【作者】 曾志；

【导师】 杨建民；

【作者基本信息】 上海交通大学 ， 船舶与海洋结构物设计制造， 2009， 硕士

【摘要】 目前在深海油气田钻采工程中获得广泛应用的浮式生产系统主要有FPSO、SEMI-SUBMERSIBLE、SPAR和TLP四种。其中半潜式平台由于总投资小,甲板面积和可变载荷大,移动灵活,稳定性好,作业可靠,在石油勘探开发领域中发挥着重要作用。尤其是其工作水深范围广,能够适应较恶劣的海况条件,在我国南海等深水海域有着广泛的应用前景。气隙是指波浪表面到平台下甲板下表面的垂直距离,它是平台设计过程中要考虑的关键问题之一。为了减小波浪载荷,海洋工程结构物的垂向支撑结构(如半潜平台的立柱,导管架平台的支腿等)一般较为细长,而甲板面积则相对巨大以增加作业能力。因此,若波浪直接砰击甲板,则可能造成严重的结构破坏,甚至导致平台倾覆。本论文通过理论分析、数值计算和模型试验相结合的研究方法,以一座深水半潜式钻井平台为例,1、引入了一种新的试验数据处理方法,得到概率对应的气隙响应曲线。该响应曲线近视为直线。(1)它可以更准确地对各测点发生波浪砰击的危险程度进行比较;(2)还可以用来分析各测点相对波面升高对入射波高的敏感程度,曲线斜率越高,敏感程度也越高;(3)同时,还可以使用其对未进行水池模型试验的海况下的平台气隙响应进行预报。2、对平台在5种海况下的气隙响应进行了数值计算,并与相应的模型试验相比较。从比较结果可以看出:(1)在海况条件恶劣,波高较大时,一阶数值计算和Stokes二阶统计修正的结果均低估了相对波面升高的极值,且波陡越大,低估越严重。但是,它可以较好的预报危险点的位置,因此,可以用来在进行模型试验之前确定探针的布置位置和试验浪向;(2)垂荡对半潜平台的垂向运动的影响最大,但横摇和纵摇的影响也不可忽视,尤其是波浪谱峰周期与摇动的固有周期接近时; (3)平台在斜浪和横浪时,在立柱的外角隅区域上浪的危险最大,在数值预报和试验测量时须予以特别关注,同时在进行结构设计时可进行适当的局部加强;(4)高阶散射和立柱处的波浪爬升效应对气隙的影响不可忽略,但目前尚无较好的数值计算软件和方法,因此,在新平台设计时,一般需进行水池模型试验。3、在原平台的基础上,保持吃水和重心位置、惯性半径等参数(除排水量外)均不变,分别选取三种典型的下浮体结构型式和三种典型的立柱型式,对其运动性能和气隙性能进行了比较。从比较结果可以看出:(1)下浮体连接构件的型式对各点的影响不尽一致,但在气隙响应最为恶劣的立柱角隅处,横撑杆型式的连接构件优于翼型和环形下浮体型式;(2)在各海况下的气隙响应均为圆柱形立柱优于方形立柱。更多还原

【Abstract】 FPSO, Semi-submersible, Spar and TLP are the four main floating platform types used for deepwater oil and gas exploitation at present. Among them, Semi-submersible has priority of less total investment, more deck space、deck variable load and production ability. It also has multiple functions of drilling, well repairing, production and so on. And it could also be easily transformed according to different requirements. Especially its ability to adapt wide range of water depth and harsh sea states make it has an extensive application prospect in the deepwater oil field development in South China Sea.The air gap response, and potential deck impact, is a very important issue in the design of floating offshore systems. Usually it is desirable to maintain the main deck of any offshore platform above the sea surface throughout all anticipated environmental events. Main decks generally support a vast array of production equipment and accommodations for resident platform workers. Accordingly, there is some level on the platform, generally the underside of the main deck, which is the minimum level intended to remain above the largest wave elevation the platform will experience throughout its design life. Air gap is defined as the vertical clearance between the water surface and this design level.Most types of offshore platforms have relatively slender vertical structures supporting bulky deck structures. The slender supports have reasonably low horizontal loads induced by passing ocean waves. However, if a wave directly impacts on the deck structure, the horizontal loads could be dramatically larger than those for which the structure is designed, and cause serious subsequence, like stability problems, severe local structural damage or even toppling of the structure.This dissertation mainly investigates the following items of a deepwater semi-submersible:1.Introduce a fractile-based analysis to process the model test results, and obtained an approximate straight line. This can be used for (1) comparing the risk of wave impact at different measure points; (2) comparing the sensitivity of relative wave elevation at different measure points referring to the incident wave elevation; and (3) predicting the air gap demand at sea states that haven’t been model tested.2.Presents the linear numerical prediction results with Stokes 2 nd order correction and compares with the corresponding experimental results, under 5 different sea states, including regular and irregular waves. The results show that (1) the linear analysis usually underestimates the air gap demands in harsh sea states, since the non-linear effects might some times play an important role, but it’s also demonstrated that the theoretical models are able to reproduce the spatial variation of the wave elevation quite well and can be used to determine the arrangement of wave probes before model test; (2) heave response is the uppermost platform motion for air gap prediction, and the roll & pitch response also play an important roll, especially when its natural period is close to the wave spectrum peak period; (3) the most critical position that a minus air gap phenomenon will happen is the column outer corner, at beam or quartering sea states. Careful examination should be carried out and proper local structural reinforcement is also considerable; and(4) high order diffraction and wave run-up effect near the columns are un-ignorable, but there’s no software that can reproduce these effects accurately at present, and a basin test is still necessary for the platform design.3.Compares the air gap response of different semi-submersible types, including 3 typical pontoon-transverse-connection structure types and 3 typical column types. The results show that (1) the pontoon-transverse-connection structure types have different affects to the air gap responses at different locations. But at the most critical position, that is, the column outer corner, circular cylinder bracing is better than wing type structure and ring pontoon type structure; (2) circular column has better air gap performance than rectangular column at any sea state.更多还原