The stress distribution in a rotating solid shaft with temperature dependent yield stress subject to a temperature cycle is investigated. It is presumed that the shaft is in a state of generalized plane strain and obeys Tresca&rsquo / s yield criterion and the flow rule associated with it. By the temperature cycle it is meant that the surface temperature of the shaft is increased to a limiting value, it is held at this temperature for a while, and then slowly decreased at the same rate to the reference temperature. The isothermal shaft is rotated up to around elastic limit rotation speed and then the temperature cycle is applied to the surface of the shaft. Even in an initially purely elastic shaft, two plastic regions with different forms of the yield condition emerge simultaneously at the centre and expand into the elastic region. However, the expansion of the plastic zone ceases soon thereafter, and an unloaded region spreads into the plastic core. It is shown that the stress distribution is altered significantly by the temperature cycle, hence also leading to non-zero residual stresses at stand-still.

The present study describes the flow characteristics of swirling flows induced by twisted tape inserts in circular pipes. The study is focused on the secondary flow which is investigated experimentally and with numerical models. The results are expected to improve the paper manufacturing process by identifying and removing the detrimental secondary flow. Experimental tests show for the first time the existence of two co-rotating helical vortices superimposed over the main swirling flow, downstream of twisted tapes. The close proximity of the two co-rotating vortices creates a local counter-rotating flow at the pipe centerline. The flow is analyzed using LDV measurements and high speed camera visualization with fine air bubbles seeding which confirm that the helical vortices are stable. After extracting the characteristic tangential velocity profiles of the main vortex and of the two secondary vortices, it was observed that the maximum tangential velocity of all three vortices is the same, approximately half of the bulk velocity. The winding of the helical vortices is in the swirl direction and the pitch of the helical vortices is found to be independent of the inlet velocity. The experimental findings are confirmed by numerical simulations. The numerical results show that the helical vortices originate inside the swirler and evolve from single co-rotating vortices on each side of the tape. The flow characteristics are analyzed in detail. Swirlers with multiple twists and multiple chambers are shown to have less stable secondary motion and could be employed in applications were the secondary motion is detrimental.

<p>A diesel fuel injector has been modified to allow rotationaround its axis, driven by an electric motor. Injections at upto 6000 rpm from the rotating injector have been investigatedunder the influence of air swirl on one optical research engineand one optically accessible heavy-duty diesel engine.</p><p>The experiments show that changing from a normal, staticinjection to a sweeping injection has profound effects on sprayformation, dispersion and penetration. This influences thefuel/air-mixing, autoignition, combustion rate and emissionsformation. The spray propagation is stronger influenced byinjector rotation than by air swirl.</p><p>The air entrainment into the spray increases forcounter-swirl rotation of the injector and this speeds up thevaporization and decreases the formation of soot. In addition,the oxidation of soot is enhanced since the counter-swirlinjection forces the intense fuel-rich and soot containingspray core to penetrate into fresh air instead of replenishingthe rich regions in the head of the spray. Fuel accumulationalong the piston bowl wall decreases as an effect of thereduced penetration with counter-swirl injection. Altogether,this decreases the smoke emissions for low and intermediateengine loads.</p><p>For the combustion system studied, counter-swirl rotation ofthe injector cannot decrease the smoke emissions at high engineload since the reduced spray penetration impairs the airutilization. Fast and efficient combustion at high loadrequires spray induced flame spread out into the squish region.Spray induced flow of cool fresh air from the bottom of thepiston bowl in towards the injector is also important for lowsoot formation rates.</p><p>Co-swirl rotation of the injector reduces the airentrainment into the spray and increases the soot formation.The increased smoke and CO emissions with co-swirl injectionare also attributed to the excessively large fuel-rich regionsbuilt up against the piston bowl wall.</p><p>Increased air swirl generally reduces smoke and COemissions. This is mainly an effect of enhanced burnout due tomore intense mixing after the end of fuel injection.</p><p>Changes in smoke as an effect of injector rotation aregenerally accompanied with opposite, but relatively small,changes in NO. Fast and efficient burnout is important for lowsmoke emissions and this raises both the temperature andproduction of NO. NO production is strongly influenced by thein-cylinder conditions during the latter part of themixing-controlled combustion and in the beginning of theburnout.</p><p><b>Keywords:</b>diesel spray combustion, rotating injector,air swirl, air/fuel-mixing, soot, NO, CO, flame visualization,Chemkin modeling, soot deposition</p>

An experimental study on the application of Digital Image Correlation (DIC) to measure the deformation and strain of rotating blades is described. Commercial DIC software was used to obtain measurements on three different types of rotors with diameter ranging from 18 to 39 and with varying flexibility to explore applicability of the technique over a breadth of scales. The image acquisition was synchronized with the frequency of rotation such that images could be obtained at the same phase and the consistency of measurements was observed. Bending and twist distributions were extracted from the data with deformation as high as 0.4 measured with a theoretical accuracy of 0.0038 and span-wise resolution of 0.066. The technique was demonstrated to have many advantages including full-field high resolution results, non-intrusive measurement, and good accuracy over a range of scales. The span-wise deformation profiles from the DIC technique are used in conjunction with Blade Element Momentum Theory to calculate the thrust and power consumed by the rotor with rigid vi blades; results are comparable to load cell measurements albeit thrust is somewhat under-predicted and power is over-predicted. Overall, the correlation between DIC calculated thrust and BEMT approximations for comparable blades with constant pitch were within 12% through the onset of stall. Measurement of flexible blade deformation that would not have been possible with other techniques demonstrated the utility of the DIC method and helped to confirm predictions of flexible blade behavior. / text

Το αντικείμενο της εργασίας αυτής είναι η μελέτη των μετανευτώνειων προσεγγίσεων στο πλαίσιο της Γενικής Σχετικότητας, με έμφαση στους αστέρες νετρονίων. Λόγω του οτι, η μελέτη των αστέρων νετρονίων βασίζεται στην υδροδυναμική περιγραφή της ύλης, το κύριο ενδιαφέρον μας αφορά στον τρόπο που εισάγονται οι μετανευτώνειες προσεγγίσεις στις υδροδυναμικές εξισώσεις της Γενικής Σχετικότητας. Στο πρώτο κεφάλαιο παρουσιάζονται ορισμένα θεωρητικά στοιχεία γύρω απο φυσικά χαρακτηριστικά και τις ιδιότητες των συμπαγών αστέρων. Στο δεύτερο κεφάλαιο παρουσιάζονται τα γενικά χαρακτηριστικά των καταστατικών εξισώσεων των συμπαγών αστέρων, με έμφαση στην πολυτροπική καταστατική εξίσωση. Στο τρίτο κεφάλαιο παρουσιάζεται η θεωρία των μετανευτώνειων προσεγγίσεων, καθώς και οι μετανευτώνειες εξισώσεις πρώτης τάξης της υδροδυναμικής, στη Γενική Σχετικότητα όπως εισήχθησαν απο τον Chandrasekhar. Στο τέταρτο κεφάλαιο παρουσιάζεται η διαταρακτική μέθοδος που χρησιμοποιείται απο τους Fahlman και Anand, για την μελέτη των περιστρεφόμενων πολυτρόπων στο πλαίσιο της πρώτης μετανευτώνειας προσέγγισης στη Γενική Σχετικότητα. Στο πέμπτο κεφάλαιο παρουσιάζεται η μετανευτώνεια προσέγγιση δεύτερης τάξης όπως διατυπώθηκε απο τους Chandrasekhar και Nutku. Στο έκτο, και τελευταίο, κεφάλαιο παρουσιάζεται ένα υπολογιστικό αλγεβρικό πακέτο για μετανευτώνειους υπολογισμούς στη Γενική Σχετικότητα, το PROCRUSTES. Με την βοήθεια του πακέτου αυτού υπολογίσαμε διάφορες ποσότητες στη δεύτερη μετανευτώνεια προσέγγιση, όπως τον τανυστή ενέργειας - ορμής, 𝑇𝑖𝑗, τον τανυστή Ricci, 𝑅𝑖𝑗, τις εξισώσεις κίνησης, Τ𝑖𝑗;𝑗 = 0, και άλλες. Το PROCRUSTES είναι ένα πολύ χρήσιμο εργαλείο στη μετανευτώνεια μελέτη καθώς μπορεί κανείς να παράξει τις περίπλοκες εκφράσεις διαφόρων ποσοτήτων σε ελάχιστο χρόνο και χωρίς την πιθανότητα λάθους. Επίσης, με την βοήθεια του πακέτου αυτού, υπολογίσαμε τις αναλυτικές εκφράσεις των εξισώσεως κίνησης, Τ𝑖𝑗;𝑗 = 0, στην δεύτερη μετανευτώνεια προσέγγιση. Με κατάλληλη μετατροπή των εκφράσεων αυτών, μπορούμε να εφαρμόσουμε την μέθοδο των Fahlman και Anand, με σκοπό την μελέτη των περιστερόμενων πολυτρόπων στη μετανευτώνεια προσέγγιση δεύτερης τάξης. Στο τέλος της εργασίας παρατίθεται ένα συμπλήρωμα με τη δομή του προγράμματος και ορισμένες απο τις ποσότητες που υπολογίστηκαν στο πλαίσιο της εργασίας. / The main subject of my master thesis is the study of,the post-Newtonian approximations (PNA) in General Relativity (G-R), mainly those that concern the neutron stars. Owing to the study of neutron stars is on the hydrodynamic description of matter, our main interest lies uponthe way the PNA affects the hydrodynamic equations of G-R. In the first chapter there is presented the main theory around the physical attributes of compact stars. The second chapter reffers to the general features of the equations of state (EoS) of compact stars, giving emphasis to the polytropic EoS. In the yhird chapter, there is presented the theory of the PNA. There are also presented the the hydrodynamic equations in the PNA as the were introduced by Chandrasekhar. The fourth chapter is dedicated to the presentation of the method that was introduced by Fahlman and Anand, on the study of rotating polytropes in the PNA to G-R. The fifth chapter focuses on the second PNA as it formulated by Chandrasekhar and Nutku. During the sixth and final chapter there is presented a computer algebra package for post-Newtonian calculations in G-R, the PROCRUSTES. Whith the aid of thiw package, we calculated several quantities in the second PNA, as for example the E-M tensor 𝑇𝑖𝑗„ the Ricci tensor 𝑅𝑖𝑗 and the equations of motion (EoM) Τ𝑖𝑗 ;𝑗 = 0. PROCRUSTES is a very useful tool for the post-Newtonian study, as someone can produce the compicated equations of several quantities in no time and eliminating the possibility of making some mistake during the calculation. Moreover, using PROCRUSTES we calculated the expressions of the EoM’s in the second PNA. Under appropriate transformation of these expressions, we are able to apply the method of Fahlman and Anand onto these equations with a view to the study of rotating polytropes in the second PNA. At the end of this work there is quoted a supplement with the structure of the programm we used, along with some of the quantities that were calculated during this work.

Dealloying refers to the partial, selective dissolution of the less noble component(s) of a binary or ternary alloy precursor, resulting in a noble-rich, porous structure that has high surface area. Such surface structure is beneficial for fuel cells (FC) because FC uses platinum (Pt), a scarce metal, to catalyze the oxygen reduction reaction (ORR) at the cathode surface. In order to characterize the benefit of the dealloying process in FC ORR catalysts with the rotating disk electrode (RDE) technique, a high surface area catalyst support, namely 3M Co’s nanostructured thin film (NSTF), was incorporated into the RDE measurements. NSTF-coated glassy carbon (GC) disks were used in RDE experiments on a Pt/Pt1-xIrx (0.05 < x < 0.3) composition spread. ORR measurements using NSTF-coated GC disks measure the catalytic properties with the same morphology, composition and surface structure as would be found in a fuel cell. A series of Pt1-xCox and Pt1-xNix (0.5 < x < 0.8) dealloy catalyst precursor films were tested using NSTF-coated GC disks in RDE studies. The value of x in Pt1-xMx (M = Ni, Co) was selected to be high in order to examine the dealloying process. The catalyst films were examined by a RDE test protocol that tracked the surface enhancement factor (SEF) and ORR current densities over a large number of test cycles. The aim was to measure the catalytic performance of the Pt-M materials as dealloying took place. The SEF of the PtCo and PtNi materials increased rapidly at the beginning and reached a plateau as high as 50 cm2/cm2 while the specific ORR activities increased as the initial M content in the catalyst precursor increased. The impact of the dealloying process on morphology was examined by completely dealloying a Pt3Ni7 precursor, deposited on mirror-polished GC disks, at a constant potential. As the dealloying process continued, the SEF of the material increased from about 1 cm2/cm2 to > 30 cm2/cm2 and resulted in the formation of whisker-like structures.

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No description available.

[Truncated abstract] Centrifugal pumps are the most prevalent, electrically powered rotating machines used today. Each pump is designed to deliver fluid of a given flow rate at a certain pressure. The point at which electrical energy is converted most efficiently into increased pressure is known as the Best Efficiency Point. For a variety of reasons, pumps often operate away from this point (intentionally or otherwise), which not only reduces efficiency, but also increases the likelihood of premature component failure. Acoustic emissions (AE) are high frequency elastic waves, in the range of 20-2000kHz, released when a material undergoes localised plastic deformation. Acoustic emission testing is the process of measuring and analysing these stress waves in an attempt to diagnose the nature and severity of the underlying fault. AE sensors mounted on the surface of a machine or structure also detect any stress waves generated within the fluid being transmitted through to the structure. Unfortunately, attempts to detect incipient component faults in centrifugal pumps using acoustic emission analysis have been complicated by the sensitivity of AE to a pump?s operating state. Therefore, the aim of this thesis was to determine how acoustic emission monitoring could be used to identify the hydraulic conditions within a pump. Data was collected during performance tests from a variety of small end-suction pumps and from one much larger double-suction pump. A system was developed to collect, process and analyse any number of AE features (be they related to discrete AE events, or due to the continuous background AE level) from continuously operating equipment. ... Unfortunately, results from smaller pumps were less conclusive, particularly at low flows, probably due to the relatively small changes in hydraulic energy across the range of flows, and consequent sensitivity to the testing process. However, even in these pumps consistent patterns in hit energies were observed resulting in the conclusion that low to medium flows in centrifugal pumps are typified by a very large number of very low energy (VLE) events. These decrease in number and increase in energy as flow approaches BEP and/or is reduced to very low flows. High flows above BEP are marked by an absence of these VLE events, with bursts having significantly higher energies and spread over a much greater range. Unfortunately, these VLE events are too small to affect averaged trends, indicating that further work on a suitable filter is required. vi

Thesis (Ph.D.)--University of Melbourne, School of Physics, 2007. / Typescript. Includes bibliographical references (leaves 275-308).