|
|
Modelled pressure pulsations in a fluid with the influence of a second viscosity
Dzjamko, Vladislav ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
The aim of this thesis is to determine the value of the speed of sound and the second dynamic viscosity of the fluid using numerical optimization of analytical model. Theoretically, the speed of sound and the second viscosity can be determined from three measured pressure waveforms in time along the length of the tube, while the speed of sound is traced to determine the correctness of the result. The thesis is divided into seven successive chapters. The first two define all the necessary concepts and the 1D analytical model used. The following chapters deal with the design of the experiment, data evaluation and numerical optimization of the search parameters in the frequency domain.The range of measured frequencies was from 1 kHz to 20,59 kHz. Einstein´s notation is used this this thesis. All graphs associated with the analytical model and the evaluation of the results are created in Matlab. The optimization functions fminsearch and lsqnonlin are used to evaluate the speed of sound and the second viscosity, however the fminsearch function overestimates the magnitude of the second viscosity. The thesis includes the calculation of the problem using Ansys and the subsequent comparison of all results.
|
|
|
Study of the Dissipation in Spiraling Vortical Structures
Štefan, David ; Drábková, Sylva (referee) ; Koutník,, Jiří (referee) ; Skoták, Aleš (referee) ; Rudolf, Pavel (advisor)
This work deals with study of swirling flows where the spiral vortical structure appears. The main relation is to flow seen in the draft tube cone of hydraulic turbines operated out of the design point (i.e. best efficiency point). In this cases large coherent vortex structure (vortex rope) appears and consequently high pressure pulsations are propagated to the whole machine system leading to possible restriction of turbine operation. This flow features are consequence of flow instability called vortex breakdown in case of Francis turbine operated at part load (flow rate lower than optimal one). The present study is carried out using simplified device of swirl generator in order to access similar flow conditions as can be found in real hydraulic turbines. Both the dynamic and dissipation effect of spiral vortex breakdown are investigated. The first part of thesis deals with spiral form of vortex breakdown. The experimentally measured velocity profiles (LDA) and wall static pressures are correlated with numerical simulations carried out using open-source CFD package OpenFOAM 2.2.2. The high speed camera recording of cavitating vortex core is used to obtain image ensemble for further post-processing. The dissipation effect of spiral vortex structure is in detail discussed based on computed flow fields. The second part of thesis is dedicated to the application of POD decomposition to the study of spatio-temporal features of spiral vortex dynamics. Firstly the POD is applied to the both the experimentally obtained image ensemble of cavitating vortex and numerically computed static pressure fields. Secondly the comprehensive analysis of spiral vortex mitigation effect by the axial water jet is analyzed. The collaborative study employing the swirl generator apparatus designed by the researchers from Politehnica University of Timisoara in Romania is performed and changes in spatio-temporal vortex dynamic are studied. In this study the numerical data (in a form of three-dimensional pressure and velocity fields) are obtained using commercial CFD software ANSYS Fluent R14.
|
|
|
Machine diagnostics based on models
Kapusta, Juraj ; Habán, Vladimír (referee) ; Huzlík, Rostislav (advisor)
The main idea is focused on the diagnostics of a specific hydraulic system, i.e. sensing the physical quantities of the hydraulic circuit with a tank and a centrifugal pump driven by an asynchronous motor. It is a system of pipes connected to the pump, where due to its work it creates a water flow and a pressure increase. In practice, this issue is also addressed in the energy and nuclear industries. Primary circuits in some cases cannot be designed or modified to be able measure locally the pressure value. It is necessary to measure this quantity indirectly - from the motor currents. The main idea of the work is to diagnose the system by an indirect method - specifically to detect the state of the hydraulic circuit (pressure, flow) from the values that we are able to measure and detect damage in advance. In the second part of the thesis is the application of the parts of a specific hydraulic system in the simulation environment MATLAB Simulink. The model of the hydraulic circuit contains mathematical-physical relations that simulate the course of the mentioned experiment. The results of the simulation are compared with the results of the experiment. The model also investigates the simulation of a fault condition, when we supply pressure pulsations to the hydraulic circuit. It is these changes in the hydraulic part that affect the characteristics of the pump and the asynchronous motor, so we are able to diagnose this system.
|
|
|
Monitoring of hydraulic machines using acoustic emissions
Závorka, Dalibor ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
The goal of this diploma thesis is to clarify possibilities of usage of acoustic emission as a hydraulic machinery diagnostics tool. Especially for exposing presence of ruptures or cracks in the parts of machine, assuming changes in acoustic exposure of the part during operation. This clarification is based on series of simple measured experiments, which consist of monitoring the bolt placed in fluid stream inside of a pipe. This bolt was preloaded against inner wall of pipe by appropriate tightening torque. This preload is supposed to simulate effects of the size of rupture. High preload simulates small rupture or none in object and respectively small preload is supposed to simulate big rupture. A group of pressure sensors and accelerometers measures experiments and their evaluations are processed by script created in software MATLAB. Outputs of this script are charts with effective values of respective sensors from the entire record split into individual frequency spectrums. These charts compare spectrums of each configuration to judge effects of parameters changes.
|
|
|
Dialysis pump
Švagera, Roman ; Rudolf, Pavel (referee) ; Fialová, Simona (advisor)
Dialysis is still very important treatment process today which needs to be constantly improved. This thesis focuses on the development of a pump for dialysis units, specifically on the pressure pulsations reduction in the rotary peristaltic pump. Using experiments, the problem of peristaltic pumps is explained. With the computational modelling there are proposed design modifications leading to the pressure pulsations reduction.
|
|
|
Pressure pulsation propagation in elastic hoses
Čapoš, Eduard ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
This thesis deals with propagation of pressure and flow pulsations, which are strongly affected by the tube flexibility. There are two mathematic models introduced, which are derived from basic physical relations. First model assumes velocity only in the axis direction. Second one assumes also non-zero radial velocity. Kelvin-Voigt model for viscoelasticity was used. Furthermore, experimental measurement was designed and evaluated. Measured data was used to calculate material properties. In addition, dynamic transfer was determined.
|
|
|
Axial force and pressure pulsations in double-suction pump.
Vacula, Jiří ; Franc, Zdeněk (referee) ; Habán, Vladimír (advisor)
This diploma thesis deals with axial thrust existence in a double suction pump rotor. Axial thrust appears especially in low flow rates modes. The aim of this work is finding information about this issue and deriving mathematical model of calculation which will be subsequently applied on experimental data received from double suction pump measurement in laboratory. It is important to examine the whole dynamics of axial thrust development and find its cause of formation in measured double suction pump.
|
|
| |
|
|
Mutual interaction of pressure pulsations and pipe vibration
Hrazdíra, Zdeněk ; Fialová, Simona (referee) ; Habán, Vladimír (advisor)
The aim of this thesis is to find out the effects of pipe vibrations on pressure pulsations in liquids. The pipe-liquid system is mathematically described by proper boundary conditions and wave equations, which are derived from basic physical laws. Firstly, simplified model of only liquid is considered, which is then compared to the results obtained from analysis of pipe-liquid mutual interaction.
|
|
|
Mutual interaction of pressure pulsations and pulsations of undirect pipe
Hrazdíra, Zdeněk ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
This thesis deals with mathematical modeling of multiphysics FSI (fluid-structure interaction) problem, describing mutual interaction of pressure pulsations and vibrations of indirect pipe in a 2D region. Firstly, physical partial differential equations are derived separately for both media, which are in turn coupled and solved analytically. Results of mentioned models include natural frequency values, amplitude-frequency characteristics and both natural and driven damped oscillations of pipe and liquid.
|
guest ::
