Planetesimals may form from the gravitational collapse of dense particle clumps initiated by the streaming instability. We use simulations of aerodynamically coupled gas-particle mixtures to investigate whether the properties of planetesimals formed in this way depend upon the sizes of the particles that participate in the instability. Based on three high-resolution simulations that span a range of dimensionless stopping times 6 X 10(-3) <= tau <= 2, no statistically significant differences in the initial planetesimal mass function are found. The mass functions are fit by a power law, dN/dM(p) proportional to M-p(-p), with p = 1.5-1.7 and errors of Delta p approximate to 0.1. Comparing the particle density fields prior to collapse, we find that the high-wavenumber power spectra are similarly indistinguishable, though the large-scale geometry of structures induced via the streaming instability is significantly different between all three cases. We interpret the results as evidence for a near-universal slope to the mass function, arising from the small-scale structure of streaming-induced turbulence.

Aquatic propulsion by means of undulatory movements of the median (dorsal and anal) fins is the primary mode of transport for the Picasso triggerfish (Rhinecanthus aculeatus). Known as balistiform locomotion, this form of propulsion is an adaptation for highly efficient movement within complex environments such as coral reefs. A principle component of balistiform locomotion has been the development of momentum enhancement, a fin-force multiplier that increases swimming efficiency. This study examines the kinematics and energetics of balistiform locomotion employing theoretical models of thrust, power, and efficiency. Thrust and power were calculated and compared with theoretical values modeled by Lighthill and Blake (1990). This model has heretofore not been thoroughly vetted and was tested for accuracy and applicability. Thrust force was estimated from resistance (drag) using a vertical dead drop to determine terminal velocity; power was calculated from oxygen consumption measurements at different speeds. The Lighthill and Blake (1990) model requires median fin kinematics (frequency, wavelength, amplitude, wave angle), which were measured from high-speed videography and followed statistically predicted trends with frequency being the dominant variable, and the others changing little or not at all with speed. Momentum enhancement was found to be 3.6, close to Lighthill and Blake’s (1990) theoretically predicted value of 2.5. Momentum enhancement is experimentally proven here for the first time. Theoretical and empirical thrust force values are closely matched; theoretical thrust is greater at lower speeds and lower at higher speeds. The ratio of theoretical thrust to drag-estimated thrust averages 1.08. Theoretical values for power are greater than those measured by a factor of about 3.6 and cannot be explained by measurement error. / Science, Faculty of / Zoology, Department of / Graduate

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The movement of organisms and resources within ecosystems are essential elements in the productivity, stability, and distribution of communities. This thesis examines how water velocity, a defining factor of lotic systems, influences the dispersion of benthic organisms and particulate organic matter in small stream ecosystems. Variation in movement-related behaviours in two rheophilous (‘flow-loving’) mayflies (Epeorus and Baetis) and two rheophobic (‘flow-avoiding’) mayflies (Ameletus and Paraleptophlebia) were compared to determine how benthic organisms disperse between and within habitat patches in hydrodynamically complex landscapes. The degree to which water velocity and particle shape influence the retention of organic matter (including deciduous leaves, conifer needles, red-cedar fronds, and branch fragments) was examined to determine how physical factors determine detrital resource availability in streams. Although water velocity did not influence the crawling rates of Baetis and Ameletus in daylight conditions, both mayflies dispersed rapidly upstream in low-velocity flows in dark conditions. Drift rates of both mayflies were lower in daylight than dark conditions, and were generally inversely related to their habitat preferences. Escape responses in grazing Epeorus, Baetis, and Ameletus larvae in a range of flow conditions showed that retreat distance was more sensitive than flight initiation distance to variation in water velocity, suggesting that hydrodynamics mediate the risks of predation and the costs of flight in stream systems. Comparisons of the transport distances of live larvae, dead larvae, and passive tracer particles in low and high water velocities showed that drift distance varied substantially among taxa, and that behavioural control over drift distance generally declined as water velocity increased. While organic matter particles generally travelled further in high-velocity reaches, leaves were retained in riffles when they impacted on protruding clasts, while ‘stiff’ particles were retained when they settled into streambed interstices. Leaves placed in high-velocity microhabitats were broken down more slowly than leaves in low-flow areas, likely due to the exclusion of large-bodied detritivores. In conclusion, this thesis supports the view that hydrodynamic forces control trophic interactions and local population dynamics in stream ecosystems by directly altering the physical – and sometimes behavioural – processes of particle entrainment, transport, and deposition. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

In the pulp and paper industry, the interaction between the gas, liquid, and solid phases occurring in various unit operations is often not clearly understood. Such multi-phase operations include flotation deinking (a separation process of paper fibres in the recycling process) as well as the delignification and bleaching operations in the kraft pulping process. Much of the design, operation, and optimization of such processing equipment are dependent upon past experience as well as trial-and-error methodologies. Pulp fibre suspensions possess a complex and unique rheology. The unpredictability of the behaviour of pulp suspensions at any given mass concentration is due to the bonding between the fibres resulting in network formation (which depends on suspension consistency) with this interaction creating complexity in fluid flow in various unit operations. This thesis describes the gas hydrodynamic behaviour and gas-liquid mass transfer characteristic in low- and medium-consistency pulp suspensions in batch operation. First, the hydrodynamic behaviour of the gas phase (air) in water and pulp suspensions having mass concentrations up to Cm = 7% is examined by visually observing and recording the bubble shape, size, and rise velocity in a rectangular channel. Results are obtained using a high-speed video camera. Second, the hydrodynamic behaviour is described in terms of the gas holdup along with axial and radial gas phase distributions in water and kraft pulp suspensions having mass concentrations between Cm = 0.5 and 9% in a batch-operated cylindrical bubble column. The gas holdup results are compared using three methods: the suspension height method, the pressure difference method, and the electrical resistance tomography (ERT) method. Finally, the volumetric gas-liquid mass transfer characteristic of air in water and kraft pulp suspensions having mass concentrations up to Cm = 4% is examined in the same bubble column in batch-operation using a dissolved oxygen probe. Experimental results were comparable to that in literature for water and for pulp fibre suspensions having Cm < 2%. The presence of fibres had a significant effect on the gas holdup and mass transfer characteristic with results providing insight on the limitations that exist in industrial pulp unit operations. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

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The effects of wave directionality on the loads and motions of long structures is investigated in this thesis. A numerical method based on Green's theorem is developed to compute the exciting forces and hydrodynamic coefficients due to the interaction of a regular oblique wave train with an infinitely long, semi-immersed floating cylinder of arbitrary shape. Comparisons are made with previous results obtained using other solution techniques. The results obtained from the solution of the oblique wave diffraction problem are used to determine the transfer functions and response amplitude operators for a structure of finite length and hence the loads and amplitudes of motion of the structure in short-crested seas. The wave loads and body motions in short-crested seas are compared to corresponding results for long-crested seas. This is expressed as a directionally averaged, frequency dependent reduction factor for the wave loads and a response ratio for the body motions. Numerical results are presented for the force reduction factor and response ratio of a long floating box subject to a directional wave spectrum with a cosine power type energy spreading function. Applications of the results of the present procedure include such long structures as floating bridges and breakwaters. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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