Cette thèse présente l’étude analytique et expérimentale d’un système de compression axial constitue d’un compresseur, d’un plenum et d’une vanne de régulation du débit. Fondée sur le modèle de Moore-Greitzer, une approche analytique est utilisée par la suite pour interpréter les données expérimentales. Les analyses linéaires et non linéaires sont présentées, ainsi que les résultats obtenus par intégration numérique des équations du modèle non linéaire complet. Un modèle théorique simple pour les modes acoustiques observes est aussi présente. Dans les expériences, les mesures de pression ont été réalisées pour différents taux de rotation et différents vannages. Ceci a permis la détermination de l’augmentation de pression au travers du compresseur et du débit en utilisant un Venturi, ceux qui fournissent la courbe de fonctionnement du compresseur. Les fluctuations de pression sont mesurées par quatre microphones places en amont du compresseur. Nous n’avons pas observé de pompage, mais un décrochage tournant s’est produit quand le système était suffisamment vanne. Avant ceci, des fluctuations correspondant aux modes acoustiques de la conduite ont été trouvées. Au début du décrochage, une cellule de décrochage tournante d’amplitude croissante a été observée. Cependant, la cellule a rapidement éclaté, remplacée par des fluctuations aléatoires. Ainsi, pour le système de compression considéré, la situation de décrochage est mieux décrite comme étant aléatoire plutôt que rotative. Le traitement du signal (spectres en fréquence ainsi que les autocorrélations et corrélations croisées) a permis d’analyser les fluctuations de pression des modes acoustiques et du décrochage développé. Les modes acoustiques montrent des pics spectraux proches des valeurs prédites par la théorie. En présence de décrochage, le spectre est à large bande, et contient un pic de fréquence basse (∼20 Hz) suivi d’une queue s’étendant jusqu’à 1 kHz, bien au-dessus de la fréquence de rotation du rotor (∼150 Hz). Il apparait une gamme fréquentielle située entre le pic à basse fréquence et la chute à haute fréquence, dans laquelle le spectre évolue en loi de puissance. Les autocorrélations et corrélations croisées entre les différents microphones montrent des oscillations à ∼20 Hz. En appliquant un filtre passe-bas aux données, les fonctions de corrélations croisées des signaux filtres des différents microphones suggèrent l’existence d’une cellule rotative qui effectue une rotation complète en ∼0.05 s. Ceci pourrait expliquer le pic spectral a ∼20 Hz et les oscillations des fonctions de corrélation. De ce fait, les fluctuations de pression apparaissent comme contenant une forte composante aléatoire à haute fréquence, et une cellule rotative. La décorrelation du signal filtre quand la séparation en temps augmente indique que la cellule elle-même a un caractère aléatoire, plutôt qu’une forme et une vitesse rotative fixes comme dans une cellule de décrochage classique. / This thesis presents an analytical and experimental study of an axial compression system consisting of a compressor, plenum and throttle. The analysis is based on the Moore-Greitzer model, the results being later employed to interpret the experimental ones. Linear and weakly nonlinear analyses are presented, as are some results obtained by numerical integration of the fully nonlinear model equations. A simple theoretical model of the experimentally observed acoustic modes is also presented. In the experiments, pressure measurements were carried out for different rotation rates and throttle settings. This allowed the determination of the pressure rise across the compressor and the flow rate using a Venturi, yielding the compressor characteristic function. Pressure fluctuations were measured using four microphones placed upstream of the compressor. We did not observe surge, but rotating stall occurred when the system was sufficiently throttled. Prior to stall, fluctuations corresponding to acoustic duct modes were found. At stall onset, a rotating stall cell of growing amplitude was observed. However, the cell rapidly broke down and gave way to random fluctuations. Thus, for the given compression system, developed stall is perhaps better described as random, rather than rotating. Signal processing (frequency spectra, as well as auto- and cross-correlations) was used to analyse the pressure fluctuations of the acoustic modes and developed stall. The acoustic modes give spectral peaks located close to the expected theoretical values. In the presence of stall, the spectrum is broadband, having a low frequency (∼20 Hz) peak followed by a tail which extends up to ∼1 kHz, well above the rotation frequency (∼150 Hz) of the rotor. There appears to be a frequency range between the low-frequency peak and the high-frequency fall-off in which the spectrum approximates a power law. The autocorrelations and cross-correlations between different microphones show ∼20 Hz oscillations. Low pass filtering the data, the cross-correlation functions of the filtered signals of different microphones suggest a rotating cell which takes ∼0.05 s for a complete rotation. This could explain the ∼20 Hz spectral peak and oscillations of the correlation functions. Thus, the pressure fluctuations appear to consist of a strong high-frequency, random component and a rotating cell. Decorrelation of the filtered signal as separation time increases indicates that, rather than maintaining form and rotational velocity like a classical stall cell, the cell itself exhibits randomness.

Note:

The Karakoram Axial Batholith in N. Pakistan records the magmatic development of the Eurasian continental margin since the late Jurassic. Magmatism prior to the collision of India with Eurasia at c.45Ma is represented by subduction-related, calc-alkaline granodiorite plutonism. The chemical variation within these plutons is caused by high-level fractionation processes. However, heterogeneous isotope data suggests that the source of these magmas was the mantle wedge, enriched by87 a subducted slab component, with the melts being contaminated by a Sr-rich crustal component. There are two types of post-collisional leucogranite. The Sumayar pluton is related to restricted partial melting of sillimanite-grade metapelites triggered by fluxing of fluids from the underthrust Indian crust. This water-saturated, minimum melt is considered to be an analogue of the High Himalayan leucogranites. The other Karakoram leucogranites are related by fractionation to a more basic monzogranitic parent, whose geochemistry indicates a lower crustal source. However, melting of typical crust cannot explain the anomalously high large ion lithophile element (LILE) content of the monzogranites. Associated with the granites are ultra- potassic, LILE-enriched lamprophyres. This LILE-enrichment is attributed to alteration of the mantle wedge by fluids and/or siliceous melts from the slab. Amphibole in the resulting metasomatic assemblage acts as a sink for the otherwise incompatible LILE. As a result of heating and thermal relaxation beneath the thickened continental crust, enriched amphibole, stable in the pre-collisional mantle wedge beneath the Karakoram, dehydrated or melted some 20Ma after collision to give the lamprophyres. Fluid precursors to this melting contaminated the source region of the granites selectively enriching it in LILE and triggering/promoting melting. The identification of the above magma-types, which have different generative processes and magmatic triggers, in other collisional environments will lead to information about the evolution of similar orogenic belts.

Steady state, inter row measurements in multistage axial compressors are relevant to the current design process. The objective in obtaining such data is for evaluation of compressor blading as well as validation for the computer programmes used in compressor design. Multi-hole pressure probes are a reliable and economical method of collecting detailed flowfield data in compressors for these purposes. These probes are calibrated in a uniform flow in a wind tunnel prior to use, to determine their response to a range of flow angles and speeds. When the probe is subsequently used for measurements in the compressor, often the small inter row spacing means that the probe has to be close to the downstream stator passage and upstream rotor. The result is that the probe is no longer situated in the uniform flow in which it was calibrated, in terms of influences from both the upstream rotor and downstream stator. This project presents the investigation of these two effects on steady state pressure probe measurements. The effects of blockage on a probe positioned in front of a stator row in a high speed compressor were studied using CFD. This was also carried out on a large scale probe in a low speed compressor. It was found that the blockage effect caused a reduced mass flow in the downstream stator passage which in turn lead to an altered flow angle and a small reduction in measured total pressure. Experimental in rig calibrations showed that the change in flow angle was due to an angular offset of the pressure distribution about the probe. These calibrations also showed that the wind tunnel calibration was valid in the compressor within a small angular range. The influence of the upstream rotor passing was studied using an unsteady CFD model. Responses of the individual probe ports and the deduced flow angle and total pressure indicated that the steady state blockage effect is present throughout the wake passing. The wake passing was found to be a largely two dimensional effect in that the radial flow component changes in the low speed compressor wakes had little influence. The Total Technology thesis incorporates a management project on the relevant topic of project selection within companies. An existing project selection model was applied to a sample group of projects to determine the applicability of such models. The main findings were that these models can generate useful information for further selection decisions and that the applicability is towards lower budget projects where a structured approach is often not used.

No description available.

While it is clear that myocardium responds to mechanical stimuli, it is unknown whether myocytes transduce stress or strain. It is also unknown whether myofibers maintain lateral connectivity or move freely over one another when myocardium is deformed. Due to the lack of information about the relationship between macroscopic and cellular deformations, we sought to develop an experimental method to examine myocyte deformations and to determine their degree of affinity. A set of protocols was established for specimen preparation, image acquisition, and analysis, and two experiments were performed according to these methods. Results indicate that myocyte deformations are non-affine; therefore, some cellular rearrangement must occur when myocardium is stretched.

While it is clear that myocardium responds to mechanical stimuli, it is unknown whether myocytes transduce stress or strain. It is also unknown whether myofibers maintain lateral connectivity or move freely over one another when myocardium is deformed. Due to the lack of information about the relationship between macroscopic and cellular deformations, we sought to develop an experimental method to examine myocyte deformations and to determine their degree of affinity. A set of protocols was established for specimen preparation, image acquisition, and analysis, and two experiments were performed according to these methods. Results indicate that myocyte deformations are non-affine; therefore, some cellular rearrangement must occur when myocardium is stretched.

Thesis--Auburn University, 2009. / Abstract. Includes bibliographic references (p.90-92).

No description available.

The stress state at the boundary of any underground mine opening is that of plane stress. This planar state of stress can be simulated in laboratory by subjecting a cubic rock specimen to a biaxial loading condition. Thus, research on the behaviour of biaxially loaded rock is important for better understanding of the stability of mining fronts such as crown pillar skin, drift face or shaft floor. / The objective of this research is to study the geomechanical behaviour of biaxially loaded rock. Three rock types were selected, namely limestone, granite and sandstone. / The laboratory work was conducted using a newly developed, 500-tonne biaxial loading frame, that is equipped with a servo-controlled load and displacement system. Recently patented in China, the new biaxial loading frame is spatially symmetric and equally rigid in both directions. Steel brush platens and solid platens with and without MoS2 were developed to help examine the end friction effect on biaxial strength. It is found that the biaxial strength can decrease up to 26.7% with the increase of cubic specimen size from 75 mm to 150 mm. The biaxial strength increases by 29.3% with the increase of loading rate from 1 MPa/s to 10 MPa/s, for granite. The biaxial strength of granite specimen decreases by nearly 6% when either solid platens with MoS 2 lubricant or brush platens are used. A comparison of the sigma 1-sigma2 failure envelopes reveals that the shape of the envelope and the location of the peak biaxial strength are dependent on the rock type. / Varying intensities of rock spalling generally initiate at the free faces of the specimen when sigma1 and sigma2 exceed sigma c/2. Ultimate failure occurs in the form of an out-of-plane shear failure, which splits the rock specimen into two or more wedges. / It is shown that both Mohr-Coulomb and Hoek-Brown criteria underestimate the biaxial strength of the rock. The Drucker-Prager failure criterion appears to provide poor correlation with experimental results. A new empirical biaxial rock failure criterion for intact rock is derived and another, accounting for rock mass characteristics through the Geological Strength Index (GSI), is then proposed.