Experimental investigation on a two-part underwater towed system

An experimental set-up is developed and proved to be effective for laboratory study of an underwater towed system. The experimental technique gives a practical method for monitoring the kinematic and dynamic performance of an underwater towed system in a ship towing tank. Both the theoretical and experimental results in the investigation indicate that the hydrodynamic response of a towed vehicle to the wave induced motion of a towing ship can be significantly reduced by applying a two-part tow method. A comparison of the numerical and experimental results in the investigation demonstrates that the numerical simulation results are close to the experimental data, overall agreement between experimental and theoretical results is satisfactory. The results qualitatively verify the mathematical model of a two-part underwater towed system proposed by Wu and Chwang [Wu, J., Chwang, A.T., 2000. A hydrodynamic model of a two-part underwater towed system. Ocean Engineering 27 (5), 455–472].     

黄、东海陆架2011年秋季活体浮游有孔虫生态分布

现代活体浮游有孔虫的生态研究是其古环境重建应用的重要基础。根据黄、东海陆架2011年秋季采集的20个垂直浮游拖网样品,分析了该海域浮游有孔虫的秋季生态分布特征。结果表明,黄海秋季基本上没有浮游有孔虫的出现。东海共发现13种活体浮游有孔虫,主要优势属种依次为Globigerinoides sacculifer、Pulleniatina obliquiloculata、Globigerina bulloides、Neogloboquadrina dutertrei和Globigerinoides ruber。浮游有孔虫丰度整体上呈现东南高,西北低的分布格局,这种分布格局反映了浮游有孔虫在黄、东海陆架区的分布主要受外海水影响强弱控制。浮游有孔虫主要属种在东海陆架呈现明显的区域分布差异:暖水种G. sacculifer是秋季陆架海区的主要优势种,其分布格局与总丰度基本一致,相对含量从南至北、从东至西逐渐降低,主要受区域表层海水温度变化的控制。G. bulloides与G. sacculifer呈相反的含量分布变化,其高含量主要出现在东海中陆架,从北往南逐渐降低,此外,在闽浙沿岸也有较高含量,表明了温度和生产力是影响G. bulloides在黄、东海陆架分布的主要因素。秋季P. obliquiloculata和N. dutertrei的高含量主要出现在东海南部中陆架区和济州岛西南黄海暖流影响区,可能受暖水与生产力的共同制约。     

A hydrodynamic model of a two-part underwater towed system

A three-dimensional model of a two-part underwater towed system is studied. In the model, the governing equations of cables are established based on the Ablow and Schechter method. The boundary conditions for the two-part underwater towed system are derived. The six-degrees-of-freedom equations of motion for submarine simulations are adopted to predict the hydrodynamic performance of a towed vehicle. The established governing equations for the system are then solved using a central finite difference method. In this paper several algorithms are used to solve this special form of finite difference equations. The results in this paper indicate that the two-part underwater towed system improves the dynamic behavior of the towed vehicle and is an easy way to decouple the towing ship motion from the towed vehicle. Because the model uses an implicit time integration, it is stable for large time steps and is an effective algorithm for simulation of a large-scale underwater towed system.     

浅海底瞬变电磁探测技术研究新进展

瞬变电磁法应用于浅海底进行资源勘探或工程地质勘查时,需要将仪器系统和观测装置置于海底,以克服海水屏蔽效应。因此,要求能够远程控制仪器进行自动化数据采集;同时,受工作环境影响,需要将观测装置小型化;另外,通过拖曳式测量提高工作效率。总结课题组目前的研究成果,就仪器系统研制、观测装置小型化、拖曳式测量及海水影响等内容的研究进展进行了简要叙述。     

Methane,carbon monoxide and methylchloroform in the southern hemisphere

New observational data on CH₄, CO and CH₃CCl₃ in the southern hemisphere are reported. The data are analysed for long term trends and seasonal cycles. CH₃CCl₃ data are used to scale the OH fields incorporated in a two dimensional model, which in turn, is used to constrain the magnitude of a global CH₄ source function. The possible causes of observed seasonality of CH₃CCl₃, CH₄ and CO are identified, and several other aspects of observed CH₄ variability are discussed.Possible future research directions are also given.     

Two types of marine controlled source electromagnetic transmitters

Marine controlled source electromagnetic methods are used to derive the electrical properties of a wide range of sub‐seafloor targets, including gas hydrate reservoirs. In most marine controlled source electromagnetic surveys, the deep‐tow transmitter is used with a long horizontal electric dipole being towed above the seafloor, which is capable of transmitting dipole moments in the order of up to several thousand ampere‐metres. The newly developed deployed transmitter uses two horizontal orthogonal electrical dipoles and can land on the seafloor. It can transmit higher frequency electromagnetic signals, can provide accurate transmission orientation, and can obtain higher signal stacking, which compensates for the shorter source dipole length. In this paper, we present the study, key technologies, and implementation details of two new marine controlled source electromagnetic transmitters (the deep‐tow transmitter and the deployed transmitter). We also present the results of a marine controlled source electromagnetic experiment conducted from April to May 2014 in the South China Sea using both the deep‐tow transmitter and the deployed transmitter, which show that the two types of marine transmitters can be used as effective source for gas hydrate exploration.     

南海北部秋季活体浮游有孔虫的组成与分布

对2004年9月采自南海北部海区19个站位40个垂直浮游拖网样品中的活体浮游有孔虫进行了定量分析, 探讨了该区秋季现代有孔虫的组成、分布及其影响因素.研究表明, 该区秋季现代浮游有孔虫以热带暖水群落为主, 呈现出明显的区域变化.浮游有孔虫的丰度主要呈西北高、东南低的分布格局.浅层水种G. sacculifer和G. ruber的高含量主要出现在近岸带; N. dutertrei的高含量主要出现在外陆架和陆坡区域; G. menardii的高含量主要出现在深水区域; G. calida和G. aequilateralis两水种的含量分布有明显的相似性, 主要出现在深水区, 在越南岸外站位其含量远高出区域其他站位.研究认为, 南海北部秋季水体浮游有孔虫的分布主要受初级生产力和水深的共同制约, 高初级生产力水平下浮游有孔虫的丰度明显要高, 水深则对中深层水种G. menardii、G. calida和G. aequilateralis的分布有明显的制约作用.南海北部秋季温跃层的温盐结构对中层水种N. dutertrei、G. glutinata、G. calida和G. aequilateralis的分布有一定的影响.此外, 暖涡水体对浮游有孔虫的丰度和组成也有明显影响, 位于暖涡中心区的浮游有孔虫丰度明显增高, 特征属种G. sacculifer的含量明显高出周边站位.P. obliquiloculata的高含量主要出现在东北部黑潮分支影响区.      

南海南部水体和沉积物中的浮游有孔虫氧碳同位素分析

通过对2002年南海南部春季水体和表层沉积物中浮游有孔虫的δ^18O和δ^13C分析，初步探讨该区有孔虫氧碳同位素的海洋环境指示意义及其与沉降过程的关系。结果表明，南海南部春季表层水体中Gltbigerinoides ruber （G．ruber）与Globigerinoides sacculifer（G．sacculifer）的δ^18O均值基本相似，相对它们在表层沉积物中的δ^18O明显要小；但在表层沉积物中G．ruber的δ^18O则比G．sacculifer相对要小0．34‰。这种差异可能与G．sacculifer的配子生殖二次钙化以及2个种属的季节性差异有关。Pulleniatinaobliquiloculata（P．obliquiloculata）的δ^18O在沉积物和水体中均较G．ruber和G．sacculifer明显偏大，表现出较大的种间差异。P．obliquiloculata的δ^18O在春季水体中比其在沉积物中平均约小0．7‰，差值较大，可能是因为P．obliquiloculata为冬季种，主要出现在冬季低温水体中。3种浮游有孔虫的δ^13C以G．sacculifer最大，G．ruber次之，P．obliquiloculata最低，这种差异可能主要由属种间的生命效应所引起。表层沉积物中G．ruber和G．sacculifer的δ^18O从区域的西北往东南有逐渐变小的趋势，可能受区域年均表层水温西北低东南高的影响。在上升流发育区，P．obliquiloculata的δ^18O和δ^13C均明显偏高，其δ^13C与水体营养的关系与南海北部的明显相反，有待进一步深入研究。     

Effects of diel period and tow duration on estuarine fauna sampled with a beam trawl over bare sediment: Consequences for designing more reliable and efficient surveys

The effects of diel period and tow duration (5, 10 and 20 min) on samples of estuarine fauna in a beam trawl, were tested over bare sediment in Tuggerah Lake (New South Wales, Australia). Mean catch rates (numbers of fish caught 5 min⁻¹) were significantly larger at night for the total numbers of individuals and abundant, economically important species of fish and invertebrates (e.g. Gerres subfasciatus, Metapenaeus macleayi, Penaeus plebejus). Greater proportions of larger fish were also caught at night for some species (e.g. G. subfasciatus, Acanthopagrus australis, Rhabdosargus sarba), but not across all tow durations. Multivariate analyses detected dissimilarities in the composition and structure of assemblages between diel periods, which were driven by species caught predominately, or in larger proportions, at night. Short tows (5 min) were more efficient than longer tows (10 or 20 min) for sampling the diversity of species (i.e. most species were caught in the first 5 min of a tow). There were, however, no clear or consistent patterns relating to the effect of tow duration on the catch rates of other variables, the size ranges of abundant species, or the structure and composition of assemblages. Our data confirm that at night, bare sediment is an important habitat for a wide size- and species-range of estuarine fish and invertebrates. In future, more cost-effective and reliable information concerning these taxa would be achieved by sampling with the beam trawl at night, using tow durations of 5 min. We also highlight a problem inherent in the design of many studies of diel variation of fauna (i.e. the potential non-independence of data among day and night periods) and discuss its solution.