Nonlinear response of a moored buoy

The nonlinear dynamic analysis of a multipoint slack moored buoy is performed under the action of first and second order wave forces. The nonlinearity of the system is caused by the geometric nonlinearity of the mooring lines. The resulting nonlinear equation of motion is solved by an incremental time marching scheme. The nonlinear responses of the system are analysed to investigate different kinds of dynamic instability phenomena that may arise due to the nonlinearity of the system. As an illustrative example, a hollow cylindrical buoy anchored to the sea bed by means of six slack mooring lines is considered. The responses of the system are obtained and analysed for three regular waves namely, 5 m/5 s, 12 m/10 s and 18 m/15 s. The results of the study show that different kinds of instability phenomena like nT subharmonic oscillations, symmetry breaking bifurcation and aperiodic responses may occur in slack mooring systems. Further, a second order wave force may considerably influence the dynamic stability of such systems.     

Drag force on a circular cylinder in unseparated laminar high Reynolds number nonlinear random oscillatory flow

The stochastic properties of the drag force maxima on a circular cylinder subjected to nonlinear random waves are investigated. Unseparated laminar high Reynolds number flow is considered. A simplified approach based on second order Stokes waves is presented, including the sum-frequency effect only. It is demonstrated how a drag force formula valid for regular linear waves can be used to find the cumulative distribution function of individual drag force maxima for nonlinear irregular waves. Here the [Wang, 1968] drag force coefficient is used.     

Seasonal variations in the speciation of dissolved iodine in the Chesapeake Bay

The speciation of dissolved iodine and the distributions of the iodine species in the deep Chesapeake Bay underwent seasonal variations in response to changes in the prevailing redox condition. In the deep water, the ratios of iodate to iodide and iodate to inorganic iodine decreased progressively from the Winter through the Summer as the deep water became more poorly oxygenated before they rebounded in the Fall when the deep water became re-oxygenated again. The composition of the surface water followed the same trend. However, in this case, the higher biological activities in the Spring and the Summer could also have enhanced the biologically mediated reduction of iodate to iodide by phytoplankton and contributed to the lower ratios found during those seasons. Superimposed on this redox cycle was a cycle of input and removal of dissolved iodine probably as a result of the interactions between the water column and the underlying sediments. Iodine was added to the Bay during the Summer when the deep water was more reducing and removed from the Bay in the Fall when the deep water became re-oxygenated. A third cycle was the inter-conversion between inorganic iodine and ‘dissolved organic iodine’, or ‘‘DOI’’. The conversion of inorganic iodine to ‘DOI’ was more prevalent in the Spring. As a result of these biogeochemical reactions in the Bay, during exchanges between the Bay and the North Atlantic, iodate-rich and ‘DOI’-poor water was imported into the Bay while iodide- and ‘DOI’-rich water was exported to the Atlantic. The export of iodide from these geochemically reactive systems along the land margins contributes to the enrichment of iodide in the surface open oceans.     

Modeling bed-load transport of coarse sediments in the Great Bay Estuary, New Hampshire

Current, sea level and bed-load transport are investigated in the Lower Piscataqua River section of the Great Bay Estuary, New Hampshire, USA—a well-mixed and geometrically complex system with low freshwater input, having main channel tidal currents ranging between 0.5 and 2 m s⁻¹. Current and sea level forced by the M₂M₄M₆ tides at the estuarine mouth are simulated by a vertically averaged, non-linear, time-stepping finite element model. The hydrodynamic model uses a fixed boundary computational domain and accounts for flooding–drying of tidal flats by making use of a groundwater component. Inertia terms are neglected in comparison with pressure gradient and bottom friction terms, which is consistent with the observed principal dynamic balance for this section of the system. The accuracy of hydrodynamic predictions in the study area is demonstrated by comparison with four tidal elevation stations and two cross-section averaged current measurements. Simulated current is then used to model bed-load transport in the vicinity of a rapidly growing shoal located in the main channel of the lower system. Consisting of coarse sand and gravel, the shoal must be dredged every five to eight years. Two approaches are taken—an Eulerian parametric method in which nodal bed-load flux vectors are averaged over the tidal cycle and a Lagrangian particle tracking approach in which a finite number of sediment particles are released and tracked. Both methods yield pathways and accumulations in agreement with the observed shoal formation and the long-term rate of sediment accumulation in the shoal area.     

Code of Practice For Ocean Mining: An International Effort to Develop a Code For Environmental Management of Marine Mining

A code of practice for ocean mining has been developed by the International Marine Minerals Society. The code provides general guiding Principles for development of marine mineral resources and delineates Operating Guidelines for application, as appropriate, at specific mining sites. In total 11 operating guidelines are provided to serve as benchmarks for industry and targets for regulatory agencies and other stakeholders. They include the following commitments: •To sustainable development, •To environmentally responsible corporate ethics, •To the development of effective community partnership, •To implementation of environmental risk management, •To the integration of environmental management into all phases of development, •To the establishment of corporate environmental performance targets, •To timely environmental improvements and upgrading, •To responsible rehabilitation of operations sites and decommissioning of facilities, and •To accurate and timely, reporting and documentation, archiving, and performance review.     

Patterns and controls of surface sediment distribution: west-central Florida inner shelf

The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems.     

The distributions of particulate atmospheric trace metals and mineral aerosols over the Indian Ocean

Data are presented for the concentrations of Al, Fe, Mn, Ni, Co, Cr, V, Cu, Zn, Pb and Cd in aerosols collected over two contrasting regions of the Indian Ocean. These are: (1) the northern Arabian Sea (AS), from which samples were collected in the northeast monsoon, during which the region receives an input of crustal material from the surrounding arid land masses; and (2) the Tropical Southern Indian Ocean (TSIO), a remote region from which samples were collected from air masses for which there were no large-scale up-wind continental aerosol sources. The TSIO samples can be divided into two populations: Population I aerosols, collected from air masses which have probably impinged on Madagascar, and Population II aerosols, which have been confined to open-ocean regions to the south of the area.The data indicate that there are strong latitudinal variations in the chemical signatures of aerosols over the Indian Ocean. The input of crustal material to the Arabian Sea gives rise to an average Al concentration of about 1000 ng m⁻³ of air in the northeast monsoon regime. As a result, the concentrations of all trace metals are relatively high, and the values of crustal enrichment factors are less than 10 for most metals, in the AS aerosols. In contrast, TSIO Population II ‘open-ocean southern air’ sampled during the southwest monsoon season, has an average Al concentration of only about 10 ng m⁻³ of air. Trace metal concentrations in the TSIO ‘open-ocean southern air’ during the southwest monsoon season are representative of ‘clean’ remote marine air and are generally similar to those reported over the central North Pacific.Mineral dust concentrations over the Indian Ocean decrease in a north to south direction, from about 15–20 μg m⁻³ of air in the extreme north to about 0.01–0.25 μg m⁻³ of air in the far south. The deposition of mineral dust over the northern Arabian Sea can account for approximately 75% of the non-carbonate material incorporated into the underlying sediments.In the Arabian Sea the dissolved atmospheric inputs of all the trace metals, with the exception of Cu and Co, exceed those from fluvial run-off by factors which range from 9.6 for Pb to 1.6 for Cr.     

Joint Soviet-Turkish expedition in the Black Sea

The hydrological and hydrochemical structures of the upper 300 m water column of the Black Sea in autumn 1988 have been studied. Regularities in the distribution of the physico-chemical characteristics in the zone of interaction between aerobic and anaerobic waters as well as the topography of the H₂S zone boundary and its connection with a certain density gradient have been found.Translated by Mikhail M. Trufanov.     

Sample Disturbance in Soft and Sensitive Clays: Analysis and Assessment

Despite the sophisticated methods employed to obtain high quality samples, they are prone to disturbance, due to stress release, let apart, due to sampling tools and techniques adopted. Critical reappraisal of different methods suggest that any method of sample quality assessment involving strength and deformation parameters would enable easier implementation and correct other engineering parameters for estimated sample disturbance. In this technical paper, sample disturbance index, using merely the slopes of compression paths, (representing mechanical response), in the pre- and post-yield stress regimes under odeometric loading conditions is proposed. This method is based on single oedometer test results on samples of unknown degrees of disturbance during sampling and handling. The unique feature of this approach is that the ideal rigid plastic material behavior is taken as reference. This eliminates the need for any additional experimental data or any calculations from the relationships formulated with any set of assumptions.