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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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Compensatory Vocal Folds for Source Voice Generation: Computational Modeling of Vocal Folds Function
Matug, Michal ; Vampola, Tomáš (referee) ; Horáček, Jaromír (referee) ; Švancara, Pavel (advisor)
This doctoral thesis focuses on computational modelling of human vocal folds and vocal tract functions using finite element method (FEM). Human voice is crucial in human communication. Therefore one of the main targets of current medicine is creation of artificial vocal folds, which would substitute the original vocal folds. The computational modelling can be used to understand principles of voice production, determination of parameters that the artificial vocal folds have to meet and verification of their functionality. First part of this thesis focuses on modelling of human voice creation by whisper. Influence of intraglottal gap on eigenvalues distribution for individual vowels was analysed using FEM vocal tract and trachea model. Further there is presented two-dimensional (2D) finite element model of the flow-induced self-oscillation of the human vocal folds in interaction with acoustic spaces of the vocal tract. The 2D vocal tract model was created on the basis of converting the data from magnetic resonance images (MRI). Explicit coupling scheme with separated solvers for structure and fluid domain was used for modelling of the fluid-structure interaction. Created computational model comprises: large deformations of the vocal folds tissue, contact between vocal folds, fluid-structure interaction, morphing the fluid mesh according to the vocal-fold motion (Arbitrary Lagrangian-Eulerian approach), unsteady viscous compressible or incompressible airflow described by the Navier-Stokes equations and airflow separation during glottis closure. This model is used to analyse the influence of stiffness and damping changes in individual vocal fold tissue layers (in particular in superficial lamina propria). Part of this computational analysis is also comparison of vocal folds behaviour for compressible and incompressible flow model. Videokymograms (VKG) are subsequently created from obtained results of FEM calculations which enable to compare individual variants between themselves and with motion of real human vocal folds. In next part of this thesis is presented three-dimensional (3D) finite element model of the flow-induced self-oscillation of the human vocal folds. This 3D model was created from a previous 2D model by extrude to the third direction. Using this model was again compared influence of compressible and incompressible flow model on vocal folds motion and generated sound by using videokymograms and acoustic spectra. The last part of this thesis focuses on the possibility to replace missing natural source voice in form reed-based element. Behaviour of reed-based element was analysed using computational modelling and using measurements on experimental physical model. The physical model enables changes in setting gap between reed and reed stop and performing acoustical and optical measurements.
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Evaluation of aerodynamic damping and natural frequencies from numerical simulations and experiments
Chládek, Štěpán ; Horáček, Jaromír ; Zolotarev, Igor
The paper describes different ways for aerodynamic damping and natural frequencies evaluation in a problem of fluid-structure interaction. It is useful for both numerical simulations and experimental measurements. The Fourier transform is used for the frequency evaluation and the damping is evaluated both in time and frequency domain. Significant influence of the chosen sampling frequency and the length of time record on the accuracy of the results are demonstrated both in the numerical simulation and in the experiment that was performed with the flexibly supported profile NACA 0012 with two degrees of freedom.
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Acoustic resonance characteristics of the human vocal tract with respect to a soft tissue
Radolf, Vojtěch ; Horáček, Jaromír
A mathematical model, which can help to clarify physical background of an influence of the soft tissue of vocal cavities on the formant frequencies, has been extended. Strong acoustic-structural interaction is demonstrated on the vocal tract cavity for vowel /u:/ prolonged by a tube that is used for voice training and therapy purposes. The glottis is closed by a yielding wall, considering a mass, compliance and structural damping. Viscous losses of the acoustic cavities and radiation impedance at the output are assumed. Significant change in the first acoustic resonance frequency caused by the compliance of the soft tissue at the glottis corresponds to the data found experimentally in earlier study.
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On numerical approximation of fluid-structure interactions of air flow with a model of vocal folds
Valášek, J. ; Horáček, Jaromír ; Sváček, P.
This paper deals with flow driven vibration of an elastic body. Our goal is to develop and mathematically describe a simplified model of the human vocal fold. The developed numerical schemes for viscous incompressible fluid flow in ALE formulation and the elastic body are implemented by two solvers, specific for each domain. The studied problem is coupled by Dirichlet-Neumann boundary conditions. Both solvers are based on the finite element method. Particularly, for the fluid model the crossgrid elements are used. Numerical results focus on the verification of the developed program.
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On application of finite element method for approximation of 3D flow problems
Sváček, P. ; Horáček, Jaromír
This paper is interested to the interactions of the incompressible flow with a flexibly supported airfoil. The bending and the torsion modes are considered. The problem is mathematically described. The numerical method is based on the finite element method. A combination of the streamline-upwind/Petrov-Galerkin and pressure stabilizing/Petrov-Galerkin method is used for the stabilization of the finite element method. The numerical results for a three-dimensional problem of flow over an airfoil are shown.
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Finite element simulation of aeroelasticity problems
Horáček, Jaromír ; Sváček, P. ; Feistauer, M.
The paper presents results achieved by the authors in development of in-house codes based the finite element (FE) method and applied to solution of fluid-structure problems in aeroelasticity of airfoils. We consider flexibly supported airfoil with two- or three degrees of freedom (2- or3-DOF) in two-dimensional (2D) incompressible viscous flow. The airfoil vibration is described by nonlinear ordinary differential equations of motion for large vibration amplitudes. The flow is medeled by the Navier-Stokes equations for laminar flow or by the Reynolds averaged Navier-Stokes (RANS) equations for turbulent model.
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Acoustic-structural interaction in human vocal tract prolonged by a tube
Radolf, Vojtěch ; Horáček, Jaromír
Phonation into tubes is often used for voice training and therapy. This paper introduces a mathematical model, which can help to clarify physical background of an influence of the soft tissues of vocal cavities on the acoustic resonances (formant frequencies). Substantial change in the first formant frequency caused by the soft tissues in the human vocal tract is in principle in the acoustic-structural interaction of the acoustic cavity semiocluded by the tube, with the yielding wall created for example by the soft tissues in the larynx.
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Air-pressure characteristics and visualization of bubbling effect in water resistance therapy
Radolf, Vojtěch ; Horáček, Jaromír ; Bula, Vítězslav ; Laukkanen, A. M.
This study investigates the influence of a widely used method in voice training and therapy, phonation into a resonance tube with the outer end submerged in water (‘water resistance therapy’ with bubbling effect). Acoustic and electroglottographic (EGG) signals and air pressures in the mouth cavity were registered and the formation of bubbles was studied using high speed camera. Bubbling frequency dominates in the spectra of the pressure signal being about 15 dB higher than the amplitude of the first harmonic, which reflects the fundamental frequency of the vocal folds’ vibration. Separation of the bubbles 10 cm under water surface starts when the buoyancy force acting on the bubble is approximately equal to the aerodynamic force in the tube.
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