National Repository of Grey Literature 40 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Self-balancing of vertical disc rotors supported by contactless bearings
Zapoměl, Jaroslav ; Kozánek, Jan ; Košina, Jan
Article discusses the self-balancing of the vertical disc rotors supported by contactless bearings on principle of diamagnetic levitation. There are three possibilities of contactless supports: permanent magnet levitation with the help of bismuth, graphite and pyrolitic graphite.
Study of the oscillation of a pendulum in a magnetic field
Zapoměl, Jaroslav ; Kozánek, Jan ; Košina, Jan ; Cibulka, Jan
Realization of some technological processes requires application of rotating machines with a vertical rotor mounted in rolling element bearings. One of the requirements put on their operation is minimization of energy losses in the support elements. The proposed design variant consists in supporting the vertical rotor by one rolling element bearing placed at its upper part and by one axial magnetic bearing mounted in its lower end. The magnetic bearing is composed of an electric coil coupled with the stationary part and of a permanent magnet attached to the rotating part. The magnetic force attracts the permanent magnet, which reduces radial displacement of the lower end of the rotor. The magnetic field between the magnets represents a force coupling between the rotor and the stationary part, which shows some stiffness and affects the system natural frequencies. The controlled change of the stiffness makes it possible to reduce the rotor lateral oscillations in the resonance area. The investigated pendulum is coupled with the frame by a revolute joint at its upper end. The permanent magnet is attached to its lower end. The electric coil is coupled with the stationary part and placed under the pendulum. The system is excited by a moment of harmonic time history, which sets the pendulum into a seesaw motion.\n\n
Approaches to dynamical analysis of rotors with parameters of uncertain magnitudes
Zapoměl, Jaroslav ; Kozánek, Jan ; Košina, Jan ; Cibulka, Jan
In many cases, the rotor configuration or loading characteristics are described by parameters of uncertain magnitude. Several procedures were developed to analyse such systems. This paper deals with the approach based on application of the fuzzy numbers. The investigated mechanical system is a rotor supported by hydrodynamic bearings. The parameters of its loading have uncertain values.
Estimation of damping in human vocal folds vibration: measurements in vivo and on model
Horáček, Jaromír ; Radolf, Vojtěch ; Bula, Vítězslav ; Košina, Jan ; Geneid, A. ; Laukkanen, A. M.
This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal folds damping is important for testing and further development of mathematical modelling of phonation. The measurements of the damping ratio, based on high-speed videolaryngoscopic registrations, were realized in vivo on a male subject and in vitro using an originally developed silicon replica of the human vocal folds. In both cases the results show remarkable decrease of vibration frequency of the vocal folds and increase of damping ratio D in the phonation offset limiting to the values D=0.12 in vivo measurement and D=0.11 in vitro measurement. The results for vocal folds’ damping are in good agreement with previous measurements performed in humans using different methods.
Weight transfer during the putting stroke
Kosina, Jan ; Gryc, Tomáš (advisor) ; Hráský, Pavel (referee)
Title Weight transfer during the putting stroke Objectives Description of weight transfer during the putting stroke and comparison of interindividual and intraindividual stability due to parametres accuracy and weight transfer. Methods Theory was build up by researching method alongside with studiing technical literature. Testing group consisted of professional golfers. Weight transfer was measured by two plattens KISTLER a kinematics of movement was observed by kinematic analysartor CODA motion system. The analysis of interindividual and intraindividual stability was based on data collected during the testing of professional golf players. Results High interindiviual and intraindividual stability of execution was proved due to parametres weight transfer and accuracy. It was proved that capability of accuracy and stability of execution weight transfering is decreasing alongside with longer distance. For description of weight transfer critical phazes of movement were estabilished. By the measurement was discovered how the weight is transferred during the putting stroke. Key words Golf, weight transfer, putting stroke, force effect, accuracy
Models of Lobachevskij's geometry and possibilities of their use at secondary school
Kosina, Jan ; Kvasz, Ladislav (advisor) ; Jančařík, Antonín (referee)
This thesis Models of Lobachevskij's geometry and the possibilities of their use at secondary school focuses on one kind of non-Euclidean geometries, the Bolyai - Lobachevskij's geometry. The first chapter describes the history of non-Euclidean geometry, shows difficulties of understanding of one publication dedicated to these problems by current students of secondary schools and shows some chosen methods in the didactics of mathematics, especialy the constructivist method. The second chapter is dedicated to elemental concepts of projective geometry, Bolyai - Lobachevskij's geometry and it shows its basic models. It further analyses the specific features of this kind of geometry in Beltrami - Klein's model, especially mutual positions of straight lines. This theses further contains a set of gradual tasks. The third chapter is dedicated to the description of a didactical experiment. In this experiment were students of secondary school acquainted with this theory and tasks, which they solved. Student's solution were writen down and than analysed in the constructivist methodology term in the didactics of mathematics.
Analysis of muscle shortening and range of upper body movement and their relation to selected golf swing parameters in junior age players
Kosina, Jan ; Gryc, Tomáš (advisor) ; Hráský, Pavel (referee)
Title: Muscle tightness and range of motion analysis of selected upper body segments an its connection to selected parametres of experienced junior golf players swing. Objectives: The aim of this work is to assess muscle tightness, range of motion and golf swing kinematics of experienced junior golf players and to evaluate possible connections between muscle tightness, range of movement and golf swing kinematics Methods: Golf swing kinematics was observed by kinematic analyzer CODA Motion System. Selected parametres of golf swing were: shoulder rotation; pelvis rotation; X - factor; angle between shoulders and left arm. Parametres were measured in key moments of a goflf swing: end of backswing; impakt. Muscle tightness was measured by clinical test of muscle tightness according to Janda for selected muscles: m. triceps surae; m. iliopsoas; m. rectus femoris; m. tensor fascies latae; knee flexors; hip adductors; m. piriformis; m. quadratus lumborum; paravertebral muscles; m. pectoralis major; m. trapezius - upper part; m. levator scapulae and m. sternocleidomastoideus. Clinical test of range of motion according to Janda and standart two - arm goniometer was used for range of motion evaluation of selected body segments: hip joint - internal and external rotatio, flexion, extension; shoulder joint -...
Evaluating the amount of physical activity of football players at grade level.
Kosina, Jan ; Kokštejn, Jakub (advisor) ; Frýbort, Pavel (referee)
Bachelor thesis "Evaluating the amount of physical activity of football players at grade level" deals with finding new knowledge concerning the size and composition of the physical activity of adolescent football players. In the theoretical part are being collected knowledge about physical activity and health recommendations concerning the composionfor the age group of adolescents. Amount of physical activity was measured by heart rate sensor, accelerometers and a written record. The evaluation, which is given in the final part of the thesis shows that adolescent football players at grade level are below health recomendations for daily energy expenditure in the prevailing numberof days of the week. In cotrast, in the days when ongoing trining units, they exceed recommendations several times. Regarding the average lenght of sleep, it was found, that the majority of players younger from both categories exceeds recommendations for their age while the results of most players of the older dategory correspond health recommendations.
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.
Analysis of measurement of temperature dependence inside rubber sample under dynamic harmonic load
Šulc, Petr ; Pešek, Luděk ; Bula, Vítězslav ; Šnábl, Pavel ; Cibulka, Jan ; Košina, Jan
This work deals with the preparation and methodology of temperature measurement inside a rubber sample. In this paper, a rubber sample with temperature sensors is described and a description with a temperature measurement scheme under torsional dynamic stress with the possibility of measurement in a temperature chamber is proposed. Large torsional deformations are considered for harmonic torsional loads. The reason for these measurements is to determine the temperature dependence and sensitivity of the heat output parameters.

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See also: similar author names
2 KOŠINA, Jiří
10 Kosina, Jan
2 Kosina, Jiří
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