Dynamics of a moored barge under regular and random waves

Developments in the study of wave forces and construction techniques in deep water by the offshore oil industry have increased the use of marine terminals at deep water locations. A thorough understanding of moored ship dynamics when subjected to waves, wind and current combined with the use of flexible mooring lines would help to design berthing terminals for exposed areas. In this paper, the three dimensional problem of wave interactions with a barge moored to a single point is dealt with, based on the finite element method. The effect of flexibility of the mooring line and the point of mooring on the response of the barge as well as the mooring line tension is investigated. The paper compares the numerical results with model tests carried out on a barge moored to a fixed support under regular and random waves in head sea. The effect of stiffness of the mooring line on the barge response for different mooring points is discussed, which would be useful for the designers. The effect of viscous damping is also considered. The analytical results are in good agreement with the experimental results in both regular and random waves.     

About the relationship between acoustic fields and hydrological fields in the area of a mesoscale eddy in the Black Sea

This paper discusses the application of acoustic sounding with the purpose of identifying vortical features in the sea. Analysis of the results of a multidisciplinary acoustic/hydrological experiment conducted in the Black Sea has revealed a stable recurrent correlation between the amplitudinal variance of echo signals, on the one hand, and the peculiarities of water temperature fields, on the other. Given these characteristics, the peripheral and the central areas of a mesoscale eddy essentially differed. This allows us to apply acoustic sounding to identify mesoscale eddies in the sea. Translated by Vladimir A. Puchkin.     

Sensitivity to stress of the estuarine bivalve Macoma balthica from areas between the Netherlands and its southern limits (Gironde)

Variation in the sensitivity to stress of Macoma balthica was measured in several French and Dutch estuaries. For adult and juvenile Macoma balthica exposed to copper under conditions of starvation, differences in mortality rate, condition, glycogen, burrowing rate and copper content were assessed. No significant differences were observed between adults and juveniles; the influence of treatment and origin was always evident. Animals from the most southern estuaries, Loire and Gironde, near to the species's southern limit of distribution, showed, in the field, the strongest deviations for the ecophysiological traits measured, and were in the experiments the most sensitive to stress.     

Effect of core porosity on stability and run-up of breakwaters

The commonly used formulae like Hudson's [(1959), Laboratory investigations of rubblemound breakwaters. WES report, Vicksburg], Iribarren's or Vander meer's [(1988), Rockslopes and gravel beaches under wave attack. Ph.D. thesis, Delft University of Technology, The Netherlands], do not give us the design cross section of a rubblemound breakwater for varying core porosity values. The paper presents the results of the experimental study carried out to compute the effects of core porosity on the stability and run-up characteristics of rubblemound breakwaters. Regular waves were made to attack the structure, with different core porosity values in a normal direction. The porosity of the armour and the secondary layers was neglected. It was observed that as core porosity increased the stability also increased considerably within the limits of the experimental data values. This may be due to large inflow and energy dissipation within the core of the structure. The run-up on the rubblemound slope was found to decrease with the increase in the porosity for the same reason.     

The status of geological dredging techniques

Scientific sea-floor dredging is currently used in marine geology primarily by the hard-rock community interested in the recovery of basement rock samples from the unsedimented deep ocean floor. The technique has generally been eclipsed by ocean drilling for recovery of sedimentary rocks, because of perceived uncertainties in the location of sampling and in the representativeness of recovered material. This contribution reviews dredging equipment currently in use by marine geological institutions and refers to pinger attachments that allow precise information on the behaviour of the dredge to be telemetered back to the ship. We argue that improvements in ship navigation and transponder navigation at the seafloor, when used in conjunction with surface and/or deeply towed sidescan and swathemapping surveys, now allow for considerably less uncertainty on the location of dredge sampling. Refined sorting criteria for dredge hauls are now also available. Recent comparisons of regional sample recovery by ocean drilling and by dredge sampling indicate that the dredge hauls can usefully supplement the drilling data in the construction of sedimentary and tectonic histories of seafloor areas.     

Morphology and tectonics of the Galapagos Triple Junction

We describe the results of GLORIA and SEABEAM surveys, supplemented by other marine geophysical data, of the Galapagos Triple Junction where the Pacific, Cocos and Nazca plates meet. The data allowed detailed topographic and tectonic maps of the area to be produced. We located each spreading axis with a precision of about 1 km. All three plate boundaries change character as the triple junction is approached to take on morphologies typical of slower spreading axes: the fast-spreading East Pacific Rise develops the morphology of a medium-spreading rise, and the medium-spreading Cocos-Nazca Rise takes on the appearance of a slow-spreading ridge. The axis of the East Pacific Rise was found to be completely continuous throughout the survey area, where it runs along the 102°05 W meridian. The Cocos-Nazca axis, however, fails to meet it, leaving a 20-km-wide band of apparently normal East Pacific Rise crust between its tip and the East Pacific Rise axis. As a consequence there must be considerable intra-plate deformation within the Cocos and Nazca plates. A further 40 km of the Cocos-Nazca axis is characterised by oblique faulting that we interpret to be a sign of rifting of pre-existing East Pacific Rise crust. We infer that true sea-floor spreading on the Cocos-Nazca axis does not begin until 60 km east of the East Pacific Rise axis. Other areas of similar oblique faulting occur on the Pacific plate west of the triple junction and along the rough-smooth boundaries of the Galapagos Gore. We present a model involving intermittent rifting, rift propagation, and sea-floor spreading, to explain these observations.     

Isolation and characterisation of pristane metabolites formed in vivo by rainbow trout

Pristane (2,6,10,14 -tetramethylpentadecane) occurs ubiquitously in the marine environment. This hydrocarbon may be of biogenic or petrogenic origin.¹ Recently it has been shown that residual amounts of this branched alkane increased in marine organisms after an oil spill.^2,3 The lack of data on the fate of pristane in fish, added with the fact that this compound was considered by some authors as a non-metabolisable substance in vertebrates, including man,⁴ led us to investigate the capability of fish to metabolise pristane. In this study, urinary and fecal excretion, tissue distribution and metabolism of ³H-pristane were analysed in Salmo gairdneri R. after a single intragastric dose. In addition to unchanged hydrocarbon, various labelled compounds have been isolated and identified in liver, bile, faeces, urine and surrounding water, demonstrating that pristane was first oxidised to alcohols (pristanol and pristane-diol) and to acid (pristanic acid). The elimination of these compounds occurred in the form of conjugated products (primarily glucuronides) as well as free metabolites.     

Wave drift enhancement effects in multi column structures

A theoretical assessment is made of mean wave drift forces on groups of vertical circular cylinders, such as the columns of a floating offshore platform. A complete analytical solution is obtained for two cylinders extending from seabed to free surface, and a long wave approximation is found to provide reliable predictions of the drift force in line with the waves at low frequencies. For moderate separation between the two cylinders, this force is found to tend at low frequencies to a value four times the force on an isolated cylinder.A numerical method is employed to study two surface piercing cylinders truncated below the free surface, and an arrangement of four vertical cylinders characteristic of a floating offshore platform. The mean vertical drift force is found to be reasonably well approximated, over the frequency range of practical interest, by the force on an individual cylinder considered in isolation multiplied by the number of cylinders in the group. Interaction effects, however, have a profound influence on the total horizontal drift force. At low frequencies this force is found to tend to the force on an isolated cylinder multiplied by the squate of the number of cylinders in the group.     

Low-frequency damping of a moored semisubmersible obtained from simulated extinction tests and mean wave drift forces

Low-frequency damping of a moored semisubmersible drilling platform was obtained from numerical extinction tests simulated in still water and in regular waves and from mean wave drift forces calculated at zero forward speed. The influence of drag forces was represented by the modified Morison equation. The platform as used for the 18th ITTC Comparative Mooring Study was analyzed in irregular beam waves. The computed time series of sway as well as the corresponding sway response spectrum compared favourably with model test measurements, demonstrating that this procedure to determine low-frequency damping can be effective.     

Accumulation and effects of organotin compounds in oysters and mussels: Correlation with serum biochemical and cytological factors and tissue burdens

Oysters and mussels exposed to a concentration of 0·7 ppb (μg/liter) tributyltin from painted panels in flowing seawater accumulated tin in the digestive glands to comparable levels. The mussels experienced approximately 50% mortality during the 60-day test period, but the oysters suffered virtually no deaths. There was no evidence from either bivalve of elevated numbers of hemocytes during the test period and no evidence for cellular disruption as detected by increased levels of serum lysosomal hydrolases. Serum protein of exposed mussels relative to controls increased with time of exposure to the toxicant, while oyster serum protein, normally 10 x higher than in mussels, did not. No evidence was found for elevated stress proteins (heat shock proteins) or metallothioneins in the serum hemocytes of either bivalve. Responses by these animals to fatal or near fatal doses of TBT were thus very different from responses to copper that we have reported elsewhere.^1,2