No description available.

Axially-moving materials arise in problems associated with spacecraft antennas, pipes conveying fluid and telescopic robotic manipulators. Flexible extendible beams are a special class of axially-moving materials, in which the axially-moving material is modelled as a slender beam and the mechanism of elastic deformation is transverse bending. Hamilton's principle is used to derive the governing differential equation of motion and system invariant properties of a flexible extendible beam protruding from a rigid wall with prescribed extrusion profile. The mass of the system is not constant and the general analytical solution to the equation of motion is not known. In this study, numerical solutions are obtained using finite-element analysis. However, instead of following the obvious (but cumbersome) approach of using fixed-size elements and increasing their number, in a stepwise fashion, as mass elements enter the domain of interest, a more elegant approach is followed wherein the number of elements is fixed, while the sizes of the elements change with time. To this end, a variable-domain beam finite element whose size is a prescribed function of time is formulated. The accuracy of this variable-domain beam element is demonstrated through the time-integration of equations of motion using various extrusion profiles. Additional verification is performed by the evaluation of the system's invariant quantities, comparison with a special analytical solution, and the dynamic stability analysis of pipes conveying fluid. The effects of wall flexibility, tip mass, and high-frequency axial-motion perturbations to the transverse response of the flexible extendible beam are also examined. In order to gain a deeper insight into the mechanics of this system, the dynamic stability characteristics of the flexible extendible beam are also investigated using various extrusion profiles. The effects of physical damping, tip mass, tip support and wall flexibility on the stability characteristics of this system are examined. The power and versatility of this finite-element formulation is demonstrated in a simulation of an extruding flexible extendible beam which carries a tip mass and protrudes from a flexible envelope beam which imparts three-dimensional rigid-body rotations to the system. / Graduate

Bibliography: leaves 189-195. / xii, 197 leaves ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study investigates feedforward active control of harmonic vibratory power transmission in simple structures, theoretically and experimentally. The structures investigated are a beam, a plate and a cylinder. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1997?

Thesis (Ph.D.)--University of California, Berkeley, 1963. / "UC-28 Particle Accel. and High Volt. Mach." -t.p. "TID-4500 (19th Ed.)" -t.p. Includes bibliographical references (p. 302-303).

Thesis (M.S. in Physics)--United States Naval Postgraduate School, California. / "Unclassified Physics." Includes bibliographical references (p. 20). 8

The elasto-dynamics of flexible frame structures is of interest in many areas of engineering. In certain structural systems the deflections can be large enough to warrant a nonlinear analysis. For example, offshore structures, long suspension bridges and other relatively slender structures used in space applications require a geometrically nonlinear analysis. In addition, if the structure has deployable elements, as in some space structures, the required analysis becomes even more complex. Typical examples are spacecraft antennae, radio telescopes, solar panels and space-based manipulators with deployable elements. The main objective of the present work is to formulate the problem of sliding beams undergoing large rotations and small strains. Further we aim to develop efficient finite element technique for analysis of such complex systems. Finally we wish to examine the nature of the motion of sliding beams and point out its salient features. We start with two well known approaches in the nonlinear finite element static analysis of highly flexible structures, namely, the updated Lagrangian and the consistent co-rotational methods and extend these techniques to dynamic analysis of geometrically nonlinear beam structures. We analyse several examples by the same methods and compare the performance of each for efficiency and accuracy. Next, using McIver's extension of Hamilton's principle, we formulate the problem of geometrically flexible sliding beams by two different approaches. In the first the beam slides through a fixed rigid channel with a prescribed sliding motion. In this formulation which we refer to as the sliding beam formulation, the material points on the beam slide relative to a fixed channel. In the second formulation the material points on the fixed beam are observed by a moving observer on a sliding channel and the beam is axially at rest. The governing equations of motion for the two formulations describe the same physical problem and by mapping both to a fixed domain, using proper transformations, we show that the two sets of governing equations become identical. It is not, possible to find analytical solutions to our problem and we choose the Galerkin numerical method to obtain the transient response of the problem for the special case axially rigid beam. Next we follow a more elegant approach wherein we use the developed incremental nonlinear finite element approaches (the updated Lagrangian and the consistent co-rotational method) in conjunction with a variable time domain beam finite elements (where the number of elements is fixed and as mass enters the domain of interest, but the sizes of elements change in a prescribed manner in the undeformed configuration). To verify the formulation and its computational implementation we analyse many examples and compare our findings with those reported in the literature when possible. We also use these illustrative examples to identify the importance of various terms such as axial flexibility and foreshortening effects. Finally we look into the problem of parametric resonance for the beam with periodically varying length and we show that the regions of stability obtained in the literature, using a linear analysis, do not hold when a more realistic nonlinear analysis is undertaken. / Graduate

No description available.

Beams of polarized protons play an important part in the study of the spin dependence of the nuclear force by measuring the analyzing power in nuclear reactions. The source at iThemba LABS produces a beam of polarized protons that is pre-accelerated by an injector cyclotron (SPC2) to a energy of 8 MeV before acceleration by the main separated-sector cyclotron to 200 MeV for physics research. The polarized ion source is one of the two external ion sources of SPC2. Inside the ion source hydrogen molecules are dissociated into atoms in the dissociator and cooled to a temperature of approximately 30 K in the nozzle. The atoms are polarized by a pair of sextupole magnets and the nucleus is polarized by RF transitions between hyperfine levels in hydrogen atoms. The atoms are then ionized by electrons in the ionizer. The source has various sensitive devices, which influence beam intensity and polarization. Nitrogen gas is used to prevent recombination of atoms after dissociation. The amount of nitrogen and the temperature at which it is used plays a very important role in optimizing the beam current. The number of electrons released in the ionizer is influenced by the size and shape of the filament. Optimization of the source will ensure that beams of better quality (a better current and stability) are produced.

The non-linear beam dynamics of a circular accelerator, such as the Large Hadron Collider, can have a significant impact on its operation. In order to avoid limitations on the performance reach of the accelerator, and ensure machine protection, it is vital that the beam dynamics are well understood and controlled. This thesis presents the results of studies of non-linear beam dynamics undertaken on the Large Hadron Collider at CERN, during the 2010 to 2013 period. It sets out to quantify the understanding of the non-linear beam dynamics through the comparison of beam-based measurements to simulation, and where able and appropriate seeks to explain deviations of measurement from the model, and define corrections for relevant aspects of the dynamics. The analyses presented in this thesis represent considerable advances in the understanding of the LHC beam dynamics which should allow for an improved operation of the machine in the coming years.

As a cutting-edge technology for photoinjectors, SRF guns are expected to provide CW electron beams with high bunch charge and low emittance, which is critical to the development of future FELs, ERLs and 4th/5th generation light sources. However, existing research has not explored the full potential of SRF guns as predicted by theory. Currently, the research activities at ELBE focus on solving technological challenges of a 3.5 cell SRF gun as well as applying it to high-bunch-charge experiments. This thesis aims to optimize the ELBE SRF gun and the relevant beam transport for future high-bunch-charge applications at pELBE, nELBE, TELBE and CBS experimental stations. Chapter 1 describes the demands of these applications on the SRF gun in detail. Chapter 2 outlines the development of a simulation tool based on ASTRA and Elegant, followed by the optimized gun parameters and the beam transport for the four experimental stations. Chapter 3 introduces beam diagnostic methods and data processing applied in this thesis. Chapter 4 presents results of experiments, including the pulse length measurement of the UV laser for generating electrons from the photcathode, the commissioning of ELBE SRF Gun II, a verification experiment on the LSC effect conducted at PITZ and a beam transport experiment with the bunch charge of 200 pC. Simulation results have determined the effect of each SRF gun parameter on the beam quality and have provided optimized settings according to the requirements in Chapter 1. Experimentally, the LSC effect was confirmed at PITZ, in agreement with simulations which indicated that LSC significantly influences beam quality. The performance of ELBE SRF Gun II was improved and a beam with a bunch charge of 200 pC and an emittance of 7.7 μm from ELBE SRF Gun II has been transported through ELBE without visible beam loss. The development of the simulation tool and beam diagnostics will serve further research at ELBE. Results of both simulations and experiments enrich the understanding of the existing SRF gun as well as the ELBE beamline and will guide continuing improvements. Already, ELBE SRF Gun II can deliver twice the bunch charge and lower emittance compared to the thermionic injector routinely used for ELBE. Ongoing modifications and development of the gun-cavity and photocathodes are expected to provide still further improvements. Progress on high-bunch-charge experiments at ELBE can be expected by applying the SRF gun.