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

The conventional design of steel beams considers that any deformation of a member due to applied load must be a combination of the four rigid body modes (axial deformation, major axis bending, minor axis bending and twisting) i. e. the member retains its cross sectional shape without distortion. In a hot rolled member the warping stresses which arise due to violation of the assumption that plane sections remain plane can often be neglected. In thin walled sections, however, these warping stresses are typically of the same order of magnitude as the primary bending stresses induced in the member by the applied loading and therefore cannot be neglected. In addition, if plane sections do not remain plane, the cross section distorts when a load is applied. The first part of this Thesis presents a method of analysis for any open unbranched thin walled section which considers both rigid body movement and cross section distortion (including local buckling). The method is such that the four rigid body modes are automatically identified and separated from the remaining cross section distortion modes. The second part of this Thesis develops a finite difference method of analysis, in conjunction with the theory of part I, to consider the behaviour of a member subject to any arbitrary loading condition and end restraint. Both first order linear problems and second order elastic critical buckling problems are solved, including the interaction of local buckling, overall buckling and cross section distortion.

No description available.

Modern day structures are reaching higher, spanning longer and undergoing new design methods. In addition to regular loads, it is becoming increasingly important to consider the potential risks of intentional and accidental explosions on structures. In the case of reinforced concrete buildings, critical elements such as beams and columns must de designed with sufficient strength and ductility to mitigate against the effects of blast loads to safekeep the public and prevent progressive structural collapse. Recent advancements in structural materials have led to the development of ultra-high-performance concrete (UHPC) with high compressive strength, tensile resistance, toughness and energy absorption capacity, properties which are ideal for blast protection of structures. Combining UHPC with high-performance steels, such as and high strength reinforcement is another potential solution to enhance the blast resilience of structures. This experimental and analytical research program investigates the advantages of combining high performance materials to increase the blast capacity of reinforced concrete beams. The experimental program includes tests on 21 beam specimens, fourteen of which are subjected to extreme blast loading using the University of Ottawa shock-tube, with seven companion specimens tested statically. Parameters investigated include: effect of concrete type (NSC vs. UHPC), effect of steel reinforcement type (NSR vs. HSR), effect of longitudinal reinforcement ratio, effect of fiber type/content and effect of transverse reinforcement on structural performance under static and dynamic loads. The experimental study includes three series having specified material combinations as follows: series 1 (NSC & NSR), series 2 (UHPC & NSR) and series 3 (UHPC & HSR). Each dynamically tested beam specimen is subjected to gradually increasing blast shockwaves until reaching failure. Performance assessment criteria included; maximum and residual displacements, overall blast resistance and resistance to secondary fragmentation. Results show that the specimens detailed with UHPC can resist greater blast loads with reduced mid-span displacement and debris generation when compared to beams built with conventional concrete. The combination of UHPC and high strength reinforcement further enhances blast performance and delays failure as both high strength materials balance themselves for optimum efficiency. Similarly, for specimens subjected to static loading, the use of UHPC increased the maximum load resisted by the beams, although failure mode alters from concrete crushing to rebar rupture. The combination of UHPC and high strength reinforcement further heightens beam resistance, at the expense of reduced specimen ductility. The analytical component of this thesis presents an analysis program called UO Resistance which is capable of predicting structural element resistance curves and conducting a dynamic inelastic single degree of freedom (SDOF) analysis of members subjected to blast loads. Resistance curves generated using UO Resistance were compared to data obtained through static testing and were found to effectively predict specimen response. Similarly, dynamic analysis methods implemented in UO Resistance prove to be effective at predicting specimen response under blast load. Additionally, a sensitivity analysis was performed to evaluate the effect of various modeling parameters on the static and SDOF dynamic predictions of specimen response.

Multiple thin films which are conducting, insulating and semiconducting are important components of integrated circuit technology. Circuits are fabricated from these layers by patterning the films to form isolated circuit elements which are themselves interconnected by patterned films (1).

The interaction of ultrashort laser pulses with materials is the subject of much modern research due to their ability to reach terawatt peak powers. Novel methods for temporally structuring femtosecond pulses have led to a new regime of burst mode ablation. The combination of burst mode operation with laser filamentation has been used to generate stitched filaments which form long-lasting plasma channels and can lead to increased laser ablation upon material interaction. In this work, laser ablation theory is discussed and compares the ablation effects of single, smoothly varying nanosecond pulses to a nanosecond envelope containing a GHz burst of femtosecond pulses. To directly compare the ablation efficiency by bursts of femtosecond pulses, a high-power nanosecond laser is used to ablate silicon and aluminum samples with energies comparable to the envelope energies of a burst of 32 hundred-femtosecond pulses each separated by 400 ps, as well as a bursts of 16 pulses separated by 400 or 800 ps. This experiment showed clear superiority of femtosecond burst mode over traditional nanosecond pulses at ablation at high fluences, with efficiencies forty times higher in aluminum and fourteen times higher in silicon. For the first time ever, burst mode operation was outfitted on a filamentation laser for outdoor propagation, and ablation measurements were measured after 250 meters of propagation. Single femtosecond pulses were compared to bursts of 8 pulses separated by 400 ps, and ablation craters were found only for burst modes at the highest energy during periods of low turbulence. The lack of ablation under other conditions suggests that turbulence plays a pivotal role in burst mode ablation efficacy during outdoor propagation and gives cause for further experiments at a distance.

Laser filaments are beneficial in long range outdoor applications. An intense ultrashort pulse will propagate nonlinearly through air and experience a balance of self-focusing and defocusing effects to generate a filament consisting of a plasma channel and high-intensity light beam over a long range of propagation. Filaments can propagate several times the Rayleigh distance, allowing the projection of high energy densities in a small spot size over kilometer scale distances. However, filaments are limited by clamped values of their intensity, plasma electron density, plasma lifetime, and spot size. We have previously demonstrated the "stitching" of filaments to extend the plasma lifetime. This was accomplished via our burst mode optical pulse system (BMOPS), which produces a 13 ns burst of pulses separated by an interval shorter than the plasma lifetime at the 10 Hz laser repetition rate, resulting in a higher average power than a single pulse. Stitching temporally separates and precisely spatially overlaps pulses to produce a filament with a lifetime many times that of a filament formed by a single pulse. This enhanced lifetime can improve the performance of many filamentation applications. We have recently implemented BMOPS into MU-HELF, our mobile ultrafast laser sitting on a 1 km range. Here, we present initial results of stitching and spatial confinement of burst mode energy over a 250 m range through turbulent conditions.

A wide range of laboratory and naturally occurring plasmas are frequently attributed a fluid description and as such, demonstrate turbulent flows. We will investigate a variety of forms which may be taken by the correlation functions of these turbulent flows. The most commonly discussed isotropic symmetry is not generally applicable since most systems of interest have been shown to be strongly anisotropic. This thesis will develop an axi-symmetric description from which the magnetic helicity may be extracted together with its spectrum. This description will be compared to the form taken by axi-symmetric, helical Navier Stokes turbulence which will also be derived here. The microscales for this geometry will be tabulated and for completeness, the Von Karman Howarth equations will be derived.

The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic (MHD) turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magnetic field and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave numbers.;The statistical structure of two-dimensional MHD turbulence is also considered. It is shown that the three known rugged invariants of the isotropic case reduce to two for the anisotropic case. Randomness and ergodicity are also briefly discussed.

The stability and transition properties of a bounded, current carrying magnetofluid are explored, using the hydrodynamic theory developed for plane shear flows as a guide. A driven magnetohydrodynamic sheet pinch equilibrium is employed. A sixth order, complex eigenvalue equation which governs the normal modes of small oscillations is derived, and solved numerically by the Chebyshev tau method. Eigenfunctions are shown, as well as the curve of neutral stability. The locus of critical Lundquist numbers has the form of a hyperbola. The nonlinear stability of a primary disturbance of the system is considered. For regions in parameter space close to criticality, a nonlinear stability equation of the Landau type is derived. These regions are characterized by low values of the Lundquist numbers, in contrast with the inviscid, highly conducting limit considered by Rutherford (1973). Amplitude phase planes for these disturbances are exhibited. The full set of two dimensional magnetohydrodynamic equations is solved numerically by a semi-implicit, mixed Fourier pseudospectral-finite difference algorithm. Both linear and random perturbations of the system are followed numerically into the nonlinear regime. Current sheets and deflection currents are nonlinear structures found to be significant to the evolution of the system. A secondary instability mechanism, the dynamic rupturing of the current density sheet, is also observed.