摘 要
隨著陸地油氣資源的不斷枯竭，海洋成了未來能源的主戰(zhàn)場(chǎng)。作為深海油氣開發(fā)的主流裝備，新型半潛式海洋鉆井平臺(tái)對(duì)我國(guó)而言，還有很大的空間有待探究。其一，就水動(dòng)力性能而言，半潛平臺(tái)的低垂蕩運(yùn)動(dòng)有利于更高的時(shí)間比例進(jìn)行鉆探，較低橫搖、縱搖幅值運(yùn)動(dòng)有助于平臺(tái)操作和運(yùn)輸，以及其他水動(dòng)力性能的研究有利于動(dòng)力定位系統(tǒng)的開發(fā)，等等；其二，就結(jié)構(gòu)強(qiáng)度分析而言，結(jié)構(gòu)強(qiáng)度是平臺(tái)良好運(yùn)行的先決條件，其意義不言自明；其三，由于波浪載荷的循環(huán)作用，就必須考慮疲勞強(qiáng)度；其四，在結(jié)構(gòu)設(shè)計(jì)階段，往往只考慮強(qiáng)度，而工藝建造水平以及經(jīng)濟(jì)效益才是真正決定該領(lǐng)域的發(fā)展方向，故在結(jié)構(gòu)設(shè)計(jì)時(shí)也要多考慮工藝和經(jīng)濟(jì)效益；等等。
本文依托ABS規(guī)范，用DNV.SESAM軟件完成了平臺(tái)結(jié)構(gòu)強(qiáng)度分析、水動(dòng)力性能分析和關(guān)鍵部位疲勞可靠性分析。其主要研究?jī)?nèi)容和結(jié)論如下：
1）統(tǒng)計(jì)了半潛式鉆井平臺(tái)的發(fā)展歷史和現(xiàn)行狀況，分析了平臺(tái)結(jié)構(gòu)和技術(shù)特點(diǎn)，總結(jié)了國(guó)內(nèi)外波浪載荷和疲勞可靠性的研究現(xiàn)狀。
2）闡述了水動(dòng)力分析的基本理論，其中包括零航速的三維勢(shì)流理論求解，任意位置任意點(diǎn)的morison桿上波浪力的求解，平臺(tái)水動(dòng)力參數(shù)的物理意義以及波浪載荷長(zhǎng)期預(yù)報(bào)的理論推導(dǎo)。根據(jù)ABS《近海結(jié)構(gòu)物疲勞評(píng)估》規(guī)范，從理論上推導(dǎo)了采用S-N曲線與Miner線性累積損傷理論為基礎(chǔ)的疲勞譜分析法，總結(jié)了結(jié)構(gòu)熱點(diǎn)譜疲勞可靠性分析的完整過程。
3）完成了三種半潛平臺(tái)的波浪載荷計(jì)算和水動(dòng)力性能比較分析，得出斜撐平臺(tái)的垂蕩響應(yīng)運(yùn)動(dòng)最優(yōu)，以及撐桿結(jié)構(gòu)的變化對(duì)平臺(tái)一階波浪激勵(lì)力影響不大。
4）總結(jié)了目標(biāo)半潛平臺(tái)的結(jié)構(gòu)強(qiáng)度分析方法和流程，并采用隨機(jī)性設(shè)計(jì)波法，確定了三種半潛平臺(tái)的設(shè)計(jì)波參數(shù)，得出中縱剖面的最大縱向剪切狀態(tài)時(shí)波浪載荷最惡劣。同時(shí)，根據(jù)ABS規(guī)范對(duì)三種平臺(tái)的關(guān)鍵部位進(jìn)行了屈服強(qiáng)度校核，得到斜撐平臺(tái)最好，但疲勞熱點(diǎn)數(shù)較多，推薦改用空間交叉型的撐桿結(jié)構(gòu)。此外，還分析了水平撐桿的焊接工藝技術(shù)和探討了不同撐桿形式對(duì)建造的影響，可知斜撐結(jié)構(gòu)工藝相對(duì)復(fù)雜。
5）采用疲勞譜分析法，預(yù)報(bào)了撐桿趾端疲勞壽命，結(jié)果顯示符合ABS規(guī)范的設(shè)計(jì)壽命20年要求，并得到了97.13%以上的可靠度。

關(guān)鍵詞：半潛平臺(tái)；譜分析法；結(jié)構(gòu)強(qiáng)度；水動(dòng)力性能分析；疲勞可靠性






Abstract
As the hydrocarbon resources inland is unceasingly decreasing, the exploitation of those resources is transferring to the ocean, and the marine energy is becoming the major energy resources in the future. Nowadays, the semi-submersible drilling platforms have played key roles in the deep-sea exploitation, and still, with a lot of scope of development. Firstly, as to hydrodynamic performance, for instance, reducing the heave motion of the semi-submersible platform can bring more time for drilling; decreasing the amplitude of roll and pitch can contribute to platform operation and transportation; studying on further hydrodynamic performance will benefit to the development of the dynamic positioning, etc. Secondly, since structural strength analysis is treated as the priority of maintaining the platform in good condition, the further research on it is of great significance. Moreover, due to the effect of cyclic loading, we should take fatigue assessment into consideration when we get down to analysis. Additionally, in the stage of structure design, we should pay more attention to the construction level and economic returns instead of the mechanical properties.
The analysis of structural strength analysis, hydrodynamic analysis, and fatigue reliability analysis of a hotspot location for aimed semi submersible platform will be carried out by DNV.SESAM software, which are based on ABS specifications. So the following problems are emphatically investigated.
1) In this paper, the development history and current status for the deep-water semi-submersible drilling platform will be introduced as well as the analysis of structure and technical characteristics. Besides, the status quo of wave loads and fatigue reliability in China and abroad will be summarized.
2) The basic theory of hydrodynamic analysis is represented which includes solution for 3D potential theory at zero speed, solution for wave force in any location which be based on Morison theory, physical significance of hydrodynamic parameter for platform, and theoretical derivation of long-term forecast for wave load. With the requirements of ABS Guide for the Fatigue Assessment of Offshore Structures, the spectral-based fatigue analysis approach is derived theoretically by using S-N curve and Miner’s rule in accordance. The complete process of the spectral fatigue reliability analysis for hotspots is summarized.
3) With the calculation of wave load and comparative analysis of hydrodynamic performance for three semi submersible platforms, it was deduced that the third platform in diagonal brace has the minimum heave RAO swing motion response and the changes of brace structural make very little difference on 1st order wave exciting force.
4) The method and process of analysis for structural strength of semi submersible platform is summarized. The design wave parameters of three semi submersible platforms are determined by using random design wave method, thus the conclusion that the wave load in the state of longitudinal shear force between pontoons is the worst is put forward. Meanwhile, ..