Dissertations / Theses on the topic 'Damping of pressure pulsations'

The diploma thesis deals with pressure pulsations in pipeline system with dynamic muffler. There is presented original geometry of side-branch resonator. Pressure pulsations are solved by a created mathematical model, numerical simulations and verified by an experimental approach. The influence of dynamic and bulk viscosity is involved in derived governing equations. A system of nonlinear equations is solved by genetic algorithm and frequency dependent relationship of bulk viscosity of air is determined afterwards. The correct function of used pressure sensors is tested. The processing of experimental data is performed by the fast Fourier transform with coherent sampling. Finally, a comparison of analytical, numerical and experimental approaches is introduced for different geometric variants of presented muffler.

The work presented in this thesis involves preparation and execution of measurements on Francis runners. The measurements were performed by means of onboard measuring equipment both in model runners and full-scale prototype runners. Also, analysis of the measured data, and the discussion of the results, is presented. The measurements resulted in large data sets. These data sets were used by the author to investigate the dynamic pressure and strain in the runners. The results of the analysis can be used as input in future turbine design. Andritz Hydro AG has used the data for verification of their numerical simulation tools. In connection with the refurbishment of Tokke power plant, two model runners were made available for onboard pressure measurements. To investigate the dynamic pressure in these runners, methods for integration of pressure transducers in the runner blades needed to be developed. After initial difficulties during the preparation, successful measurements were obtained from both model runners. At Tokke power plant, both the original and replacement runners were made accessible for onboard pressure and strain gauge measurements. On the original Kværner Brug AS runner, the test was prepared and performed by the author. This test failed, due to water intrusion in the logging chain. The second test was performed on the Andritz Hydro AG replacement runner. This test was prepared and performed by the author in close cooperation with Andritz Hydro AG, and the results were successful. The analysis results from both model and prototype runners show that the wake leaving the guide vanes is the most severe source of dynamic pressure in the runner. The draft tube vortex rope pulsation propagates upstream the runner, but does not appear as a significant frequency in the runner strain measurements.

An experimental investigation of noise in a pressure-balanced sliding vane pump was conducted. The test pump for this research was used in an automobile's hydraulic power steering system. As currently designed, a small portion of the manufactured pumps generate excessive noise during operation. An experimental test stand facility was used to represent a power steering system for analysis of the excessive noise problem with the objective of determining ways to reduce the noise. Through signature analysis techniques, the sliding vane pump noise was related to the pump's pressure pulsations. The pulsations consisted of three types of pressure oscillations: the pressure ripple with a fundamental component at the vane passage frequency together with harmonics; the low-frequency pressure oscillation with a fundamental component at the rotational frequency together with harmonics; and the high-frequency pressure oscillation. The fundamental vane passage frequency and its harmonics dominated the noise signal frequency spectrum. The pump's internal leakage, which was a function of three clearances in the pumping chamber, determined the magnitude of the pressure pulsations. If the pumping chamber components had inadequate clearances, the pump produced excessive pressure pulsations for a given discharge pressure and, consequently, excessive fluid-borne noise generation. Thus, this study indicated increasing the pump's clearances would minimize the pump's noise generation.
M.S.

Stricter pollution norms have led to increased efforts to achieve lower emissions. Exhaust Gas Re-circulation (EGR) is a well known measure to reduce NOx internally in the engine. In order to achieve better performance of an engine in terms of emissions it is very essential to control the flow of exhaust gases through EGR valve. Generally, an Engine Control Unit (ECU) uses mean value models or map-based approaches to calculate the mass flow through EGR valve. The main driving factor of the mass flow through an EGR valve i.e. the exhaust gas pressure is continuously fluctuating throughout an engine cycle. This continuous change in the pressure lead to variations in the mass flow through EGR valve, thus introducing inaccuracies in the desired flow through EGR valve, thereby affecting the engine performance greatly. Hence it is very essential to consider the pulsations in a combustion cycle. In this thesis an EGR valve model is developed in Matlab/Simulink environment. The model is able to consider the effect of exhaust pressure pulsations and is found to be more accurate than the mean value models used in the ECU.

This diploma thesis deals with numerical simulation of pressure pulsations in elastic pipes. Continuity relation of fluid in elastic pipes, when calculating some damping in pipe material, is derived into practice. Rheological model of such a pipe corresponds to Voigt (Kelvin) model. For analysing dynamic effects in time periods are used numerical methods that deal with flow of compressible fluid: FTCS, Lax-Friedrichs and Lax-Wendroff method. The numerical results are confronted with the experiment. During the experiment simulation the method considers speed of sound in liquid like a function of pressure. This diploma thesis lays partial principles for finding elastic constants for describing dynamic characteristics of elastic pipes by measuring the pressure pulsations.

The operation of centrifugal pumps can generate instabilities and pressure pulsations that may be detrimental to the integrity and performance of the pump. Until recently these pressure pulsations could only be determined experimentally which resulted in a limited understanding of pressure pulsations around the pump. Industrial pump guarantees are limited to pulsation levels measured at the discharge. However, numerical analysis techniques have advanced to such a stage that they can now be used to explore these effects. The multi-block, structured grid CFD code TASCflow was used to investigate the time variation of pressure within a complete centrifugal pump. A parametric study covered four geometric parameters, namely the cutwater gap, vane arrangement, snubber gap and the sidewall clearance. Taguchi methods allowed the number of transient analyses to be limited to a total of twenty seven. Three flow rates were investigated and the pulsations were extracted at fifteen different locations covering important pump regions. The velocity flow patterns from the transient analyses exhibited important features that were in agreement with two independent sources. The transient flow results compared reasonably with the Weir experimental tests and clearly indicated the pump locations experiencing the largest pulsation levels. It was also noted that monitoring pulsations at the top dead centre of the pump volute casing would provide a better indication of internal pump pulsations than monitoring at the discharge. Taguchi post-processing analysis tools were used to rank the relative importance of the four geometric parameters at each location for each flow rate. The cutwater gap and vane arrangement were found to exert the greatest influence across the various monitored locations and the flow range. However the snubber gap had a dominant influence on the pressure differential across the impeller shroud and pulses in the pressure differential were evident at reduced flows. Through a rationalisation process reductions in pressure pulsations aimed at increased component life and reduced noise/vibration have resulted in a single recommended geometric arrangement. Further analyses confirmed that the new arrangement did indeed produce lesser pulsations levels. Multiple steady state simulations were analysed to determine if they were a viable substitute for the transient analyses. However it was demonstrated that the steady state pulsations did not adequately capture the magnitude and phase of the pulsations shown by the transient results. Likewise the steady state analyses were unable to predict trends for two differing pump geometries. In order to identify the implications of the CFD data for mechanical integrity, the pressure differential predicted by the transient analyses was compared with the pressure loadings currently utilised in Weir design guidelines; this resulted in a new recommendation for use in future designs. Also finite element analyses were conducted using four pressure loadings taken from the numerical results and a centrifugal loading. These supported the recommendation for an increased loading to be used in the design guidelines. The stress levels at the impeller outlet were found to be extremely sensitive to the snubber gap. The completion of this project has allowed a useful set of recommendations to be made regarding the design of high head double entry pumps.

Magister Scientiae - Msc
This thesis reports the results of a twofold study on the recently proposed phenomenon of ‘stellar pulsations’ in young brown dwarfs by the seminal study of Palla and Baraffe (2005) (PB05, thereafter). The PB05 study presents results of a non-adiabatic linear stability analysis showing that young brown dwarfs should become pulsationally unstable during the deuterium burning phase of their evolution.
South Africa

In hydraulic-mechanically controlled variable displacement pumps, the actual pump controller produces additional power losses. Due to the low damping coefficients of all pump controller’s components, hydraulic-mechanically pressure controlled pumps use to oscillate while adjusting the pressure level in the hydraulic system. In several state-of-the-art variable pump controllers, a damping orifice connects the control actuator’s displacement chamber with the reservoir. This bypass dampens the movement of the control actuator but also leads to bypass losses during steady-state operation of the pump. A new concept for damping via feedback loops avoiding bypass losses is presented in t his paper.

This thesis is performed to evaluate the design consideration and performance characteristics of a surge tank for a diaphragm pump operation and to evaluate the proper volume and inlet area of surge tank in order to reduce the pulsations of the discharge pressure. An experimental set up is constructed for a three diaphragm positive displacement pump and the experiments are conducted afterwards. The surge tanks having different volumes and the surge tank inlet area configurations are tested in order to achieve the minimum peak to peak pulsations. Experiments showed that among the different sizes of the surge tanks, the minimum peak to peak pulsations are achieved with the largest volume which is the original surge tank of the test pump used by the pump manufacturer. This result is supported by the literature which states that with greater surge tank size the magnitude of pulsations can be diminished more. Regarding the surge tank inlet area design
among the eight different adaptors a proper inlet area value is concluded having the minimum peak to peak pulsations also smaller than the original configuration.

The use of renewable energy such as water and wind to produce electricity has been proven extremely effective in Sweden. The ability of these renewable resources to produce clean output energy counters the adversities caused by non-renewable resources. The use of hydraulic turbines is a good example of favoured technique for energy and power production using renewable resources. The hydro-turbines are designed to operate at best efficiency point (BEP). Varying energy demands in recent years implies on the need of flexible operation of hydraulic turbines. The issue of pressure pulsations in the draft tube of hydro-turbines, observed at lower operating conditions has been unresolved for many years. These pressure pulsations are related to the ‘rotating vortex rope’ (RVR) observed at part load operation and, affects the lifespan and performance of the hydro-turbine adversely. Several techniques have been investigated in the past to reduce the pressure pulsations in the draft tube at part load operation and enhance the flexibility of the turbine. During the present research study, a passive flow control technique was investigated numerically by implementing a guide vane system in the draft tube of the Francis-99model turbine. Guide vanes are mechanical devices that can direct the flow in a desired direction. The current study presents the possibility of reducing the pressure pulsations in the draft tube by mitigating the RVR using a guide vane system in the draft tube. At the initial stages of the research study, a reduced numerical model of the Francis model turbine was developed by only considering the draft tube domain. The motive was to develop a reduced model to perform the parametric analysis for the guide vane system in the draft tube with reduced computational time, power, and storage. The results obtained from the numerical study were found to be in good agreement with theFrancis-99 semi-model with passage domains. A parametric study was performed to achieve a guide vane system design that could mitigate RVR with minimum losses. During this study, the number of guide vanes, the chord and the span of the guide vanes were investigated. It was found that a set of three guide vane system with chord of 86% of runner radius and leading-edge span of 30% of runner radius is an ideal design that mitigates RVR above 95%.

The aim of this thesis is to develop and evaluate a prototype for measuring volumetric changes of the blood with PPG. The prototype consist of a sensor plate controlled in Lab-view and algorithms for signal processing and analysis of results developed in Matlab. A study divided into three parts is performed, where the collected data is used for further development and alternations of the prototype between the study parts. A measurement in the study is divided into three stages before, during and after pressure, where the subject is changing body position between each stage in order to either apply or relieve pressure from the sensor plate. The amplitude changes of the recorded signals are analysed and the results from the stable parts of the measurements are presented as the ratio between before and during pressure. A ratio separated from 1 either show a decrease or an increase of pulsating blood volume as a response to the applied pressure. The results from the study show that there are both large spatial variations and large variations over time in the measurements. Today the prototype does not give repeatable results and there are several uncertainties in the measurement method. An optimal sensor plate would be flexible and have several LEDs over a larger area in order to give reliable result despite spatial variations.

Le couplage entre un écoulement instable et des résonances acoustiques dans des systèmes de conduites peut conduire à des phénomènes d’oscillations auto-induites. Ce type de phénomènes trouve principalement place dans des conduites latérales fermées, par exemple dans des systèmes de transport ou de compression de gaz. L’objectif de ce travail est d’étudier les oscillations auto-induites dans le cas où le fluide transporté ne se limite pas à un gaz, mais est un mélange de gaz et de liquide. Les pulsations sont mesurées dans des conduites latérales fermées, pour deux types de configurations (en tandem et en croix), avec écoulement d’un mélange variable d’air et d’eau. La position de l’injection d’eau est variable afin d’obtenir plusieurs régimes d’écoulement diphasique. Les résultats indiquent que la présence d’eau a un effet important sur les niveaux de pulsations dans les conduites. Cet effet a pu être attribué à deux mécanismes dus à la présence d’eau : les instabilités de couches de mélange sont modifiées et l’amortissement des ondes acoustiques est amplifié.Le deuxième mécanisme a été quantifié à l’aide de mesures sur un montage expérimental dédié conçu pour avoir un écoulement stratifié. On a observé que, dans tous les cas, la présence d’eau augmente l’amortissement. Cette augmentation a pu être attribuée à la réduction de la section effective de la conduite (due au remplissage partiel par l’eau) et à l’augmentation de la friction turbulente à l’interface entre les phases liquide et gazeuse
Coupling between flow instabilities and acoustic resonances in ducts with closed side branches leads to Flow Induced Pulsations (FIPs). This is a typical phenomenon in engineering applications (gas transport systems, compressor installations, and chemical plants). The objective of this work is to extend the knowledge about FIPs when the transported medium is not uniquely gas but a combination of gas and (a small quantity of) liquid. For two configurations of double side branches (in tandem and in quasi-cross), the amplitude of pressure pulsations in the side branches was measured for different liquid injection rates. This was repeated with the liquid injection point located at different places to allow different flow regimes at the pipe connections. The results show a strong effect of the water content on the pulsations. On basis of these results and additional measurements, the following hypotheses for the effect of liquid were made: (1) interaction of the liquid with the flow instability and (2) increase of the acoustical damping in the ducts in presence of liquid.The effect of liquid on damping was measured with a dedicated test setup designed to have a stratified flow. It was found that the liquid always increases the acoustical damping, mainly due to the reduction of the effective cross section by the liquid, and because of the increased turbulent friction at the interface between gas and liquid

The running of gas turbines with low emissions causes high pressure pulsations to arise in the combustion chamber. These pulsations are high amplitude sound vibrations. At some frequencies these are harmful to the gas turbine. Hence these pulsations are monitored to avoid operating conditions where pulsations are specifically harmful. It is necessary to expose the system of known pulsations to verify the functionality of the monitoring process.

This report describes the development of a generator of pressure pulsations to verify the monitoring system. The output should be of harmonic form with a frequency of greater than 160 Hz and 15 mbar in amplitude. To begin with, a few alternatives to a pulsation generator are described. In light of studies of these possibilities the alternative based on a roller bearing is selected. This is considered as one of the easier alternatives to design.

An existing generator of pressure pulsations has been analyzed. The calculations from this analysis supported the construction of the new device. The new generator far exceeded the specification regarding frequency, amplitude and harmonics of the pulsations. With a few modifications, such as encapsulation, the pulsation generator will be ready for usage. It could then serve as a mobile device for the inspection of the pulsation monitoring system. Possibly the device could be equipped with a faster and stronger motor. This would permit the device to be used for the calibration of pulsation monitoring sensors.

Combustion instabilities (thermo-acoustic pressure oscillations) have been recognised for some time as a problem limiting the development of low emissions (e.g., lean burn) gas turbine combustion systems, particularly for aviation propulsion applications. Recently, significant research efforts have been focused on acoustic damping for suppression of combustion instability. Most of this work has either been experimental or based on linear acoustic theory. The last 3-5 years has seen application of density based CFD methods to this problem, but no attempts to use pressure-based CFD methods which are much more commonly used in combustion predictions. The goal of the present work is therefore to develop a pressure-based CFD algorithm in order to predict accurately acoustic propagation and acoustic damping processes, as relevant to gas turbine combustors. The developed computational algorithm described in this thesis is based on the classical pressure-correction approach, which was modified to allow fluid density variation as a function of pressure in order to simulate acoustic phenomena, which are fundamentally compressible in nature. The fact that the overall flow Mach number of relevance was likely to be low ( mildly compressible flow) also influenced the chosen methodology. For accurate capture of acoustic wave propagation at minimum grid resolution and avoiding excessive numerical smearing/dispersion, a fifth order accurate Weighted Essentially Non-Oscillatory scheme (WENO) was introduced. Characteristic-based boundary conditions were incorporated to enable accurate representation of acoustic excitation (e.g. via a loudspeaker or siren) as well as enable precise evaluation of acoustic reflection and transmission coefficients. The new methodology was first validated against simple (1D and 2D) but well proven test cases for wave propagation and demonstrated low numerical diffusion/dispersion. The proper incorporation of Characteristic-based boundary conditions was validated by comparison against classical linear acoustic analysis of acoustic and entropy waves in quasi-1D variable area duct flows. The developed method was then applied to the prediction of experimental measurements of the acoustic absorption coefficient for a single round orifice flow. Excellent agreement with experimental data was obtained in both linear and non-linear regimes. Analysis of predicted flow fields both with and without bias flow showed that non-linear acoustic behavior occurred when flow reversal begins inside the orifice. Finally, the method was applied to study acoustic excitation of combustor external aerodynamics using a pre-diffuser/dump diffuser geometry previously studied experimentally at Loughborough University and showed the significance of boundary conditions and shear layer instability to produce a sustained pressure fluctuation in the external aerodynamics.

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.

In hydraulic pumps, typically in axial piston pumps, reduction of pressure and flow ripples was attempted by providing relief grooves and pre-compression for noise reduction. Pre-compression is normally achieved by using the dead space between pump ports in the valve plate. Also valve plate profile modification is required, if system operating conditions such as pump output pressure and flowrate change, to maintain optimum operating conditions for reduced pressure/flow ripple. An earlier simulation study confirmed effectiveness of varying dead centre position to reduce pressure and flow ripples. A specifically designed mechanism, outlined in the earlier work, achieves this goal by varying the dead centre position of the pump swash plate. This study reports on the findings of the effect of varying dead centre position and groove configurations on forces and moments acting on the swash plate for various operating conditions. The simulation model cited in the earlier work was used in this study. This information is vital for the design of an actuating mechanism to vary dead centre position of a pump valve plate. These simulations were run using MATLAB/Simulink and S-functions. Results of this study are promising.

Les garnitures mécaniques sont utilisées dans de multiples applications pour réaliser l'étanchéité autour d'arbres en rotation. Ces composants peuvent fonctionner efficacement pendant plusieurs années en conditions stables, mais leur durée de vie est significativement réduite lorsque les conditions varient. L'objectif de ce travail de recherche est de développer et d’utiliser un banc d'essais et code de calcul pour étudier l'impact de pulsations de pression, d’inversions de pression et du chargement dynamique résultant sur les performances de garnitures mécaniques ayant des faces mésalignées et présentant des défauts de planéité.Le solveur fluide d'un modèle numérique de garnitures mécaniques a été étendu aux conditions transitoires. Un module résolvant la dynamique des forces et des moments a été ajouté afin de prédire le déplacement axial et les déplacements angulaires de la face montée de manière flexible. Afin de caractériser les performances de garnitures, un banc d'essais générant des pulses de pression a été instrumenté et des méthodes de mesure de perte de volume d'huile et d'entrée d'eau mises en place.Des garnitures mécaniques à faces parallèles puis mésalignées, fonctionnant sous pulsations et inversions de pression, ont été testées expérimentalement et simulées. Seules de très faibles augmentations d'eau dans l'huile ont été observées, sans augmentation au cours du temps, et sans fuite d'huile mesurable. Les faibles valeurs d'entrées d'eau sont dues à la faible épaisseur de film et à la courte durée des inversions de pression. Une garniture mécanique expérimentale à fort défaut de planéité a aussi été testée. Contrairement aux autres paramètres, le défaut de planéité semble augmenter significativement la fuite et promouvoir les entrées d'eau et pourrait ainsi être à l'origine de certaines défaillances
Face seals are mechanical devices used to seal rotating shafts in numerous applications. While they can operate efficiently under steady conditions for years, they tend to fail prematurely when operating in severe, or rapidly varying conditions. The focus of this research work is the development and use of an experimental and a numerical method to investigate the impact of pressure pulses, pressure inversions and induced dynamic loading on the performance of mechanical face seals exhibiting face misalignment and waviness.The fluid solver of a state-of-the art face seal numerical model was extended to transient conditions and a module solving the dynamics for the axial and angular degrees of freedom of the flexibly-mounted stator added. A system-level experimental setup generating pressure pulses was instrumented and methods to characterise face seal performance in terms of oil volume loss and ingression of water outer-fluid selected and implemented.Face seals, with flat and misaligned faces, operating under pressure pulses and pressure inversions were experimentally tested and simulated. They show only slight increase of water in the oil, no increase over time, and no measurable oil leakage. The low water ingression is due to low film thickness combined with the short duration of pressure inversions. An exploratory face seal of high waviness was also experimentally tested. Contrary to the other parameters, the waviness appears to significantly increase the leakage and promote water ingression and could thus be at the origin of some seal failures

In high-pressure centrifugal compressors, honeycomb seals are often used as replacements for labyrinth seals to enhance dynamic stability. A concern exists with the loss of this enhanced stability if the honeycomb cavities become clogged with debris over time. So, as a first objective, static and dynamic tests were conducted on a constant-clearance honeycomb and a constant-clearance smooth-bore seal under three inlet preswirl conditions to determine the effects of inlet preswirl. The resulting leakage flowrate and dynamic parameters, effective stiffness and damping of the seal, were measured for each seal and then compared, with the smooth-bore seal representing the honeycomb seal with completely clogged cells. The second objective was to evaluate a two-control volume theory by Kleynhans and Childs with the measured data under the influence of preswirl. Both seals have a 114.7mm bore with a radial clearance of 0.2mm from the test rotor. The honeycomb seal has a cell width of 0.79mm and cell depth of 3.2mm. The target test matrix for each preswirl setting consisted of three exit-to-inlet pressure ratios of 15%, 35%, and 50%, and three rotor speeds out to 20,200 rpm. The target inlet air pressure was 70 bar-a. Experimental results show that, for a clean honeycomb seal, preswirl has little effect on effective stiffness, Keff*, and decreases effective damping, Ceff*, by about 20% at the high inlet preswirl ratio (~0.6). However, comparing smooth and honeycomb seal results at higher inlet preswirl shows a potential reduction in Keff* by up to 68%, and a large drop and shift in positive Ceff* values, which could cause an instability in the lower frequency range. Measured leakage shows a potential increase of about 80%, regardless of test conditions. A swirl brake at the seal entrance would fix this loss in stability by significantly reducing inlet preswirl. The two-control-volume theory model by Kleynhans and Childs seems to follow the frequency-dependent experimental data well for the honeycomb seal. Theory predicts conservatively (under-predicts) for stability parameters such as k* and Ceff* and for leakage. Predictions for K and Keff may possibly be improved with better measured friction factor coefficients for each seal.

This master’s thesis deals with the draft tube and its optimization for various operating conditions. The research investigates the theoretical description and function of the draft tube and explains known methods of suppressing pressure pulsation so far. In the computational part, the author proposes a new method and designs optimal geometry of adjustable installations (ribs) for the draft tube. Finally, the comparison with the default geometry without ribs is performed.

This master's thesis deals with CFD simulation of vortex rope in the elbow draft tube for overload operation of Francis turbine. The main objective of the thesis is to compare results of the CFD simulations of the original elbow draft tube with a derived straight cone draft tube considering volume and the shape of the cavitation region and dynamic flow characteristic. Results of the 3D simulations are also compared with axi-symmetric simulations, which reduce demands for computing time and power.

The effects of a composite overwrapped gun barrel with viscoelastic damping layers are investigated. Interlaminar stresses and constrained layer damping effects are described. The Modal Strain Energy method is developed for measuring the extent to which the barrel is damped. The equations of motion used in the finite element analysis are derived. The transient solution process is outlined. Decisions for selected parameters are discussed. The results of the finite element analyses are presented using the program written in FORTRAN. The static solution is solved with a constant internal pressure resulting in a calculated loss factor from the Modal Strain Energy Method. The transient solution is solved using the Newmark-Beta method and a variable internal pressure. The analyses conclude that strategically placed viscoelastic layers dissipate strain energy more effectively than a thick single viscoelastic layer. The optimal angle for maximizing the coefficient of mutual influence in a composite cylinder is not necessarily the optimal angle when viscoelastic layers are introduced between layers.

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.

This master’s thesis deals with CFD simulation of spiral vortex structure in the diffuser of swirl generator. The objective of the thesis is to evaluate influence of change in diffuser opening angle on frequency and amplitude of pressure pulsation. All results are compared in charts which shows courses of frequencies and amplitudes along the diffuser. Two different turbulence models and several types of mesh were tested

Oil lubrication film plays an important role in analysis of dynamic behavior of the internal gear motors and pumps. During operation, the oil film is considered as the spring and damping system. Therefore, calculation of the dynamic stiffness and damping coefficients is necessary to build the mathematical model for studying of dynamic problem. In order to calculate these coefficients, the dynamic pressure and perturbing pressure distribution must be determined firstly. In this paper, the infinitesimal perturbation method (IFP) is used to calculate the dynamic pressure distribution. Based on that the dynamic stiffness and damping coefficients can be computed. The calculation results point out that the dynamic stiffness and damping coefficients are much dependent on the eccentricity ratio.

The master thesis deals with the possibility of using dynamic damper in hydrodynamics. Specifically, the assessment of the impact of dynamic damper on the dynamic stability of the fluid system when the system exhibited unstable behaviour prior to damper installation due to self-excited vibration. In the thesis is presented the algorithm for the calculation of pressure and flow pulsations based on the transfer matrix method, the transition matrices for different damper designs variants are derived. Using the algorithm, the effect of a damper placed in a stable and unstable fluid system is solved. The output of this work is software for solution of pressure and flow pulsations in the system with serially arranged hydrodynamic elements created in the MATLAB program.

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.

Les Stations de Transfert de l’Énergie par Pompage (STEP) munies de turbines-pompes réversibles de type Francis (TP) permettent de stocker et de restituer de grandes quantités d’énergie avec des rendements très élevés. Celles-ci apparaissent comme un moyen viable d’assurer la réactivité et la stabilité du réseau électrique vis-à-vis de l’augmentation croissante des sources d’énergie renouvelables intermittentes. Pour répondre aux nouveaux besoins en régulation du réseau électrique, la technologie actuelle des STEP doit être adaptée. Accroître la réactivité requiert d’optimiser les procédures de démarrage et d’arrêt des machines. Dans les quadrants turbine, turbine-frein et pompe inverse, les TP de haute chute ont des courbes caractéristiques présentant la forme d’un « S ». Cette forme particulière peut engendrer des coups de béliers lors des phases d’arrêts d’urgences, exposant les conduites à de sévères surpressions et dépressions. De plus, pour ces points de fonctionnement associés au « S » les écoulements sont fortement instationnaires et induisent des fluctuations de pression responsables de chargements dynamiques sur les parties mécaniques. Les objectifs de ce travail sont la modélisation et la compréhension des phénomènes hydrauliques complexes liés au « S ». Des simulations numériques instationnaires sont réalisées en utilisant le modèle de turbulence SAS-SST. Moins couteux que les modèles LES, ce modèle permet de résoudre d’une partie du spectre turbulent et ainsi de prendre en compte les principaux effets instationnaires. Trois configurations de turbine-pompe de même vitesse spécifique (nq=40) sont étudiées. Une seule (grande) ouverture de directrices est retenue pour chaque configuration. Les points de fonctionnement considérés couvrent une large gamme de conditions d’opération, allant du fonctionnement en régime continu (rendement élevé) jusqu’au débit nul, en passant par le point d’emballement. Les résultats des calculs sont comparés aux mesures expérimentales. La bonne corrélation entre valeurs numériques et expérimentales valide la pertinence du modèle numérique. Les analyses des performances de la machine et des fluctuations de pression permettent d’identifier les régions de l’écoulement associées aux principales instabilités. Enfin, les visualisations de l’écoulement couplées à une étude des mécanismes de dissipation de l’énergie mettent en évidence les principaux phénomènes à l’origine de la forme en « S » des courbes caractéristiques
Pumped Storage Plants (PSP) using reversible Francis pump-turbines can store large amounts of energy with high efficiency. They therefore appear as a cost-effective tool to provide stability to the energy production network against the intermittency of renewable energy sources. Nevertheless, start-up and shutdown procedures still need to be improved to increase the reactivity of the PSP. Reversible high head pump-turbines have characteristic curves that exhibit an S-Shape in the turbine, turbine-brake and reverse pump quadrants. This S-Shape may be responsible for surge transient phenomena in the case of an emergency shutdown (for large guide vane opening). Moreover, for operating point in the S-Shape region, the flow is highly unsteady and leads to a high level of pressure fluctuations and strong dynamic loadings on the mechanical parts. The objective of the current work is to perform a comprehensive study of the complex hydraulic phenomena linked with the S-Shape. Unsteady numerical computations are carried out using the turbulence model SAS-SST. Such a model can resolve part of the turbulent spectrum while maintaining affordable computational cost. It therefore offers an interesting alternative to more expensive LES computations. Three different configurations of pump-turbine with the same specific speed (nq=40) are investigated. Several operating conditions from optimal efficiency point to zero discharge condition for a given large guide vane opening are studied. Numerical results show good agreement with the experimental data. Accuracy of the numerical model is thus assessed. The investigations of the global performances of the pump-turbine and the pressure pulsations help to identify the region of the flow which are associated with the main instabilities. Finally, flow visualizations linked with the analysis of the mechanisms of energy dissipation reveal the major flow phenomena at the origin of the S-Shape

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.

o presente estudo teve por objetivo investigar a influência de duas diferentes resiliências de materiais de amortecimento e de dois tipos de cabedais de calçados esportivos na cinemática e cinética de membro inferior e na percepção do conforto durante a corrida. Também investigamos as possíveis relações entre o conforto percebido e as variáveis biomecânicas capturadas. Para tal, foram avaliados 42 corredores recreacionais adultos, com no mínimo de um ano de experiência em corrida de rua, com mínimo de dois treinos regulares por semana, e com volume de treino semanal superior a 5 km. Foram avaliadas quatro condições de calçados aleatorizadas para cada corredor (material de amortecimento de baixa resiliência e cabedal estruturado, material amortecimento de alta resiliência e cabedal estruturado, material de amortecimento de baixa resiliência e cabedal minimalista, e material amortecimento de alta resiliência e cabedal minimalista). Após avaliação antropométrica e postural do complexo tornozelo/pé, os corredores realizaram corridas em uma pista de 25 metros em laboratório. A avaliação biomecânica foi realizada usando seis câmeras infravermelhas (VICON T-40, Oxford, UK) a 300 Hz, sincronizadas a duas plataformas de força (AMTI BP-600600, Watertown, USA) para aquisição da força reação do solo a 1200 Hz, e palmilhas instrumentas com sensores capacitivos (Pedar X System, Novel, Munique, Alemanha) a 100 Hz. A percepção subjetiva de conforto em cada condição foi avaliada por meio de um questionário de conforto para calçados. As comparações estatísticas entre os calçados foram verificadas por meio de análises de variância (ANOVAs) para medidas repetidas, e correlação de Pearson para verificar as relações entre o conforto e as variáveis biomecânicas (a=O,05). Realizou-se uma análise de Machine Learning para capturar variáveis da série temporal completa das curvas de cinemática e cinética que discriminassem os calçados estudados. Construímos uma matriz de entrada nas dimensões 1080 x 1242 para a análise por Machine learning. Os resultados demonstram que há uma interação entre as condições de cabedal e material de amortecimento que faz com que as comparações de resiliência se comportem de forma distinta para cabedais minimalistas e para cabedais estruturados. Contrariamente ao esperado, para os calçados de cabedal estruturado, as resiliências não foram diferentes entre si, e para o cabedal minimalista, os corredores apresentaram impactos mais altos com o material de baixa resiliência. A estrutura de cabedal influenciou a absorção de impacto, onde o cabedal minimalista apresentou impactos mais altos que o cabedal estruturado. Sobre o conforto, a condição de cabedal minimalista e material de baixa resiliência obteve as piores notas em cinco de nove quesitos do questionário. Em alguns quesitos ele foi o pior avaliado dentre todas as demais condições (como no amortecimento do calcanhar e no conforto geral). O cabedal minimalista recebeu pior avaliação que os cabedais estrutura dos no quesito controle médio-lateral da avaliação de conforto. Observou-se que a correlação entre as variáveis biomecânicas e as variáveis de conforto considerando todos os calçados conjuntamente, apesar de apresentarem valores significativos para algumas associações, foram sempre correlações fracas, abaixo de 30%. Ao se analisar cada condição de calçado isoladamente, em algumas se observou correlação moderada entre as variáveis biomecânicas e o conforto (r >31%, p < O,05), o que não se verificou em outras condições de calçados. Cada calçado gera condições particulares que favorecem ou não a associação entre conforto e repostas biomecânicas. Sobre a análise de Machine Learning, a metodologia foi capaz de diferenciar com sucesso os dois materiais de resiliência diferentes utilizando 200 (16%) variáveis biomecânicas disponíveis com uma precisão de 84,8%, e os dois cabedais com uma precisão de 93,9%. A discriminação da resiliência da entressola resultou em níveis de acurácia mais baixos do que a discriminação dos cabedais de calçados. Em ambos os casos, no entanto, as forças de reação do solo estavam entre as 25 variáveis mais relevantes. As 200 variáveis mais relevantes que discriminaram as duas resiliências estavam distribuídas em curtas janelas de tempo, ao longo de toda série temporal da cinemática e força. Estas janelas corresponderam a padrões individuais de respostas biomecânicas, ou a um grupo de indivíduos que apresentaram as mesmas respostas biomecânicas frente aos diferentes materiais de amortecimento. Como conclusão, destacamos que o cabedal tem maior influência que o material de amortecimento quando se trata da biomecânica da corrida e conforto subjetivo. Nos cabedais estruturados, a resiliência do material da entressola não diferenciou a biomecânica da corrida. A resiliência do material de amortecimento causa efeitos importantes sobre o impacto do calcanhar (menores loading rate, frequência mediana, pico de pressão em retropé) durante a corrida em cabedais com pouca estrutura. Alterações biomecânicas devido à resiliência do material de amortecimento parecem ser dependentes do sujeito, enquanto as relacionadas à estrutura de cabedal parecem ser mais sujeito independente. Sugere-se ter cautela ao afirmar que um calçado mais confortável também gerará respostas positivas biomecânicas, pois as associações entre essas variáveis analisando todos os calçados conjuntamente foram sempre correlações fracas. As correlações moderadas e particulares de cada condição de calçado com determinadas variáveis de conforto nos levam a concluir que os materiais aplicados nos calçado favorecem mais ou menos a percepção de determinada característica de conforto
The aim of this study was to investiga te the influence of two cushioning materiais with different resiliencies and two types of uppers of sportive shoes on kinematics and kinetics of lower limb and on the subjective perception of comfort during running. We also investigated the potential relationship between the perceived comfort and biomechanical variables analyzed. For this purpose, 42 adult recreational runners were evaluated. lhey had at least one year of experience on running, minimum of two regular running workouts per week, and weekly training volume above 5 km. We evaluated four randomized shoes conditions for each athlete (Iow resilience cushioning material and structured upper, high resilience cushioning material and structured upper, low resilience cushioning material and minimalist upper, and high resilience cushioning material and minimalist upper). After anthropometric and postura I assessment of the foot/ankle complex, runners held trials on a 25 meters long indoor track. Biomechanical data were collected by six infrared cameras (VICON l-40, Oxford, UK) at 300 Hz, synchronized with two force platforms (AMll BP-600600, Watertown, USA) at 1200Hz, and in- shoe plantar pressure insoles (Pedar X System, Nove\" Munich, Germany) at 100 Hz. Subjective perception of comfort in each shoe condition was assessed by a questionnaire of footwear comfort. lhe statistical comparisons between the shoes were verified by analysis of variance (ANOVA) for repeated measures and Pearson\'s correlation to verify the relationship between comfort and biomechanical variables (a=0.05). We conducted a Machine Learning analysis to capture variables from the complete kinematics and kinetics time series, which would be able to discriminate the studied footwear. We build an input matrix in the dimensions of 1080 x 1242 for Machine Learning analysis. There was an interaction between the upper structure and the resilience of cushioning material that made comparisons between resiliencies to behave differently for minimal uppers and for structured uppers. Contrary to expectation, for structured uppers, resiliencies were not different from each other, and for the minimal upper, runners had higher impact with the low-resilience material. lhe upper structure influenced the absorption of impact, in which the minimalist upper presented higher impacts than the structured upper. About comfort, minimalist upper condition and low resilience materiais had the worst grades for five of nine questions of the questionnaire. In some questions it was the worst of ali conditions (such as for the comfort in the heel cushioning and overall comfort). lhe minimalist upper received worse assessment than the structured uppers in the question about the mediolateral control. It was observed that the correlation between biomechanical variables and comfort, considering ali shoe conditions together, despite having significant values for some correlations were weak correlations (r <30%, p <0.05). When each shoe condition is analyzed alone, some footwear conditions had moderate correlation between comfort and biomechanical variables (r >31%, p <0.05L although the same behavior was not observed in other shoe conditions. Each shoe represents a specific condition that favor or not the association between comfort and biomechanical responses. On Machine Learning analysis, the method was able to successfully distinguish between the two different resiliencies using 200 (16%) of available biomechanical variables with an accuracy of 84.8%, and between the 2 uppers with an accuracy of 93.9 %. Discrimination of the resiliencies resulted in lower levels of accuracy than the discrimination of shoe uppers. In both cases, however, the ground reaction forces were among the 25 most important features. The 200 most relevant features which discriminate the two resiliencies were distribuited in short time windows along the kinematic and force time series. These windows corresponded to individual biomechanical patterns, or patterns of a group of people with similar behavior. In conclusion, we emphasize that the upper has greater influence than the resilience of cushioning material when it is about biomechanics of running and subjective comfort of the shoes. In structured uppers, the biomechanics did not differenciate the resiliencies of the midsole materiais. The resilience of the cushioning material has important effects on the heel impact (Iower loading rate, median frequency, peak pressure in rearfoot) during running on shoes with little structure on the upper. Biomechanical changes due to the resilience of the cushioning material seems to be dependent on the subject, while related to the upper structure seems to be more independent of the subject. It is suggested to be cautious to affirm that more comfortable footwear will also let to positive biomechanical responses. That is because the correlations between these variables when analyzing ali the footwear together were always weak. Moderate and positive correlations of each shoe condition with some of comfort variables lead us to conclude that the materiais applied on each footwear favors more or less the comfort perception

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.

A series of lateral load tests were performed on a full-scale pile cap with three different backfill conditions, namely: with no backfill present, with densely compacted clean sand in place, and with loosely compacted clean sand in place. In addition to being displaced under a static loading, the pile cap was subjected to low frequency, small displacement loading cycles from load actuators and higher frequency, small displacement, dynamic loading cycles from an eccentric mass shaker. The passive earth pressure from the backfill was found to significantly increase the load capacity of the pile cap. At a displacement of about 46 mm, the loosely and densely compacted backfills increased the total resistance of the pile cap otherwise without backfill by 50% and 245%, respectively. The maximum passive earth pressure for the densely compacted backfill occurred at a displacement of approximately 50 mm, which corresponds to a displacement to pile cap height ratio of 0.03. Contrastingly passive earth pressure for the loosely compacted backfill occurred at a displacement of approximately 40 mm. Under low and high frequency cyclic loadings, the stiffness of the pile cap system increased with the presence of the backfill material. The loosely compacted backfill generally provided double the stiffness of the no backfill case. The densely compacted backfill generally provided double the stiffness of the loosely compacted sand, thus quadrupling the stiffness of the pile cap relative to the case with no backfill present. Under low frequency cyclic loadings, the damping ratio of the pile cap system decreased with cap displacement and with increasing stiffness of backfill material. After about 20 mm of pile cap displacement, the average damping ratio was about 18% with the looser backfill and about 24% for the denser backfill. Under higher frequency cyclic loadings, the damping ratio of the pile cap system was quite variable and appeared to vary with frequency. Damping ratios appear to peak in the vicinity of the natural frequency of the pile cap system for each backfill condition. On the whole, damping ratios tend to range between 10 and 30%, with an average of about 20% for the range of frequencies and displacement amplitudes occurring during the tests. The similar amount of damping for different ranges of frequency suggests that dynamic loadings do not appreciably increase the apparent resistance of the pile cap relative to slowly applied cyclic loadings.

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.

Pile groups are often used to provide support for structures. Capping a pile group further adds to the system's resistance due to the passive earth pressure from surrounding backfill. While ultimate passive earth pressure under static loading conditions can be readily calculated using several different theories, the effects of cyclic and dynamic loading on the passive earth pressure response are less understood. Data derived from the full-scale testing of a pile cap system with a densely compacted sand backfill under static, cyclic, and dynamic loadings was analyzed with particular focus on soil pressures measured directly using pressure plates. Based on the testing and analyses, it was observed that under slow, cyclic loading, the backfill stiffness was relatively constant. Under faster, dynamic loading, the observed backfill stiffness decreased in a relatively linear fashion. During cyclic and dynamic loading, the pile cap gradually developed a residual offset from its initial position, accompanied by a reduction in backfill force. While the pile cap and backfill appeared to move integrally during static and cyclic loadings, during dynamic loading the backfill exhibited out-of-phase movement relative to the pile cap. Observed losses in backfill contact force were associated with both cyclic softening and dynamic out-of-phase effects. Force losses due to dynamic loading increased with increasing frequency (which corresponded to larger displacements). Losses due to dynamic loading were offset somewhat by increases in peak force due to damping. The increase in contact force due to damping was observed to be relatively proportional to increasing frequency. When quantifying passive earth forces with cyclic/dynamic losses without damping, the Mononobe-Okabe (M-O) equation with a 0.75 or 0.8 multiplier applied to the peak ground acceleration can be used to obtain a reasonable estimate of the force. When including increases in resistance due to damping, a 0.6 multiplier can similarly be used.

The main objective of this Master´s thesis is the appropriate calculation proposal of pressure and discharge conditions in extensive ducts in unsteady flow. The calculation proposal was aimed at the conenction of two commercial programmes. Exacly the programme Ansis Fluent and Matlab, which deals with the connection of onedimensional (1D) calculation in Matlab and multidimensional (2D) calculation in Ansys Fluent programme. This Mastr’s thesis also deals with creation of the independent 1D model (Matlab, method of characteristic) and independent 2D model flow (Ansys Fluent, Inviscid model).

Die vollständige Ausnutzung des Leichtbaupotentials bei der Dimensionierung von mehrschichtigen endlosfaserverstärkten Strukturbauteilen erfordert die Bereitstellung von geeigneten Optimierungswerkzeugen, da bei der Auslegung eine große Anzahl von Entwurfsvariablen zu berücksichtigen sind. In dieser Arbeit werden Optimierungsalgorithmen und -strategien zur Lösung wissenschaftlicher Fragestellungen für industrielle Anwendungen bei der Konstruktion von entsprechenden Faserkunststoffverbunden entwickelt und bewertet. Um das breite Anwendungsspektrum aufzuzeigen, werden drei unterschiedliche repräsentative Problemstellungen bearbeitet. Dabei wird für Mehrschichtverbunde die Festigkeitsoptimierung hinsichtlich eines bruchtypbezogenen Versagenskriteriums vorgenommen, ein Dämpfungsmodell zur Materialcharakterisierung entworfen sowie eine bivalente Optimierungsstrategie zur Auslegung von gewickelten Hochdruckbehältern erstellt. Die Grundlage der entwickelten Methoden bilden dabei jeweils stochastische naturanaloge Optimierungsheuristiken, da die betrachteten Aufgabenstellungen nicht konvex sind und derartige Verfahren flexibel eingesetzt werden können
The full utilization of the light weight potential in the dimensioning of multilayer fiber reinforced composites requires suitable optimization tools, since a large number of design variables has to be taken into account. In this work, optimization algorithms and strategies for the solution of scientific questions for industrial applications are developed and evaluated in the design of corresponding fiber-plastic composites. In order to show the wide range of applications, three different representative topics have been chosen. It will carry out a strength optimization for multilayer composites with regard to a type-related failure criterion, devolop a damping model for material characterization and established a bivalent optimization strategy for the design of wound high-pressure vessels. The developed methods are based on stochastic natural-analog optimization heuristics, since the considered tasks are not convex and such methods can be used in a very flexible manner

Etude d'un amortisseur hydraulique de suspension automobile. Calcul de l'amortissement et des pertes de charge. Influence du piston et du clapet. L'ecoulement au niveau du clapet est assimile a un ecoulement radial visqueux. On etudie la loi de deformation du clapet (flexion d'un disque mince)

Práce se zabývá návrhem magnetoreologické (MR) vzpěry vibroizolačního systému (VIS) pro kosmický nosič. V rešeršní části jsou popsány vybrané VIS a vzpěry těchto systémů, které byly v kosmických nosičích využity v minulosti. Každá z těchto vzpěr obsahující kapalinu byla těsněna pomocí statických těsnění a pružných vlnovců vyrobených z oceli. Důkladněji byla analyzována vzpěra pasivního systému VIS s označením ELVIS, jehož konstrukce se stala inspirací pro tuto práci. Jedná se o tříparametrický systém, v němž je tlumič uložen na pružině, jejíž tuhost přibližně odpovídá objemové tuhosti vlnovců respektive jejímu průmětu do axiálního směru (pressure thrust stiffness). V práci je představena metodika pro stanovení “pressure thrust stiffness” na základě geometrie vlnovce a také uvedeny parametry vlnovce díky kterým je možné měnit poměr mezi axiální a “pressure thrust stiffness” vlnovce. Tento poměr ovlivňuje v dané koncepci vzpěry její dynamické chování a tím i chování celého VIS. Pro predikci dynamického chování vzpěry byl vytvořen multi-body model VIS založeného na Stewartově plošině a detailnější model jediné vzpěry. Simulace provedené v tomto modelu odhalily parametry, které mají vliv na výkonost tlumiče ve VIS: časová odezva a dynamický rozsah. Díky modelu byl určen rozsah těchto parametrů, ve kterých bude zaručena efektivní funkce vzpěry ve VIS, konkrétně: časová odezva: 0-5ms, dynamický rozsah: 5-10. Před finálním návrhem vzpěry byla sestrojena vzpěra experimentální vzpěra, jejíž parametry byly přesně naměřeny a využity pro verifikaci jednotlivých modelů. Poznatky získané během experimentů byly využity při návrhu finální vzpěry. Jeden z nejdůležitějších poznatků byla nutnost náhrady feritového magnetického obvodu s ohledem na jeho křehkost. Proto byl odvozen tvarový přístup k navrhování rychlých magnetických obvodů z oceli s využitím 3D tisku, který byl následně patentován. Navržená vzpěra obsahuje magnetoreologický ventil jehož odezva je predikována na 1.2 ms a dynamický rozsah 10. V závěru práce je představena metodika, díky které byla vzpěra navržena.

Gurtförderanlagen werden im Bergbau und anderen Industriezweigen zum Transport von Schüttgütern eingesetzt. Der Anlagenbetrieb ist mit Geräuschemissionen verbunden. Dies kann bei Kontrolle und Wartung eine erhöhte Lärmbelastung für betroffene Mitarbeiter hervorrufen. Im Umfeld von Wohnbebauungen oder schutzbedürftigen Objekten kann die Überschreitung von Immissionsrichtwerten zu einer zeitlichen Betriebseinschränkung der hocheffizienten Anlagen führen. Zur Lärmminderung an der Quelle oder deren Nähe erfordert dies technische Schallschutzmaßnahmen. Die Tragrollen im Obertrum der Gurtförderanlagen sind bei der akustischen Wirkung von entscheidender Bedeutung. Mit einem Prüfstand für Tragrollen ist deren Schallleistung bei unterschiedlichen Geschwindigkeiten bestimmbar. Die Ergebnisse lassen Rückschlüsse auf die mechanische Belastung und die Schallemission beim Betrieb in einer Förderanlage zu. Die Arbeit benennt die Ursachen der Geräuschemissionen beim Ablauf der Rollen und stellt diese in Verbindung mit den Eigenschaften der Oberfläche und der Außermittigkeit der Drehachse dar. Die Prüfung beider Parameter basiert auf einer Rundlaufmessung. Die gewonnenen winkelabhängigen Daten erlauben eine Berechnung der Exzentrizität der Drehachse und des Verlaufs der Kreisformabweichung auf dem Rollenmantel. Daraus abgeleitete Kennwerte dienen als Vorgaben zur Anpassung und Entwicklung von Herstellungsverfahren sowie zur gezielten Auswahl geräuscharmer Tragrollen für Gurtförderanlagen
Belt conveyor systems are used in mining operations and other industry sectors to transport bulk material. The plant operation is being linked to noise emissions. During inspections and maintenance this can cause an increased noise exposure for affected employees. In the environment of residential buildings or areas in need of protection the exceedance of immission guideline values can lead to a temporary operational limitation of these highly efficient plants. Noise abatement measures primarily at the source or in the vicinity are required to reduce noise immission. The idlers on the carrying belt side of the belt conveyor systems are of crucial importance to the acoustical properties. Their sound power level is determinable at different belt speeds with a test stand for idlers. The results allow conclusions about the mechanical stress and sound emissions during operation in a belt conveyor system. The thesis identifies the sources of noise during the roll process and places them in conjunction with the properties of the surface and the centre offset of the axis. The examination of these two parameters is based on a total indicator reading (TIR) measurement. The angle-dependent data obtained allow a calculation of the eccentricity of the axis and the curve of the circular deviation of the roller tubes. Therefrom derived characteristic values serve as specifications for the adaptation and development of manufacturing processes as well as for a careful selection of low noise idlers for belt conveyors

This thesis presents validation and application of advanced soil constitutive models in cases of seismic loading conditions. Firstly, results of three advanced soil constitutive models are compared with examples of shear stack experimental data for free field response in dry sand for shear and compression wave propagation. Higher harmonic generation in acceleration records, observed in experimental works, is shown to be possibly the result of soil nonlinearity and fast elastic unloading waves. This finding is shown to have high importance on structural response, real earthquake records and reliability of conventionally employed numerical tools. Finally, short study of free field response in saturated soil reveals similar findings on higher harmonic generation. Secondly, two advanced soil constitutive models are used, and their performance is assessed based on examples of experimental data on piles in dry sand in order to validate the ability of the constitutive models to simulate seismic soil-structure interaction. The validation includes various experimental configurations and input motions. The discussion on the results focuses on constitutive and numerical modelling aspects. Some improvements in the formulations of the models are suggested based on the detailed investigation. Finally, the application of one of the advanced soil constitutive models is shown in regard to temporary natural frequency wandering observed in structures subjected to earthquakes. Results show that pore pressure generated during seismic events causes changes in soil stiffness, thus affecting the natural frequency of the structure during and just after the seismic event. Parametric studies present how soil permeability, soil density, input motion or a type of structure may affect the structural natural frequency and time for its return to the initial value. In addition, a time history with an aftershock is analysed to investigate the difference in structural response during the earthquake and the aftershock.

Die vollständige Ausnutzung des Leichtbaupotentials bei der Dimensionierung von mehrschichtigen endlosfaserverstärkten Strukturbauteilen erfordert die Bereitstellung von geeigneten Optimierungswerkzeugen, da bei der Auslegung eine große Anzahl von Entwurfsvariablen zu berücksichtigen sind. In dieser Arbeit werden Optimierungsalgorithmen und -strategien zur Lösung wissenschaftlicher Fragestellungen für industrielle Anwendungen bei der Konstruktion von entsprechenden Faserkunststoffverbunden entwickelt und bewertet. Um das breite Anwendungsspektrum aufzuzeigen, werden drei unterschiedliche repräsentative Problemstellungen bearbeitet. Dabei wird für Mehrschichtverbunde die Festigkeitsoptimierung hinsichtlich eines bruchtypbezogenen Versagenskriteriums vorgenommen, ein Dämpfungsmodell zur Materialcharakterisierung entworfen sowie eine bivalente Optimierungsstrategie zur Auslegung von gewickelten Hochdruckbehältern erstellt. Die Grundlage der entwickelten Methoden bilden dabei jeweils stochastische naturanaloge Optimierungsheuristiken, da die betrachteten Aufgabenstellungen nicht konvex sind und derartige Verfahren flexibel eingesetzt werden können.
The full utilization of the light weight potential in the dimensioning of multilayer fiber reinforced composites requires suitable optimization tools, since a large number of design variables has to be taken into account. In this work, optimization algorithms and strategies for the solution of scientific questions for industrial applications are developed and evaluated in the design of corresponding fiber-plastic composites. In order to show the wide range of applications, three different representative topics have been chosen. It will carry out a strength optimization for multilayer composites with regard to a type-related failure criterion, devolop a damping model for material characterization and established a bivalent optimization strategy for the design of wound high-pressure vessels. The developed methods are based on stochastic natural-analog optimization heuristics, since the considered tasks are not convex and such methods can be used in a very flexible manner.

Due to the increase of rotor size in horizontal axis wind turbine (HAWT) during the past 25 years in order to achieve higher power output, all wind turbine components and blades in particular, have to withstand higher structural loads. This upscalingproblem could be solved by applying technologies capable of reducing aerodynamic loads the rotor has to withstand, either with passive or active control solutions. These control devices and techniques can reduce the fatigue load upon the blades up to 40% and therefore less maintenance is needed, resulting in an important money savings for the wind farm manager. This project consists in a study of load control techniques for offshore wind turbines from an aerodynamic and aeroelastic point ofview, with the aim to assess a cost effective, robust and reliable solution which could operate maintenance free in quite hostile environments. The first part of this study involves 2D and 3D aerodynamic and aeroelastic simulations to validate the computational model with experimental data and to analyze the interaction between the fluid and the structure. The second part of this study is an assessment of the unsteady aerodynamic loads produced by a wind gust over the blades and to verify how a trailing edge flap would influence the aerodynamic control parameters for the selected wind turbine blade.
På grund av ökningen av rotorstorleken hos horisontella vindturbiner (HAWT) under de senaste 25 åren, en design som har uppstod för att uppnå högre effekt, måste alla vindkraftkomponenter och blad stå emot högre strukturella belastningar. Detta uppskalningsproblem kan lösas genom att använda metoder som kan minska aerodynamiska belastningar som rotorn måste tåla, antingen med passiva eller aktiva styrlösningar. Dessa kontrollanordningar och tekniker kan minska utmattningsbelastningen på bladen med upp till 40 % och därför behövs mindre underhåll, vilket resulterar i viktiga besparingar för vindkraftsägaren. Detta projekt består av en studie av lastkontrolltekniker för havsbaserade vindkraftverk ur en aerodynamisk och aeroelastisk synvinkel, i syfte att bedöma en kostnadseffektiv, robust och pålitlig lösning som kan fungera underhållsfri i tuffa miljöer. Den första delen av denna studie involverar 2D- och 3D-aerodynamiska och aeroelastiska simuleringar för att validera beräkningsmodellen med experimentella data och för att analysera interaktionen mellan fluiden och strukturen. Den andra delen av denna studie är en bedömning av de ojämna aerodynamiska belastningarna som produceras av ett vindkast över bladen och för att verifiera hur en bakkantklaff skulle påverka de aerodynamiska styrparametrarna för det valda vindturbinbladet.

碩士
國立清華大學
電子工程研究所
106
The purpose of this paper is to investigate the application of the squeeze-film damping effect for barometric pressure sensing. Unlike traditional pressure sensors, a sealed cavity is not required for operation of this type of sensors; therefore the fabrication process can be simplified. The rapid movement between the two plates causes an elastic damping effect between the air. 　　The sensors are fabricated in the TSMC 2P4M 0.35 μm CMOS process. The resonant microstructure utilizes silicon as the proof mass and metallization layers as the electrodes for capacitive driving and sensing, with sensing circuitry monolithically integrated on a single chip. Signal modulation is used to overcome the significant coupling effect observed during the experiment. The total area of the chip is 2.8 mm × 2.8 mm. The fabrication starts with deep silicon etch from the backside, followed by front-side metal wet etch, deep silicon etch and isotropic XeF2 silicon etch to release the structures. The desired structural thickness is 40 μm. Five different pressure sensors with different plate area and elastic coefficient are designed. Capacitively sensed resonance changes with pressure are compared with the simulation results. The design with an area of 200 μm × 200 μm has a simulated sensitivity of 1.23 Hz/Pa. The improved sensitivity is owing to the use of a small plate spacing of 0.64 μm. The measured sensitivity is 0.78 Hz/Pa, which is attributed to the increased structural thickness up to 60 m.

This thesis reports the results of a twofold study on the recently proposed phenomenon of &lsquo
stellar pulsations&rsquo
in young brown dwarfs by the seminal study of Palla and Baraffe (2005) (PB05, thereafter). The PB05 study presents results of a non-adiabatic linear stability analysis showing that young brown dwarfs should become pulsationally unstable during the deuterium burning phase of their evolution.

碩士
國立清華大學
電子工程研究所
105
In this thesis, we discuss the use of squeeze-film damping effect for pressure sensing. In the field of microelectromechanics system(MEMS), this effect has been extensively studied, but mostly focused on the non-ideal effect it causes on dynamic structures. Recently, the concept of applying this effect to atmospheric pressure sensing has been proposed. In this work, 9 pressure sensors of 40μm in thickness are designed in a 4mm×4mm chip, which is fabricated by the TSMC MEMS shuttle process. The sensor chip is integrated with a piezoelectric actuator and the corresponding sensing circuit on a printed-circuit board(PCB). The PCB is placed in a pressure controlled chamber for testing. Combined with piezoelectric driving and capacitive sensing mechanism, the resonant frequency shift is comparable to the simulations. The sensitivity of an 800μm×800μm structure is 0.945 Hz/Pa.