Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H26: Biofluids: Phonation, Speech and Airway Mechanics |
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Chair: Xudong Zheng, University of Maine Room: 306 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H26.00001: Flow-Structure-Acoustic Interaction Computational Modeling of Voice Production inside an Entire Airway Weili Jiang, Xudong Zheng, Qian Xue Human voice quality is directly determined by the interplay of dynamic behavior of glottal flow, vibratory characteristics of VFs and acoustic characteristics of upper airway. These multiphysics constituents are tightly coupled together and precisely coordinate to produce understandable sound. Despite many years' research effort, the direct relationships among the detailed flow features, VF vibration and aeroacoustics still remains elusive. This study utilizes a first-principle based, flow-structure-acoustics interaction computational modeling approach to study the process of voice production inside an entire human airway. In the current approach, a sharp interface immersed boundary method based incompressible flow solver is utilized to model the glottal flow; A finite element based solid mechanics solver is utilized to model the vocal vibration; A high-order immersed boundary method based acoustics solver is utilized to directly compute sound. These three solvers are fully coupled to mimic the complex flow-structure-acoustic interaction during voice production. The geometry of airway is reconstructed based on the in-vivo MRI measurement reported by Story et al.( 1995) and a three-layer continuum based vocal fold model is taken from Titze and Talkin(1979). Results from these simulations will be presented and further analyzed to get new insight into the complex flow-structure-acoustic interaction during voice production. This study is expected to improve the understanding of fundamental physical mechanism of voice production and to help to build direct cause-effect relationship between biomechanics and voice sound. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H26.00002: The effect of vocal fold vertical stiffness gradient on sound production Biao Geng, Qian Xue, Xudong Zheng It is observed in some experimental studies on canine vocal folds (VFs) that the inferior aspect of the vocal fold (VF) is much stiffer than the superior aspect under relatively large strain. Such vertical difference is supposed to promote the convergent-divergent shape during VF vibration and consequently facilitate the production of sound. In this study, we investigate the effect of vertical variation of VF stiffness on sound production using a numerical model. The vertical variation of stiffness is produced by linearly increasing the Young's modulus and shear modulus from the superior to inferior aspects in the cover layer, and its effect on phonation is examined in terms of aerodynamic and acoustic quantities such as flow rate, open quotient, skewness of flow wave form, sound intensity and vocal efficiency. The flow-induced vibration of the VF is solved with a finite element solver coupled with 1D Bernoulli equation, which is further coupled with a digital waveguide model. This study is designed to find out whether it's beneficial to artificially induce the vertical stiffness gradient by certain implanting material in VF restoring surgery, and if it is beneficial, what gradient is the most favorable. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H26.00003: Dynamic and energetic relevance of glottal jet asymmetry Jubiao Yang, Michael Krane, Lucy Zhang Numerical simulation of phonation is performed using the fully-coupled Immersed Finite Element Method (IFEM), for both half-space and full-space domains. The full and half-space domains are identical, except that symmetric flow and structure motion is enforced in the half-space domain simulations. We evaluate and examine various terms in the momentum and energy equations to assess the dynamic relevance of glottal jet symmetry, as well as energy utilization in phonation. Specifically, control volume analyses based on simulation results are used to estimate glottal resistance and aeroacoustic source strengths, the level and character of radiated sound, and the various types of work done by laryngeal flow. [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H26.00004: Phonatory sound sources in terms of Lagrangian Coherent Structures Michael McPhail, Michael Krane Lagrangian Coherent Structures (LCS) are used to identify sound sources in phonation. Currently, it is difficult to causally relate changes in airflow topology from voice disorders to changes in voiced sound production. LCS reveals a flow's topology by decomposing the flow into regions of distinct dynamics. The aeroacoustic sources can be written in terms of the motion of these regions in terms of the motion of the boundaries of the distinct regions. Breaking down the flow into constituent parts shows how each distinct region contributes to sound production. This approach provides a framework to connect changes in anatomy from a voice disorder to measurable changes in the resulting sound. This approach is presented for simulations of some canonical cases of vortex sound generation, and a two-dimensional simulation of phonation. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H26.00005: Measurements of the three-dimensional oscillatory flow in a double bifurcation Andras Nemes, Sahar Jalal, Tristan van de Moortele, Filippo Coletti Above a certain ventilation frequency, the unsteady nature of the respiratory flow becomes apparent, and inhalation and exhalation cannot be approximated as quasi-stationary processes. This is especially important in the upper and central airways, where length and velocity scales are the largest, making inertia and acceleration effects dominant over viscous dissipation. We experimentally investigate the primary features of the oscillatory flow through a symmetric double bifurcation which models the self-similar branching of the human bronchial tree. We consider a range of Reynolds and Womersley numbers relevant to physiological conditions between the trachea and the lobar bronchi. Three-component, three-dimensional velocity fields are acquired at multiple phases within the ventilation cycle using magnetic resonance imaging (MRI), and are complemented with instantaneous two-dimensional fields obtained by particle image velocimetry (PIV). The phase-averaged volumetric data provide a description of the rich flow topology, characterizing the main secondary flow structures and their spatio-temporal evolution. The instantaneous measurements reveal some of the dynamics of the laminar-to-turbulent transition in the bifurcations, and its aperiodicity throughout the respiratory cycle. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H26.00006: CFD simulations of a deforming human lung using dynamic and static CT images Shinjiro Miyawaki, Eric A. Hoffman, Ching-Long Lin The authors have developed a CFD model to simulate airflow in deforming lungs using dynamic (4D) CT images. After obtaining the surface mesh for one CT image, we deformed the surface mesh to match other CT images using an image registration technique. During the CFD simulations, we deformed the surface mesh by cubic interpolation as a function of lung volume, and deformed the volume mesh using a computational solid mechanics-based algorithm. To investigate the effect of CT scanning method and relative hysteresis with respect to lung volume on pressure drop along the central airways, we performed CFD simulations using different numbers of 4D and static CT images of one healthy subject. Based on the simulation with 13 4DCT images, we found that air flow fractions in airways remain nearly constant over time. By comparing the simulations with 13, 2, and 1 4DCT images, we found that the overall effect of relative hysteresis of lung structure on pressure drop along each branch at peak inspiration was 12{\%}, and the effect of deformation was 16{\%}. As a result of the comparison between simulations with 2 and 1 of 4D and static CT images, the effect of CT scanning method was 16-39{\%}, depending on the deformation of the lung. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H26.00007: Energy utilization in phonation Michael Krane A control volume analysis of energy utilization in phonation is presented. Conversion of subglottal airstream potential energy into work done vibrating the vocal folds, air flowing through the glottis, and radiating sound are described. An approximate numerical model is used to compute the contributions of each of these mechanisms, as a function of subglottal pressure, for normal phonation. An efficiency measure for each energy conversion mechanism is proposed. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H26.00008: The evolution of viscous flow structures in the esophagus during tracheoesophageal speech Byron Erath, Frank Hemsing A laryngectomy is an invasive surgical procedure whereby the entire larynx is removed, usually as a result of cancer. Removal of the larynx renders conventional voiced speech impossible, with the most common remediation following surgery being tracheoeosphageal (TE) speech. TE speech is produced by inserting a one-way valve to connect the posterior wall of the trachea with the anterior wall of the esophagus. As air is forced up from the lungs it passes through the prosthesis and into the esophagus. The resulting esophageal pressure field incites self-sustained oscillations of the pharyngoesophageal segment (PES), which ultimately produces sound. Unfortunately, the physics of TE speech are not well understood, with up to 50{\%} of individuals unable to produce intelligible sound. This failure can be related to a lack of understanding regarding the esophageal flow field, where all previous scientific investigations have assumed the flow is one-dimensional and steady. An experimental TE speech flow facility was constructed and particle image velocimetry measurements were acquired at the exit of the model prosthesis (entrance of the esophagus). The flow is observed to be highly unsteady, and the formation and propagation of vortical flow structures through the esophageal tract are identified. Observations regarding the influence of the flow dynamics on the esophageal pressure field and its relation to the successful production of TE speech are discussed. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H26.00009: Altered vocal fold kinematics in synthetic self-oscillating models that employ adipose tissue as a lateral boundary condition. Hiba Saidi, Byron D. Erath The vocal folds play a major role in human communication by initiating voiced sound production. During voiced speech, the vocal folds are set into sustained vibrations. Synthetic self-oscillating vocal fold models are regularly employed to gain insight into flow-structure interactions governing the phonation process. Commonly, a fixed boundary condition is applied to the lateral, anterior, and posterior sides of the synthetic vocal fold models. However, physiological observations reveal the presence of adipose tissue on the lateral surface between the thyroid cartilage and the vocal folds. The goal of this study is to investigate the influence of including this substrate layer of adipose tissue on the dynamics of phonation. For a more realistic representation of the human vocal folds, synthetic multi-layer vocal fold models have been fabricated and tested while including a soft lateral layer representative of adipose tissue. Phonation parameters have been collected and are compared to those of the standard vocal fold models. Results show that vocal fold kinematics are affected by adding the adipose tissue layer as a new boundary condition. [Preview Abstract] |
Monday, November 23, 2015 12:32PM - 12:45PM |
H26.00010: Study of human phonation in a full-body domain Shakti Saurabh, Daniel Bodony The generation and propagation of the human voice is studied in two-dimensions using a full-body domain, using direct numerical simulation. The fluid/air in the vocal tract is modeled as a compressible and viscous fluid interacting with the non-linear, viscoelastic vocal folds (VF). The VF tissue material properties are multi-layered, with varying stiffness, and a finite-strain model is utilized and implemented in a quadratic finite element code. The fluid-solid domains are coupled through a boundary-fitted interface and utilize a Poisson equation-based mesh deformation method. The full-body domain includes the near VF region, the vocal tract, a simplified model of the soft palate and mouth, and extends out into the acoustic far-field. A new kind of inflow boundary condition based upon a quasi-one-dimensional formulation with constant sub-glottal volume velocity, which is linked to the VF movement, has been adopted. The sound pressure levels (SPL) measured are realistic and we analyze their connection to the VF dynamics and glottal and vocal tract geometries. [Preview Abstract] |
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