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
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.
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.