National Repository of Grey Literature 215 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Acoustic resonances can support self-oscillations of a dynamic system.
Horáček, Jaromír ; Radolf, Vojtěch ; Košina, Jan ; Laukkanen, A. M.
Flutter instability of human vocal folds is a necessary condition for speaking, because airflow induced vibrations of the vocal folds create the voice source. The present study shows that the vocal fold self-oscillations can be strongly influenced by interaction with acoustic resonances of the human vocal tract.
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.
Experimental modelling of vibroacoustics of the human vocal tract with compliant walls
Radolf, Vojtěch ; Horáček, Jaromír ; Košina, Jan
Experimental model of human vocal tract cavities with hard walls has been modified to take into account the compliance of the soft tissue of the human vocal tract. The paper presents the studied acoustic-structural interaction of the vocal tract cavities with a dynamical system originated in vibration of the soft tissue. The experimental results are in qualitative agreement with the results of mathematical modelling. Compliant walls of acoustic cavities generate additional low frequency acoustical-mechanical resonances of the system and increase acoustic resonance frequencies.
Human vocal tract models with yielding walls – preliminary experimental results
Radolf, Vojtěch ; Horáček, Jaromír ; Košina, Jan
Yielding walls of acoustic cavities cause an additional low frequency acoustical – mechanical resonance of the system. This resonance changes also the higher acoustic resonance frequencies. Experimental model of human vocal tract cavities with hard walls has been modified to take into account the compliance of the soft tissue of human vocal tract. The unique experimental set-up has been assembled to study in detail acoustic-structural interaction of the vocal tract cavities with a dynamical system originated in vibration of the soft tissue. The experimental results are in qualitative agreement with the results of mathematical modelling.
Influence of tissue changes in superficial lamina propria on production of Czech vowels
Hájek, P. ; Švancara, P. ; Horáček, Jaromír ; Švec, J.
Superficial lamina propria (SLP) is a water-like vocal fold (VF) layer located directly under overlying epithelium. Its material properties affect VF motion and thus resulting spectrum of produced sound. Influence of stiffness and damping of the SLP on sound spectrum of Czech vowels is examined using a two-dimensional (2D) finite element (FE) model of a human phonation system. The model consists of the VF (structure model) connected with an idealized trachea and vocal tract (VT) (fluid models). Five VTs for all Czech vowels [a:], [e:], [i:], [o:] and [u:] were used and their geometry were based on MRI data. Fluid flow in the trachea and VT was modelled by unsteady viscous compressible Navier-Stokes equations. Such a formulation enabled numerical simulation of a fluid-structure-acoustic interaction (FSAI). Self-sustained oscillations of the VF were described by a momentum equation including large deformations and a homogeneous linear elastic model of material was used. Fluid and structure solvers exchange displacements and boundary forces in each iteration. During closed phase VFs are in contact and fluid flow is separated. We can observe that both the damping and the stiffness of the SLP substantially influence the amplitude and frequency of VFs vibration as well as the open time of the glottis.\n
Experimental and computer modelling study of glottal closing velocity during phonation
Horáček, Jaromír ; Radolf, Vojtěch ; Bula, Vítězslav ; Šidlof, P. ; Geneid, A. ; Laukkanen, A. M.
This preliminary study shows that the impact stress between the colliding vocal folds during phonation should not be evaluated from the maximum velocity of the glottal closing because the velocity of the closing diminishes just before the glottal closure. This phenomenon, which can be caused by a pressure cushion effect in the fast narrowing glottal gap, is demonstrated with measurements from high speed camera images recorded from human and on a physical laboratory model for vowel [u:] phonation and on a three-mass computer model employing a Hertz model of impact force. For a more detailed future study of this phenomenon a faster camera has to be used. \n
Aerodynamic transfer of energy to vibrating vocal folds for different driving mechanisms
Valášek, J. ; Sváček, P. ; Horáček, Jaromír
This paper studies the mutual energy transfer between the fluid flow, described by incompressible Navier-Stokes equations, and the elastic body represented by vocal folds. The aerodynamic energy transfer function describes the amount and more importantly the sign of the energy exchange. It determines if the vocal fold vibrations are self-excited or prescribed.The energy transfer function is studied for three different driving mechanisms introduced by different inlet boundary conditions (BC). The most frequently used inlet BCs for incompressible model of fluid flow approximated by the finite element method are either Dirichlet BC giving the inlet velocity or do-nothing type of BC prescribing the pressure difference between the inlet and the outlet. Since the numerical simulations with both aforementioned BCs do not provide results observed experimentally the newly introduced BC based on the penalization approach seems as remedy. The numerical model consists of strongly coupled partitioned scheme based on the stabilized finite element method.\n\n
Acoustic characteristics of 3D human vocal tract model with nasal cavities – preliminary experimental results
Radolf, Vojtěch ; Horáček, Jaromír ; Košina, Jan ; Vampola, T.
Acoustic resonance characteristics of 3D human vocal tract model with nasal and paranasal cavities were measured in three different ways: The excitation was realized by (1) self-oscillating vocal folds replica, (2) by a swept harmonic signal from an earphone placed instead of the vocal folds and (3) by a white noise signal from a loudspeaker located in front of the open mouth of the model. Resulting resonance frequencies are comparable for all excitation signals. These experiments were carried out to verify a complex mathematical model.
Experimental investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities
Radolf, Vojtěch ; Horáček, Jaromír ; Košina, Jan ; Vampola, T.
The following experiments were carried out to be later used in the verification of a complex\nmathematical model of human voice production. Acoustic resonance characteristics of a 3D human voca tract model without and with nasal and paranasal cavities were measured in two different ways: The excitation was realized by (1) self-oscillating vocal folds replica and (2) by sine-tone sweeps from an earphone placed instead of the vocal folds. The resulting resonance and antiresonance frequencies were found to be comparable for both excitation signals.
Numerical investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities
Vampola, T. ; Štorkán, J. ; Horáček, Jaromír ; Radolf, Vojtěch
Acoustic resonance characteristics of 3D human vocal tract model without and with nasal and\nparanasal cavities were computed. Nasal cavities (NC) form the side branches of the human vocal tract and exhibit antiresonance and resonance properties which influence the produced voice quality. Developed FE models of acoustic spaces of nasal and vocal tract for vowel /a:/ are used to study the influence of (NC) on phonation. Acoustics frequency-modal characteristics are studied by modal analysis and numerical simulation of acoustic signals in time domain is performed by transient analysis of the FE models.

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See also: similar author names
6 HORÁČEK, Jakub
1 Horáček, J.
6 Horáček, Jakub
14 Horáček, Jan
9 Horáček, Jaroslav
23 Horáček, Jiří
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