科考船多波束导流罩优化设计

针对已建成科考船加装中水多波束的实际技术需求,结合中水多波束加装科考船的船舶线型及其系统安装要求,通过设计两种不同类型的导流罩线型,并与船体线型一体化进行计算流体动力学(Computational Fluid Dynamics,以下简称CFD)仿真分析,了解实船舶航行过程中船体型线和导流罩型线之间的相互影响,分别对圆弧型导流罩和折角型导流罩的防气泡性能和阻力性能进行了CFD预报和分析。最后经海试验证折角型导流罩能够完全满足中水多波束的安装线型流线及湍流动能的性能指标,为科考船多波束导流罩的设计安装或加装提供一定的借鉴和参考作用。     

Effect of upward internal flow on dynamics of riser model subject to shear current

Numerical study about vortex-induced vibration(VIV) related to a flexible riser model in consideration of internal flow progressing inside has been performed.The main objective of this work is to investigate the coupled fluid-structure interaction(FSI) taking place between tensioned riser model,external shear current and upward-progressing internal flow(from ocean bottom to surface).A CAE technology behind the current research which combines structural software with the CFD technology has been proposed.According to the result from dynamic analysis,it has been found that the existence of upward-progressing internal flow does play an important role in determining the vibration mode(/dominant frequency),vibration intensity and the magnitude of instantaneous vibration amplitude,when the velocity ratio of internal flow against external current is relatively high.As a rule,the larger the velocity of internal flow is,the more it contributes to the dynamic vibration response of the flexible riser model.In addition,multi-modal vibration phenomenon has been widely observed,for asymmetric curvature along the riser span emerges in the case of external shear current being imposed.     

10kW漂浮点吸收直线发电波力装置

点吸收式是目前世界上发展较多、转换效率较高的一种波浪能利用技术,介绍我国自主研发的一台10 kW漂浮点吸收波浪能直线发电装置。该装置主要由4 m直径蝶形振荡浮子、6 m直径水下阻尼板、1 t重直线发电机组成,整个装置漂浮在海面上,是一个钢结构体。装置外形为煤油灯形,采用共振聚波和阻尼匹配技术提高装置的转换效率,有效发电时间不受来波方向和潮位的影响,针对构成装置的不同材料采用不同的防腐技术提高装置的整体抗海水腐蚀能力,采用下潜方式躲避台风打击,采用蓄能技术提高锚泊系统抗走锚和断链能力。直线发电机是一个圆筒型结构体,具有较高的转换效率和防海水腐蚀能力。发电装置进行了实海况试验,为后续的研究工作提供了相关经验。     

多波束条带测深仪研究发展动态

多波束条带测深仪是一种近年发展起来的具有高测量效率、高测量精度、高分辨率的海洋海底地形测量设备,特别适合于大面积的扫海测绘作业。本文较详细地总结了这种水声测量仪器目前在国内、外研究发展的概况,并分析了其未来研究发展的可能方向     

Deriving regional vertical fluid migration rates offshore southwestern Taiwan using bottom-simulating reflectors

Fluid migration rates are important parameters for understanding the structural characteristics and evolution of the crustal tectonics and hydrocarbon exploration. However, they are difficult to measure on the seafloor. Densely sampled temperature measurements might shed light on our study of the fluid migration rates. In this study, we first use reflection seismic data to derive geothermal gradient patterns at different sub-seafloor depths, then calculated 1D vertical fluid flow models by analyzing the Péclet numbers in the offshore regions of SW Taiwan. We found Péclet numbers ranging from 2 to 5, implying that vertical fluid flow velocities are between 6 and 44 cm/year. Assumed a homogenous permeable layer and no lateral variation of the temperature fields, we analyzed possible errors caused by depth-dependent thermal conductivity and velocity-depth function. They probably cause less than 2 cm/year of errors in the estimated vertical fluid flow rate. In terms of regional fluid flow patterns, we found higher fluid flow rates near the toe of the trench, and a dramatic increase in fluid flow rate when the continental slope of the Chinese passive margin enters into the trench, and reduced fluid flow rates in the hinterland. We propose that this is a new and potentially useful method to derive regional fluid flow rate models for studying geochemical and biological processes in shallow seafloor sediments and the regional hydrological budget.     

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.     

<Superscript>234</Superscript>Th/<Superscript>238</Superscript>U disequilibrium and particulate organic carbon export in the northern South China Sea

We utilized ²³⁴Th, a naturally occurring radionuclide, to quantify the particulate organic carbon (POC) export rates in the northern South China Sea (SCS) based on data collected in July 2000 (summer), May 2001 (spring) and November 2002 (autumn). Th-234 deficit was enhanced with depth in the euphotic zone, reaching a subsurface maximum at the Chl-a maximum in most cases, as commonly observed in many oceanic regimes. Th-234 was in general in equilibrium with ²³⁸U at a depth of ∼100 m, the bottom of the euphotic zone. In this study the ²³⁴Th deficit appeared to be less significant in November than in July and May. A surface excess of ²³⁴Th relative to ²³⁸U was found in the summer over the shelf of the northern SCS, most likely due to the accumulation of suspended particles entrapped by a salinity front. Comparison of the ²³⁴Th fluxes from the upper 10 m water column between 2-D and traditional 1-D models revealed agreement within the errors of estimation, suggesting the applicability of the 1-D model to this particular shelf region. 1-D model-based ²³⁴Th fluxes were converted to POC export rates using the ratios of bottle POC to ²³⁴Th. The values ranged from 5.3 to 26.6 mmol C m⁻²d⁻¹ and were slightly higher than those in the southern SCS and other oligotrophic areas. POC export overall showed larger values in spring and summer than in autumn, the seasonality of which was, however, not significant. The highest POC export rate (26.6 mmol C m⁻²d⁻¹) appeared at the shelf break in spring (May), when Chl-a increased and the community structure changed from pico-phytoplankton (<2 μm) dominated to nano-phytoplankton (2–20 μm) and micro-phytoplankton (20–200 μm) dominated.     

The role of horizontal impulses of the faulting continental slope in generating the 26 December 2004 tsunami

For a long time, people have believed that the vertical displacement of seafloor due to undersea earthquakes is the primary cause of tsunami genesis. However, seismically-inverted seafloor deformation of the 2004 Sumatra–Andaman earthquake shows that the total vertical displacement is not enough to have generated the powerful Indian Ocean tsunami. Based on the seismically-inverted data and a three-dimensional ocean general circulation model (OGCM), we show that the momentum force, transferred by the horizontal impulses of the faulting continental slope in that earthquake, has accounted for two thirds of the satellite-observed tsunami height and generated kinetic energy 5 times larger than the potential energy due to the vertical displacement. The asymmetric tsunami pattern, recorded by tide-gauges showing leading-elevation waves toward Sri Lanka and leading-depression waves toward Thailand, is best explained by the horizontally-forced mechanism. The same mechanism has also explained the March 2005 Nias earthquake and tsunami data, suggesting that the horizontal motions of faulting have played more important roles in tsunami genesis than previously thought.     

Vision-based tracking with projective mapping for parameter identification of remotely operated vehicles

Parameter identification of a remotely operated vehicle (ROV) is often based on the dynamic responses collected by its onboard sensors. However, for commercial ROVs, the required data for identification may not be available due to the absence of suitable sensors or limitations in accessing onboard sensor data. Therefore, this study proposes a vision-based tracking system to measure the dynamic response of an ROV. The tracking system is independent of the ROV, and is able to localize an ROV to a high degree of precision by means of projective mapping. The validity of the proposed tracking system is demonstrated through identification of a commercial ROV. A simplified nonlinear ROV dynamic model with six degrees of freedom (DOF) is used for identification. Uncoupled motions, including surge, sway, and yaw, are obtained from the ROV dynamic model, and the corresponding experiments are carried out for each DOF. Hydrodynamic parameters are then estimated with numerical optimizations by comparing the measured ROV responses with the output of the mathematical model. The experimental results show that the vision-based tracking system can accurately measure the transient and steady-state responses of an ROV. Additionally, the simulations of the ROV dynamic model, with the optimal parameter estimates, give results in agreement with the measured data.     

The penetration experiment to predict liquefaction resistance of reclaimed soils

The liquefaction resistance of the soils used to be estimated through the in situ tests, such as standard penetration test and cone penetration test; or by means of cyclic triaxial test in laboratory. However, both in situ tests and cyclic triaxial test are time-consuming and costly; this study introduces a quick and cost-effective method to evaluate the liquefaction resistance of soils under certain confining pressure in laboratory. A particular device modified from the conventional triaxial compression test apparatus, namely “Triaxial Cone Penetration Test”, was developed to obtain the peak values of cone resistance in soils so as to correlate the liquefaction resistance of the reclaimed soils evaluated by cyclic triaxial tests. The test result indicates a good correlation between the peak value of cone resistance and the corresponding cyclic stress ratio (CSR) at the state of initial liquefaction, in which the correlation for loose samples is better than that for dense samples. Besides, both peak values of cone resistance and corresponding CSR increase with fine content of soils reaches 10% and decreased with fine content varying between 10% and 50%. By examining the compositions of the soils with scanning electron microscopy and X-ray diffraction, it is found that the proportion and characteristics of the fines plays an important role on the liquefaction resistance of the reclaimed soils.