近壁圆柱绕流水动力特性数值模拟与实验研究

通过数值模拟和物理模型实验,对距壁面一定高度的圆柱绕流水动力特性进行了研究。数值模拟采用有限体积法对标准k-ε模式方程进行离散,采用SIMPLE算法进行求解,模拟绕流流场。在物理模型实验中,将PVC圆管制作的实验模型安放在水槽内,在圆管的跨中沿表面周向均匀布置水下压力传感器,用于测量绕流圆柱体表面动水压力分布。通过改变Re数和间隙比来分析它们对近壁圆柱绕流水动力特性的影响。基于数值流动显示技术,给出了近壁绕流流场的尾流流态分析。通过数值结果与实验结果的对比,对近壁绕流圆柱体的升力系数及其表面动水压力分布进行了研究,对比结果显示了较好的一致性。     

考虑自由面反射作用的圆柱流噪声计算

对于现代舰船而言噪声是其关键性能之一,目前水下航行体的流激噪声预测方法已经较为成熟,但是水面舰船的水动力噪声研究起步较晚,还没有形成系统的预报方法和控制手段。使用开源CFD工具包OpenFOAM求解器,流场通过大涡模拟方法求解,自由液面则依靠VOF方法捕捉,通过Curle方程预测远场噪声,基于镜像法考虑自由面的反射作用,数值模拟近自由面圆柱周围的声场分布。开展了Re=3 900下距离自由液面不同高度的圆柱辐射噪声求解,主要结合流场分析自由面对声场的扰动作用和不同深度对水下几何体流噪声的影响。初步考虑了自由液面波形对辐射噪声的反射作用,为后续预测水面舰船的水动力噪声特性提供依据,自由面对辐射噪声的阻抗等作用还需进一步研究。     

Terpenoid marker compounds derived from biogenic precursors in volcanic ash from Mount St. Helens,Washington

A volcanic-ash sample obtained after the 1980 eruption of Mount St. Helens, Washington, was analyzed for cyclic terpenoid organic compounds and polycyclic aromatic hydrocarbons using capillary gas chromatography-mass spectrometry-computer techniques. Various tricyclic diterpenoid acids and hydrocarbons were identified including dehydroabietic acid, dehydroabietin, dehydroabietane, simonellite, and retene. Preliminary evidence indicates that these compounds were derived from forest soils or atmospheric aerosols or both in the vicinity of coniferous forests. A diagenetic scheme involving three possible pathways for the conversion of abietic acid to retene is presented.     

用相对灰色关联分析法综合评价金刚石钻头

根据ＴＯＰＳＩＳ法原理，提出一种同时考虑“理想方案”和“负理想方案”的金刚石钻头综合评价灰色关联分析法，结合φ６０ｍｍ绳索取心金刚石钻头评价，说明了该方法的具体应用，并与用其它方法评价的结果进行了对比。     

Pollution studies on Tolo Harbour,Hong Kong

Eight stations were chosen for this 14 month survey of Tolo Harbour in Hong Kong, four of them in the harbour proper and four in the estuaries of the major streams entering the harbour. Various chemical and physical factors were measured twice each month. Water samples were collected for nutrient, phytoplankton, chlorophyll and bacteriological analysis.The annual discharge of nutrients from the four streams into Tolo Harbour has been estimated, based on the nutrient analyses and computation of annual discharge (QA) values for these streams. The seasonal and spatial variations in nutrient content are discussed in relation to the increasing organic pollution of Tolo Harbour. Calculations of various ratios between SiO₃, PO₄, NO₃ and total inorganic N reveal that excessive amounts of phosphate are entering the harbour and subsequently accumulating in the bottom waters and sediments, leading to changes in the trophic condition of this water body and the development of anoxic conditions in the bottom layer.Significant correlation has been demonstrated between standing crop and various environmental parameters in both estuarine and marine waters and similarly between chlorophyll a concentration and various environmental parameters. However, no significant correlation values were obtained between either standing crop or chlorophyll a concentrations, SiO₃Si (the latter presumably due to the predominance of diatoms in the phytoplankton). Neither standing crop nor chlorophyll determinations reveal any evidence of alternating periods of high productivity and decomposition which could explain the deteriorating bottom water conditions. This again is taken as evidence that the high organic inputs are responsible for such deterioration.Increasing TC, FC and FS densities have been noted in Tolo Harbour as a direct result of the increasing organic pollution and ratios between FC and FS densities indicate that in 55% of the samples pollution was derived from human sewage. The bacterial levels well exceeded various international standards for bathing waters and shellfish collection for at least a part of the survey period and at a number of stations for the entire survey period. Pathogenic organisms were also present. This underlines the potential health risks in these waters.Finally, the future prospects for this harbour are discussed in relation to activities such as reclamation and the development of new towns and their impact on water quality.     

Wave Uplift Forces on the Bottom of a Circular Cylinder

The analysis of the data of model tests of two large deep wharves and monographic experimental studies show that two aspects are to be improved so as to predict the wave uplift forces on the bottom of a circular cylinder. The first aspect is the uplift pressure distribution on the bottom, and the second is the correct determination of the phase for maximum horizontal wave forces. The second problem has been solved. Synthesizing the results of theoretical analysis and experiments, we suggest a diagram for the determination of the phase when the maximum horizontal wave force appears. On the basis-ef the diagram the simultaneous wave uplift forces can be obtained for the structural stability analysis.     

Three-Dimensional Instability of Flow Around Two Circular Cylinders in Tandem Arrangement

The spatial evolution of vortices and transition to three-dimensionality in the wake of two circular cylinders in tandem arrangement have been numerically studied. An improved virtual body method developed from the virtual boundary method is used here. A Reynolds number range between 220 and 270 has been considered, and the spacing between two cylinders is selected as L/D = 3 and L/D = 3.5. When L/D = 3, the secondary vortices of Mode-A are seen to appear at Re = 240 and persist over the range of the Reynolds number of 240 - 270. When L/D = 3.5, the similar critical Reynolds number has been found at Re = 250. No obvious discontinuity has been found in the Strouhal-Reynolds number relationship, and this is different from three-dimensional flow around a single cylinder at the critical Reynolds number. The spanwise wavelength is about four times the diameter of the cylinder, and it is the characteristic wavelength for ModeA instability. This paper can give some foremost insight into the three-dimensional instability of flow by complicated geometrical configuration.     

The fate of polyaromatic hydrocarbons in an intertidal sediment exposure system: Bioavailability to macoma inquinata (mollusca: Pelecypoda) and abarenicola pacifica (annelida: Polychaeta)

Macoma inquinata, a detritus feeding clam, was exposed for 60 days to coarse-grained, and Abarenicola pacifica, a burrowing polychaete, to fine-grained, sediment. Each sediment contained ¹⁴-C-labelled phenanthrene, chrysene or benzo(a)pyrene. Over 70% of the chrysene and benzo(a)pyrene, but only 8% of the phenanthrene, remained in the coarse sediment during the exposure. Essentially all of the chrysene and benzo(a)pyrene and 70% of the phenanthrene remained in the fine sediment. The concentrations of chrysene and benzo(a)pyrene in the clams rose steadily, reaching levels 11·6 and 5·2 times as high as those in the sediment. The tissue phenanthrene concentration rose for 3 days, then fell to one-eighth of the initial concentration. The concentrations of each of the aromatic hydrocarbons in Abarenicola tissue increased for 2 weeks to four to six times the sediment levels. The tissue concentration of chrysene remained constant thereafter, but the levels of phenanthrene and benzo(a)pyrene fell to three-quarters of their peak values. No intermediate degradation products of any of the hydrocarbons were identified in extracts of sediment from either exposure system, or in solvent extracts of tissue or of tissue digestates.Significant ¹⁴C-activity, associated with non-solvent extractable compounds, remained in tissue digestates of individuals of both species exposed to phenanthrene.     

Analytical and experimental investigation on transverse vibrations of solid, circular and annular plates carrying a concentrated mass at an arbitrary position with marine applications

This investigation arose from the practical necessity of placing a centrifugal pump rigidly attached to a thin, circular cover plate of a water tank in a medium size ocean vessel. Due to lack of space, it was necessary to locate the system off—center of the circular configuration. It was considered necessary to calculate the fundamental frequency of the coupled system.The first part of the present study is concerned with the determination of the fundamental frequency of vibration of a circular plate carrying a concentrated mass at an arbitrary position, using a variational approach.Numerical results are obtained for the stated problem for several combinations of the intervening geometric and mechanical parameters.An experimental investigation is also performed in the case of clamped plates.Based on the results for solid circular plates, the fundamental frequency of annular plates with a free inner edge and a concentrated mass is also obtained.Circular plates are fundamental structural elements in ocean engineering applications: from off-shore platforms to underwater acoustic transducers. In a great variety of circumstances, they must carry operational systems in an eccentric fashion. Since the dynamic performance is always of interest, one must know at least some of the basic dynamic parameters.