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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
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Observation of human sperm cell immunogenic properties
Cibulka, Jan ; Ulčová-Gallová, Zdeňka (advisor) ; Fingerová, Helena (referee) ; Madar, Jindřich (referee) ; Šíma, Petr (referee)
The issue of human infertility is becoming increasingly pressing, especially in so- called industrially developed countries. Formally, we can share the infertility attributes between the male and the female partner (as a male and female infertility factor), but the problem finally affects the whole parental couple. Perhaps, due to the complexity of the female reproductive tract, it is estimated that over 40% of the reproductive failure is hidden in one or more of its parts. The "strong point" of the male factor is derived from the pathological sperm count. For the remaining 15 to 20% of causes, whether morphological or functional, cannot be to find either clearly or not at all. We talk about the otherwise unexplained infertility, that can be caused in up to 30% immunologically. Due to broad concept of immunology of reproduction, we have chosen literally as a probe into this issue in all respects unique spermatic cell that represents not only a carrier of genetic information, but also a set of antigenic structures. This cell seems to be perfect for this task, because of its availability to most basic laboratory techniques. We will try to familiarize ourselves with some of the obstacles that may prematurely end its mission, especially with the antibodies against its antigenic structures (ASA -...
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Modelling and simulation of self-balanced vertical rigid rotors
Zapoměl, Jaroslav ; Kozánek, Jan ; Košina, Jan ; Cibulka, Jan
Unbalance of rotors of rotating machines is mostly caused by the manufacturing and assembling inaccuracies. In some cases it can be induced by the rotor operation or can be variable during the rotor running. In these cases the classical approach based on attaching the balancing weights to the rotor surface is not efficient. The technological solution is offered by application of a self-balancing device. This paper deals with its design, modelling, and investigation of its functionality in dependence of the rotor operation parameters.
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Influence of contact region size between damping wire andand metal ring on overall damping
Šnábl, Pavel ; Pešek, Luděk ; Bula, Vítězslav ; Cibulka, Jan
Damping wire curved to circular shape is inserted into a groove of slightly smaller diameter in damped steel ring. Deformation of circular-shaped wire causes uneven distribution of pressure in the groove and evenno contact between the wire and the groove in some regions. Experimentaimed for nding those regions was performed and the results are shown.Axial pre-stress of the wire was then applied and it was proven that it helps to reduce the regions with no contact. Dynamic test were made to see how larger contact region achieved by axial pre-stress inuences overall damping of damped steel ring.
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Experimental analysis of bladed wheel modelwith tie-boss couplings – steady and rotational states
Pešek, Luděk ; Bula, Vítězslav ; Šnábl, Pavel ; Cibulka, Jan
Experimental modal analysis of the proposed model of bladed wheel with tie-boss couplings was performed for validation of the numerical FE model. The pre-stresses in contacts were set and evaluated indirectly by the magnetic torque sensor. Then dynamical tests of bladed wheel under revolutions were performed. Theelectromagnetic synchronized pulses were used for excitation of forced vibration of the wheel. The Campbell diagram of the wheel with prestressed contacts was created from the measurement under revolutions. From the attenuation of resonant vibration of the wheel the dampingwas evaluated.
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EXPERIMENTAL ANALYSIS OF BLADED WHEEL MODEL WITH TIE-BOSS COUPLINGS – STEADY AND ROTATIONAL STATES
Pešek, Luděk ; Bula, Vítězslav ; Šnábl, Pavel ; Cibulka, Jan
Experimental modal analysis of the proposed model of bladed wheel with tie-boss couplings was performed for validation of thenumerical FE model. The pre-stresses in contacts were set and evaluated indirectly by the magnetic torque sensor. Then dynamical tests of bladed wheel under revolutions were performed. The\nelectromagnetic synchronized pulses were used for excitation of forced vibration of the wheel. The Campbell diagram of the wheel with prestressedcontacts was created from the measurement under revolutions. From the attenuation of resonant vibration of the wheel the dampingwas evaluated.
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Deformation energy of Yeoh hyperelastic model and constant hyperelastic proportional damping
Šulc, Petr ; Pešek, Luděk ; Bula, Vítězslav ; Košina, Jan ; Cibulka, Jan
The paper deals with a proposal of the dissipated energy of hard rubbers as a function of the deformation energy expressed by the Yeoh hyperelastic model. Then the deformation energy may be dependent only on the first invariant of deformation. Based on the experiment, a “hyperelastic proportional damping” (HPD) is proposed for hard rubbers under finite strains. It is analogical to the model of proportional damping in the elastic theory, i.e. the dissipated energy is proportional to the deformation energy multiplied by the frequency of dynamic harmonic loading. The Yeoh model is chosen since the deformation function is dependent only on the first strain invariant for a description of the simple shear of a surface cylinder. The constants are used to an enumeration of the deformation energy of the Yeoh model for the specific cases of tested rubbers. The coefficients of hyperelastic proportional damping are evaluated on the basis of experimental results,too.
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