Protection of subsea infrastructure in ice environments

This thesis begins with an outlook of the offshore Newfoundland oil and gas industry. While hydrocarbon resources are plentiful, adverse operating conditions and risk of impact from encroaching icebergs leads to challenges in design, project execution and operation. Acceptable risk levels regarding hydrocarbon release to the environment have to be met by providing sufficient protection for vulnerable assets. A discussion on the parameters involved in determining contact risk between the keel of an iceberg and a subsea structure is provided. -- For subsea structures, many protection concepts have been considered for application in ice environments such as the Beaufort Sea and Grand Banks. Glory holes have been the selected concept for major field development and production schemes on the Grand Banks, however, this method may not be feasible in the development of marginal fields that only require limited subsea infrastructure. Other protection concepts which have been considered are discussed as well. -- The protection of subsea installations required for subsea tie-back developments via tubular frame protection structures is proposed in the present study. Three different geometric configurations are analyzed. The first configuration consists of a rectangular framework similar to overtrawlable structures used in the North Sea. The second structure has a large circular base and a smaller circular top portion, with the top and base connected using straight inclined members, to give the appearance of a truncated conical skirt. The third is a modification of the second, incorporating curved instead of straight inclined members. Structural based finite element models were employed to predict the structural response of the frames subjected to ice loading. Primary failure mechanisms during ice-subsea structure interaction are assessed using an energy approach. Design loads are estimated using a simple ice load model accounting for crushing failure of the ice keel over the contact area. The rectangular frame model behaved well in comparison to the other configurations. This concept also offers relative ease of design and construction. For the circular base models, the benefit of introducing curved members was evident. -- Progress in this research area should involve simulation of a wider range of ice contact events. It is suggested that the finite element model be improved toward continuum interaction of a deformable tubular protection frame structure with an iceberg keel substructure modeled using kinematic constraints representing iceberg size and stability

Physical and numerical modelling of pipe/soil interaction events for large deformation geohazards

Large deformation, differential ground movement events on buried pipelines involve large strain, nonlinear contact interaction, and soil strain localization and failure mechanisms. This study is focused on advancing finite element modelling procedures through laboratory tests to enhance soil constitutive models, physical models to verify simulation tools and algorithms to improve simulation tools that capture realistic behaviour for cohesive and cohesionless soils. The outcomes provide a robust framework for improved confidence in predicted outcomes to support engineering design. The large deformation, ice gouge events, in cohesive soil, and pipe/soil interaction events, in cohesive and cohesionless soil, were simulated using the Coupled Eulerian Lagrangian (CEL) formulation within ABAQUS/Explicit modelling framework. For ice gouge events, the numerical simulation was conducted using total stress analysis and the von Mises yield criterion. The numerical modelling procedures are improved by incorporating the distribution of soil properties, including elastic modulus and shear strength, throughout the domain without the need to develop complex user material subroutines. The numerical predictions were in agreement with available data in the literature and exhibited improved accuracy with respect to the keel reaction forces and subgouge soil deformations. The major contribution was to improve the benchmark and state-of-art for the numerical simulation of ice gouge events in cohesive soil. Having developed confidence in the numerical simulation of large deformation events in cohesive soil, the research focused on advancing the modelling procedures for cohesionless soil. Large-scale, physical tests on lateral pipe/soil interaction events in sand investigated the effects of pipe diameter (254 mm, 609.6 mm), burial depth to pipe diameter ratio (1, 3, 7) and soil density (14.7 kN/m³, 15.6 kN/m³). The main objective was to provide a verification basis for the numerical modelling procedures with respect to the force–displacement response and localized soil failure mechanisms. The physical tests contributed to the limited database, for the range of pipe diameters examined, and the first large-scale lateral pipe/soil interaction tests to provide detailed soil deformation and strain fields using particle image velocimetry (PIV) technique. In parallel with the physical testing program, an enhanced constitutive model for cohesionless soil was advanced through the development of a user-subroutine that accounts for the effects of soil friction angle and dilation angle as a function of plastic shear strain. Laboratory triaxial and direct shear tests were used to characterize the strength parameters. This contribution has practical applications for pipe/soil interaction events in granular soils, particularly at shallow burial depth with low confining pressure, large soil deformations and strains, and dense sand states with strain softening behaviour. Integrating the enhanced constitutive soil models, the numerical modelling procedures, were verified through comparison with the large-scale pipe/soil interaction tests conducted in this study and third-party physical modelling data. An extended study was conducted to assess the verified simulation tool across a range of practical engineering design scenarios. The outcomes from this study illustrated the improved accuracy and confidence in the numerical predictions, based on the tools developed in this study, that provide a significant contribution to the field of buried pipeline design against large deformation ground movement events

Assessing Hurricane Katrina Vegetation Damage at Stennis Space Center using IKONOS Image Classification Techniques

Hurricane Katrina hit southwestern Mississippi on August 29, 2005, at 9:45 a.m. CDT as a category 3 storm with surges up to approx. 9 m and sustained winds of approx. 120 mph. The hurricane's wind, rain, and flooding devastated several coastal towns, from New Orleans through Mobile. The storm also caused significant damage to infrastructure and vegetation of NASA's SSC (Stennis Space Center). Storm recovery at SSC involved not only repairs of critical infrastructure but also forest damage mitigation (via timber harvests and control burns to reduce fire risk). This presentation discusses an effort to use commercially available high spatial resolution multispectral IKONOS data for vegetation damage assessment, based on data collected over SSC on September 2, 2005

A reinterpretation of the evidence for endothelial glycocalyx filtration structure

The endothelial glycocalyx is thought to be the primary macromolecular filter for fluid flux out of the vasculature. This filter maintains the higher protein concentration within the vessel lumen relative to the tissue. Whilst the arguments for the endothelial glycocalyx being the size filter are convincing the structural evidence has been limited to specialized stains of perfusion fixed tissue, which are further processed for resin embedding for transmission electron microscopy. The staining and processing of the delicate pore structure has left many researchers struggling to interpret the observed surface coat. Previous work has alluded to a 19.5nm spacing between fibers; however, whilst repeatable it does not give an endothelial glycocalyx pore size consistent with known glycosaminoglycan molecular structure due to the required fiber thickness of >10nm. Here a new interpretation is proposed based on the likelihood that the electron micrographs of are often of collapsed endothelial glycocalyx. The 19.5nm spacing measured may therefore be the core protein of the proteoglycans with the glycosaminoglycans wrapped up around them rather than in an expanded in-vivo state. The concept is explored to determine that this is indeed consistent with experimental measurements of permeability if the syndecans are predominately dimerized. Further an alteration of core protein lattice from hexagonal packing to square packing dramatically changes the permeability which could be facilitated via known mechanisms such as transient actin binding

Distinct subdivisions of the cingulum bundle revealed by diffusion MRI fibre tracking: Implications for neuropsychological investigations

The cingulum is a prominent white matter tract that supports prefrontal, parietal, and temporal lobe interactions. Despite being composed of both short and long association fibres, many MRI-based reconstructions ( tractography ) of the cingulum depict an essentially uniform tract that almost encircles the corpus callosum. The present study tested the validity of dividing this tract into subdivisions corresponding to the ‘parahippocampal’, ‘retrosplenial’, and ‘subgenual’ portions of the cingulum. These three cingulum subdivisions occupied different medial–lateral locations, producing a topographic arrangement of cingulum fibres. Other comparisons based on these different reconstructions indicate that only a small proportion of the total white matter in the cingulum traverses the length of the tract. In addition, both the radial diffusivity and fractional anisotropy of the subgenual subdivision differed from that of the retrosplenial subdivision which, in turn, differed from that of the parahippocampal subdivision. The extent to which the radial diffusivity scores and the fractional anisotropy scores correlated between the various cingulum subdivisions proved variable, illustrating how one subdivision may not act as a proxy for other cingulum subdivisions. Attempts to relate the status of the cingulum, as measured by MRI-based fibre tracking, with cognitive or affective measures will, therefore, depend greatly on how and where the cingulum is reconstructed. The present study provides a new framework for subdividing the cingulum, based both on its known connectivity and MRI-based properties

Blood Mercury Levels of Zebra Finches Are Heritable: Implications for the Evolution of Mercury Resistance

Mercury is a ubiquitous metal contaminant that negatively impacts reproduction of wildlife and has many other sub-lethal effects. Songbirds are sensitive bioindicators of mercury toxicity and may suffer population declines as a result of mercury pollution. Current predictions of mercury accumulation and biomagnification often overlook possible genetic variation in mercury uptake and elimination within species and the potential for evolution in affected populations. We conducted a study of dietary mercury exposure in a model songbird species, maintaining a breeding population of zebra finches (Taeniopygia guttata) on standardized diets ranging from 0.0–2.4 μg/g methylmercury. We applied a quantitative genetics approach to examine patterns of variation and heritability of mercury accumulation within dietary treatments using a method of mixed effects modeling known as the \u27animal model\u27. Significant variation in blood mercury accumulation existed within each treatment for birds exposed at the same dietary level; moreover, this variation was highly repeatable for individuals. We observed substantial genetic variation in blood mercury accumulation for birds exposed at intermediate dietary concentrations. Taken together, this is evidence that genetic variation for factors affecting blood mercury accumulation could be acted on by selection. If similar heritability for mercury accumulation exists in wild populations, selection could result in genetic differentiation for populations in contaminated locations, with possible consequences for mercury biomagnification in food webs

Using size-selected gold clusters on graphene oxide films to aid cryo-transmission electron tomography alignment

A three-dimensional reconstruction of a nano-scale aqueous object can be achieved by taking a series of transmission electron micrographs tilted at different angles in vitreous ice: cryo-Transmission Electron Tomography. Presented here is a novel method of fine alignment for the tilt series. Size-selected gold clusters of ~2.7 nm (Au(561 ± 14)), ~3.2 nm (Au(923 ± 22)), and ~4.3 nm (Au(2057 ± 45)) in diameter were deposited onto separate graphene oxide films overlaying holes on amorphous carbon grids. After plunge freezing and subsequent transfer to cryo-Transmission Electron Tomography, the resulting tomograms have excellent (de-)focus and alignment properties during automatic acquisition. Fine alignment is accurate when the evenly distributed 3.2 nm gold particles are used as fiducial markers, demonstrated with a reconstruction of a tobacco mosaic virus. Using a graphene oxide film means the fiducial markers are not interfering with the ice bound sample and that automated collection is consistent. The use of pre-deposited size-selected clusters means there is no aggregation and a user defined concentration. The size-selected clusters are mono-dispersed and can be produced in a wide size range including 2–5 nm in diameter. The use of size-selected clusters on a graphene oxide films represents a significant technical advance for 3D cryo-electron microscopy

Assessment of cognitive safety in clinical drug development

Cognitive impairment is increasingly recognised as an important potential adverse effect of medication. However, many drug development programmes do not incorporate sensitive cognitive measurements. Here, we review the rationale for cognitive safety assessment, and explain several basic methodological principles for measuring cognition during clinical drug development, including study design and statistical analysis, from Phase I through to postmarketing. The crucial issue of how cognition should be assessed is emphasized, especially the sensitivity of measurement. We also consider how best to interpret the magnitude of any identified effects, including comparison with benchmarks. We conclude by discussing strategies for the effective communication of cognitive risks