潜艇指挥台围壳对阻力和伴流场影响数值研究

采用Reynolds平均Navier-Stokes(RANS)方法计算潜艇三维粘性流场,分析潜艇指挥台围壳对潜艇水动力性能的影响.采用全附体SUBOFF模型验证了CFD方法,通过将螺旋桨盘面处的实效伴流场、艇体表面压力分布以及模型总阻力的模拟结果与Taylor船池的实验结果进行对比.比较结果显示CFD计算结果与实验数据具有很好的一致性,表明CFD方法可以用于潜艇指挥台围壳设计的水动力计算.通过数值计算研究指挥台围壳的高度和在艇上的分布位置对其后方的流场、螺旋桨盘面处的伴流场和阻力的影响.     

超大型浮体水弹性分析的平板格林函数法

采用Eatock Taylor ＆ Ohkusu提出的一种矩形平板的挠度格林函数进行超大型浮式结构物在波浪中的水弹性响应分析，计算结果与试验结果比较，相当吻合，证实此平板挠度格林函数可以用于超大型浮式结构物的水弹性分析。     

一种基于状态空间模型的浮式海上升压站平台动力响应计算方法研究

浮式海上升压站的动力响应分析是其设计阶段的重要内容,对浮式升压站进行结构优化进而改进其水动力性能意义重大。提出一种基于状态空间模型的浮式海上升压站平台动力响应算法,该方法通过频域拟合的方法计算延迟函数频响函数有理分式的系数,得到延迟函数的极值和留数,进而构建延迟函数的状态空间模型,通过状态空间模型代替Cummins方程中的卷积项,从而计算浮式海上升压站的动力响应。采用日本福岛示范项目的浮式升压站模型对方法进行验证,结果表明计算得到的动力响应与商业软件SESAM计算结果吻合较好,说明方法的有效性。     

远海浮式结构物与供应船旁靠系泊特性研究

针对远海浮式结构物与供应船进行旁靠作业时,水动力干扰、两船的相对运动、旁靠系缆系统和护舷系统的受力特征等问题开展研究。建立各船的有限元模型,设计出两船旁靠连接缆系统,选取合适的系泊缆和护舷参数。研究表明:浮式结构物和供应船的横荡、纵荡方向存在一定的同步性或跟随性,幅值相差不大,其它方向的运动并不存在明显的同步特征;供应船的各自由度运动幅值均比浮式结构物偏大;旁靠护舷的受力时历出现了明显的低频效应,说明护舷的受力较大程度上受船体低频慢漂运动的影响;浮式结构物对供应船的水动力干扰较大,当浮式结构物在供应船的上风位置时,表现为屏蔽效应,供应船的运动较小;在其背风位置时,运动加剧,出现多次共振、峰值放大现象,供应船对浮式结构物的水动力性能几乎无影响,因此,供应船从浮式结构物的下风口一侧靠泊作业将更有利于船舶的安全性能。这些研究结论可为实际工程操作提供参考。     

水平轴潮流能水力涡轮数值模拟与试验研究

首先,使用叶素动量理论对所设计的室内试验用小型水平轴潮流能水力涡轮叶片模型进行初步计算,获得其性能参数,此后借助NUMECA软件,采用三维计算流体动力学(CFD)方法对水平轴水力涡轮进行三维水动力分析,得到其性能曲线,最后通过试验水槽进行模型试验,对BEM计算结果和CFD计算结果进行验证,结果表明:叶素动量理论和CFD方法均能对水力涡轮性能进行有效预测,且CFD方法具有更高的精度;此外,根据CFD方法得到叶片表明的压力分布,根据空化条件可知,该水力涡轮会发生空化。     

波浪作用下锚链系泊浮式防波堤动力响应的数值模型研究

浮式防波堤充分利用波能在水深方向的分布特性,在满足工程消浪要求的同时对海域水沙交换影响较小,且能够快速布置,在某些实际工程有一定应用前景。为了深入了解波浪作用下浮式防波堤的动力响应,基于OpenFOAM标准求解器olaFlow,在刚体运动求解计算中植入锚链求解模块MOODY(mooring cable dynamics),实现了基于重叠网格方法的浮体运动与锚链受力耦合求解,建立了锚链系泊浮式防波堤动力响应的二维数值模型。利用该数值模型对锚链系泊单方箱浮式防波堤在波浪作用下的透射系数、运动响应、锚链张力进行了模拟,并和相关试验结果进行了比较。结果表明,模型能够准确模拟二维波浪和浮式防波堤的相互作用,并用于三维模型的改进。     

不同曲率球面体入水砰击载荷数值计算

从三维边界元方法出发,基于Wagner的自由液面抬升理论,采用数值仿真的方法研究了圆球入水的问题。通过数值模拟与轴对称体入水试验结果的正确性及适用性进行验证的基础上,并分析了不同半径的球体在不同速度下的入水总体受力和表面压力的变化规律。计算结果表明随着球体半径和入水速度的增加,峰值压力迅速增加,受力峰值与球体半径的平方和入水速度平方成正比关系;球体表面压力系数的分布计算结果表明,在测试点与水开始接触时压力系数最大,然后迅速减小;压力系数和入水速度无关,但和入水深度相关。     

箱形船在波浪上运动的工程计算方法

箱形船是海洋工程结构物的基本结构形式之一。本文采用纵横切片的思想,对长宽比接近于1的箱形船在波浪上的运动特性,提出了一种工程估算方法。剖面的二维水动力系数由源汇分布法求取。尽管纵横切片法在理论上不甚严密,但可获得与试验以至三维理论计算相当一致的结果。本方法可进行箱形船六个自由度的运动计算,计算时间远低于三维方法,在工程上有实际应用的价值。作为校核,将本方法的计算结果与前人的试验及三维理论计算结果作了比较,吻合程度是令人满意的。     

小型自主水下航行器尾舵设计与研究

针对小型自主水下航行器(AUV)尾舵设计的关键问题,采用二维计算流体力学(CFD)方法模拟了流速为2m/s时.常用NACA00××系列翼型在不同来流下的情况,得到了小型自主水下航行器常用翼型的水动力特性;采用DNV规范计算得到了尾舵面积的大小;采用三维CFD方法研究了舵轴位于不同位置时的铰链力矩.找到了具有最小铰链力矩的舵轴位置.文中的研究结果为小型水下自航行器尾舵的设计提供了理论依据和参考.     

三维复杂结构Spar平台垂荡板垂荡水动力性能研究

对三维复杂结构Spar平台垂荡板进行垂荡运动的数值模拟,并对垂荡板附近流场及水动力系数进行对比分析。结果表明:在主板尺寸相同情况下,主板边缘附近较小的角钢结构会对垂荡板流场产生明显影响,并导致水动力性能的较大差距;水动力系数计算结果与流场分析的结论一致。虽然复杂板架结构的三维建模及网格划分难度很大,但是在Spar平台垂荡板工程设计中不能完全采用简化光滑平板代替真实、复杂结构形式的垂荡板进行水动力性能的计算。     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.     

INFORMATION FOR AUTHORS

<正>Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.The journal publishes scholarly papers on marine science and technology,including physics,chemistry,biology,     

Evaluation of the Risk of Marine Slope Instability: A Pseudo-3D Approach for Application to Large Areas

This article presents a methodology developed to evaluate the instability of submarine slopes that extend over a large area. Special attention was paid to (1) the complex geometry (bathymetry) and the expanse of the slope, (2) the heterogeneity of the sediment, and (3) the distribution of the pore pressure. The safety factor was considered as a spatially varying quantity. The General Formulation (GLE, Fredlund and Krahn 1977), which fully satisfies equilibrium conditions, was used for evaluating the stability of the marine slope. The submarine slope failure, which occurred on 16 October 1979 during the construction of the new Nice airport, was studied in order to test the developed model. Geotechnical parameters were taken from experimental tests carried out by IFREMER on 19 cores extracted at different depths (from 27 m to 1300 m) (Cochonat, Bourillet, and Savoye, 1993; Mulder et al., 1994). Many scenarios were proposed in order to explain the cause of the Nice slope failure (Habib, 1994). In this article, two of those scenarios were tested. Simulation results are presented and discussed.