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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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FE model of the human vocal folds considering fluid-structure interaction
Švancara, P. ; Horáček, Jaromír ; Hrůza, V.
The study presents three-dimensional finite element (FE) model of flow induced oscillations of the human vocal folds in interaction with acoustic processes in the simplified vocal tract model. The FE model includes vocal folds pretension before phonation, large deformations of the vocal fold tissue, vocal folds contact, fluid-structure interaction, morphing the fluid mesh according the vocal folds motion, unsteady viscous compressible airflow and airflow separation during the glottis closure. Fluid-structure interaction is solved using partitioned approach, where the results of solution for the flow are transferred as loads on the vocal folds surface, then the vocal folds motion is computed and then again the equations for the flow are solved. Numerical results confirmed that the developed model can be used for simulation of the vocal folds self-oscillations, and especially for numerical simulations of quantities that are difficult to measure in clinical research.
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FE model of interaction between oscilating vocal folds and acoustic space of the vocal tract
Švancara, Pavel ; Hrůza, V.
A 2D and 3D finite element models of interaction between oscillating vocal folds and acoustic space of the vocal tract were developed in program system ANSYS, where the only one driving parameter is velocity of flow under vocal folds. The interaction is based on Sequential Coupled Analysis, where results of transient fluid analysis in ANSYS/Flotran CFD are used as loads for transient analysis of motion of the vocal folds. Models respect large deformations, vocal folds pretension, contact of vocal folds, flow separation and compressible flow.
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Computational and Experimental analysis of Effect of Tonillectomy on Production of Czech Vowels
Švancara, P. ; Vokřál, J. ; Horáček, Jaromír
The effect of tonsillectomy on production of Czech vowels is numerically and experimentally examined. Experimental results show statistically significant shift down to lower frequencies of 3rd formant frequency for vowels /a/, /e/ and /o/. The finite element (FE) models of the acoustic spaces corresponding to the human vocal tracts and acoustic space around the human head are used in numerical simulations of phonation. Computed results show that tonsillectomy causes frequency shifts of some formant frequencies mostly down to lower frequencies. The frequency shifts of the formants are significantly dependent on position and size of th tonsils. Experimental and computational results are consistent.
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Computational modelling of efect of tonsillectomy on production of czech vowels
Švancara, P. ; Horáček, Jaromír
Effects of tonsillectomy on production of Czech vowels are numerically examined. The finite element (FE) models of the acoustic spaces corresponding to the vocal tracts and acoustic space around the human head are used in numerical simulations of phonation. Models for vowels /a/,/e/,/i/,/o/ and /u/ are analyzed. The acoustic resonant characteristics of the FE models are studied using modal and transient analyses (excitation by a short pulse). The production of vowels is simulated in time domain using transient analysis of the FE models excited by Liljencrants-Fantś (LF) glottal signal. Calculated results show that tonsillectomy causes frequency shifts of some formant frequencies mostly down to lower frequencies. Biggest shifts were obtained for 2nd and 3rd formants for vowel /o/-300Hz down to lower frequencies and for 2nd (-450Hz) and 3rd(-150 Hz) formants for vowel /u/ down too. The frequency shifts of the formants are significantly dependent on position and size of the tonsils.
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Influence of tonsillectomy on voice and 3D mathematical models
Vokřál, J. ; Černý, L. ; Lavička, L. ; Švancara, Pavel ; Horáček, Jaromír
After the phoniatric examination the tape-recording of voice was carried out on 14 patients (6male, 8 female, age from 16 to 39 years) in a studio. The second recording was performed appproximately 1 month after tonsillectomy. Patients phonated five Czech vowels /a:/, /e:/, /i:/, /o:/, /u:/. The acoustic analysis was performed by Multi-Dimensional Voice Program and the position of the first four formants was evaluated. The finite element (FE) models of the acoustic spaces corresponding to the human vocal tract for the Czech vowels /a:/ and /i:/ were used in the mathematical modelling. The acoustic resonant characteristics of the FE models were studied by modal and transient analyses. The acoustic analyses were realised by the software code SYSNOISE.
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