Date of Graduation

12-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Millett, Paul C.

Committee Member

Walters, Keith

Second Committee Member

Jensen, Morten O.

Third Committee Member

Hu, Han

Fourth Committee Member

Tung, Chao-Hung Steve

Keywords

Cellulose; Computational Fluid Dynamics; Congenital Heart Disease; Lumped Parameter Model; Molecular Dynamics; Williams Syndrome

Abstract

The study of anisometric particle suspensions and congenital heart defects (CHDs) involve exploring complex phenomena within the biological sciences. The former subject dives into the phase behavior of liquid crystals (LCs), particularly the influence of the shape anisotropy of rod-like nanoparticles on phase transitions, through the implementation of statistical techniques involving molecular dynamics (MD). Conversely, the latter topic focuses on the assessment and management of severe congenital arterial stenoses, such as those found in Williams-Beuren syndrome (WS), through advanced multi-scale computational fluid dynamics (CFD) simulations. Both areas emphasize the importance of detailed analysis and the use of advanced numerical modeling techniques to gain insights that are crucial for practical applications, whether in material design or clinical intervention.

Some suspensions of anisotropic particles are recognized for their ability to form various LC phases, which can often be driven solely by excluded volume effects. Control over the formation of such phases can prove to be challenging experimentally due to their existence at higher concentrations. The abundance and mechanical properties of some natural bio-molecular particles such as cellulose nanocrystals (CNCs) which can exhibit mesogenic behavior in solvent-induced systems have the potential to drive innovation, if the characterization of surface modifications can be better understood. This dissertation examines how a localized weak attractive interaction affects the phase behavior of a system of rod-like colloidal particles. Large-scale MD simulations were conducted for a rod-like coarse-grained model – rigidly connected overlapping beads – varying in length, uniformity and shape anisotropy. The interactions between beads on different rods are described using a combination of Lennard-Jones (LJ) and Weeks-Chandler-Anderson (WCA) potentials. As the attraction between rod tips increases, there is a preference for the more ordered smectic LC phase over the less ordered nematic phase at reduced volume fractions, with the nematic phase diminishing when the attractive forces become too significant. Additionally, the influence of polydispersity on the competition between liquid crystal phases is also demonstrated.

Frequently associated with WS, a genetic disorder, is the CHD supravalvar aortic stenosis (SVAS), which pose significant health risks. Traditional methods for assessing the severity of these conditions, which include clinical evaluation and pressure gradient measurements, often prove inadequate due to their vulnerability to transient physiological fluctuations and the progression of the disease. The evaluation and monitoring of CHDs require a thorough understanding of intracardiac blood flow. Existing imaging technologies struggle to provide accurate flow data, especially in situations where flow velocities are high. This dissertation provides a multi-scale computational framework that integrates zero-dimensional (0D) lumped parameter models with patient-specific geometries, to investigate blood flow hemodynamics via CFD simulations. Detailed analysis and visualization of complex blood flow patterns offer insight into the affects of changes in geometry and flow dynamics on cardiac function. Patient-specific models of the thoracic aorta were used to evaluate the effectiveness of surgical intervention in correcting a severe aortic defect in a WS patient, resulting in the observation of reductions in wall shear stress (WSS), velocity magnitude, pressure gradient, and a subsequent decrease in left ventricular workload.

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