Tomáš Vampola

Vocal tract changes caused by phonation into a tube: a case study using computer tomography and finite-element modeling.

Phonation into a glass tube is a voice training and therapy method that leads to beneficial effects in voice production. It has not been known, however, what changes occur in the vocal tract during and after the phonation into a tube. This pilot study examined the vocal tract shape in a female subject before, during, and after phonation into a tube using computer tomography (CT). Three-dimensional finite-element models (FEMs) of the vocal tract were derived from the CT images and used to study changes in vocal tract input impedance. When phonating on vowel [a:] the data showed tightened velopharyngeal closure and enlarged cross-sectional areas of the oropharyngeal and oral cavities during and after the tube-phonation. FEM calculations revealed an increased input inertance of the vocal tract and an increased acoustic energy radiated out of the vocal tract after the tube-phonation. The results indicate that the phonation into a tube causes changes in the vocal tract which remain also when the tube is removed. These effects may help improving voice production in patients and voice professionals.

FE Modeling of Human Vocal Tract Acoustics. Part I: Production of Czech Vowels

Finite element (FE) models open up new possibilities in simulating and understanding production of human voice and speech. This study presents FE models of the human vocal tract for the Czech vowels /a:/, /e:/, /i:/, /o:/, /u:/ which were created from magnetic resonance images of an adult male subject. The high number of elements in the FE models was reduced by introducing acoustic superelements. A novel algorithm for parameterization of the FE models was derived to allow modifying and tuning the model shape according to prescribed acoustic characteristics (formants) of the vocal tract. The sound radiation losses at the lips and sound absorption at the vocal tract walls were taken into account. The frequency modal characteristics of the three-dimensional (3D) and one-dimensional (1D) vocal tract models were compared. The results showed that the ID models can closely replicate the behavior of the 3D vocal tract up to 3000 Hz. At higher frequencies transverse modes occurred in the 3D model which were not present in the ID model. The developed FE models can be useful for studying the influence of vocal tract alterations (e.g. such as cleft palate or tonsillectomy) on acoustic voice quality.

Human vocal tract resonances and the corresponding mode shapes investigated by three-dimensional finite-element modelling based on CT measurement

Abstract Resonance frequencies of the vocal tract have traditionally been modelled using one-dimensional models. These cannot accurately represent the events in the frequency region of the formant cluster around 2.5–4.5 kHz, however. Here, the vocal tract resonance frequencies and their mode shapes are studied using a three-dimensional finite element model obtained from computed tomography measurements of a subject phonating on vowel [a:]. Instead of the traditional five, up to eight resonance frequencies of the vocal tract were found below the prominent antiresonance around 4.7 kHz. The three extra resonances were found to correspond to modes which were axially asymmetric and involved the piriform sinuses, valleculae, and transverse vibrations in the oral cavity. The results therefore suggest that the phenomenon of speakers and singers formant clustering may be more complex than originally thought.

FE Modeling of Human Vocal Tract Acoustics. Part II: Influence of Velopharyngeal Insufficiency on Phonation of Vowels

Developed FE models of acoustic spaces of nasal and vocal tract for vowels /u:/, /a:/ and /i:/ are used to study the influence of velofaryngeal insufficiency on phonation of these vowels. 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. The vocal tract is excited by time dependent airflow at the position of vocal folds, and the time and frequency responses are calculated near the lips and nose. The theoretical results are partly compared with acoustic measurements on physical models designed by the rapid prototyping technique from the FE models, and by clinical investigation.

The Human Vocal Fold Layers. Their Delineation Inside Vocal Fold as a Background to Create 3D Digital and Synthetic Glottal Model.

OBJECTIVES To distinguish the layers of the vocal fold at the submacroscopic level and determine their boundaries, thereby creating a basis for the construction of a digital 3D model of the human vocal folds. STUDY DESIGN The submacroscopic delineation of individual layers of fixed vocal ligaments based on their structural differences. METHODS Following tasks were performed: (1) Submicroscopic dissection of the vocal folds fixed in a solution with a low concentration of fixation substance (in this case, the muscular parts of the vocal folds were removed); (2) Using the CT and micro-MRI methods, we determined the position of the dense parts of the vocal folds; and (3) Using a modified plastination method, we preserved macroscopically natural appearance of all ligamentous and muscular layers. RESULTS The vocal ligament is composed of several volumes of connective tissue. It is surrounded by layers of fibrous material permeated by liquid. Individual fibers stretch all the way to the fibrous casing (fascia) of the vocal muscle. The vocal fold layer surrounding the ligament externally has a stratified character. CONCLUSIONS According to our findings, we infer that this ligament is a complex of several fibrous bundles which are surrounded by a thin layer of connective tissue. Below the surface of epithelium of the vocal fold run several separate bands which are closely adjacent to it. Therefore, we propose using the term ligamentous complex involving closely adjacent structures, instead of the vocal ligament only. We feel that it better reflects the functional and structural character of the whole formation.

Design of Redundant Parallel Robots by Multidisciplinary Virtual Modelling

The paper deals with the description of design methodology for redundant parallel robots based on multidisciplinary virtual modelling. The redundant parallel robots means redundantly actuated parallel robots. The parallel robots have many advantages as low moving masses, higher stiffness of truss structure, all drives on the frame, but they suffer from many problems like appearance of singularities and thus smaller workspace, collisions of links. These drawbacks of parallel structures can be removed by the principle of redundant actuation [4, 1]. This means that the platform is supported and driven by more bars with drives than the necessary number of degrees of freedom (DOF). This principle not only deletes the singularities from workspace as more combinations of links in number of DOF are not simultaneously in singular positions, but it brings further advantages, especially increased and more uniform dynamic capabilities, stiffness, accuracy.

Dynamic Model of Aircraft Passenger Seats for Vibration Comfort Evaluation and Control

The paper deals with the development of the seat dynamical model for vibration comfort evaluation and control. The aircraft seats have been tested extensively by vibrations on the 6 DOF vibrating platform. The importance of the careful comfort control together with the flight mechanics control is namely stressed for the blended wing body (BWB) aircrafts. They have a very large fuselage, where the mechanical properties (accelerations, angular accelerations) vary considerably for different seat places. The model have been improved by adding of dynamical models of the aircraft passenger seats identified by the measurements on the 6 DOF vibrating platform. The experiments, their results and the identification of the dynamical seat model are described. The model is further modified by adding of the comfort evaluation norms represented by dynamical filters. The structure and identification of the seat model is briefly described and discussed.

Reduced-Order Modeling

In this chapter, the full-order state-space models presented in Chap. 3 are reduced in order and parametrized in the main parameters of the flight envelope. Order reduction is achieved by a multistep procedure: A modal reduction is followed by a reduction of the complete aeroelastic model and finally a balanced reduction is performed. Parametrization of the resulting reduced-order models (ROM) is done by spline or radius function interpolation, respectively. The second section is dedicated to the Linear Fractional Representation (LFR) of the parametrized models. The process of LFR modeling is introduced in a general form and then applied to the ACFA blended wing body (BWB) models.

AN INTERPOLATION METHOD FOR DETERMINING THE FREQUENCIES OF PARAMETERIZED LARGE-SCALE STRUCTURES

Parametric Model Order Reduction (pMOR) is an emerging category of models developed with the aim of describing reduced first and second-order dynamical systems. The use of a pROM turns out useful in a variety of applications spanning from the analysis of Micro-Electro-Mechanical Systems (MEMS) to the optimization of complex mechanical systems because they allow predicting the dynamical behavior at any values of the quantities of interest within the design space, e.g. material properties, geometric features or loading conditions. The process underlying the construction of a pROM using an SVD-based method [18] accounts for three basic phases: a) construction of several local ROMs (Reduced Order Models); b) projection of the state-space vector onto a common subspace spanned by several transformation matrices derived in the first step; c) use of an interpolation method capable of capturing for one or more parameters the values of the quantity of interest. One of the major difficulties encountered in this process has been identified at the level of the interpolation method and can be encapsulated in the following contradiction: if the number of detailed finite element analyses is high then an interpolation method can better describe the system for a given choice of a parameter but the time of computation is higher. In this paper is proposed a method for removing the above contradiction by introducing a new interpolation method (RSDM). This method allows to restore and make available to the interpolation tool certain natural components belonging to the matrices of the full FE model that are related on one side, to the process of reduction and on the other side, to the characteristics of a solid in the FE theory. This approach shows higher accuracy than methods used for the assessment of the system’s eigenbehavior. To confirm the usefulness of the RSDM a Hexapod will be analyzed.