共查询到20条相似文献，搜索用时 450 毫秒
1.
2.
由于腐蚀、海生物附着等因素导致老龄化海洋平台在与船舶碰撞的事故作用下,桩腿变形加大,降低了承载性能。为减少碰撞对桩腿的损伤,提高其耐撞性能,提出了利用吸收能力较强的高弹模CFRP材料加固平台桩腿的方法。以某自升式海洋平台桩腿为例,利用有限元法建立简化的碰撞模型,通过在局部损伤部位粘贴高弹模CFRP材料来提高桩腿的耐撞性能,验证高弹模CFRP加固方法,提高其耐撞性能的有效性。研究表明,相同的碰撞条件下,加固前碰撞力使桩腿产生了接近屈服强度的应力;粘贴2层CFRP布后,桩腿吸能下降56.3%,极值应力下降了14.7%;粘贴CFRP板后,桩腿吸能下降70.68%,桩腿的极值应力下降57.36%。 相似文献
3.
为了分析带支腿浮式结构水下桩腿处于不同的长度时振动固有频率的变化情况,采用有限元方法和三维线性水弹性理论对一理想的带支腿浮式结构进行研究,分工况计算了3种弹性模态的干、湿固有频率。结果表明对于同一阶弹性模态来说,结构主体平台振型是决定水动力系数大小的主要因素,桩腿水下长度是次要因素,而振型又受到桩腿长度的制约;桩腿水下长度的改变对带支腿浮式结构的干模态固有频率以及湿固有频率都有较明显地调制作用。对于干模态固有频率来说,桩腿关于船身越趋于对称分布时结构的共振频率越高;对于湿固有频率来说,水下桩腿长度地增加有迫使共振频率趋向低频方向移动趋势。 相似文献
4.
5.
本文对某自升式钻井平台结构进行了模态和地震反应分析。用等效桩腿的处理方法把平台结构简化为空间梁系有限元力学模型,采用我国《海上固定平台入级与建造规范》中规定的标准地震谱曲线.首先计算了平台结构前五阶固有频率和模态,然后用基于模态叠加法的谱分析法求出平台结构和桩腿各部位的最大位移和应力反应。最后给出了该平台结构在30m和50m水深海域、桩腿为插桩式和沉垫式两种固定型式下的计算结果和比较。 相似文献
6.
7.
针对传统无损检测方法对自升式海洋平台检测工作量大、费时费力等问题,提出了一种金属磁记忆(MMM)与交流电磁场(ACFM)联合检测的新方法。在简介MMM和ACFM检测机理之后,将其应用到自升式海洋平台关键部位的无损检测中。分别以齿条座板与桩腿之间的T型焊缝和桩腿环焊缝为例,首先通过MMM快速全面扫描待检测表面,基于磁场分布及梯度值确定应力集中部位;在此基础上,利用ACFM方法重点对应力集中部位进行裂纹缺陷的定量化检测,结果表明MMM对应力集中或微观缺陷非常敏感,而ACFM方法可精确给出裂纹缺陷的深度信息,为平台结构的安全可靠运行和维修方案制定提供了方法参考和理论依据。 相似文献
8.
现有服役海洋平台正逐步走向老龄化,海洋平台拆除成为海洋工程新的经济增长点。针对达到服役年限的导管架平台,基于数值分析方法模拟拆除过程,开展平台在不同拆除阶段和环境载荷等参数下的稳定性及影响规律研究。基于钢结构整体稳定性理论,以导管架平台拆除过程中顶点位移为参考,定义导管架平台拆除作业稳定性指标,提出拆除作业阶段划分方法,通过分析导管架平台在不同影响因素作用下拆除过程稳定性响应,给出拆除作业建议。选取我国南海某4裙12腿进行实例分析,结果表明:主桩腿对导管架平台起决定性承载作用,拆除部分主桩腿后需要引入外部支撑力,以保证拆除作业安全进行;拆除构件越多,来浪方向和环境载荷大小对平台影响越加显著。研究结果可为导管架平台拆除作业提供参考。 相似文献
9.
10.
本文对某自升式海上石油钻井平台的振动模态进行了计算和分析。平台长57.6米、宽34米,采用4根直径为3米的管形桩腿,腿高78米,工作水深40米,桩腿插入泥面以下约3米。本文提出了计算该平台振动模态的两种模型:空间薄壁结构模型和空间框架模型,用 SAP5结构分析程序进行了计算,获得了该平台的第一至第廿谐调的振动频率和模态,为我国自升式钻井平台动态特性的设计、分析和使用提供了有用的数据和可行的方法。文中对上述两种计算模型作了分析和比较,指出本文提出的空间薄壁结构模型是计算这类平台整体振动模态的一种简单易行而又经济的合理模型。此外,本文还指出了这类平台振动周期的跳跃现象,讨论了桩腿的支承条件对平台振动周期的影响以及平台结构的质量和附连水质量的处理等问题。 相似文献
11.
Arne Schnack-Friedrichsen Angela M. Davis Jim D. Bennell Dei G. Huws 《Marine Georesources & Geotechnology》2001,19(4):221-243
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths. 相似文献
12.
Shigehisa Nakamura 《Marine Geodesy》2000,23(1):55-61
Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone. 相似文献
13.
The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics. 相似文献
14.
Coastal inundation associated with extreme sea levels is the main factor which leads to the loss of life and property whenever a severe tropical cyclonic storm hits the Indian coasts. The Andhra and Orissa coasts are most vulnerable for coastal inundation due to extreme rise in sea levels associated with tropical cyclones. Loss of life may be minimized if extreme sea levels and associated coastal flooding is predicted well in advance. Keeping this in view, location specific coastal inundation models are developed and applied for the Andhra and Orissa coasts of India. Several numerical experiments are carried out using the data of past severe cyclones that struck these regions. The simulated inland inundation distances are found to be in general agreement with the reported flooding. 相似文献
15.
16.
《海洋学报(英文版)》2014,(9):F0003-F0003
<正>Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.The journal publishes scholarly papers on marine science and technology,including physics,chemistry,biology, 相似文献
17.
Hoi-Soo Jung Kap-Sik Jeong Yong-Shik Chu Sung-Hyun Park Ki-Hyune Kim 《Marine Georesources & Geotechnology》2001,19(3):181-195
Grain size and water content in box-core sediments from the Clarion-Clipperton fracture zone (C-C zone) in the northeast equatorial Pacific were analyzed in detail to understand the downcore variations across a hiatus between Quaternary and Tertiary layers. Grain-size distributions in the topmost core sediments show two modes: a coarse mode (peaked at 50 μm) and a fine mode (at 2-25 μm). The coarse mode disappears gradually with depth accompanied by the dissolution of siliceous fossil tests, whereas the fine mode coarsens due to the formation of authigenic minerals. Water content increases abruptly across a color boundary between an upper pale brown layer and a lower dark brown layer that is the hiatus between Quaternary and Tertiary layers. Abundant smectites and microvoid molds, which are created by the prolonged fossil dissolution in the underlying sediment, are attributed for the abrupt downcore variation of water content. Overall variations in grain size and water content in the topmost core sediments in the western C-C zone are possibly constrained by the dissolution of biogenic siliceous fossils. Variations in geotechnical properties related to these changes must be considered in the design of nodule collectors. 相似文献
18.
Shigehisa Nakamura 《Marine Geodesy》2001,24(1):27-33
This article concerns an interrelation between the sea levels and the western boundary flow near a tectonic boundary in a local zone in the Northwestern Pacific. In this zone, sea level variations at stations located on the coast facing the Pacific are studied to find the interrelation between variations of the Kurosio flow as an index of the distance of the flow axis off a specific coast. The result is discussed after data processing of the monthly means of the sea levels, and a notice is taken of variations caused by active crustal upheavals during a seismic event, a local earthquake. 相似文献
19.
This study tests the hypothesis that the in situ void ratio of surficial marine sediments may be predicted from shear wave velocity-depth data with a reliability equal to that of other methods currently available. Shear wave velocity is fundamentally controlled by the number of grain-to-grain contacts per unit volume of material and by the effective stress across those contacts. In this study, three previously established empirical formulae are used to predict void ratio from velocity-depth data. Field data were acquired along a transect off the northern Californian coast across which water depth increased from 35 to 70 m and seafloor sediment type varied from sand to silty-sand, respectively. A towed seafloor sled device was used to collect shear wave refraction data, and a marked, systematic decrease in velocity was observed along the line, ranging from 35-70 m/s for the coarse, near-shore material to 25-40 m/s for the finer, offshore deposits. Void ratios predicted from these velocities were compared with data measured directly from box-core samples. Of the formulae used for prediction, two agree remarkably well with the control data. Both predicted and control values increase from 0.6-0.8 for the sandy material to 1.1-1.5 for the silty-sand. Thus, this study does not disprove the hypothesis set and demonstrates the potential of field shear wave velocity-depth data as a means of delineating spatial variation in void ratio for surficial marine sediments in a remote, nondestructive manner. 相似文献
20.
Particulate samples were collected from the Changjiang river system during a flood period, in May 1997, and POC, stable isotope and lipids associated with particles were examined. Results showed the decrease (0.84% ～ 1.88%) of organic carbon content from the upper reaches to the estuary.δ13C values of particulate organic carbon was in the range of -24.9×10-3 to -26.6×10-3, which were close to the isotopic signature of continental C3 vegetation. Total particulate n-alkanes concentrations varied from 1.4 to 10.1μg/dm3,or from 23.7 to 107μg/g of total suspended matter. Fatty acids were present in all the samples, from 1.4 to 5.4μg/dm3, with saturated and unsaturated straight-chain and branched compounds in the carbon number range from C12 to C30. Both δ13C and the ratio of carbon content to nitrogen content indicate the predominance of terrestrial inputs (soil organic matter) among the particles. The biomarker approach has been used to identify the relative portion of terrigenous and autochthonous fraction in the particulate samples. The distribution of fatty acids suggests a striking phytoplanktonic and microbial signal in most particle samples. The terrestrial alkanes are used to estimate the contribution of terrestrial inputs along the mainstream. 相似文献