Comparison of flow patterns in the near wake of a circular cylinder and a square cylinder placed near a plane wall

The flow patterns in the near wake of a cylinder (either circular or square in shape, D=25 mm) placed in the proximity of a fully developed turbulent boundary layer (thickness δ=0.4D) are investigated experimentally using particle image velocimetry (PIV). The effects of changing the gap height (S) between the cylinder bottom and the wall surface, over the gap ratio range S/D=0.1–1.0, have been investigated. The results show that both the ensemble-averaged and instantaneous flow fields are strongly dependent on S/D. The flow patterns for the two types of cylinders share many similarities with respect to the change in S/D, such as the reduced recirculation length and increased velocity fluctuation in the near wake with increasing S/D, as well as the trend of suppression of vortex shedding at small S/D and onset of vortex shedding at large S/D. However, developments of the shear layers, in terms of wake width, flow curvature, etc., are considerably different for these two types of cylinders. In general, the wake development and momentum exchange for the square cylinder are slower those for the circular cylinder at the same gap ratio. Correspondingly, it is shown that the periodic vortex shedding is delayed and weakened in the case of square cylinder, as compared to that of the circular cylinder at the same S/D.     

Wind impact on pollutant transport in a shallow estuary

A three-dimensional numerical model, EFDC （ environmental fluid dynamics code） is applied to the Pamlico River Estuary （PRE） in eastern North Carolina of the United States to examine the wind impact on pollutant age distributions and residence time. A series of model experiments representing base case, remote-wind-induced water level set-up and local winds cases are conducted. Model results indicate that the pollutant mean age and the system residence time are functions of gravitational circulation in the PRE. The system responses to remote-wind-induced water level set-up are different in different portions of the PRE. Under such condition, dissolved substances in the upstream portion of the PRE have a younger age and shorter residence time （compared with the base case） , by contrast, they have a older age and longer residence time in the downstream portion of the PRE. Upriver and downriver local winds appear to have opposite impacts on pollutant age distributions. The substances are retained much longer within the PRE under upriver wind than those under downriver wind. The model results also suggest that across - river winds may lead to longer residence time through enhanced turbulence mixing, which slows down the gravitational circulation in the PRE.     

Statistical analysis and forecasts of long-term sandbank evolution at Great Yarmouth, UK

A data-driven model has been developed to analyse the long-term evolution of a sandbank system and to make ensemble predictions in a period of 8 years. The method uses a combination of empirical orthogonal function (EOF) analysis, (to define spatial and temporal patterns of variability), jack-knife resampling, (to generate an ensemble of EOFs), a causal auto-regression technique, (to extrapolate the temporal eigenfunctions), and straightforward statistical analysis of the resulting ensemble of predictions to determine a ‘forecast’ and associated uncertainty. The methodology has been applied to a very demanding site which includes a curved shoreline and a group of mobile nearshore sandbanks. The site is on the eastern coast of the UK and includes the Great Yarmouth sandbanks and neighbouring shoreline. A sequence of 33 high quality historical survey charts reaching back to 1848 have been used to analyse the patterns and to predict morphological evolution of the sandbank system. The forecasts demonstrate an improved skill relative to an assumption of persistence, but suffer in locations where there are propagating features in the morphology that are not well-described by EOFs.     

Changes in the abundance and composition of picophytoplankton in relation to the occurrence of a Kyucho and a bottom intrusion in the Bungo Channel,Japan

The Bungo Channel in southwestern Japan receives both warm, called Kyucho, and cold deep-water intrusions (bottom intrusion) from the Pacific Ocean. Abundances of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton were monitored from 18 July to 17 August 2001 to clarify whether advected picophytoplankton from the Pacific Ocean can grow in the channel or not. Synechococcus cells were further discriminated into low- and high-PUB types according to their fluorescence property in flow cytometry. From 18 to 25 July, the water temperature decreased by 3 °C at a 5-m depth at all stations, indicating the occurrence of a bottom intrusion. From 25 July to 4 August, a Kyucho occurred and the water temperature rapidly increased. From 4 to 17 August, a bottom intrusion and a Kyucho both occurred twice, although the intensities were smaller than those occurring until 4 August. From 18 to 30 July, the abundance of both Prochlorococcus and a high-PUB type of Synechococcus drastically decreased because of a bottom intrusion; however, the abundances rapidly increased due to the advection by a Kyucho. These advected cells increased from 4 to 17 August in the channel and Kitanada Bay. Changes in the abundance of low-PUB type of Synechococcus and eukaryotic picophytoplankton were less noticeable than those in the abundance of Prochlorococcus and high-PUB type. The present study demonstrated that oceanic picophytoplankton advected by the Kyucho could grow in the channel. However, abundances of low-PUB type and eukaryotic picophytoplankton increased higher than those of Prochlorococcus and high-PUB type did. Thus, these oceanic phytoplankters will be excluded when Kyucho does not occur for a long time. The co-occurrence of various types of picophytoplankton found in the channel is probably achieved by both Kyucho event and their growth capability in the channel.     

Compliance costs and the small fisher: A study of exiters from the New Zealand fishery

Over 3000 predominantly small-scale fishers have exited the New Zealand's quota management system (QMS) between its inception in 1986 and 2000. This study, based on the Ministry of Fisheries database and a questionnaire sent to the exiters, establishes that compliance costs in general, and those specifically related to the QMS, were one of the most consistent reasons for exit. Uncertainty about future QMS policy and the high cost of quota were also significant factors. It appears that the small fishers’ perception of high compliance cost can be supported by industry data.     

Hill Instability Analysis of TLP Tether Subjected to Combined Platform Surge and Heave Motions

This paper presents the Hill instability analysis of Tension keg Platform （TLP） tether in deep sea. The 2-D nonlinear beanl model, which is undergoing coupled axial and transverse vibrations, is applied. The governing equations are reduced to nonlinear Hill equation by use of the Galerkin＇ s method and the modes superposition principle. The Hill instability charted up to large parameters is obtained. An important parameter M is defined and can be expressed as the functions of tether length, the platform surge and heave motion amplitudes. Some example studies are performed for various envirotnnental conditions. The results demonstrate that the nonlinear coupling between the axial and transverse vibrations has a significant effect on the response of structure. It needs to be considered for the accurate dynamic analysis of long TI2 tether subjected to the combined platfolna surge and heave motions.     

Dissolved inorganic carbon (DIC) and its carbon isotopic composition in sediment pore waters from the Shenhu area,northern South China Sea

The Shenhu area is one of the most favorable places for the occurrence of gas hydrates in the northern continental slope of the South China Sea. Pore water samples were collected in two piston cores (SH-A and SH-B) from this area, and the concentrations of sulfate and dissolved inorganic carbon (DIC) and its carbon isotopic composition were measured. The data revealed large DIC variations and very negative δ ¹³C-DIC values. Two reaction zones, 0–3 mbsf and below 3 mbsf, are identified in the sediment system. At site SH-A, the upper zone (0–3 mbsf) shows relatively constant sulfate and DIC concentrations and δ ¹³C-DIC values, possibly due to bioturbation and fluid advection. The lower zone (below 3 mbsf) displays good linear gradients for sulfate and DIC concentrations, and δ ¹³C-DIC values. At site SH-B, both zones show linear gradients, but the decreasing gradients for δ ¹³C-DIC and SO₄ ²⁻ in the lower zone below 3 mbsf are greater than those from the upper zone, 0–3 mbsf. The calculated sulfate-methane interface (SMI) depths of the two cores are 10.0 m and 11.1 m, respectively. The depth profiles of both DIC and δ ¹³C-DIC showed similar characteristics as those in other gas hydrate locations in the world oceans, such as the Blake Ridge. Overall, our results indicate an anaerobic methane oxidation (AMO) process in the sediments with large methane flux from depth in the studied area, which might be linked to the formation of gas hydrates in this area.     

Factors controlling dissolved silica in coral reef surface water of Urasoko Bay, Ishigaki Island, Japan

From August 2006 to August 2007, the concentrations of dissolved silica (Si(OH)₄) were monitored in the surface water of Urasoko Bay and the mouth of the stream that runs into the bay. Urasoko Bay is located on the northern coast of Ishigaki Island, Okinawa, Japan, which is in a subtropical area of the North Pacific Ocean and is surrounded by a relatively poorly developed fringing reef. Added to these samples were freshwater from the upstream area and brackish water that exudes at the beach site, which were collected from April to June 2007. Rainwater samples were also collected during the study period. The concentration of Si(OH)₄ generally decreased from upstream to the bay site, and, on clear days, Si(OH)₄ data from all study sites (the bay, beach, stream mouth, and upstream) plotted against salinity fell on a single straight line. When the influence of rainwater was, the results were scattered below the straight line, which suggests dilution by rainwater with a much lower Si(OH)₄ concentration. These findings show that offshore seawater, rainwater, and upstream freshwater regulate the concentration of Si(OH)₄ in the surface water of Urasoko Bay.     

Discrimination of spurious self-correlation in nondimensionalized analyses of fluid dynamical data

Nondimensionalization of variables enables us to treat experiment data much more simply and efficiently by decreasing the number of variables. In some cases, trivial conclusions (which Kenney, 1982, called spurious self-correlation) result from a formal application of dimensional analyses. In contrast, in some cases fully significant conclusions can be derived. We first discuss how to construct nondimensional variables retaining the physical meanings of variables. We then propose simple and efficient methods, especially the use of “spurious triangle (SpT)”, to discriminate between significant conclusions and spurious self-correlations in the analysis of nondimensionalized variables.     

军曹鱼染色体组型分析

为了解军曹鱼(Rachycentron canadum)的细胞遗传学特征,采用植物血球凝集素(PHA)、秋水仙碱胸腔注射,取头肾细胞经空气干燥法制片,分析了军曹鱼染色体核型。结果表明,军曹鱼核型为:2n=48=48t,染色体总臂数(NF)为48。