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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
261

Topographic and material controls on the Scottish debris flow geohazard

Milne, Fraser Dalton January 2008 (has links)
Debris flows can be considered the most significant geological hazard in areas of high relief in Scotland having impacted upon slope foot infrastructure several times in recent years. The potency of this geohazard is anticipated to increase over the coming decades due to a climatologically enforced upturn in debris flow frequency. In thisresearch material and topographic controls on debris flow activity are investigated using a combination of field and laboratory based analysis of debris flows at six study sites across upland Scotland. Centrifuge modelling is also used to simulate theinitiation of debris flows in soils with varying particle size distributions.Spatial densities of debris flow measured in the field indicate that hillslopes underlain by sandstone and granitic bedrocks, which tend to be mantled by coarser sand rich soils, have a greater frequency of flows than those underlain by schist andextrusive lava bedrocks. Higher debris flow densities on slopes underlain by sandstone and granite lithologies are facilitated by high permeability in overlying regolith matrixes allowing more rapid increase in pore water pressures duringrainstorms although this is likely to be further influenced by packing and organic content. Centrifuge modelling of hillslope debris flows also demonstrate that sandier soils are generally geotechnically more susceptible to slope failure.The susceptibility of a hillslope to debris flow is strongly influenced by slope geometry and morphology. Hillslopes with persistently steep slopes and a high incidence of concavities, gullies and couloirs are topographically more predisposed todebris flow activity due to greater shear stresses and morphologically controlled, gravity induced concentrations of hillslope hydrology. The majority of material in channelised debris flows is entrained during the gully propagation stage of the massmovement. Consequently, such events can be considered accumulative channelised debris flows. Longer and steeper gullies with greater sediment capacities are more likely to yield larger flow mass movements. Coupling between open hillslopes andbedrock gullies is shown to be an essential component for conceptualisation of the debris flow geohazard.Due to the role they play in amplifying debris flow magnitude, hazard management should be focussed around bedrock gullies and stream channels. Highesthazard rankings should be assigned to slope foot infrastructure in proximity to gullied stream channels with high sediment capacities and long, steep profiles conducive to large accumulative channelised debris flows. To avoid detrimental aesthetic impact, hazard management should be strongly geared towards utilisation of lower impactexposure reduction techniques and less visually intrusive engineering approaches such as increasing culvert capacity to accommodate debris flows. During realignment or the planning of future transport infrastructure, culverts with capacities significantly exceeding those required for purely hydrodynamic considerations should be placed straight on to stream channels avoiding proximal gully bends.
262

Modeling Transportation Planning Applications via Path Flow Estimator

Ryu, Seungkyu 01 May 2015 (has links)
The Path Flow Estimator (PEE) concept was originally developed to estimate path flows (hence origin-destination flows) and link flows for a whole road network (given some counts at selected roads). It is now further developed as an alternative for modeling different transportation planning applications: (1) a bicycle network analysis tool for non-motorized transportation planning, (2) a multi-class traffic assignment model for freight planning, and (3) a simplified travel demand forecasting framework for small community planning. The first application of the redeveloped PFE is to develop a two-stage bicycle traffic assignment model for estimating/predicting bicycle volumes on a transportation network. The first stage considers key criteria (e.g., distance related attributes, safety related attributes, air quality related attributes etc.) to generate a set of non-dominated (or efficient) paths, while the second stage adopts several traffic assignment methods to determine the flow allocations to the network. This two-stage approach can be used as a stand-alone bicycle traffic assignment to the transportation network given a bicycle origin-destination (O-D) matrix. The second application aims to enhance the realism of traffic assignment models for freight planning by incorporating different modeling considerations into the multi-class traffic assignment problem. These modeling considerations involve developing both model formulation and customized solution algorithm, which in turn involve asymmetric interactions among different vehicle types (i.e., cars versus trucks), a path-size logit (PSL) model (for accounting random perceptions of network conditions with explicit consideration of route overlapping), and various traffic restrictions imposed either individually or together to multiple vehicle types in a transportation network. In the third application, a simplified planning framework is developed to perform planning applications in small communities where limited planning resources hinder the development and application of a full four-step model. Two versions (i.e., base year and future year) of the PFE are proposed to address the specific transportation planning issues and needs of small communities. These new PFE developments for planning applications are tested with different realistic transportation networks. The results suggest that the new PFE applications proposed in this dissertation provide an alternative to the traditional four-step travel demand forecasting model that can be used as a stand-alone application with better modeling capability and fewer resources.
263

Mineralogy and Petrology of Lava Flows (Tertiary-Quaternary) In Southeastern Idaho and at Black Mountain, Rich County, Utah

Puchy, Barbara J. 01 May 1981 (has links)
Lava flows of Tertiary-Quaternary age occur in Enoch Valley, Upper Valley, and Slug Valley in southeastern Idaho. The basalts in Upper Valley and Enoch Valley contain olivine (Fo69 to Fo37), plagioclase (An62 to An39), augite and Fe-Ti oxides. The lava in Slug Valley lacks plagioclase, but contains sanidine (Or70 to Or56) with a trace of biotite and amphibole, and thus, has been termed alkali trachyte. Black Mountain, on the eastern side of Bear Lake, northeastern Utah, is capped by basalt. Minerals present include olivine (Fo83 to Fo72), plagioclase (An71 to An53 J, augite, and magnetite. Chemically, the basalt of Enoch Valley is comparable to olivine tholeiite of the Snake River Plain, as it contains olivine and hypersthene in the norm. The basalt of Upper Valley contains a greater amount of Si02 and K2O and less MgO than tholeiite of the Snake River Plain. This basalt contains normative quartz and hypersthene and is classified as tholeiite. The presence of nepheline and olivine in the norm of the basalt from Black Mountain indicates that it is an alkali-olivine basalt. The lava from Slug Valley contains high K and Mg, moderate Si, and low Al and Na. It is similar to lamproites of orenditic affinity. The temperatures of crystallization calculated from co-existing olivine and pyroxene, range from 1,015 degrees C to 996 degrees C for the valley basalts, and range from 1,021 degrees C to 1,002 degrees C for the alkali trachyte. The temperature calculated for the basalt sample from Black Mountain is 1,015 degrees C. The temperatures estimated using coexisting magnetite and ilmenite range from 1,021 degrees C to 978 degrees C for the valley basalts. The proposed origin of the Enoch Valley basalt is that it is a direct product of partial melting of a mantle of pyrolite composition. Fractionation, during ascent of the magma, could possibly have produced the Upper Valley lava. The basalt on Black Mountain was possibly derived as the result of partial melting of a pyrolitic mantle as well, but due to differences in mineralogy and normative constituents, it seems to be unrelated to the valley basalts. The origin of the Slug Valley alkali trachyte is uncertain. This lava may have been generated from a mica peridotite mantle and is possibly related to the Leucite Hills lava in Wyoming.
264

Imports and oligopoly behaviour in Australian manufacturing

Chong, Han Hwee January 2003 (has links)
Oligopoly behaviour by domestic firms faced with foreign competition in a small open economy is examined in the context of a market for differentiated products. This paper concentrates on the responsiveness of import flows to import price in the context of trade with imperfect competition. The empirical work analyses the behaviour over time of the interaction between domestic industry prices and domestic costs as well as foreign competitors' prices. A structural model is employed for estimation purposes with consumer demand derived from a CES (constant elasticity of substitution) utility function of domestic and foreign composites of goods. Domestic firms are assumed to face Leontief production functions and maximise profit independently subject to their conjectures about the reactions of rivals. Firm behaviour is modelled using conjectural variations to identify market power, distinguishing two models of oligopoly, namely, Cournot and Bertrand conjectural variations. This leads to the econometric specification of pricing, import and budget share equations consistent with oligopolistic equilibrium. The interrelationship between the budget share equations and the price-cost margin provides encompasses either Cournot or Bertrand conjectural variations. The econometric specification is applied to each of the two digit Australian manufacturing industries using quarterly data covering the period from 1984 to 2000. Results of the industrial behaviour indicate that industries that produce consumer products are generally react to price movements The classification of industry 21 to 24 is more proximate to consumer products as compared to higher industrial numbering. The regression results for industry 25 to 28 suggest quantity reactions. This is in line with the nature of the products produce by these industries, which are heavy industrial manufacturing products. / The elasticity with respect to foreign price is distinguished between the "partial" and the "total" effect. The partial elasticity of import demand ranges from .6205 to 4.9497, while the total elasticity of import demand ranges from .6505 to 19.8132. The elasticity of demand ranges from .0191 for Wood and Paper Product manufacturing to 3.4093 for Food, Beverage and Tobacco manufacturing.
265

Boundary Layer Separation in Hypersonic Ducted Flows

Andrew Dann Unknown Date (has links)
Experiments to generate multiple shock waves in an axisymmetric model at hypersonic speeds were conducted in a small reflected shock tunnel. Conical surfaces were used to generate shock waves inside a circular duct chosen to be representative of a scramjet combustor. These shock waves impinged on turbulent boundary layers to produce shock wave/boundary layer interactions (SWBLIs). In the process of observing this phenomenon, the commonly used empirical correlations of Korkegi were tested for accuracy, i.e. the combined pressure ratio across these shocks can be measured and compared to that predicted by these correlations. Korkegi correlates only with Mach number, and is independent of Reynolds number and on how the pressure is applied. A major contribution of this work is to examine how the details of the compression process effect separation. In this study, the history of applying the compression was varied. An analytical method was developed for theoretically estimating the onset of incipient separation using an integrated computation of the momentum flux contained in the boundary layer. By including the summed (negative) contribution of wall shear stress on the integrated momentum flux, the upstream history of the boundary layer was considered. The overall result has a form similar to the Korkegi correlations, plus an additional correction term relating to momentum loss through wall shear stress. The correction term was determined to be a second order effect, which explains why the Reynolds number independent Korkegi correlations work so well over such a large range of conditions. A hypersonic flow test condition conducive to the generation of high Reynolds number flows and turbulent boundary layer production was developed in a small reflected shock tunnel. The experimentally measured flow parameters were matched by numerical simulation using a number of in-house codes at The University of Queensland. This has allowed the unmeasured parameters which are numerically derived to be stated with greater confidence. An internal centre-body with a conical forebody was used to generate conditions of incipient separation. This provided benchmark data for comparison with subsequent experiments with multiple compressions. A semi-vertex angle of 15o was selected based on Large Eddy Simulation (LES) numerical results once the experimental and numerical static wall pressure and heat flux were matched. A two-cone experimental model, which provided for adjustment of the axial separation between the two shock systems, was tested at the same flow conditions as used in the single-cone experiments. A technique of incrementally moving the instrumentation (relative to the centre-body) and repeating the same condition to achieve high resolution in pressure and heat flux distributions with a limited number of transducers was successful. The results verified that it was possible to subject a hypersonic turbulent boundary layer to two quantified compression-expansion systems with an adjustable axial separation between them and capture the first reflected shock in a “shock trap” to remove it's influence from the second SWBLI. The data from this initial two-cone model provided non-separated pressure and heat flux data which was used as a reference to help interpret data from separated flows. The commercially available Reynolds Averaged Navier-Stokes (RANS) numerical code, CFD-Fastran, was used to help design an experimental model which produces boundary layer separation. Algebraic and two-equation turbulence models were applied to a modified two-cone model to show greater pressure rises which would produce boundary layer separation. A modified two-cone model was tested and demonstrated boundary layer separation. Three configurations with varying axial separation between SWBLIs were tested which all produced separation. The configuration that produced the largest pressure ratio and largest separation region at the second SWBLI may represent a geometry whereby the distance from the hollow cylinder inlet and the second cone may represent a critical value. The amount of viscous interaction, generated from the leading edge of the shock trap, and the proximity of the two interactions may be coupled to produce higher than expected values. It is postulated that the boundary layer momentum recovery for the configuration where the second SWBLI was furthest downstream (30 mm configuration), prevented severe separation from occurring. An in-house RANS code, elmer3, was used to simulate the flow of the modified two-cone model. An algebraic turbulence model was applied to this model and comparisons of experimentally measured static wall pressure and heat flux have given good agreement. The wall shear stress was investigated to provide further information concerning the position and size of flow reversal regions. The use of the numerical codes utilised in this study has reinforced their effectiveness for model design and comparison of experimental results.
266

A new Laplace operator in Finsler geometry and periodic orbits of Anosov flows

Barthelm��, Thomas 24 January 2012 (has links) (PDF)
In the first part of this dissertation, we give a new definition of a Laplace operator for Finsler metric as an average, with regard to an angle measure, of the second directional derivatives. This operator is elliptic, symmetric with respect to the Holmes-Thompson volume, and coincides with the usual Laplace--Beltrami operator when the Finsler metric is Riemannian. We compute explicit spectral data for some Katok-Ziller metrics. When the Finsler metric is negatively curved, we show, thanks to a result of Ancona that the Martin boundary is H��lder-homeomorphic to the visual boundary. This allow us to deduce the existence of harmonic measures and some ergodic preoperties. In the second part of this dissertation, we study Anosov flows in 3-manifolds, with leaf-spaces homeomorphic to .... When the manifold is hyperbolic, Thurston showed that the (un)stable foliations induces an "orthogonal" flow. We use this second flow to study isotopy class of periodic orbits of the Anosov flow and existence of embedded cylinders.
267

A new Laplace operator in Finsler geometry and periodic orbits of Anosov flows

Barthelm��, Thomas 24 January 2012 (has links) (PDF)
In the first part of this dissertation, we give a new definition of a Laplace operator for Finsler metric as an average, with regard to an angle measure, of the second directional derivatives. This operator is elliptic, symmetric with respect to the Holmes-Thompson volume, and coincides with the usual Laplace--Beltrami operator when the Finsler metric is Riemannian. We compute explicit spectral data for some Katok-Ziller metrics. When the Finsler metric is negatively curved, we show, thanks to a result of Ancona that the Martin boundary is H��lder-homeomorphic to the visual boundary. This allow us to deduce the existence of harmonic measures and some ergodic preoperties. In the second part of this dissertation, we study Anosov flows in 3-manifolds, with leaf-spaces homeomorphic to .... When the manifold is hyperbolic, Thurston showed that the (un)stable foliations induces an "orthogonal" flow. We use this second flow to study isotopy class of periodic orbits of the Anosov flow and existence of embedded cylinders.
268

Simulation of three-dimensional two-phase flows : coupling of a stabilized finite element method with a discontinuous level set approach

Marchandise, Emilie 14 December 2006 (has links)
The subject of this thesis is the development of an accurate, general and robust numerical method capable of predicting the flow behavior of two-phase immiscible fluids, separated by a well defined interface. In the quest of an accurate and robust numerical method for the modeling of two-phase flows, one has to keep in mind the intrinsic properties and difficulties associated with the problem: (i) those flows are mostly three-dimensional, (ii) some flows are steady, others unsteady, (iii) the interface might encounter a lot of topology changes (like merger or break-up), (iv) large jumps of density and viscosity might exist across the interface (e.g. ratio of density of 1/1000 for water and air), (v) surface tension forces may play a very important role in the interface dynamics. Hence, the influence of this force should be accurately evaluated and incorporated into the model, (vi) mass conservation is of primary importance. All these issues are addressed in this thesis, and special techniques are proposed for their treatment, which enables to construct the desired computational method. The chosen computational method combines a pressure stabilized finite element method for the Navier Stokes equations with a discontinuous Galerkin (DG) method for the level set equation. Such a combination of those two numerical methods results in a simple and effective algorithm that allows to simulate diverse flow regimes presenting large density and viscosity ratios (ratio up to 1/1000).
269

A Parallel Implicit Adaptive-mesh-refinement Scheme for Hypersonic Flows with an Equilibrium High-temperature Equation of State

Wood, Alistair Henry Cameron 30 July 2008 (has links)
A parallel implicit adaptive-mesh-refinement scheme is proposed for the solution of the Navier-Stokes equations as applied to two-dimensional steady-state hypersonic laminar flows in conjunction with an equilibrium high-temperature equation of state. A finite-volume discretization is applied to the governing equations. Limited piecewise-linear solution reconstruction and Riemann solvers (Roe and HLLE, both modified for a general equation of state) are used to evaluate the inviscid fluxes. The gradients in the viscous fluxes are calculated using diamond-path reconstruction. The system of non-linear algebraic equations resulting from the finite-volume discretization are solved using an inexact Newton method with GMRES to solve the update step of the Newton method. GMRES is preconditioned with Schwarz preconditioning with local block-fill incomplete lower-upper factorization. Multigrid and pseudo-transient continuation are used for startup. Numerical results, including flows at Mach numbers of 7.0, are discussed and demonstrate the validity and efficiency of the scheme.
270

A Parallel Implicit Adaptive-mesh-refinement Scheme for Hypersonic Flows with an Equilibrium High-temperature Equation of State

Wood, Alistair Henry Cameron 30 July 2008 (has links)
A parallel implicit adaptive-mesh-refinement scheme is proposed for the solution of the Navier-Stokes equations as applied to two-dimensional steady-state hypersonic laminar flows in conjunction with an equilibrium high-temperature equation of state. A finite-volume discretization is applied to the governing equations. Limited piecewise-linear solution reconstruction and Riemann solvers (Roe and HLLE, both modified for a general equation of state) are used to evaluate the inviscid fluxes. The gradients in the viscous fluxes are calculated using diamond-path reconstruction. The system of non-linear algebraic equations resulting from the finite-volume discretization are solved using an inexact Newton method with GMRES to solve the update step of the Newton method. GMRES is preconditioned with Schwarz preconditioning with local block-fill incomplete lower-upper factorization. Multigrid and pseudo-transient continuation are used for startup. Numerical results, including flows at Mach numbers of 7.0, are discussed and demonstrate the validity and efficiency of the scheme.

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