Modeling the dynamics of the human vocal folds
Dr. Lewis Fulcher's present research on the dynamics of the vocal folds (cords) and on their role in the production of human speech focuses on the aerodynamic forces that drive them. Typically, the vocal folds are viewed as lumped elements with elastic and inertial properties and intrinsic viscous damping forces. Pressure measurements with a scaled-up model of the normal male larynx (M5) are used inform a Bernoulli-like approach to airflow through the narrow channel between the vocal folds (the glottis). These data embody important information about entrance loss, aerodynamic viscous effects, and the pressure recovery associated with the glottal exit. Incorporating such information into the vocal fold driving forces has the potential to increase our understanding of both normal and pathological phonation. Thus, such information carries implications for clinical practice in voice therapy as well as for surgical interventions designed to deal with lesions and other laryngeal irregularities.
The ultimate goal of the mathematical models is to provide a conceptual framework of sufficient scope, power, and generality to unify the analysis of measurements of in-vivo phonation, experiments with excised human and animal larynges, and experiments with physical models of the vocal mucosa such as those recently done by implanting biomaterials under a thin silicone membrane. Such a framework should be useful in elucidating the connections that physical models and excised larynx experiments have with particular aspects of human speech.
On the right:
Schematic diagram (A) of model M5 showing the wind tunnel with vocal fold inserts. The minimal glottal diameter is the smallest separation between the vocal folds. Locations of the 14 pressure taps on one of the plastic inserts (B).
1. L. Fulcher, R. Scherer, and T. Powell, "Pressure distributions in a static physical model of the uniform glottis: Entrance and exit coefficients," J. Acoust. Soc. Am. 129, 1548-1553 (2011).
2. L. Fulcher and R. Scherer, "Phonation threshold pressure: comparison of calculations and measurements taken with physical models of the vocal fold mucosa," J. Acoust. Soc. Am.130, 1597-1605 (2011).
Rayleigh-Benard Convection; Lattice Boltzmann Methods
A major portion of Dr. Haowen Xi's research in the rich physics of spatially extended non-equilibrium systems, and especially in the dynamics of spatiotemporal chaos which occurs widely in fluid, chemical, laser, and biological systems. A major thrust of the research is to understand the complex behavior of far from equilibrium systems. This research involves studies of thermodynamic descriptions of non-equilibrium transitions in Rayleigh-Benard systems. We study simplified nonlinear models and develop conceptual insight from numerical results. This work entails implementing efficient numerical methods for simulating large scale non-equilibrium systems and supercomputer simulations in CRAY C-90 and CM-5 parallel computers.
Another area of Xi's research is the development and application of advanced computer simulation techniques (e.g. Lattice-Boltzmann method) in the studies of multiphase fluid flow through porous media and in polymer droplets breakup and coalescence in a mixing shear flow. The understanding of multiphase fluid flow, and transport and reaction in porous media, has direct applications for solution driven oil recovery.
1) Bruno Ullrich, Haowen Xi, "Photocurrent limit in nanowires" Optics Letters, 38, 22 (2013) 4698-4700
2) Bruno Ullrich, Haowen Xi, "Photocurrent theory based on coordinate
dependent lifetime" Optics Letters, 35, 23 (2010),
- Rayleigh-Behard Convection; Lattice Boltzmann Methods