Assimilation of buoy and satellite data in wave forecasts with integral control variables

The quality of numerical wave forecasts can be improved significantly by assimilating wave observations prior to the forecast. In the present study a technique for such assimilation is developed that exploits (a) the efficiency of a limited number of integral control variables, and (b) the effectiveness of variational (model-consistent) assimilation. The formal procedure is independent of the type of control variables and of the wave model (moreover, no adjoint wave model is required). In the present study, integral control variables are chosen to represent large-scale errors in the driving wind fields and uncertainties in the wave model. The assimilation technique is validated with observations of the ERS-1 satellite altimeter and two waverider buoys in two consecutive storms in the Norwegian Sea. The assimilation of the observations reduced the errors in the forecasted significant wave height at the buoy locations typically from 25% to 12%. For low-frequency waves the effect of the assimilation is similarly significant at one buoy location but marginal at the other buoy location.     

New species of the genus Xanthocalanus (Copepoda, Calanoida, Phaennidae) from the Laptev Sea

Sampling of the near-bottom calanoid copepods was performed on board of the research vessel Polarstern in 1993 in the Laptev Sea (Siberian Arctic). Three new species of Xanthocalanus were identified as such, and are described and figured here: X. spinodenticulatus sp. nov., X. laptevorum sp. nov. and X. polarsternae sp. nov.     

On the background level of Tc, Sr and Cs in the North Atlantic

Mean concentrations of the anthropogenic radioactive oceanographic tracers ⁹⁹Tc, ⁹⁰Sr and ¹³⁷Cs have been measured as 0.005, 1.6 and 2.5 Bq m⁻³ in oceanic Northeast Atlantic surface water, east and northeast of the Azores, in 1992. This is, apparently, the first published value for fallout “background” ⁹⁹Tc in oceanic Atlantic water.Comparison with older data indicates an observed half life for ⁹⁰Sr and ¹³⁷Cs in the northeast Atlantic surface water of 20 yr corresponding to a mean residence time of 80–100 yr for the stable elements.The observed ⁹⁹Tc/⁹⁰Sr ratio (3 × 10⁻³) in the Azores samples is 10 times higher than the theoretical fission yield decay corrected to 1992. This is in agreement with published data on rain water samples and may be characteristic for 1960's global fallout. Furthermore, the measured ¹³⁷Cs/⁹⁰Sr ratio is not significantly different from that observed for global fallout. There do not appear to be any additional significant sources of artificial radionuclides in this region.     

The weldability of steels used in jack-up drilling platforms

Weldability problems in jack-up rigs arise principally in leg construction where particularly high-strength steels (690 N mm⁻² yield) are used for chords and racks. Attainment of mechanical properties is not usually difficult, although procedural trials are advisable.

Of potential fabrication problems, hydrogen cracking (heat-affected zones or weld metal) is of greatest concern, and consideration of solidification cracking is advisable. Lamellar tearing is not generally a problem with modern steels, and the risk of stress-relief cracking will be confined to the limited number of joints which can be heat-treated.

Fatigue cracking is probably the major cause of service failure of jack-up rigs, and the use of high-strength steels, which permits higher static stress limits, can exacerbate this problem. Hydrogen-induced stress corrosion can also occur, either due to cathodic polarisation or corrosion, particularly in the presence of H₂S in foul sea-water. For this reason weld hardness limits need to be maintained.     

RECENT RESEARCH AND DEVELOPMENT OF POLYMER OPTICAL FIBRES

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A comparison between conventional and advanced handling systems for low volume container maritime terminals

In this paper a conventional low volume maritime terminal equipped with straddle carriers is compared against an advanced automatic stacking crane/automatic guided vehicle alternative. For both configurations a convenient layout was designed, a reasonable level of service (common for both terminals) was adopted, and the required amount of equipment was determined using computer simulation. The results indicate that the total cost per container and the area requirements do not differ considerably between the two configurations although there exist differences in the investment capital and the personnel required.     

A Simplified Framework for String Stability Analysis of Automated Vehicles*

Automated vehicles traveling in platoons must exhibit stability both individually and as a group, a property referred to as “string stability”. We propose a new framework for evaluating the longitudinal string stability properties of platoons of automated vehicles. In this framework, the platoon is considered to be a mass-spring-damper system with linear characteristics. The resulting closed-loop representation yields transfer functions and impulse responses that can be analyzed to determine the string stability properties of the platoon. This framework facilitates qualitative comparisons of the effects of various controller characteristics, such as time headway and intervehicle communication, on string stability.     

Novel Manufacturing Technology of Hyperbolic Plates for Shipbuilding

On the basis of the principle of dieless hydrobulging technology, a novel hydrobulging technology for manufacturinghyperbolic plates is proposed. First, a toroidal pipe elbow or a partial toroidal pipe elbow is formed, then the single hydrobulgedstructure can be cut up into some desired plates. It is proved by experiments and finite element simulation that manufacturingtechnology of hyperbolic plates adopting integrated hydrobulging forming technology is feasible.     

Exchange of carbon by an upwelling filament off Cape Ghir (NW Africa)

We have studied the physicochemical and biological structure of a permanent filament off Cape Ghir (31°N) and estimated the transport of organic matter associated with it. The seaward filament exported coastal upwelled water, with low temperature and salinity and high organic matter, to the open ocean even in the absence of upwelling-favorable conditions. The estimated flux of excess organic carbon (the nonrefractory pool) expressed in annual basis yielded a value of 3.1×10⁹ kg C, from which 90% was transported as dissolved organic carbon. This flux represents about 63% of the average annual primary production for the region of study. We conclude that the net-offshore transport may contribute to the enrichment of offshore oligotrophic waters throughout the year, partly explaining the metabolic imbalance found in open ocean waters of the subtropical Northeast Atlantic.