Engineering Commons^™

Structural And Hemodynamic Analysis Of Transcatheter Aortic Valves, Dong Qiu

Electronic Theses and Dissertations

The transcatheter aortic valve replacement (TAVR) procedure has become a well-established procedure for high, intermediate-risk, and low-risk patients. However, there is limited clinical data on the TAV's long-term durability, unlike SAV devices. Computational simulations can be an alternative way to evaluate the TAV devices. This dissertation aims to conduct structural and hemodynamic analyses on the TAV devices under different conditions using computational simulation approaches.

Initially, the impact of the bicuspid aortic valve on the TAV devices was evaluated. The result indicated that the CoreValve-like supra-annular self-expandable device was likely to have increased stress and strain on the leaflet when it …

Development Of Triangular And Tetrahedral Finite Elements For Solutions To Thermoelastic Instabilities Using Hotspotter, Cortney Samuel Leneave

Electronic Theses and Dissertations

The objective of the work presented in this thesis is to develop first-order triangular and tetrahedral elements for solutions to Thermoelastic Instabilities (TEI) regarding sliding friction systems in Hotspotter.

Hotspotter software uses a finite element method and an eigenvalue method and is an important tool because currently no other commercial software exists which solves the TEI problem for critical velocities and wave numbers of a system. Hotspotter currently uses quadrilateral and hexahedral elements for two and three dimensional analysis, respectively. Typically, tri and tet elements are used in industry when doing static and dynamic stress analysis. Therefore, the Hotspotter user …

The Relative Contribution Of Fixation Features, Activity, And Tibiofemoral Conformity On Initial Stability Of Cementless Tibial Trays, James Sullivan Deacy

Electronic Theses and Dissertations

Initial stability of cementless total knee replacements (TKR) is critical to implant success as excessive motion between the bone and implant prevents bony ingrowth that is critical to the long-term survivability of cementless implants. Prior studies have shown that excessive micromotion causes fibrous tissue growth instead of beneficial bony growth. There are many factors that influence initial stability including the design of the tibial tray and the tibiofemoral articulations. Understanding the impacts of these design features on micromotion between the bone and implants is crucial to improving the performance of cementless TKR. Prior studies only tested for the effect of …

Computational Prediction Of Conductivities Of Disk-Shaped Particulate Composites, Jian Qiu

Electronic Theses and Dissertations

The effective conductivities are determined for randomly oriented disk-shaped particles using an efficient computational algorithm based on the finite element method. The pairwise intersection criteria of disks are developed using a set of vector operations. An element partition scheme has been implemented to connect the elements on different disks across the lines of intersection. The computed conductivity is expressed as a function of the density and the size of the circular disks or elliptical plates. It is further expressed in a power-law form with the key parameters determined from curve fittings. The particle number and the trial number of simulations …

Computational Modeling Of Percolation Conduction And Diffusion Of Heterogeneous Materials, Jian Qiu

Electronic Theses and Dissertations

Heterogeneous materials provide a unique combination of desirable mechanical, thermal or electrical properties. This dissertation presents several micro-structure modeling approaches to predict the effective properties of heterogeneous materials and demonstrates its certain application toward two highly heterogeneous, unconventional structural composite materials (carbon fiber reinforced composite materials and graphene nanoplatelets composite). By using the efficient computational algorithm based on the FEA, a randomly oriented disk-shaped particles system are generated. A new element partition scheme based on the vector operations and geometry of inclusion has been implemented to mesh the intersected disks. The computed equivalent conductivity is expressed as a power-law function …

Methods And Implementation Of Fluid-Structure Interaction Modeling Into An Industry-Accepted Design Tool, Donn R. Sederstrom

Electronic Theses and Dissertations

Fluid-structure interaction (FSI) modeling is a method by which fluid and solid domains are coupled together to produce a single result that cannot be produced if each physical domain was evaluated individually. The work presented in this dissertation is a demonstration of the methods and implementation of FSI modeling into an industry-appropriate design tool. Through utilizing computationally inexpensive equipment and commercially available software, the studies presented in this work demonstrate the ability for FSI modeling to become a tool used broadly in industry.

To demonstrate this capability, the cases studied purposely include substantial complexity to demonstrate the stability techniques required …

Finite Element And Probabilistic Analysis Of Soft Tissue Structures Of The Human Lumbar Spine, Dana Joseph Coombs

Electronic Theses and Dissertations

Human lumbar spine mechanics are influenced by soft tissue structures. Understanding and properly modeling these structures can help determine pathology, treatment, and implant design and performance. Finite element models of the L4-L5 level of the lumbar spine are often used, which include a representation of the intervertebral disc and spinal ligaments. Validation of these models are typically based on torque rotation data from a single subject or the models use average properties reported in literature. However, experimental testing reports variation up to 40% in ligament stiffness and even greater variability for annulus fibrosis properties. Probabilistic approaches enable consideration of the …

Thermomechanical Stabilities In Automotive Brakes & Clutches Systems, Ali Bendawi

Electronic Theses and Dissertations

This thesis involves three related topics in the area of thermal stress resulting from sliding contact of frictional materials. These three contributions collectively and the discussion of them herein form a collective basis furthering the research and understanding within this field. Firstly, the effect of convective cooling on thermoelastic instability is evaluated using finite element analysis involving insertion of a thermal convection term in the formula for frictional heat generation. It has been found that convection or radiation heat dissipation can stabilize the thermal-mechanical feedback process, leading to a raised critical sliding velocity. Two representative models for brake and clutch …

Representing Intersubject Variability With A Statistical Shape And Alignment Model Of The Knee, Chandreshwar Rao

Electronic Theses and Dissertations

Prior statistical shape models have not considered multiple structures in the knee joint to characterize anatomic variation which are required to investigate joint mechanics further for the successful knee replacement. Accordingly, the study's objective was to develop statistical shape and alignment model (SSAM) to capture intersubject variability and demonstrate the ability to generate realistic instances for use in finite element analysis (FEA). SSAM described the variability in the training set of 20 subjects with a series of modes of variation obtained by performing principal component analysis (PCA). PCA produced modes of variation with the first 3 modes representing 70% and …

Finite Element Analysis Of Thermomechanical Processes In Disk Clutch Systems, Zhuo Chen

Electronic Theses and Dissertations

The engagement of clutch system is a typical dynamic coupled temperature-displacement process which contains two or more sliding surfaces involved in frictional contact. This process influences evidently the thermal fatigue, noise and vibration of the clutch system. This effect can be more remarkable if the temperature distribution over the clutch disk is not uniform.

This thesis is organized into five chapters:

The first chapter is an introduction which reviews the background and previous work of thermoelastic instability and finite element analysis of clutch system and disk brake.

A parametric analysis of TEI (thermoelastic instability) is elaborated in the second chapter. …

Explicit Finite Element Modeling Of The Human Lumbar Spine, Milind Rao

Electronic Theses and Dissertations

Validated finite element (FE) models of the functional spinal unit (FSU) and lumbar spine are essential in design-phase device development and in assessing the mechanics associated with normal spine function and degenerative disc disease (DDD), as well as the impact of fusion and total disc replacement (TDR). Although experimental data from fully intact specimens can be used for model calibration and validation, the contributions from the individual structures (disc, facets, and ligaments) may be inappropriately distributed. Hence, creation of decompression conditions or device implantations that require structure removal may not have the proper resulting mechanics. An explicit FE formulation may …