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Shear layer-synthetic jet interaction.Qualitative solution
Falta, Jiří ; Maršík, František (advisor) ; Popelka, Lukáš (referee) ; Uruba, Václav (referee)
This thesis investigates possibilities of suppressing the boundary layer separation which is made by controling boundary layer stability. Orr-Sommerfeld equation is numerically solved for this purpose and its solution was tested on Blasius boundery layer which stability is described in many specialized publications. Transition to turbulence is found out by eN method. Single-variable description of velocity pro les on own surface, which is based on the aproximative properties of Falkner-Skan equation, was used. Process of transition on the aerofoil NACA 63-418 was solved as an example of using proposed computational programs.
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Self-excited oscillations of elastic tubes induced by fluid-structure interactin
Štembera, Vítězslav ; Maršík, František (advisor) ; Okrouhlík, Miloslav (referee) ; Žitný, Rudolf (referee)
1 Introduction The aim of this thesis was to develop a mathematical model that could describe the phe- nomenon of self-excited oscillations of flexible tubes induced by fluid-structure interaction between the tube wall and the inner fluid flow. The term self-excited means that the studied system has no oscillatory inner sources or bound- ary conditions, the harmonic motion originates in the system itself. Let us show some examples for the occurrence of this phenomenon in the human body: Pedley ([?]) mentions that vessel collapse is most readily seen in veins, such as in the veins of a hand raised above the level of the heart or in the jugular vein when a person is standing erect ([?]). In arteries1 , such a collapse can be observed only in some special cases, for example in the case when additional outer pressure is applied to the artery. One example is blood pressure measurement using a sphygmomanometer cuff. During this measurement, the so- called Korotkoff sounds, which are strongly believed to be connected to these self-excited oscillations of the brachial artery wall, appear. These Korotkoff sounds are used by medical doctors for pressure diagnostics and are known from the beginning of the 20th century2 . They disappear when the cuff is removed. Artery collapse is also probable if an artery is filled with...
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Termodynamická analýza procesů v polymerní elektrolytické membráně palivového článku
Pavelka, Michal ; Maršík, František (advisor) ; Málek, Josef (referee)
Thermodynamic analysis of processes in electrolytic fuel cell membrane Michal Pavelka April 12, 2012 Abstract Hydrogen fuel cells1 may become a key technology of 21st century, and it is important to be able to describe their behavior, therefore. In this work we focus on hydrogen fuel cells with a polymer-electrolyte membrane. For the membrane we adopt an existing model2 . We for- mulate the model in the framework of the mixture theory which we develop similarly as has been done in the classical textbook of Mazur and de Groot3 . However, refining the concept of potential energy of a material point, we introduce new terms called internal potential ener- gies which enable us to describe macroscopic consequences of internal forces between water and polymer in the membrane and to describe the influence of gradient of surface tension of water in the membrane. We solve the model in 1D approximation. Consequently, we calculate the influence processes in the membrane have on efficiency of the fuel cell. 1 see for example Larminie, J. and A. Dicks. Fuel Cell Systems Explained. 2nd edition. John Wiley & Sons Ltd., 2003. ISBN 0-470-84857-X. 2 Weber, A. Z. and J. Newman. Transport in Polymer-Electrolyte Membranes I, II, III. J. Electrochem. Soc., 150 (7), A1008-A1015, 2003; 151 (2), A1311-A1325, 2004.; 151 (2), A1326-A1339,...
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Interaction of a Fluid Flow with an Elastic Body
Mádlík, Martin ; Maršík, František (advisor) ; Kozel, Karel (referee) ; Rajagopal, K.R. (referee)
The interaction problem of incompressible fluid and incompressible elastic material in the so-called Arbitrary Lagrangian-Eulerian formulation is be- ing studied in this thesis. After giving an overview of the essential principles of continuum mechanics in the moving domains, the fluid-structure interaction model is defined. Next, appropriate numerical scheme in three-dimensional space, based on finite element method, is presented and suitable numerical implementation is proposed. The properties of the presented numerical method are demonstrated on the number of numerical examples. The simplest approach, decoupling the problem into the fluid and solid parts and treating the interaction between them as an external boundary condition, is later revised by introducing the single continuum formulation. The interaction is then seen as an internal boundary, which does not require any special treatment. The proposed method allows to model the large deformations of an incom- pressible Neo-Hookean material, a flow of an incompressible power-law fluid and a mutual material interaction. The quasi-Newton method is used to solve with the original non-linear problem, while a direct solver is the tool that deals with the resulting linearized form. The numerical implementation takes advantage of parallel programming...
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Identification of an intervertebral disc properties by using a free oscillation method in in vitro condition
Zemanová, Petra ; Otáhal, Stanislav (advisor) ; Šorfová, Monika (referee) ; Maršík, František (referee)
Identification of an intervertebral disc properties by using a free oscillation method in in vitro condition This disertation thesis introduces the original measuring method and its results aimed at identifying the character of viscoelastic forces in the respective motion components of an intervertebral disc and their mutual interactions. The method is based on the identification of the motion of a freely oscillating object placed in a center comprising the intervertebral disc when using the step mechanical excitation in the specific direction. The research was carried out on ovine and porcine (ovis domestica, sus scrofa) intervertebral discs. The measurements were performed safely within the physiological range of motions and using as fresh a sample as possible, free of preservatives. Result is a new methodology, a measurement device, a mathematically precise and original description of the non-linearity of stiffness, verification of linearity of the viscous component, and a promising description of interaction properties with the individual degrees of freedom. This method could provide more accurate values for development of intervertebral discs replacements. Key words: intervertebral disc, spinal disc, free oscillations, viscoelasticity, stiffness, intervertebral disc replacements.
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Identification of changes in mechanical characteristics of human axial system as a result of loading and relaxation regime
Van der Kamp Kloučková, Kateřina ; Jelen, Karel (advisor) ; Maršík, František (referee) ; Rosina, Jozef (referee)
Problem: A lot of attention is given to the safety of the driving and the possibility to register fatigue of the drivers. Driving cars is monotony and static. Vibration loading, which causes changes in the axial system. This causes discomfort and fatigue to drivers after some time of exposure to the loading. Hypothesis: It is possible to prove the changes of mechanical characteristics (indicators) of the axial system using the TVS (transfer vibration through spine) method. By using TVS method before and after different types of loading or before and after relaxation it is possible to detect changes of the viscoelastic properties. This can be done by checking changes in the way of waves transfer through the axial system of the observed participants. Objective: Verify the possibility of use of TVS method to register changes of the viscoelastic characteristics of the axial system. Method: The TVS was chosen as a detection method. The method is based on the use of five-msec semi-bandwidth γ pulse stimuli and consequent application of continuously changing harmonic stimuli which periodically differ between 5Hz and 160Hz to the vertebrae C7 and L5. This wave is carried through the axial system and its acceleration on the spinous processes between C7 and S1 is scanned with the help of accelerometric...
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The biomechanics problems of thinwalled brain veins
Hemza, Jan ; Maršík, František (advisor) ; Otáhal, Jakub (referee) ; Vašků, Anna (referee)
Biomechanical material properties of the bridging brain veins are investigated experimentally (A Nikon light microscope was used for the histo-anatomical study and viskoelastic properties was measured on a MTS 858.2 Mini Bionix system ) and theoretically. The main goal of the developed theory was to formulate the biomechanical conditions (geometrical dimensions, viscoelastic properties of veins and blood fluid flow conditions) at which unstable behavior or even vein collapse can occur. The study of the geometry and topology of bridging veins was carried out by a magnetic resonance (Siemens Magnetom Symphony1,5 T) and a stereomicroscope (Nikon SMZ 1500) complemented with a digital camera (Nikon Coolpix E995) and Lucia Net software. From the biomechanical point of view, experimental findings can be summarized as follows: the existence of two types of venous brain systems; thin and thick wall veins with a one order difference in elastic modulus magnitude high sensitivity of the thin wall veins on the blood flow rate and extension or contraction on their structural stability the existence of continuing small wall vibration under physiological conditions Under small deformations conditions, the shear modulus was shown experimentally to be in the range (2÷4)·10 4 Pa with a Young modulus E= (0.6÷1.2)·10 5...
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Mathematical Simulation of Osteodegenerative Process in Cervical Spine segment
Barsa, Pavel ; Maršík, František (advisor) ; Otáhal, Stanislav (referee) ; Hemza, Jan (referee)
Aim: The aim of following study is to simulate different types of loading on cervical vertebra and to identify if mechanical stress concentration in utmost positions corresponds with osteophytes localization find in clinical practice. The objective of our investigation is to develop a theoretical model that may elucidate clinical observation regarding the predilection site of bone remodeling. We will focus our attention on the physiological changes inside the cervical vertebral body. Methods: Real 3D-geometry of the fourth cervical vertebra had been made by commercially available system ATOS II. It is high-resolution measuring system using principles of optical triangulation. Such flexible optical measuring machine projects fringe patterns on the surface of selected object and the pattern is observed with two cameras. 3D coordinates for each camera pixel were calculated with high precision and a polygon mesh of the object's surface was further generated. ANSYS program has been used in the next step to calculate strains and stresses in each finite element of the virtual vertebra. Applied forces used in the experiment were of physiological magnitude and direction and mechanical stress distribution inside the vertebra has been calculated. Mechanical loading in neutral position has been characterized by...
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Biomechanical aspects of the dynamics of intracranial pressure in traumatic brain injury
Mayer, Martin ; Jelen, Karel (advisor) ; Maršík, František (referee) ; Pokorný, Jan (referee)
Title: Biomechanical aspects of the dynamics of intracranial pressure in traumatic brain injury Author: Ing. Martin Mayer e-mail: mayercz@seznam.cz Department: Department of Anatomy and Biomechanics Supervisor: doc. PaedDr. Karel Jelen, CSc. This PhD thesis "Biomechanical aspects of the dynamics of intracranial pressure in traumatic brain injury" is about the dynamics of intracranial pressure, particularly in relation to the external mechanical action of the patient. Severe head injury is the leading cause of death in patients under 35 years of age. Despite constantly-improving medical and nursing care only one third of patients, after recovery, regained the ability to live independently in the long term. Two-thirds of patients were severely disabled or died. The lifetime cost of such a patient who was not completely cured has been calculated to be $4,000,000. A significant consequence of craniocerebral injuries are secondary brain lesions, which among other means the rise in intracranial pressure (ICP), which can further exacerbate due to intracerebral or extracerebral causes. Therefore, the objective of the treatment is minimizing secondary injury, optimally at the phase of the primary lesion. However, realization of this requirement, about which we can say that is a conditio sine qua non, sometimes leads...
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Numerical modelling of unstable fluid flow past heated bodies
Pech, Jan ; Maršík, František (advisor)
Title: Numerical modeling of unstable fluid flow past heated bodies Author: Jan Pech Department: Mathematical Institute of Charles University Supervisor: prof. Ing. František Maršík, DrSc., Mathematical Institute of Charles University Abstract: Presented work brings new results to numerical computations of flow influenced by temperature changes. Constructed numerical algorithm takes into account variable coefficients of the differential operators in the system of in- compressible Navier-Stokes equations coupled with thermal heat equation. The spatial discretisation of the problem targets to application of high order method, the spectral element method. Phenomenons connected with high order approxi- mations are discussed on a number of examples and comparisons with methods of lower order, which are more common. Results were achieved for two fluids with opposite response to heating, air and water. The observed quantity is par- ticularly a frequency of vortex shedding, the Strouhal number, as dependent on temperature and Reynolds number. The calculated values were compared with experimental results and exhibit a good coincidence. Numerical analysis of sep- aration angle in flow around heated circular cylinder may give a new impulse to verification of accuracy and reliability of the developed method. Keywords:...
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