Date of Award

Fall 12-30-2020

Level of Access

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Advisor

Xudong Zheng

Second Committee Member

Qian Xue

Third Committee Member

Senthil S. Vel

Additional Committee Members

Kimberly Huguenard

Zhaoyan Zhang

Abstract

This research aims to improve the fundamental understanding of the multiphysics nature of voice production, particularly, the dynamic couplings among glottal flow, vocal fold vibration and airway acoustics through high-fidelity computational modeling and simulations. Built upon in-house numerical solvers, including an immersed-boundary-method based incompressible flow solver, a finite element method based solid mechanics solver and a hydrodynamic/aerodynamic splitting method based acoustics solver, a fully coupled, continuum mechanics based fluid-structure-acoustics interaction model was developed to simulate the flow-induced vocal fold vibrations and sound production in birds and mammals. Extensive validations of the model were conducted by comparing to excised syringeal and laryngeal experiments. The results showed that, driven by realistic representations of physiology and experimental conditions, including the geometries, material properties and boundary conditions, the model had an excellent agreement with the experiments on the vocal fold vibration patterns, acoustics and intraglottal flow dynamics, demonstrating that the model is able to reproduce realistic phonatory dynamics during voice production. The model was then utilized to investigate the effect of vocal fold inner structures on voice production. Assuming the human vocal fold to be a three-layer structure, this research focused on the effect of longitudinal variation of layer thickness as well as the cover-body thickness ratio on vocal fold vibrations. The results showed that the longitudinal variation of the cover and ligament layers thicknesses had little effect on the flow rate, vocal fold vibration amplitude and pattern but affected the glottal angle in different coronal planes, which also influenced the energy transfer between glottal flow and the vocal fold. The cover-body thickness ratio had a complex nonlinear effect on the vocal fold vibration and voice production. Increasing the cover-body thickness ratio promoted the excitation of the wave-type modes of the vocal fold, which were also higher-eigenfrequency modes, driving the vibrations to higher frequencies. This has created complex nonlinear bifurcations. The results from the research has important clinical implications on voice disorder diagnosis and treatment as voice disorders are often associated with mechanical status changes of the vocal fold tissues and their treatment often focus on restoring the mechanical status of the vocal folds.

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