|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
Advances in pulsating water jet technology
Foldyna, Josef
A research in the area of pulsating water jets is carried out systematically at the Institute of Geonics of the ASCR, v. v. i., in Ostrava since 2000. The research was oriented primarily at the study of processes of generating and forming of pulsating water jets and their effects on various materials. The paper presents results obtained in the area of numerical modelling of the process of generation of pulsating water jets and results of tests of pulsating water jets effects on materials.
|
|
|
Study of propagation of pressure pulsations in high-pressure system
Foldyna, Josef ; Říha, Zdeněk ; Sitek, Libor
Various alternatives of high pressure-system geometry including square elbows and prolongation of liquid waveguide were elaborated to be able to simulate real tools used to generate high-speed water jets. Variable geometrical parameters of the model were selected and the computational model was prepared in such a way that the geometry and meshing of the model is generated automatically after entering the parameters. This approach facilitates and speeds up preparation of models for simulation of propagation of pressure pulsations in high-pressure system for generation of pulsating water jets. The paper presents results of simulation of propagation of pressure pulsations through various geometries of the high-pressure system.
|
|
|
Research in the area of pulsating water jets
Foldyna, Josef
A research in the area of pulsating water jets is carried out systematically in the Institute of Geonics AS CR, v. v. i., in Ostrava since 2000. The research was oriented primarily at the study of processes of generating and forming of pulsating water jets and their effects on various materials. The presented paper summarizes results obtained in the above mentioned areas during the period from 2000 to 2007.
|
|
|
Simulation of transmission of pressure pulsations in high-pressure system
Foldyna, Josef ; Říha, Zdeněk ; Sitek, Libor ; Švehla, B.
The paper presents results of numerical simulation of 3D, unsteady, turbulent flow of compressible water in a high-pressure system equipped with an acoustic generator. The generator vibrates at frequency of 20 kHz with amplitude of 6 µm. Acoustic waves (pressure pulsations), generated in water pressurized to 30 MPa and amplified by appropriately designed liquid waveguide, results in generation of very high velocity pulsations at the nozzle outlet. The influence of various geometrical configurations on acoustic wave propagation in the high-pressure system was simulated and results were verified by laboratory measurement of pressure pulsations upstream to the nozzle exit.
|
|
| |
guest ::
