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Computational Modelling of Self- oscillations of the Human Vocal Folds
Hájek, Petr ; Šidlof,, Petr (referee) ; Radolf, Vojtěch (referee) ; Švancara, Pavel (advisor)
The presented dissertation thesis deals with a simulation of the human phonation in terms of latest theories. Phonation is considered here as a bi-directional fluid-structure-acoustic interaction, where the interaction between all three physical domains occurs due to the unsteady viscous compressible Navier-Stokes equations. There is a solid knowledge background in the first part of the thesis. It concerns the latest concepts in computational modeling of the human phonation, the most important and recent theories about the human voice production and some key aspects of the human anatomy, physiology and pathology. Also voice assessment is discussed. The second part of the thesis describes an in-depth analysis of a phonation simulation in a planar computational model. The basic concepts proceed from algorithms developed in the Institute of Solid Mechanics, Mechatronics and Biomechanics. Created models are able to reproduce sounds of all Czech vowels and the most common evaluated parameters very close to physiological ranges. The simulated pathology, Reinke's edema, is demonstrated in order to explore its influence on the vowel sound. The third part focuses on modeling of phonation in a spatial computational model. All Czech vowels are simulated also here and compared to the planar model and to actual measurement. The spatial model serves as the starting point to modeling of a longitudinal pretension incorporated in the vocal folds. In the last part of the thesis, a modeling of the phonation with vocal folds pretension is investigated. Although the models are tuned to a rather soft phonation, the results are in agreement with the relevant physiologic phenomena. While the spatial model is highly computationally expensive, a hybrid planar model with pretension is proposed. A special attention is paid to the analysis of self-sustained oscillation of the vocal folds. It is shown, the planar model cannot reproduce such kind of oscillation in the actual version, albeit time of oscillation was considerably extended. On the other hand, oscillation of the spatial vocal folds are stabilized without effects accompanying subduing of oscillation. It can be supposed that the spatial model is able to reproduce self-sustained oscillation as a basic principle present during the human phonation.
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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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Computational Modelling of Self- oscillations of the Human Vocal Folds
Hájek, Petr ; Šidlof,, Petr (referee) ; Radolf, Vojtěch (referee) ; Švancara, Pavel (advisor)
The presented dissertation thesis deals with a simulation of the human phonation in terms of latest theories. Phonation is considered here as a bi-directional fluid-structure-acoustic interaction, where the interaction between all three physical domains occurs due to the unsteady viscous compressible Navier-Stokes equations. There is a solid knowledge background in the first part of the thesis. It concerns the latest concepts in computational modeling of the human phonation, the most important and recent theories about the human voice production and some key aspects of the human anatomy, physiology and pathology. Also voice assessment is discussed. The second part of the thesis describes an in-depth analysis of a phonation simulation in a planar computational model. The basic concepts proceed from algorithms developed in the Institute of Solid Mechanics, Mechatronics and Biomechanics. Created models are able to reproduce sounds of all Czech vowels and the most common evaluated parameters very close to physiological ranges. The simulated pathology, Reinke's edema, is demonstrated in order to explore its influence on the vowel sound. The third part focuses on modeling of phonation in a spatial computational model. All Czech vowels are simulated also here and compared to the planar model and to actual measurement. The spatial model serves as the starting point to modeling of a longitudinal pretension incorporated in the vocal folds. In the last part of the thesis, a modeling of the phonation with vocal folds pretension is investigated. Although the models are tuned to a rather soft phonation, the results are in agreement with the relevant physiologic phenomena. While the spatial model is highly computationally expensive, a hybrid planar model with pretension is proposed. A special attention is paid to the analysis of self-sustained oscillation of the vocal folds. It is shown, the planar model cannot reproduce such kind of oscillation in the actual version, albeit time of oscillation was considerably extended. On the other hand, oscillation of the spatial vocal folds are stabilized without effects accompanying subduing of oscillation. It can be supposed that the spatial model is able to reproduce self-sustained oscillation as a basic principle present during the human phonation.
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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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