The East Greenland Spill Jet as an important component of the Atlantic Meridional Overturning Circulation

The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean׳s role in climate.     

Reliability analysis of soil nail internal limit states using default FHWA load and resistance models

Abstract

Reliability analyses of nail pullout, nail-in-tension, and system reliability of internal limit states are presented for both permanent and temporary soil nails that are designed using default Federal Highway Administration nail load and resistance models within traditional deterministic allowable stress design (ASD) framework. The model uncertainty, correlations between soil strength parameters, between model factor, and nominal load term, and between the two internal limit states, and influence of model factor fittings are all addressed in the analyses. This study provides a general idea of the reliability that is implicitly embedded in current ASD-based soil nail internal limit state designs.     

An unusual nursing interaction between two adult Cape fur seals Arctocephalus pusillus pusillus

Given the high costs of lactation and the importance of milk for pup growth and survival in pinnipeds, nursing behaviour directed by a lactating female towards another adult is unexpected. Here, details were noted of a nursing interaction that occurred between two Cape fur seal Arctocephalus pusillus pusillus adults. After discussing the event in the light of various hypotheses that have been previously proposed to explain uncharacteristic nursing behaviour in pinnipeds, a mother–son relationship between the interacting pair was considered to be the most likely explanation.     

Higher Harmonics Induced by Waves Propagating over A Submerged Obstacle in the Presence of Uniform Current

To investigate higher harmonics induced by a submerged obstacle in the presence of uniform current, a 2D fully nonlinear numerical wave flume（NWF） is developed by use of a time-domain higher-order boundary element method（HOBEM） based on potential flow theory. A four-point method is developed to decompose higher bound and free harmonic waves propagating upstream and downstream around the obstacle. The model predictions are in good agreement with the experimental data for free harmonics induced by a submerged horizontal cylinder in the absence of currents. This serves as a benchmark to reveal the current effects on higher harmonic waves. The peak value of non-dimensional second free harmonic amplitude is shifted upstream for the opposing current relative to that for zero current with the variation of current-free incident wave amplitude, and it is vice versa for the following current. The second-order analysis shows a resonant behavior which is related to the ratio of the cylinder diameter to the second bound mode wavelength over the cylinder. The second-order resonant position slightly downshifted for the opposing current and upshifted for the following current.     

渤海地区平台结构设计环境条件选取分析

随着平台的使用年限增长,环境条件随着海洋环境的变化而变得日益恶劣,对于渤海地区,提出了是否采用100年一遇环境条件替换50年一遇环境条件进行结构设计.经过对渤海地区的部分中心平台和井口平台50年/100年环境条件对比分析,提出了对于渤海地区海上平台结构采用100年一遇环境条件替换50年一遇环境条件.     

海洋微微型蓝藻与异养细菌相互作用的研究进展

菌藻相互作用是海洋生态学领域研究的重要方向之一.海洋微微型蓝藻(Marine picocyanobacteria)是遍布全球海洋的重要初级生产者,在全球碳循环和微食物网中发挥重要作用.原绿球藻属(Prochlorococcus)和聚球藻属(Synechococcus)是海洋微微型蓝藻最重要的两个类群.原位调查和培养实验...     

水下多路液压快速接头的夹头结构分析与优化

深海油气田水下生产系统装备之间的精准连接是国际公认的技术难题,对接一般通过深海连接器完成。弹性夹头是水下连接器的重要组成部分,其性能关系到海洋油气生产系统的安全性和可靠性。弹性夹头的主要作用是在水下机器人的辅助下连接和锁紧连接器的固定端和移动端。采用ABAQUS软件的显式动力学分析模块计算夹头夹紧心轴这一过程中的应力、反作用力状态。三维模型仿真结果表明,锁紧过程中弹性夹头的最大应力不超过430 MPa,小于所选取的材料屈服强度480 MPa。采用正交试验和方差分析的方法研究夹头的长度、夹头与心轴的间隙等几个关键尺寸从而分析影响夹头应力和连接所需推力的最显著因素。对夹头的结构进行优化设计,同时也为夹头心轴结构的设计提供了理论依据。最后,通过试验研究对样机进行测试,测试结果表明,夹紧动作所需的最大推力在700 N以下。     

Impact of Sea-Land Interaction on Evolution of Taihu Lake

1 .IntroductionFor Lakes near the middle andlower reaches of the Yangtze River ,theformationof lake basinsisgreatly affected by geological structures ,andthe interaction betweenrivers and seas .The Taihu Lakeis locatedinthelow-lying plain nearthe east coa…     

基于遗传算法的浮式防波结构物形状最优化设计

采用遗传算法作为优化手段,以透射系数为目标函数,对给定横剖面面积的浮式防波结构物在规则波中的消波性能及剖面形状进行了最优化计算研究,探讨了透射系数最小的剖面形状与波浪周期之间的关系,为浮式防波结构物的设计提供了一定的理论依据     

Multi-variable adaptive back-stepping control of submersibles using SDU decomposition

A multi-variable adaptive autopilot for the dive-plane control of submarines is designed. The vehicle is equipped with bow and stern hydroplanes for maneuvering. It is assumed that the system parameters are not known, and the disturbance force is acting on the vehicle. Based on a back-stepping design approach, an adaptive control law is derived for the trajectory control of the depth and the pitch angle. To prevent singularity in the control law, the SDU decomposition of the high-frequency gain matrix is used for the design. In the closed-loop system, asymptotic tracking of the reference depth and pitch angle trajectories is accomplished. Simulation results are presented which show that the submarine performs dive-plane maneuvers in spite of the uncertainties in the system parameters and disturbance forces.