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1
Short, David James. "Swirling flow induced by a rotating magnetic field." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338644.
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Ferreira, Hugo Ricardo Colaço. "Quantum field theory on rotating black hole spacetimes." Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/29626/.
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This thesis is concerned with the development of a general method to compute renormalised local observables for quantum matter fields, in a given quantum state, on a rotating black hole spacetime. The rotating black hole may be surrounded by a Dirichlet mirror, if necessary, such that a regular, isometry-invariant vacuum state can be defined. We focus on the case of a massive scalar field on a (2+1)-dimensional rotating black hole, but the method can be extended to other types of matter fields and higher-dimensional rotating black holes. The Feynman propagator of the matter field in the regular, isometry-invariant state is written as a sum over mode solutions on the complex Riemannian section of the black hole. A Hadamard renormalisation procedure is implemented at the level of the Feynman propagator by expressing its singular part as a sum over mode solutions on the complex Riemannian section of rotating Minkowski spacetime. This allows us to explicitly renormalise local observables such as the vacuum polarisation of the quantum field. The method is applied to the vacuum polarisation of a real massive scalar field on a (2+1)-dimensional warped AdS3 black hole surrounded by a mirror. Selected numerical results are presented, demonstrating the numerical efficacy of the method. The existence of classical superradiance and the classical linear mode stability of the warped AdS3 black hole to massive scalar field perturbations are also analysed.
3
Yamada, Satoru. "Field Ionization Processes of Highly Excited Rydberg States under a Rotating Electric Field." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147813.
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Miller, Kenneth Elric. "The star thrust experiment, rotating magnetic field current drive in the field reversed configuration /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/9996.
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Peter, Andrew Maxwell. "Paramagnetic spin-up of a field reversed configuration with rotating magnetic field current drive /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9983.
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Simitev, Radostin D. "Convection and magnetic field generation in rotating spherical fluid shells." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97154249X.
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Frierson, Robert V. Jr. "Spectroscopic diagnostics of a plasma in a rotating magnetic field." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/17236.
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Ghoshal, Probir Kumar. "AC loss characteristic of high-Tc superconductors in rotating magnetic field." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611582.
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Wongsa-Ngasri, Pisit. "Ohmic heating of biomaterials: peeling and effects of rotating electric field." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1078447669.
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Hird, Lee D. "Analysis of the flow field between two eccentric rotating cylinders in the presence of a slotted sleeve." Thesis, Curtin University, 1997. http://hdl.handle.net/20.500.11937/859.
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Overend et al [68] designed a viscometer to measure the viscosity of slurries that have a tendency to settle. This viscometer consists of a rotating ribbed rotor surrounded by a stationary slotted sleeve; this system is then placed eccentrically within an inclined rotating bowl. It, is claimed that this overcomes most of the difficulties encountered when attempting to obtain accurate measurements for these types of mixtures. If the mixture being sheared within the annulus does not represent the true composition of the slurry being, tested then the results are expected to be inaccurate. The presence of sediment at the bottom of the rotor or the formation of large masses of particles within the flow domain will affect the accuracy of the measurements obtained. This dissertation studies the amount of flow through the slotted sleeve and the region, or regions, of low shear rate within the flow domain. Assuming that end-effects are unimportant and that the slurries can be replaced by a single-phase fluid, three two-dimensional models are proposed. These models are designed to capture the large-slot construction of the sleeve and the, approximate, non-Newtonian behaviour of the slurries. The first two models solve analytically (using a regular perturbation scheme) and numerically (using a finite volume method) the moderate-and large-Reynolds-number flow, and the third model uses a finite volume method to study the flow patterns developed by pseudoplastic fluids. The results show that the mixing of the slurry is expected to be enhanced by moving the concentric system (i.e., the rotor and the slotted sleeve) close to the rotating bowl and using low to moderate speeds for the rotor and bowl. In addition, when the cylinders rotate in the same directions, two (counter-rotating) eddies are present within the flow domain; whereas, only one eddy (rotating counter-clockwise) is present when the cylinders rotate in opposite directions. The presence of eddies in the former situation inhibits the flow through the sleeve; while, for moderate rotorspeeds, the flow through the sleeve is enhanced in the latter. When the slurry assumed pseudoplastic, we observe a region of low shear rate located near the dividing streamline present within the flow field. The distribution of shear rate within the flow field is shown to be affected by factors such as the rate of diffusion of the apparent viscosity and the value of the power law index. Therefore, this study suggests that for certain types of slurries, concentrations of particles exist within the domain and that the mixing of slurries can be impeded by the presence of eddies within the main flow field.
11
Mayo, Yague Ignacio. "Flow field and heat transfer in a rotating rib-roughened cooling passage." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19529/1/MayoYague_Ignacio.pdf.
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A great effort has been carried out over the recent years in the understanding of the flow field and heat transfer in the internal cooling channels present in turbine blades. Indeed, advanced cooling schemes have not only lead to the increase of the gas turbine efficiency by increasing the Turbine Inlet Temperature above the material melting temperature, but also the increase of the turbine lifespan. To allow such progresses, modern experimental and numerical techniques have been widely applied in order to interpret and optimize the aerodynamics and heat transfer in internal cooling channels. However, the available data is limited in the case of internal cooling channels in turbine rotor blades. Rotation and temperature gradients introduce Coriolis and centripetal buoyancy forces in the rotating frame of reference, modifying significantly the aerothermodynamics from that of the stationary passages. In the case of turbine rotor blades, most of the investigations are either based on point-wise measurements or are constraint to low rotational regimes. The main objective of this work is to study the detailed flow and heat transfer of an internal cooling channel at representative engine dimensionless operating conditions. This work introduces a laboratory test section that operates ribbed channels over a wide range of Reynolds, Rotation and Buoyancy numbers. In the present work, the Reynolds number ranges from 15,000 to 55,000, the maximum Rotation number is equal to 0.77, and the maximum Buoyancy number is equal to 0.77. The new experimental facility consists in a versatile design that allows the interchangeability of the tested geometry, so that channels of different aspect ratios and rib geometries can be easily fitted. Particle Image Velocimetry and Liquid Crystal Thermography are performed to provide accurate velocity and heat transfer measurements under the same operating conditions, which lead to a unique experimental data set. Moreover, Large Eddy Simulations are carried out to give a picture of the entire flow field and complement the experimental observations. Additionally, the numerical approach intends to provide a robust methodology that is able to provide high fidelity predictions of the performance of internal cooling channels.
12
Di, Gennaro Sofia. "Quantum rotating black holes and extra dimensions." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/19851/.
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We employ the formalism of the Horizon Quantum Mechanics to describe the gravitational radius of compact sources by means of an operator and derive a Horizon Wave Function which will allow us to estimate the probability of formation of black holes in scattering processes. If the Planck scale is kept at its standard value, however, it will be impossible to test that regime with any foreseeable technology. We then review how the introduction of extra dimensions can potentially lower the Planck scale down to the TeV range in an attempt to solve the hierarchy problem. In this context, we proceed by studying black holes described by a generalisation of the Kerr metric for higher dimensional spacetime known as the Myers-Perry metric. Our computation of the probability that a rotating source in higher dimensions is a black hole suggests that, even if the fundamental Planck scale is as low as a few TeV's, we should not be able to detect any black hole in colliders as is indeed the case.
13
Yuen, Rai. "Pulsar Magnetosphere Revisited: Emission Geometry and the Synthesis of the Vacuum-Dipole and the Rotating-Magnetosphere Models." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10011.
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We reconsider the vacuum-dipole model (VDM) and the corotating-magnetosphere model (CMM) for pulsar electrodynamics. Both the VDM and the CMM are fatally flawed as stand-alone models. The former model is used for deriving certain pulsar parameters, such as the surface magnetic field strength and characteristic age, but it lacks the plasma required to emit the observed radiation. The latter model introduces important concepts, such as the Goldreich-Julian charge density and corotation electric field, which form the basis for more detailed models, but it neglects the inductive electric field. When this field is included, the model is unstable to growth of large-amplitude electric oscillations when subject to a temporal perturbation. Furthermore, the predicted highly-relativistic magnetospheric plasma given by the two models is inconsistent with results obtained from observations with the Double Pulsar system. We therefore propose a way of synthesizing the VDM and the CMM for obliquely rotating pulsars. We first modify the VDM to a "minimal" model by assuming that the parallel component of the inductive electric field is screened by charges. We define a class of synthesized models as a linear combination of a fraction y times the minimal model and 1 - y times the CMM. We suggest that the synthesized model provides a basis for understanding the abrupt changes in the magnetospheres of some pulsars, which can alter their slowing down rates. The synthesized model also implies that the velocity of the magnetospheric plasma depends on y and the position of the emission point, which is determined numerically based on the obliquity and viewing angles for emission heights close to stellar surface in dipolar magnetic field structure. We also explore the field structure by including higher order terms in the ratio of the radius to the light-cylinder radius in the magnetic field and explore the implications of these additional terms.
14
Abuhdima, Esmail M. M. "Simulation of the Scattered EM Field of a Moving Dynamic Object Using Static Data." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1500725371636494.
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Hird, Lee D. "Analysis of the flow field between two eccentric rotating cylinders in the presence of a slotted sleeve." Curtin University of Technology, School of Mathematics and Statistics, 1997. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=11104.
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Overend et al [68] designed a viscometer to measure the viscosity of slurries that have a tendency to settle. This viscometer consists of a rotating ribbed rotor surrounded by a stationary slotted sleeve; this system is then placed eccentrically within an inclined rotating bowl. It, is claimed that this overcomes most of the difficulties encountered when attempting to obtain accurate measurements for these types of mixtures. If the mixture being sheared within the annulus does not represent the true composition of the slurry being, tested then the results are expected to be inaccurate. The presence of sediment at the bottom of the rotor or the formation of large masses of particles within the flow domain will affect the accuracy of the measurements obtained. This dissertation studies the amount of flow through the slotted sleeve and the region, or regions, of low shear rate within the flow domain. Assuming that end-effects are unimportant and that the slurries can be replaced by a single-phase fluid, three two-dimensional models are proposed. These models are designed to capture the large-slot construction of the sleeve and the, approximate, non-Newtonian behaviour of the slurries. The first two models solve analytically (using a regular perturbation scheme) and numerically (using a finite volume method) the moderate-and large-Reynolds-number flow, and the third model uses a finite volume method to study the flow patterns developed by pseudoplastic fluids. The results show that the mixing of the slurry is expected to be enhanced by moving the concentric system (i.e., the rotor and the slotted sleeve) close to the rotating bowl and using low to moderate speeds for the rotor and bowl. In addition, when the cylinders rotate in the same directions, two (counter-rotating) eddies are present within the flow domain; whereas, only one eddy (rotating counter-clockwise) is ++present when the cylinders rotate in opposite directions. The presence of eddies in the former situation inhibits the flow through the sleeve; while, for moderate rotorspeeds, the flow through the sleeve is enhanced in the latter. When the slurry assumed pseudoplastic, we observe a region of low shear rate located near the dividing streamline present within the flow field. The distribution of shear rate within the flow field is shown to be affected by factors such as the rate of diffusion of the apparent viscosity and the value of the power law index. Therefore, this study suggests that for certain types of slurries, concentrations of particles exist within the domain and that the mixing of slurries can be impeded by the presence of eddies within the main flow field.
16
Snively, Michael John. "Effects of demagnetizing factors on transient motion of ferrofluid in a uniform rotating magnetic field." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68699.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 105).
The mechanisms that lead to bulk flow within a ferrofluid-filled container subjected to a rotating uniform magnetic field are experimentally studied. There are two prevailing theories: spin diffusion theory and flow due to non-uniformities in magnetic field within the ferrofluid due to nonuniform demagnetizing factors. This research sought to confirm previous measurements that indicated demagnetizing factors are the primary cause of bulk ferrofluid flow. Flattened spherical containers of various volumes, and thus different demagnetizing factors, were filled with EFH1 oil-based ferrofluid and subjected to a uniform rotating magnetic field of varying conditions (rotation direction and field strength). The shapes and magnitudes of the velocity profiles measured by an ultrasound velocimeter system differed between containers, indicating that demagnetizing factors did affect flow. The complicated flows within the flattened spheres that affected both the shape and magnitude of the flow velocity prevented a direct magnitude comparison between profiles but the flows differed enough to safely conclude that spatial non-uniformities within the fluid likely caused the bulk flow of fluid in the uniform rotating magnetic field.
by Michael John Snively.
S.B.
17
Денисов, Станіслав Іванович, Станислав Иванович Денисов, Stanislav Ivanovych Denysov, Олександр Юрійович Поляков, Александр Юрьевич Поляков, Oleksandr Yuriiovych Poliakov, Тарас Володимирович Лютий, Тарас Владимирович Лютый, and Taras Volodymyrovych Liutyi. "Lifetime of the precession mode of a nanoparticle magnetic moment in a rotating magnetic field." Thesis, Видавництво СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20967.
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Giersch, Louis Roy Miller. "Experimental investigation of plasma sail propulsion concepts using cascaded arcs and rotating magnetic field current drive /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9958.
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Payne, Thomas A. "Inlet flow-field measurements of a transonic compressor rotor prior to and during steam-induced rotating stall." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Dec%5FPayne.pdf.
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Chen, Jian-Xin. "Modification of organic polymers with vacuum ultraviolet radiation from inert gas plasmas rotating in a magnetic field /." Online version of thesis, 1990. http://hdl.handle.net/1850/11059.
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Bilson, Matthew James. "Momentum and scalar transport in the straight pipe and rotating cylinder : a comparison of transport mechanisms /." St. Lucia, Qld, 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17836.pdf.
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Pfeffer, Sina [Verfasser], and Dominik [Akademischer Betreuer] Weiß. "Anwendung der Rotating-Field-Elektrophorese zur Auftrennung der Multimere des von-Willebrand-Faktors / Sina Pfeffer. Gutachter: Dominik Weiß." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2015. http://d-nb.info/1080362568/34.
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Bekeraitė, Simona Verfasser], Lutz [Akademischer Betreuer] [Wisotzki, Martin M. [Akademischer Betreuer] Roth, and Jakob [Akademischer Betreuer] Walcher. "Distribution functions of rotating galaxies : an Integral Field Spectroscopy perspective / Simona Bekeraitė ; Lutz Wisotzki, Martin M. Roth, Jakob Walcher." Potsdam : Universität Potsdam, 2017. http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-420950.
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Bekeraitė, Simona [Verfasser], Lutz [Akademischer Betreuer] Wisotzki, Martin M. [Akademischer Betreuer] Roth, and Jakob [Akademischer Betreuer] Walcher. "Distribution functions of rotating galaxies : an Integral Field Spectroscopy perspective / Simona Bekeraitė ; Lutz Wisotzki, Martin M. Roth, Jakob Walcher." Potsdam : Universität Potsdam, 2017. http://d-nb.info/1219149802/34.
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Bruce, David P. "Flow field analysis of some mixing and conveying screw element regions, within a closely intermeshing, co-rotating twin-screw extruder." Thesis, Aston University, 1997. http://publications.aston.ac.uk/9602/.
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Grafting of antioxidants and other modifiers onto polymers by reactive extrusion, has been performed successfully by the Polymer Processing and Performance Group at Aston University. Traditionally the optimum conditions for the grafting process have been established within a Brabender internal mixer. Transfer of this batch process to a continuous processor, such as an extruder, has, typically, been empirical. To have more confidence in the success of direct transfer of the process requires knowledge of, and comparison between, residence times, mixing intensities, shear rates and flow regimes in the internal mixer and in the continuous processor. The continuous processor chosen for the current work in the closely intermeshing, co-rotating twin-screw extruder (CICo-TSE). CICo-TSEs contain screw elements that convey material with a self-wiping action and are widely used for polymer compounding and blending. Of the different mixing modules contained within the CICo-TSE, the trilobal elements, which impose intensive mixing, and the mixing discs, which impose extensive mixing, are of importance when establishing the intensity of mixing. In this thesis, the flow patterns within the various regions of the single-flighted conveying screw elements and within both the trilobal element and mixing disc zones of a Betol BTS40 CICo-TSE, have been modelled using the computational fluid dynamics package Polyflow. A major obstacle encountered when solving the flow problem within all of these sets of elements, arises from both the complex geometry and the time-dependent flow boundaries as the elements rotate about their fixed axes. Simulation of the time dependent boundaries was overcome by selecting a number of sequential 2D and 3D geometries, used to represent partial mixing cycles. The flow fields were simulated using the ideal rheological properties of polypropylene and characterised in terms of velocity vectors, shear stresses generated and a parameter known as the mixing efficiency.
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Grunhut, J., G. Wade, M. Leutenegger, V. Petit, G. Rauw, C. Neiner, F. Martins, et al. "Discovery of a Magnetic Field in the Rapidly-Rotating O-Type Secondary of the Colliding-Wind Binary HD 47129 (Plaskett’s Star)." Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/etsu-works/6247.
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We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada–France–Hawaii Telescope and the Narval spectropolarimeter at the Télescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of −810 ± 150 and +680 ± 190 G, implying a minimum surface dipole polar strength of 2850 ± 500 G. In contrast, we derive an upper limit (3σ) to the primary's surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission – previously interpreted as a consequence of colliding stellar winds – in this context. We conclude that HD 47129 represents a heretofore unique stellar system – a close, massive binary with a rapidly rotating, magnetized component – that will be a rich target for further study.
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Bevacqua, Davide. "Internal kinematics and stellar populations for the largest sample to date of galaxies with counter-rotating stellar disks." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/22222/.
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SAURON and ATLAS3D spectroscopic surveys provided a new classification of Early-Type Galaxies, based on their stellar kinematic maps. In this work we focus on the class of galaxies with two counter-rotating stellar disks, so far called ‘’2sigma-galaxies’’ because of the two peaks in the velocity dispersion map. These galaxies show different observed properties, and to date we do not have a clear picture of how they form; this is mostly because few counter-rotators have been found to date. The first goal of this work was to use data from the integral-field survey MaNGA, which observed ~10,000 galaxies, to build a large sample of such galaxies. Since in this survey the kinematic maps do not always show both the counter-rotation and the two peaks in sigma, we checked for at least one of these features to select counter-rotators candidates, and we designate them as ‘CRD’. To identify CRDs, we first selected a set of 603 galaxies from MaNGA, and, by visually inspecting the kinematic maps of the Pipeline, applying specific classification criteria, we obtained a final sample of 53 CRDs, the largest to date for such galaxies. The second goal was to produce the stellar velocity and dispersion maps for the sample; by fitting two components, we found spectroscopically confirmation of the two disks in about 1/3 of the sample. We then compared the velocity fields of the ionized gas and of the stars, and mostly found cases with gas corotating one of the two stellar disks, but also many cases of misalignment, suggesting recent gas accretion. Finally, we extracted the stellar population maps, looking for radial trends: almost all galaxies have higher metallicity in the central regions, and some also show radial trends in age. Evidences of multimodality in age and metallicity have been found, by performing regularized fits, in 13 galaxies, suggesting the presence of different stellar populations. Overall, our results support different formation paths for the class of CRDs.
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Moran, Declan [Verfasser], Gernot [Gutachter] Neugebauer, Thomas [Gutachter] Henning, and Hanns [Gutachter] Ruder. "Light rays in the gravitational field of rotating disks of dust in general relativity / Declan Moran ; Gutachter: Gernot Neugebauer, Thomas Henning, Hanns Ruder." Jena : Friedrich-Schiller-Universität Jena, 2000. http://d-nb.info/1178255832/34.
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Isaac, Christopher Aled. "Axialisation of particles in a Penning-type trap by the application of a rotating dipole electric field and its application to positron accumulation." Thesis, Swansea University, 2010. https://cronfa.swan.ac.uk/Record/cronfa43044.
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Thul, Andreas Christian [Verfasser]. "Application of the Principles of Field-Oriented Control for the Measurement and Metrological Characterization of Soft-Magnetic Steel at Rotating Magnetization / Andreas Christian Thul." Düren : Shaker, 2021. http://nbn-resolving.de/urn:nbn:de:101:1-2021100305202053876624.
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Finke, Konstantin [Verfasser], Andreas [Akademischer Betreuer] Tilgner, and Christensen [Akademischer Betreuer] Ulrich. "Kinematic dynamo onset and magnetic field saturation in rotating spherical Couette and periodic box simulations / Konstantin Finke. Gutachter: Andreas Tilgner ; Christensen Ulrich. Betreuer: Andreas Tilgner." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://d-nb.info/1044420634/34.
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Blauch, David N. Anson Fred C. Anson Fred C. "Part I. Improvements in the rotation-rate step experiment for the evaluation of diffusion coefficients at rotating disk electrodes. : Part II. Ion-pairing and electric field effects on electron hopping in the Nafion-tris(2,2'-bipyridine)osmium(3+/2+) system /." Diss., Pasadena, Calif. : California Institute of Technology, 1991. http://resolver.caltech.edu/CaltechETD:etd-06152007-081035.
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Leto, P., Corrado Trigilio, Lidia M. Oskinova, Richard Ignace, C. S. Buemi, G. Umana, A. Ingallinera, H. Todt, and F. Leone. "The Detection of Variable Radio Emission from the Fast Rotating Magnetic Hot B-Star HR 7355 and Evidence for Its X-Ray Aurorae." Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etsu-works/2695.
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In this paper we investigate the multiwavelengths properties of the magnetic early B-type star HR7355. We present its radio light curves at several frequencies, taken with the Jansky Very Large Array, and X-ray spectra, taken with the XMM X-ray telescope. Modeling of the radio light curves for the Stokes I and V provides a quantitative analysis of the HR7355 magnetosphere. A comparison between HR7355 and a similar analysis for the Ap star CUVir, allows us to study how the different physical parameters of the two stars affect the structure of the respective magnetospheres where the non-thermal electrons originate. Our model includes a cold thermal plasma component that accumulates at high magnetic latitudes that influences the radio regime, but does not give rise to X-ray emission. Instead, the thermal X-ray emission arises from shocks generated by wind stream collisions close to the magnetic equatorial plane. The analysis of the X-ray spectrum of HR7355 also suggests the presence of a non-thermal radiation. Comparison between the spectral index of the power-law X-ray energy distribution with the non-thermal electron energy distribution indicates that the non-thermal X-ray component could be the auroral signature of the non-thermal electrons that impact the stellar surface, the same non-thermal electrons that are responsible for the observed radio emission. On the basis of our analysis, we suggest a novel model that simultaneously explains the X-ray and the radio features of HR7355 and is likely relevant for magnetospheres of other magnetic early type stars.
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Boy, Felix, and Hartmut Hetzler. "Transiente Rotordynamik elektrischer Drehfeldmaschinen unter Berücksichtigung der vollen elektromagnetischen Kopplung." TU Bergakademie Freiberg, 2019. https://tubaf.qucosa.de/id/qucosa%3A38460.
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Höhere Drehzahlen, neue Anwendungen in elektrischen Fahrzeugen und der damit verbundene Leichtbau führen zu stärkeren Schwingungsphänomenen in elektrischen Drehfeldmaschinen. Besondere Bedeutung kommt dabei lateralen Rotorschwingungen zu, die sich akustisch bemerkbar machen und im Extremfall sogar zum Versagen des gesamten Systems führen können. In diesem Beitrag wird ein neuartiges Modell vorgestellt, welches rotordynamische Phänomene beliebiger Drehfeldmaschinen in transienten Fahrzuständen unter Berücksichtigung der vollen elektromagnetischen Kopplung abbilden kann. Im vorliegenden Beitrag wird eine FEM-Validierung des vorgeschlagenen Modells präsentiert. Danach wird ein Szenario vorgestellt, bei dem magnetisch angefachte Lateralschwingungen aufklingen.Higher Speeds, new applications in electric vehicles and the need for lightweight structures lead to increasing occurrence of vibration phenomena in rotating field electrical machines. Lateral rotor oscillations take a particular role in this context, as they produce noise and may cause the entire system to fail in an extreme case. In this contribution, a novel modelling approach is presented, which allows for the fully coupled simulation of transient rotordynamics in all kinds of rotating field machines. This paper includes a FEM-validation of the proposed model. After that a scenario where self-excited lateral oscillations occur is presented.
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Chen, Chun-Ming. "Data Summarization for Large Time-varying Flow Visualization and Analysis." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469141137.
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Zhu, Zhenzhou. "Study of pulsed electric fields (PEF) assisted inulin extraction from chicory root and chicory juice purification." Thesis, Compiègne, 2014. http://www.theses.fr/2014COMP2135/document.
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Le procédé industriel d’extraction d'inuline consiste en une diffusion de longue durée et à température élevée. Ce procédé induit l’extraction des sucres mais également des impuretés. Les étapes de purification de jus deviennent alors plus complexes. Pour pallier à ces problèmes, il est essentiel de réduire la température de diffusion pour limiter l’extraction des impuretés. Récemment, la technique de champs électriques pulsés (CEP) a démonté ses avantages dans le domaine sucrier et également dans d’autres applications agro-alimentaires. L’objectif de ce travail de thèse est de d’optimiser et valider la faisabilité de cette techniques dans le cas de la chicorée. Une purification par filtration dynamique est envisagée et proposée pour remplacer la purification classique. Les résultats de l’extraction montrent qu’il est possible d’intensifier l’extraction de l’inuline par application de CEP. Le prétraitement des cossettes de chicorées à 600 V/cm et 50 ms, réduit de 20°C la température de diffusion (60°C au lieu de 80°C actuellement). Une économie d’énergie importante est réalisée (gain 90 kJ/kg chicory juice). La combinaison innovante d’un prétraitement électrique et un traitement thermique (chauffage ohmique) provoque une perméabilisation importante des cellules et permet de réaliser des diffusions « à froid ». Les analyses qualitatives de jus de diffusion classique et jus CEP montrent que la pureté des extraits CEP est plus élevée (87.2% vs 86.7%). Les essais de filtration sur membrane montrent que les performances de la filtration (pureté, flux, colmatage,…) dépendent énormément de l’origine de l’extrait. Le jus CEP contient moins d’impureté que le jus thermique, est donc plus facile à filtré. Cependant, col matage de membrane restent dans les deux cas important. Un module de filtration dynamique avec disque rotatif a été utilisé pour améliorer les performances de la filtration. Ce module a permit de réduire le colmatage des membranes, améliorer la pureté des extraits et atteindre des facteurs de réduction volumique important (10)Industrial inulin extraction requires high temperature and long duration to ensure inulin productivity. In addition complex steps are necessary to purify extracted chicory juice and to obtain inulin with desirable purity. In order to avoid the extracting of inulin at high temperature, to obtain chicory juice with better quality and to purify chicory juice with more simple operation, pulsed electric fields (PEF) and membrane filtration were applied to this study : PEF was used to intensify inulin extraction from chicory roots. By pre-treatment of chicory slices at 600 V/cm, diffusion temperature at pilot scale can be decreased to 60oC from about 80oC (industrial extraction condition) to obtain comparable juice inulin concentration. Moreover, this moderate temperature diffusion brought out interesting energy savings compared to that of conventional diffusion. For the goal of extracting inulin at “cold” condition (for example 30oC) PEF induced combined electroporation/ohmic heating pretreatment was applied for chicory tissue denaturation. Better solute extraction was observed after effective damage of chicory tissue diffusivity.Juice extracted from PEF assisted diffusion (PEF juice) was confirmed had higher inulin purity and less impurity in comparison to juice from conventional thermal diffusion process. The juice was purified by membrane filtration in order to investigate a simple chicory juice purification method. Since it contains less impurity, dead-end filtration performance of PEF juice was significantly improved, with less membrane fouling and higher inulin purity in filtrate. However, permeate flux of membrane filtration was seriously restricted by the membrane fouling. In order to improve filtration flux, rotating disk module was introduced in this study for clarification and purification of chicory juice. Elevated shear rate of rotating disk (1500–2000 rpm) could effectively control or even eliminate membrane fouling and lead to satisfying carbohydrate transmission (98%) and desirable permeate flux even at high volume reduction ratio (10). In view of energy saving, optimization of RDM assisted chicory juice filtration was carried out and yielded optimal operation conditions to maximize average flux and minimize specific energy consumption
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Cardenas, Cabada Edouard. "L'imagerie acoustique au service de la surveillance et de la détection des défauts mécaniques." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI124/document.
Full textAbstract:
L’analyse vibratoire constitue une part très importante des moyens de mesures pour la surveillance et la détection des défauts mécaniques des machines tournantes. Le positionnement des accéléromètres est stratégique et contribue fortement à la réussite du diagnostic ; la proximité du capteur de l’élément défaillant est une condition très utile, mais pas toujours réalisable. La corrélation entre le bruit émis par une machine et son état est assez étroite et montre l’apport des mesures acoustiques pour l’optimisation du diagnostic. L’imagerie acoustique, très appliquée pour détecter des sources dans le domaine du transport, avec ses multiples méthodes (holographie, beamforming, etc…) peut être un moyen pour remonter aux défauts mécaniques. Dans cet objectif, plusieurs stratégies basées sur l’algorithme de beamforming sont développées. Premièrement, des indicateurs communément utilisés pour le diagnostic des machines sont visualisés en fonction de l’espace. Le kurtosis permet de localiser les sources impulsives qui peuvent être reliées à un défaut. De nouveaux indicateurs basés sur le spectre d’enveloppe des signaux focalisés sont également mis en place pour détecter les défauts de roulement de bague interne et externe. D’autre part, la moyenne synchrone angulaire est utilisée pour extraire le champ acoustique synchrone avec la rotation d'un composant de la machine. Les sources reliées à un défaut sont affectées au champ résiduel et peuvent être identifiées dans les cartographies. Enfin, une nouvelle méthode d'imagerie acoustique qui exploite les fonctions de transfert vibroacoustiques entre des accéléromètres positionnés sur la machine et une antenne acoustique est développée. Elle permet d'obtenir des cartographies de la pression rayonnée sur une surface de la machine uniquement à partir d'accéléromètres. Son applicabilité à la détection de défaut est également démontrée sur un banc à engrenagesVibration analysis is mainly used in condition monitoring and fault detection of rotating machine domain. The success of the diagnosis is strongly related to the position of the accelerometers. However, the machine geometry sometimes prevents the sensors to be placed close enough to the faulted part causing the diagnostic failure. The sound emitted by a mechanism and its condition are related. Using microphones to optimize condition monitoring is then justified. Acoustic imaging techniques (acoustic holography, beamforming, etc…) are mainly used as a source localization and quantification tool but they can be turned into a powerful diagnosis tool. Several strategies based on the beamforming algorithm are developed in this work. Firstly, diagnosis features commonly used in condition monitoring of rotating machinery are mapped as a function of space. Kurtosis allows localizing impulsive sources which eventually can be related to a mechanism failure. New features based on the squared envelope spectrum of the focused signals are also introduced. They aim toward the detection of inner and outer race fault in roller element bearings. On the other hand, angular synchronous average is used to extract the acoustic field synchronous with one component rotation. The sources related to a fault are localized in the residual field mappings. Finally, a new imaging technique based on the vibroacoustic transfer functions between a few accelerometers placed on the machine and the microphone array is developed. It allows obtaining the mappings of the radiated pressure on the machine surface only thanks to the accelerometers. It is tested as a fault detection tool on a test bench
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Morgan, Manuel Alfredo Caldas. "Ruído magnético de Barkhausen contínuo rotacional." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-26062014-214352/.
Full textAbstract:
Este trabalho apresenta os avanços no desenvolvimento de um novo método de ensaio não-destrutivo magnético. O método está baseado na técnica do Ruído Magnético de Barkhausen (RMB), particularmente em uma variante denominada Barkhausen Contínuo. O RMB é gerado devido à ação de um campo magnético variável magnetizante que produz mudanças abruptas e irreversíveis na estrutura magnética do material. Essas mudanças são influenciadas pela microestrutura e a distribuição de tensões dentro do mesmo. As medições podem ser usadas para construir uma distribuição bidimensional do RMB ao redor de um ponto fixo, cujo resultado irá refletir o nível de anisotropia magnética, usualmente indicando um eixo de fácil magnetização, parâmetro relevante dado que o comportamento da grande maioria de materiais ferromagnéticos de engenharia é usualmente anisotrópico. As mudanças no eixo de fácil magnetização podem indicar a presença de anomalias mecânicas ou abnormalidades no processo de fabricação e no caso da aplicação de uma tensão externa, podem refletir a magnitude e a direção da mesma. O presente trabalho descreve uma metodologia que faz uso de um campo magnético rotacional para obter sinais RMB relacionados ao angulo de giro, possibilitando a identificação da direção do eixo de fácil magnetização, ultrapassando as capacidades oferecidas pela técnica RMB convencional mediante o fornecimento de informação em tempo real, que permite a obtenção de um conjunto de parâmetros que quantificam a anisotropia magnética de uma amostra. A técnica foi usada para a detecção do eixo de fácil magnetização e o nível de anisotropia magnética em materiais diferentes devida aos efeitos do processo de fabricação. Posteriormente foi demonstrado que a técnica é capaz de monitorar a evolução da tensão uniaxial aplicada, obtendo curvas de calibração, sensíveis ao sentido de aplicação da tensão. Para o caso pouco estudado de amostras submetidas a tensões biaxiais, o uso da técnica do Barkhausen contínuo rotacional fez possível de verificar que as características morfológicas das medições de anisotropia magnética obtidas, guardam relação com a direção das tensões principais. Foi realizada uma avaliação do método aplicado para a medição dinâmica de anisotropia magnética em juntas soldadas, indicando estados de tensão e características microestruturais coerentes com as esperadas. O método tem a possibilidade de ser implementado para medições anisotropia magnética em alta resolução/alta velocidade.This works presents the current advances on the development of a new method of magnetic non-destructive testing. The method is based on the magnetic Barkhausen noise (MBN), more specifically in one branch known as Continuous Barkhausen. MBN is produced due to the effect of a variable magnetic field, which causes abrupt and irreversible changes to the magnetic structure of the material. These changes are influenced by the microstructure of the material and the stress distributions within. Measurements can be used to construct a bi dimensional MBN distribution around a fixed point, which in turn will be a reflect of its magnetic anisotropy level, usually characterized by an easy axis of magnetization, an important parameter given that more often than not, the behavior of most engineering ferromagnetic materials is anisotropic. Variations of the easy axis could be the indication of mechanical anomalies or abnormalities that appear as a result of the fabrication process. If there is an external stress applied to the sample, it can provide information about its magnitude and direction. The present work describes a methodology which uses a precise rotating magnetic field in order to obtain MBN signals related to a given magnetization angle, making possible the finding of the easy axis, exceeding the limits of conventional MBN measurements by providing real time data which in turn will allow to infer a set of parameters that quantify the magnetic anisotropy of the sample. The proposed technique was successfully used to find both the easy axis and a quantitative level of magnetic anisotropy between different materials, consequence of the fabrication process. Subsequently, it was shown that the technique was able to perform a monitoring of the evolution of both uniaxial and biaxial applied stress, obtaining linear relationships (uniaxial case), sensitive to the direction of loading. In not so much studied case of biaxial loading, the use of the continuous rotational Barkhausen method made possible to observe that the morphologic characteristics of the magnetic anisotropy measurements bear a close resemblance to the direction of the principal stress field. An evaluation of the technique as a tool for the dynamic measurement of magnetic anisotropy on welded joints, indicating stress states and microstructural features coherent with the ones expected in this scenario. The method has the possibility of being implemented as a technique for high speed/high resolution measurements of magnetic anisotropy.
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Cupitt, Philip Leslie. "Static magnetic fields and nerve function." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/1717/.
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Spornic, Sorin Aurel. "Automatisation de bancs de caractérisation 2D des tôles magnétiques : influence des formes d'onde sur les mécanismes d'aimantation." Phd thesis, Grenoble INPG, 1998. http://www.theses.fr/1998INPG0154.
Full textAbstract:
Le travail de notre thèse porte sur le comportement des matériaux magnétiques doux soumis à des variations 2D quelconques du vecteur induction magnétique dans le plan de la tôle. De telles conditions apparaissent par exemple dans les machines électriques tournantes ou les transformateurs triphasés. Les travaux précédents ont été limités à des inductions de formes simples (cercles ou ellipses parcourues à vitesse angulaire constante), qui ne permettent pas de décrire de manière complète le comportement des matériaux. Dans un premier temps nous avons dû élaborer un outil de caractérisation magnétique complète en 2D. Nous avons équipé les deux RSST du LEG d'un système de pilotage informatisé. La précision et la stabilité des mesures ont été nettement améliorées, tout en élargissant l'intervalle des fréquences. Son asservissement numérique a permis l'obtention pour la première fois de formes d'onde 2D complexes de l'induction. Finalement le banc de mesures a été entièrement automatisé. Par la suite cet outil nous a permis l'étude de plusieurs matériaux magnétiques doux, tels que le FeNi, le FeCo et le FeSi NO. - D'abord ces trois matériaux ont été soumis à des inductions circulaires. Nous avons étudié le comportement en fonction du niveau de l'induction et de la fréquence et le comportement réversible, qui permet la mise en évidence de Panisotropie. Le FeNi a permis d'obtenir la courbe complète et atypique des pertes en fonction du niveau d'induction en champ tournant et de valider un modèle de prédiction de celles-ci. Le comportement vectoriel de la loi B(H) dans ce matériau a été également analysé et une tentative de modélisation de l'évolution du champ magnétique a été proposée. - Ensuite nous avons étendu notre étude aux formes d'onde observées dans un moteur asynchrone triphasé. Nous avons testé une méthode de calcul approchée pour les pertes 2D. Finalement, nous avons mis en évidence l'importance de la dérivé temporelle du vecteur induction sur le comportement magnétique et les pertesThe aim of this dissertation is the study of soft magnetic materials under arbitrary vector 2D excitation, turning into the sheet plane. Such conditions appear, for example, inside rotating electric machines or inside three-phase transformers. Previous work has used simplified flux density paths, such as circles or ellipsis covered at constant angular speed, that cannot completely describe the materials'behaviour. The first part of this work was accomplished by the élaboration of a complète 2D magnetic characterisation device. The two RSST of LEG received a computerised driving System (CDS), which clearly improved the measurements accuracy and stability and enlarged the frequency domain. The CDS digital waveform control part allowed for the first time the obtention of complex flux density paths. Finally, the measurement System was completely automated. Thanks to the CDS, the investigation of some soft magnetic materials, such as NiFe, CoFe and NO SiFe, was realised. - First, thèse three materials were characterised under circular flux. The magnetic behaviour was studied with respect to flux and frequency level and also the réversible behaviour, in order to get an anisotropy image. The complète atypical losses évolution could be seen in this manner in the case of NiFe, and a prédiction model was validated. The vector law B(H) was also analysed and a model for the field strength évolution was attempted. - Then this study was enlarged to waveforms observed inside a three-phase induction motor. A2D losses estimation was tested. Finally, the importance of the derivative of the flux density vector with respect to time was highlighted on the magnetic behaviour and the magnetic losses development
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Martin, Witkowski Laurent. "Écoulements engendrés par un champ magnétique tournant en géométrie cylindrique." Grenoble INPG, 1997. http://www.theses.fr/1997INPG0218.
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L'utilisation d'un champ magnetique tournant est un moyen permettant, sans contact mecanique direct, d'engendrer ou de controler des ecoulements de metaux liquides lors de l'elaboration de materiaux dans diverses technologies et plus particulierement la croissance cristalline. L'etude, en geometrie cylindrique, des effets d'un champ tournant sur un fluide conducteur d'electricite est proposee dans deux geometries : - un cylindre de section circulaire de hauteur infinie - un cylindre de section circulaire de hauteur finie un apercu de la bibliographie est d'abord expose afin d'illustrer, dans les deux geometries, les principaux mecanismes qui controlent le champ de vitesse et la distribution du champ magnetique. Dans le cas d'un cylindre de hauteur infinie, nous avons mene une etude sur les champs intenses tournants a une frequence suffisamment elevee pour qu'on ne puisse pas negliger l'effet de peau. La richesse de ce regime vient du fort couplage entre le champ magnetique et le champ de vitesse. Dans ce regime, l'ecoulement se compose d'un ecoulement principal azimutal auquel se superposent des recirculations dans le plan transverse dont les lignes de courant restent alignees avec les ligens du champ magnetique. Dans la deuxieme geometrie, l'ecoulement devient plus complexe du fait d'un ecoulement secondaire apparaissant dans le plan meridien et qui est induit par la variation verticale de la vitesse azimutale. Plusieurs regimes sont distingues en fonction de l'intensite du champ magnetique et de sa frequence. Il est montre que l'effet de peau peut conduire a des situations ou l'ecoulement presente des zones de contre rotation par rapport au champ magnetique. La stabilite hydrodynamique de l'ecoulement est egalement discutee.
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Rosenthal, Adam D. (Adam David) 1978. "Ferrofluid flow and torque measurements in rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16857.
Full textAbstract:
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (leaves 117-121).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
The purpose of this research is to provide data from ferrofluid flow and torque measurements in uniform and nonuniform rotating magnetic fields that can be compared to theoretical analyses in order to fully understand observed paradoxical ferrofluid behavior. In the presence of rotating magnetic fields, ferrofluid particles will rotate to try to align their magnetic moment with the field but because of the fluid viscosity, magnetization M will lag behind the rotating H field, thereby resulting in a body torque on the ferrofluid. The viscous torque from this fluid flow is measured using a Couette viscometer as a function of magnetic field amplitude, frequency, and direction of rotation. The first three sets of experiments measure this torque on the outer wall of a Lexan spindle that is attached to a viscometer, functioning as a torque meter. The spindle is immersed in a beaker of ferrofluid centered inside a 2-pole or 4-pole motor stator winding, creating uniform or nonuniform rotating magnetic fields, respectively. The spindle rotates at a constant speed up to 100 rpm or is stationary in these measurements. Anomalous behaviors such as zero and negative magnetoviscosity are demonstrated and discussed. The next set of experiments measure the magnetic torque on the inner wall of a hollow spindle attached to the torque meter and filled completely with ferrofluid so that there is no free surface. The spindle is centered inside the motor stator windings and exposed to clockwise (CW) or counterclockwise (CCW) rotating magnetic fields. The last set of experiments measures the surface spin rate of a small floating plastic ball placed on the ferrofluid surface at a fixed location as a function of magnetic field parameters and radial position on the surface. When the rotating magnetic fields induce ferrofluid flows, the ball spins in the opposite direction to magnetic field rotation and this spin rate is determined using frame-by-frame video analysis.
by Adam D. Rosenthal.
M.Eng.
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Mussa, Ali Ibrahim Al. "Convection and magnetoconvection problems in rapidly rotating spherical geometry." Thesis, University of Exeter, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324033.
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Elborai, Shihab M. (Shihab Mahmoud) 1977. "Ferrofluid surface and volume flows in uniform rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37846.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 255-260).
Ferrofluid surface and volume effects in uniform dc and rotating magnetic fields are studied. Theory and corroborating measurements are presented for meniscus shapes and resulting surface driven flows, spin-up flows, and Hele-Shaw cell flows and instabilities. To characterize the water-based and oil-based ferrofluids used in experiments, measurements were made of the magnetization curve, surface tension, viscosity, density, and the speed of sound. Extensive measurements of the height and shape of ferrofluid menisci in applied uniform dc magnetic fields show that the height of the meniscus increases for vertical applied magnetic fields, whereas horizontal magnetic fields decrease meniscus height. An approximate energy minimization analysis agrees with the observed trends in ferrofluid meniscus height. The effects of ferrofluid meniscus curvature on spin-up flow were modeled under simplified assumptions. Analytical solutions were derived for two dimensional low Reynolds number flows and extended results were obtained numerically using COMSOL's Multiphysics finite element software package (FEMLAB) to solve for three dimensional recirculating flows at higher Reynolds numbers.
(cont.) Familiar magnetostatic energy expressions in linear magnetic media were extended to non-linear magnetization relations. These energy expressions were applied to study the effects of linear and non-linear magnetization on flows and instabilities in Hele-Shaw cells with simultaneously applied in-plane rotating and dc axial magnetic fields. Ultrasound velocimetry of the spin-up flow in the bulk region of water-based ferrofluids conclusively demonstrates the co-rotation of the bulk of the ferrofluid with the applied rotating magnetic field with and without a free surface. Careful ultrasound investigation of flow profiles at different heights in uncovered ferrofluid cylinders showed flow direction reversal between the counter-rotating top free surface and the co-rotating bulk region of the ferrofluid. A framework for a numerical solution of the coupled governing equations of conservation of linear and angular momentum in magnetic spin-up flows that considers all the terms in the first Shliomis magnetization relaxation equation was formulated and solved. Previous solutions in the literature which decouple the magnetic and fluid mechanical dynamics by neglecting the linear and spin velocities in the magnetization relaxation equations result in no spin-up flow in uniform magnetic fields in the absence of spin diffusion effects.
(cont.) Contrary to the commonly held view in the literature, spin-up flows develop in rotating uniform magnetic fields even in the absence of spin diffusion effects. Including the linear and spin velocity terms in the magnetization relaxation equation results in non-zero spin-up flow. Numerical solutions using FEMLAB software are shown for flow profiles with zero and non-zero spin viscosity. Fitting numerical simulations to velocity profile ultrasound measurements allows the estimation of the magnetization relaxation time and the spin viscosity for Ferrotec Corp.'s MSG Wll and EMG705 water-based ferrofluids.
by Shihab Mahmoud Elborai.
Ph.D.
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Dozier, Kahlil A. "Characterizing ferrofluid spin-up flow in rotating uniform magnetic fields." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91442.
Full textAbstract:
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.6
Cataloged from PDF version of thesis.
Includes bibliographical references (page 85).
A ferrofluid is a collection of nanoscale ferromagnetic particles with a stabilizing surfactant in a liquid to form a colloid. The dynamic behavior of ferrofluids in the presence of magnetic fields has long been an area of research interest. A particular area of interest deals with the "spin-up" mechanisms of ferrofluids, which describe how a container of ferrofluid comes to a steady state of bulk flow when subjected to a uniform rotating external magnetic field. There are two prevailing theories that attempt to explain the spin-up mechanisms of ferrofluids: spin diffusion theory, and the presence of non-uniformities in the magnetic field, due to "demagnetizing factors" introduced by the shape of the container. This research attempts to confirm previous measurements indicating that non-uniformities in the magnetic field are the primary cause of ferrofluid bulk flow. Partial spheres and cylindrical containers of different volumes -- and thus different demagnetizing factors -- were filled with Ferrotec EFH1 oil-based ferrofluid and subjected to an external uniform rotating magnetic field for various parameters of rotation direction and magnetic field. Ferrofluid bulk flow was measured using ultrasound velocimetry, and the magnitudes and shapes of the velocity profiles were compared. Despite the complicated flows observed within the containers, enough of a trend was established to safely conclude that demagnetizing factors are often the primary cause of ferrofluid bulk flow.
by Kahlil A. Dozier.
M. Eng.
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Rhodes, Scott E. (Scott Edward) 1981. "Magnetic fluid flow phenomena in DC and rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/17670.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 299-301).
An investigation of magnetic fluid experiments and analysis is presented in three parts: a study of magnetic field induced torques in magnetorheological fluids, a characterization and quantitative measurement of properties relating to the transition of a ferrofluid drop from a continuous phase into a discrete phase and also into a spiral flow, and a study of magnetic field induced ferrofluid flow reversals. The torque exerted on a spindle filled with magnetorheological fluid (MR fluid) and placed inside a uniform rotating magnetic field is measured with varying rotating magnetic field amplitude and frequency, total fluid volume, and MR fluid volume ratio. When compared to similar ferrofluid torque measurements where the torque increased with rotating magnetic field frequency, the torque frequency dependence of the MR fluid decreases with increasing magnetic field frequency. A simple analysis determines the dependence of the magnetic body torque on particle size to describe the different behavior between the ferrofluid and MR fluid. When a fluorocarbon based ferrofluid is contained between two glass plates separated by a small gap (Hele-Shaw cell) and excited by an applied uniform rotating magnetic field first and then a DC axial magnetic field, a phase like transition occurs that transforms the ferrofluid drop from a continuous phase to a discrete phase. Considering the dominant energy in the configuration to be contributed from the magnetostatic energy of the DC magnetic field and interfacial surface energy, a calculus of minimization of free energy is performed to determine the number of smaller ferrofluid drops that will result from the transition and the threshold axial magnetic field for the transition to occur.
(cont.) When the order of the applied magnetic fields is reversed, the DC axial magnetic field is applied first causing the ferrofluid droplet to form the labyrinth instability. The rotating magnetic field is then applied creating a spiral formation. Experiments are conducted for varying Hele-Shaw cell separation gap, and rotating magnetic field amplitude and frequency. Measurements were consistent with our model. A cylindrical vessel is filled with a water-based ferrofluid and excited by a uniform rotating magnetic field that induces a counter-rotating circular flow in the vessel. A DC axial magnetic field is slowly raised to change the curvature of the fluid surface and results in a change in the ferrofluid flow direction to co-rotating with the applied magnetic field. Measurements are taken of the threshold axial magnetic field that results in the change of flow direction for varying rotating magnetic field direction, amplitude, and frequency. An analysis is included that describes the change in flow direction due to surface curvature.
by Scott E. Rhodes.
S.M.
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He, Xiaowei Ph D. Massachusetts Institute of Technology. "Ferrohydrodynamic flows in uniform and non-uniform rotating magnetic fields." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/38574.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 233-241).
Ferrofluids are conventionally used in such DC magnetic field applications as rotary and exclusion seals, stepper motor dampers, and heat transfer fluids. Recent research demonstrates ferrofluid use in alternating and rotating magnetic fields for MEMS/NEMS application of microfluidic devices and bio-applications such as targeted drug delivery, enhanced Magnetic Resonance Imaging, and hypothermia. This thesis studies ferrofluid ferrohydrodynamics in uniform and non-uniform rotating magnetic fields through modeling and measurements of ferrofluid torque and spin-up flow profiles. To characterize the water-based and oil-based ferrofluids used in the experiments, measurements were made of the mass density, surface tension, viscosity, magnetization curve, nanoparticle size, and the speed of sound. Initial analysis for planar Couette and Poiseuille flows exploit DC magnetic field effects on flow and spin velocities with zero spin viscosity. Above critical values of magnetic field strength and flow velocity, multiple values of magnetic field, spin velocity, and effective magnetoviscosity result, indicating that zero spin viscosity may be non-physical. Torque and spin-up flow profile measurements show the effect of volume torque density and body force density in uniform and non-uniform rotating magnetic fields.
(cont.) Ferrofluid "negative viscosity" measurements in uniform and non-uniform rotating magnetic fields occur when magnetic field induced flow creates torque that exceeds the torque necessary to drive a viscometer spindle. Numerical simulations of torque and spin-up flow in uniform and non-uniform rotating magnetic fields, including contribution from the spin velocity and spin viscosity terms, are fitted to measurements to estimate the value ranges of relaxation time r - 1.3-30 gs and spin viscosity n' - 1-11.8x109 Nos in waterbased ferrofluid. Based on the ferrohydrodynamic theory and models, theory of the complex magnetic susceptibility tensor is derived, which depends on spin velocity, that can be a key to external magnetic field control of ferrofluid biomedical applications. Preliminary impedance analysis and measurements investigate complex magnetic susceptibility change of ferrofluid in oscillating and rotating uniform magnetic fields and allow calculation of the resulting dissipated power or mechanical work in pumping fluid.
by Xiaowei He.
Ph.D.
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Al-Salti, Nasser S. "Aspects of three-dimensional MHD : magnetic reconnection and rotating coronae." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/947.
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Solutions of the magnetohydrodynamic (MHD) equations are very important for modelling laboratory, space and astrophysical plasmas, for example the solar and stellar coronae, as well as for modelling many of the dynamic processes that occur in these different plasma environments such as the fundamental process of magnetic reconnection. Our previous understanding of the behavior of plasmas and their associated dynamic processes has been developed through two-dimensional (2D) models. However, a more realistic model should be three-dimensional (3D), but finding 3D solutions of the MHD equations is, in general, a formidable task. Only very few analytical solutions are known and even calculating solutions with numerical methods is usually far from easy. In this thesis, 3D solutions which model magnetic reconnection and rigidly rotating magnetized coronae are presented. For magnetic reconnection, a 3D stationary MHD model is used. However, the complexity of the problem meant that so far no generic analytic solutions for reconnection in 3D exist and most work consists of numerical simulations. This has so far hampered progress in our understanding of magnetic reconnection. The model used here allows for analytic solutions at least up to a certain order of approximation and therefore gives some better insight in the significant differences between 2D and 3D reconnection. Three-dimensional numerical solutions are also obtained for this model. Rigidly rotating magnetized coronae, on the other hand, are modeled using a set of magnetohydrostatic (MHS) equations. A general theoretical framework for calculating 3D MHS solutions outside massive rigidly rotating central bodies is presented. Under certain assumptions, the MHS equations are reduced to a single linear partial differential equation referred to as the fundamental equation of the theory. As a first step, an illustrative case of a massive rigidly rotating magnetized cylinder is considered, which somehow allows for analytic solutions in a certain domain of validity. In general, the fundamental equation of the theory can only be solved numerically and hence numerical example solutions are presented. The theory is then extended to include a more realistic case of massive rigidly rotating spherical bodies. The resulting fundamental equation of the theory in this case is too complicated to allow for analytic solutions and hence only numerical solutions are obtained using similar numerical methods to the ones used in the cylindrical case.
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Шилкова, Лариса Василівна. "Удосконалення проєктного аналізу електромагнітних параметрів та характеристик індукторів обертового магнітного поля для технологічної обробки різних речовин." Thesis, Національний технічний університет "Харківський політехнічний інститут", 2020. http://repository.kpi.kharkov.ua/handle/KhPI-Press/49278.
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Дисертація на здобуття наукового ступеня доктора філософії за спеціальністю 141 – Електроенергетика, електротехніка та електромеханіка. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2020. Об'єктом дослідження є індуктори обертового магнітного поля для технологічної обробки різних речовин. Предметом дослідження є електромагнітні параметри та характеристики індукторів обертового магнітного поля. Дисертація присвячена вирішенню актуального наукового завдання з удосконалення проєктного аналізу електромагнітних параметрів в режимі неробочого ходу і характеристик індукторів обертового магнітного поля для технологічної обробки різних речовин в режимі навантаження за наявністю феромагнітних елементів, що обертаються в його робочій камері, на основі чисельно-польових розрахунків. У вступі обґрунтовано актуальність задач дослідження, показано зв'язок роботи з науковими програмами, планами, темами, наведена наукова новизна та сформульоване практичне значення отриманих результатів. В першому розділі установлено, що існуючі методи проєктування індукторів обертового магнітного поля на базі статора трифазного асинхронного двигуна базуються на розрахунках магнітного поля в режимі ідеального неробочого хода і не використовують чисельних методів, які, як представлено в дисертації, дозволяють розраховувати характеристики індуктора в режимі навантаження за наявності феромагнітних елементів в його робочій камері, і дають істотний прогрес в можливостях проєктування та вдосконаленні їхньої конструкції. У другому розділі показано, що застосування квазі-тривимірної математичної моделі індуктора, заснованої на методі плоско-ортогональних розрахункових моделей, що поєднують магнітні поля поперечного та поздовжнього перерізів індуктора, дозволяє проаналізувати розподіли магнітної індукції у його поперечному і поздовжньому перерізах та проявити у достатньо повній мірі його тривимірний характер. Представлена методика на основі чисельно-польових розрахунків магнітного поля для проведення аналізу впливу скорочення обмотки статора індуктора на його електромагнітні параметри. Запропонована методика розрахунку потужності магнітних втрат на основі середньоквадратичного значення максимумів модуля магнітної індукції, яка виявилась універсальною з точки зору різних геометричних форм зубцево-пазової структури і ярма осердя статора, оскільки не вимагає спрощень геометрії розрахункових моделей цих частин конструкції. В третьому розділі вперше визначено, що кут навантаження індуктора відповідає куту повороту магнітного поля, але виявляється в два рази меншим, ніж кут фази струмів обмотки індуктора. Період моментної кутової характеристики виявляється в два рази меншим періоду струмів обмотки індуктора, що відповідає класичним уявленням про кутові функції реактивного моменту електричних машин. Це дозволяє віднести розглянутий індуктор, разом з анізотропним магнітним середовищем в робочій камері, до класу реактивних синхронних машин, а конкретно – двигунів. Запропоновано метод врахування магнітної анізотропії робочої камери індуктора залежно від концентрації феромагнітних елементів в ній. Це дозволило отримати математичну модель для визначення кількісних і фазових співвідношень його електромагнітних величин в режимі навантаження: магнітної індукції, магнітного потокозчеплення, ЕРС, струму, напруги обмотки статора, а також електромагнітний момент в його робочій камері. Представлена методика на основі чисельних розрахунків магнітних полів, яка дозволяє організувати ітераційний процес для розрахункового аналізу характеристик індуктора, що працює зі змінною навантаження при стабільному струмі або напрузі живлення його обмотки. Тестовими розрахунками виявлено, що на ділянці сталої роботи в енергетичному відношенні індуктор характеризується досить високим ККД і вельми низьким значенням коефіцієнта потужності. При порівнянні кутових характеристик індуктора виявлено, що більш раціональним для експлуатації індуктора є режим при стабілізації напруги, який в бажаному робочому діапазоні кута навантаження до 25° забезпечує кращі його електричні, магнітні, силові і енергетичні параметри. Запропонований струмовий метод контролю концентрації феромагнітних елементів у робочій камері індуктора в процесі його експлуатації. Практичні розрахунки показали, що такий метод є більш чутливим і не вимагає ускладнення конструкції індуктора у порівнянні з альтернативним методом контролю за допомогою вимірювальних витків. Спостереження за струмом обмотки індуктора дозволяє контролювати заповнення його робочої камери феромагнітними елементами, не перериваючи процесу експлуатації. Це дає можливість своєчасно поповнювати камеру такими елементами і, тим самим, підтримувати на заданому рівні технологічну обробку різних речовин, що пропускаються через цю камеру. У четвертому розділі представлені експериментальні дослідження фізичної моделі індуктора, які підтвердили результати математичного моделювання електромагнітних процесів індуктора в режимі неробочого ходу і в його робочому режимі.The thesis is submitted to obtain a scientific degree of Doctor of Philosophy, specialty 141 – Electricity, electronics and electrical engineering – National Technical University "Kharkiv Polytechnic Institute", Kharkiv, 2020. The object of research are inductors of rotating magnetic field for technological operation of various substances. The subject of research are electromagnetic parameters and characteristics of inductors of rotating magnetic field. The dissertation is dedicated to solve actual scientific task of the design analysis development of electromagnetic parameters and characteristics of rotating magnetic field inductors for various substances technological operation. The introduction substantiates the relevance of the research tasks, shows the relationship of the work with scientific programs, plans, themes, provides scientific novelty and the practical significance of the results was formulated. In the first section, it is established that the existing methods for designing rotating magnetic field inductors based on the stator of a three-phase asynchronous motor are based on calculations of the magnetic field in the ideal idle mode and do not use numerical methods, which, as presented in the thesis, allow calculating the characteristics of the inductor in the load mode at the presence of ferromagnetic elements in its working chamber and give significant progress in the possibilities of designing and improving their design. The second chapter shows that the application of the quasi-three-dimensional mathematical model of the inductor, that was based on the method of plane-orthogonal calculated models, that combines the magnetic fields of the transverse and longitudinal sections of the inductor, allows us to analyze the distributions of magnetic induction in the transverse and longitudinal sections and to show fully its three-dimensional character. Based on the numerical-field calculations of rotating magnetic field the calculation methodology was presented in order to analyze the effect of shortening the stator winding of the inductor on its electromagnetic parameters. The proposed calculation methodology of the magnetic loss power based on the RMS maximums value of the magnetic induction module, that turned out to be universal from the point of view various geometric shapes of the toothed-groove structure and the stator yoke, because it doesn't need require simplifications of the design models geometry of these parts of the construction design. The third chapter deals with the inductor load angle that corresponds to the angle of rotation of the magnetic field and it was defined for the first time, but turns out that the inductor load angle two times less than the phase angle of the inductor winding currents. It turns out that the period of the angular torque characteristic two times less than the period of the inductor winding currents, which corresponds to the classical ideas about the angular functions of the reactive torque of electrical machines. Eventually, it allows to classify the considered inductor, together with the anisotropic magnetic environment in the working chamber, to the class of reluctance synchronous machines, and specifically, motors. The accounting method of the magnetic anisotropy of the inductor working chamber in dependence to concentration of ferromagnetic elements in it was proposed. It allows to obtain a mathematical model for determining the quantitative and phase correlations of its electromagnetic values in the load mode: magnetic induction, magnetic flux linkage, EMF, current voltage of the stator winding, and the electromagnetic torque in the working chamber. The presented methodology which is based on numerical calculations of magnetic fields, allows organizing an iterative process for the computational analysis of the characteristics of the inductor, that operates with a variable load at a stable current or supply voltage of its winding. By the test calculations it was found, that in the area of constant operation in terms of energy, the inductor is characterized by a sufficiently high efficiency and a very low power factor. During the comparison of the inductor angular characteristics, it was found that the more rational for the inductor working is the voltage stabilization mode, which in the desired working range of the load angle up to 25° provides the best electrical, magnetic, power and energy parameters. The current method for monitoring the concentration of ferromagnetic elements in the working chamber of the inductor during its operation was proposed. The practical calculations have shown that this method is more sensitive and doesn't require a complication of the inductor design in comparison with the alternative monitoring method using measuring coils. Observing the winding current of the inductor allows us to control the filling with ferromagnetic elements of its working chamber without interrupting the working process. It allows to replenish the working chamber in time with such elements and thereby maintain the technological operation of various substances on a given level, which are passed through this chamber. In the fourth chapter experimental studies of the inductor physical model are presented and it confirmed the results of mathematical modeling of the electromagnetic processes of the inductor in the no-load mode and in the operate mode.
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Weir, Kenneth. "Electric field induced optical rotation changes in chiral macromolecules." Thesis, University of Reading, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329144.
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