesis presents various techniques to achieve ultra-high-efficiency for Cascaded-Buck-Boost converter. A rigorous loss model with component non linearity is developed and validated experimentally. An adaptive-switching-frequency control is discussed to optimize weighted efficiency. Some soft-switching techniques are discussed. A low-profile planar-nanocrystalline inductor is developed and various design aspects of core and copper design are discussed. Finite-element-method is used to...
Show moreThis thesis presents various techniques to achieve ultra-high-efficiency for Cascaded-Buck-Boost converter. A rigorous loss model with component non linearity is developed and validated experimentally. An adaptive-switching-frequency control is discussed to optimize weighted efficiency. Some soft-switching techniques are discussed. A low-profile planar-nanocrystalline inductor is developed and various design aspects of core and copper design are discussed. Finite-element-method is used to examine and visualize the inductor design. By implementing the above, a peak efficiency of over 99.2 % is achieved with a power density of 6 kW/L and a maximum profile height of 7 mm is reported. This converter finds many applications because of its versatility: allowing bidirectional power flow and the ability to step-up or step-down voltages in either direction.
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Date Issued: 2017
Identifier: CFE0007277, ucf:52181
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007277

Title: Experimental study and modeling of mechanical micro-machining of particle reinforced heterogeneous materials.
Creator: Liu, Jian, Xu, Chengying, An, Linan, Gordon, Ali, Bai, Yuanli, Gong, Xun, University of Central Florida
Abstract / Description: This study focuses on developing explicit analytical and numerical process models for mechanical micro-machining of heterogeneous materials. These models are used to select suitable process parameters for preparing and micro-machining of these advanced materials. The material system studied in this research is Magnesium Metal Matrix Composites (Mg-MMCs) reinforced with nano-sized and micro-sized silicon carbide (SiC) particles.This research is motivated by increasing demands of miniaturized...
Show moreThis study focuses on developing explicit analytical and numerical process models for mechanical micro-machining of heterogeneous materials. These models are used to select suitable process parameters for preparing and micro-machining of these advanced materials. The material system studied in this research is Magnesium Metal Matrix Composites (Mg-MMCs) reinforced with nano-sized and micro-sized silicon carbide (SiC) particles.This research is motivated by increasing demands of miniaturized components with high mechanical performance in various industries. Mg-MMCs become one of the best candidates due to its light weight, high strength, and high creep/wear resistance. However, the improved strength and abrasive nature of the reinforcements bring great challenges for the subsequent micro-machining process.Systematic experimental investigations on the machinability of Mg-MMCs reinforced with SiC nano-particles have been conducted. The nanocomposites containing 5 Vol.%, 10 Vol.% and 15 Vol.% reinforcements, as well as pure magnesium, are studied by using the Design of Experiment (DOE) method. Cutting forces, surface morphology and surface roughness are characterized to understand the machinability of the four materials. Based on response surface methodology (RSM) design, experimental models and related contour plots have been developed to build a connection between different materials properties and cutting parameters. Those models can be used to predict the cutting force, the surface roughness, and then optimize the machining process.An analytical cutting force model has been developed to predict cutting forces of Mg-MMCs reinforced with nano-sized SiC particles in the micro-milling process. This model is different from previous ones by encompassing the behaviors of reinforcement nanoparticles in three cutting scenarios, i.e., shearing, ploughing and elastic recovery. By using the enhanced yield strength in the cutting force model, three major strengthening factors are incorporated, including load-bearing effect, enhanced dislocation density strengthening effect and Orowan strengthening effect. In this way, the particle size and volume fraction, as significant factors affecting the cutting forces, are explicitly considered. In order to validate the model, various cutting conditions using different size end mills (100 (&)#181;m and 1 mm dia.) have been conducted on Mg-MMCs with volume fraction from 0 (pure magnesium) to 15 Vol.%. The simulated cutting forces show a good agreement with the experimental data. The proposed model can predict the major force amplitude variations and force profile changes as functions of the nanoparticles' volume fraction. Next, a systematic evaluation of six ductile fracture models has been conducted to identify the most suitable fracture criterion for micro-scale cutting simulations. The evaluated fracture models include constant fracture strain, Johnson-Cook, Johnson-Cook coupling criterion, Wilkins, modified Cockcroft-Latham, and Bao-Wierzbicki fracture criterion. By means of a user material subroutine (VUMAT), these fracture models are implemented into a Finite Element (FE) orthogonal cutting model in ABAQUS/Explicit platform. The local parameters (stress, strain, fracture factor, velocity fields) and global variables (chip morphology, cutting forces, temperature, shear angle, and machined surface integrity) are evaluated. Results indicate that by coupling with the damage evolution, the capability of Johnson-Cook and Bao-Wierzbicki can be further extended to predict accurate chip morphology. Bao-Wierzbiki-based coupling model provides the best simulation results in this study. The micro-cutting performance of MMCs materials has also been studied by using FE modeling method. A 2-D FE micro-cutting model has been constructed. Firstly, homogenized material properties are employed to evaluate the effect of particles' volume fraction. Secondly, micro-structures of the two-phase material are modeled in FE cutting models. The effects of the existing micro-sized and nano-sized ceramic particles on micro-cutting performance are carefully evaluated in two case studies. Results show that by using the homogenized material properties based on Johnson-Cook plasticity and fracture model with damage evolution, the micro-cutting performance of nano-reinforced Mg-MMCs can be predicted. Crack generation for SiC particle reinforced MMCs is different from their homogeneous counterparts; the effect of micro-sized particles is different from the one of nano-sized particles.In summary, through this research, a better understanding of the unique cutting mechanism for particle reinforced heterogeneous materials has been obtained. The effect of reinforcements on micro-cutting performance is obtained, which will help material engineers tailor suitable material properties for special mechanical design, associated manufacturing method and application needs. Moreover, the proposed analytical and numerical models provide a guideline to optimize process parameters for preparing and micro-machining of heterogeneous MMCs materials. This will eventually facilitate the automation of MMCs' machining process and realize high-efficiency, high-quality, and low-cost manufacturing of composite materials.
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Date Issued: 2012
Identifier: CFE0004570, ucf:49196
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004570

Title: A THREE-DIMENSIONAL BAY/ESTUARY MODEL TO SIMULATE WATER QUALITY TRANSPORT.
Creator: Yu, Jing, Yeh, Gour-Tsyh, University of Central Florida
Abstract / Description: This thesis presents the development of a numerical water quality model using a general paradigm of reaction-based approaches. In a reaction-based approach, all conceptualized biogeochemical processes are transformed into a reaction network. Through the decomposition of species governing equations via Gauss-Jordan column reduction of the reaction network, (1) redundant fast reactions and irrelevant kinetic reactions are removed from the system, which alleviates the problem of unnecessary and...
Show moreThis thesis presents the development of a numerical water quality model using a general paradigm of reaction-based approaches. In a reaction-based approach, all conceptualized biogeochemical processes are transformed into a reaction network. Through the decomposition of species governing equations via Gauss-Jordan column reduction of the reaction network, (1) redundant fast reactions and irrelevant kinetic reactions are removed from the system, which alleviates the problem of unnecessary and erroneous formulation and parameterization of these reactions, and (2) fast reactions and slow reactions are decoupled, which enables robust numerical integrations. The system of species transport equations is transformed to reaction-extent transport equations, which is then approximated with two subsets: algebraic equations and kinetic-variables transport equations. As a result, the model alleviates the needs of using simple partitions for fast reactions. With the diagonalization strategy, it makes the inclusion of arbitrary number of fast and kinetic reactions relatively easy, and, more importantly, it enables the formulation and parameterization of kinetic reactions one by one. To demonstrate the general paradigm, QAUL2E was recasted in the mode of a reaction network. The model then was applied to the Loxahatchee estuary to study its response to a hypothetical biogeochemical loading from its surrounding drainage. Preliminary results indicated that the model can simulate four interacting biogeochemical processes: algae kinetics, nitrogen cycle, phosphorus cycle, and dissolved oxygen balance.
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Date Issued: 2006
Identifier: CFE0001372, ucf:46991
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001372

Finite Element Analysis (3)	+ -
Finite Element Method (3)	+ -
Fast/ Equilibrium Reactions (2)	+ -
Finite Element Mesh (2)	+ -
Finite Element Model (2)	+ -

Fully-implicit (2)	+ -
Kinetic-Variable (2)	+ -
Lagrangian-Eulerian approach (2)	+ -
Modeling (2)	+ -
Operator-splitting (2)	+ -
Predictor-corrector (2)	+ -
Reactive Chemical Transport (2)	+ -
Slow/Kinetic Reactions (2)	+ -
finite element model (2)	+ -
finite element modeling (2)	+ -
ADCIRC (1)	+ -
Abutment components (1)	+ -
All-strain Based Modified-Mohr-Coulomb Fracture Model (1)	+ -
Anisotropic Fracture (1)	+ -
Anisotropic plasticity (1)	+ -
Aspiration (1)	+ -
Bay/Estuary Model (1)	+ -
Biomechanical Modeling (1)	+ -
Cascaded Buck Boost Converter (1)	+ -
Coexistence of Brittle and Ductile Fractures (1)	+ -
Component Non-Linearity (1)	+ -
Composites Modeling Framework (1)	+ -
Computerized simulation (1)	+ -
Correlation (1)	+ -
Cough Dynamical Model (1)	+ -

University of Central Florida (22)	+ -
Bai, Yuanli (5)	+ -
Chopra, Manoj (4)	+ -
Gordon, Ali (4)	+ -
Gou, Jihua (4)	+ -

Hagen, Scott (4)	+ -
Kassab, Alain (4)	+ -
Mackie, Kevin (3)	+ -
An, Linan (2)	+ -
Moslehy, Faissal (2)	+ -
Yeh, Gour-Tsyh (2)	+ -
Ardila, Orlando (1)	+ -
Ashok Pise, Anirudh (1)	+ -
Bacopoulos, Peter (1)	+ -
Batarseh, Issa (1)	+ -
Bilskie, Matthew (1)	+ -
Catbas, F. Necati (1)	+ -
Catbas, Fikret (1)	+ -
Catbas, Necati (1)	+ -
Darwash, Haider (1)	+ -
DeMara, Ronald (1)	+ -
Divo, Eduardo (1)	+ -
Fang, Jiyu (1)	+ -
Ge, Zhibing (1)	+ -
Ghosh, Ranajay (1)	+ -
Gokce, Hasan (1)	+ -
Gong, Xun (1)	+ -
Hagen, Scott C. (1)	+ -
Hoffman Ruddy, Bari (1)	+ -
Ilegbusi, Olusegun (1)	+ -

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