The primary aim of this study was to investigate the sedimentation processes within Buffalo Bay, particularly within and adjacent to the Whitianga tidal inlet, in order to ascertain reasons for the shoaling at both the inlet, and the identified shallow zone around Pandora Rock. Comparison of historic bathymetries suggests the ebb delta and ebb discharge channel of the Whitianga tidal inlet are rapidly accreting and the ebb tidal discharge channel is gradually migrating northeast towards Whakapenui Point. Accretion rates of up to 25 cm y-1 were calculated in the ebb delta and inlet discharge channel area between 1979 and 1995 and aerial photo comparisons suggest the ebb delta area had increased by 400 % between 1990 and 2002. Results of the hydrodynamic and sediment transport modelling suggest the rapid accretion in the ebb delta vicinity is likely to be caused by a combination of catchment estuary inputs, which are deposited on the ebb tide as the ebb flow decelerates over the ebb delta, and inputs that have been moved south along Buffalo Beach by flood currents and an eddy that forms landward of the ebb tidal discharge. Residual tidal velocities further suggest a deposition zone in the ebb delta vicinity resulting from opposing currents and the deceleration of currents. Hydrodynamic modelling results indicate the isolated shallow zone around Pandora rock appears to be caused by a transient eddy in the southern section of Buffalo Bay. The eddy is formed by the ebb tidal discharge from the inlet. Accretion probably occurs in the centre of the eddy which moves north as the ebb tide progresses. Results obtained from a current meter and sediment trap deployed in northern Buffalo Bay suggest suspended sediment transport is minimal in northern Buffalo Bay, only occurring with large wave activity. Results of the hydrodynamic and sediment transport modelling further demonstrate that this area experiences low flow velocities, and has little interaction with the rest of Buffalo Bay. The minimal sediment input to this area, combined with the occasional erosion of the seafloor, primarily by wave activity, is thought to have resulted in long term erosion of northwestern Buffalo Bay between 1938 and 1979. Although the beach and nearshore is eroding, it is likely the addition of sediment would act to stabilise this section of eroding beach. Renourishment material could be provided by the ebb delta, the southern tip of Buffalo Bay or the isolated sandbar northeast of the inlet entrance.

A new buoyant jet model is presented in this thesis to simulate the trajectory and dilution of a fluid from a single port or line source. The new features include: A generalised derivation of the governing equations so that buoyant jets discharged from a source of any shape can be modelled within the one framework, and the effects of high-frequency internal waves on the motion of the buoyant jet. Past buoyant jet models were constructed for specific cases and their application is necessarily restricted. In this thesis, a new model is developed in a Lagrangian framework that can be applied to buoyant jet discharges at any angle into ambient waters that may be stratified or unstratified, flowing or stagnant. The model is validated using both laboratory and field data. Furthermore, the model is applicable to the continuous discharge of a buoyant jet from line, axisymmetric or elliptic sources and to the instantaneous discharge of a spherical puff. No previously published model is capable of unifying and solving all of these problems within the one framework. Transforming the governing equations to their non-dimensional form shows that the trajectory and dilution of discharges from line or axisymmetric sources or of spherical puffs into a flowing, stratified ambient environment are uniquely specified using three parameters. These are: the non-dimensional size of the outlet port, the relative importance of the initial fluxes of momentum and buoyancy, and the number of orthogonal planes through which entrainment can occur. This is a significant advance in the understanding of the processes affecting buoyant jets. When high-frequency internal waves are present in the receiving waters they can have significant effects on the buoyant jet. These effects are incorporated into the present model. Using data obtained from an experiment conducted off Sydney the effects of internal waves on the height of rise and dilution of the buoyant jet were found to exceed a factor of two. Consequently, it is important that the effects of internal waves (when present) be incorporated into any buoyant jet model.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Graduation date: 2006

Lake Kinneret is Israel's only fresh water lake (unless you count the Dead Sea). It spans roughly 20km from north to south, and about 12km at its widest east west extent. It is not quite 50m deep at its deepest point. In late spring, the lake stratifies significantly and remains stratified throughout the fall. During the time the lake is stratified, it exhibits low horizontal mode semi-diurnal inertial motions in response to surface forcing from diurnal winds. This internal motion is known to be important in the ecological and chemical balances of the lake, and is suspected to be responsible for episodes in which large numbers of fish are killed. The physical response of the lake to wind forcing is studied. The lake hydrodynamics is approximated by a (x,y,t) two and three layer model on the f-plane (rotating frame) with detailed bathymetry. The numerical method for the integration of the nonlinear partial differential equation is presented, as well as, the generation of the elliptic grid used in the spatial discretization of the Kinneret domain. A suite of numerical simulations are compared to the available data in the northwestern part of the lake. The nonlinear effects, as well as, the sloping beach problem are discussed in the appendixes. / Graduation date: 2000

Graduation date: 1999

Thesis (Sc. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1983. / Cover title: Flow and skin friction over natural rough beds. Includes bibliographical references (p. 325-333).

In the event of a small break loss of coolant accident (SBLOCA) in a nuclear reactor, cold fluid is injected through the reactor system high pressure injector to compensate for the coolant loss. When this flow rate is less than a critical value, however, the hot fluid in the cold leg penetrates into the vertical injection line in a process called buoyant backflow. Because the resulting penetrations induce thermal stresses in the pipe, the presence of backflow in the injection lines is potentially significant. Since these penetrations could potentially damage the pipe, it was the purpose of this study to evaluate the backflow behavior. To this end, both the critical injection conditions and the subcritical penetration depth were experimentally determined through flow simulation in a 1/5 scale model. In addition, the experimental trends wi-re modeled theoretically. By matching the theoretical results to the experimental data, it was determined that backflow began below a critical Froude number of .65 and increased in depth with the negative logarithm of the injection velocity. The agreement between theory and experiment was excellent. For a certain class of reactor systems, the full scale Froude numbers were then compared to the critical value obtained in the analysis. For the systems involved in this comparison, the full scale Froude numbers were shown to be less than .65 for all practical flow rates. As a consequence, buoyant backflow is expected within the injection lines of these reactors, under safety injection conditions. / Graduation date: 1991

Plumes are formed when a continuous buoyant forcing is supplied at a localized source. Buoyancy can be created by either a heat flux, a compositional difference between the fluid coming from the source and its surroundings, or a combination of both. In this thesis, two types of laminar plumes with different forcing mechanisms were investigated: forced plumes and autocatalytic plumes. The forced plumes were compositionally buoyant and were injected with inertial forcing into a fluid filled tank. The autocatalytic plumes were produced without mechanical forcing by buoyancy that was entirely the consequence of a nonlinear chemical reaction -- the iodate-arsenous acid (IAA) reaction. This reaction propagates as a reacting front and produces buoyancy by its exothermicity, and by the compositional difference between the reactant and product. Both the forced and autocatalytic plumes were examined in starting and steady states. The starting, or transient, state of the plume occurs when it initially rises through a fluid and develops a plume head on top of a trailing conduit. The steady state emerges after the plume head has risen to the top of a fluid filled tank leaving only a persistent conduit. Plume behaviour was studied through experimentation, simulation, and by using simple theoretical analysis. We performed the first ever study of plumes as they crossed over the transition between buoyancy-driven to momentum-driven flow. Regardless of the driving mechanism, forced plumes were found to exhibit a single power law relationship that explains their ascent velocity. However, the morphology of the plume heads was found to depend on the dominating driving mechanism. Confined heads were produced by buoyancy-driven plumes, and dispersed heads by momentum-driven plumes. Autocatalytic plumes were found to have rich dynamics that are a consequence of the interplay between fluid flow and chemical reaction. These plumes produced accelerating heads that detached from the conduit, forming free vortex rings. A second-generation head would then develop at the point of detachment. The detachment process for plumes was sensitively dependent on small fluctuations in their initial formation. In some cases, head detachment could occur multiple times for a single experimental run, thereby producing several generations of autocatalytic vortex rings. Head detachment was reproduced and studied using autocatalytic plume simulations. Autocatalytic flame balls, a phenomenon closely related to autocatalytic plumes, were also simulated. Flame balls were found to have three dynamical regimes. Below a critical radius, the smallest flame balls experienced front death. Above this radius, they formed elongating, reacting tails. The largest flame balls formed filamentary tails unable to sustain a reaction.

Fluidized bed dryers (FBDs) are used in the pharmaceutical industry to remove excess moisture from granule prior to tablet formation. As granule moisture content is reduced from its initial to final state, the velocity required to fully fluidize the granule decreases and the bed voidage decreases. The change in these fluidization properties are attributed to the decrease in the interparticle force load created by a reduction in liquid bridging as moisture is removed. During constant velocity drying, these fluidization properties result in a bubbling fluidization state, which evolves into a bubble coalescing regime as drying proceeds. This behaviour was identifiable using pressure fluctuation time-series analysis techniques.<p> Distributor design studies using dry and wet granule in a conical fluidized bed suggest that the punched plate design limits bubble coalescence when compared to the perforated plate and Dutch weave mesh designs. Furthermore, the Dutch weave results in extensive segregation, which is undesirable from a fluidization perspective. Local drying hydrodynamic measurements using x-ray densitometry found that the punched and perforated plates generate a centralized bubbling core region during drying with a defluidized bed periphery. This fluidized core region grows as drying proceeds until the defluidized region disappears. Under the same operating conditions, a porous plate distributor creates extensive channelling and defluidization across the entire bed cross-section during the constant rate period of drying. These poor fluidization characteristics are a result of the porous plate introducing the gas into the bed as a fine dispersion.<p> Lastly, the hydrodynamics associated with the conical vessel geometry improves the circulation and mixing patterns in fluidized bed dryers. This is especially the case in the entry region of the conical bed where the high inlet gas velocity prevents defluidization around the periphery of the bed. The straight walled geometry of the cylindrical bed resulted in defluidization in this area. As a result, the hydrodynamics associated with bubbling differ significantly between the geometries over the course of drying.