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Kavitace a nukleace bublin ve vodě s příměsemi
Zima, Patrik ; Maršík, František ; Sedlář, M.
The latest advances in modeling of cavitation in water flows and experimental investigation of bubble nucleation in a cavitation nozzle will be presented. The emphasis will be put on presenting the results of the recent measurements with cavitation nozzle and the critical assessment of the applicability of the cavitation nozzle principle for determining the size of critical bubble radii. Some results of numerical modeling of cavitation in pumps will be summarized.
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Simulace kavitační nestability v induktoru se 3 lopatkami
Sedlář, M. ; Maršík, František ; Zima, Patrik
Axial-flow inducers are used to improve cavitation performance of radial-flow or mixed-flow pumps. There is a wide range of cavitation instabilities, which can be observed during inducer operation, even at the design flow rate. The type of cavitation instability is determined by the frequency analysis. Two cavitation models were used to determine the frequency range of four different types of cavitation instabilities – CEV and VOF built in the ANSYS CFX software – for a 3-blade inducer and suction impeller of a multistage pump. The calculated values of NPSH3 were compared with experimental data for SST, SST-SAS and RSM SSG turbulence models for fully unsteady solutions. It was found that the SST-SAS model provides the most realistic picture of the backflow vortices and their oscillations.
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Energie rázové vlny vzniklé při růstu bubliny ve vodě a generované při jejím kolapsu
Müller, M. ; Maršík, František
The Kirkwood – Brinkley theory of propagation of spherical shock wave is used to evaluate the amount of the energy transformed into the shock wave generated during the rise of cavitation bubble generated by Nd-Yag laser. The energy was according to the theory calculated from known shock wave velocity, shock wave position and shock wave pressure-time profile at the defined position. Method of characteristic in the Kirkwood – Bethe modification was used for the calculation of the shock wave pressure time profile. The initial conditions for the calculation of the outgoing characteristic were obtained by solving Rayleigh-Plesset equation in Gilmore modification.
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Elastic tubes in the mode of self-excited oscillation
Chlup, Hynek ; Maršík, František ; Konvičková, S.
Our paper studies experimentally the self-excited oscillations of thin-walled elastic tubes with respect to the Korotkoff sounds. The self-excited oscillation is a phenomenon, when an elastic tube looses stability of its shape and starts to oscillate, loaded only by continual flow, therefore without any external excitation. The mean flow rates, pressures at the ends of the tube, external pressures and photographs of the shape in two planes were recorded under various modes of oscillation. The effective cross-section and Young’s modulus of the tube wall were calculated by simplified formulas. The data analysis showed an increase of the oscillation frequency with a decrease of the tube wall compliance. It means the frequency of the oscillation is dependent on ratio of the wall thickness and the tube diameter. The mode of the oscillation is also influenced by the transmural pressure. The influence of the axial pretension of the tube is being studied now.
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Self-excited oscillation of the thin-walled elastic tubes
Chlup, Hynek ; Maršík, František ; Konvičková, S.
The simulation of the fluid flow through elastic pipes has many applications in a blood flow through human vessels – investigation of such phenomena as an atherosclerosis generation in artery walls, the Korotkoff's sounds generation or modeling of vascular mechanical substitutes (the so called "stents") and is therefore widely studied. Aim task is to solve the blood flow through the elastic tubes analytically, numerically and experimentally and to analyze the relation of the mechanical properties of the blood and of the vessel wall and flow instabilities, all focused on biomechanics of the cardio-vascular system. The analysis shows that frequency of self-excited oscillations increases with the decrease of arterial compliance.
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Samobuzené oscilace elastické trubice
Chlup, Hynek ; Macková, H. ; Maršík, František ; Konvičková, S.
Our paper studies experimentally the self-excited oscillations of thin-walled elastic tubes with respect to the Korotkoff sounds. The self-excited oscillation is a phenomenon, when an elastic tube looses stability of its shape and starts to oscillate, loaded only by continual flow, therefore without any external excitation. An experimental set-up was designed for the experiments. The mean flow rates, pressures at the ends of the tube and external pressures were recorded under various modes of oscillation. The effective cross-section and elastic modulus of the tube were calculated by simplified formulas. The data analysis showed an increase of the oscillation frequency with a decrease of the tube wall compliance. It means the frequency of the oscillation is dependent on ratio of the wall thickness and the tube diameter. The mode of the oscillation is also influenced by the transmural pressure.
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Hydrodynamika mozkomíšní tekutiny v páteřním kanálu
Kaczmarská, A. ; Vaněk, P. ; Maršík, František ; Převorovská, Světlana ; Otáhal, S. ; Otáhal, J.
In previous modelling study of the cerebrospinal fluid transportation we have shown that main source of the hydrodynamical resistance and compliance of the craniospinal system is cervical part of the spinal canal. The aim of our present study is the investigation of the influence of the cervical spine degenerative changes on the hydrodynamical parameters of the craniospinal system. The results obtained by using of the numerical model of the cerebrospinal fluid flow show the significant influence of the cervical spine degenerative changes on the hydrodynamics of this system.
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Numerická simulace účinků léčiv na srdeční akční potenciál
Převorovská, Světlana ; Maršík, František
The aim of the paper is a numerical simulation of the antiarrhythmic drugs effects on the cardiac action potential realized by the numerical model of the human cardiovascular system. The pulsating blood flow of the cardiovascular system is generated by the electrochemical and mechanical activity of heart muscle. This system is being modelled by four segments of the pulsating heart and by twenty three vascular segments of pulmonary and systemic circuits connected with the heart segments in series. The behaviour of the cardiovascular system is described by the heart rate and by its hemodynamical variables, i.e. the blood pressure, volume, flow, by the cardiovascular parameters such as the blood inertia, compliances and resistances in corresponding segments and by the physicochemical variables such as the cardiac action potential, the calcium, sodium and potassium ionts concentration.
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