An updated Lagrangian finite element formulation for large displacement dynamic analysis of three-dimensional flexible riser structures     

S.A. Hosseini Kordkheili  H. Bahai  M. Mirtaheri 《Ocean Engineering》2011,38(5-6):793-803

An updated Lagrangian finite element formulation of a three-dimensional annular section beam element is presented for large displacement and large rotation dynamic analyses of flexible riser structures. In this formulation a new linearization method is used to avoid inaccuracies normally associated with other linearization schemes. The effects of buoyancy force as well as steady state current loading are considered in the finite element solution for riser structures response. The formulation has been implemented in a nonlinear finite element code and the results are compared with those obtained from other schemes reported in the literature.  相似文献   

Design and testing of a non-linear power take-off simulator for a bottom-hinged plate wave energy converter     

J.C.C. Henriques  M.F.P. Lopes  M.C. Lopes  L.M.C. Gato  A. Dente 《Ocean Engineering》2011,38(11-12):1331-1337

Eddy current brakes provide a versatile way of simulating the power take-off system (PTO) in model testing of small scale wave energy converters (WECs). This type of PTO simulator is based on the principle that a conductive material moving in a magnetic field generates a braking force proportional to its velocity. A bottom-hinged pitching plate WEC model has been designed using an eddy current brake as a PTO simulator. A dedicated electric current source unit was developed to provide a controllable and reliable level of DC current intensity to feed the magnetic field generating coils. Using a real-time data acquisition and control, this unit can be used to impose non-linear damping PTO characteristic curves in several types of WEC models based on eddy current brakes. In the present case, this current source has been used to simulate a constant damping PTO on a small scale pitching WEC model that has been tested in the IST wave flume. Two different cases were considered: one corresponding to a surface piercing plate and another to a fully submerged plate. Experimental results are presented for plate motion and for non-dimensional capture width.  相似文献   

A set of canonical problems in sloshing. Part 0: Experimental setup and data processing     

A. Souto-Iglesias  E. Botia-Vera  F. Pérez-Arribas 《Ocean Engineering》2011,38(16):1823-1830

In a series of attempts to research and document relevant sloshing type phenomena, a series of experiments have been conducted. The aim of this paper is to describe the setup and data processing of such experiments. A sloshing tank is subjected to angular motion. As a result pressure registers are obtained at several locations, together with the motion data, torque and a collection of image and video information. The experimental rig and the data acquisition systems are described. Useful information for experimental sloshing research practitioners is provided. This information is related to the liquids used in the experiments, the dying techniques, tank building processes, synchronization of acquisition systems, etc. A new procedure for reconstructing experimental data, that takes into account experimental uncertainties, is presented. This procedure is based on a least squares spline approximation of the data. Based on a deterministic approach to the first sloshing wave impact event in a sloshing experiment, an uncertainty analysis procedure of the associated first pressure peak value is described.  相似文献   

Upwelling in the Alaskan Beaufort Sea: Atmospheric forcing and local versus non-local response     

Robert S. Pickart  Michael A. Spall  G.W.K. Moore  Thomas J. Weingartner  Rebecca A. Woodgate  Knut Aagaard  Koji Shimada 《Progress in Oceanography》2011,88(1-4):78-100

The spin up and relaxation of an autumn upwelling event on the Beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models. The event occurred in November 2002 and was driven by an Aleutian low storm. The wind field was strongly influenced by the pack-ice distribution, resulting in enhanced winds over the open water of the Chukchi Sea. Flow distortion due to the Brooks mountain range was also evident. Mooring observations east of Barrow Canyon show that the Beaufort shelfbreak jet reversed to the west under strong easterly winds, followed by upwelling of Atlantic Water onto the shelf. After the winds subsided a deep eastward jet of Atlantic Water developed, centered at 250 m depth. An idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm. The disparity in wave speeds between the sea surface height signal—traveling at the fast barotropic shelf wave speed—versus the interior density signal—traveling at the slow baroclinic wave speed—leads to the deep eastward jet. The broad-scale response to the storm over the Chukchi Sea is investigated using a regional numerical model. The strong gradient in windspeed at the ice edge results in convergence of the offshore Ekman transport, leading to the establishment of an anti-cyclonic gyre in the northern Chukchi Sea. Accordingly, the Chukchi shelfbreak jet accelerates to the east into the wind during the storm, and no upwelling occurs west of Barrow Canyon. Hence the storm response is fundamentally different on the Beaufort slope (upwelling) versus the Chukchi slope (no upwelling). The regional numerical model results are supported by additional mooring data in the Chukchi Sea.  相似文献   

Latitudinal variation in the aerial/aquatic ratio of oxygen consumption of a supratidal high rocky‐shore crab     

Marco A. Lardies  José Luis Muñoz  Kurt A. Paschke  Francisco Bozinovic 《Marine Ecology》2011,32(1):42-51

The colonisation of the terrestrial environment by crustaceans is more apparent in tropical latitudes because of the high diversity of semi‐terrestrial and terrestrial crabs. However, in temperate regions there are also great numbers of crustaceans that inhabit ecological niches at the water–air interface. Grapsidae crabs (Decopoda) are especially important in studies of water‐to‐land transition as the family contains species occupying the intertidal and adjacent regions. A way to evaluate the ability of intertidal invertebrates to breathe air is to measure the aerial/aquatic oxygen consumption ratio. The objective of this study was to test the effect of thermal variation on the aquatic and aerial metabolism. We selected as study model the decopoda crab Cyclograpsus cinereus Dana and utilised five populations of the species spread over 2000 km along the Chilean coast. To determine the compensation capacity in respiration with respect to latitude, we evaluated metabolic rate at the same temperature in a common garden design in the laboratory, to examine the extent to which variation in crab physiology is environmentally determined. Whereas in our study, m_b (body mass) varied significantly with latitude, the difference in mass‐independent metabolism both in air and water persisted, indicating that observed differences in MR (Metabolic Rate) were not an effect of differences in body size. We demonstrated that C. cinereus is able to breath oxygen from air and water as expected for an amphibious crab. Almost all the studied populations of C. cinereus show a aerial/aquatic metabolism ratio near 1. The pattern found indicates an increase in metabolic rate, both aerial and aquatic, in low latitudes and therefore does not support the latitudinal compensation hypothesis for temperate habitats. Finally, these kinds of studies are required to make the necessary link between ecological physiology and macroecology and to help develop a global understanding of organismal function in marine systems.  相似文献   

Characterisation and preliminary quantification of the methane reservoir in a coastal sedimentary source: San Simón Bay,Ría de Vigo,NW Spain     

S. García-Gil  E. de Blas  N. Martínez-Carreño  J. Iglesias  R. Rial-Otero  J. Simal-Gándara  A.G. Judd 《Estuarine, Coastal and Shelf Science》2011

Ría de Vigo is a river valley flooded by the sea, with a bay (San Simón Bay) at its innermost part. The accumulation of Holocene sediment in San Simón Bay has been studied by the integration of 1) large scale high resolution seismic data, and 2) detailed geochemical analysis of a gravity core. In San Simón Bay the majority of the seismic records are obscured by acoustic turbidity which represents gassy sediments, but on records from Rande Strait it is possible to distinguish two Quaternary seismic sequences; an Upper Pleistocene sequence (SQ1) and a Holocene sequence (SQ2). Only SQ2 is recognized in San Simón Bay where it is comprised of two seismic units; the upper unit represents the HST sediment, i.e. the period of highest sea level. A gravity core taken within the gassy zone at 10 m water depth provided 3.55 m of fine-grained sediments (muds) from the youngest seismic unit (4 m thick). Geochemical analysis show high values (4 to 10%) of TOC. Sediment and porewater analyses indicate a distinct sulphate–methane transition zone (SMTZ) between 60 and 80 cm where sulphate is depleted (to <1.7 mM) and methane increases (to >0.4 mM). The top of the acoustic turbidity (the gas front) at 80 cm corresponds to the lower limit of the SMTZ. The methane cannot have been derived from the underlying metamorphic and granitic rocks, but was probably derived by microbial degradation of the organic matter in the Holocene sediments. We estimate that the sediments of the Bay contain approximately 1.8 × 10⁶ m³ of organic carbon and 275 ton of methane.  相似文献   

Large-scale experiments on beach profile evolution and surf and swash zone sediment transport induced by long waves,wave groups and random waves   总被引：1，自引：0，他引：1  

T.E. Baldock  J.A. Alsina  I. Caceres  D. Vicinanza  P. Contestabile  H. Power  A. Sanchez-Arcilla 《Coastal Engineering》2011

New large-scale laboratory data are presented on the influence of long waves, bichromatic wave groups and random waves on sediment transport in the surf and swash zones. Physical model testing was performed in the large-scale CIEM wave flume at UPC, Barcelona, as part of the SUSCO (swash zone response under grouping storm conditions) experiment in the Hydralab III program (Vicinanza et al., 2010). Fourteen different wave conditions were used, encompassing monochromatic waves, bichromatic wave groups and random waves. The experiments were designed specifically to compare variations in beach profile evolution between monochromatic waves and unsteady waves with the same mean energy flux. Each test commenced with approximately the same initial profile. The monochromatic conditions were perturbed with free long waves, and then subsequently substituted with bichromatic wave groups with different bandwidth and with random waves with varying groupiness. Beach profile measurements were made at half-hourly and hourly intervals, from which net cross-shore transport rates were calculated for the different wave conditions. Pairs of experiments with slightly different bandwidth or wave grouping show very similar net cross-shore sediment transport patterns, giving high confidence to the data set. Consistent with recent small-scale experiments, the data clearly show that in comparison to monochromatic conditions the bichromatic wave groups reduce onshore transport during accretive conditions and increase offshore transport during erosive conditions. The random waves have a similar influence to the bichromatic wave groups, promoting offshore transport, in comparison to the monochromatic conditions. The data also indicate that the free long waves promote onshore transport, but the conclusions are more tentative as a result of a few errors in the test schedule and modifications to the setup which reduced testing time. The experiments suggest that the inclusion of long wave and wave group sediment transport is important for improved near-shore morphological modeling of cross-shore beach profile evolution, and they provide a very comprehensive and controlled series of tests for evaluating numerical models. It is suggested that the large change in the beach response between monochromatic conditions and wave group conditions is a result of the increased significant and maximum wave heights in the wave groups, as much as the presence of the forced and free long waves induced by the groupiness. The equilibrium state model concept can provide a heuristic explanation of the influence of the wave groups on the bulk beach profile response if their effective relative fall velocity is larger than that of monochromatic waves with the same incident energy flux.  相似文献   

Emerging fisheries,emerging fishery interactions with sea turtles: A case study of the large-mesh gillnet fishery for flounder in Pamlico Sound,North Carolina,USA     

Barbie L. Byrd  Aleta A. Hohn  Matthew H. Godfrey 《Marine Policy》2011

Emerging fisheries and changes in fishery practices are not always readily apparent, nor are their impacts on non-target species such as seabirds, sea turtles, and marine mammals. Data from several different sources led managers to discover high rates of sea turtle bycatch in an inshore large-mesh gillnet fishery in North Carolina, USA, particularly the emerging deep-water gillnet fishery. This paper reviews the history of how increased numbers of observed stranded sea turtles in 1999 led to the discovery that turtles were becoming entangled in the large-mesh gillnet fishery in Pamlico Sound, North Carolina. It also demonstrates how a variety of data sets from fisheries observers, aerial surveys, and fisheries statistics programs contributed to shaping management of the large-mesh gillnet fishery in Pamlico Sound to decrease turtle bycatch and now point towards the need of additional assessment of gillnet bycatch in other parts of North Carolina. Finally, potential approaches are discussed for a more timely detection of future fishery conflicts and development of a plan to reduce otherwise inevitable bycatch and disruptions to fishing effort.  相似文献   

Marine biodiversity in the Caribbean UK overseas territories: Perceived threats and constraints to environmental management     

J. Forster  I.R. Lake  A.R. Watkinson  J.A. Gill 《Marine Policy》2011

Islands are often considered to be a priority for conservation, because of their relatively high levels of biodiversity and their vulnerability to a range of natural and anthropogenic threats. However, the capacity of islands to conserve and manage biodiversity may depend upon their governance structures. Many island states are affiliated to other countries through an ‘overseas territory’ status, which may provide them with access to resources and support mechanisms, but which may also influence the capacity for local-scale management of environmental issues. The United Kingdom has 12 island Overseas Territories (UKOTs), most of which support biodiversity of high conservation concern. This study investigates perceptions of current and future threats to marine ecosystems and constraints to environmental protection on the six Caribbean UKOTs, through semi-structured interviews with officials from UK and UKOT government departments and non-governmental organisations. Coastal development, pollution and over-fishing were perceived as threats of most concern for the next decade, but climate change was perceived as by far the greatest future threat to the islands' marine ecosystems. However, a series of common institutional limitations that currently constrain mitigation and conservation efforts were also identified, including insufficient personnel and financial support, a lack of long-term, sustainable projects for persistent environmental problems and inadequate environmental legislation. These findings highlight the need for regional cooperation and capacity-building throughout the Caribbean and a more concerted approach to an UKOT environmental management by the UK and UKOTs' governments.  相似文献   

Evolution of deep-water stratigraphic architecture, Magallanes Basin, Chile     

B.W. Romans  A. FildaniS.M. Hubbard  J.A. CovaultJ.C. Fosdick  S.A. Graham 《Marine and Petroleum Geology》2011,28(3):612-628

The ˜4000 m thick and ∼20 Myr deep-water sedimentary fill of the Upper Cretaceous Magallanes Basin was deposited in three major phases, each with contrasting stratigraphic architecture: (1) the oldest deep-water formation (Punta Barrosa Formation) comprises tabular to slightly lenticular packages of interbedded sandy turbidites, slurry-flow deposits, and siltstone that are interpreted to record lobe deposition in an unconfined to weakly ponded setting; (2) the overlying, 2500 m thick and shale-dominated Cerro Toro Formation includes a succession of stacked conglomeratic and sandstone channel-fill deposits with associated finer-grained overbank deposits interpreted to record deposition in a foredeep-axial channel-levee system; (3) the final phase of deep-water sedimentation is characterized by sandstone-rich successions of highly variable thickness and cross-sectional geometry and mudstone-rich mass transport deposits (MTDs) that are interpreted to record deposition at the base-of-slope and lower slope segments of a prograding delta-fed slope system. The deep-water formations are capped by shallow-marine and deltaic deposits of the Dorotea Formation.These architectural changes are associated with the combined influences of tectonically driven changes and intrinsic evolution, including: (1) the variability of amount and type of source material, (2) variations in basin shape through time, and (3) evolution of the fill as a function of prograding systems filling the deep-water accommodation. While the expression of these controls in the stratigraphic architecture of other deep-water successions might differ in detail, the controls themselves are common to all deep-water basins. Information about source material and basin shape is contained within the detrital record and, when integrated and analyzed within the context of stratigraphic patterns, attains a more robust linkage of processes to products than stratigraphic characterization alone.  相似文献