Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session AL: Biofluids: Physiological General |
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Chair: Amir Hirsa, Rensselaer Polytechnic Institute Room: Long Beach Convention Center 202A |
Sunday, November 21, 2010 8:00AM - 8:13AM |
AL.00001: Aeroacoustic sources in phonation Michael Krane An analysis of the flow through a time-varying duct constriction is used to identify the primary aeroacoustic source mechanisms in human vocalization. The acoustic fields on either side of the constriction are matched using equations describing the flow through the constriction. The form of the resulting sound fields indicates that the primary source of sound is the unsteady aerodynamic drag due to separated flow, and that secondary sources arise from changes in glottis volume and the movement of the separation point. The source strengths are shown to depend on the incident sound field, calling into question the ``source-filter'' theory of voice production. A control volume analysis supports these results. [Preview Abstract] |
Sunday, November 21, 2010 8:13AM - 8:26AM |
AL.00002: The impact of asymmetric flows on pathological speech Byron D. Erath, Sean D. Peterson, Michael W. Plesniak In voiced speech the vocal folds form a divergent glottal passage during the closing phases of the phonatory cycle. Due to the adverse pressure gradient, asymmetric flow develops within the glottis causing the glottal jet to separate from one vocal fold wall, and fully-attach to the opposing wall. The asymmetric pressures that arise from this flow configuration directly influence the vocal fold energy exchange process, and are expected to have the greatest influence on vocal fold motion when pathologies that affect the vocal fold musculature are present. A theoretical flow solution that produces the pressure distributions arising from asymmetric glottal flows is implemented into a two-mass model of speech. The impact of flow asymmetries on pathological vocal fold motion is investigated by modifying the tissue parameters of the speech model to represent unilateral paralysis. The influence of asymmetric flow behavior on pathological vocal fold motion is quantified and compared to the commonly-reported simplified case involving symmetric flow behavior. [Preview Abstract] |
Sunday, November 21, 2010 8:26AM - 8:39AM |
AL.00003: Effect of subglottic stenosis on the flow-induced vibration of a self-oscillating computational vocal fold model Simeon L. Smith, Scott L. Thomson The subglottis plays an important role in voice production; however, in general the role of subglottal geometry in phonation is not well understood. This research focuses on studying how subglottic stenosis, or a narrowing of the airway below the vocal folds, affects the response of a self-oscillating computational vocal fold model. Methods are described for computational model development, including stenotic geometry definition from CT scan images, incorporation of the stenosis into a finite element fluid-structure interaction model, and parametric variation of the degree of stenosis severity. Results are presented for a normal (no stenosis) case and five cases of varying degrees of stenosis severity. Qualitative and quantitative comparisons of vocal fold vibratory motion and of flow behavior for the six cases are made, including characterization of flow patterns in the subglottis, glottal width and flow rate time histories, vibration frequency, and airway resistance. [Preview Abstract] |
Sunday, November 21, 2010 8:39AM - 8:52AM |
AL.00004: Examination of Flow in a Scaled-Up Vocal Fold Model for Diseased Conditions Erica Sherman, Lucy Zhang, Wang Xinshi, Wei Timothy, Michael Krane An experiment to provide DPIV measurements in a scaled up dynamic human vocal fold model is presented. The 10x scale vocal fold model is a new design that incorporates both the rocking as well as the oscillatory open/close motions characteristic of vocal fold motions. The experiment is run in a free-stream water tunnel where the oscillation frequencies and flow speeds are dynamically matched to physiologic conditions for both male and female phonation. The effects associated with vocal fold paralysis will be discussed. Flow measurements showing fluid kinematics including jet velocity and orientation, and vortex shedding as a function of time through an oscillation cycle will be presented. In addition, key data relevant to phonation, such as volumetric flow rate and glottal behavior will be presented. [Preview Abstract] |
Sunday, November 21, 2010 8:52AM - 9:05AM |
AL.00005: Numerical study of the fluid-solid interactions in human vocal folds using finite element method Xingshi Wang, Erica Sherman, Michael Krane, Timothy Wei, Lucy Zhang The goal of this study is to investigate the motion and deformation of human vocal folds during phonation using finite element method. The voice process is a fluid-structure interaction problem and it is also a self-oscillated system induced by the airflow with constant pressure difference. Here, the vocal folds are modeled with 2-D hyperelastic structures embedded in a channel with applied constant pressure difference at the inlet and outlet to represent the lung pressure. Our fully coupled fluid-structure interaction numerical method can capture the open/close process and the deformed shape of the vocal folds based on the given pressure. From the numerical results, we are able to capture the periodical features for the variables of interest at the throat, such as volume flow rate, velocity and pressure. These dynamic variable outputs may assist us to perform further energy balance analysis to fully understand the physical mechanisms of in normal and disordered phonation. [Preview Abstract] |
Sunday, November 21, 2010 9:05AM - 9:18AM |
AL.00006: Experimental study of the aeroacoustic-aeroelastic behavior of model vocal folds Elizabeth Campo, Ernesto Camarena, Michael Krane The effect of vocal fold body stiffness and bilateral asymmetry was studied using a life-size physical model of the human airway using interchangeable silicone rubber models of the human vocal folds. The two layer vocal fold models are comprised of an inner body layer and an outside cover layer. The following measures were used to assess the effect of body stiffness and asymmetry: radiated sound power, phonation threshold pressure and aeroacoustic source strengths. Results obtained from the human airway model compared favorably with behavior observed in human subjects. Furthermore, the results reveal that the asymmetric cases required a higher subglottal pressure to initiate phonation and radiated less intense sound, in comparison to the symmetrical configuration. [Preview Abstract] |
Sunday, November 21, 2010 9:18AM - 9:31AM |
AL.00007: Bird song: in vivo, in vitro, in silico Aryesh Mukherjee, Shreyas Mandre, Lakshminarayan Mahadevan Bird song, long since an inspiration for artists, writers and poets also poses challenges for scientists interested in dissecting the mechanisms underlying the neural, motor, learning and behavioral systems behind the beak and brain, as a way to recreate and synthesize it. We use a combination of quantitative visualization experiments with physical models and computational theories to understand the simplest aspects of these complex musical boxes, focusing on using the controllable elastohydrodynamic interactions to mimic aural gestures and simple songs. [Preview Abstract] |
Sunday, November 21, 2010 9:31AM - 9:44AM |
AL.00008: Thin Film Evolution Over a Thin Porous Layer: Modeling a Tear Film on a Contact Lens Daniel Anderson, Kumnit Nong We examine a mathematical model that describes the behavior of the pre-contact lens tear film of a human eye. Our work examines the effect of contact lens thickness and lens permeability and slip on the film dynamics. A mathematical model for the evolution of the tear film is derived using a lubrication approximation applied to the hydrodynamic equations of motion in the fluid film and the porous layer. The model is a nonlinear fourth order partial differential equation subject to boundary conditions and an initial condition for post-blink film evolution. We find that increasing the lens thickness, permeability and slip all contribute to an increase in the film thinning rate although for parameter values typical for contact lens wear these modifications are minor. The presence of the contact lens can, however, fundamentally change the nature of the rupture dynamics as the inclusion of the porous lens leads to rupture in finite time rather than infinite time. [Preview Abstract] |
Sunday, November 21, 2010 9:44AM - 9:57AM |
AL.00009: A Model for the Precorneal Tear Film with Osmolarity and Corneal Supply R.J. Braun, P.E. King-Smith In the human tear film, a thin liquid layer is spread with a blink; it subsequently levels due to surface tension and evaporates more slowly than pure water due to the floating lipid layer. While eventually the tear film almost always ruptures, recent evidence suggests that in some cases supply of fluid from the cornea or conjunctiva may prolong the life of the tear film and prevent the osmolarity (combined concentration of certain salts and sugars) from reaching very large values that can cause irritation and damage. We incorporate osmolarity into a lubrication model for the tear film and study the dynamics of the tear film with osmotic supply from the corneal surface by numerically solving equations for the film thickness and osmolarity. It is treated as a classical osmotic semi-permeable barrier with parameters appropriate to the cornea. The tear film thinning may be slowed by these effects, and in some cases rupture prevented. The value of the osmolarity in regions thinned by evaporation is reduced by osmosis from the underlying surface. [Preview Abstract] |
Sunday, November 21, 2010 9:57AM - 10:10AM |
AL.00010: Viscoelastic Properties of Vitreous Gel H. Pirouz Kavehpour, Pooria Sharif-Kashani We studied the rheological properties of porcine vitreous humor using a stressed-control shear rheometer. All experiments were performed in a closed environment at body temperature to mimic in-vivo conditions. We modeled the creep deformation using a two-element retardation spectrum model. By associating each element of the model to an individual biopolymeric system in the vitreous gel, a separate response to the applied stress was obtained from each component. The short time scale was associated with the collagen structure, while the longer time scale was related to the microfibrilis and hyaluronan network. We were able to distinguish the role of each main component from the overall rheological properties. Knowledge of this correlation enables us to relate the physical properties of vitreous to its pathology, as well as optimize surgical procedures such as vitrectomy. [Preview Abstract] |
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