A New Method of Surveying Underwater Parts of Self Elevating Drilling Platform

It is a new method of surveying leg spuds of self-elevating drilling platforms to lift them out of water with the help of additional middle guide blocks. Its main advantages in comparison with other methods normally used up to now are: less expensive, time saving, no need for specially designated water area, direct visual observation, good reliability and safety. The working principle has been presented with the example of two platforms "Bohai No. 8" and "Bohai No. 10", to which the method was used. Also a comprehensive comparison with other methods in technological and economical aspects is given in the paper.     

Efficient estimation of extreme response of drag-dominated offshore structures by Monte Carlo simulation

The paper describes a novel approach to the problem of estimating the extreme response statistics of a drag-dominated offshore structure exhibiting a pronounced dynamic behaviour when subjected to harsh weather conditions. It is shown that the key quantity for extreme response prediction is the mean upcrossing rate function, which can be simply extracted from simulated response time histories. A commonly adopted practice for obtaining adequate extremes for design purposes requires the execution of 20 or more 3-h time domain analyses for several extreme sea states. For early phase considerations, it would be convenient if extremes of a reasonable accuracy could be obtained based on shorter and fewer simulations. The aim of the work reported in the present paper has therefore been to develop specific methods which make it possible to extract the necessary information about the extreme response from relatively short time histories.The method proposed in this paper opens up the possibility to predict simply and efficiently both short-term and long-term extreme response statistics. The results presented are based on extensive simulation results for the Kvitebjørn jacket structure, in operation on the Norwegian Continental Shelf. Specifically, deck response time histories for different sea states simulated from an MDOF model were used as the basis for our analyses.     

考虑桩土作用独桩海洋平台横向振动特性研究

采用动Winkler弹性地基梁模型模拟桩土问动力相互作用，并考虑了流体与桩问相互作用，通过组合成层土中、水中桩单元的刚度阵，推得了独桩海洋平台连续系统横向振动的动刚度阵及在波浪力作用下平台甲板处的频率响应函数，进而求得了在确定性波浪力及随机波浪力作用下桩身任意点的位移响应。最后，通过算例研究和分析了在随机波浪力作用下成层土参数、甲板上重量及冲刷淘深等因素对平台振动响应的影响。     

极端荷载作用下海洋导管架平台体系可靠度分析

采用非线性倒塌分析方法，考虑桩－土－结构的非线性相互作用，研究了导管架平台在极端荷载作用下承载能力的计算模型，分析了平台结构体系在极端荷载作用下的全倒塌全过程，在此基础上，结合蒙特卡洛法，提出了海洋导管架平台结构的体系可靠度计算方法。最后对工程实例－涠11－4C海洋平台的结构进行了体系可靠性分析，并对比分析了不同的荷载效应计算公式对计算经的影响，研究表明计算经满足工程设计要求，便于工程应用。     

Dynamic Response of Fluid-Single Leg Gravity Platform-Soil Interaction System

- An approximate method is presented to investigate the earthquake response of the fluid-single leg (shortened for S. L.) gravity platform-soil interaction system. By assuming a suitable form of the velocity potential of the radiation waves and by using the motion equation and the boundary conditions, the unknown coefficients can be obtained. Thereafter the function of frequency for the interaction system may also be obtained. In this paper, the difference of the system dynamic response between rigid foundation is analyzed and the influences of the various foundation geometric dimension and the various water-depth on the hydrodynamic loading and dynamic response of the system is illustrated.     

Modal Identification of Offshore Platforms Using Statistical Method Based on ERA

Identification of modal parameters of a linear structure with output-only measurements has received much attention over the past decodes. In the paper, the Natural Excitation Technique (NEXT) is used for acquisition of the impulse signals from the structural responses. Then Eigensystem Realization Algorithm (ERA) is utilized for modal identification.For disregarding the fictitious ‘computational modes’, a procedure, Statistically Averaging Modal Frequency Method (SAMFM), is developed to distinguish the true modes from noise modes, and to improve the precision of the identified modal frequencies of the structure. An offshore platform is modeled with the finite element method. The theoretical modal parameters are obtained for a comparison with the identified values. The dynamic responses of the platform under random wave loading are computed for providing the output signals used for identification with ERA. Results of simulation demonstrate that the proposed method can determine the system modal frequency with high precision.     

Torsionally Coupled Response Control of Offshore Platform Structures Using Circular Tuned Liquid Column Dampers

In this paper, the control performance is investigated of Circular Tuned Liquid Column Dampers (CTLCD) over torsional response of offshore platform structures excited by ground motions. Based on the equation of motion for the CTLCD-structure system, the optimal control parameters of CTLCD are given through some derivations on the supposition that the ground motion is a stochastic process. The influence of systematic parameters on the equivalent damping ratio of the structures is analyzed with purely torsional vibration and translational-torsional coupled vibration, respectively, The results show that the Circular Tuned Liquid Column Damper (CTLCD) is an effective torsional response control device.     

Dynamic behavior of tension-leg platform with net-cage system subjected to wave forces

In this study a typical tension-leg platform with net cage system is presented, and a set of equations of motion for the platform with a net-cage system of a simplified two-dimensional case are derived. Subsequently a close form solution is obtained when the wave-structure interaction between the top platform structure and the incident wave is considered. The parameter of solidity as a ratio of the twine diameter and the mesh size of the cage is also taken into account in the analysis. The purpose of this study is to investigate the dynamic behavior for the tension-leg platform with a net-cage system and its pre-tensioned tethers when subjected to incident waves and flow drags, and furthermore, to understand the relationship between the structure behavior and the properties of the net-cages. Numerical examples are carried out and the results are discussed focusing on the motion of both the platform and net-cages when subjected to waves of a range of periods. It is found that there is a close relationship between the dynamic behavior of the platform and the net-cage features such as the solidity ratio between the twine diameter and the mesh size of the net-cage while the parameters related to waves are held constant.     

新型船载气象卫星接收系统

新型船载气象卫星接收系统为南极考察船的航海气象保障和在南大洋冰区中航行导航专门研制.该系统能够适应高温、高湿和低温超饱和的气候环境,在12级以上大风和船在破冰时剧烈摇摆和振动以及有雷达等强磁场信号干扰的情况下,具有自我保护能力.有极轨高分辨和静止低分辨卫星的双套接收和图像处理系统.该系统的关键创新之处:(1)采用了有源陀螺仪稳定平台.利用惯性测量和三轴伺服机构控制天线和隔离船摇.解决极轨卫星低仰角和过顶轨道高仰角跟踪丢线的矛盾,解决了船在运动状态下,不断改变位置、方向以及摇摆的状态下,准确地跟踪和捕捉到卫星,接收到清晰的卫星云图.(2)图像处理系统用了最新的BORLAND-DELPHI语言编程,采用两行元素的轨道模式计算动态定位套网格系统.利用电子地图网格数据,用迭代法画出地形海岸线.计算出每一像元素的位置;能够在图上显示任意一点的经纬度,标出任意目标物.解决了在海洋中航行找不到参照物时的困惑.能够监测云和温度、林火、海洋及陆地的异常变化.能够输出24位真彩色的高清晰度的卫星云图.该系统整体结构技术先进,体积小,重量轻,适应恶劣气候和海洋环境,图像处理系统功能齐全、分辨率高,操作方便.既适用于各种船只,也适用于陆地.     

近岸区直墙波浪力的模拟

在水槽中进行了几种不同坡度的斜坡平台上规则波作用下直墙波浪力试验，系统分析了直墙上相对最大压强和相对最大总力，给出了它们之间的比较关系。还进行了不同坡度的不规则波模型试验，并讨论了波浪力之间的特性。结果表明采用1：10、1：15的斜坡与平台相结合的试验室模拟，可得到与平底地形相近的直墙波浪力。