A simple model of propulsive oscillating foils

The design of thrusters inspired by the locomotion of fishes is currently investigated in many research centres for unmanned underwater vehicles. Fast fishes propel themselves in water through the rhythmic motion of their tail. Propulsion is achieved by means of the periodic shedding of vortex structures by the edges of the tail. Thrust is produced because the vortices give rise to a steady jet of fluid which leaves the tail in the direction which is opposite to the forward motion of the fish. Assuming that the fish tail can be modelled by a two-dimensional plate in steady forward motion and oscillating with a combination of harmonic heaving and pitching movements, Brown and Michael’s model is presently used to determine the dynamics of the vortex structures shed by plate edges. Numerical simulations have been carried out to investigate the effects on the flow field of varying the physical parameters of the phenomenon. The knowledge of the strength and trajectory of the vortex structures shed by the plate allows the characteristics of the jet producing the thrust to be quantified.     

The dynamic force on a two-dimensional planing plate of arbitrary camber

The thin wing methodology of Llewelyn (1964) is employed to calculate the pressure distribution of a two-dimensional cambered planing plate behind the stagnation line. A simplification of the jet flow in front of the stagnation line, solved exactly by Pierson and Leshnover (1949) and generalized to the case of arbitrary camber by Payne (1980) is then “patched on” to give the complete solution.Although the resulting pressure distributions can in principle be integrated analytically to find the normal force, pressure drag and pitching moment, the result is very cumbersome. It is simpler to integrate numerically on a computer. The paper presents examples obtained using this approach.     

Review of experimental work in biomimetic foils

Significant progress has been made in understanding some of the basic mechanisms of force production and flow manipulation in oscillating foils for underwater use. Biomimetic observations, however, show that there is a lot more to be learned, since many of the functions and details of fish fins remain unexplored. This review focuses primarily on experimental studies on some of the, at least partially understood, mechanisms, which include 1) the formation of streets of vortices around and behind two- and three-dimensional propulsive oscillating foils; 2) the formation of vortical structures around and behind two- and three-dimensional foils used for maneuvering, hovering, or fast-starting; 3) the formation of leading-edge vortices in flapping foils, under steady flapping or transient conditions; 4) the interaction of foils with oncoming, externally generated vorticity; multiple foils, or foils operating near a body or wall.     

Global change ecotoxicology: Identification of early life history bottlenecks in marine invertebrates,variable species responses and variable experimental approaches

Climate change is a threat to marine biota because increased atmospheric CO₂ is causing ocean warming, acidification, hypercapnia and decreased carbonate saturation. These stressors have toxic effects on invertebrate development. The persistence and success of populations requires all ontogenetic stages be completed successfully and, due to their sensitivity to environmental stressors, developmental stages may be a population bottleneck in a changing ocean. Global change ecotoxicology is being used to identify the marine invertebrate developmental stages vulnerable to climate change. This overview of research, and the methodologies used, shows that most studies focus on acidification, with few studies on ocean warming, despite a long history of research on developmental thermotolerance. The interactive effects of stressors are poorly studied. Experimental approaches differ among studies. Fertilization in many species exhibits a broad tolerance to warming and/or acidification, although different methodologies confound inter-study comparisons. Early development is susceptible to warming and most calcifying larvae are sensitive to acidification/increased pCO₂. In multistressor studies moderate warming diminishes the negative impact of acidification on calcification in some species. Development of non-calcifying larvae appears resilient to near-future ocean change. Although differences in species sensitivities to ocean change stressors undoubtedly reflect different tolerance levels, inconsistent handling of gametes, embryos and larvae probably influences different research outcomes. Due to the integrative ‘developmental domino effect’, life history responses will be influenced by the ontogenetic stage at which experimental incubations are initiated. Exposure to climate change stressors from early development (fertilization where possible) in multistressor experiments is needed to identify ontogenetic sensitivities and this will be facilitated by more consistent methodologies.     

The feasibility of Doppler sonar fish counting

In the course of monitoring and evaluating fish population in the seas, sonar systems have proved a practical and efficient measurement approach. The results obtained, however, from the use of sonar for monitoring fish migration in rivers have been somewhat disappointing-the most troublesome problems being the inability to recognize invalid targets. It has been proposed [1] that a high-resolution Doppler sonar which recognizes a valid target on the basis of its Doppler signature would be a solution to this problem. This paper examines the feasibility of such a target identification scheme. In particular, an examination is made of the nature of returns to be expected from a fish, and of interference sources-principally surface reverberation. From this it is concluded that the Doppler approach is indeed feasible, but that the use of a high-resolution pulsed system capable of separating multiple targets is only possible in a channel width of a few meters.     

Opto-acoustic feasibility design of a conical acoustic lens

The opto-acoustic design of a liquid-filled conical acoustic lens is discussed. An approximate model of stacked cylindrical elements is used to estimate the focal line. Final optimization is to be achieved experimentally. Diffraction enables point hydrophones to cover a vertical range of60deg. An iterative optimization procedure yields cone angle and window aperture size that give diffraction patterns to accomplish this with 3-dB maximum loss at the extreme elevations. Baffles are positioned by a ray-tracing analysis to minimize internal acoustic reflections. Reflection losses <1 dB are predicted above the critical angle (for total internal reflection) at the water-window boundary.     

Fishery cooperatives in Cuba: Potential benefits,legal feasibility,and governance pre-conditions

Currently there is a strong interest in Cuba in improving the performance of the fisheries sector with respect to social, biological, and economic outcomes. Many important fishery resources appear to be overexploited, and previous fishery regulations have had mixed success in restoring fishery stocks. The current fishing pressure could also have adverse impacts on other valuable ecosystem services that support economic activities such as dive tourism and recreational fishing. A new State policy to expand cooperative enterprises to non-agricultural sectors provides an opportunity for fishery cooperatives to be created for the first time since the early years of the Cuban Revolution. This paper explores the potential ecological, social, and economic benefits of adopting fishery cooperatives as a co-management scheme for Cuba's marine fisheries. It concludes that well-designed fishery cooperatives can offer substantial benefits to the management of the fishery sector. Based on an analysis of the relative success of fishing cooperatives worldwide, guidelines are provided for the design of fishery cooperatives in Cuba.     

Distinctly variable mudscapes: Distribution gradients of intertidal macrofauna across the Dutch Wadden Sea

The Wadden Sea is a shallow coastal region, with a large area of sedimentary tidal flats that extends from The Netherlands to Denmark and has been declared a site of international importance in the Dutch and German parts (Ramsar status and UNESCO World Heritage Site). Benthic macrofauna are central to the ecosystem functioning of this area, as they recycle nutrients, decompose organic matter and are an important food source for many secondary consumers, like fish and waterbirds. Due to the environmental gradients characteristic of estuarine systems, it is expected that changes in assemblage composition will be observed across the physical and environmental gradients of the Wadden Sea. First, we explored the spatial variation in assemblage composition of benthic macrofauna across the intertidal part of the Dutch Wadden Sea using 3 years of biomass data. Then, we identified the relative importance of six environmental variables for explaining and predicting changes in assemblage composition across the intertidal areas of the Wadden Sea using generalised dissimilarity modelling (GDM). In accordance with the environmental gradients across this system, the biomass contributed by a few common species differed from west to east and were distinct in the Dollard. In the west, bivalves Mya arenaria, Cerastoderma edule and Ensis directus contributed a relatively large and equal share of the total biomass, whereas C. edule contributed the sole largest share of the total biomass towards the east. The polychaete Alitta succinea became a large share of the total biomass in the upper Ems and in the Dollard estuary, but contributed little elsewhere. Similar to the observed differences in species composition, the spatial patterns in assemblage composition, as predicted by the GDM models, identified the Dollard as distinct and that the prevalence of assemblage types in the west differed to the east. Median grain size, followed by microphytobenthic biomass, and exposure time were the most important variables describing differences in assemblage composition. That the Wadden Sea forms a heterogeneous landscape where assemblage composition varies across multiple gradients has repercussions for management and monitoring.     

Assessing the feasibility of ecosystem-based fisheries management in tropical contexts

This analysis documents the reasons for emerging interest in ecosystem-based fisheries management (EBFM) and relates this management model to others. It highlights the central challenges to EBFM in the tropical context and examines an ongoing project, Fisheries Improved for Sustainable Harvest (FISH), in the Philippines—likely the first EBFM project in the tropics. The Philippine legal and institutional context provides major governance challenges to EBFM, especially as management is scaled up. A monitoring framework with process and output criteria is applied to FISH to establish progress to date. Major institutional and governance challenges for EBFM will require monitoring, evaluation, and adaptation.     

On the feasibility of some photochemical reactions of iodide in seawater

Aerated solutions of potassium iodide in de-ionised water, of between 5–20% (w/v), were exposed to ambient spring sunlight to estimate the rate of photochemical production of molecular iodine from iodide and oxygen in seawater. This rate cannot be measured directly as other reactions, for example the reduction of molecular iodine by organic matter, interfere. Also, a parallel photo-oxidation, initiated by organic matter in real seawater, may also occur. The experiments yield a half-life for iodide in tropical surface waters of about 29 months suggesting that the reaction is insignificant. At this rate it will not compete effectively against the reduction of molecular iodine by organic matter, and hence molecular iodine should not appear. The experiments also consider the photo-oxidation by nitrate, and iodate, a combination of nitrite and oxygen, and eliminate significant interference by chloride, bromide and the phosphate buffer. The rate of photo-oxidation with each of the first three oxidations is found to be first order with respect to oxidant concentration. The variation of photo-oxidation rate with pH is also studied, with a brief investigation without conventional oxidant, where electron cage complexes still promote photo-oxidation. The photochemical action spectrum for these reactions in sunlight is shown to extend between 300 and 425 nm. The photo-oxidation of iodide by iodate is more interesting to marine chemistry as the photo-reduction of iodate. Nevertheless, the reduction-rate is judged to be several orders too low to be significant in seawater. The mechanism of the reactions are discussed and lessons drawn on the stability of potassium iodide solutions used in iodate analysis. The KI actinometer is recommended to those studying other photochemical systems activated by UV-A light as it is linear and very simple and reliable.     

Seiches in a circular basin of variable depth

Free waves (seiches) in a circular basin of variable depth are studied numerically within the framework of the linear theory of long waves taking into account the action of the Coriolis force. We determine the frequencies of axisymmetric and circular waves, study the structure of the modes of elevation of the free surface and wave velocities, and establish the dependences of the phase velocities of circular waves on the number of mode and wavelength. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

变黏酸的室内合成及性能研究

酸化是油气井增产的重要手段,而均匀有效地解除地层污染是酸化成功的关键。对于非均质性储层,酸液会优先处理高渗透层,难以进入低渗透层,无法实现均匀酸化。常规变黏酸、胶凝酸中由于含有聚合物,酸岩反应结束后酸液破胶困难,且残酸中含有残渣不溶物,对低渗透油气储层伤害严重。为此,在室内合成了一种黏弹性表面活性剂JX,利用该表面活性剂配制了新型的黏弹性表面活性变黏酸VDA—JX,并对其进行了性能评价。室内研究结果表明：该酸液体系黏度随酸浓度的增加先增大后减小,当酸浓度在13％左右时黏度出现最大值,可以达到350mPa·s,能够满足酸化过程中的抗温和抗剪切性能,破胶时间短,易返排,且破胶后与煤油分层,不污染油层。     

Searching speeds and the energetic feasibility of an obligate whale-scavenging fish

Two recently published models reach opposite conclusions on the energetic feasibility of a scavenging fish that specialises on whale carcasses. We argue that the key difference between these models lies in their estimate of the likely searching speed of such a hypothetical scavenger. Neither of the previous models considers that although faster searching will allow food sites to be found more quickly, it will also reduce the time between meals that the fish can survive on its reserves. Hence, we present a novel model that encapsulates this trade-off, and use this model to predict the optimal searching speed for such a hypothetical scavenger. The model predicts that the optimal speed should increase with mass and be in the range 0.1–0.2 m s⁻¹ for fish of the range of sizes found for the ubiquitous grenadier Coryphaenoides armatus. These values accord with most estimates of the swimming speeds for this species. Hence, we conclude that rejection of a whale-carcass feeding specialist fish on energetic grounds is premature. Although, we see no reason to dismiss such a specialist on energetic grounds, we argue that such a fish will be unlikely on ecological grounds, although a deep-sea fish that gathered much of its energy from scavenging at relatively large food packages on the ocean floor should be feasible.     

Modeling and identification of open-frame variable configurationunmanned underwater vehicles

A lumped parameter model of open-frame unmanned underwater vehicles (UUV's) including the effects of propeller-hull and propeller-propeller interactions is presented. The identification of the model parameters consists of a least squares method using only on-board sensor data without requiring any towing tank tests. The identification scheme is based on separate tests for the estimation of drag and thruster installation coefficients, taking into account propeller-hull and propeller-propeller effects first and inertia parameters subsequently. The scheme has been experimentally implemented on ROMEO, the latest UUV developed by CNR-IAN. Experimental results show both the effectiveness of the proposed method and the relevance of the propeller-hull and propeller-propeller interactions that are usually neglected in standard UUV models     

EDTA对罗非鱼嗅觉的影响及其解毒作用

将５种浓度的ＥＤＴＡ和９种含有不同比例的重金属离子、ＥＤＴＡ混合液分别灌注罗非鱼嗅囊,观测这些溶液中甲硫氨酸引起的嗅电图的影响,研究ＥＤＴＡ对重金属染毒钱瓣可行性和最佳配方,并探讨了其可能机理,结果如下：（１）ＥＤＴＡ对ＥＯＧ有抑制和促进两方面影响。当浓度低于３７２ｍｇ／ｄｍ＾３时,ＥＤＴＡ抑制ＥＯＧ反应、浓度越低,抑制作用越明显。当浓度大于３７２ｍｇ／ｄｍ＾３时,则促进ＥＯＧ反应,浓度越高,促进     

Nitrogen isotopic composition of sinking particles from the southern Bay of Bengal: Evidence for variable nitrogen sources

An 8-year record of N fluxes and δ¹⁵N of sinking particles from the deep southern Bay of Bengal, northern Indian Ocean, is presented. Fluxes and δ¹⁵N vary between ∼0.1 and 3 mg m⁻² day⁻¹ and ∼2‰ and 8‰, respectively. The seasonal variation is determined mainly by oceanographic processes coupled to the Indian monsoon system. The annual pattern of δ¹⁵N is characterized by minima during spring intermonsoon (∼March–May), when nutrient inputs to the euphotic zone should be low because of stratification, and lighter nitrate/particulate matter is expected to be advected from the central Bay. Highest δ¹⁵N are associated with peak fluxes during southwest monsoon (∼June–September), when the southern Bay comes under the influence of the SW monsoon current, which appears to advect particulate matter with distinctly higher δ¹⁵N. The impact of this process, however, varies interannually under the influence of factors such as ENSO and the Indian Dipole Mode. Weakened advection leads to relatively low N fluxes and reduced δ¹⁵N. The data highlight the necessity of multi-annual studies to comprehend the natural variability of a system.     

Weakly non-linear free oscillations in a basin of variable depth

Weakly non-linear free oscillations in a basin of variable depth filled with non-viscous fluid are investigated in terms of the long waves theory using the perturbation technique. Solutions to the initial two approximations for the horizontal velocity component and free surface departure are numerically derived. An attempt is made to determine the area of applicability of the linear theory by applying a parabolic bottom profile to the basin.Translated by V. Puchkin.