Non-linear analysis of a dynamically positioned platform in stochastic seaway     

S. Surendran  T.P. Pramod 《Ocean Engineering》2006,33(7):878-894

Safety is the topmost priority considered by the designers of floating systems or any other structural systems. Reliability, economy and environmental pollutions and the liability of the structure in the case of accidents are also considered by the designers. The paper concentrates on the non-linear behavior of a moored floating platform in stochastic seaway generated using the Pierson–Moskowitz spectrum. Second-order wave forces (slow drift force) acting on the structure is considered as they contribute to a major percentage of the excursion of a large platform. Wave drift damping and skin friction damping have also been considered.It has been shown that the principal frequency of the second-order motion of the platform due to drift forces closely matches the natural frequency of the system in surge motion. This has been subsequently used in tuning a PID (proportionate integral and differential)-based control system for the surge mode, where reduction in the order of 90% has been observed.  相似文献   

Spatio-temporal variability of micro- and meiobenthic communities in a White Sea intertidal sandflat     

A. I. Azovsky  E. S. Chertoprood  M. A. Saburova  I. G. Polikarpov 《Estuarine, Coastal and Shelf Science》2004,60(4):663-671

Meiobenthos (harpacticoids), microzoobenthos (ciliates) and microphytobenthos (epipelic diatoms and dinoflagellates) were collected during July 1999 using nested sampling at the scales of decimeters, meters and tens of meters. Similarity between samples decreased rapidly with distance for all groups, but unicellular organisms were distributed more heterogeneously at a large scale than meiobenthos. Microspatial (decimeter scale) variations contributed the main part of total variation of harpacticoid abundance, while the large-scale differences were less important. On the contrary, these differences yielded the main variability for ciliates and especially for microalgae. The relative role of temporal variability decreased steadily for the smaller-sized organisms. Stability of spatial structure at multiple scales was estimated by Mantel correlations, R_m, between the successive similarity matrices. For harpacticoids, the results showed intensive and chaotic turnover of microaggregations. For microbenthos, rather high R_m values were found in smaller scales: tens of meters—for ciliates, from meters on—for dinoflagellates, and already from decimeter scale and on—for diatoms. Thus, the general spatial pattern (that is the arrangement of micropatches) was more stable for microbenthos than for meiobenthos. Temporal variability of species structure, in contrast to the spatial one, was highest for the smallest organisms. Correlations between size groups, using both total abundance and species composition, differed for microspatial, meso-spatial or temporal distribution. At the microscale, there were slight but significant negative correlations between harpacticoids and microalgae. Meso-scale distribution of dinoflagellates and diatoms differed significantly due to their different preferences in sediment properties. Ciliates were strongly positively correlated with dinoflagellates. At the microscale, each group had an individual community pattern. At larger scales, species composition of diatoms, ciliates and harpacticoids varied in space in coordination, while dinoflagellates behaved independently. It is hypothesized that body size determines the spatio-temporal scale of the perception of environmental heterogeneity.  相似文献   

Geographical Variations in Prosome Length and Body Weight of Neocalanus Copepods in the North Pacific     

Toru Kobari  Kazuaki Tadokoro  Akihiro Shiomoto  Shinji Hashimoto 《Journal of Oceanography》2003,59(1):3-10

Geographical variations in prosome length and body weight of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were investigated on samples from North-South and East-West transects in the North Pacific during spring to early summer in 1998 and 1999. Southward and eastward increasing patterns were pronounced for water temperature, although no significant pattern was observed for chlorophyll a concentrations. All Neocalanus species showed large geographical variations in prosome length and body weight, being smaller in the southern and eastern waters. Comparing the relationship between prosome length and body weight, large deviations (lower body weight at a given prosome length) were evident for the eastern specimens of N. cristatus and N. plumchrus. In stepwise regression analysis, the geographical variations of prosome length and body weight revealed a significantly negative correlation with temperature variations. These results suggest that temperature is a more important environmental factor than chlorophyll a concentration in its effect on geographical variations in prosome length and body weight of Neocalanus copepods in the North Pacific. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

传统节庆、身体与展演空间——基于人文地理学视觉量化方法的研究   总被引：5，自引：1，他引：4  

王敏  林钿  江荣灏  朱竑 《地理学报》2017,72(4):671-684

采用人文地理学视觉量化的研究方法,结合照片评定、眼动分析及定性分析对广东汕头澄海区上社村传统节庆活动（其“拖神”活动具有鲜明的身体表达特征）的空间进行了解译。研究发现,在传统节庆活动中,身体的仪式化实践和体验可对特定的节庆时间—空间进行生产和维持,身体成为传统节庆意义生产的最小空间尺度。身体所能感受和分享的节庆情感作用于地方共同感和认同的建构,而持续的身体参与是传统节庆活动得以不断再生产和保持强盛生命力的关键。在具体研究中,照片评定和眼动仪实验等视觉量化方法的使用,通过对地方居民的空间情感体验进行直观而有效的测度,借助眼动轨迹的热点及瞳孔数据,有力地表明在传统节庆的展演空间内外,现场观众和外界“他者”的“凝视”与身体化的感知存在不同,表现出身体的空间差异性。研究对身体地理学内容的拓展和人文地理学新方法的应用都有一定价值。  相似文献   

黄河水下三角洲沉积厚度、沉积速率及砂体形态   总被引：9，自引：3，他引：9  

李广雪  薛春汀 《海洋地质与第四纪地质》1993,13(4):35-44

本文通过多年水下实测剖面对比,对黄河水下三角洲现今活动叶瓣沉积厚度、沉积速率和砂体形态进行了研究。厚度分布等值线呈椭圆形,长轴与海岸平行。口门处沉积速率最大,平均最高值可达240cm/a之多,前三角洲沉积速率小于30cm/a,平均约15cm/a,三角洲侧缘小于50cm/a,平均约30cm/a。三角洲叶瓣砂体成分受物源控制,主要由粗粉砂组成。通过与世界六种典型三角洲砂体模式对比,认为黄河三角洲叶瓣砂体有其特殊性,代表具高密度流的三角洲砂体特征。  相似文献   

复合载体夯扩桩技术在青岛地区的应用   总被引：1，自引：0，他引：1  

李玉岩 《海岸工程》2005,24(1):68-74

详细介绍了复合载体夯扩桩的构造、承载机制、设计和施工程序，总结了它的优点和适用范围，并用青岛地区的应用实例说明其桩基计算方法和基桩检测试验结果。应用结果表明，此技术在青岛地区有广泛的应用前景。  相似文献   

地下曲流河道单砂体内部薄夹层建筑结构研究方法   总被引：26，自引：1，他引：25  

马世忠  孙雨  范广娟  郝兰英 《沉积学报》2008,26(4):632-639

单砂体内部薄夹层因规模小、薄、不稳定、参数与分布难于确定等,致使覆盖盆地单砂体内部薄夹层及其建筑结构研究较少且难度很大,为此,本文以曲流河道沉积、建筑结构模式为指导,充分利用岩芯、测井、密井网等油田现有资料,提出了‘一整套地下曲流河道单砂体内部薄夹层建筑结构研究方法’,特别是以‘侧积泥、侧积面、废弃河道的识别、恢复、测算;河道几何学、河流工程参数计算;建筑结构理论模式为基础的‘单一侧积泥岩薄夹层建筑结构参数（倾角、倾向、规模）三类13种提取方法’及薄夹层分布密度与河道侧积轨迹研究技术,为这一难题的解决提供了可行的思路与方法。并以杏南油田PⅠ31b单元为靶区,应用该方法确定了曲流河道单砂体内部薄夹层及其建筑结构理论模式和研究区实际模式。  相似文献   

音频大地电磁测深在西藏某斑岩铜矿深部找矿中的应用          下载免费PDF全文

吴小勇  左焕成  王阳玲 《地质找矿论丛》2016,31(4):576-579

文章阐述了在西藏尼木县某斑岩铜矿区开展的音频大地电磁测深工作,并取得了较好的勘查效果。经由钻孔验证,在4 800~5 300m段见铜、钼矿化二长花岗斑岩,品位w(Cu)=0.05%~1.4%、w(Mo)=0.1%~0.27%。利用音频大地电磁测深勘探深度大、不受高阻层屏蔽、对低阻体敏感等优点,结合高精度磁测、激电资料,有效指导该区隐伏矿体的勘查工作。实践证明,音频大地电磁测深在斑岩铜矿深部找矿中行之有效,值得借鉴。  相似文献   

三维地质建模的用途、现状、问题、趋势与建议   总被引：4，自引：0，他引：4  

李青元 《地质与勘探》2016,52(4):759-767

文章论述了三维地质建模技术的用途、现状、存在问题、发展趋势和几点建议。笔者认为三维地质建模的用途是:1真三维的立体场景;2精准的储量计算;3平、剖面构造形态相容并联动编辑;4多源、异构数据的集成与同化;5各种三维空间分析与过程模拟;6便于向客户与领导介绍复杂的地质条件。从行业应用和国内软件发展两个方面论述了当前三维地质建模的应用现状,该技术应用中存在的问题:1软件操作太复杂,难以为基层广大地质作图人员所掌握;2三维建模约束条件太严苛,编辑工作量巨大;3没有三维地质模型数据标准,模型数据难以交换与共享;4勘探规范没有要求,地质队积极性不高;5三维地质模型的建模成本由谁支付。三维地质建模的发展趋势:1软件将更加成熟、稳定、易用;2由早期的注重形态建模向形态与属性建模并重的方向发展;3与地震、测井等物探数据结合更加紧密;4与矿藏描述、成藏模拟、沉积环境分析、构造演化分析、构造演化模拟等专业应用结合更加紧密;5融入大数据、云计算、物联网等IT主流技术。向国家相关主管部门、企业用户和软件开发商提出了几点建议:1国家应继续支持三维地质建模领域;2三维地质建模要与专业应用紧密结合;3加强相关标准的制定与维护;4逐步在勘探规范中增加对三维建模的要求;5软件开发者设法降低软件的操作复杂度,提高容错能力。  相似文献   

东营凹陷北部陡坡带丰1扇背斜的特征、成因及其与油气的关系   总被引：2，自引：0，他引：2       下载免费PDF全文

钟建华  王国壮  高祥成  夏景生  王洪宝  王志坤  陈志鹏 《地质科学》2008,43(4):625-636

东营凹陷北部陡坡带在沙河街组三-四段沉积时期堆积了很厚的砂砾质碎屑沉积物,发育扇背斜,成为油气聚集的重要场所,近期的油气勘探证明了这一点。扇背斜有别于一般意义上的构造背斜、滚动背斜和披覆背斜,它是一种由低位沉积扇体(包括坡积扇、洪积扇和冲积扇)形成的主体,尔后被高位体系域形成的细碎屑沉积物覆盖而形成的背斜;是砂砾岩体堆积后,其上又由盖层覆盖而成的背斜。虽同为沉积背斜,扇背斜与披覆背斜有很多不同之处。扇背斜油藏本质上是一种岩性油藏,其成藏条件受控于砂砾岩扇体的特性、距油源的距离、砂砾岩扇体和油源之间的连通性以及砂砾岩扇体上覆盖层的封堵能力。该类型的油气藏大多发育在断陷湖盆的陡坡带区域。  相似文献