Les rotors sont excités non seulement par le balourd tournant mais aussi par les différents mouvements de leur support : turbocompresseurs de véhicules, turbomoteurs aéronautiques, pompes à vide portées en sont des exemples industriels. Ainsi la conception de rotors robustes capables de bien fonctionner sous de telles conditions (excitations extrêmes) est nécessaire pour éviter des instabilités, source de défaillance catastrophique. Le présent travail a pour objectif de prévoir le comportement dynamique d’un rotor embarqué monté sur des paliers rigides ou élastiques hydrodynamiques et soumis à des excitations du support rigide. Les énergies cinétiques et de déformation ainsi que le travail virtuel des composants d’un rotor flexible tournant sont calculés. Le modèle proposé de rotor embarqué est basé sur les éléments finis de poutre de TIMOSHENKO. Il contient les effets relatifs à l’inertie de rotation des sections droites, à l’inertie gyroscopique, à la déformation de cisaillement d’arbre et à la dissymétrie géométrique de l’arbre et/ou du disque rigide et considère six types de mouvements déterministes (rotations et translations) du support. Suivant le type d’analyse utilisé pour le palier, les forces de rappel hydrodynamiques agissant sur l’arbre et calculées avec l’équation de REYNOLDS sont linéaires/non linéaires. L’utilisation des équations de LAGRANGE fournit les équations différentielles linéaires/non linéaires du mouvement du rotor embarqué en flexion par rapport au support mobile supposé rigide, qui représente un système de coordonnées non inertiel. Les équations du mouvement contiennent des termes paramétriques périodiques en raison de la dissymétrie géométrique du rotor et des termes paramétrique variables dans le temps en raison des rotations du support. Ces termes paramétriques sont considérés comme des sources d’excitation intérieure et conduisent à une instabilité dynamique latérale. Dans les applications numériques proposées, trois configurations de rotor embarqué sont analysées. Tout d’abord, un rotor symétrique monté sur des paliers rigides est soumis à un balourd combiné avec des mouvements de rotation constante et de translation sinusoïdale du support. Ensuite, un rotor avec une dissymétrie géométrique du disque monté sur des paliers rigides est excité par l’effet de balourd et par des mouvements combinés de rotation constante et de translation sinusoïdale du support. Enfin, un rotor symétrique monté sur des paliers hydrodynamiques est soumis au balourd et aux excitations sinusoïdales de rotation ou de translation du support. / Rotors are excited not only by the rotating mass unbalance but also by the different motions of their support: vehicle turbochargers, aircraft turbo-engines, carried vacuum pumps, are different industrial applications. Thus the design of robust rotors able to run well under such conditions (extreme excitations) and to avoid catastrophic failure is required. The present work aims to predict the dynamic behavior of an on-board rotor mounted on rigid or elastic hydrodynamic journal bearings and subjected to rigid support excitations. The kinetic and strain energies as well as the virtual work of the rotating flexible rotor components are computed. The proposed on-board rotor model is based on TIMOSHENKO beam finite elements. It includes the effects relative to the rotating inertia, the gyroscopic inertia, the shear deformation of shaft as well as the geometric asymmetry of shaft and/or rigid disk and considers six types of deterministic motions (rotations and translations) of the support. Depending on the type of analysis used for the bearing, the restoring fluid film forces acting on the shaft and computed with the REYNOLDS equation are linear/non-linear. The use of LAGRANGE’s equations yields the linear/non-linear differential equations of vibratory motion of the on-board rotor in bending with respect to the moving rigid support which represents a non-inertial reference frame. The equations of motion contain periodic parametric coefficients because of the geometric asymmetry of the rotor and time-varying parametric coefficients because of the support rotations. These parametric coefficients are considered as sources of internal excitation and can lead to lateral dynamic instability. In the proposed numerical application examples, three rotor configurations are studied. Firstly, a symmetric rotor mounted on rigid bearings is subjected to rotating mass unbalance combined with constant rotation and sinusoidal translation of the support. Secondly, a rotor with geometric asymmetry due to the disk mounted on rigid bearings is excited by the mass unbalance effect and by the combination of a constant rotation and a sinusoidal translation of the support. Thirdly, a symmetric rotor mounted on linearized/non-linear hydrodynamic bearings is subjected to the excitation due to the mass unbalance and to the sinusoidal rotational or translational excitations of the support.

Dans le contexte actuel, l'open-rotor contrarotatif connaît un regain d'intérêt. Cependant, en l'absence de carter extérieur, la prédiction des effets d'installation devient une problématique primordiale du cycle de conception. L'objectif de ces travaux de thèse est de construire une méthode de calcul qui permette à la fois de rendre compte de l'impact du bloc moteur sur la traînée de l'avion et de l'impact de l'installation sur les performances aérodynamiques des hélices. Suite à une étude bibliographique, nous nous sommes orientés vers le couplage des codes ligne portante LPC2 et RANS elsA, développés à l'Onera. La méthode de couplage se base sur la condition de disque d'action et est itérative afin de rendre compte de l'interaction.Dans un second temps, des résultats de calculs instationnaires et d'essais en soufflerie ont été comparés aux résultats fournis par le couplage afin de confirmer que ce dernier rendait bien compte des performances aérodynamiques du moteur en configuration installée. Afin de valider sur un large domaine de calcul, plusieurs configurations ont été utilisées, prenant en compte différentes installations, différentes hélices et plusieurs points de vol.Enfin, nous avons proposé une amélioration de la condition de disque d'action par une modélisation de la turbulence représentant l'impact du passage des hélices sur l'écoulement. En effet, en l'état actuel, cette condition n'est pas en mesure de retranscrire l'impact des hélices sur la turbulence, en particulier sur l'augmentation du taux de turbulence. C'est pourquoi une formulation originale d'un modèle de turbulence, basée sur les travaux de Mr Benay, a été proposée. / The counter rotating open rotor entered a period of renewed interest because of the current circumstances. However, due to the absence of outer casing, predicting the installation's effects became an essential issue of the design process. The objective of this thesis is to elaborate a calculation method able to give the impact of the engine on the aircraft drag as well as the installation impact on the propellers aerodynamic performances. As a result of a literature review, we headed for the coupling of the LPC2 lifting-line code and elsA RANS code, developed by the Onera. The coupling method is based on the actuator disc condition and was made iterative in order to take the interaction into account.In a second phase, results from unsteady simulations and wind tunnel experiments were compared to the coupling results so as to confirm that the later was able to produce the engine's aerodynamic performances under the influence of the installation. In order to validate the coupling on a wide computational domain, multiple configurations were used, taking different installations into account, with different propellers and multiple flight conditions.Finally, an improvement of the actuator disc condition was proposed through a turbulence modeling showing the impact of the blades passages on the flow. Indeed, the actuator disc condition is currently unable to faithfully transpose the propellers impact on the turbulence, especially on the turbulence rate increase. Therefore, an original formulation of a turbulence model was given, based on the works of Mr. Benay.

No description available.

Conventional rotating machine vibration monitoring techniques are based on the assumption that changes in the measured structural response are caused by deterioration in the condition of the rotating machine. However, due to variations of the rotational speed, the measured signal may be non-stationary and difficult to interpret. For this reason, the order tracking technique is introduced. One of main advantages of order tracking over traditional vibration monitoring lies in its ability to clearly identify non-stationary vibration data and to a large extent exclude the influences of varying rotational speed. In recent years, different order tracking techniques have been developed. Each of these has their own pros and cons in analyzing rotating machinery vibration signals. In this research, three existing order tracking techniques are extensively investigated and combined to further explore their abilities in the context of condition monitoring. Firstly, computed order tracking is examined. This allows non-stationary effects due to the variation of rotational speed to be largely excluded. However, this technique was developed to deal with the entire raw signal and therefore looses the ability to focus on each individual order of interest. Secondly, Vold-Kalman filter order tracking is considered. It is widely reported that this technique overcomes many of the limitations of other order tracking methods and extracts order signals into the time domain. However because of the adaptive nature of the Vold-Kalman filter, the non-stationary effects due to the rotational speed will remain in the extracted order waveform, which is not ideal for conventional signal processing methods such as Fourier analysis. Yet, the strict mathematical filter (the Vold-Kalman filter is based upon two rigorous mathematical equations, namely the data equation and the structural equation, to realize the filter) gives this technique an excellent ability to focus on the orders of interest. Thirdly, the empirical mode decomposition method is studied. In the literature, this technique is claimed to be an effective diagnostic tool for various kinds of applications including diagnosis of rotating machinery faults. Its unique empirical way of extracting non-stationary and non-linear signals allows it to capture machine fault information which is intractable by other order tracking methods. But since there is no precise mathematical definition for an intrinsic mode function in empirical mode decomposition and – as far as could be ascertained – no published assessment of the relationship between an order and an intrinsic mode function, this technique has not been properly considered by analysts in terms of order tracking. As a result, its abilities have not really been explored in the context of order related vibrations in rotating machinery. In this research, the relationship between an order and an intrinsic mode function is discussed and it is treated as a special kind of order tracking method. In stead of focusing individually on each order tracking technique, the current work synthesizes different order tracking techniques. Through combination, exchange and reconciliation of ideas between these order tracking techniques, three improved order tracking techniques are developed for the purpose of enhancing order tracking analysis in condition monitoring. The techniques are Vold-Kalman filter and computed order tracking (VKC-OT), intrinsic mode function and Vold-Kalman filter order tracking (IVK-OT) and intrinsic cycle re-sampling (ICR). Indeed, these improved approaches contribute to current order tracking practice, by providing new order tracking methods with new capabilities for condition monitoring of systems which are intractable by traditional order tracking methods, or which enhances results obtained by these traditional methods. The work commences with a discussion of the inter-relationship between the order tracking methods which are considered in the thesis, and exposition of the scope of the work and an explanation of the way these independent order tracking techniques are integrated in the thesis. To demonstrate the abilities of the improved order tracking techniques, two simulation models are established. One is a simple single-degree-of-freedom (SDOF) rotor model with which VKC-OT and IVK-OT techniques are demonstrated. The other is a simplified gear mesh model through which the effectiveness of the ICR technique is proved. Finally two experimental set-ups in the Sasol Laboratory for Structural Mechanics at the University of Pretoria are used for demonstrating the improved approaches for real rotating machine signals. One test rig was established to monitor an automotive alternator driven by a variable speed motor. A stator winding inter-turn short was artificially introduced. Advantages of the VKC-OT technique are presented and features clear and clean order components under non-stationary conditions. The diagnostic ability of the IVK-OT technique of further decomposing an intrinsic mode function is also demonstrated via signals from this test rig, so that order signals and vibrations that modulate orders in IMFs can be separated and used for condition monitoring purposes. The second experimental test rig is a transmission gearbox. Artificially damaged gear teeth were introduced. The ICR technique provides a practical alternative tool for fault diagnosis. It proves to be effective in diagnosing damaged gear teeth. / Thesis (PhD)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

No description available.

Swirling flows abound in nature and numerous engineering applications. Under conditions which are not completely understood, the swirling cores could undergo a sudden enlargement of their vortex core, leading to a ’vortex breakdown’. The physics of vortex breakdown and strategies to control it have been active areas of research for nearly half a century. There are many competing theories of vortex breakdown in the literature; broadly, these are surmised on similarities to flow separation, hydrodynamic instability or transition from a supercritical to a subcritical state. However, a rational criterion for vortex breakdown continues to be elusive. One of the most well known criteria in the literature is the one due to Brown and Lopez (1990) based on an inviscid vortex dynamics model which suggests that the helix angle of the velocity vector should enclose the helix angle of the vorticity vector. However it appears that this only suggests that the stream surface would diverge and not necessarily constitute a condition for breakdown. In this work, we propose a new criterion based on helicity (scalar product of velocity and vorticity vectors) for characterizing breakdown since it has fundamental topological interpretations relating to change in linkages of vortex lines. In particular, it is suggested that the breakdown location corresponds to the location where helicity becomes zero. We study the problem of vortex breakdown in a cylindrical container with a rotating top lid in order to clarify and elucidate our hypothesis. We present results from Direct Numerical Simulation of this problem for three different Reynolds numbers and evaluate the utility of our proposed helicity criterion. Our studies indicate that helicity is indeed a better choice for characterizing vortex breakdown.

This master thesis deals with the vibration diagnostics of machine vibrations during unit tests in industrial company Siemens Electric Machines s.r.o Drásov. In the master thesis is elaborated a design of the diagnostic system which contains selected methods of vibration diagnostics, methology, procedure of measurement and evaluation of measured values. The part of master thesis is also a practical example of measurement on which the mentioned system is tested.

This diploma thesis deals with the simulation of various operating situations in the network with many non-rotating power sources, especially focusing on frequency stability. Non-rotating power source is any source that delivers its power to the grid via power electronics. The first part of the thesis describes power system of the Czech Republic and its future development. In the next section, there is short description of today's most common non-rotating power sources. The third part deals with power regulation of the frequency in the grid. The following part describes the models of electrical circuit created for use in PSCAD simulations. The penultimate part describes simulations performed on a model of the network with many non-rotating power sources, which also includes rotating sources. The last part describes simulations performed on a model of the network that is composed of non-rotating power sources only.

This diploma thesis serves as a constructional study of an axial pump with a tandem arrangement of impellers. It may also be perceived as proposal of possible constructional variants that could be used as cardiac replacements. The thesis offers several conceptual variants, while the selected ones are elaborated in detail. Drawing documentation and 3D models are included in the attachment. The components were dimensioned according to the parameters necessary for proper heart function.

The master thesis deals with the influence of a local change of temperature due to advection from disc brake to axial velocity field close to the rotating wheel of a car. The second goal is to set parameters applicable to various wheel discs and study of the influence of these parameters to aerodynamical properties of car and thermodynamical properties of the disc brake. The thesis is numerically executed in StarCCM+. The first part focuses on theoretical background about the numerical solution and current status of research. There are described disc parameters, geometry input and solver settings in the second part. The final part deals with a comparison of velocity fields for isothermal and thermodynamical model and evaluates the influence of parameters to velocity field, aerodynamical drag and thermodynamical performance of the brake.