Modeling Vocal Fold Motion with a New Hydrodynamic Semi-Continuum Model

Vocal fold (VF) motion is a fundamental process in voice production, and is also a challenging problem for direct numerical computation because the VF dynamics depend on nonlinear coupling of air flow with the response of elastic channels (VF), which undergo opening and closing, and induce internal flow separation. A traditional modeling approach makes use of steady flow approximation or Bernoulli's law which is known to be invalid during VF opening. We present a new hydrodynamic semi-continuum system for VF motion. The airflow is modeled by a quasi-one dimensional continuum aerodynamic system, and the VF by a classical lumped two mass system. The reduced flow system contains the Bernoulli's law as a special case, and is derivable from the two dimensional compressible Navier-Stokes equations. Since we do not make steady flow approximation, we are able to capture transients and rapid changes of solutions, e.g. the double pressure peaks at opening and closing stages of VF motion consistent with experimental data. We demonstrate numerically that our system is robust, and models in-vivo VF oscillation more physically. It is also much simpler than a full two-dimensional Navier-Stokes system.Comment: 27 pages,6 figure

Numerical simulation of the influence of the orifice aperture on the flow around a teeth-shaped obstacle

The sound generated during the production of the sibilant [s] results from the impact of a turbulent jet on the incisors. Several geometric characteristics of the oral tract can affect the properties of the flow-induced noise so that the characterization of the influence of different geometric parameters on the acoustic sources properties allows determining control factors of the noise production. In this study, a simplified vocal tract/teeth geometric model is used to numerically investigate the flow around a teeth-shaped obstacle placed in a channel and to analyze the influence of the aperture at the teeth on the spectral properties of the fluctuating pressure force exerted on the surface of the obstacle, which is at the origin of the dipole sound source. The results obtained for Re = 4000 suggest that the aperture of the constriction formed by the teeth modifies the characteristics of the turbulent jet downstream of the teeth. Thus, the variations of the flow due to the modification of the constriction aperture lead to variations of the spectral properties of the sound source even if the levels predicted are lower than during the production of real sibilant fricative

Mechanism of and Threshold Biomechanical Conditions for Falsetto Voice Onset

The sound source of a voice is produced by the self-excited oscillation of the vocal folds. In modal voice production, a drastic increase in transglottal pressure after vocal fold closure works as a driving force that develops self-excitation. Another type of vocal fold oscillation with less pronounced glottal closure observed in falsetto voice production has been accounted for by the mucosal wave theory. The classical theory assumes a quasi-steady flow, and the expected driving force onto the vocal folds under wavelike motion is derived from the Bernoulli effect. However, wavelike motion is not always observed during falsetto voice production. More importantly, the application of the quasi-steady assumption to a falsetto voice with a fundamental frequency of several hundred hertz is unsupported by experiments. These considerations suggested that the mechanism of falsetto voice onset may be essentially different from that explained by the mucosal wave theory. In this paper, an alternative mechanism is submitted that explains how self-excitation reminiscent of the falsetto voice could be produced independent of the glottal closure and wavelike motion. This new explanation is derived through analytical procedures by employing only general unsteady equations of motion for flow and solids. The analysis demonstrated that a convective acceleration of a flow induced by rapid wall movement functions as a negative damping force, leading to the self-excitation of the vocal folds. The critical subglottal pressure and volume flow are expressed as functions of vocal fold biomechanical properties, geometry, and voice fundamental frequency. The analytically derived conditions are qualitatively and quantitatively reasonable in view of reported measurement data of the thresholds required for falsetto voice onset. Understanding of the voice onset mechanism and the explicit mathematical descriptions of thresholds would be beneficial for the diagnosis and treatment of voice diseases and the development of artificial vocal folds

Modelling of voiced sounds production using a modified two-mass model

The two-mass model is very often presented as a simple but efficient model quite well adapted for the purpose of voiced sounds numerical simulation. It appear however that the description of the flow through the glottis is usually oversimplified. To some extent this point could explain the limits of the model. This paper proposes a more precise description of the flow through the glottis. In particular a quasi-steady moving flow separation point is introduced. A validation of the theory under unsteady-flow conditions is presented here. The importance of the revised flow model for phonation modelling is evaluated and discussed using a simple model for the vocal cords based on the well-known two-mass model

Airflow driven fluid–structure interaction subjected to aqueous-based liquid spraying

International audienceArtificial saliva sprays are commonly used to remedy vocal folds surface hydration. Vocal folds surface hydration and its effect on their auto-oscillation are studied experimentally using artificial vocal folds. The airflow is used to excite the vocal folds into auto-oscillation after whichthe vocal folds surface is sprayed with a liquid. The validity of the findings described in a previous study [A. Bouvet, X. Pelorson, and A. VanHirtum, “Influence of water spraying on an oscillating channel,” J. Fluids Struct.93, 102840 (2020)] concerning the effect of water sprayingis further investigated. First, artificial saliva sprays (up to 5 ml) are sprayed instead of water. It is shown that this allows us to address theeffect of increased dynamic viscosity (up to 8 times compared to water) as other artificial saliva properties affecting air–liquid mixing andsurface wettability remain similar to water. Second, the Reynolds number in the dry stage is systematically increased (with 60%) for constantspraying volume≥3 ml. Regardless of the sprayed liquid and Reynolds number, oscillation cycles are characterized by an increase in meanupstream pressure, cycle-to-cycle variability, and a decrease in oscillation frequency due period doubling. Increasing the dynamic viscositytends to reduce the magnitude of these tendencies for spraying volumes smaller than 3 ml, indicating that viscous liquid–gas mixing affectsthe flow regime. Systematic Reynolds number variation shows that liquid spraying increases the oscillation onset threshold pressure and thatthe magnitude of general tendencies is reduced. The assessed conditions and features are pertinent to human voice production after hydrationwith an artificial saliva spray burst

Physical modeling of vowel-bilabial plosive sound production

Downstream of the vocal folds, it is often assumed that all the kinetic energy of the glottal jet is dissipated by turbulence. Although this assumption is reasonable for normal voicing, there are many configurations for which a constriction or even an occlusion of the vocal tract occurs and leads to a significant pressure recovery. Such a phenomenon occurs during the production of vowel-bilabial plosive sequences. In this paper, we will first present results from measurements on a human speaker during production of vowel-bilabial plosive-vowel sequences. These measurements concern intra-oral pressure, acoustical pressure, EGG and lips video recording of a female subject. The relative timings between the motion of the lips, the glottal signals and the intra-oral pressure are analyzed and related with Voice Onset/Offset Times. A theoretical model for air flow in the lips is validated by experiments on a mechanical replica of the vocal tract including a self-oscillating glottis and a controlled moving constriction to mimic the closure of the lips. This theoretical model is used to achieve numerical simulations of an /apa / utterance. The differences between the intra-oral pressure observed in vivo and the simulated one lead to an investigation on the influence of the cheeks expansion during bilabial plosive production. hal-00700404, version 1- 22 May 2012

On the fluid mechanics of bilabial plosives

In this paper we present a review of some fluid mechanical phenomena involved in bilabial plosive sound production. As a basis for further discussion, firstly an in vivo experimental set-up is described. The order of magnitude of some important geometrical and fluid dynamical quantities is presented. Different theoretical flow models are then discussed and evaluated using in vitro measurements on a replica of the lips and using numerical simulations