The subject of this thesis is an extension of a two-dimensional, axisymmetric, Timoshenko-beam finite-element rotordynamic code to include a three-dimensional non-axisymmetric solid-element casing model. Axisymmetric beams are sufficient to model rotors. Spring and damper forces provide the interface between the rotor and its casing and capture the dynamics of the full model. However, axisymmetric beams limit the modeling of real-case machine structures, where the casing is not axisymmetric. Axisymmetric and non-axisymmetric 3D finite element casing structures are modeled. These structures are then reduced using a technique called substructuring. Modal equations are developed for axisymmetric and non-axisymmetric casing models. In a 3D non-axisymmetric model, structural dynamics modes can be modeled by lateral modes in two orthogonal planes. Modal information of the complex 3D casing structures are generated, and then incorporated into the 2D code after a series of pre-processing steps. A reduction method called Component Mode Synthesis (CMS) is used to reduce the large dimensionality involved in calculation of rotordynamic coefficients. The results from the casing structures are merged with the rotor model to create a combined rotor-casing model. The analysis of the combined structure shows that there is a difference in the natural frequencies and unbalance response between the model that uses symmetrical casing and the one that uses non-axisymmetric casing. XLTRC2 is used as an example of a two-dimensional axisymmetric beam-element code. ANSYS is used as a code to build three-dimensional non-axisymmetric solid-element casing models. The work done in this thesis opens the scope to incorporate complex non-axisymmetric casing models with XLTRC2.

The aerodynamic steering forces and moments on a wind tunnel model of an axisymmetric bluff body are altered by induced segmented attachment of the separated flow over an azimuthal Coanda surface. The model is suspended in the wind tunnel by eight thin wires for minimal support interference within the wake. Each wire is instrumented with a miniature strain gage sensor for direct dynamic force measurements. Control is effected by an array of synthetic jet actuators that emanate from narrow, azimuthally-segmented slots, within a backward facing step. The aerodynamic effects are characterized using hot-wire anemometry and PIV measurements. In the first set of experiments, the array of synthetic jets is distributed around the perimeter of the circular tail end which is extended into a Coanda surface. The fluidic actuation results in segmented vectoring of the separated base flow along the rear Coanda surface and induces asymmetric aerodynamic forces and moments that can effect steering during flight. Transitory modulation of the actuation waveform of multiple actuators around the tail leads to the generation of significant dynamic side forces of controlled magnitude and direction with the potential utility for flight stabilization and fast maneuvering. In a second set of experiments the array of the synthetic jets is placed upstream of a mid-body axisymmetric cavity. A single jet induces a quasi-steady, nearly-matched force couple at the upstream and downstream ends of the cavity. Furthermore, transitory activation of multiple jets can be used to control the onset and sequencing of the couple forces and therefore the resultant force and moment.

Η διδακτορική διατριβή με τίτλο «Μελέτη Διατάξεων Σταδιακής Καύσης» έχει ως αντικείμενο την περιγραφή και την ανάλυση του ροϊκού πεδίου της αλληλεπίδρασης αξονοσυμμετρικών δεσμών διαφορετικού αριθμού Reynolds. Ο έλεγχος των μηχανισμών που διέπουν το ροϊκό αυτό πεδίο είναι σημαντικό εργαλείο για την βελτιστοποίηση της ανάμιξης ρευμάτων οξειδωτικού και καυσίμου και αποτελεί τον κρισιμότερο τεχνολογικό στόχο κατά τη διερεύνηση της αποδοτικότητας σε ένα ευρύ φάσμα σχημάτων σταδιακής καύσης. Στόχος της διατριβής είναι ο χαρακτηρισμός και ο έλεγχος της μίξης κατά την διαδικασία της σύγκλισης των δεσμών, συνεισφέροντας στην κατανόηση των βασικών μηχανισμών που αναπτύσσονται στο μέσο και τυρβώδες πεδίο, αλλά και στη βελτιστοποίηση της μίξης από την οποία εξαρτάται η μείωση των περιβαλλοντικών επιπτώσεων και η αύξηση της απόδοσης της καύσης, τόσο σε συστήματα παραγωγής ενέργειας όσο και σε θαλάμους καύσης κινητήρων αεροσκαφών, τα οποία αποτελούν τις πιο «φιλικές» ως προς το περιβάλλον αλλά και τις πιο αποδοτικές πρακτικές σε συστήματα καύσης. Παρά το γεγονός αυτό, η γνώση των επιμέρους φαινομένων και μηχανισμών που κυριαρχούν στο πεδίο της αλληλεπίδρασης αξονοσυμμετρικών δεσμών χαρακτηρίζεται από σημαντικές ελλείψεις, όσο αφορά την λεπτομερή καταγραφή του μέσου και τυρβώδους πεδίου ταχυτήτων. Η Ανεμομετρία Laser Doppler αποτελεί τα βασική μετρητική διάταξη που χρησιμοποιήθηκε για την καταγραφή των μέσων και τυρβωδών όρων του πεδίου της ταχύτητας. Το πλεονέκτημα της μεθόδου, που αποτελεί ένα από τα βασικά εργαλεία για τη μέτρηση τυρβωδών χαρακτηριστικών, είναι το γεγονός ότι δεν παρεμβαίνει στη ροή, καθώς στηρίζεται στην καταγραφή της συχνότητας του φωτός που σκεδάζεται από τροχιοδεικτικά σωματίδια, τα οποία ακολουθούν πιστά τη ροή. Η μελέτη στηρίζεται στην ανάλυση των μηχανισμών που αναπτύσσονται στο μέσο και τυρβώδες πεδίο και στον χαρακτηρισμό της μίξης των συστατικών των δεσμών, όπως αυτή αντικατοπτρίζεται στις πρώτης, δεύτερης και τρίτης τάξης ροπές της ταχύτητας, αλλά και στους αδιάστατους συντελεστές λοξότητας και επιπεδότητας. Σε αυτήν την κατεύθυνση, η παρούσα εργασία έχει σαν στόχο την ανάδειξη της ανάλυσης του ροϊκού πεδίου ως την πιο κρίσιμη παράμετρο ανάπτυξης σχημάτων καύσης, καθώς τα μεγέθη και η εξέλιξή τους έτσι όπως καταγράφονται μπορούν να χρησιμοποιηθούν άμεσα ως κριτήρια για την απόδοση τέτοιων σχημάτων, προσφέροντας την δυνατότητα της επιλογής των καλύτερων λειτουργικών παραμέτρων πριν ακόμα δοκιμαστούν σε περιβάλλον καύσης. Η τυρβώδης δομή και τα ανώτερα στατιστικά των ροπών της ταχύτητας κατά την αλληλεπίδραση των δεσμών χρησιμοποιούνται αρχικά ως βασικό εργαλείο της μελέτης των συγκεκριμένων διατάξεων σταδιακής καύσης και επιπλέον χρησιμοποιούνται για να χαρακτηρίσουν τη μίξη των συστατικών των δεσμών στις διαφορετικές περιοχές της αλληλεπίδρασης, πριν, κατά τη διάρκεια και μετά την σύγκλισή τους. Τα αποτελέσματα της εργασίας δείχνουν ότι δέσμες σχετικά μικρού αριθμού Reynolds (της τάξης των λίγων χιλιάδων) μπορούν να χρησιμοποιηθούν για την παραγωγή τυρβωδών δομών, όπου η μίξη ενισχύεται μέσω της αλληλεπίδρασής τους, γεγονός που μπορεί να έχει σημαντική επίδραση στην ανάπτυξη παρόμοιων εφαρμογών σε πραγματικής κλίμακας εγκαταστάσεις. / Τhis study aims to the assessment and analysis of the flow field produced by the interaction between two axisymmetric jets with different Reynolds numbers. The scheme is considered as a generic staged combustion configuration. In this frame, the identification and control of the mechanisms that dominate the flow field is one of the most significant issues towards the enhancement of mixing, thus the increasing of combustion operational and environmental efficiency. The scope of the study is to characterize and control the mixing process during the interaction and merging of the jets. The study contributes to the understanding of the dominating mechanisms occurring in the flow, through the assessment of the mean and turbulent flow features. The initial conditions used in the experiments diverge from the marginal conditions that refer to the interaction of equal momentum jets and the combining of a “strong” and a “weak” jet. In addition, due to the particularly low, although turbulent, Reynolds numbers used at jets’ exits, the capability of the jets to produce and maintain strongly turbulent structures during and after their interaction is also evaluated. During the experiments included in this thesis, a two dimensional Laser Doppler Anemometry (LDA) was used to measure the main components of the velocity vector (i.e. in the axial and the radial or horizontal directions). A pair of similar optical systems were used to produce two ellipsoidal control volumes and collect the light scattered by tracer particles, that faithfully represent the flow. Axisymmetric turbulent jets constitute the main component regarding the realization of staged combustion configurations based on multiple jets arrangements. Jet flow fields have been extensively studied during the last decades, mainly focusing on the self-similar region, i.e. the region where the mean and turbulent features are dynamically preserved. Recently, most of the studies are related to the identification of divergences arising from the different initial conditions and specific parameters, such as the shape of the orifice, the type of the confinement imposed at the exit, the jet density etc. The effects of these features are briefly summarized within the context of the thesis. In particular, the low Reynolds number effect is under consideration, as the jets recorded in the experiments are compared to typical previous studies devoted to the self-similarity region of jets with significantly higher Reynolds numbers. In the first part of the experiments, a jet of reference is monitored within an area covering the initial development and extends to the boundaries of the self-similarity region. Measurements include axial and radial distributions of the mean and turbulent axial and radial velocity components, turbulent shear stresses and terms that represent the turbulent transport of the Reynolds stresses. The budget of the turbulent kinetic energy is presented at the final measurement station, showing the particular mechanisms occurring in the flow. Measurements on the jets’ interaction field are presented afterwards. The distributions are systematically presented in comparison to the distributions recorded during the sole action of the primary jet Characteristic profiles are presented at locations within the merging and the mixing zones. In the early stages of development, the patterns of both jets can be identified. Within the merging region, besides the absorption of the secondary jet, the measurements indicate a spatial suppression of primary jet’s characteristics. Further downstream, the profiles resemble to those of a standalone jet. Higher values of the mean and turbulent terms are observed while the profiles extend over a wider region, in accordance with the secondary jet’s Reynolds number. Results of the present study demonstrate that skewness and flatness factors can be used as indicators of small scale mixing. The field of the interaction is further analyzed and discussed for a third pair of initial conditions and the proper decomposition of the mean and turbulent profiles using three different types of seeding conditions. In the early stages, the measurements confirm the independent action of the jets, although the tendency of the secondary jets’ pattern to be deformed. Within the merging zone, the distributions referring to the different types of seeding are characterized by humps and increased turbulent features in the secondary jet’s development region. The shape, the intensity and the extent of the humps depends on the seeding type. Most of the characteristics observed in this region are related to the probability density function distributions, which are composed by samples that correspond to tracers emanating from the individual sources. However, within the mixing zone, the profiles are nearly similar for the individual types of seeding, leading to the conclusion that all the samples contributing to measurements have been adapted by the flow field due to the small scale mixing, which is continuously improved further downstream.

No description available.

A hot isostatic press (HIP) is a system which utilises high temperatures and pressure in order to densifyand enhance the material properties of components in the aerospace, automotive and additive manufacturingindustries, to mention a few. Quintus is a world leading manufacturer of HIP systems, and this master’s thesiswork has been written in collaboration with them. A HIP consists of a cylinder which gets filled with an inert gas, a gas which is then pressurised using compressors.Inside of the cylinder are heaters which ensure that the gas and load reach the desired temperature. Quintus’HIP construction has a wire wound cylinder. This means that a pre-stressed wire is wound around the cylinderfor a number of laps, resulting in the cylinder always being in a compressive stress state, thus ensuring a safeconstruction if a crack were to propagate in the material. This construction also allows for a more slim design ofthe cylinder which is beneficial when the gas is to be cooled, as the heat gets transported through the cylinder.An alternative design to this wire wound cylinder is a so called monoblock cylinder. This is a solid, thicker,cylinder, not wound by any wire. Quintus does not manufacture the monoblock HIP system, but these HIPs areon the market and therefore Quintus is keen to learn more about them. In this work, differences in the cooling capabilities with respect to the cylinders’ strength has been investigated,regarding the wire wound and monoblock cylinders. This has been done by the means of CFD and FEM(ANSYS CFX and ANSYS Mechanical), where a simplified 2D axisymmetric model of each HIP version wasused. In CFX, both a steady state and transient simulation was run for each model in order to capture the coolingof the gas. The resulting temperature load on the cylinder was then exported to the Mechanical setup to solvefor the arising stresses of the cylinders. The results of the work showed that the wire wound HIP does indeed exceed the monoblock cylinder when itcomes to the cooling rate, especially after some time when the gas has cooled off. Neither one of the cylinderswere at risk of yielding, and the monoblock cylinder was calculated to withstand >20 000 cycles, which is alsothe fatigue life of the wire in Quintus’ HIPs. The models and boundary conditions used in this work weresubjected to approximations, but the results obtained have still brought a lot of new insights to the monoblockconstruction, and have provided a good foundation for further analyses.

京都大学 / 0048 / 新制・課程博士 / 博士(情報学) / 甲第22861号 / 情博第740号 / 新制||情||127(附属図書館) / 京都大学大学院情報学研究科先端数理科学専攻 / (主査)教授 青柳 富誌生, 教授 磯 祐介, 教授 田口 智清 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

Title: Impact crater relaxation throughout the Solar System Author: Martin Kihoulou Department: Department of Geophysics Supervisor: RNDr. Klára Kalousová, Ph.D., Department of Geophysics Abstract: In this thesis, we study the viscous relaxation of an impact-deformed icy shell of a dwarf planet Pluto. Motivation for this work is the position of Sputnik Planitia, a 1000 km wide, nitrogen-filled elliptic basin, which is located very close to Pluto-Charon tidal axis. Given this unlikely position on Pluto's sur- face, it was suggested that the basin was formed elsewhere and the whole body reoriented afterwards. For the reorientation to occur, the basin has to generate a positive gravity anomaly for which a combination of impact-related subsurface ocean uplift, ejecta blanket and accumulation of nitrogen ice was suggested. How- ever, to maintain the orientation towards the minimum principal axis of inertia until today, the ocean uplift must be present on timescales of billions of years, which may be achieved due to an insulating layer of high viscosity clathrates at the ice/ocean interface. We solve Pluto's ice shell evolution by the finite element method in 2D spherical axisymmetric geometry with an evolving free surface and assuming a viscous rheology. Our results show that the thermal effect of the im- pact...

No description available.

The filament-winding process produces quality consistent composite parts for many industries. Filament winding allows for consistent quality parts by automating the winding process. A recent development of filament winding is the Lotus process. The Lotus process reverses conventional filament winding by leaving the mandrel stationary and winding composite fiber around the mandrel. The automated Lotus filament-winding machine is controlled by four-axis control manipulating the Lotus ring around a fixed mandrel. This allows Lotus filament winding to wind parts that do not have a linear axis. Lotus filament winding is in its early stages of development. As a second step in the development of Lotus filament winding a method of automatic part-to-machine manipulation has been developed. Parts wound on the new automatic-manipulated Lotus machine have comparable quality and appearance to those made by conventional winding.

Axisymmetric radial Bernstein modes are known to exist in non-neutral plasmas and have been studied theoretically and computationally in 1D, but detection of these modes has still proven to be difficult due to self-shielding. To help advance the work on this front we created a 2D particle-in-cell (PIC) code that simulates a non-neutral plasma in a Malmberg-Penning trap. A detailed description of the PIC code itself has been included that highlights the benefits of using an $r^2$--$z$ grid and how it can be tested. The focus of the PIC simulation was to discover how best to drive and detect these modes. While it is improbable that radial Bernstein modes will be detected in long plasmas, we show that it may be a possible due to the axial nodal structure in the potential and electric field generated by confining plasmas of any finite-length. Additionally, we find that for a short plasma the strongest detection signal along the trap wall occurs at the plasma's midpoint rather than near the ends. Results show that oscillating the confinement potentials is sufficient to excite the fundamental radial Bernstein mode, but not any of the higher order modes. The higher order modes can be seen in the simulation, however, by sinusoidally driving the radial electric field. Unfortunately, the individual modes are difficult to isolate which we suspect is due to mode mixing. Finally, we report frequencies and mode shapes for the fundamental mode and the (lower) first higher order mode.