Tidal wetting and drying on shore platforms: An experimental study of surface expansion and contraction

Laboratory experiments have been conducted to measure rock expansion and contraction induced by wetting and drying on intertidal shore platforms in eastern Canada. Almost 800 rock cores and cubes were subjected to between 800 and 1000 tidal cycles. The rocks were put into tidal simulators and inundated in de-ionized water for 1, 6, or 11 h of each 12 h cycle, replicating conditions at the high, mid-, and low tidal levels, respectively. Micro-erosion meter (MEM) stations were also installed in slabs of argillite, sandstone, and basalt. The slabs were subjected to conditions at the high, mid-, and low tidal levels, and a traversing MEM was used to measure rock expansion and contraction as the slabs dried in air with variable temperature and humidity during low tide. The slabs were also exposed for long periods to air with variable humidity. Cores and cubes often gained in weight when they absorbed or adsorbed water and retained it for periods ranging from 1 month to 1 year or more, although this did not appear to be a prelude to rock breakdown. Tidal wetting and drying and exposure to humid air caused the argillite and basalt slabs to expand and contract by up to 0.14 and 0.04 mm, respectively. Wetting and drying did not induce expansion or contraction of the sandstone, but the sandstone did respond slightly to changes in air humidity. The greatest amount of expansion and contraction was at the high tidal level in the argillite and at the mid-tidal level in the basalt, which is consistent with previously measured rates of downwearing.     

礼乐盆地碳酸盐岩时空分布特征及构造意义

对碳酸盐岩(台地与生物礁)的研究具有重要的油气地质意义和科学价值。渐新世以来, 礼乐盆地及周缘开始了大规模的碳酸盐建造, 至今还有一定规模生物礁持续发育。文章通过拖网约束、井震对比和地震相类比方法对礼乐盆地周缘碳酸盐岩的发育特征、构造背景和时空分布规律进行系统研究。结果表明, 礼乐盆地主要发育孤立、前隆、掀斜断块型台地及生物礁。碳酸盐岩时空发育特征为: 1) 渐新世—早中新世以构造前隆和掀斜断块控制的开阔台地为主, 生物礁零星发育; 2) 早中新世—中中新世表现为大量孤立台地和生物礁; 3) 中中新世之后, 发生台地和礁的淹没, 盆地内主要发育点礁。结合构造背景和重磁特征分析表明, 古隆起、掀斜断块、前隆迁移和岩浆活动为控制礼乐盆地不同时期碳酸盐岩发育的主要构造要素。现今礼乐盆地及周缘大量生长的珊瑚礁, 主要发育在上新世—更新世岩浆活动形成的海山之上。     

A Method for Analyzing System Reliability of Existing Jacket Platforms

Owing to the ageing of the existing structures worldwide and the lack of codes for the continued safely management of structures during their lifetime, it is very necessary to develop a tool to evaluate their system reliability over a time interval. In this paper, a method is proposed to analyze system reliability of existing jacket platforms. The influences of dint, crack and corrosion are considered. The mechanics characteristics of the existing jacket platforms to extreme loads are analyzed by use of the nonlinear mechanical analysis. The nonlinear interaction of pile-soil-structure is taken into consideration in the analysis. By use of FEM method and Monte Carlo simulation, the system reliability of the existing jacket platforul can be obtained. The method has been illustrated through application to BZ28-1 three jacket platforms which have operated for sixteen years. Advantages of the proposed method for analyzing the system reliability of the existing jacket platform is also highlighted.     

Short‐term rock surface expansion and contraction in the intertidal zone

Transverse micro‐erosion meter (TMEM) stations were installed in rock slabs from shore platforms in eastern Canada. The slabs were put into artificial sea water for 1, 6 or 11 hours, representing high, mid‐ and low tidal areas, respectively. The TMEMs were used to record changes in surface elevation as the rocks dried during the remainder of the 12 h of a semi‐diurnal tidal cycle. A similar technique was used on the same rock types at intertidal TMEM stations in the field, as the rocks dried during low tide. Argillite and basalt surface contraction was from 0 to 0·04 mm: there was little surface expansion. Sandstones contracted by up to 0·03 mm in the field, but there was almost no contraction in the laboratory. Argillite and basalt contraction tended to be greatest in the upper intertidal zone, and to increase with rates of longer‐term surface downwearing, but there was little relationship with rock hardness or air temperature and humidity. Changes in elevation at the same points at TMEM stations in the laboratory and field were quite consistent from one tidal cycle to the next, but there were considerable variations within single tidal cycles between different points within each station. The data suggest that contraction within the elevational zone that is normally submerged twice a day by the tides is by alternate wetting and drying. Short‐term changes in elevation are generally low compared with annual rates of downwearing owing to erosion, but they may generate stresses that contribute to rock breakdown. Copyright © 2007 John Wiley & Sons, Ltd.     

导管架海洋平台优化设计中约束的有效处理

对导管架海洋平台优化设计中的应力约束、桩基横向承载力约束和构件长细比约束进行了分析,论证了应力约束取构件截机最大Ｍｉｓｅｓ应力、桩基横向承载力约束取桩顶侧位移或最大抗力比和构件长细约束取受压构件长细比许用值作为约束的合理性。提出了精细一维搜索算法,并用此法求我件截面Ｍｉｓｅｓ应力最大值。     

Optimal Design of Equivalent Water Depth Truncated Mooring System Based on Baton Pattern Simulated Annealing Algorithm简

The highest similarity degree of static characteristics including both horizontal and vertical restoring force-displacement characteristics of total mooring system, as well as the tension-displacement characteristics of the representative single mooring line between the truncated and full depth system are obtained by annealing simulation algorithm for hybrid discrete variables （ASFHDV, in short）. A“baton” optimization approach is proposed by utilizing ASFHDV. After each baton of optimization, if a few dimensional variables reach the upper or lower limit, the boundary of certain dimensional variables shall be expanded. In consideration of the experimental requirements, the length of the upper mooring line should not be smaller than 8 m, and the diameter of the anchor chain on the bottom should be larger than 0.03 m. A 100000 t turret mooring FPSO in the water depth of 304 m, with the truncated water depth being 76 m, is taken as an example of equivalent water depth truncated mooring system optimal design and calculation, and is performed to obtain the conformation parameters of the truncated mooring system. The numerical results indicate that the present truncated mooring system design is successful and effective.     

长江中游城市群创新平台空间分布及其影响因素分析

创新是引领发展的第一动力。创新平台作为区域创新体系的重要组成部分和集聚创新资源的核心支撑载体,是推动创新驱动发展的主要抓手。论文以长江中游城市群为研究区域,运用最邻近指数、核密度估计、Ripley's K函数、地理探测器等方法,探究2017年长江中游城市群省级以上创新平台的空间分布特征及其影响因素。结果表明：① 长江中游城市群创新平台整体呈现出集聚分布特征,以武汉、长沙和南昌为核心呈“品字形”的分布格局;② 基于不同等级和不同功能类型划分的各类创新平台均呈现出显著集聚的特征,但集聚强度和集聚状态存在一定差异;③ 创新平台总体和不同类型创新平台的空间集聚存在尺度效应,随地理距离的变化空间集聚趋势先增强后减弱;④ 创新平台的空间分异是多因素综合作用的结果,金融实力、信息化程度、利用外资水平、人力资本条件的影响最为显著,其次为交通可达性、城镇化水平、经济基础和创新氛围。     

The distribution of meiofauna on back‐reef sandy platforms in the Maldives (Indian Ocean)

The Maldivian archipelago comprises some of the most characteristic and significant world atoll systems, but the meiobenthic assemblages of these islands continue to be largely unknown. To investigate variations in meiofaunal spatial distribution and biodiversity in back‐reef platforms, three transects were studied, two at Felidhoo (the north and east sides) and one at South Malé. The sedimentological features of the samples obtained were also analyzed to further current knowledge on the relationships that exist between sediments and meiofauna. Our results reveal that the meiofaunal assemblage at these locations is well diversified and includes 20 major taxa. Nematodes and copepods are dominant, together forming 68% of the total meiofauna, followed by platyhelminthes, polychaetes and ostracods. The nematode assemblage is very rich and composed of 34 families and 123 genera – 96 of which (78%) set new records for the Maldives. The structures of the meiofaunal and nematode assemblages are relatively similar on the ‘large‐scale’ level (i.e. when the different platforms are compared) and reveal a low β‐diversity. However, significant dissimilarities were detected within each platform, emphasizing that such ‘small‐scale’ differences are the main factors determining the structure of the meiofauna and, in particular, the nematode assemblages. Although significant differences were not detected between the transects, greater levels of dissimilarity were recognized at North Felidhoo. Here, the building of inclined deposit layers plays a significant role in increasing the heterogeneity of the platform habitats and sediments, confirming the great importance of sediment granulometry as an environmental variable. Indeed, a close relationship is observed between meiofauna (especially for the nematodes) and grain size, which appears to control the structure, diversity and trophic composition of the Maldivian meiofauna assemblages, thus highlighting the high biodiversity existing in the medium‐coarse sands.     

岛礁地震资料特征分析及处理流程——以西沙永乐环礁为例

岛礁为国际科学研究前沿,其内部结构是揭示深海地质演变、古环境古气候变化等科学问题和解决岛礁建设、人造岛礁等工程问题的关键。西沙永乐环礁历经南海地质演变过程,发育了世界最深海洋蓝洞,为我国岛礁研究重点区域,但受限于探测手段和成像方法目前尚未窥得其内部结构。以西沙永乐环礁为例,利用3.125m道间距高分辨地震探测试验数据,开展岛礁地震资料特征分析,探索岛礁地震资料处理流程和岛礁地震处理方法,提升岛礁地震资料信噪比、分辨率和成像准确度,获取反映岛礁内部结构的高精度地震成像剖面。研究结果表明：本文提出的岛礁地震资料处理流程在海底珊瑚礁绕射波偏移归位、岛礁内部浅层结构和深水盆地区域地震同相轴刻画方面具有优势,将为我国下一步的南海岛礁地震资料采集和处理提供借鉴。     

南海新生代碳酸盐台地淹没事件记录的海底扩张

本文通过对南海4个碳酸盐台地及其淹没事件的分析来阐明南海海底扩张的演化史.南海碳酸盐台地出现在最大海底扩张期,淹没事件出现在海底扩张和地壳下降速率进一步加快时期,因而它记录了海底扩张的阶段性和不均一性.南海共经历了早中新世晚期(距今17±0.5 Ma)、晚中新世早期(距今10.0～8.2 Ma)和上新世早期(距今3.4～3.0 Ma)等3次大的淹没事件,表明南海经历了3次大的海底扩张,短暂淹没事件是与海底扩张有关的各种地质事件的反映.