title: Investigation of Flow Parameters for Titanium Cold Spraying using CFD Simulation

authors: Singh, Tejinder

subjects: Cold Spraying

abstract: A comprehensive study of cold gas dynamic spray technology is required for optimising performance and gun design for spraying various materials. Cold spraying technology is a new technique in industry and very limited data is available. This thesis focuses on the investigation of cold spray parameters for spraying ductile titanium alloys through a de-Laval convergent-divergent nozzle and optimisation of the nozzle dimensions. This work describes a detailed study of the various parameters, namely applied gas pressure, gas temperature, size of titanium particles and dimensions of the nozzle on the outlet velocity of the titanium particles. A model of a two-dimensional axisymmetric nozzle was used to generate the flow field of titanium particles with the help of a gas stream flowing at supersonic speed. ANSYS FLUENT software was used for the simulation of a cold spray nozzle. A standard k-ɛ model has been used to account for the turbulence produced due to the very high velocity flow. Differences in the velocity of titanium particles were modelled over the range of applied gas pressure, gas temperature and size of titanium particles. From the CFD simulation results optimum values of gas pressure and temperature were found for making a successful coating of titanium particles. The optimum nozzle dimensions were also found as the diverging length and exit diameter of the nozzle were found to affect the outlet velocity of titanium particles. The simulation results show good agreement with previous cold spray work using different spraying materials. Validation of the CFD model was done by referring to the experimental work and CFD work done for a similar kind of flow field. The grid quality of the model was investigated to get the results to converge and be independent of the grid size to give good agreement between the accuracy of results and the computational time.

text: Investigation of Flow Parameters for Titanium Cold Spraying using CFD Simulation A comprehensive study of cold gas dynamic spray technology is required for optimising performance and gun design for spraying various materials. Cold spraying technology is a new technique in industry and very limited data is available. This thesis focuses on the investigation of cold spray parameters for spraying ductile titanium alloys through a de-Laval convergent-divergent nozzle and optimisation of the nozzle dimensions. This work describes a detailed study of the various parameters, namely applied gas pressure, gas temperature, size of titanium particles and dimensions of the nozzle on the outlet velocity of the titanium particles. A model of a two-dimensional axisymmetric nozzle was used to generate the flow field of titanium particles with the help of a gas stream flowing at supersonic speed. ANSYS FLUENT software was used for the simulation of a cold spray nozzle. A standard k-ɛ model has been used to account for the turbulence produced due to the very high velocity flow. Differences in the velocity of titanium particles were modelled over the range of applied gas pressure, gas temperature and size of titanium particles. From the CFD simulation results optimum values of gas pressure and temperature were found for making a successful coating of titanium particles. The optimum nozzle dimensions were also found as the diverging length and exit diameter of the nozzle were found to affect the outlet velocity of titanium particles. The simulation results show good agreement with previous cold spray work using different spraying materials. Validation of the CFD model was done by referring to the experimental work and CFD work done for a similar kind of flow field. The grid quality of the model was investigated to get the results to converge and be independent of the grid size to give good agreement between the accuracy of results and the computational time.

year: 2010

title: Groundwater flow dynamics beneath a wastewater irrigation site, Hautapu, Cambridge

authors: Whatnall, Natasha

subjects: Soil dynamics

abstract: In this study, a qualitative groundwater hydrological model is developed to assist in evaluating the long-term environmental sustainability of a wastewater irrigation system at Hautapu, Cambridge. The model relies on the integration of site information, numerical groundwater modelling, geochemical data, and surface geophysical data.

The characteristics of the site relating to the groundwater system are examined including climate, topography, natural and artificial recharge, hydrogeology, hydraulic characteristics, seasonal variations, and abstraction activities. Integration of this information indicates groundwater movement is predominantly horizontal and northwestward, with highly restricted vertical movement downwards due to the presence of thick sequences of silt-based materials beginning at an average depth of ~10m:

A numerical groundwater model was developed incorporating the site information to estimate groundwater flow patterns within the study area. The model suggests that lateral flow northwestward within the unconfined aquifer predominates in the study area and that there is probably minimal vertical movement from the upper aquifer zones to the deep aquifer.

An analysis of recent geochemical data is undertaken in this study to (i) determine the horizontal and vertical extent of modified groundwater movement; and (ii) provide ground truth for the electrical resistivity technique. The results of the analysis reveal elevated levels of sodium in shallow groundwater in a zone centred on the wastewater irrigation farm, with some localised lateral migration to the South, West and Northwest. Movement of modified groundwater vertically has occurred to a maximum depth of ~16 m on-site.

The surface geophysical technique, electrical resistivity was employed at the site to: (i) provide input about flow dynamics beneath the site, through the delineation of the low resistivity modified groundwater plume; and (ii) evaluate the success of the technique in detecting spatial variations in groundwater quality. A comprehensive survey was undertaken involving vertical soundings and horizontal profiling measurements. In general, a modified groundwater plume consistent with that defined by geochemical data was identified thereby validating the application of the technique and confirming recognised movement patterns. However, the application of the technique is limited to areas where high conductivity modified groundwater controls the resistivity signal. Beyond these areas it is proven that the resistivity data may be an artefact of lithology.

The development of the qualitative groundwater hydrological model was achieved through the integration of the flow information obtained via the outlined investigative methods. The main outputs of the groundwater model are that modified groundwater movement is:
(i) Constrained within the unconfined aquifer; and
(ii) Predominantly horizontal, therefore 2-dimensional.

It is concluded that the current wastewater disposal activity appears to be performing sustainably in terms of nitrogen disposal, however consistent increases in sodium levels over the wastewater disposal site to the boundaries raises the possibility of future increases in sodium in groundwater just beyond the boundaries in some locations.

text: Groundwater flow dynamics beneath a wastewater irrigation site, Hautapu, Cambridge In this study, a qualitative groundwater hydrological model is developed to assist in evaluating the long-term environmental sustainability of a wastewater irrigation system at Hautapu, Cambridge. The model relies on the integration of site information, numerical groundwater modelling, geochemical data, and surface geophysical data.

The characteristics of the site relating to the groundwater system are examined including climate, topography, natural and artificial recharge, hydrogeology, hydraulic characteristics, seasonal variations, and abstraction activities. Integration of this information indicates groundwater movement is predominantly horizontal and northwestward, with highly restricted vertical movement downwards due to the presence of thick sequences of silt-based materials beginning at an average depth of ~10m:

A numerical groundwater model was developed incorporating the site information to estimate groundwater flow patterns within the study area. The model suggests that lateral flow northwestward within the unconfined aquifer predominates in the study area and that there is probably minimal vertical movement from the upper aquifer zones to the deep aquifer.

An analysis of recent geochemical data is undertaken in this study to (i) determine the horizontal and vertical extent of modified groundwater movement; and (ii) provide ground truth for the electrical resistivity technique. The results of the analysis reveal elevated levels of sodium in shallow groundwater in a zone centred on the wastewater irrigation farm, with some localised lateral migration to the South, West and Northwest. Movement of modified groundwater vertically has occurred to a maximum depth of ~16 m on-site.

The surface geophysical technique, electrical resistivity was employed at the site to: (i) provide input about flow dynamics beneath the site, through the delineation of the low resistivity modified groundwater plume; and (ii) evaluate the success of the technique in detecting spatial variations in groundwater quality. A comprehensive survey was undertaken involving vertical soundings and horizontal profiling measurements. In general, a modified groundwater plume consistent with that defined by geochemical data was identified thereby validating the application of the technique and confirming recognised movement patterns. However, the application of the technique is limited to areas where high conductivity modified groundwater controls the resistivity signal. Beyond these areas it is proven that the resistivity data may be an artefact of lithology.

The development of the qualitative groundwater hydrological model was achieved through the integration of the flow information obtained via the outlined investigative methods. The main outputs of the groundwater model are that modified groundwater movement is:
(i) Constrained within the unconfined aquifer; and
(ii) Predominantly horizontal, therefore 2-dimensional.

It is concluded that the current wastewater disposal activity appears to be performing sustainably in terms of nitrogen disposal, however consistent increases in sodium levels over the wastewater disposal site to the boundaries raises the possibility of future increases in sodium in groundwater just beyond the boundaries in some locations.

year: 1999

title: Historical translocations by Maori may explain the distribution and genetic structure of a threatened surf clam in Aotearoa (New Zealand)

authors: Ross, Philip M.

subjects: Science & Technology

abstract: The population genetic structure of toheroa (Paphies ventricosa), an Aotearoa (New Zealand) endemic surf clam, was assessed to determine levels of inter-population connectivity and test hypotheses regarding life history, habitat distribution and connectivity in coastal vs. estuarine taxa. Ninety-eight toheroa from populations across the length of New Zealand were sequenced for the mitochondrial cytochrome c oxidase I gene with analyses suggesting a population genetic structure unique among New Zealand marine invertebrates. Toheroa genetic diversity was high in Te Ika-a Māui (the North Island of New Zealand) but completely lacking in the south of Te Waipounamu (the South Island), an indication of recent isolation. Changes in habitat availability, long distance dispersal events or translocation of toheroa to southern New Zealand by Māori could explain the observed geographic distribution of toheroa and their genetic diversity. Given that early-Māori and their ancestors, were adept at food cultivation and relocation, the toheroa translocation hypothesis is plausible and may explain the disjointed modern distribution of this species. Translocation would also explain the limited success in restoring what may in some cases be ecologically isolated populations located outside their natural distributions and preferred niches.

text: Historical translocations by Maori may explain the distribution and genetic structure of a threatened surf clam in Aotearoa (New Zealand) The population genetic structure of toheroa (Paphies ventricosa), an Aotearoa (New Zealand) endemic surf clam, was assessed to determine levels of inter-population connectivity and test hypotheses regarding life history, habitat distribution and connectivity in coastal vs. estuarine taxa. Ninety-eight toheroa from populations across the length of New Zealand were sequenced for the mitochondrial cytochrome c oxidase I gene with analyses suggesting a population genetic structure unique among New Zealand marine invertebrates. Toheroa genetic diversity was high in Te Ika-a Māui (the North Island of New Zealand) but completely lacking in the south of Te Waipounamu (the South Island), an indication of recent isolation. Changes in habitat availability, long distance dispersal events or translocation of toheroa to southern New Zealand by Māori could explain the observed geographic distribution of toheroa and their genetic diversity. Given that early-Māori and their ancestors, were adept at food cultivation and relocation, the toheroa translocation hypothesis is plausible and may explain the disjointed modern distribution of this species. Translocation would also explain the limited success in restoring what may in some cases be ecologically isolated populations located outside their natural distributions and preferred niches.

year: 2018