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1
Whitlow, C. D. "Rotating and non-rotating flows of internally heated fluids." Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375519.
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Rump, Owen James. "Non-rotating and rotating free surface flows over topography." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1446071/.
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An important effect in atmosphere and ocean dynamics is the drag exerted by topography, in the form of mountain ranges and individual mountains, on incident flows. Because the scale of topographic variations are usually small compared to the resolution of global-scale numerical models, drag effects must often be parameterised. This thesis aims to understand topographic drag in highly idealised numerical models with a view to demonstrating where efforts in parameterisation may be best directed. Specifically, the thesis considers single-layer and one and one half layered flow (where a single layer lies below an infinitely deep layer of slightly lower density) over topography, inspired by a series of rotating tank experiments. The flow behaviour is strongly affected by the Proude number F of the flow - the ratio of the oncoming flow to the speed of long free gravity waves. The transcritical regime F 1, in which there is a close analogy with compressible gas dynamics, is investigated as a novel limit of the Shallow-Water Equations. Scaling laws for the drag are verified against numerical integrations and various flow regimes for rotating and non-rotating flows delineated. Supercritical flow {F > 1) is also investigated, focusing on both the drag and breaking waves in the far-field, which in the rotating case is shown to depend on a single parameter.
3
Seshasayanan, Kannabiran. "Rotating turbulent dynamos." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066158/document.
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Dans cette thèse, nous étudions l’effet de la turbulence en rotation sur l’instabilité dynamo. Nous étudions les différentes limites de la turbulence en rotation numériquement et théoriquement. D’abord, nous avons considéré l’effet dynamo engendré par les écoulements quasi-bidimensionnel (un écoulement avec trois composantes de vitesse qui dépendent de deux directions), qui modélise la limite de rotation très rapide. Nous avons étudié l’amplitude de saturation du champ magnétique en fonction du nombre de Prandt magnétique pour ce type d’écoulement. Un modèle théorique est développé et comparé avec les résultats numériques. Nous avons aussi regardé l’effet d’une vitesse bruitée sur le taux de croissance des différents moments du champ magnétique. Nous avons étudié l’écoulement 3D en rotation globale pour différents régimes du paramètre de contrôle. Pour l’écoulement hydrodynamique, nous avons étudié la transition vers une cascade inverse et les différents types de saturation de la cascade inverse. Nous avons regardé l’instabilité dynamo de ces écoulements. Nous avons montré que la rotation modifie le mode le plus instable et dans certains cas peut réduire le seuil de l’instabilité dynamo<br>In this thesis, we study the effect of rotating turbulent flows on the dynamo instability. We study the different limits of rotating turbulence using numerical simulations and theoretical tools. We first look at the dynamo instability driven by quasi-twodimensional flows (flows with three components varying along two directions), which models the limit of very fast rotation. We look at the saturation amplitude of the magnetic field as a function of the magnetic Prandtl number for such flows. A theoretical model for the dynamo instability is later developed and compared with the numerical results. We also study the effect of a fluctuating velocity field on the growth rate of different moments of the magnetic field. The three dimensional rotating flow is then studied for different range of parameters. For the hydrodynamic problem, we study the transition to an inverse cascade and the different saturation mechanism of the inverse cascade. Later the dynamoinstability driven by such flows is investigated. We show that the effect of rotation modifies the most unstable mode and in some cases can reduce the dynamo threshold
4
Moss, T. R. "Rotating machinery reliability." Thesis, Loughborough University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311046.
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Yang, Chunping. "Rotating Drum Biofiltration." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1092668752.
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Granfeldt, Caroline. "Rotating Workforce Scheduling." Thesis, Linköpings universitet, Optimeringslära, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122507.
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Several industries use what is called rotating workforce scheduling. This often means that employees are needed around the clock seven days a week, and that they have a schedule which repeats itself after some weeks. This thesis gives an introduction to this kind of scheduling and presents a review of previous work done in the field. Two different optimization models for rotating workforce scheduling are formulated and compared, and some examples are created to demonstrate how the addition of soft constraints to the models affects the scheduling outcome. Two large realistic cases, with constraints commonly used in many industries, are then presented. The schedules are in these cases analyzed in depth and evaluated. One of the models excelled as it provides good results within a short time limit and it appears to be a worthy candidate for rotating workforce scheduling.
7
Ahn, Jaeyong. "Film cooling effectiveness measurements on rotating and non-rotating turbine components." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4664.
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Detailed film cooling effectiveness distributions were measured on the stationary
blade tip and on the leading edge region of a rotating blade using a Pressure Sensitive
Paint technique. Air and nitrogen gas were used as the film cooling gases and the
oxygen concentration distribution for each case was measured. The film cooling
effectiveness information was obtained from the difference of the oxygen concentration
between air and nitrogen gas cases by applying the mass transfer analogy. In the case of
the stationary blade tip, plane tip and squealer tip blades were used while the film
cooling holes were located (a) along the camber line on the tip or (b) along the span of
the pressure side. The average blowing ratio of the cooling gas was controlled to be 0.5,
1.0, and 2.0. Tests were conducted in a five-bladed linear cascade with a blow down
facility. The free stream Reynolds number, based on the axial chord length and the exit
velocity, was 1,100,000 and the inlet and the exit Mach number were 0.25 and 0.59,
respectively. Turbulence intensity level at the cascade inlet was 9.7%. All
measurements were made at three different tip gap clearances of 1%, 1.5%, and 2.5% of
blade span. Results show that the locations of the film cooling holes and the presence
of squealer have significant effects on surface static pressure and film-cooling effectiveness. Same technique was applied to the rotating turbine blade leading edge
region. Tests were conducted on the first stage rotor of a 3-stage axial turbine. The
Reynolds number based on the axial chord length and the exit velocity was 200,000 and
the total to exit pressure ratio was 1.12 for the first rotor. The effects of the rotational
speed and the blowing ratio were studied. The rotational speed was controlled to be
2400, 2550, and 3000 rpm and the blowing ratio was 0.5, 1.0, and 2.0. Two different
film cooling hole geometries were used; 2-row and 3-row film cooling holes. Results
show that the rotational speed changes the directions of the coolant flows. Blowing
ratio also changes the distributions of the coolant flows. The results of this study will
be helpful in understanding the physical phenomena regarding the film injection and
designing more efficient turbine blades.
8
Mehdigholi, Hamid. "Forced vibration of rotating discs and interaction with non-rotating structures." Thesis, Imperial College London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445321.
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Kryeziu, O. "Rotating and non-rotating flows through gaps by the hodograph method." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1310257/.
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Steady, two-dimensional flows of a single layer of inviscid fluid discharging through an aperture are treated in the hodograph or velocity plane on a rectangular grid. The following problems are considered individually: irrotational planar and axisymmetric flow of air through a nozzle, incompressible flow through an aperture with bottom topography and lastly rotating flow of a uniform potential vorticity fluid issuing from a passage on the wall. The rotating case differs from other cases in that three parameters are required to describe the solutions instead of two. In all cases the problems are formulated so that flows range from subcritical to supercritical including choked flow. The rectangular domain for the supercritical problems results from the way the information travels in the hodograph plane in the region that is image of the flow that occurs around the lip of the nozzle wall. Supercritical jets are solved up to a short distance away from the aperture, hence shocks that occur further downstream are avoided although limiting lines develop in the vicinity of the exit plane depending on the strength of the topography. The equations governing irrotational flows are expressed in terms of the Legendre potential and those for the rotating flow are expressed in terms of the streamfunction. Solutions of these equations are computed using standard finite-differences approximations. Knowledge of the characteristics directions and the corresponding compatibility equations in the supercritical region of the domain is not required which demonstrates the robustness of solving in the hodograph plane. All that is necessary is that the general direction in which information propagates is perceived so that explicit or implicit finite-differences can be employed.
10
Vestman, Christopher. "The rotation of a stored cylinder body by an outer rotating structure." Thesis, Luleå tekniska universitet, Rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75021.
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HEAT-grenades are wing-stabilized grenades using shaped charge technology. Theshaped charge is a method, producing a jet-beam, with the use of a copper linerin which the aim is to focus the detonation energy to be able to penetrate armourand structures. This jet-beam is only eective under a rotational frequency of 15Hz, any frequency above this and the produced jet-beam loses its eciency and willnot be able to penetrate its target. One approach to minimize the inner body'srotation is by using bearings. By the use of ball bearings the intention is to with-hold transferring the angular momentum from the outer rotating body to the innercylinder body. This thesis have been analysing how much rotation the warhead haveacquired from the outer rotation of the grenade divided in an acceleration phase anda ying phase. During the acceleration phase the rotation of the warhead is reach-ing a frequency of 0.35 Hz. Proposals are presented for improving and lowering therotational speeds for future studies.
11
Bambrey, Ross R. "Strong interactions between two co-rotating vortices in rotating and stratified flows /." St Andrews, 2007. http://hdl.handle.net/10023/341.
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Bambrey, Ross R. "Strong interaction between two co-rotating vortices in rotating and stratified flows." Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/341.
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In this study we investigate the interactions between two co-rotating vortices. These vortices are subject to rapid rotation and stable stratification such as are found in planetary atmospheres and oceans. By conducting a large number of simulations of vortex interactions, we intend to provide an overview of the interactions that could occur in geophysical turbulence. We consider a wide parameter space covering the vortices height-to-width aspect-ratios, their volume ratios and the vertical offset between them. The vortices are initially separated in the horizontal so that they reside at an estimated margin of stability. The vortices are then allowed to evolve for a period of approximately 20 vortex revolutions. We find that the most commonly observed interaction under the quasi-geostrophic (QG) regime is partial-merger, where only part of the smaller vortex is incorporated into the larger, stronger vortex. On the other hand, a large number of filamentary and small scale structures are generated during the interaction. We find that, despite the proliferation of small-scale structures, the self-induced vortex energy exhibits a mean `inverse-cascade' to larger scale structures. Interestingly we observe a range of intermediate-scale structures that are preferentially sheared out during the interactions, leaving two vortex populations, one of large-scale vortices and one of small-scale vortices. We take a subset of the parameter space used for the QG study and perform simulations using a non-hydrostatic model. This system, free of the layer-wise two-dimensional constraints and geostrophic balance of the QG model, allows for the generation of inertia-gravity waves and ageostrophic advection. The study of the interactions between two co-rotating, non-hydrostatic vortices is performed over four different Rossby numbers, two positive and two negative, allowing for the comparison of cyclonic and anti-cyclonic interactions. It is found that a greater amount of wave-like activity is generated during the interactions in anticyclonic situations. We also see distinct qualitative differences between the interactions for cyclonic and anti-cyclonic regimes.
13
Zhu, Qun. "Rotating orthogonal polarization imaging." Thesis, University of Nottingham, 2009. http://eprints.nottingham.ac.uk/13518/.
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Non-invasively characterizing the polarization properties of tissues has potential for in vivo clinical applications such as monitoring the healing state of wounds and burns. Conventional methods, which measure the polarization difference of a tissue and usually involve a co-polarized detection, are either restricted by a sample's surface reflections or can only be performed in off-axial systems with the use of matching fluid and a glass plate applied to the sample's surface. In this thesis a new technique called rotating orthogonal polarization imaging (ROPI) is presented. The technique involves illumination in a single polarization state and detection in the orthogonal polarization state in a coaxial system. Synchronously rotating both the illumination and orthogonal detection states can provide a polarization difference image that is free from surface reflections and sensitive to the polarization property of a target embedded within a scattering medium. The basic theoretical principle of the technique is demonstrated using Mueller calculus. Monte Carlo (MC) simulations are used to simulate the ideal performance when detecting a polarizing target embedded in a scattering medium at different depths. Tissue phantom experiments also investigate the imaging of a polarizing target embedded within a scattering medium at different depths using manual rotation of polarisers and liquid crystal tunable filters. ROPI is far more effective than conventional polarization difference imaging due to the significant reduction in surface reflections. The technique is sensitive to polarizing targets embedded at depths of up to 17 mean free paths within the medium. Accurate quantification of dichroism is difficult due to scattering that occurs between the target and the exit surface of the medium. In addition, preliminary measurements of the linear dichroism of different real tissues (bovine tendon, lamb tendon, chicken breast and human skin) and a tissue engineered tendon orientated at two orthogonal directions are demonstrated. It should be noted that the majority of simulation and tissue phantom results that are presented in this thesis are for performing ROPI for polarizing targets embedded in a scattering solution. Much further work is required before the technique can be taken into clinical practice. Issues such as image alignment and the inversion of the data to produce clinically useful images still need to be addressed.
14
Zahniser, Russell 1982. "Instabilities of rotating jets." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32752.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2004.<br>Includes bibliographical references (p. 33-34).<br>When a jet of water is in free fall, it rapidly breaks up into drops, since a cylinder of water is unstable. This and other problems involving the form of a volume of water bound by surface tension have yielded a wealth of theoretical and experimental results, and given insight into such phenomena as the shape of the Earth. Particularly interesting behaviors tend to emerge when the fluid in question is rotating; a drop may, for example, form a toroidal or ellipsoidal shape or even stretch out into some multi-lobed, non-axisymmetric form. In this paper, we investigate the properties of a rotating jet of water, and determine what regime of the parameter space are dominated by the various forms of instability. This is both predicted theoretically and demonstrated to be accurate experimentally. If we watch a jet of water as the rotation rate is gradually increased from zero, the drop size will start shrinking gradually, and then suddenly, rather than a single row of drops, we will see the jet breaking up into two-lobed, bar shaped forms, like the rung of a ladder. The point at which this transition occurs is characterized in terms of the rotational Bond number, B₀ = ... . The critical B₀ may be as low as 6, if there is a strong bias imparted by vibration of the table at an appropriate frequency, but for a perfectly quiescent rotating jet the second mode does not become dominant until a higher B₀. As the rotation rate is increased above this, the instability grows gradually more dramatic, and eventually the two lobes of each drop are breaking apart and flying outward. Then a transition to a third mode will occur, with three lobes in each drop; this is possible from a B₀ of 12, and dominant above a B₀ slightly higher than that. In general, mode m may occur whenever<br>(cont.) B₀ > m(m + 1).<br>by Russell Zahniser.<br>S.B.
15
Eckold, Matthew. "The rotating cavity laser." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/374674/.
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This thesis describes a new technique for mitigating the detrimental thermal phenomena that often limit the power scaling potential of solid state lasers. The unavoidable heating effect that arisesfrom the quantum defect leads to a degradation in beam quality, reduced efficiency and, eventually catastrophic failure. However, lasing processes occur on a faster time scale than those associated with heat flow through a typical laser gain medium. This is made use of whenever a laser is operated in a QCW mode, the laser is operated within an adiabatic window then turned off whilst the gain medium cools. This adds a constraint to the maximum duty cycle of the laser and thus reduces the average power output. Alternatively to separating the two processes in time they can be separated in space. The thermal process can be separated from lasing with the introduction of motion to the system. By passing a collinear pump beam and laser mode through a rotating periscope placed in front of a gain medium the lasing spot can be moved into cold material before heat is able to flow. We call this arrangement the Rotating Cavity Laser (RCL). Unlike previously demonstrated solid state lasers which make use of motion, the RCL keeps the gain medium stationary. This allows it to be heat sunk directly, simplifying the mechanical arrangement. Within this thesis the first results from an RCL are presented with theoretical predictions of the influence motion has both on the lasing and thermal properties of the system. Attention is paid to the regime where stimulated emission is negligible and the losses due to motion are therefore greatest. The analysis of this regime allowed the threshold under motion to be calculated and the approach was verified experimentally. The RCL architecture allowed 120 W of 1064 nm light to be generated from a single end pumped Nd:YAG ceramic slab. The presence of moving intracavity components was found to have consequences for the stability of the power output. When producing 72 W the output power varied with a standard deviation of 2.8%, importantly this variation was cyclic suggesting it would be straightforward to correct by modulating the pump source. Whilst excellent beam quality was found at low powers the M2 became poor as the pump power increased. At output powers less than 51 W the beam quality was found to be constant over a rotation period. It is postulated that the increase in M2 at high pump powers, as well as the increase in variation in beam quality over a rotation period, is partly due to the presence of a thermally induced wedge compromising the alignment of the resonator. A number of experiments are also presented that demonstrate the effectiveness of introducing motion as a method to reduce the thermal load within a laser gain medium. Losses due to stress induced birefringence were reduced from 8% for the stationary case to less than 0.5% by rotating the periscope. The aberrating nature of the thermal lens present in the RCL was also investigated by passing a 1064 nm probe beam through it. When the periscope was stationary the probe beam degraded from an M2 of 1.1 to 2.0 under 16.3 W of pump power. Introducing motion and pumping the slab with 180 W resulted in the M2 increasing to 1.4, clearly demonstrated the greater resilience a system with motion has to detrimental thermal effects.
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Chilakamarri, Kiran Babu. "Rotating and stratified fluids /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487584612163036.
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Anand, Vijay G. "Rotating Detonation Combustor Mechanics." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1530798871271548.
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Garnier, Vincent Hubert. "Experimental investigation of rotating waves as a rotating stall inception indication in compressors." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/41584.
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Schultz, Frederick William. "Loss of rotation of a rotating two-body tethered spacecraft, analytical and experimental techniques." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0019/MQ48473.pdf.
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Schultz, Frederick William Carleton University Dissertation Engineering Mechanical and Aerospace. "Loss of rotation of a rotating two-body tethered spacecraft-analytical and experimental techniques." Ottawa, 1999.
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Pfannes, Jan M. M. "Explosions of rotating white dwarfs." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983425930.
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Frimodig, Love. "Energy efficiency in rotating equipment." Thesis, KTH, Marina system, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-101905.
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This paper reports the findings of the first stage of a study on how the efficiency of a centrifugal pump depends on the eccentricity of the impeller (rotor). The geometry of the pump is based on the ERCOFTAC centrifugal pump that has been used to validate computational fluid dynamics software with laboratory measurements. The pump is modelled using the CFD-code Comsol multi physics (tm) in order to get the pressure and velocity field. From the pressure and velocity field the efficiency and output power for the pump is calculated. The energy efficiency of the same pump with different static eccentricities is then compared, showing the effect of eccentricity To validate the CFD-model the velocity and pressure field for the pump is compared to results from another simulation of the same pump and an experiment. The comparison shows that the results are comparable and shows good agreement with experimental data. It is showed that the energy losses of the pump increase with increased static eccentricity of the impeller. The losses at 10% eccentricity are about 0.5% of the produced energy. The main contribution to the losses is the introduced asymmetry, eccentricity, of the pump, which causes an unsteady flow and also increases the total unbalance force on the rotor. It is further noted that rotor-stator interactions of the impeller and the stator blades have small influence on the energy losses. It is concluded that rotordynamic design can improve the energy efficiency of the process that the rotating equipment is involved in. Further research is suggested on whirling eccentric motion, experimental verification and more detailed simulation models.
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Slade, James. "Synchronization of multiple rotating systems." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Thesis/Summer2007/j_slade_072607.pdf.
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Hacker, Jacob. "Gravity currents in rotating channels." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426506.
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Edwards, S. "Fault diagnosis of rotating machinery." Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636771.
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In this thesis, topics of importance to the fault diagnosis of rotating machinery in the power generation industry have been addressed, including a review of the relevant literature and an overview of the associated rotordynamics modelling and analysis techniques. For faults involving rotor-stator interaction it has been shown that the inclusion of torsion in mathematical models used for rotor-stator contract analyses can have a significant influence on the dynamic behaviour of the system. A 3 degrees-of-freedom model based on the Jeffcott rotor was developed and, for physically realistic systems, it was shown that very different results were obtained when including torsion, compared to when torsion was neglected, as has generally been the case in the past. An identification method for estimating both the excitation and flexible support parameters of a rotor-bearings-foundations system has been presented. Excitation due to both mass unbalance and a bent rotor were included in the analysis, which has been verified both in simulation and experimentally. The method has great practical potential, since it allows balancing to be performed using data obtained from just a single run-up or run-down, which has obvious benefits for field balancing. Using this single-shot balancing technique in experiment, vibration levels were successfully reduced by as much as 92% of their original levels. A bent rotor has been accurately identified in both simulation and experiment. It was also shown that including bend identification in those cases where only unbalance forcing was present in no way detracted from the accuracy of the estimated unbalance or foundation parameters. The identification of the flexible foundation parameters was generally successful, with measured and estimated parameters matching very closely in most cases. The identification method was tested for a wide range of conditions and proved suitably robust to changes in the system configuration, noisy data and modelling error.
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Cattley, Robert. "The contra-rotating hydraulic turbine." Thesis, Lancaster University, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.539635.
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Khan, Raja S. R. "TERA for Rotating Equipment Selection." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/9338.
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This thesis looks at creating a multidisciplinary simulation tool for rotating plant equipment
selection, specifically gas turbines, for the liquefaction of natural gas (LNG). This is a
collaborative project between Shell Global Solutions and Cranfield University in the UK. The
TERA LNG tool uses a Techno-economic, Environmental and Risk Analysis (TERA)
approach in order to satisfy the multidisciplinary nature of the investigation. The benefits of
the tool are to act as an aid to selection, operations and maintenance planning and it also acts
as a sensitivity tool for assessing the impact of changes in performance, environmental and
financial parameters to the overall economic impact of technology selection. The aim is to not
only select technology on the basis of techno-economics but also on the basis of risk analysis.
The LNG TERA tool is composed of a number of modules starting with the performance
simulation which calculates the thermodynamic conditions in the core of the engine. Next, life
estimates of the hot gas path components are made using a mixture of parametric and
probabilistic lifing models for the turbine first stage blades, coatings, and combustor liner.
This allows for a risk analysis to be conducted before maintenance and economics issues are
dealt with. In parallel, emissions estimations are made based on empirical correlations. The
modelling exemplifies a methodology which is uniquely applied to this application and there
are no studies previous to this which look at so many aspects before making conclusions on
plant machinery selection.
Comparisons have been done between industrial frame engines based on the General Electric
Frame 9E (130 MW) and Frame 7EA (87 MW) engines as well as more complex cycles
involving aero-derivation and inter-cooling such as the LM 6000 (42 MW) and LMS 100 (100
MW). Work has also been carried out to integrate the tool to Shell based systems in order to
utilise the database of information on failure and maintenance of machinery as well as its
performance.
The results of the integrated TERA show a clear favour for the aero-derivative engines and
the main benefit is the fuel saving, though the life of the hot gas path components is
deteriorated much faster. The risk results show that the industrial frame engines have a wider
variation in expected life compared to aero-derivatives, though the industrial frames have
longer component lives. In the context of maintenance and economics, the aero-derivative engines are better suited to LNG applications. The modular change out design of the aero-
derivatives also meant that time to repair was lower, thus reducing lost production.
Application of the LNG TERA tool was extended to power generation whereby a series of 6
engines were simulated. The changes required to the modelling were minimal and it shows
the flexibility of the TERA philosophy. This study was carried out assuming a given ratio of
load split between the engines and hence is sensitive to the way an operator demands power
of the engine as opposed to LNG application where the operator tries to drive the engine as
hard as possible to get the most production out of the train.
The study was limited in the modes of failure which were investigated, a major further work
would be to extend the methodology to more components and incorporate fatigue failure.
Further, the blade creep and probabilistic coating models were very sensitive to changes in
their respective control parameters such as coating thickness allowances and firing
temperature.
The contribution to the project from the MBA is the statistical techniques used to conduct the
risk analysis and data handling as well as financial management techniques such as the Net
Present Value (NPV) methodology for project evaluations.
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Hartmann, Derek R. "Denitrification using rotating biological contactors." Thesis, Bradley University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1554015.
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<p> Nitrogen and phosphorus are known to cause eutrophic conditions in lakes and rivers, resulting ultimately in deteriorating water quality in these natural systems. Nitrate poses a threat to the ecosystem and aquatic life, and also has an adverse impact on human health when present in water in large concentrations. Regulatory bodies such as the Federal EPA and state agencies are imposing increasingly stringent effluent standards on point sources to protect and preserve natural water bodies. Technologies using biological nutrient removal processes are being incorporated into the waste treatment scheme at most wastewater treatment plants in an attempt to limit nutrient discharge. The use of completely-submerged anoxic rotating biological contactors (RBCs) to remove NO<sub>3</sub>-N is a relatively new concept, although RBCs have been used for removal of ammonia and biochemical oxygen demand (BOD) for some time. In this study, HDPE disks (10” x 9”) obtained from the Greater Peoria Sanitary District (GPSD) were used as RBC media and mounted on a shaft rotating at 1 rpm in two 20-liter enclosed reactors. At a flowrate of 45 liters per day, synthetic wastewater containing sodium citrate as the carbon source and nitrate as the electron acceptor was used as influent. The duration of each experiment was about 30 days, during which, overall nitrate removal and denitrification rate constants were estimated under different experimental conditions. Factors affecting startup growth were also identified. </p>
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Kilic, Muhsin. "Flow between contra-rotating discs." Thesis, University of Bath, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357401.
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Surgeoner, Donna Agnes. "Studies of rotating biological contactors." Thesis, Queen's University Belfast, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263488.
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Osman, Maslan Bin Haji. "Rotating magnetoconvection with ohmic heating." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363534.
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Padley, Robert William. "Fluid flow past rotating bodies." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396927.
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Worland, Steven John. "Magnetoconvection in rapidly rotating spheres." Thesis, University of Exeter, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403250.
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Cole, Steven James. "Nonlinear rapidly rotating spherical convection." Thesis, University of Exeter, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410805.
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Williams, Rhiannon Lowri. "Perturbations of rotating compact objects." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432728.
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Ranjan, Avishek. "Inertial waves in rotating turbulence." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709436.
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Cockerill, Aaron. "Damage detection of rotating machinery." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/105671/.
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Acoustic emission (AE) is an emerging technique for the condition monitoring of rotating machinery components, including both rolling element bearings and gears. Due to the high frequency range over which AE is sensitive to, AE potentially offers advantages for detection of incipient damage at an early stage of failure when compared to traditional techniques such as vibration. This thesis first investigates the effects of increased speed and load on the generation of AE within cylindrical roller bearings, and determines similarities and differences between AE and vibrational data. A traditional AE sensor was used in conjunction with a Dual Function Sensor (DFS) capable of recording both low frequency AE and vibration. It was shown that increasing speed has the greatest influence on the AE signals produced whereas the effect of load was limited. Order analysis of both AE and vibrational data also demonstrated that characteristic bearing defect frequencies are visible in the AE spectrum but not in the vibrational spectrum. Bearings with seeded defects upon the outer raceway were investigated under a fixed speed and it was found that load increased the energy within the signal frequency spectrum as the damaged increased. Two bearing life tests were also conducted, one accelerated to 12 hours and the second extended to over 2800 hours however as damage detection only occurred after significant damage had developed, it is concluded that AE of seeded defects indicate a false sensitivity. Both life tests were able to demonstrate that signal levels increase as damage propagates over the bearing raceway however it was not possible to determine any advantage of using AE over vibration. AE sensors were also applied to test rigs of increased complexity, including the monitoring a wind turbine planet bearing and a helical gear pair. AE was able to detect cracking of the shaft surface within the wind turbine bearing test rig which was mistaken for being an inner raceway failure, highlighting the difficulty in damage location. A tooth failure occurred during the testing of the helical gear pair however AE was not able to detect growing damage, instead only increasing in amplitude after the tooth had sheared off, similar to the detection from vibrational signals.
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Venkatrayappa, Darshan. "Image matching using rotating filters." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS200/document.
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De nos jours les algorithmes de vision par ordinateur abondent dans les applications de vidéo-surveillance, de reconstruction 3D, de véhicules autonomes, d'imagerie médicale, etc… La détection et la mise en correspondance d'objets dans les images constitue une étape clé dans ces algorithmes.Les méthodes les plus communes pour la mise en correspondance d'objets ou d'images sont basées sur des descripteurs locaux, avec tout d'abord la détection de points d'intérêt, puis l'extraction de caractéristiques de voisinages des points d'intérêt, et enfin la construction des descripteurs d'image.Dans cette thèse, nous présentons des contributions au domaine de la mise en correspondance d'images par l'utilisation de demi filtres tournants. Nous suivons ici trois approches : la première présente un nouveau descripteur à faible débit et une stratégie de mise en correspondance intégrés à une plateforme vidéo. Deuxièmement, nous construisons un nouveau descripteur local en intégrant la réponse de demi filtres tournant dans un histogramme de gradient orienté (HOG) ; enfin nous proposons une nouvelle approche pour la construction d'un descripteur utilisant des statistiques du second ordre. Toutes ces trois approches apportent des résultats intéressants et prometteurs.Mots-clés : Demi filtres tournants, descripteur local d'image, mise en correspondance, histogramme de gradient orienté (HOG), Différence de gaussiennes<br>Nowadays computer vision algorithms can be found abundantly in applications relatedto video surveillance, 3D reconstruction, autonomous vehicles, medical imaging etc. Image/object matching and detection forms an integral step in many of these algorithms.The most common methods for Image/object matching and detection are based on localimage descriptors, where interest points in the image are initially detected, followed byextracting the image features from the neighbourhood of the interest point and finally,constructing the image descriptor. In this thesis, contributions to the field of the imagefeature matching using rotating half filters are presented. Here we follow three approaches:first, by presenting a new low bit-rate descriptor and a cascade matching strategy whichare integrated on a video platform. Secondly, we construct a new local image patch descriptorby embedding the response of rotating half filters in the Histogram of Orientedgradient (HoG) framework and finally by proposing a new approach for descriptor constructionby using second order image statistics. All the three approaches provides aninteresting and promising results by outperforming the state of art descriptors.Key-words: Rotating half filters, local image descriptor, image matching, Histogram of Orientated Gradients (HoG), Difference of Gaussian (DoG)
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Govatzidakis, George John. "Heat transfer in rotating passages." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/49954.
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Staplehurst, Philip John. "Structure formation in rotating turbulence." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611973.
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Lim, Sing-Yong. "Particle dynamics in rotating cylinders." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619608.
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Strauß, Frank. "Design optimization of rotating bodies." [S.l. : s.n.], 2005. http://nbn-resolving.de/urn:nbn:de:bsz:16-opus-59798.
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Bhat, Rajiv. "Bosons in rotating optical lattices." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3315808.
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Ryan, Richard Daniel. "An investigation of rotating magnetospheres." Thesis, University of St Andrews, 2002. http://hdl.handle.net/10023/11294.
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In this thesis we will construct simple models of rotating stellar and planetary magnetospheres within the framework of ideal MHD. These models will take the basic outline of a stellar magnetosphere that we have outlined above as a starting point from which to proceed further. In summary, this simple magnetosphere will be that of a single, rapidly rotating star' with an axisymmetric dipole magnetic field at the base of its corona and with an axis that is in alignment with that of the rotation axis. It is the isothermal plasma associated with this field that will give rise to the magnetospheric emission and which is held in strict corotation with the stellar surface. Equatorial and rotational symmetry reduce the domain to one quarter of a two dimensional quadrant. We will consider timescales that are much longer than the typical time scales of the system, which will allow us to model the evolution of the system quasi-statically by calculating sequences of MHS equilibria. This is achieved by numerical solution of the Grad-Shafranov equation (in terms of the flux function. A) Which requires us to specify a suitable surface pressure distribution and specify the toroidal component of the magnetic field as a function of A. The second chapter will outline the numerical procedure that will be employed to calculate these equilibrium sequences, and the practical realisation of this procedure. The third chapter will discuss different models which will be characterised by different surface pressure distributions but all of which will lack a toroidal magnetic field component. The fourth chapter will discuss results from a model which includes a toroidal magnetic field component. The models successfully reproduce the observed saturation and supersaturation of stellar emission with rotation. The fifth chapter will address the question of analytically constructing three dimensional equilibria that may be of use in the modelling of magnetospheres with magnetic field geometries that are not in alignment with their rotation axes or which are displaced from the centre of the rotating body, such as the giant gas planets Uranus and Neptune. The last section of the thesis will be a brief discussion of our conclusions, a review of the work of the thesis and will consider the outlook for further development, extension and refinement of our models.
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Gordon, Kenneth A. (Kenneth Andrew) 1970. "Three-dimensional rotating stall inception and effects of rotating tip clearance asymmetry in axial compressors." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/8183.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999.<br>"June 1999."<br>Includes bibliographical references (p. 383-388).<br>The effects of two types of flow nonuniformity on stall inception behavior were assessed with linearized stability analyses of two compressor flow models. Response to rotating tip clearance asymmetries induced by a whirling rotor shaft or rotor height variations were investigated with a two-dimensional flow model. A 3-D compressor model was also developed to study the stability of both full-span and part-span rotating stall modes in annular geometries with radial flow variations. The studies focussed on (1) understanding what compressor designs were sensitive to these types of circumferential and spanwise flow nonuniformities, and (2) situations where 2-D stability theories were inadequate because of 3-D flow effects. Rotating tip clearance nonuniformities caused the greatest performance loss for shafts whirling at the rotating stall frequency. A whirling shaft displacement of 1% chord caused the stalling mass flow to rise by as much as 10% and the peak pressure rise to decrease by 6%. These changes were an order of magnitude larger than for equivalent-sized stationary or rotor-locked clearance asymmetries. Spanwise flow nonuniformities always destabilized the compressor, so that 2-D models over-predicted the stall margin compared to 3-D theory. The difference increased for compressors with larger spanwise variations of characteristic slope and reduced characteristic curvature near the peak. Differences between 2-D and 3-D stall point predictions were generally unacceptable (2-4% of flow coefficient) for single-stage configurations, but were less than 1% for multistage compressors. 2-D analyses predicted the wrong stall mode for specific cases of radial inlet flow distortion, mismatching and annulus area contraction, where higher-order radial modes led to stall.<br>(cont.) The stability behavior of flows with circumferential or radial nonuniformity was unified through a single stability criterion. The stall point for both cases was set by the integral around the annulus of the pressure rise characteristic slope, weighted by the amplitude of the mode shape. For the case of steady circumferential variations, this criterion reduced to the integrated mean slope (IMS) condition associated with steady inlet distortions. The rotating tip clearance asymmetry model was also used to demonstrate the feasibility of actively controlling the shaft position to suppress rotating stall. In axisymmetric mean flow, this method only stabilized the first harmonic mode, increasing the operating range until surge or higher harmonic modes became unstable.<br>by Kenneth A. Gordon.<br>Ph.D.
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Carvalho, Gustavo Bifaroni de [UNESP]. "Estudo experimental do escoamento em torno de cilindros circulares em movimento de rotação." Universidade Estadual Paulista (UNESP), 2003. http://hdl.handle.net/11449/88895.
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carvalho_gb_me_ilha.pdf: 3399591 bytes, checksum: 93cf9ce80b863df9a4e44fe804f03aa6 (MD5)<br>O presente trabalho traz uma investigação experimental do escoamento em torno de um cilindro rotativo posicionado perpendicularmente à direção principal do escoamento, para números de Reynolds inferiores a 103. Os experimentos foram conduzidos em um túnel hidrodinâmico vertical, com seção de teste 146x146x500 mm e intensidade turbulenta da corrente livre inferior a 0,5%. O diâmetro do corpo de prova foi fixado em 6 mm, proporcionando um bloqueio sólido no interior da seção de testes pouco superior a 4%. A influência do número de Reynolds e da rotação específica do corpo de prova sobre a configuração do escoamento foi bastante estudada. A freqüência de emissão dos vórtices, necessária ao cálculo do número de Strouhal, foi determinada a partir da obtenção do sinal de velocidades, adquirido com o auxílio de um anemômetro de filme quente, ou através da técnica de contagem de fotogramas. Técnicas de visualização de escoamento foram, também, empregadas, em diferentes circunstâncias, tanto na análise qualitativa do escoamento, como para auxiliar o correto posicionamento das sondas de filme quente. Em vários ensaios, a visualização do escoamento por injeção de corante líquido a montante do corpo de prova foi utilizada, mostrando-se bastante eficiente, sobretudo no que concerne à qualidade das imagens obtidas. No entanto, esta técnica só possibilita a visualização de uma região bastante restrita do escoamento e, dependendo do posicionamento da agulha de injeção, diferentes configurações do escoamento podem ser observadas, dificultando a interpretação dos resultados. Para contornar esta situação, utilizou-se, também, a técnica de geração de bolhas de hidrogênio, que permite uma visão mais abrangente do campo de escoamento. De maneira geral, os resultados foram bastante satisfatórios quando comparados com a literatura, mostrando que a... .<br>This work presents an experimental investigation on the flow around a rotating cylinder positioned perpendicularly to the free stream, for Reynolds numbers up to 103. The experiments have been carried out inside a 146x146x500 mm test section of a vertical water tunnel, using a 6mm diameter cylinder, which has provided a lower than 4% blockage ratio inside the test section, under a less than 0.5% maximum free-stream turbulence intensity. The influence of both diameter-based Reynolds number and specific rotation of the cylinder on the flow configuration has been analyzed. The vortex shedding frequency, parameter necessary to evaluate the Strouhal number, has been determined from the velocity signal from hot film anemometer as well as directly through a framecounting technique. Two different methods of flow visualization, liquid dye and hydrogen bubble generation, has been also used under distinct circumstances, in order to provide a qualitative analysis of the flow, as well to obtain the correct location of the hot-film probes. In some experiments, flow patterns have been visualized by liquid dye injection upstream the test cylinder, propitiating a good image quality. Dye injection, however, allows for the visualization of a quite restricted area of the flow, in such a way that, depending on the needle location, several distinct flow configurations appear, making it very difficult the interpretation of the results. In order to mitigate those drawbacks, the technique of hydrogen bubble generation has also been employed, reaching for a far wider vision of the flow field. The achieved results have showed that the wake structure is strongly affected by the cylinder rotation, in such a way that the vortices generation can be totally inhibited for a values upper than 2, in the all range of the Reynolds number.
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Garcia, Gonzalez Ferran. "Thermal convection in rotating spherical shells." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285778.
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The study of thermal convection in rotating spherical geometry is fundamental to explain many geophysical and astrophysical phenomena such as the generation of the magnetic fields, or the differential rotation observed in the atmospheres of the major planets. The difficulties associated with the experimental studies enhance the importance of the three-dimensional numerical simulations, such as those presented in this dissertation.
In order to obtain the evolution equations, the Boussinesq approximation is applied to the mass, momentum and energy conservation equations, which are rewritten in terms of toroidal and poloidal potentials. Together with the temperature field, they are expanded in spherical harmonics over the sphere, and in the radial direction a collocation method is used. Semi- implicit schemes, based in backward differentiation formulae (IMEX-BDF), implemented with order and time step control (VSVO), are used for time integration.
Applying non-slip boundary conditions with internal heating and very low Prandtl numbers (ratio between the thermal diffusive and the viscous time scales), one of the first exhaustive analysis of the linear stability of the conductive state has been performed. In addition, the existence of preferred polar antisymmetric modes at the onset of convection for high rotation rates has been described.
A study of the efficiency of different high order time integration schemes, either with fixed time-step or VSVO, has been carried out. In our own time evolution codes we apply the IMEX-BDF formulae with an explicit treatment of the nonlinear terms of the equations. The use of 'matrix-free' methods allows the implicit treatment of the Coriolis term, and makes the implementation of a step and order control easier. The results show that the use of high order methods, especially those with time-step and order control, increase the efficiency of the time integration, and allows to obtain more accurate solutions.
Finally, at low Prandtl number, and with non-slip boundary conditions, the nonlinear dynamics is deeply explored by means of temporal evolutions. The type of solutions is described, and the nonlinear mean flow properties are studied. Using parameters as close as possible to those of the Earth's outer core, the numerical simulations are compared with laboratory experiments and realistic measurements.<br>L'estudi de la convecció tèrmica en geometria esfèrica en rotació es fonamental per explicar molts fenòmens geofísics i astrofísics, com la generació de camps magnètics, o la rotació diferencial observada en l'atmosfera dels planetes majors. Les dificultats associades amb els estudis experimentals afavoreixen que les simulacions numèriques tridimensionals, com les que es presenten en aquesta memòria, siguin una eina molt important en aquest camp. Per a l'obtenció de les equacions d'evolució, s'aplica l'aproximació de Boussinesq a les equacions de conservació de la massa, la quantitat de moviment i l'energia, i es reescriuen en funció dels potencials toroidal i poloidal. Els potencials i la temperatura es desenvolupen, sobre l'esfera, en harmònics esfèrics i en la variable radial s'usa col·locació. Per a la integració es fan servir esquemes semi-implícits, que en el nostre cas, estan basats en les fórmules de diferenciació regressiva (IMEX-BDF), que s'han implementat amb control d'ordre i pas (VSVO). En primer lloc, sota condicions de contorn d'adherència, calentament intern i nombre de Prandtl (quocient entre les escales de temps de difusió tèrmica i viscosa) molt baix s'ha realizat un dels primers anàlisis exhaustius de l'estabilitat lineal de l'estat conductiu, gràcies a la millora dels mètodes numèrics emprats. Així mateix, s'ha descrit per primera vegada l'existència de modes polars antisimètrics a l'inici de la convecció amb rotacions elevades. En segon lloc s'ha realizat un estudi de l'eficiència de diferents integradors temporals d'ordre alt, amb pas fix o VSVO. En els nostres propis codis temporals apliquem les fórmules IMEX-BDF amb un tractament explícit dels termes no lineals de les equacions. L'ús de mètodes 'matrix-free' fa rentable el tractament implícit del terme de Coriolis i facilita la implementació d'un control d'ordre i pas temporal adequat. Els resultats mostren que amb ordre elevat, amb o sense control de pas i ordre, s'incrementa l'eficiència de la integració i s'obtenen solucions més acurades. Finalment, amb nombre de Prandtl baix i condicions de contorn d'adherència, s'explora exhaustivament la dinàmica no lineal mitjançant evolucions temporals, tot descrivint el tipus de solucions. També s'estudien les propietats mitjanes de fluxos no lineals. Utilizant paràmetres el més similars possible als del nucli extern de la Terra es comparen els resultats de les simulacions numèriques amb experiments de laboratori i amb medicions de situacions reals.
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Maccarrone, Heredia Alessandro. "Microscopic analysis of rotating black holes." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/395196.
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The main objective of this thesis is to understand from a microscopic point of view some of the characteristic phenomena of rotating black holes.
The inclusion of rotation gives rise to physics that allows a more precise and detailed understanding of the microscopic string theory of black holes. In this thesis we focus on two models of particular interest: one is based on the D0-D6 system and the other on the D1-D5-P system. The former is interesting because, through its connection to M-theory, it yields a statistical-mechanics description of neutral black holes. The latter allows to have better control over the microscopic conformal field theory and yields a cleaner picture of the origin of superradiance.
We extend the microscopic analysis of extremal dyonic Kaluza-Klein (D0-D6) black holes to cover the regime of fast rotation in addition to slow rotation. Fastly rotating black holes, incontrast to slow ones, have non-zero angular velocity and possess ergospheres, so they are more similar to the Kerr black hole. The D-brane model reproduces their entropy exactly, but the mass gets renormalized from weak to strong coupling, in agreement with recent macroscopic analyses of rotating attractors.
We discuss how the microscopic model accounts for the fact that fastly rotating extremal KK black holes possess an ergosphere and exhibit superradiance while slow ones don't. In addition, we show in full generality how Myers-Perry black holes are obtained as a límit of Kaluza-Klein black holes, and discuss the slow and fast rotation regimes and superradiance in this context.
A, perhaps surprising, consequence of our analysis is that both slowly and fastly-rotating KK black holes provide microscopic accounts of the entropy formula of MP black holes, even if they correspond to rather different microscopic states. As we discuss, this does not pose any problem, since the microscopic theory always retains a memory of how the 5D black hole is embedded within Taub-NUT.
For a more detailed and quantitative study of black hole superradiance from the stringy
microscopic side, we consider the D1-D5-P system. In order to disentangle superradiance from finite-temperature effects, we consider an extremal, rotating D1-D5-P black hole that has an ergosphere and is not supersymmetric.
We explain how the microscopic dual accounts for the superradiant ergosphere of this black hole. The bound 0 < ω < mΩH on superradiant mode frequencies is argued to be a consequence of Fermi-Dirac statistics for the spin-carrying degrees of freedom in the dual CFT. We also compute the superradiant emission rates from both sides of the correspondence, and show their agreement. This is an extension of previous analyses of radiation from the D1-D5-P black holes. We generalize those results to include momentum for the bulk scalar.
It would be interesting to extend our picture for superradiance to the smooth SUGRA solitons with D1-D5-P charges which correspond to CFT states such that both sectors are in pure states. Another issue to be investigated would be the absence of fermionic superradiance emission by the previously considered systems with ergoregion.<br>L'objectiu principal d'aquesta tesi és comprendre des d'un punt de vista microscòpic alguns dels fenòmens característics dels forats negres amb rotació.
Ens centrem en forats negres amb rotació, extremals, però no supersimètrics. Aquesta mena de solucions són les més adequades per al nostre propòsit. A diferència del cas supersimètric, presenten una ergosfera i, per tant, s'hi pot produir el fenomen de la superradiància. Però, en tenir temperatura nul·la aquest fenomen no apareix “barrejat” amb la radiació de Hawking d'origen purament tèrmic. Alhora, aquestes geometries extremals també preserven el nombre de microestats en passar d'acoblament feble a acoblament fort.
La primera part de la tesi, se centra en l'estudi microscòpic de l'entropia dels forats negres de Kaluza-Klein amb rotació. Aquesta família de solucions, presenta dos límits extremals: el de “rotació lenta” i el de “rotació ràpida”. Treballs anteriors ja havien aconseguit reproduir l'entropia del primer cas. Aquí, estenem aquest càlcul al límit extremal amb rotació ràpida. Alhora, mostrem que el fenomen de la superradiància es pot explicar de manera anàloga a la radiació de Hawking, en termes de dues excitacions que xoquen i provoquen l'emissió d'una corda tancada. En aquest cas, aquest mode emès té necessàriament un moment angular diferent de zero.
A la segona part, ens centrem en aquesta interpretació microscòpica de la superradiància amb un tractament més quantitatiu. En aquest cas, considerem les solucions extremals no supersimètriques del sistema D1-D5-P amb rotació. A partir de la seva descripció microscòpica, aconseguim reproduir la condició de superradiància ω < mΩH i mostrem que es pot entendre com a conseqüència de l'estadística de Fermi-Dirac. També avaluem els ritmes d'emissió de superradiància des del punt de vista macroscòpic i microscòpic i analitzem si concorden.
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Souza, Max Oliveira de. "Instabilities of rotating and unsteady flows." Thesis, University of Cambridge, 1998. https://www.repository.cam.ac.uk/handle/1810/251641.
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This dissertation is divided into two parts. The first part discusses the stability and breakdown of swirling flows. The second one deals with the stability of time periodic flows. Chapter 1 gives the background and reviews previous work in vortex breakdown. Chapter 2 deals with various aspects of axisymmetric breakdown. These include the study of basic states that do not support waves, and the role played by the downstream boundary conditions in steady solutions to the Euler equations. A description of the bifurcation diagram for pipes is presented, and we also show how the process of wave-steepening can lead to the formation of a highly oscillatory shock. In chapter 3, we study the weakly non-linear stability of trailing vortices. Following numerical calculations by Yang (1992), who found a viscous instability for arbitrary large values of the swirl at sufficiently large Reynolds number, we present an analysis for the steady states and their stability. We obtain fast-swirling, steady states, and study their linear stability to viscous centre-modes. For nearly neutral modes, we investigate their weakly nonlinear stability, accounting for non-parallel effects. Previous work on stability of time-periodic flows is reviewed in chapter 4. In chapter 5, we extend the critical-layer analysis by Lin (1955) to unsteady flows, and use it to investigate the stability of several oscillatory flows. For slightly oscillatory Plane-Poiseuille flow, the method is able to recover periodic modes (asymptotic Floquet modes for large Reynolds numbers). Nevertheless, the method fails for the Stokes layer; the reasons for such failure are discussed. Finally, we present in chapter 6 some results on the completeness of Floquet modes in channels.
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Rashid, Dewan Md Harunur Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Wake survey behind a rotating ventilator." Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2002. http://handle.unsw.edu.au/1959.4/19076.
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With environmental concern growing in both affluent and developing countries, roof top ventilators, a form of natural ventilation requiring only wind energy to ensure quality air circulation and comfort is becoming a considered choice of many households and industries. Unfortunately, however, many of these ventilators have evolved through trial and error and the flow physics associated with these ventilators is barely understood. The present experimental project was, therefore, undertaken as part of UNSW- Industry collaboration program funded under an Australian Research Council Grant to explore whether the aerodynamics forces acting on these ventilators during their operation could be obtained. A commercial roof top ventilator supplied by industry was, therefore, tested in an open jet wind tunnel of the University of New South Wales and the results are presented in this thesis. A novel feature of this project is the examination of the suitability of ???the three dimensional wake traverse??? technique to the wake of rotating ventilator. This technique has so far been applied with limited success to the wake of lifting bodies of fixed wing configuration only. In the absence of adequate data in the literature on rotating ventilator, the aerodynamics force components obtained by this technique have been compared against force balance measurements. The results show that the wake traverse technique is capable of determining lift and total drag forces associated with the ventilator flow during its operation from the pressure and velocity information gathered downstream of a ventilator in its wake. Generally, from these data, the technique also allows isolation of the profile and induced components of the drag force. However, from the induced drag value, while it is possible to determine the lift force, it is however, found that a more accurate value of lift force can be evaluated using axial vorticity formulation. The availability of the above technique which does not require measurements on the test specimen itself, will aid in providing a cost efficient investigation of the aerodynamic forces and consequently the performance of a roof top ventilator.