Ultimate strength of ship hulls under torsion

For a ship hull with large deck openings such as container vessels and some large bulk carriers, the analysis of warping stresses and hatch opening deformations is an essential part of ship structural analyses. It is thus of importance to better understand the ultimate torsional strength characteristics of ships with large hatch openings. The primary aim of the present study is to investigate the ultimate strength characteristics of ship hulls with large hatch openings under torsion. Axial (warping) as well as shear stresses are normally developed for thin-walled beams with open cross sections subjected to torsion. A procedure for calculating these stresses is briefly described. As an illustrative example, the distribution and magnitude of warping and shear stresses for a typical container vessel hull cross section under unit torsion is calculated by the procedure. By theoretical and numerical analyses, it is shown that the influence of torsion induced warping stresses on the ultimate hull girder bending strength is small for ductile hull materials while torsion induced shear stresses will of course reduce the ship hull ultimate bending moment.     

The Mid-atlantic Ridge (31°S–34°30′S): Temporal and spatial variations of accretionary processes

The ridge located between 31° S and 34°30′S is spreading at a rate of 35 mm yr⁻¹, a transitional velocity between the very slow (≤20 mm yr⁻¹) opening rates of the North Atlantic and Southwest Indian Oceans, and the intermediate rates (60 mm yr⁻¹) of the northern limb of the East Pacific Rise, and the Galapagos and Juan de Fuca Ridges. A synthesis of multi-narrow beam, magnetics and gravity data document that in this area the ridge represents a dynamically evolving system. Here the ridge is partitioned into an ensemble of six distinct segments of variable lengths (12 to 100 km) by two transform faults (first-order discontinuities) and three small offset (< 30 km) discontinuities (second-order discontinuities) that behave non-rigidly creating complex and heterogeneous morphotectonic patterns that are not parallel to flow lines. The offset magnitudes of both the first and second-order discontinuities change in response to differential asymmetric spreading. In addition, along the fossil trace of second-order discontinuities, the lengths of abyssal hills located to either side of a discordant zone are observed to lengthen and shorten creating a saw-toothed pattern. Although the spreading rate remains the same along the length of the ridge studied, the morphology of the spreading segments varies from a deep median valley with characteristics analogous to the rift segments of the North Atlantic to a gently rifted axial bulge that is indistinguishable from the shape and relief of the intermediate rate spreading centers of the East Pacific Rise (i.e., 21°N). Like other carefully surveyed ridge segments at slow and fast rates of accretion, the along-axis profiles of each ridge segment are distinctly convex upwards, and exhibit along-strike changes in relief of 500m to 1500 between the shallowest portion of the segment (approximate center) and the segment ends. Such spatial variations create marked along-axis changes in the morphology and relief of each segment. A relatively low mantle Bouguer anomaly is known to be associated with the ridge segment characterized by a gently rifted axial bulge and is interpreted to indicate the presence of focused mantle upwelling (Kuo and Forsyth, 1988). Moreover, the terrain at the ends of each segment are known to be highly magnetized compared to the centers of each segment (Carbotte et al, 1990). Taken together, these data clearly establish that these profound spatial variations in ridge segment properties between adjoining segments, and along and across each segment, indicate that the upper mantle processes responsible for the formation of this contrasting architecture are not solely related to passive upwelling of the asthenosphere beneath the ridge axis. Rather, there must be differences in the thermal and mechanical structure of the crust and upper mantle between and along the ridge segments to explain these spatial variations in axial topography, crustal structure and magnetization. These results are consistent with the results of investigations from other parts of the ridge and suggest that the emplacement of magma is highly focused along segments and positioned beneath the depth minimum of a given segment. The profound differences between segments indicate that the processes governing the behavior of upwelling mantle are decoupled and the variations in the patterns of axis flanking morphology and rate of accretion indicate that processes controlling upwelling and melt production vary markedly in time as well. At this spreading rate and in this area, the accretionary processes are clearly three-dimensional. In addition, the morphology of a ridge segment is not governed so much by opening rate as by the thermal structure of the mantle which underlies the segment.     

Large-scale vertical hydroacoustic structure of the North Atlantic and its seasonal variability

A classification based on the number and types of large-scale acoustic waveguides is proposed for the mean seasonal profiles of sound speed propagation. A scheme for North Atlantic zoning, using typical curves of the sound speed vertical distribution, is given. The channel axis's position is shown not to depend on the water mass haline properties, being controlled by the temperature field vertical stratification.Translated by Vladimir A. Puchkin.     

Seasonal variation of Mn adsorption on to calcareous surfaces in the English Channel, and its implication on the manganese distribution coefficient

Dissolved and particulate manganese in seawater samples derived from the English Channel has been analyzed using graphite furnace atomic absorption (GFAAS), and inductively coupled plasma atomic emission (ICP—AES) spectroscopies. Because of the high contents of carbonate minerals found in the suspended matter samples, the English Channel constitutes an ideal field area for the study of the Mn²⁺/Ca²⁺/CaCO₃ system. Owing to the chemical speciation of particulate manganese and the combined use of the X-ray diffraction and electron spin resonance spectroscopy we have shown the importance of the carbonate phase in the stabilization of manganese (II). This has been confirmed by p-pH measurements in the field. All these studies have also indicated that: (1) manganese is associated with calcite in the form of a solid solution, Mn_xCa_1−xCO₃; and (2) significant increases in the concentrations of particulate manganese, especially in offshore waters, occur in summer. This seasonal phenomenon has been attributed to the proliferation of coccolithophorids, which are known to be covered with calcified skeletons at high specific surface areas. To appraise the implication of the coccolithophorid-blooms phenomenon on the Mn²⁺/Ca²⁺/CaCO₃ system, we have used the manganese distribution coefficient, D_i, between the liquid phase and CaCO₃ particles. Overall we have shown that: (1) D_i in summer (i.e. when coccoliths considered as very fine-grained calcite are abundant) is much higher than that obtained in winter; and (2) in the vicinity of the French coast, D_i does not vary significantly even in summer. This is because of the high content of chalk-derived particles found in the near-shore waters.     

Uptake and transformation of C-labelled tributyltin chloride by the dog-whelk, nucella lapillus: Importance of absorption from the diet

The importance of the diet as a source of tributyltin (TBT) in Nucella lapillus was studied using [¹⁴C]tributyltin chloride. In N. lapillus provided with prelabelled mussels, Mytilus edulis, in labelled water (mean 20·5 ng/litre TBT) the rate of accumulation of total ¹⁴C was 2–3 times that in unfed animals. Owing to its degradation in the tissues of both fed and unfed animals, concentrations of [¹⁴C]TBT tended to reach a plateau after only 28 days. However, total concentrations of ¹⁴C were still increasing after 49 days. Under experimental conditions (15°C, ample food, no disturbance) the diet accounted for about 50% of the body burden of TBT in N. lapillus after 49 days exposure: concentration factors (dry tissue/water) for [¹⁴C]TBT in both male and female N. lapillus were similar at about 60 000 in fed and 30 000 in unfed animals. It is concluded that the diet may contribute less than half of the body burden of TBT found in natural populations subjected to life-long exposure.     

黄海西部底栖海藻记录的评论

黄海西部是指北起鸭绿江口,南至长江口(包括渤海)的中国沿岸。这一带的海藻研究,迄今将近百年,目前已掌握的海藻分类研究文献共有45篇。我们在研究和分析这些文献后,把这些海藻记录归的为3类。(1)可以接受的记录：根据我们十多年来在黄海沿岸的调查采集经验证实所记录的产生于黄海西部的海藻,或虽尚未采到,但就目前的资料分析,估计该项记录可能是正确的。(2)待证实的记录：有些海藻记录无法肯定其鉴定是否正确,需待重新检查其原标本后始能确定的。(3)不能接受的记录：这类记录中,有些是已被藻类学家所否定,有些经检查原定名标本后证实是错误的,有些则根据地理分布观点,被认为是不可能生长在这个海区的种类。 根据黄海西部的海藻研究的发展情况,我们把过去的工作划分为两个历史阶段。     

Automatic Registration of TOBI Side-Scan Sonar and Multi-Beam Bathymetry Images for Improved Data Fusion

Deep towed side-scan sonar vehicles such as TOBI acquire high quality imagery of the seafloor with very high spatial resolution but poor locational accuracy. Fusion of the side-scan sonar data with bathymetry data from an independent source is often desirable to reduce ambiguity in geological interpretations, to aid in slant-range correction and to enhance seafloor representation. The main obstacle to fusion is accurate registration of the two datasets.The application of hierarchical chamfer matching to the registration of TOBI side-scan sonar images and multi-beam swath bathymetry is described. This matches low level features such as edges in the TOBI image, with corresponding features in a synthetic TOBI image created by simulating the flight of the TOBI vehicle through the bathymetry. The method is completely automatic, relatively fast and robust, and much easier than manual registration. It allows accurate positioning of the TOBI vehicle, enhancing its usefulness as a research tool. The method is illustrated by automatic registration of TOBI and multi-beam bathymetry data from the Mid-Atlantic Ridge.     

Plastic buckling of ring-stiffened conical shells under external hydrostatic pressure

The paper describes experimental tests carried out on three ring-stiffened cones that were tested to destruction under external hydrostatic pressure. The cones were carefully machined from EN1A Steel. All three cones failed by plastic non-symmetric bifurcation buckling in a mode commonly known as general instability. In this mode the entire ring-shell combination buckles bodily.The paper also provides a design chart using the results obtained from these three vessels, together with the results of six other vessels obtained from other tests. The design chart allows the possibility of obtaining a plastic knock down factor, so that the theoretical buckling pressures, based on elastic theory, can be divided by the plastic knockdown factor, to give the predicted buckling pressure. This method can also be used for the design of full-scale vessels.