Motivated by the motion of a ship in a heavy sea, a mathematical model for the vertical impact of a two-dimensional solid body onto a half-space of quiescent, inviscid, incompressible fluid is formulated. No solutions to the full problem are known, but in the case when the impacting body has small deadrise angle (meaning that the angle between the tangent to the profile and the horizontal is everywhere small) a uniformly valid solution is obtained by using the method of matched asymptotic expansions. The pressure on the body is calculated and is in fair agreement with experimental results. The model is generalised for more complicated impacts and the justifications for the model are discussed. The method is extended to three-dimensional bodies with small deadrise angle and solutions are obtained in some special cases. A variations! formulation of the leading order outer problem is derived, which gives information about the solution and leads to an fixed domain scheme for calculating solutions numerically. A partial linear stability analysis of the outer problem is given which indicates that entry problems are stable but exit problems are unstable to small perturbations. A mathematical model for the effect of a cushioning air layer between the body and the fluid is presented and analysed both numerically and in appropriate asymptotic limits. Finally, the limitations of the models are discussed and directions for future work indicated.

The durability of a polymer trileaflet valve is dependent on leaflet stress concentrations, so valve designs that reduce stress can, hypothetically, increase durability. Design aspects that are believed to contribute to reduced leaflet stress include stent flexibility, parabolic coaptation curvature, and leaflet anisotropy. With this in mind, the purpose of this investigation was to elucidate what specific combinations of these parameters promote optimal acute and long-term valve function. A combination of four stent designs, seven leaflet reinforcement materials, and three coaptation geometries were evaluated through a combination of experimentation and modeling. Static tensile and Poisson’s ratio tests and dynamic tensile fatigue testing were used to evaluate the individual leaflet components; and hydrodynamic testing and accelerated valve fatigue was used to assess complete valve prototypes. The two most successful designs included a 0.40 mm thick knit-reinforced valve with a fatigue life of 10.35 years, and a 0.20 mm thick knit-reinforced valve with a 28.9 mmHg decrease in pressure drop over the former. A finite element model was incorporated to verify the impact of the above-mentioned parameters on leaflet stress concentrations. Leaflet anisotropy had a large impact on stress concentrations, and matching the circumferential modulus to that of the natural valve showed the greatest benefit. Varying the radial modulus had minimal impact. Varying coaptation geometry had no impact, but stent flexibility did have a marked effect on the stress at the top of the commissure, where a completely rigid stent resulted in a higher peak stress than a flexible stent (E = 385 MPa). In conclusion, stent flexibility and leaflet anisotropy do effect stress concentrations in the SIBS trileaflet valve, but coaptation geometry does not. Regions of high stress concentrations were linked to failure locations in vitro, so a fatigue prediction model was developed from the S/N curves generated during dynamic tensile testing of the 0.20 mm knit-reinforced leaflets. Failure was predicted at approximately 400 million cycles (10 years) at the top of the commissure. In vitro fatigue of this valve showed failure initiation after approximately 167 million cycles (4.18 years), but it was related to a design defect that is subsequently being changed.

The following study investigates hydrodynamic stability for two-dimensional, incompressible flow past a cylinder and compares it alongside four different variations of a wave-like ground introduced within the wake region of the cylinder wake. These different variations include changing the distance of the cylinder both horizontally from the wave-like structure and vertically from the ground. The geometry and meshes were initially constructed using GMSH and imported into Nektar++. The baseflows were then obtained in Nektar++ using the Velocity Correction Scheme, continuous Galerkin method, and Unsteady Navier Stokes solver. Then, the Implicitly Restarted Arnoldi Method driver was used to retrieve the various eigenvalues/eigenmodes and growth rates. Finally, the results were visualized in Paraview which allowed clear comparisons between the stability of the flow between each case. The findings obtained show a clear effect on stability when considering different cases, for a plain cylinder and for each case there are observations to be made in how the various eigenmodes varied in terms of magnitude and shape, other observations were made in the differing critical Reynolds number and frequencies among the cases. This study is relevant to various natural environments where a blunt object may come in range of a bumpy or wavy ground. In these scenarios it can be important to monitor how instabilities propagate and cause effects such as turbulence or drag. Additionally, investigation like these can detail how to effectively avoid undesirable characteristics of instability.

No description available.

No description available.

No description available.

<p> This study deals with the use of mass balance and hydrodynamic/pollutant transport models for wetland restoration. The models were applied to Cootes Paradise marsh, located at the western end of Hamilton Harbour, Lake Ontario. Regulated water levels, excess nutrients and high suspended solids have contributed to declining vegetation and a subsequent change in wildlife in this wetland ecosystem. The Royal Botanical Gardens (RBG), which manages Cootes Paradise, has developed goals for the restoration of this wetland which focus primarily on improving water quality. </p> <p> A mass balance approach was applied to Cootes Paradise in order to gather more information on the inputs of phosphorus and suspended solids to the ecosystem. Although data were not complete for many aspects of the model, the mass balance calculations provided an acceptable agreement with field values. The mass balance models also revealed that more than 50% of the inputs of phosphorus and suspended solids were being contributed by the internal sediments. </p> <p> A two-dimensional depth averaged hydrodynamic/pollutant transport model provided an explanation for the movement of substances through the marsh as a result of wind and inflow generated currents. The resulting pollutant distribution patterns could be explained by environmental conditions in the marsh ecosystem. The computer model predicted phosphorus concentrations reasonably well, both for an overall average of the entire marsh and for individual sites. The model also simulated suspended solids and accounted for contributions of particulate matter due to carp and due to wind resuspension of the bottom sediments. Both overall averages and sample site comparisons for suspended solids were within one standard deviation of field values. According to data generated by the computer model for suspended solids, carp and wind are contributing to the concentrations in Cootes Paradise on an almost equal level; both contribute approximately one third to the overall concentration for suspended solids based on the available data. Further information is needed, however, to improve on the data set for Cootes Paradise in order to better validate the results produced by the mass balance and computer models. </p> / Thesis / Master of Engineering (ME)

No description available.

No description available.

The affects of hydrodynamic shock wave treatment on the bacterial flora of raw beef and poultry were evaluated. Hydrodynamic shock waves were generated in an aqueous treatment medium by either the detonation of two types of explosive charges (explosively-generated hydrodynamic shock waves [EHSW]) (a binary or a molecular explosive) or by electrical discharge (high voltage arc discharge Hydrodyne (TM [HVADH; Hydrodyne, Inc.]). A variety of sample types (whole steaks, ground beef, a water and ground beef slurry) were used to determine the lethality affects of EHSW on cells of the marker microorganism Listeria innocua suspended in a simple broth medium. These sample types were used in order to evaluate the affects of the process not only on the surface, but throughout the bulk of the samples in order to determine whether EHSW could also be used as a non-thermal alternative to reduce the bacterial flora of non-intact or ground meats. The levels of psychrotrophic, lactic, and coliform populations on the surface of whole eye of round steaks submitted to EHSW processing did not differ (P> 0.05) from those of untreated whole eye of round steaks. Parameters expected to influence the nature, magnitude, and propagation of the hydrodynamic shock wave were also varied and evaluated in order to determine which individual parameter or combination of parameters affected the bactericidal potential of EHSW or HVADH processing. Treatment with EHSW failed (P > 0.05) to produce lethality effects on the psychrotrophic, lactic, and coliform populations of ground beef, regardless of the composition and mass of explosive used, the number of successive EHSW treatments used, the relative distance between the explosive charge and the top surface of the sample, or the temperature of the water used in the treatment chamber. EHSW processing did not change (P >0.05) the bacterial population of treated ground beef samples when compared to untreated controls during a five day refrigerated storage study. No lethality effects were observed (P >0.05) in ground beef samples treated by HVADH when samples were subjected to one, two, or three successive HVADH treatments. Minimal penetration of surface inoculated bacteria was observed for both beef steaks and boneless skinless chicken breasts subjected to EHSW and HVADH, respectively. In EHSW-treated beef eye of round steaks, marker bacteria were detected within the first 300 um of tissue below the inoculated surface, 50-100 um beyond the depth of untreated surface inoculated steaks. In HVADH-treated boneless skinless chicken breasts, marker bacteria were detected within the first 200 um below the inoculated surface, 50-100 um beyond the depth of untreated surface inoculated boneless skinless chicken breasts. This suggests that although no difference in the bacteriological populations was observed between EHSW treated, HVADH treated, and untreated control samples of whole steaks (and ground beef treated with both HVADH and EHSW), HVADH and EHSW treatments affect the movement of surface bacteria. United States Department of Agriculture (USDA) guidelines suggest intact beef steaks be cooked to achieve a cooked color appearance on the surface and raw poultry be cooked to an internal temperature of 77° C to inactivate the pathogens Escherichia coli O157:H7 and salmonellae which are of concern in beef and poultry, respectively. By following these guidelines during proper cooking, consumers achieve thermal inactivation of these pathogens. Since the movement of the marker bacterium observed in treated steaks and boneless skinless chicken breasts was minimal, proper cooking of the products would be expected to inactivate vegetative bacterial cells at this depth. Therefore, EHSW and HVADH treated whole beef steaks and boneless skinless chicken breasts would not be expected to pose a bacterial hazard if the products were properly cooked. / Ph. D.