>Magister Scientiae - MSc / In this work we have determined the spectroscopic or static quadrupole moment of the rst excited state (QS (2+1) lying at 2230.6 keV in 32S using the reorientation e ect. The Coulomb-excitation experiment at safe bombarding energies was performed at iThemba LABS's AFRODITE vault, where 32S beams at 120.3 MeV were bombarded onto a 194Pt target of 1 mg/cm2 thickness. The beam energy has been chosen such that the separation between nuclear surfaces is greater than 6.5 fm at all scattering angles, in order to avoid nuclear interactions. A double-sided CD-type S3 silicon detector, with 24 rings and 32 sectors, has been placed upstream (at backward angles) to detect the scattered particles. Gamma rays have been detected with the AFRODITE clover array. This particle-gamma coincidence experiment allows for an angular distribution and Doppler correction of the gamma rays emitted at 9% the speed of light. The cross sections (or gamma-ray integrated yields) measured as a function of scattering angle at backward angles are sensitive to second-order perturbation e ects in Coulomb excitation, i.e., diagonal matrix elements which are directly related to the spectroscopic quadrupole moment. The gamma-ray integrated yields obtained from this experiment are compared with the GOSIA simulations, yielding a new measurement of QS (2+1) = 􀀀0:10 0:7 eb, which corresponds to a prolate shape in the intrinsic frame of the nucleus. The uncertainty of this measurement is limited by statistics. This result agrees with previous measurements and con rms the zig zag of shapes at the end of the sd shell when approaching the doubly-magic nucleus 40Ca. Nonetheless, the mystery continues as a prolate shape for the rst 2+ disagrees with modern theoretical mean- eld calculations and the pairing coupling model.

Electron impact excitation phenomena play an important role in atomic and molecular physics. The different energy levels of an atom or molecule interact differently with incoming electrons with different energies and that affects the excitation of the energy levels of the atoms and molecules. Studies involving electron impact excitation process are generally conducted with optical emission techniques or by the electron energy loss method. In the present study, for the first time, cavity ringdown spectroscopy (CRDS) has been used to investigate electron impact excitation phenomena of electronatom collision processes. The technique, i.e., electron impact excitation-cavity ringdown spectroscopy (EIE-CRDS), was employed for the purposes of fundamental study and of real-time applications. The fundamental study which was carried out in terms of determining electron impact excitation cross section (EIECS) has been demonstrated by measuring EIECS of a few excited levels of mercury (Hg) atom. For the application side, the EIE-CRDS technique has been employed for trace element detection. This dissertation first describes the fundamentals of electron impact excitationcavity ringdown spectroscopy (EIE-CRDS); afterwards its applications are demonstrated. A novel method of measuring excitation cross sections using this EIE-CRDS technique has been explained. In this method, first the excitation of atoms are achieved by electron impact excitation process, subsequently, CRDS measured absolute number density is utilized to determine the absolute EIECS values. Steps of the method are described in detail. Applicability of the method is demonstrated by measuring EIECS of three different energy levels of Hg, namely 6s6p 3P0, 6s6p 3P1, and 6s7s 3S1, and the obtained values are in agreement with those reported in the literature. Secondly, the EIE-CRDS technique was employed to investigate the absorption spectrum of mercury atom in the vicinity of 404.65 nm, corresponding to the transition 6s7s 3S1 -> 6s6p 3P0 levels of mercury. Elemental mercury was measured using a laser of wavelength 404.65 nm. The technological feasibility of developing a portable size instrument for mercury detection was explored. Subsequently, a portable size, dual-mode, plasma-CRDS based prototype instrument, capable of real-time trace element monitoring, was developed. The design, functioning, and specifications of the instrument are also explained.

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The seismic risk of a nuclear power plant (NPP) depends on structures, systems and components (SSCs) that are seismically qualified to a design basis earthquake (DBE) in Canada or a safe shutdown earthquake (SSE) in the United States. On the other hand, there exist some components that are not essential to safety but their seismic interaction with seismically-qualified SSCs adversely affects the seismic risk of such SSCs. Rocking frames consisting of a rigid beam freely supported by piers (e.g., a 150 Ton spare turbine rotor, or a 100 Ton idle steam generator resting on triangular or trapezoidal rigid piers) are common to NPPs. Seismic interaction of such frames with seismically-qualified safety components or their host structure may be detrimental to nuclear safety as witnessed in the 2013 Arkansas Nuclear One accident where the drop of a 500 Ton stator adversely impacted the severe core damage frequency of the entire plant, negatively affecting the nuclear risk. In order to ensure nuclear safety, it is essential to quantify the risk of a heavy component’s drop owing to a rocking frame’s instability caused by design basis accidents including seismic. A rocking frame’s beam support may be concentric or eccentric with respect to the pier’s center of mass depending on it’s geometry, for example, triangular or trapezoidal respectively. The current nuclear standards, ASCE 43-19 and CSA N289.1-2018 are silent about rocking frames. Literature has also not addressed the eccentricity variation. This thesis addresses the gap on seismic qualification of rocking frames by, establishing an equivalent rocking block for rocking frames with symmetrical support eccentricities, obtaining the response of frames with unsymmetrical support eccentricities and finally examining the stability of the two types of frames under slide restrained conditions. / Thesis / Doctor of Philosophy (PhD) / Rocking frames, each consisting of a heavy rigid horizontal beam freely supported on unanchored rigid piers, are common to nuclear power plants (NPPs) (e.g., a turbine rotor freely supported by triangular or trapezoidal piers). The support points for the beam on the pier in such frames may be concentric or eccentric with respect to the pier’s center of mass as in a triangular or trapezoidal pier configuration. The current Canadian and American nuclear standards do not provide guidance on rocking frames. Support eccentricity variation has not been addressed in the literature. Consequently, the seismic risk of rocking frame configurations, common to NPPs, remains unknown. This thesis addresses this gap by employing an equivalent rocking block model for frames with symmetrical eccentricities, with an equation of motion representing those with unsymmetrical eccentricities; and examining the stability of the two under slide-restrained conditions.

The flexibility of the floor slabs is quite often ignored in the seismic analysis of structures. In general, the rigid behavior assumption is appropriate to describe the in-plane response of floors. For seismic excitations with vertical components, however, the flexibility of the floor slabs in the out-of-plane direction may play a significant role and it can result in an increase in the seismic response. The simplified procedures used in the current practice to include the floor flexibility can lead to highly conservative estimates of the slab and supported equipment response. To include floor flexibility, a detailed finite element model of the structure can be constructed, but this procedure leads to a system with large degrees of freedom the solution of which can be time consuming and impractical. In this study, a new dynamic condensation approach is developed and proposed to reduce the size of the problem and to calculate the seismic response of structures with flexible floor slabs. Unlike other currently available dynamic condensation techniques, this approach is applicable to classically as well as nonclassically damped structures. The approach is also applicable to structures divided into substructures. The approach can be used to calculate as many lower eigenproperties as one desires. The remaining higher modal properties can also be obtained, if desired, by solving a complementary eigenvalue problem associated with the higher modes. The accuracy of the calculated eigenproperties can be increased to any desired level by iteratively solving a condensed and improved eigenvalue problem. Almost exact eigenproperties can be obtained in just a few iterative cycles. Numerical examples demonstrating the effectiveness of the proposed approach for calculating eigenproperties are presented. To calculate the seismic response, first the proposed dynamic condensation approach is utilized to calculate the eigenproperties of the structure accurately. These eigenproperties are then used to calculate the seismic response for random inputs such as a spectral density function or inputs defined in terms of design response spectra. Herein, this method is used to investigate the influence of the out-of-plane flexibility of the floor slabs on the response of primary and secondary systems subjected to vertical ground motions. The calculated results clearly show that inclusion of the floor flexibility in the analytical model increases the design response significantly, especially when computing acceleration floor response spectra. This has special relevance for secondary systems and equipment the design of which are based on the floor response spectra. The accuracy of the results predicted by two of the most popular methods used in practice to consider the floor flexibility effects, namely the cascade approach and the modified lumped mass method, is also investigated. The numerical results show that the cascade approach overestimates the seismic response, whereas the modified lumped mass method underestimates the response. Both methods can introduce significant errors in the response especially when computing accelerations and floor response spectra. For seismic design of secondary systems supported on flexible slabs, the use of the proposed condensation approach is thus advocated. / Ph. D.

Striving to improve performance and lower weight of aircraft engines, modern compressor blades become thinner and lighter but higher loaded resulting in an increased vulnerability towards flutter. This trend is further aggravated through blisk designs that diminish structural damping and therewith flutter margin. Modern 3D wide-chord blade designs result in complex structural behaviors that add to the difficulty of correctly predicting flutter occurrence. To counteract above tendencies by driving the physical understanding of flutter and thereby helping to improve aero engine design tools, free flutter as well as forced response will be investigated in the 1.5 stage transonic compressor at TU Darmstadt. Aim of the forced response campaign is to determine the system damping in the stable compressor regime. Hence a novel excitation system capable of dynamically exciting specific rotor blade modes is needed. It is aim of the present work to find a promising concept for such a system. In the present work, the requirements for an excitation system to be used in the TUD compressor are defined with respect to achievable frequency, phase controllability, transferred excitation level, mechanical robustness, integrability and cleanliness. Different excitation system concepts, i.e. oscillating VIGVs, rotating airfoils, tangential and axial air injection are investigated numerically. An evaluation of the results obtained through 2D numerical studies proposes axial air injection as the most favorable concept. / Master of Science

<p> This thesis describes the analytical study of the stability of the structural system under circulatory loading and/or parametric excitation. The model is a double pendulum, composed of two rigid weightless bars of equal length and two concentrated masses at the ends of each bar, on an oscillating base. The vertical oscillation of the base produces parametric excitation to the system. A circulatory force is applied at the free end. At the joints the restoring moments are produced by spring and damping. The damping coefficients are taken as positive, and the gravitational effects are included. </p> <p> The combined effect of the circulatory loading and parametric excitation on stability of the system is investigated. The problem is so formulated that the stability of the system is represented by coupled Mathieu equations. The effect of damping on the boundary of stability is also determined. </p> / Thesis / Master of Engineering (ME)

The world’s oceans absorb a significant percentage of anthropogenic carbon emissions, and CO2 levels have profound effects on the marine environment. Of primary concern is the acidification of the oceans due to dissolved CO2. The goal of this research is to design new sensing technologies for deployment in the marine environment to detect CO2 pollutant. A series of carbon dioxide (CO2) receptors that are complexed to fluorene oligomers were studied computationally. In chapter 1, an overview of CO2 chemistry and various CO2 sensors is discussed. A short overview of the method (Kohn-Sham density functional theory and time-dependent density functional theory (TDDFT)) employed in this work is given. Chapter 2 presents a study on the interaction energy and electronic excitations of fluorene-receptors as CO2 sensors. The aim of this work is to gain an understanding of the nature of interactions between these receptors and CO2. The structural, electronic, and optical properties of these receptor complexes have been determined computationally. The monomer-receptor complexes show remarkable redshifts in their absorption spectra, which decrease on moving to dimer and trimer-receptor complexes (all blue-shifted).

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