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Finite element modal analysis of a silicone vocal fold filled with fluid
Hájek, P. ; Radolf, Vojtěch ; Horáček, Jaromír ; Švec, J. G.
A three dimensional (3D) finite element (FE) model of a silicone vocal fold (VF) filled with fluid is presented here. The silicone part of the model is based on partial differential equations of the continuum mechanics and consider large deformations. The fluid domain encapsulated in the silicone VF is defined semianalytically as a lumped-element model describing the fluid in hydrostatic conditions. The elongated and pressurized silicone VF was subjected to perturbed modal analysis. Results showed that the choice of the fluid inside the VF substantially influences the natural frequencies. Namely, the water-filling lowers the natural frequencies approximately by half over the air-filling. Besides, the procedure of reverse engineering for obtaining the geometry of the VF from already 3D-printed mold is introduced.
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Three-dimensional numerical analysis of Czech vowel production
Hájek, P. ; Švancara, P. ; Horáček, Jaromír ; Švec, J. G.
Spatial air pressures generated in human vocal tract by vibrating vocal folds present sound sources of vowel production. This paper simulates phonation phenomena by using fluid-structure-acoustic scheme in a three-dimensional (3D) finite element model of a Czech vowel [o:]. The computational model was composed of four-layered M5-shaped vocal folds together with an idealized trachea and vocal tract. Spatial fluid flow in the trachea and in the vocal tract was obtained by unsteady viscous compressible Navier-Stokes equations. The oscillating vocal folds were modelled by a momentum equation. Large deformations were allowed. Transient analysis was performed based on separate structure and fluid solvers, which were exchanging loads acting on the vocal folds boundaries in each time iteration. The deformation of the fluid mesh during the vocal fold oscillation was realized by the arbitrary Lagrangian-Eulerian approach and by interpolation of fluid results on the deformed fluid mesh. Preliminary results show vibration characteristics of the vocal folds, which correspond to those obtained from human phonation at higher pitch. The vocal folds were self-oscillating at a reasonable frequency of 180 Hz. The vocal tract eigenfrequencies were in the ranges of the formant frequencies of Czech vowel [o:] measured on humans, during self-oscillations the formants shifted to lower frequencies.
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METHODOLOGY OF VOICE DISORDER EVALUATION FROM VIDEOKYMOGRAPHY RECORDS
Vydrová, J. ; Švec, J. G. ; Zitová, Barbara ; Novozámský, Adam ; Zita, Aleš ; Šorel, Michal
The aim of the methodology „Evaluating voice disorders from videkymographic data“ is to provide a comprehensive information on a new diagnostic method for diagnosis of functional and organic disorders of the voice - videokymography (VKG). The methodology is intended for otorinolaryngology and phoniatry specialists. The methodology will also serve as a study material for both trainers and trainees of the certified course „Videokymography in Medical Practice“. The diagnostic method consists of a patient examination technique and of an evaluation of the examination results. Thie data are automatically evaluated by software created to support the VKG diagnostics.
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Effect of turbulence in FE model of human vocal folds self-oscillation
Hájek, P. ; Švancara, Pavel ; Horáček, Jaromír ; Švec, J.G.
The purpose of the study is to determine whether a turbulence model in fluid flow calculation affects the vocal folds (VF) vibration and the acoustics of human vocal tract (VT). The objective is examined using a two-dimensional (2D) finite element (FE) model of the fluid-structure-acoustic interaction for self-sustained oscillations of the VF. The FE model consists of the models of the VF, the trachea and a simplified model of the human VT. The developed FE model includes large deformations of the VF tissue and VF contact interrupting the airflow during glottis closure. The airflow is modelled by the unsteady viscous compressible Navier-Stokes equations, without and with the Shear Stress Transport (SST) turbulence model. Fluid-structure interaction (FSI) and morphing of the fluid mesh are realized using Arbitrary Lagrangian-Eulerian (ALE) approach. The method is applied on the FE model of the VT shaped for the Czech vowel [a:]. Also effect of varying stiffness of the superficial lamina propria (SLP) is analyzed. The numerical simulations showed that considering of the turbulence affects mainly higher frequencies apparent in a frequency spectrum of the VT acoustics.
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Numerical simulation of the effect of stiffness of lamina propria on the self-sustained oscillation of the vocal folds
Hájek, P. ; Švancara, P. ; Horáček, Jaromír ; Švec, J. G.
A two-dimensional (2D) finite element (FE) model of the fluid-structure-acoustic interaction during selfsustained oscillation of the human vocal folds (VF) is presented in this paper. The aim is to analyze the effect of stiffness of lamina propria on VF vibrations. Such stiffness change can be caused by some VF pathologies. The developed FE model consists of the FE models of the VF, trachea and a simplified human vocal tract. The vocal tract model shaped for simulation of phonation of Czech vowel [a:] was created by converting data from the magnetic resonance images (MRI). The developed FE model includes VF contact, large deformations of the VF tissue, fluid-structure interaction (FSI), moving boundary of the fluid mesh (Arbitrary Lagrangian-Eulerian (ALE) approach), airflow separation during the glottis closure and solution of unsteady viscous compressible airflow described by the Navier-Stokes equations. The numerical simulations showed that higher values of lamina propria Young's modulus (stiffer lamina propria) result in a decrease of the maximum glottis opening. Stiffer lamina propria also requires the use of higher subglottal pressure to initiate self-sustained vibration of the VF.
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Numerical simulation of videokymographic images from the results of the finite element model
Švancara, P. ; Horáček, Jaromír ; Martínek, T. ; Švec, J. G.
The study presents a two-dimensional (2D) finite element (FE) model of the fluid-structure-acoustic interaction during flow induced self-oscillation of the human vocal folds. The FE model combines the FE models of the vocal folds, the trachea and the simplified human vocal tract shaped for phonation of vowel [a:]. The fluid-structure interaction is solved using explicit coupling scheme with separated solvers for structure and fluid domain. The developed FE model comprises large deformations of the vocal-fold tissue, vocal-fold contact, fluid-structure interaction, morphing the fluid mesh according to the vocal-fold motion (Arbitrary Lagrangian-Eulerian approach), solution of unsteady viscous compressible airflow described by the Navier-Stokes equations and airflow separation during the glottis closure. The effect of lamina propria thickness and material properties on simulated videokymographic (VKG) images of vocal-fold vibrations are analyzed. Such variation of the lamina propria properties can be caused by certain vocal-fold pathologies such as Reinke's edema. The developed FE model can be used to study relations among pathological changes in vocal folds tissue, the resulting VKG images and the produced sound spectra.
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Finite element modelling of sound pressure around the human head during phonation
Švancara, P. ; Tomeček, V. ; Horáček, Jaromír ; Švec, J. G.
The study presents finite element (FE) model of sound propagation through the vocal tract and around the human head during speech production. Similar experimental studies are not easily realisable. The FE model of the acoustic spaces corresponding to the human vocal tract for Czech vowel [a:] and acoustic space around the human head was created from computer tomography (CT) images. Modal and transient analyses (excitation by a short pulse) are used for analysis of resonant characteristics of the FE model. The production of vowel is then simulated using transient analysis of the FE models excited by Liljencrants-Fant’s (LF) glottal signal model. Formant frequencies detected from computed spectra are in good agreement with results of modal analysis and with literature. The results of numerical simulation enable evaluating of the transfer functions between a reference point and any point in the space around the head.
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Computer modeling of effects of vocal exercising with a tube on vocal tract sound power transfer
Horáček, Jaromír ; Vampola, T. ; Laukkanen, A. M. ; Švec, J. G.
Two 3D finite element (FE) models were constructed, based on CT measurements of a subject phonating on [a:] before and after phonation into a tube. Acoustic analysis was performed exciting the models by acoustic flow velocity at the vocal folds. The generated acoustic pressure of the response was computed in front of the mouth and inside the vocal tract for both FE models. Average amplitudes of the pressure oscillations inside the vocal tract and in front of the mouth were compared to display a cost-efficiency of sound energy transfer at different formant frequencies. Comparison of the pressure oscillation inside and outside the vocal tract showed that formants differ in their efficiency, F4 (at about 3.5 kHz, i.e. at the speaker’s or singer’s formant region) being the most effective. The results suggest that exercising on semi-occlusions help in improving the vocal economy.
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