Local Forcing Mechanisms of Centrifugal Compressor Blades Excited by Impeller-Diffuser-Interaction

Centrifugal compressors allow the realisation of compact and robust designs which provide high-pressure ratios for a single stage, compared to axial compressor designs. Hence centrifugal compressors are found in a wide range of applications from aerospace propulsion to process industry. The demand for high efficiencies, pressure ratios, and flow rates are increasing the mean stress levels in the material. Due to this, the material becomes more vulnerable to cyclic stress, induced by vibrations and leading to high cycle fatigue failures. The reliable prediction of stationary and cyclic stress levels in mechanical structures during the design phase is essential to ensure mechanical integrity and to assess component lifetimes correctly. Vibrations in turbomachines, unfortunately, cannot be avoided and require a careful assessment during the design process. Various excitation sources exist, caused by the mechanical interaction of components or unsteady fluid-structure interaction. Research in the field of forced vibrations aims at a better understanding of the systems damping properties and excitation mechanisms. A correct prediction during the design phase would allow reducing the development cost and time since the number of design iterations can be reduced. However, the correct assessment of high cycle fatigue is challenging due to a lack of representative experimental data. The goal of this work was to investigate variations in the local impeller blade excitation mechanisms with changing operating conditions. Therefore, a state-of-the-art industrial design compressor from a turbocharging application has been integrated into the high-speed centrifugal compressor facility 'RIGI', located at ETH Zurich. The excitation source of the impeller blades is the unsteady fluid-structure interaction originating from the vaned diffusers potential field effect. An experimental approach has been developed to investigate the blade forcing function resulting in resonant response conditions. The experiments are based on in-house developed approaches. To investigate the forcing, an experimental approach was required to extend the variations of the forcing function while minimising the effects of damping avoid changes in modal response properties. This assumption requires leaving the compressor geometry unchanged but instead change the thermodynamic conditions of the stage by changing the working fluid properties. A CO2 injection and control system has been developed and integrated into the closed loop of the facility which allows changes in the circumferential Mach numbers for selected resonance crossings. Experimental techniques to measure the vibrational response of the stage are applied to separate the contribution of blade damping and the forcing function from the resonance amplitudes. The work has been complemented with a numerical investigation of the time-resolved 3D flow field, validated with flow measurement techniques and, by applying a finite element response model, validated against response measurements. The flow simulations are used to determine the local excitation mechanisms on the blade by applying a generalised force approach at resonance. Evaluation of the resonance response measurements revealed changes in response amplitudes reach up to a factor of 4, between air and air-CO2 mixtures and up to a factor of 2.5 with flow rate setting. Changes in the damping of the system were found partially responsible, but changes in the forcing function are the main contributor. The experimental investigation outlines potential limitations arising from low amplitude resonances which increasingly occur at part load conditions and low inlet pressure settings, required for the experimental approach. The numerical FE model to simulate the resonance response amplitudes, using measured damping and the simulated unsteady blade pressure distribution as boundary conditions, provided results within the measurement uncertainties for mode 4 resonance crossings. Some cases for mode 3 resonances showed increasingly insufficient prediction due to flow vortex emerging from part load operation. The local blade forcing distribution found deflective anti-nodes to contribute most to the excitation while high-pressure unsteadiness at the rigid impeller trailing edge area is neglectable. Changes in the forcing function caused by mass flow variations at a given resonance crossing speed are driven by scaling effects of local pressure unsteadiness amplitudes. The variations on flow rate have a minor effect on the flow Mach number distribution, which influences the pressure wave propagation. Hence it has a minor impact of the upstream travelling wave pattern. Variation of the gas properties by CO2, for a constant resonance crossing, lead to changes in the flow Mach number distribution. This has an impact on the spatial distribution of the pressure wave pattern. The phase relation between pressure and mode shape changes considerably as well as the resulting force. Ultimately the forcing not only depends on the local amplitude of pressure unsteadiness but also on how the wave pattern matches the mode shape. A high dependency on the operating condition was found and must be addressed in the design process. The applied numerical approach allows determining the local blade forcing on unsteady flow simulations only without the requirement of computationally expensive response simulations. This provides an efficient way to estimate critical operation conditions in an early design phase

Mechanisms and Biological Consequences of Damage to Extracellular Matrix Proteins by Peroxynitrite

Peroxynitrite (ONOO–) is a potent oxidizing and nitrating agent, formed under inflammatory conditions by the diffusion-controlled reaction of superoxide radicals (O2•–) with nitric oxide (•NO). This species reacts rapidly, via both non-radical and radical reactions, with proteins resulting in protein damage. As there are limited antioxidant and repair enzymes extracellularly, damage to extracellular matrix (ECM) proteins is likely to persist and accumulate over time. However, there is a lack of detailed mechanistic information on how ONOO– oxidation and nitration affects ECM proteins. This Thesis investigates the significance of these reactions and how this modulates the structure and function of three different isolated ECM proteins, laminin-111, plasma fibronectin, recombinant tropoelastin and a complex mixture of basement membrane proteins. Exposure of ECM proteins to ONOO– at physiological relevant concentrations (10 μM) lead to protein aggregation and fragmentation. Significant amounts of nitration products (3-nitroTyr, 6-nitroTrp) in the millimolar-range and depletion of corresponding parent Tyr and Trp were detected on all analysed ECM proteins with this effect being modulated by CO2. Furthermore biological function and activity was compromised post ONOO– exposure. Overall, the studies presented in this Thesis provide new information about the reactivity of ONOO– with ECM proteins, and how this affects the structure and the function of these proteins

Interactive process-network as design system

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersUnter der Annahme, dass die Kombination des Problemlösungsvermögens des menschlichen Gehirns und der Rechenkapazität des Computers komplexere Entwurfslösungen mit höherer Qualität entstehen lässt,soll in der Arbeit ermittelt werden, welche Entwurfsprozesse in Regeln gefasst und automatisiert verarbeitet werden können und welches Ergebnis dadurch erzielt werden kann, bzw. wo manuelle Vorgänge notwendig oder sinnvoll sind. Weiters überprüft die Arbeit, ob der Vorteil einer algorithmischen Definition, Änderungen im Entwurfsprozess schnell am Endergebnis überprüfen zu können, bzw. die Reduktion von zeitintensiven Iterationen von manuellen Vorgängen den Mehraufwand einer solchen aufwiegt.Assuming that the combination of the problem solving capabilities of the human brain and the processing power of computers result in more complex solutions with higher quality, the thesis determines, which drafting processes can be formalized into rules and therefore be processed automatically and which ones require manual procedures. Furthermore it investigates, wether the advantages of an algorithmic definition could outweigh the higher creational effort of such a system. Those advantages are first, the ability to quickly evaluate changes against the final result and second, the reduction of repeaded and time consuming manual tasks

Baroque roof structure MuseumsQuartier - stock analysis

Abweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassung in engl. SpracheKurzfassung Die Erhaltung bzw. Instandsetzung von Bauwerken, stellt ein umfassendes Themengebiet im Bereich des Bauwesens dar. Aufbauend auf dem Wissen jahrhundertealter Handwerkstradition in Kombination mit dem heutigen Stand der Technik, hat sich daraus sogar ein eigener Industriezweig gebildet.In der heutigen Zeit ist die Erhaltung und Instandsetzung von historischen Bauwerken sowohl kulturell als auch wirtschaftlich von großer Bedeutung. Unter dem Aspekt der Denkmalpflege, sind historische Bauten möglichst originalgetreu für nachkommende Generationen zu erhalten.Eine Bestandsanalyse stellt die Grundlage für die weiteren Schritte auf dem Gebiet der Erhaltung und Instandsetzung von Bauwerken dar. Aus diesem Grund beschäftigt sich die vorliegende Diplomarbeit mit der Bestandsanalyse des Barocken Dachstuhls im MusemsQuartier Wien. Dieser Dachstuhl stellt im Sinne der Denkmalpflege eine erhaltenswerte Konstruktion dar.Im ersten Teil der Arbeit werden ausgewählte Kapitel auf dem Gebiet der Bestandsanalyse bzw. der Bauzustandserfassung alter Holzbauwerke erläutert. Der zweite Teil der Diplomarbeit umfasst die praktische Durchführung einer Bestandsanalyse am Beispiel dieses Barocken Dachstuhls. Ziel der Arbeit ist es den Zustand der Holzkonstruktion zu eruieren und zu veranschaulichen.Die Bestandsanalyse hat ergeben, dass der untersuchten hölzerne Konstruktion ein Bauzustand mit "geringen Schäden" attestiert werden kann. Trotz ihres hohen Alters beläuft sich der Umfang der Schäden bezogen auf die Gesamtkonstruktion auf ein geringes Ausmaß. Die Tragfähigkeit der Konstruktion ist vollständig vorhanden.Die Ursache der Schäden ist in einer undichten Dachhaut zu sehen.Weiters wird die Schadensausbreitung durch die Tatsache begünstigt, dass die Holzkonstruktion den klimatischen Wechselwirkungen ausgesetzt ist.Da der Reparaturaufwand bei Schäden, welche eine Tendenz zur Ausbreitung aufweisen, nach einer exponentiellen Funktion anwächst, ist damit für die weitere Vorgehensweise hinsichtlich etwaiger Instandsetzungsarbeiten auch dieser wirtschaftliche Aspekte zu berücksichtigen.Abstract Maintenance of buildings is a big topic in the area of the building industry. Based on the centuries-old tradition of the handcraft mixed with the state of the art resulted to an own branch of industry.Nowadays the maintenance of historical buildings has cultural and economic relevance. Under the aspect of the preservation of monuments and historic buildings theses constructions should be preserved as true to the original as possible for the next generations. In the field of maintenance a broad status analysis is the basis for the next steps to preserve the basic structure of a building. This thesis deals with the analysis and evaluation of the baroque construction of the roof structure of the Museums Quartier Wien. The guidelines of the preservation of monuments and historic buildings ensure the preservation of this roof. The first part of this thesis is based on the topic status analysis and the recording of the construction level of older wooden constructions.In the second part the theory of the first chapter is applied by using the example of this baroque roof structure. This thesis determines and visualises the condition of this wooden construction.The status analysis shows that the construction level of this roof made of timber has minor damages. Regardless of the age of this building the damages are so marginal that the bearing capacity is still existent.The cause for the damage symptoms is due to leaks in the roof panel.This is supported by the climatic interaction. The input for the building repair rises exponentially in case of damages with a tendency to spread out. For this reason the next steps of the maintenance should also be considered by an economical point of few.11

Evaluation of the Morphological Characteristics of Laser-Irradiated Dentin

OBJECTIVE The aim of this study was to investigate the effect of different energy settings of Er:YAG laser irradiation on dentin surface morphology with respect to the number of opened dentinal tubules. BACKGROUND DATA An ideally prepared dentin surface with opened dentinal tubules is a prerequisite for adhesive fixation. No study, however, has yet compared the numbers of opened dentinal tubules with regard to statistical differences. METHODS Conventional preparations using a bur with or without additional acid etching acted as control groups. Dentin specimens were prepared from human third molars and randomly divided into eight groups according to the energy settings of the laser (1, 1.5, 4, 6, 7.5, and 8 W) and two controls (bur and bur plus acid etching). After surface preparation, dentin surfaces were analyzed with a scanning electron microscope, and the number of opened dentinal tubules in a defined area was counted. RESULTS The control groups showed smooth surfaces with (bur plus acid etching) and without opened dentinal tubules (bur), whereas all laser-irradiated surfaces showed rough surfaces. Using the energy setting of 4 W resulted in significantly more opened dentinal tubules than the conventional preparation technique using the bur with additional acid etching. In contrast, the energy setting of 8 W showed significantly fewer opened dentinal tubules, and also exhibited signs of thermal damage. CONCLUSIONS The Er:YAG laser with an energy setting of 4 W generates a dentin surface with opened dentinal tubules, a prerequisite for adhesive fixation

Experimental And Numerical Investigation Of Blade Resonance In A Centrifugal Compressor For Varying Gas Properties

The blades of centrifugal compressors are exposed to unsteady forces during operation which can result in resonance response conditions and failures due to high cycle fatigue. A typical source of excitation is the unsteady fluid structure interaction between the impeller blades and the downstream vaned diffuser. Centrifugal compressors are operated with various working fluids with a wide range of applications in the power and process industry. Understanding the excitation mechanisms for different working fluids will help to design aerodynamically efficient compressors, while ensuring mechanical integrity and reducing the number of experimental design validations. Experiments have been conducted at ETH Zurich’s radial compressor facility with a state of the art industrial compressor design. Dynamic strain gauge measurements on the impeller main blades were used to determine the amplitude response and damping properties at a defined resonance condition. Two different working fluids have been investigated to vary compressor flow settings, unsteady flow simulations and harmonic FSI simulations were used to complement the experiments and to investigate the blade forcing distribution. The experiments showed a change in resonance amplitude up to a factor of 4 due to a change in the applied working fluid. Estimation of the damping ratio with a single degree of freedom model found the exciting force to be the main contributor to the differences in resonant response. The unsteady flow simulations were able to identify the locations on the blade surface which are responsible for the change in forcing