Longitudinal strength of a high-speed ferry     

T.E. Schellin  A.Perez de Lucas   《Applied Ocean Research》2004,26(6):298-308

The longitudinal strength of the high-speed ferry was investigated by subjecting the ship's hull girder to long-term loads obtained from a frequency-domain panel code. Prior to the statistical analysis, linearly computed transfer functions were corrected for nonlinear effects, yielding two sets of transfer functions valid for different wave amplitudes. One set corresponded to the hogging condition; the other set, to the sagging condition. Two regular equivalent design waves were specified that resulted in loads representing the most severe global design load conditions. The still-water loading condition, yielding a still-water vertical bending moment in hogging, was superimposed on the wave-induced loads to obtain the total (design) loads in hogging. For the sagging condition only, additional impact-related loads were superimposed to obtain the total (design) loads in sagging. A finite element model of the ship's structure was subjected to pressure distributions according to the two regular design waves. For comparison with classification society rule values, a simple beam theory strength analysis of the ship's midship section was performed first, and then another finite element analysis was carried out, whereby the imposed loads were tuned to the rule values of vertical bending moments. Rule-based magnitudes of nominal maximum longitudinal stress deviated significantly (25–39%) from comparable stresses obtained by the panel code based finite element analysis. However, stresses obtained from the rule-based finite element analysis agreed more favorably, especially in hogging. In the uppermost deck, for example, the panel code based compressive stress was only 9% larger than the comparable stress from the rule-based finite element analysis.  相似文献   

The Dynamics of Covering Behaviour in Dominant Echinoid Populations from American and European West Coasts     

Emma Verling  Anne C. Crook  & David K. A. Barnes 《Marine Ecology》2004,25(3):191-206

Abstract.  The so-called 'covering behaviour' of echinoids is known to vary with habitat according to the types of covering items available, but the full extent of the role played by habitat characteristics in this behaviour is not known. Moreover, whether or not different species inhabiting similar environmental conditions and habitats also show similar patterns of this particular behaviour has yet to be investigated. In this study, two prominent west coast echinoid species, Paracentrotus lividus and Strongylocentrotus purpuratus , were examined with respect to covering behaviour and spatial organisation. Populations of both species are found in exposed intertidal zones, occupying boreholes within tidepools. Important similarities were found in the spatial organisation of both species' populations, with lowest densities in upper shore pools. However, the size distributions of the two populations differed significantly; P. lividus within upper shore pools were significantly larger than those in mid or lower shore pools, whereas S. purpuratus on the lower shore were significantly larger than those at other shore heights. We found significant between-species variability in covering item use, although the number of covering items available at both sites was not significantly different. For example, greater densities of covering items were used by P. lividus than by S. purpuratus . We also found that the percent of echinoid surface area covered varied significantly in space for both species. These data emphasise the complex and multifaceted nature of covering behaviour, but most importantly, they also strongly suggest that habitat characteristics can only partly explain the extent of this behavioural variability amongst echinoid species.  相似文献   

Mussels document loss of bioavailable polycyclic aromatic hydrocarbons and the return to baseline conditions for oiled shorelines in Prince William Sound, Alaska     

Page DS  Boehm PD  Brown JS  Neff JM  Burns WA  Bence AE 《Marine environmental research》2005,60(4):422-436

Polycyclic aromatic hydrocarbons (PAH) were measured in mussels (Mytilus trossulus) collected between 1990 and 2002 from 11 sites on the shores of Prince William Sound (PWS), Alaska, that were heavily oiled by the 1989 Exxon Valdez oil spill (EVOS). This study, utilizing the methods of the NOAA Status and Trends Mussel Watch Program, found that concentrations of PAH released from spill remnants have decreased dramatically with time and by 2002 were at or near the range of total PAH (TPAH) of 3-355 ng/g dry weight obtained for mussels from unoiled reference sites in PWS. Time-series TPAH data indicate a mean TPAH half-life in mussel tissues of 2.4 years with a range from 1.4 to 5.3, yielding an annual mean loss of bioaccumulated TPAH of 25%. The petroleum-derived TPAH fraction in mussel tissues has decreased with time, reflecting the decreasing release of EVOS residues in shoreline sediments. These results show that PAH from EVOS residues that remain buried in shoreline sediments after the early 1990s are in a form and at locations that have a low accessibility to mussels living in the intertidal zone.  相似文献   

A permanent seismic station beneath the Ocean Bottom     

David Harris  Robert K. Cessaro  Fred K. Duennebier  David A. Byrne 《Marine Geophysical Researches》1987,9(1):67-94

The Hawaii Institute of Geophysics began development of the Ocean Subbottom Seisometer (OSS) system in 1978, and OSS systems were installed in four locations between 1979 and 1982. The OSS system is a permanent, deep ocean borehole seismic recording system composed of a borehole sensor package (tool), an electromechanical cable, recorder package, and recovery system. Installed near the bottom of a borehole (drilled by the D/V Glomar Challenger), the tool contains three orthogonal, 4.5-Hz geophones, two orthogonal tilt meters; and a temperature sensor. Signals from these sensors are multiplexed, digitized (with a floating point technique), and telemetered through approximately 10 km of electromechanical cable to a recorder package located near the ocean bottom. Electrical power for the tool is supplied from the recorder package. The digital seismic signals are demultiplexed, converted back to analog form, processed through an automatic gain control (AGC) circuit, and recorded along with a time code on magnetic tape cassettes in the recorder package. Data may be recorded continuously for up to two months in the self-contained recorder package. Data may also be recorded in real time (digital formal) during the installation and subsequent recorder package servicing. The recorder package is connected to a submerged recovery buoy by a length of bouyant polypropylene rope. The anchor on the recovery buoy is released by activating either of the acoustical command releases. The polypropylene rope may also be seized with a grappling hook to effect recovery. The recorder package may be repeatedly serviced as long as the tool remains functionalA wide range of data has been recovered from the OSS system. Recovered analog records include signals from natural seismic sources such as earthquakes (teleseismic and local), man-made seismic sources such as refraction seismic shooting (explosives and air cannons), and nuclear tests. Lengthy continuous recording has permitted analysis of wideband noise levels, and the slowly varying parameters, temperature and tilt.Hawaii Institute of Geophysics Contribution 1909.  相似文献   

Side-Scan Processing of GLORI-B and SeaBeam 2000     

Liu  Zhengrong J.  Naar  David F. 《Marine Geophysical Researches》1997,19(5):397-405

  相似文献   

Quaternary geology of the Amazonian Lowland     

Georg Irion  Jens Müller  Jose Nunes de Mello  Wolfgang J. Junk 《Geo-Marine Letters》1995,15(3-4):172-178

The Quaternary history of the Amazon lowlands is characterized by deposition of sediments of Andean provenance and by the influences of changing sea levels. Areas well above the present water tables were not reached by Pleistocene high-water stages. These areas have been intensively weathered since the Tertiary, forming hard lateritic weathering horizons. These weathering horizons are best explained by the relatively constant, humid tropical climate throughout the Quaternary. In the western Amazonian Lowland, flood plains corresponding to the different Pleistocene sea-level heights were formed. During low sea level, erosion in the drainage areas increased and the water levels of the central Amazon River system were lowered. Valleys drowned and lakes formed in the lower reaches of rivers and creeks during high sea-level stages. These lakes (ria lakes) remained in the valleys with rivers having a low sediment load. Seismic profiling (3.5 kHz) in some of these lakes clearly showed deposits of the three last periods of Quaternary high sea-level stages.  相似文献   

A summary of the geology and oil habitat of the Eastern Flank Hydrocarbon Province of South Oman     

Aley Al-Marjeby  David Nash 《Marine and Petroleum Geology》1986,3(4)

The Eastern Flank Hydrocarbon Province borders the southeastern edge of the South Oman Salt Basin in the southern part of Oman. An intensive exploration programme by PDO over the past seven years has led to the discovery of almost 2 × 10⁹ m³ of oil with current production of some 15000 m³/d from six fields.In stark contrast to other oil habitats of the Arabian Peninsula, the main play involves rock units and geological events ranging in age from Late Precambrian to Quaternary Times, while trap development and charging are closely related to syn-tectonic salt dissolution.The principal reservoirs and seals are poorly consolidated, Palaeozoic clastics which drape, due to salt dissolution, over residual ‘cores’ principally composed of either Lower Palaeozoic sandstones (Haima Group), or Late Proterozoic carbonates (Huqf Group), or some combination of these. Oils have been geochemically correlated with algal source rocks of the Huqf Eastern Flank. Structures are considered to have been ‘charged’ from Late Mesozoic times onwards in conjunction with progressive subsurface salt removal and the onset of maturation of local source rocks. The effectiveness of ‘charging’ along the retreating salt edge is indicated by the small percentage of dry wells.Major oil zones are found in both anticlinal and truncation traps which are commonly developed around sandstone (Haima Group) cores. Oils show a wide range of characteristics but are typically heavy, early expulsion crudes, high sulphur with little associated gas. Bacterial transformation is not uncommon.Producing reservoirs mainly occur at relatively shallow depths (600–1200 m). Primary recovery factors of around 7% reflect the high density and viscosity of the Eastern Flank crudes and have initiated interest in Enhanced Oil Recovery (EOR) techniques. Two such pilot projects, involving steam and polymer flooding, are due to commence in 1984 and, if successful, will substantially increase the reserve base of these fields.  相似文献   

Paleoenvironment and sea-level change in the early Cretaceous Barents Sea—implications from near-shore marine sapropels     

Uwe?LangrockEmail author  Ruediger?Stein  Marcus?Lipinski  Hans-Jürgen?Brumsack 《Geo-Marine Letters》2003,23(1):34-42

The late Volgian (early "Boreal" Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottom-water conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by well-preserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.  相似文献   

赤潮生物种类特征光谱获取技术   总被引：1，自引：0，他引：1  

范学炜  张汉德 《海洋科学进展》2002,20(2):83-90

较为系统地研究了赤潮生物水体反射率曲线获取方法。通过对 2类反射率反演方法得出的反射率曲线与实际反射率曲线进行比较 ,得出在不具备大气环境参数的情况下 ,经验线性法的反演结果与实际反射率曲线最接近的结论 ,并进一步对正常海水和赤潮生物水体的光谱特性进行分析 ,提取出赤潮生物水体的特征光谱。这是进行赤潮监测和识别的重要前提  相似文献   

Trends in biomass, density and diversity of North Sea macrofauna   总被引：6，自引：2，他引：6  

Heip  C.; Basford  D.; Craeymeersch  J. A.; Dewarumez  J. M.; Dorjes  J.; de Wilde  P.; Duineveld  G.; Eleftheriou  A.; Herman  P. M. J.; Niermann  U.; Kingston  P.; Kunitzer  A.; Rachor  E.; Rumohr  H.; Soetaert  K.; Soltwedel  T. 《ICES Journal of Marine Science》1992,49(1):13-22

  相似文献