An iterative method for boundary element solution of large offshore structures using the GMRES solver   总被引：1，自引：0，他引：1  

Y. Zhao  J.M.R. Graham 《Ocean Engineering》1996,23(6):483-495

The GMRES approach is used to solve complex matrix solution arising from boundary element analysis of large offshore structures. This makes it possible to solve problems with large numbers of panels on a workstation with a much smaller memory than typical high performance computers. The speed of the solver is compatible with direct solvers when the enough RAM is available. Otherwise, an iteration procedure can be used. By using an out-of-core treatment, typical RAM requirement is reduced to a size approximately linearly proportional to the panel number n instead of being proportional to n². The code is first verified with direct solver for cases with small number of panels. The applicability to large offshore structure of the model is demonstrated for a TLP case.  相似文献   

Micromorphological characteristics of glacimarine sediments: implications for distinguishing genetic processes of massive diamicts     

Aoibheann A. Kilfeather  Colm Ó Cofaigh  Julian A. Dowdeswell  Jaap J. M. van der Meer  David J. A. Evans 《Geo-Marine Letters》2010,30(2):77-97

Glacimarine diamicts are produced by diverse processes, and genetic differentiation is often problematic using macro-sedimentological criteria alone. Micromorphology offers a potentially helpful tool in such investigations. Macroscopically massive diamict samples of known glacimarine origin, from the Polar North Atlantic, Antarctica and north Irish Sea, were prepared for micromorphological analysis to (1) identify microstructures unique to different modes of sedimentation and (2) interpret genetic processes from those structures. The samples comprised examples of debris-flow, iceberg-turbate and suspension settling deposits from late Quaternary glacier-influenced marine environments: tidewater glacier, sub- or pro-ice shelf and continental slopes in front of ice stream termini. Results show two significant features of debris-flow sediments: a bimodal grain fabric of near-horizontal and -vertical grains, and laminated clay and silt coatings on sand and pebble grains. Coatings are best developed in sediments with finer grain-size distributions and in debris-flow sediments which have had relatively long run-out distances on trough-mouth fans, suggesting continuous rotation of grains in a buoyant, turbulent aqueous environment. This is significant because it precludes debris-flow delivery by plug flow. The micromorphology of iceberg turbate has not been described previously. It contains structures similar to those described in tills, so that unambiguous identification of these sediments seems unlikely based on micromorphological criteria alone. Suspension sediments range from fine-grained massive diamicts containing microfossils to more heterogeneous coarser sediments characterised by abrupt textural variations, from ice-distal and ice-proximal glacimarine environments respectively. The ice-proximal sediments contain fine vertical lineations marking the trajectories of dropstones through wet matrix. These dropstone tracks have not been reported in previous studies.  相似文献   

Groundwater-level response to land-use change and the implications for salinity management in the West Moorabool River catchment, Victoria, Australia   总被引：1，自引：1，他引：0  

Peter G. Dahlhaus  Timothy J. Evans  Erica L. Nathan  Jim W. Cox  Craig T. Simmons 《Hydrogeology Journal》2010,18(7):1611-1623

The connection between the removal of native vegetation, rising water tables and increasing stream salinity has been established for many catchments across Australia. However, the West Moorabool River in south west Victoria is an example of a catchment where there has been little discernable effect on groundwater levels following land clearing. Over the past 150 years, a significant portion of the catchment has been cleared of dense forest for agricultural development. Historic standing water-level records from 1870–1871 and 1881 are compared with contemporary measurements (1970s to 2007) recorded in the government bore databases. The data show that the earliest recorded groundwater levels are well within the seasonal range of values observed today. By integrating geology and hydrogeology with historical observations of groundwater levels, climate data and land use, the contemporary field observations of stream salinity are linked to the changed water use and shift in rainfall. In contrast to the normally accepted axiom, reafforestation as a management strategy to mitigate the rising salinity in the West Moorabool River catchment would seem inappropriate.  相似文献   

Approaches to knowledge sharing and capacity building: The role of local information systems in marine and coastal management     

Tim Stojanovic  David R. Green  Graham Lymbery 《Ocean & Coastal Management》2010,53(12):805-815

This paper explores how coastal data and information can be mobilised in information systems and applied in coastal management. The concept of an Information System is defined and described, and the potential role of Local Information System (LIS) in integrated coastal management (ICM) is considered. Three examples, from the Severn Estuary, UK the coast of the North West of England and North Wales, and the Fal and Helford estuaries, are used to demonstrate the requirements of a LIS for coastal areas. The role of GIS as part of the solution is considered in detail. The paper demonstrates how ideas from the disciplines of information systems and information science can be practically applied in coastal areas. The findings promote a holistic approach for those involved in the development of technologies and dealing with data and information about coasts and oceans.  相似文献   

Defending and testing hypotheses: a response to John Shaw's paper ‘In defence of the meltwater (megaflood) hypothesis for the formation of subglacial bedform fields’     

David J. A. Evans 《第四纪科学杂志》2010,25(5):822-823

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Stratigraphic architecture and sedimentology of a Late Pleistocene subaqueous moraine complex,southwest Ireland     

David J. A. Evans  John F. Hiemstra  Colm Ó Cofaigh 《第四纪科学杂志》2012,27(1):51-63

Glacigenic sediments exposed in coastal cliffs cut through undulatory terrain fronting the Last Glacial Maximum laterofrontal moraine at Waterville on the Iveragh Peninsula, southwest Ireland, comprise three lithofacies. Lithofacies 1 and 2 consist of interdigitated, offlapping and superimposed ice‐proximal subaqueous outwash and stacked sequences of cohesionless and cohesive subaqueous debris flows, winnowed lag gravels and coarse‐grained suspension deposits. These are indicative of sedimentation in and around small grounding line fans that prograded from an oscillating glacier margin into a proglacial, interlobate lake. Lithofacies 3 comprises braided river deposits that have undergone significant syn‐sedimentary soft‐sediment deformation. Deposition was likely related to proglacial outwash activity and records the reduction of accommodation space for subaqueous sedimentation, either through the lowering of proglacial water levels or due to basin infilling. The stratigraphic architecture and sedimentology of the moraine at Waterville highlight the role of ice‐marginal depositional processes in the construction of morphostratigraphically significant ‘end moraine’ complexes in Great Britain and Ireland. Traditional ‘tills’ in these moraines are often crudely stratified diamictons and gravelly clinoforms deposited in ice‐proximal subaqueous and subaerial fans. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Seismic damage prediction by deterministic methods: Concepts and procedures     

Graham H. Powell  Rakesh Allahabadi 《地震工程与结构动力学》1988,16(5):719-734

Although the prediction of seismic damage is primarily a probabilistic problem, deterministic analysis can nevertheless be a valuable tool. This paper reviews the concepts which have been used in damage prediction, and identifies and classifies several specific techniques. Techniques of two types are considered, the first based on the balance between some demand on the structure and its corresponding capacity, and the second on the degradation of some structural property. For each technique, one or more damage parameters can be computed, and from these a damage index can be estimated. Several alternative choices for the damage parameters are identified. Procedures for computing values for these parameters, and relating them to damage indices, are suggested.  相似文献   

Flooding of Sinking Creek,Garretts Spring karst drainage basin,Jessamine and Woodford counties,Kentucky, USA     

J. C. Currens  C. D. R. Graham 《Environmental Geology》1993,22(4):337-344

Tashamingo Subdivision in Sinking Creek karst valley, a tributary of the Garretts Spring drainage basin in Jessamine and Woodford counties, Kentucky, was flooded in February 1989. To determine the cause of flooding, the groundwater basin boundary was mapped, discharge data were measured to determine intake capacity of swallets, and hydrologic modeling of the basin was conducted. Swallet capacity was determined to be limited by the hydraulic parameters of the conduit, rather than by obstruction by trash. Flooding from a precipitation event is more likely, and will be higher, when antecedent soil moisture conditions in the watershed are near saturation. Hydrologic modeling shows that suburban development of 20 percent of the southeast basin will cause a small increase in flood stage at Tashamingo Subdivision.  相似文献   

The relationship of precipitation seasonality to the flora and stable isotope chemistry of soils in the Vizcaíno desert, Baja California, México     

Ronald Amundson  Ernesto Franco-Vizcaíno  R.C. Graham  Michael DeNiro 《Journal of Arid Environments》1994,28(4)

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Paleolimnological studies of saline lakes   总被引：1，自引：0，他引：1  

Marlene S. Evans 《Journal of Paleolimnology》1993,8(2):97-101

Salt water lakes are located in arid to semi-arid regions where evaporation rates exceed precipitation rates. As such, saline lakes are very sensitive to changes in their hydrological cycle. Research into the current limnology of saline lakes is expanding as population growth in these regions increases. Emerging concerns include water diversions, eutrophication, and toxic substances. Paleolimnological investigations of saline lakes are providing valuable new information on paleoclimate and paleohydrology. Such studies may allow for better predictions of the environmental consequences of global warming and for a better understanding of past climate change. Paleolimnological studies may also provide some insight to more recent, anthropogenic perturbations in the arid and semi-arid regions of the world.This publication is the introduction to a series of papers presented at the Conference on Sedimentary and Paleolimnological Records of Saline Lakes. The conference was held August 13–16, 1991 at the University of Saskatchewan, Saskatoon, Canada. Dr. Evans is serving as Guest Editor.  相似文献