An experimental study of elastohydrodynamics of towed flexible cylinders aided by video image processing

Experimental studies of the elastohydrodynamics of towed flexible cylinders aided by video image processing are reported. A scale model of a prototype hydrophone array has been designed, fabricated, and tested in a speed range of 1.0 to 4.5 m/sec. The experiments were conducted in a 67-m long towing tank. The instrumented flexible member, 12.7 mm in diameter and 13.55 m long, was fixed at the one end and free at the other and was slightly lighter than neutrally bouyant. Three tail drogue configurations were employed. An integral part of the physical model tests was the development and utilization of a microcomputer based video image processing system for model configuration reconstitution. Instability characteristics, tail acceleration spectral densities, lift force due to curvature, and drag coefficients are quantified and discussed.     

Investigation of a eutrophic tidal basin: part 1—factors affecting the distribution and biomass of macroalgae

The distribution and biomass of macroalgae, principally Enteromorpha spp., have been estimated in Langstone Harbour, a 19 km² tidal basin in southenrn England. Comprehensive mapping was carried out annually at the time of maximum biomass and monthly mapping of selected areas allowed seasonal changes to be studied. Aerial false-colour photography and ground-level mapping were used for assessing the area and density of cover of macroalgae, but have identified no continuous trends between 1973 and 1982. In nine years, some 48% of the intertidal mudflat has supported >75% macroalgal cover at some stage, but generally only one-third of this potential has been achieved annually. The average peak biomass was determined by a stratified sampling method and varied about a mean of 38.5 g dry weight per square metre and showed significant annual differences. The processes controlling macroalgal growth and distribution reviewed, but, in general, factors other than nutrient availability are effective in determining areas supporting high macroalgal cover in any particular year.     

Trends in the solubility of iron,aluminium, manganese and phosphorus in aerosol collected over the Atlantic Ocean

The solubility of iron, aluminium, manganese and phosphorus has been determined in aerosol samples collected between 49°N and 52°S during three cruises conducted in the Atlantic Ocean as part of the European Union funded IRONAGES programme. Solubilities (defined at pH 4.7) determined for Fe and Al in samples of Saharan dust were significantly lower (medians 1.7% and 3.0%, respectively) than the solubilities of these metals in aerosols from other source regions (whole dataset medians 5.2% and 9.0%, respectively). Mn solubility also varied with aerosol source, but the median solubility of Mn in Saharan dust was very similar to the median for the dataset as a whole (55% and 56%, respectively). The observed solubility of aerosol P was ∼ 32%, with P solubility in Saharan aerosol perhaps as low as 10%. Laboratory studies have indicated that aerosol Fe solubility is enhanced by acid processing. No relationship could be found between Fe solubility and the concentrations of acid species (non-seasalt SO₄²⁻, NO₃⁻) nor the net acidity of the aerosol, so we are unable to confirm that this process is significant in the atmosphere. In terms of the supply of soluble Fe to oceanic ecosystems on a global scale, the observed higher solubility for Fe in non-Saharan aerosols is probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic. On a smaller scale however, higher solubility for aerosol Fe may alter our understanding of Fe cycling in regions such as the remote Southern Ocean.     

Experimental study of the breaking limit of multi-directional random waves passing over an impermeable submerged breakwater

This study investigates experimentally the breaking wave height of multi-directional random waves passing over an impermeable submerged breakwater. Experiments have been conducted in a three-dimensional wave basin equipped with a multi-directional random wave generator. A special type of wave gauge has been newly devised to record the water surface elevations in the breaker zone as accurately as possible. The records are analyzed to estimate the location and limit of wave breaking. Comparisons have also been made with the results of regular waves. The influence of the incident wave conditions on the breaking wave height normalized by the breakwater dimensions has been investigated. Empirical formulae have been presented to estimate the breaking limit of multi-directional random waves based on the experimental records. The formulae have been tested and found to work well not only for multi-directional random waves, but for regular waves as well.     

The Southern Ocean’s grip on the northward meridional flow

A ‘quasi-island’ approach for examining the meridional flux of warm and intermediate water from the Southern Ocean into the South Atlantic, the South Pacific and the Indian Ocean has recently been proposed ( [Nof, 2000a] and [Nof, 2002]). This approach considers the continents to be ‘pseudo islands’ in the sense that they are entirely surrounded by water, but have no circulation around them. The method employs an integration of the linearized momentum equations along a closed contour containing the continents. This allows the meridional transport into these oceans to be computed without having to find the detailed solution to the complete wind-thermohaline problem.The solution gives two results; one expected, the other unexpected. It shows that, as expected, about 9±5 Sv of upper and intermediate water enter the South Atlantic from the Southern Ocean. The unexpected result is that the Pacific-Indian Ocean system should contain a ‘shallow’ meridional overturning cell carrying 18±5 Sv. What is meant by shallow here is that the cell does not extend all the way to the bottom (as it does in the Atlantic) but is terminated at mid-depth. (This reflects the fact that there is no bottom water formation in the Pacific.) Both of these calculations rely on the observation that there is almost no flow through the Bering Strait and on the assumption that there is a negligible pressure torque on the Bering Strait’s sill.Here, we present a new and different approach, which does not rely on either of the above two conditions regarding the Bering Strait and yet gives essentially the same result. The approach does not involve any quasi-island calculation but rather employs an integration of the linearized zonal momentum equation along a closed open-water latitudinal belt connecting the tips of South Africa and South America. The integration relies on the existence of a belt (corridor) where the linearized general circulation equations are valid. It allows for a net northward mass flux through either the Sverdrup interior or the western boundary currents. It is found that the belt-corridor approach gives 29±5 Sv for the total meridional flux of surface and intermediate water from the Southern Ocean. This agrees very well with the quasi-island calculations, which give a total northward flux of 27±5 Sv. Given the spacing between the continents and the small variability of the southern winds with longitude, one may assume that 9 Sv of the total 29 Sv enters the Atlantic and the other 20 Sv enters the combined Pacific-Indian Ocean system, which is also in agreement with the quasi-island calculation. These agreements indicate that the assumptions made in the earlier studies regarding the Bering Strait are probably valid.     

Investigation of the electromagnetic fields induced by sea wave motion

This paper discusses a theoretical model of the electromagnetic field induced by internal waves of baric origin. Comparison of thein situ data on the differences between the horizontal electrical field potentials conditioned by internal waves in some Black Sea and tropical Atlantic areas and of the results of calculations of the model electrical field's intensity in those areas shows their good agreement. The dependences of the electromagnetic field component amplitudes on the internal waves parameters and sea-bed rock conductivity are considered. Translated by Vladimir A. Puchkin.     

The reliability of analytical data for tributyltin (TBT) in sea water and its implications on water quality criteria

To investigate the reliability of analytical data for tributyltin (TBT) in sea water, split water samples were distributed to ten laboratories in six countries. The sub-surface samples comprised: (i) an offshore (0·5 km) water sample, (ii) the same sample but spiked with an undisclosed quantity of TBT standard compound (175 ng TBT⁺ liter⁻¹), and (iii) a sample taken from a yacht marina. The seven acceptable data sets were in good agreement for the spiked sample (178 ± 26 ng TBT⁺ liter⁻¹) but showed a greater variation in concentrations reported for the yacht marina sample (366 ± 93 ng TBT⁺ liter⁻¹). Atomic absorption and gas chromatographic-flame photometric detection techniques produced results of similar accuracy and precision. Samples acidified with 1 ml of 10% (v/v) acetic acid appeared stable for more than 2 weeks when stored refrigerated and in darkness. Analyses of the offshore seawater sample revealed TBT contamination (9 ± 7 ng TBT⁺ liter⁻¹) indicating dispersion of the compound to the shelf waters off Monaco. The spread in values reported by the laboratories demonstrates inherent difficulties in obtaining good precision below approximately 20 ng TBT⁺ liter⁻¹. This observation is discussed with respect to the setting and enforcing of water quality standards.     

Circulation and currents in the southwestern East/Japan Sea: Overview and review

A review is made of circulation and currents in the southwestern East/Japan Sea (the Ulleung Basin), and the Korea/Tsushima Strait which is a unique conduit for surface inflow into the Ulleung Basin. The review particularly concentrates on describing some preliminary results from recent extensive measurements made after 1996. Mean flow patterns are different in the upstream and downstream regions of the Korea/Tsushima Strait. A high velocity core occurs in the mid-section in the upstream region, and splits into two cores hugging the coasts of Korea and Japan, the downstream region, after passing around Tsushima Island located in the middle of the strait. Four-year mean transport into the East/Japan Sea through the Korea/Tsushima Strait based on submarine cable data calibrated by direct observations is 2.4 Sv (1 Sv = 10⁶ m³ s⁻¹). A wide range of variability occurs for the subtidal transport variation from subinertial (2–10 days) to interannual scales. While the subinertial variability is shown to arise from the atmospheric pressure disturbances, the longer period variation has been poorly understood.Mean upper circulation of the Ulleung Basin is characterized by the northward flowing East Korean Warm Current along the east coast of Korea and its meander eastward after the separation from the coast, the Offshore Branch along the coast of Japan, and the anticyclonic Ulleung Warm Eddy that forms from a meander of the East Korean Warm Current. Continuous acoustic travel-time measurements between June 1999 and June 2001 suggest five quasi-stable upper circulation patterns that persist for about 3–5 months with transitions between successive patterns occurring in a few months or days. Disappearance of the East Korean Warm Current is triggered by merging the Dok Cold Eddy, originating from the pinching-off of the meander trough, with the coastal cold water carried Southward by the North Korean Cold Current. The Ulleung Warm Eddy persisted for about 20 months in the middle of the Ulleung Basin with changes in its position and spatial scale associated with strengthening and weakening of the transport through the Korea/Tsushima Strait. The variability of upper circulation is partly related to the transport variation through the Korea/Tsushima Strait. Movements of the coastal cold water and the instability of the polar front also appear to be important factors affecting the variability.Deep circulation in the Ulleung Basin is primarily cyclonic and commonly consists of one or more cyclonic cells, and an anticyclonic cell centered near Ulleung Island. The cyclonic circulation is conjectured to be driven by a net inflow through the Ulleung Interplain Gap, which serves as a conduit for the exchange of deep waters between the Japan Basin in the northern East Sea and the Ulleung Basin. Deep currents are characterized by a short correlation scale and the predominance of mesoscale variability with periods of 20–40 days. Seasonality of deep currents is indistinct, and the coupling of upper and deep circulation has not been clarified yet.