This thesis work aims at developing a model in Visual Basic for Applications and Microsoft Excel that can be used to predict temperatures in semiconductor devices for two commercial products made by Voith Hydro AB, and via simulation of the model determine the maximum current that can be conducted through the two products. The two products are called field exciters. A field exciter controls the rotor current of a generator with the help of semiconductor devices. When used in a power converter, such devices give rise to losses. A certain amount of the electrical energy passing through the converter is lost in form of heat. If the thermal energy is not dissipated, the temperature in the semiconductor device will rise. This will eventually lead to device failure when the temperature exceeds a certain temperature threshold which depends on the semiconductor material. The proposed model allows to predict these losses and the corresponding temperatures for a specified field current and ambient temperature. The model was validated experimentally. A simplified brushless excitation system was designed and constructed, temperature measurements were carried out for different field currents and later used to validate the model. This thesis concludes that the model developed in Visual Basic predicts temperatures with good results for the PWM-30A but not as good for the PWM-150A. The model simulations show that the PWM-30A can operate with a continuous current of 30 A, for a short duration of 10 seconds it can step up the current to 60 A at an ambient temperature of 50 °C. When the PWM-30A is cooled by forced convection, it can conduct a continuous current of 50 A at an ambient temperature of 50 °C. During field forcing, the PWM-30A can step up the current to 100 A for a duration of 10 seconds. It has been concluded that the PWM-150A cannot, without further testing, conduct a larger current than it was originally designed for, which is 150 A continuously at an ambient temperature of 40 °C. During field forcing it can step up the current to 240 A for 10 seconds.

The underlying structure in the region A~100, N~60 has been under intensive and extensive investigation, mainly by β-decay and γ-ray spectroscopy from fission processes. Around N~60, by adding just few neutrons, protons a rapid shape change occurs from spherical-like to well deformed g.s. shape. Shape coexistence has been observed in the Sr and Zr nuclei, and is expected to take place in the whole region. The mechanisms involved in the appearance of the deformation is not well understood. The interplay between down-sloping and up-sloping neutron Nilsson orbital is evoked as one of the main reasons for the sudden shape change. However, a clear identification of the active proton and neutron orbitals was still on-going. For that purpose, the neutron rich ⁹³′⁹⁵′⁹⁷′⁹⁹Rb isotopes have been studied by Coulomb excitation at CERN (ISOLDE) using the REX-ISOLDE post-accelerator and the MINIBALL setup. The completely unknown structures of ⁹⁷′⁹⁹Rb have been populated and observed. Prompt γ-ray coincidences of low-lying states have been observed and time correlated to build level schemes. The associated transition strengths have been extracted with the GOSIA code. The observed matrix elements of the electromagnetic operator constituted new inputs of further theoretical calculations giving new insight on the involved orbitals. The sensitivity of such experiment can be increased using nuclear spin polarized RIB. For that purpose the Tilted Foils Technique (TFT) of polarization has been investigated at CERN. A new TFT polarizer with a β-NMR setup have be created and installed after REX-ISOLDE. The uncomplete knowledge of the polarization process associated to the technique needs to be investigated. Conclusive preliminary tests have been performed on ⁸Li in order to determine the potential of the present setup. / La structure sous-jacente dans la zone A~100, N~60 a été étudié intensivement et extensivement, principalement par décroissance β et spectroscopie γ suite à des réactions de fission. Autour de N~60, en ajoutant juste quelques neutrons, protons un changement de forme rapide des états fondamentaux se produit, allant de sphérique à bien déformé. La coexistence de forme observée dans les noyaux de Sr et Zr est supposée avoir lieu dans toute la région. Les mécanismes impliqués dans l'apparition de la déformation n'étaient pas clairement identifiés. L'interaction entre les orbitales de Nilsson montantes et descendante est évoqué comme l'une des principales raisons du changement de forme. Cependant, une identification claire des orbitales proton et neutron en jeu était nécessaire. A cet effet, l'étude des isotopes ⁹³′⁹⁵′⁹⁷′⁹⁹Rb riches en neutrons a été réalisé excitation Coulombienne au CERN (ISOLDE) en utilisant le post-accélérateur REX-ISOLDE et le dispositif Miniball. Les structures excitées encore inconnues des isotopes ⁹⁷′⁹⁹Rb ont été peuplées et observées. Les coïncidences de transitions γ des états de basse énergie ont été observées et leur corrélations ont permis la construction de schémas de niveaux. Les probabilités de transitions associées ont été extraites grâce code GOSIA. Les éléments de matrice de l'opérateur électromagnétique observées constituent de nouveaux apports afin d'effectuer de nouveaux calculs théoriques permettant de statuer sur les orbitales impliquées. La sensibilité des expériences de ce type peut être accrue en utilisant des faisceaux radioactifs d'ions dont le spin nucléaire est polarisé. La technique de polarisation des feuilles orientées (TFT) fut étudiée dans ce but au CERN. Un nouveau polariseur TFT et un dispositif β-NMR ont être créés et installés après REX-ISOLDE. La connaissance du processus de polarisation associé à la technique reste incomplète à ce jour et de plus amples études sont nécessaires. Des tests préliminaires prometteurs ont été effectués sur le noyau de ⁸Li afin de déterminer le potentiel du dispositif actuel.

The Variable Inertia System Wave Energy Converter (VISWEC) is a self-reacting point absorber (SRPA) type wave energy converter (WEC) capable of changing its mechanical impedance using an internal reaction mass system. The reaction mass is coupled to a rotating assembly capable of varying its inertia and this changing inertia has the effect of creating an added inertial resistance, or effective mass, to oscillations of the reaction mass. An SRPA has two main bodies, designated Float and Spar, capable of utilizing the relative motion between the two bodies to create power through a power take-off (PTO). The implementation of the reaction mass, a 3rd body, and the variable inertial system (VIS) is designed to change the response of the Spar in order to create larger relative velocities between the two bodies and thus more power. It is also possible to lock the VIS within the Spar, and when this is done the system is reduced to a conventional 2-body SRPA configuration. To better understand the effects of the implementation of the VIS on the overall stability of the VISWEC and the power conversion performance, a numerical model simulation within ProteusDS, a time-domain modelling software, was created. Power production and parametric excitation are the metrics of comparison between the two systems. Parametric excitation is a phenomenon that correlates wave excitation frequency to roll stability and has been shown to negatively affect power production in SRPAs. Simulations of the 2 and 3-body provide a basis of comparison between the two systems and allow the assessment of parametric excitation prohibited or exacerbated by the implementation of the VIS as well as power production. The simulation executed within the commercial software ProteusDS incorporates articulated bodies defined with physical parameters connected through connections allowing kinematic constraints and relations and hydrodynamics of the hull geometries as they are exposed to regular waves. ProteusDS also has the ability to apply kinematic constrains on the entire system allowing the analysis of isolated modes of motion. The implementation of the VIS demonstrates a generally higher power production and stabilization of the system with regards to parametric excitation. While the 3-body system is more stable, the bandwidth at which rolling motion is induced increased in comparison to the 2-body system. Rolling motions in both the 2 and 3-body systems are characteristic of parametric excitation and show a direct correlation to reduced power production. Overall the 3-body VISWEC outperforms the typical 2-body SRPA representation but more research is required to refine the settings of the geometric and PTO control. / Graduate

In turbomachinery, extra excitation forces may result from non-idealised operation conditions and may sometime cause excessive vibrations and unsteady rotor motions. The goal of this thesis is to investigate the effects of such excitation forces. The extra excitation forces investigated here are the Thomas/Alford force due to the blade tip clearance change, the steam excitation force caused by the variation of inlet steam speed and state blade trailing wake and the dominant magnetic pull force due to dynamic eccentricity of the rotor. The main research results in this thesis include: (1) The modelling of the Jeffcott rotor and the 600MW steam-turbine generator. The used in-house ??transient?? program can only handle the circular short bearings with the modified short bearing method while the simulated steam-turbine should be supported by tilting pad bearings. The first critical speeds of systems supported by tilting pad bearings are more approaching to the lab data for all four rotor models while that of journal bearing supported systems are normally lower than the real operating critical speed. (2) Applying three sorts of excitation forces into the single-stage rotor-bearing system. The numerical simulation shows that for the model with each single excitation force, all of these three forces need to reach some limit to force the system into the unsteady state. For all the three forces, higher limits are needed if the machine runs at lower running speeds. Furthermore, unbalance loading also can influence the system behaviours. As the unbalance increases, the system will still stay steady while the spectra become noisier, though the amplitude still low comparing to harmonics. (3) Combing three types of excitation forces into the assembled rotor-bearing system. The numerical simulation shows that the assembled system presents similar vibration responses as the single stage rotor-bearing system. Furthermore, these three forces cannot cancel each other and the combination will unstabilise the system. Meanwhile, the influence of the dominant magnetic pull force is less than other two forces.

This thesis presents the results of a series of experiments in which electrons are superelastically scattered from various laser excited states of sodium. The atoms, once in the optically prepared state, are forced to relax via the superelastic collision with an electron. The rate of detection of superelastically scattered electrons was measured as a function of the laser polarisation which enabled pseudo Stokes parameters to be determined. These pseudo Stokes parameters are functions of both optical pumping parameters and atomic collision parameters. The optical pumping parameters describe the laser-atom interaction and the atomic collision parameters describe the electron-atom collision process. Three different laser excitation mechanisms were used to optically pump the atoms into various excited states. The first of these used a single laser tuned to the 32S 112(F'=2 hyperfine state)-~32P312 transition. The excited atoms underwent a superelastic collision with an electron leaving the atom in the ground state and pseudo Stokes parameters were measured as a function of both scattering angle and incident electron energy. The second superelastic experiment, utilised a folded step excitation mechanism which employed two lasers tuned from the two hypethne states of the 32S112 ground state respectively to the 32P312 excited state. Power broadening effects in the single laser experiment cause the atoms to be optically pumped into the F= 1 hyperfine ground state. The laser powers used were not great enough to power broaden the hyperfine ground states and as such the F'= 1 sublevel effectively acted as a sink. The folded step excitation method enabled the excited state population to be increased so that data at larger scattering angles could be obtained. Stokes parameters from both of these experiments which had an incident energy range of 10eV to 30eV and an angular range of 5°-25° were compared to three current electron-atom scattering theories and previous experimental data. Overall, fair to good agreement was found between theory and experiments for the individual Stokes parameters. Losses of coherence was observed at small scattering angles (50.200) at 20eV and 25eV incident electron energies which were poorly modelled by the three different theories. The third superelastic experiment involved the use of two lasers of specified polarisation to stepwise excite the atoms to the 32D512 excited state. Superelastic collisions with incident electron energies of 20eV from the 32D512-*32P312~312 collision were studied at three different scattering angles and pseudo Stokes parameters for the case where the polarisations of the radiation from the lasers were parallel were measured. The single step and folded step laser-atom interactions for it excitation were modelled using a full quantum electrodynamical treatment so that the optical pumping parameters from the single and folded step experiments could be investigated. Equations of motion were derived in the Heisenberg picture and it is shown that for the single laser case 59 equations of motion are required to fully model the interaction and for the folded step ease 78 equations of motion are required. The results of calculations demonstrated that the optical pumping parameters were sensitive to laser intensity, laser detuning and the Doppler width of the atomic beam. The theoretical quantum electrodynamical calculation results were in good agreement with the experimental results.

Sur N=50, une experience a ete realisee en fevrier 2001 sur la ligne ISOL PARRNe dont l'objet etait de mesurer les premiers etats excites du 83Ge (Z=32, N=51) en etudiant la decroissance beta du 83Ga produit par fission de 238U. La precision extreme du dispositif experimental, couplee au fonctionnement des sources a plasma chaud a permis d'atteindre des informations spectroscopiques des isotopes de Ge au dela de la couche magique N=50. Deux transitions ont ete attribuees au 83Ge : a 867 keV et a 1238 keV. Le schema de niveau du 83Ge a pu etre interprete en terme de particule individuelle : les etats excites de ce noyau sont dus aux couplages entre le neutron celibataire au dela de N=50 et le reste du noyau. Sur N=40, nous avons cherche a determiner la valeur de la probabilite de transition de l'etat fondamental vers le premier etat excite notee B(E2) dans les noyaux de 70Ni (N=42) et de 74Zn (N=44) a partir de reaction d'excitation coulombienne. Ces noyaux exotiques sont produits par fragmentation d'un faisceau primaire de 76Ge sur une cible de 58Ni, selectionnes par le spectrometre LISE, puis interagissent avec une cible secondaire de Pb utilisee pour induire l'excitation coulombienne. A l'issue de cette analyse, les B(E2) suivant ont ete obtenus : B(E2,70Ni)=860(170) e2fm4, B(E2,74Zn)=1960(140) e2fm4. Ces valeurs ont ete confrontees d'une part a des calculs variationnels que j'ai realises, d'autre part a des calculs de modele en couches publies. Ces calculs mettent en evidence l'aspect complexe des noyaux de Ni, qui bien que situes sur une fermeture de couche en protons (Z=28), ne semblent pas avoir un comportement typique de noyaux semi magiques.

Modification of nuclear resonant absorption by means of laser radiation is analyzed both theoretically and experimentally. Theoretical analysis is done on the basis of four-level model of atom. This model includes both electronic and nuclear excitations. It is predicted that under coherent laser driving nuclear resonant Mossbauer absorption can be significantly modified, e.g. new Mossbauer resonances can appear, some of the existing resonances can vanish, both can be Rabi-split, broadened by laser action. In addition, it is predicted that Mossbauer absorption can be completely suppressed due to coherent population trapping. Experimental observation of laser-induced transformations of Mossbauer spectra of 57Fe2+ : MgO is accomplished. New Mossbauer lines appear with laser driving while the existing are broadened. Possible explanations of the observed changes in 57Fe2+ : MgO Mossbauer spectra are population of higher-lying electronic states of iron ion and significant modification of electronic relaxation processes due to modified Jahn-Teller interaction.

Automatic voltage regulation is necessary for all power producing synchronous generators to ensure that the produced power have a constant and stable voltage level and to sustain grid stability. The aim of this thesis is to design and build an automatic voltage regulator for a synchronous generator. A six-phase permanent magnet alternator will be used to excite the rotor with solid-state relay controlled rotating bridge rectifier. The field current is regulated by a closed loop control system that is based on a programmable logic controller, PLC. Programing of the PLC is executed in the developing environment CoDeSys, IEC 61131-3, which is the international standard for programing PLC applications. Simulations for predicting the system behavior is done with a web based in-browser tool, circuitlab.com. The results show a good performance of the regulator and the closed loop system although there is room for improvement of the solid-state controlled rectifier system.

Vibration-based damage detection (VBDD) methods are structural health monitoring techniques that utilize changes to the dynamic characteristics of a structure (i.e. its natural frequencies, mode shapes, and damping properties) as indicators of damage. While conceptually simple, considerable research is still required before VBDD methods can be applied reliably to complex structures such as bridges. VBDD methods require reliable estimates of modal parameters (notably natural frequencies and mode shapes) in order to assess changes in the condition of a structure. This thesis presents the results of experimental and numerical studies investigating a number of issues related to the potential use of VBDD techniques in the structural health monitoring of bridges, the primary issue being the influence of the excitation source.<p> Two bridges were investigated as part of this study. One is located on Provincial Highway No. 9 over the Red Deer River south of Hudson Bay, Saskatchewan. The other is located near the Town of Broadview, Saskatchewan, off Trans-Canada Highway No. 1, 150 km east of the City of Regina. Field tests and numerical simulations were conducted using different types of excitation to evaluate the quality of the modal properties (natural frequencies and mode shapes) calculated using these excitation types, and thus to evaluate the performance of VBDD techniques implemented using the resulting modal data. Field tests were conducted using different sources of dynamic excitation: ambient, traffic excitation, and impact excitation. The purpose of field testing was to study the characteristics and repeatability of the modal parameters derived using the different types of dynamic excitation, and to acquire data that could be used to update a FE model for further numerical simulation.<p> A FE model of the Red Deer River bridge, calibrated to match the field measured dynamic properties, was subjected to different types of numerically simulated dynamic excitation with different noise (random variations) levels added to them. The types of dynamic excitation considered included harmonic forced excitation, random forced excitation and the subsequent free vibration decay, impact excitation, and different models of truck excitation. The bridge model was subjected to four different damage scenarios; in addition, six VBDD methods were implemented to evaluate their ability to identify and localize damage. The effects of uncertainty in the definition of controlled-force excitation sources and variation in measurement of the bridge response were also investigated.<p> Field tests on the Hudson Bay bridge showed that excitation induced by large trucks generally produced more reliable data than that of smaller vehicles due to higher signal-to-noise ratios in the measured response. It was also found that considering only the free vibration phase of the response after the vehicle left the bridge gave more reliable data. Impact excitation implemented the on Hudson Bay bridge using a spring-hammer yielded repeatable and high quality results, while using a heavy weight delectometer for impact excitation on the Broadview bridge produced results of lesser quality due to the occurrence of multiple strikes of the impact hammer. In general, wind induced vibration measurements taken from both bridges were less effective for defining modal properties than large vehicle loading or impact excitation. All of the VBDD methods examined in this study could detect damage if the comparison was made between modal parameters acquired by eigenvalue analyses of two FE models of the bridge, before and after damage. However, the performance of VBDD methods declined when the dynamic properties were calculated from response time histories and noise was introduced. In general, the damage index method performed better than other damage detection methods considered.<p> Numerical simulation results showed that harmonic excitation, impact excitation, and the free decay phase after random excitation yielded results that were consistent enough to be used for the identification of damage. The reliability of VBDD methods in detecting damage dropped once noise was introduced. Noise superimposed on the excitation force had little effect on the estimated modal properties and the performance of VBDD methods. On the other hand, noise superimposed on the measured dynamic response had a pronounced negative influence on the performance of the VBDD methods.

A delayed-coincidence spectrometer system was used to measure nuclear lifetimes in the picosecond region by the centroid-shift method. Timing signals were derived from two plastic scintillators; each plastic scintillator was located within a specially constructed NaI(Tl) detector. Each NaI(Tl) detector was used to detect the gamma ray which Compton scattered from an associated plastic scintillator. Energy identification was achieved by summing the signals from the plastic and the NaI(Tl) detectors to give full energy gamma-ray photopeaks. To test the effectiveness of the system, the half-lives of the first excited state of 134Ba and the first and second excited states of 144Nd were measured. The half life of the first excited state of 134Ba was measured as 4.4 - 1.3 psec; this result is in agreement with a previously reported value of 5.0 t 1.5 psec. The half-life for the first excited state of 144Nd was determined to be 1.5 ± 1.0 psec while the half-life for the second excited. state of 144Nd was determined to be 5.1 ± 0.5 psec. The half-life value for the second excited state of 144Nd is in disagreement with previously reported values of 21 ± 2 psec and 100 ± 30 psec which were also determined by delayed-coincidence methods. Although the result of 1.5 ± 1.0 psec for the first excited state lifetime differed from a previous result of 3.4 * 0.1 psec obtained by Coulomb excitation, this difference was due to the inability of the present spectrometer system to resolve the 618- and 696-keV gamma rays of 144Nd. It is concluded that a lower lifetime limit measurable with the system described in this study is about one picosecond, provided that the gamma rays can be resolved in the sum energy spectrum of the plastic and NaI(T1) detectors.Ball State UniversityMuncie, IN 47306