Whole document restricted until 2010, see Access Instructions file below for details of how to access the print copy. / Blind Mexican cave fish (Astyanax fasciatus) lack a functioning visual system, and are known to use self-generated water motion to sense their surroundings; an ability termed hydrodynamic imaging. Nearby objects distort the flow field created by the motion of the fish. These flow distortions are sensed by the mechanosensory lateral line. Little is known about the fluid mechanics involved in hydrodynamic imaging, or how the behaviour of the fish might influence their ability to sense the world around them. Automated image analysis was used to study the effects of swimming kinematics on the ability of the fish to sense their surroundings when introduced into a novel environment. The fish reacted to avoid head-on collisions with a wall at a remarkably short mean distance of 4.0 ± 0.2 mm. The ability of the fish to react, was dependent on whether they were beating their tail as they approached the wall. When following surfaces, such as a wall, the fish changed their swimming kinematics significantly and used both tactile and hydrodynamic information. Measuring the tendency of the fish to follow a tightening curve showed the fish to be moderately thigmotactic. The flow fields around freely swimming fish were experimentally measured using Particle Image Velocimetry (PIV). A new algorithm was developed to calculate the pressure field around the fish based on the velocity field measured using PIV. The algorithm was validated against analytical and computational fluid dynamic (CFD) solutions. The flow fields around gliding fish and the stimuli to the lateral line of the fish were calculated using CFD models, validated against the experimental PIV data. The flow fields changed in characteristic ways as the fish approached a wall head-on or swam parallel to a wall. At 0.10 body lengths from a wall, the stimulus to the lateral line was estimated to be sufficient for the fish to be able to detect the wall, but this decreased rapidly with increasing distance from the wall. The CFD models suggested that the velocity of the fish does not affect the distance at which they detect an object. Hydrodynamic imaging is a short range sensory ability and blind cave fish require their sensitive lateral line and fast reactions in order to be able to use it to sense the world around them and avoid collisions. The information gained about the fluid mechanics of hydrodynamic imaging, and the flow measurement and modelling techniques developed here will be useful for further study of this remarkable ability.

Acid Sulphate Soils (ASS) often cause acidic pollution in canal water, which negatively impacts on water quality, biodiversity and the livelihood of farmers and fishermen, especially the landless poor. The problem is particularly acute in the coastal zones, where people already suffer from the consequences of salinity intrusion. Reducing acidic pollution is important for improving agricultural and aqua-cultural production and also the living conditions of people living in coastal zones with ASS. This study aims at developing an analytical tool that can simulate the propagation of acidic pollution and that would allow planers and managers to develop water management options and other resource management measures to reduce acidic pollution in the canal network of a coastal zone. / This study utilizes a systems approach, with a series of field, laboratory studies, in combination with statistical and GIS-based analyses and simulation modelling. Field and laboratory studies were carried out during 2001 - 2006 in Ca Mau peninsula, Mekong Delta, Vietnam, to fill in knowledge gaps on the source and amount of acidic loads from soil to the water surroundings, their interaction with saline water and their propagation in the canal network. Knowledge generated from this study was used in developing and validating a model to simulate the propagation of acidity in the tidal canal network with brackish water. / Measured data showed that the acidic pollution in the canal network varies seasonally. The pH of the canal water was lowest (3 – 4.5) at the beginning of the rainy season and highest (7 – 7.5) at the end of the rainy season and during the dry season. The reduced dredging activities in year 2005 and 2006 may explain why the acidic pollution decreased in 2005 – 2006 compared with 2001 –2004. The most serious acidic pollution occurs when the two following conditions are present simultaneously: (i) The existence of newly dredged canals (and hence the deposition of the excavated spoils on the canal embankment) in areas with ASS (especially with a severe ASS); and (ii) little or a lack of water exchange from tidal flows. Field experiments showed that ASS embankments within 2-3 years after dredging represent a high acidity hazard because they can release into the canal a total acidity, mainly from runoff and seepage water, of up to 2.7 mol H+day-1 per meter length of canal embankment. Functional relationships were established allowing quantification of the daily acid load transferred from fields and canal embankments to the canal network. / A laboratory titration experiment showed that saline water could buffer the effects of acidic pollution in the canal water. A new ACIDITY module was developed and was coupled to an existing hydraulics and salinity model (the Vietnam River Systems And Plains - VRSAP). The model was calibrated with measured data from 2003 and validated with data from 2005. The Model is the first of its kind able to simulate the temporal and spatial dynamics of changes of pH (as an indicator of acidity) at a regional scale, together with salinity and water flow characteristics in a tidal canal network with brackish water. The Model can be used to investigate the effects of different scenarios of water and other resource management options on the extent of acidic pollution in a coastal area. Analysis of simulation runs for various scenarios indicate that opening the two main sluices along the East Sea at high tide in one day every week in May and June for saline water intake, combined with widening the canals that connect these sluices to the West Sea can eliminate the acidity problem in the study area. Large scale dredging of canals of ASS in fresh water zone should be avoided as it can create severe acidic pollution of the canal water.

Whole document restricted until 2010, see Access Instructions file below for details of how to access the print copy. / Blind Mexican cave fish (Astyanax fasciatus) lack a functioning visual system, and are known to use self-generated water motion to sense their surroundings; an ability termed hydrodynamic imaging. Nearby objects distort the flow field created by the motion of the fish. These flow distortions are sensed by the mechanosensory lateral line. Little is known about the fluid mechanics involved in hydrodynamic imaging, or how the behaviour of the fish might influence their ability to sense the world around them. Automated image analysis was used to study the effects of swimming kinematics on the ability of the fish to sense their surroundings when introduced into a novel environment. The fish reacted to avoid head-on collisions with a wall at a remarkably short mean distance of 4.0 ± 0.2 mm. The ability of the fish to react, was dependent on whether they were beating their tail as they approached the wall. When following surfaces, such as a wall, the fish changed their swimming kinematics significantly and used both tactile and hydrodynamic information. Measuring the tendency of the fish to follow a tightening curve showed the fish to be moderately thigmotactic. The flow fields around freely swimming fish were experimentally measured using Particle Image Velocimetry (PIV). A new algorithm was developed to calculate the pressure field around the fish based on the velocity field measured using PIV. The algorithm was validated against analytical and computational fluid dynamic (CFD) solutions. The flow fields around gliding fish and the stimuli to the lateral line of the fish were calculated using CFD models, validated against the experimental PIV data. The flow fields changed in characteristic ways as the fish approached a wall head-on or swam parallel to a wall. At 0.10 body lengths from a wall, the stimulus to the lateral line was estimated to be sufficient for the fish to be able to detect the wall, but this decreased rapidly with increasing distance from the wall. The CFD models suggested that the velocity of the fish does not affect the distance at which they detect an object. Hydrodynamic imaging is a short range sensory ability and blind cave fish require their sensitive lateral line and fast reactions in order to be able to use it to sense the world around them and avoid collisions. The information gained about the fluid mechanics of hydrodynamic imaging, and the flow measurement and modelling techniques developed here will be useful for further study of this remarkable ability.

The nearshore current field, defined here as the residual horizontal flow after averaging over the incident wave period, exhibits variability at a range of time and space scales. Some of the variable currents are low frequency gravity wave motions. However, variable, rotational (in the sense of possessing vertical vorticity) flow can also exist as part of the overall nearshore current field. A field and numerical modelling investigation of these variable rotational currents has been carried out. Drifters, which were developed for surfzone use, enabled measurement of the nearshore current structure; the design and testing of these new instruments is described. Two sets of field measurements, using the new drifters and Eulerian instruments were carried out for conditions with swell perpendicular to a plane beach and in strong longshore currents. In the perpendicular swell conditions, an interesting and well-defined feature of the measured trajectories was the development of transient rip currents. Discrete vortices were also observed. In the longshore current case, trajectories with the longshore current displacement removed had complex meandering paths. Lagrangian data were used to make estimates of length scales and dispersion, both of which provide strong evidence that the current field cannot be due to low frequency gravity waves alone. Under the assumption of equipartition of kinetic and potential energy for low frequency gravity waves, Eulerian measurements of velocities and pressure show significant energy due to non-divergent, rotational flow in both the perpendicular swell and longshore current case. A numerical model that can simulate horizontal flow with a directionally spread, random wave field incident on a plane beach was implemented. The model developed transient rip currents that are qualitatively very similar to those seen in the drifter trajectories from the field. The number and intensity of rip currents in the model depended on the beach slope and incident wave spectra. The energy content and cross-shore flux (and hence transport of material) of the rotational current flow component in the simulated flow fields is comparable to that due to low frequency gravity waves. The modelling also provided some evidence that there may be universal characteristics of the rotational currents. The field results and modelling show that variable rotational currents are ubiquitous in the field even when longshore currents and hence shear waves are not present. The term “infragravity turbulence” is suggested to describe the general class of nearshore hydrodynamics not directly associated with shear waves, which is largely disorganised, but contains well defined features such as transient rips currents and large scale horizontal vortices. The results have important implications in the understanding of the transport of material, including sediment, biological material, pollution, and sometimes bathers, in the nearshore zone.

Shark Bay is a large inverse estuary, located in Western Australia. It has a number of unique habitats that support important species. The dynamics of circulation in Shark Bay have an influence on the species that inhabit the region, on small, local scales as well as on large Bay-wide scales. Numerical modeling and field data were used to examine small-scale dynamics in relation to an important recreational fish, pink snapper (Pagrus auratus). Icthyoplankton surveys collected and recorded egg density in regions where snapper are found. A barotropic three-dimensional hydrodynamic model was coupled with a two-dimensional Lagrangian particle-tracking program to simulate the passive transport of eggs through regions where spawning is known to occur. Circulation modeling results indicated residual flows on small scales that served to retain the eggs in the region where they were originally spawned. Results corroborate genetic work on adult snapper, which found no evidence intermixing of populations in Shark Bay. The numerical model was then further refined to run in a baroclinic mode. Simulations of salinity and temperature gradients were used to recreate frontal systems in Shark Bay. Frontal regions divide the Bay into a northern and a southern section as well as separate it from the ocean. Application of an analytical method for calculating front locations was consistent with the observed results and indicated that the primary forces determining frontal locations in the Bay are tides and gravitational circulation. Winds are a secondary influence, and solar heating is minimal in influence

Local scour around bridge piers can cause serious damages and structural failure to the bridge. Correct prediction of the scour is an important criterion for the engineering design. Though the subject has been investigated for many decades, the theoretical developments have been very limited due to the complicated interaction of three-dimensional flow and the sediment transport. This thesis concerns the flow around a vertical bottom mounted cylinder exposed to currents and is considered as the initial phase of a study towards modeling local scour around vertical bottom-mounted structures. The aim of the present study is to obtain a better understanding of the complex three-dimensional flow and the mechanisms related to the scouring. The study started with the development of a three-dimensional numerical model to simulate flow around cylindrical structures. After validation of the model, the model was applied to investigate flow around an isolated rectangular cylinder. Unsteady flows around cylinders of a square cross section (A/D = 1) and a rectangular cross section (A/D = 2) were simulated to understand the flow properties around a cylinder other than a circular cross section. Three-dimensional flow patterns, pressure distribution, forces on the cylinder and vortex-shedding frequencies were discussed. It was found that the present numerical results generally agree well with the experimental data. Flow around a vertical cylinder mounted on a rigid bed was then investigated by the numerical model. A circular and a square cross sections were considered respectively. Flow structures of horseshoe vortex and the wake vortex which are the major mechanisms leading to the scouring around the base of the vertical cylinder were explored. The bed shear stress distributions that directly affect the scour processes were discussed. Finally the numerical model was applied to study the flow around a submerged square cylinder mounted on a bed, which has significant engineering relevance to the local scour around structures, such as bridge pier foundation itself, or a caisson placed underwater around the pier bottom for scour protection. The numerical calculations were carried out at different cylinder heights to investigate the effect of the cylinder height on the flow properties. It was found that for submerged cylinders with the height of less than one and a half of the cylinder side width the maximum bed shear stress amplification is about 60% of the value of an infinite long cylinder. The quantification of the shear stress reduction is important for scour protection design.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 202-207).

Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, Discipline of Geology and Geophysics, 2004. / "February 2004" Includes bibliographical references (leaves 216-227).

Thesis (Ph.D.); Submitted to the Department of Physics and Astronomy, Rice University, Houston, TX (US); 1 Sep 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "LA-14149-T" J. Koller. US DOE (US) 09/01/2004. Report is also available in paper and microfiche from NTIS.

Thesis (Ph.D.)--University of Melbourne, Dept. of Mathematics and Statistics, 2007. / Typescript. Includes bibliographical references (leaves 143-151).