Factors related to operations of a well that impact drilling uncertainties in the shallow water region of the Gulf of Mexico (GOM) can be directly linked to the site specific issues; such as water depth and local geological depositional environments. Earlier risk assessment tools and general engineering practice guidelines for the determination of the conductor casing design were based more on traditional practices rather than sound engineering practices. This study focuses on the rudimentary geological and engineering concepts to develop a methodology for the conductor setting depth criteria in the shallow water region of the GOM.

No description available.

No description available.

The Panola Mountain Research Watershed (PMRW) is a 41 ha forested watershed, located 25 km southeast of Atlanta, Georgia. Within that watershed is a 10 ha sub-catchment which contains the headwaters of the watersheds main stream, as well as two outcrops of Panola Granite (Burns et al. 2001). On the hill-slope below the northernmost outcrop, is a 20m long trench that has been excavated down to bedrock, a depth that ranges from 0.5-1.5m. In previous studies (Burns et al., 2001; Freer, et al., 2002), discharge through the overlying soils was measured along the trench in 2m sections across the full length of the trench. In those studies, it was assumed that the underlying bedrock was impermeable. However, Burns et al. (2003) showed that the riparian groundwater downslope from the trenched hillslope site was only 6 to 7 years old. The permeability of the Panola granite in question was proven by a recent Lithium- Bromide line tracer experiment -van Meerveld et al., in review. Due to the levels of bromide in the bedrock measured at the trench, it has become apparent that fluid is being lost to hidden hydraulic pathways, those probably being fractures. The objective of this thesis is to test the viability of using shallow seismic reflection to map out fracture zones at the trenched hillslope site, using GPR and shallow seismic refraction as supplemental techniques to verify the interpretation. Data from two seismic common shot point (CSP) surveys permitted an image of the soil/bedrock interface to be constructed, as well as enabling an acoustic velocity profile to be calculated for the area. This velocity profile is then used with data from five reflection surveys (one seismic and four radar) to create vertical profiles of the subsurface. Although the resulting SSR profile is less than optimum, higher amplitude arrivals related to structure were still able to be detected. From this profile, as well as those from the GPR survey, it can be concluded that the proposed hidden hydraulic pathways due indeed exist, and also that they can be accurately mapped out using the previously mentioned geophysical methods.

Estuaries depend on the transport of nutrients and sediments from the open sea to help maintain a prosperous environment. One of the major transport mechanisms is the propagation of large two dimensional vortical structures. At the mouth of an inlet, tidal flow forces the formation of two dimensional vortical structures whose lateral extent is much greater than the water depth. After the starting jet vortex dipole detaches from the inlet, secondary vortices shed due to separation from the inlet boundary and eventually reach the starting-jet dipole. An idealized inlet con figuration was utilized for laboratory experiments detailing the formation and propagation of the vortex structures with water depths of 3, 5, and 9 centimeters and flow Froude scaled to inlets along the Texas coast. Using surface particle image velocimetry, the entrainment of the secondary structures into the vortex system are shown as well as variations in characteristics such as trajectory, size, vorticity, and circulation for the vortices as they move downstream.

Shallow foundations are used when designing subsea structures on the seafloor of deep water Gulf of Mexico. In order to design these subsea shallow foundations it is important to understand the behavior of the undrained shear strength of the shallow soils (i.e. upper ten to twenty feet of soil). The objective of this research is to analyze a database of soil data from deep water Gulf of Mexico originally produced by Cheon (2011) with a focus on shallow soils. The purpose of this analysis is to gain a better understanding of the soil and how it will be usable with regards to shallow foundation design. The methodology of this analysis involves studying raw data collected from different measurements taken to aid in the creation of design profiles of undrained shear strength versus depth. Within the existing database there are 18 locations with a high resolution of point data from in-situ tests (Halibut Vane) and non in-situ tests (Minivane and Torvane) that provide the clearest picture of undrained shear strength in the shallow region. The data shows that the design profiles originally created for these locations for deep foundations are generally not representative of the strength in the shallow region. They also show that in-situ test data show more variability than non in-situ data. There are also 25 Cone Penetration Tests in the existing database that show very high resolution data in the shallow region. These Cone Penetration Tests also indicate a crust that appears to be about 1 ft thick and exists along the edge of the continental shelf. Recommended future activities to build upon this work include re-evaluating the design profiles at these 43 locations at which high resolution studies have been performed in the shallow region, collecting these design profiles as well as any new design profiles and organizing them into a new database focused on shallow soils, generating a new generic profile base on the data within the new database, and creating a model that uses spatial variability analysis to calculate undrained shear strengths at new locations based on the data in the database. / text

A particle tracking velocimetry (PTV) system is used to investigate the turbulent properties at the free surface of shallow shear flows and a shallow vortex street (VS) wake flow. The resolution of the PTV system enables information to be gathered regarding the large-scale turbulent structure of these flows, and also enables analysis to proceed in both the temporal and spatial domains. Statistical tools such as the probability density function (PDF), autocorrelation and power spectral density (PSD) are utilised to characterise the turbulent properties at the flow surface. Two supercritical flows and one subcritical shallow shear flow are analysed. Taylor's frozen turbulence hypothesis is shown to be valid for these flows, and the integral length scales indicate that 2D isotropic structures with scales larger than the flow depth are present at the free surface. Such large-scale structures at the free surface are consistent with observations from dye visualisation experiments and with "spiral eddies" identified by Kumar, et al (1998). The longitudinal extent of near and intermediate wake fields for the shallow VS wake flow is well defined by the integral wake length scale specified by v.Carmer (2005). The near wake region is characterised by high rates of exchange between the mean flow and large-scale 2D coherent structures (2DCS). In the intermediate field, the rate of decay of the turbulent stress components greatly diminishes as the 2DCS are stabilised and dissipated under the action of bed friction. Multiple peaks are observed in the power spectral density of the turbulent fluctuations. The periodic shedding of 2DCS behind the circular cylinder is characterised by an energy peak at a Strouhal number of 0.21, and further energy peaks are observed in the near-wake region. The PSD estimates are consistent with the findings of v.Carmer (2005) in which a -5/3 decay law to high frequencies is observed, and no evidence of an inverse energy cascade is present.

Thesis (Ph.D.)--University of Iowa, 2009. / Thesis supervisor: Jonathan Mark Adrain. Includes bibliographical references (leaves 71-73).

Conventional morphodynamic models are typically based on a coupled system of hydrodynamic equations, a bed-update equation, and a sediment-transport equation. However, the sediment-transport equation is almost invariably empirical, with numerous options available in the literature. Bed morphological evolution predicted by a conventional model can be very sensitive to the choice of sediment-transport formula. This thesis presents a physics-based model, where the shallow water-sediment-mixture flow is idealised as being divided into two layers of variable (in time and space) densities: the lower layer concerned with bedload transport, and the upper layer representing sediment in suspension. The model is referred to as a Quasi-2-Layer (Q2L) model in order to distinguish it from typical 2-Layer models representing stratified flow by two layers of different but constant and uniform densities. The present model, which does not require the selection of a particular empirical formula for sediment transport rates, is satisfactorily validated against widely used empirical expressions for bedload and total transport rates. Analytical solutions to the model are derived for steady uniform flow over an erodible bed. Case studies show that the Q2L model, in contrast to conventional morphodynamic approaches, yields more realistic results by inherently including the influence of the bed slope on the sediment transport. This conclusion is validated against experimental data from a steep sloping duct. An analytical study using the Q2L model investigates the influence of bed-slope on bedload transport; the resulting expressions are in turn used to modify empirical sediment transport formulae (derived for horizontal beds) in order to render them applicable to arbitrary stream-wise slopes. The Q2L model provides an alternative approach to studying sediment-transport phenomena, whose adequate analysis cannot be undertaken following coniv ventional approaches without further increasing their degree of empiricism. The Q2L model can also lead to the enhancement of conventional morphodynamic models. For coarse sediments and/or relatively low flow velocities, bedload transport is usually responsible for most sediment transport. Bedload transport consists of a combination of particles rolling, sliding and saltating (hopping) along the bed. Hence, saltation models provide considerable insight into near-bed sediment transport. This thesis also presents an analysis of the statistics and mechanics of a saltating particle model. For this purpose, a mathematically simple, computationally efficient, stochastic Lagrangian model has been derived. This model is validated satisfactorily against previously published experimental data on saltation. The model is then employed to derive two criteria aimed at ensuring that statistically convergent results are achieved when similar saltation models are employed. According to the first criterion, 103 hops should be simulated, whilst 104 hops ought to be considered according to the second criterion. This finding is relevant given that previous studies report results after only a few hundred, or less, particle hops have been simulated. The model also investigates sensitivity to the lift force formula, the friction coefficient, and the collision line level. A method is proposed by which to estimate the bedload sediment concentration and transport rate from particle saltation characteristics. This method yields very satisfactory results when compared against widely used empirical expressions for bedload transport, especially when contrasted against previously published saltation-based expressions.

The localized loss of near-surface excess ice on Mars by sublimation (and perhaps melting) can produce thermokarstic collapse features such as expanded craters and scalloped depressions, which can be indicators of the preservation of shallow ice. We demonstrate this by identifying High Resolution Imaging Science Experiment images containing expanded craters south of Arcadia Planitia (25-40 degrees N) and observe a spatial correlation between regions with thermokarst and the lowest-latitude ice-exposing impact craters identified to date. In addition to widespread thermokarst north of 35 degrees N, we observe localized thermokarst features that we interpret as patchy ice as far south as 25 degrees N. Few ice-exposing craters have been identified in the southern hemisphere of Mars since they are easier to find in dusty, high-albedo regions, but the relationship among expanded craters, ice-exposing impacts, and the predicted ice table boundary in Arcadia Planitia allows us to extend this thermokarst survey into the southern midlatitudes (30-60 degrees S) to infer the presence of ice today. Our observations suggest that the southern hemisphere excess ice boundary lies at 45 degrees S regionally. At lower latitudes, some isolated terrains (e.g., crater fill and pole-facing slopes) also contain thermokarst, suggesting local ice preservation. We look for spatial relationships between our results and surface properties (e.g., slope and neutron spectrometer water ice concentration) and ice table models to understand the observed ice distribution. Our results show trends with thermal inertia and dust cover and are broadly consistent with ice deposition during a period with a higher relative humidity than today. Shallow, lower-latitude ice deposits are of interest for future exploration.