【作者】 刘圆；

【导师】 岳前进；

【作者基本信息】 大连理工大学 ， 固体力学， 2007， 博士

【摘要】 目前抗冰平台的设计仍处于静力设计阶段。但是近几年在渤海辽东湾多座平台的现场监测表明，渤海导管架平台存在比较剧烈的冰激振动现象，并直接威胁着平台的安全。本文基于渤海抗冰平台的现场监测数据以及冰荷载研究的最新成果，对渤海抗冰海洋平台在动冰力作用的结构特性、疲劳分析方法以及结构选型等内容进行了系统的分析和研究。首先，本文对渤海现场原型试验和基于现场原型试验取得的冰荷载研究成果进行了归纳与总结。研究结果表明，圆柱桩腿平台存在冰致稳态振动，安装破冰锥体后，结构也会发生冰激共振现象。基于直接冰力与结构响应的同步测量数据已经建立了比较实用的冰力模型，这为开展抗冰结构的动力分析创造了条件。本文的研究内容是在消化了冰荷载研究成果的基础上开展的。对开展现场监测的四座平台建立了有限元模型。基于实测的自由振动衰减曲线，利用对数缩减法确定了渤海抗冰导管架结构的综合阻尼比，为提高抗冰平台动力分析的精度提供了基础。同时分析了结构的模态特征，并利用实测数据进行了对比，验证了模型的合理性，通过对四座平台的动力响应分析，阐述了渤海抗冰导管架平台的动力特性，指出渤海的抗冰导管架结构为静刚度比较大的柔性结构。在动力特性方面，无论是直立结构还是锥体结构，其基频都与冰荷载的频率接近或一致，抗冰平台呈现明显的动力放大柔性特征。在静力特性方面，渤海抗冰平台的静刚度较大，在极值静冰力作用下，结构的位移响应较小，结构具有较大的静力安全储备。这个特点对开展结构动力优化与结构振动控制有指导意义。对渤海抗冰导管架平台的疲劳问题进行了比较全面的分析，并对冰振作用下管结点疲劳寿命的详细计算方法进行了研究。基于实测冰力时程和冰激振动响应数据，论述了渤海抗冰导管架平台存在冰激疲劳失效问题。通过安全寿命分析，给出了冰激疲劳分析的流程，进一步完善了柔性抗冰导管架平台冰激疲劳寿命的分析方法，指出估计冰激疲劳寿命的关键问题是冰荷载与冰疲劳环境参数。同时根据多年的现场冰情监测与海冰数值模拟成果，建立了渤海JZ20-2海域的海冰疲劳环境模型，为进行详细冰激疲劳寿命估计提供了基础。利用谱分析方法，分别对新建的JZ20-2NW平台和现役的JZ20-2MSW平台进行了详细的冰激疲劳寿命估计。另外，还分析了冰激甲板振动对工作人员和上部管线系统的影响，指出甲板加速度引起的上部管线和作业人员的疲劳也是平台设计需要考虑的问题，设计过程需要对平台的甲板加速度进行分析。利用谱分析方法计算了渤海四座典型抗冰导管架平台在不同冰况下最大振动加速度响应幅值，并利用实测冰激振动响应验证了计算结果的合理性，同时论述了数值结果在实际工程中的应用。最后，论述了抗冰海洋平台的结构特点和类型，目前已经应用的抗冰海洋平台主要有人工岛和导管架平台两类，总结了这两类抗冰海洋平台的发展历史和结构特点，分析了四腿、三腿与单腿抗冰导管架结构的抗冰性能。结果表明，针对渤海冰区边际油田的开发，独腿导管架平台加抗冰锥体用作卫星平台是可行的，四腿导管架结构加抗冰锥体适合用作中心平台，并进一步论述了简易抗冰平台在渤海应用的可行性以及需要解决的关键问题。更多还原

【Abstract】 At present, the design of ice-resistant platforms is still in the state of static design. But itis indicated that the ice-induced vibration of ice-resistant platforms is quite intensive, anddirectly endangers the structural safety according to the field data monitored on severalplatforms in the Liaodong Bay of Bohai Sea in past years. A systematic research on thedynamic characteristic, ice-induced fatigue and structural lectotype of ice-resistant offshoreplatforms is presented based on in situ results of ice-induced vibration and the currentprogress Of ice load.Firstly, the full-scale field tests and the current achievements of ice load are summarized.It is found that the ice-induced steady vibration occurs on vertical structures, and theice-induced sympathetic vibration also happens on conical structures. The ice load model,which was developed based on the field synchronous results of ice load and structuralresponses, provides a probability to perform the dynamic analysis of ice-resistant platforms.The main works in this thesis are obtained with adopting the current achievements of ice load.The finite-element models of four ice-resistant structures are established, on whichfull-scale tests are carried on. The damping ratio of structures is determined with logarithmicreduced method using free damped curve of acceleration response obtained from field data,which can improve the precision of dynamic analysis. The modal analysis is conducted, and iscompared with the field data to prove its rationality.The dynamic characteristics of ice-resistant jacket platforms in the Bohai Sea areanalyzed, and it is pointed out that the platforms, as typical compliant structures, haverelatively large static rigidity according to dynamic response analysis of the four platforms.For the dynamic characteristics, both of the basic frequencies of vertical and conicalstructures are close or consistent with the frequency of ice load. The phenomenon of dynamicmagnifying, as a typical compliant characteristic, is obvious on the ice-resistant jacketplatforms. For the static characteristics, the static rigidity is relatively large with smalldisplacement, and the static safety stock of the structure is enough under the maximum staticice load. The characteristics above can be applied for dynamic optimization and vibrationcontrol of the structure.A general analysis about fatigue for ice-resistant jacket platform in the Bohai Sea isprocessed, and the method of computing ice-induced fatigue life of tube node is studied indetails. Based on the field data of ice load history and ice-induced response, the probability offatigue failure for ice-resistant jacket platforms is discussed. Through the safety fatigueanalysis, the flowcharts of fatigue analysis are given, and the further perfect estimationmethod of ice-reduced fatigue life is improved for ice-resistant platforms. With the analysisabove, it can be concluded that the ice load and the ice fatigue environmental parameters arethe key problems for estimating the ice-induced fatigue life. Moreover, the ice fatigueenvironmental model of JZ20-2 area in the Bohai Sea is established based on the field dataand simulated numerical results in the last decade. The ice-reduced fatigue lives ofJZ20-2NW platform that was built recently, and of JZ20-2MSW platform that is in service areanalyzed with the spectral method in details.Moreover, the influences of ice-indueed acceleration on the stuff and the pipeline systemon the platform are discussed. It is pointed out that the influence of ice-induced accelerationshould be also taken into consideration, and it is necessary to analyze the deck acceleration inthe structural design. The maximal acceleration amplitudes under ice combinationalconditions of various ice thickness and ice velocity are computed with spectrum method. Andthe accuracy of numeric results is proved with the field data. Meanwhile, the application ofnumeric results in practical engineering is discussed.At last, the ice-resistant structural types and their structural characteristics are discussed.There are two kinds of ice-resistant structures as man-made island and jacket platform. Thephylogeny and structural characteristics of the two kinds of ice-resistant structures aresummarized, and the ice-resistant performances of single-legged, three-legged andfour-legged platforms are compared. The results reveal that the monopod jacket platform withice-breaking cone is feasible for satellite platform, and the four-legged platform withice-breaking cones can be adapted as centre platform aiming at the exploitation of margin oilfield in the ice-covered zone of Bohal Sea. The feasibility of simple ice-resistant platform inthe Bohai Sea and the relative key problems are discussed briefly also.更多还原