Numerical Initial Value Problems in Ordinary Differential Equations

. This paper summarizes the formulation of the ocean component to the Geophysical Fluid Dynamics Laboratory's (GFDL) climate model used for the 4th IPCC Assessment (AR4) of global climate change. In particular, it reviews the numerical schemes and physical parameterizations that make up an ocean climate model and how these schemes are pieced together for use in a state-of-the-art climate model. Features of the model described here include the following: (1) tripolar grid to resolve the Arctic Ocean without polar filtering, (2) partial bottom step representation of topography to better represent topographically influenced advective and wave processes, (3) more accurate equation of state, (4) three-dimensional flux limited tracer advection to reduce overshoots and undershoots, (5) incorporation of regional climatological variability in shortwave penetration, (6) neutral physics parameterization for representation of the pathways of tracer transport, (7) staggered time stepping for tracer conservation and numerical efficiency, (8) anisotropic horizontal viscosities for representation of equatorial currents, (9) parameterization of exchange with marginal seas, (10) incorporation of a free surface that accomodates a dynamic ice model and wave propagation, (11) transport of water across the ocean free surface to eliminate unphysical ``virtual tracer flux" methods, (12) parameterization of tidal mixing on continental shelves. We also present preliminary analyses of two particularly important sensitivities isolated during the development process, namely the details of how parameterized subgridscale eddies transport momentum and tracers.

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Formulation of an ocean model for global climate simulations

Loads for use in the design of ships and offshore structures

Change detection captures the spatial changes from multi temporal satellite images due to manmade or natural phenomenon. It is of great importance in remote sensing, monitoring environmental changes and land use –land cover change detection. Remote sensing satellites acquire satellite images at varying resolutions and use these for change detection. This paper briefly analyses various change detection methods and the challenges and issues faced as part of change detection. Over the years, a wide range of methods have been developed for analyzing remote sensing data and newer methods are still being developed. Timely and accurate change detection of Earth’s surface features provides the basis for evaluating the relationships and interactions between human and natural phenomena for the better management of resources. In general, change detection applies multi-temporal datasets to quantitatively analyse the temporal effects of the phenomenon. As such, this study attempts to provide a comprehensive review of the fundamental processes required for change detection. The study also gives a brief account of the main techniques of change detection and discusses the need for development of enhanced change detection methods.

Change detection techniques for remote sensing applications: a survey

Slam events experienced by high-speed catamarans in irregular waves were characterised through experiments using a hydroelastic segmented model. The model was designed to represent the dynamic behaviour of the full-scale Incat 112 m vessel and to allow the measurement of the slam load on the centrebow and wet deck. It was tested in irregular head seas at two speeds relating to Froude numbers of 0.32 and 0.60. Nearly 300 slams were identified in the test data and analysed with respect to kinematic parameters. Slams were found to have a large range of magnitudes, with the largest equivalent to 1785 tonnes full scale (approximately 70% of vessel displacement); however, the majority of events were of relatively low severity. Differences in slam characteristics were found for the two model speeds tested; slams at the slower speed generally occurred further forward on the hull, prior to the wave crest and with a bow down pitch angle. Immersion of the centrebow to the two-dimensional filling height of the cross-section between the centrebow and demihulls is shown to be a better indicator of slam occurrence than immersion to the top of the archway.

Slam events of high-speed catamarans in irregular waves

Wave slamming loads on wave-piercer catamarans operating at high-speed determined by hydro-elastic segmented model experiments

In spite of numerous papers in the literature on the buckling behavior of cylindrical shell structures, the effect of local large imperfections caused by physical contacts has not been exhaustively examined yet. To this end, this paper reports on an experimental program on the buckling and post-buckling response of thin cylindrical shells with local dent imperfections under uniform external pressure. The results of this study can be used in practical structures with similar geometric features, i.e. D/t ratio.

Experiments on dented cylindrical shells under peripheral pressure

Commercial and military requirements for high-speed sea transportation has led to the evolution of large, fast, lightweight vessels. Knowledge of the effect of sea loads on the structure of such vessels is required in order to carry out structural design optimization. Wet deck slam events, which occur when the vessel's motion causes an impact between the cross-deck structure and the water surface when operating in large waves, are of particular importance for high-speed catamarans. Extensive full-scale hull stress, motion, and wave measurements have been conducted on an 86-m Incat high-speed catamaran ferry during a delivery voyage. A definition of a slam event, for this vessel, is proposed and used to identify slam events from the data records. The character and effects of these slamming events are investigated with respect to a number of factors, including structural loading, wave height and length, vessel speed and heading angle,relative vertical velocity, and frequency ofoccurrence. The results of the full-scaledata analysis are presented. Particular attention is paid to thewhipping response of the structure, with the principal structural response frequencies being identified through spectral analysis.

Slamming response of a large high-speed wave-piercer catamaran

This paper examines the effect of large local imperfections, known as dents, on the plastic buckling capacity of short steel tubes under axial compression. A total of 11 tests on such short columns were carried out. The specimens were indented through a separate process and the ultimate axial capacity was subsequently obtained through compression tests. Dent imperfections with various depths were introduced to different locations on the body of the specimens. Plastic buckling modes as well as the ultimate capacity of the specimens were thoroughly investigated. The adverse effect of such a local damage on the load carrying capacity was quantified for different values and types of imperfections.

Damien Holloway

Papers

Slam events of high-speed catamarans in irregular waves

Wave slamming loads on wave-piercer catamarans operating at high-speed determined by hydro-elastic segmented model experiments

Experiments on dented cylindrical shells under peripheral pressure

Slamming response of a large high-speed wave-piercer catamaran

Plastic buckling of dented steel circular tubes under axial compression: An experimental study