Finite Element Analysis of Deformed Legs of Offshore Platform Structures

The element stiffness matrix of the equivalent beam or pipe element of the deformed leg of the platform is derived by the finite element method. The stresses and displacements of some damaged components are calculated, and the numeri-cal solutions agree well with those obtained by the fine mesh finite element method. Finally, as an application of this method, the stresses of some platform structures are calculated and analyzed.

Reduction-Based Model Updating of a Scaled Offshore Platform Structure

This paper attempts to develop a reduction-based model updating technique for jacket offshore platform structure. A reduced model is used instead of the direct finite-element model of the real structure in order to circumvent such difficulties as huge degrees of freedom and incomplete experimental data that are usually civil engineers' trouble during the model updating. The whole process consists of three steps: reduction of FE model, the first model updating to minimize the reduction error, and the second model updating to minimize the modeling error of the reduced model and the real structure. According to the performance of jacket platforms, a local-rigidity assumption is employed to obtain the reduced model. The technique is applied in a downscale model of a four-legged offshore platform where its effectiveness is well proven. Furthermore, a comparison between the real structure and its numerical models in the following model validation shows that the updated models have good approximation to the real structure. Besides, some difficulties in the field of model updating are also discussed.

Experimental Research On Fatigue Property Of Steel Rubber Vibration Isolator For Offshore Jacket Platform In Cold Environment

Jacket platform is the most widely used offshore platform. Steel rubber vibration isolator and damping isolation system are often used to reduce or isolate the ice-induced and seismic-induced vibrations. The previous experimental and theoretical studies concern mostly with dynamic properties, vibration isolation schemes and vibration-reduction effectiveness analysis. In this paper, the experiments on steel rubber vibration isolator were carried out to investigate the compressive properties and fatigue properties in different low temperature conditions. The results may provide some guidelines for design of steel rubber vibration isolator for offshore platform in a cold environment, and for maintenance and replacement of steel rubber vibration isolator, and also for fatigue life assessment of the steel rubber vibration isolator. (C) 2009 Elsevier Ltd. All rights reserved.

The W-11-4A platform comprehensive strength monitoring system

A comprehensive strength monitoring system used on a fixed jacket platform is presented in this paper. The long-term monitoring of W-11-4A platform achieved. Structural responses (strain and acceleration) at selected locations, as well as associated environmental parameters, have been obtained. The emphasis of the paper is placed on the system design, and the instrumentation and operation methodology employed in the monitoring of the structural responses. The performance of the system and the characteristic results obtained during its 13-month operation are also summarized.

海洋平台吸力式基础的研究与进展

吸力式基础平台是近年开发的一种新型海洋平台，由于多种优越性而受到各国石油部门的重视，并引起许多研究人员的关注。对有关吸力式基础的沉贯，稳定性以及与分析密切相关的冰激振动，土的动载下的本构研究进展进行了综述。并在最后针对海洋地区的条件提出了今后研究的重点问题。包括：沉贯阻力特性，动载下基础的软化特性和液化可能性，合适的土动力本构关系和数值方法，实验方法及模型律等。

A Dynamic Loading Device for Suction Foundations in Centrifuge Modeling

Suction bucket foundations are widely used in the offshore platform for the exploitation of the offshore petroleum and natural gas resources. During winter seasons, ice sheets formed in Bohai Bay will impose strong impact and result in strong vibration on the platform. This paper describes a dynamic loading device developed on the geotechnical centrifuge and its application in modeling suction bucket foundation under the equivalent ice-induced vibration loadings. Some experimental results are presented. It is shown that when the loading amplitude is over a critical value, the sand at the upper part around the bucket softens or even liquefies. The excess pore pressure decreases from the upper part to the lower part of the sand foundation in vertical direction while decreases from near to far away from the bucket's side wall in the horizontal direction. Large settlements of the bucket and the sand around the bucket occur under the horizontal dynamic loading. The dynamic responses of the bucket with smaller size are heavier.

Study on current-random wave forces acting on a framework

The forces of random wave plus current acting on a simplified offshore platform (jacket) model have been studied numerically and experimentally. The numerical results are in good agreement with experiments. The mean force can be approximated as a function of equivalent velocity parameter and the root-mean-square force as a function of equivalent significant wave height parameter.

离心机在海洋平台基础实验研究中的应用进展

对离心机在海工结构基础实验研究中的应用进行了综述，包括模型实验的理论研究、实验设备的发展、开展的典型实验等。指出了其中的不足和今后的发展方向。

基于局部密集应变响应的海洋平台冰载荷反演方法

冰载荷的现场测量工作对于描述冰载荷与海洋平台的相互作用规律十分重要.回顾了自六十年代以来的各地冰载荷的测量情况,针对在采用压力盒进行直接测量和利用结构整体响应进行间接反算的过程中存在的困难,提出了一种利用局部应变响应信息来有效反演海洋平台冰载荷的新方法,并设计了用于反演的附加套筒结构模型.阐述了反演的基本原理,从理论上分析了反演的误差来源以及误差的稳定性,并讨论了反演时载荷作用区域的判断方法和测点的布置原则.最后,通过计算机仿真的反演算例和一缩尺模型的反演实验(包括模型应变响应的动态标定)验证了这种方法的可靠性.

基于B/S的海洋平台远程监控系统设计

本文提出基于浏览器/服务器（Browser/Server简写为B/S）海洋平台结构的远程监测控制系统,实现在客户端不间断对平台进行实时监视,获得现场采集数据,并以图形方式进行实时显示,从而为平台的安全运行和结构设计提供科学依据。

基于CAN总线的海洋平台数据采集系统

介绍了一种基于CAN总线的数据采集系统,讨论了该系统应用在海洋平台这类特殊环境下的系统结构和现场节点的具体设计。系统由上位监控机、CAN网卡、智能网桥节点和智能采集节点组成,采用总线方式的网络拓扑结构,构成一种基于CAN总线的分布式监控采集系统。智能节点以AT89S52单片机为微控制器,使用SJA1000作为CAN控制器,可构成上行和下行网络通信波特率分别为500kbps和250kbps的CAN网络。详细分析了该系统的硬件组成,应用层协议和通讯流程。系统已应用于某海上平台的环境载荷的监测,提高了数据传输的可靠性,为平台的安全运行和结构的优化设计提供了科学依据。

Nonlinear analysis of pile foundation jacket platform

In this paper, the nonlinear collapse of the BOHAI-8 pile foundation jacket platform has been analyzed. The ultimate load and collapse process of two computational models of the structure are given. One model is of fixed support whose length is eight times the pile leg diameter and the other considers the nonlinearity of the soil-pile interaction.

Nonlinear Dynamic Response of Tension Leg Platform

Tension Leg Platform (TLP) is a typical compliant offshore structure for oil exploitation in deep water. Most of the existing mathematical models for analyzing the dynamic response of TLP are based on explicit or implicit assumptions that displacements (translations and rotations) are small magnitude. Herein a theoretical method for analyzing the nonlinear dynamic behavior of TLP with finite displacement is developed, in which multifold nonlinearities are taken into account, i.e. finite displacement, coupling of the six degrees of freedom, instantaneous position, instantaneous wet surface, free surface effects and viscous drag force. Using this theoretical model, we perform the numerical analysis of dynamic response of a representative TLP. The comparison between the degenerative linear solution of the proposed nonlinear model and the published one shows good agreements. Furthermore, numerical results are presented which illustrate that nonlinearities exert a distinct influence on the dynamic responses of the TLP.

Short-Term Nonlinear Response of Tension Leg Platform in Random Sea Waves

Most of the existing mathematical models for analyzing the dynamic response of TLP are based on explicit or implicit assumptions that motions (translations and rotations) are small magnitude. However, when TLP works in severe adverse conditions, the a priori assumption on small displacements may be inadequate. In such situation, the motions should be regarded as finite magnitude. This paper will study stochastic nonlinear dynamic responses of TLP with finite displacements in random waves. The nonlinearities considered are: large amplitude motions, coupling the six degrees-of-freedom, instantaneous position, instantaneous wet surface, free surface effects and viscous drag force. The nonlinear dynamic responses are calculated by using numerical integration procedure in the time domain. After the time histories of the dynamic responses are obtained, we carry out cycle counting of the stress histories of the tethers with rain-flow counting method to get the stress range distribution.

Parametric studies of tension leg platform with large amplitude motions

Tension leg platform (TLP) is an important kind of working station for deep water exploration and development in ocean, whose dynamic responses deserve a serious thought. It is shown that for severe sea state, the effects of nonlinearities induced by large displacements of TLP may be noteworthy, and then employment of small displacements model should be restrained. In such situation, large amplitude motion model may be an appropriate alternative. The numerical experiments are performed to study the differences of dynamic responses between the two models. It is shown that for most cases, differences between results of the two models are significant. The variances of the differences vs. the wave period are the most remarkable, and that of the differences vs. wave heading angle are also apparent.