本文選題：風(fēng)暴潮 + 隨機波浪力��； 參考：《江蘇科技大學(xué)》2014年碩士論文

【摘要】：隨著全球氣候的不斷變化，海洋環(huán)境變得異常復(fù)雜。特別是近年來我國沿海地區(qū)臺風(fēng)頻發(fā)，由此產(chǎn)生的臺風(fēng)風(fēng)暴潮給近海采油平臺的安全帶來了嚴峻考驗。在高幅值隨機波浪力的長期作用下，容易引發(fā)結(jié)構(gòu)的疲勞問題。結(jié)構(gòu)疲勞壽命的影響因素大多是不確定的，必須從可靠度理論入手，對結(jié)構(gòu)的疲勞壽命作出合理的預(yù)測。應(yīng)力幅值和應(yīng)力集中系數(shù)是影響結(jié)構(gòu)疲勞壽命的兩個重要因素。選取樁腿底部和每層橫梁的部分管節(jié)點作為研究對象，考察平臺結(jié)構(gòu)在隨機波浪力作用下的疲勞性能和可靠度。本文以某一導(dǎo)管架平臺為例，對風(fēng)暴潮作用下結(jié)構(gòu)的疲勞可靠度進行了系統(tǒng)地研究。主要研究內(nèi)容包括： （1）基于隨機海浪的二維模型—Longuest-Higgins模型，以改進的JONSWAP譜作為理想海浪譜，，通過MATLAB編程實現(xiàn)風(fēng)暴潮環(huán)境下隨機海浪的數(shù)值仿真。根據(jù)Welch算法基本原理，利用MATLAB中的pwelch函數(shù)對仿真結(jié)果進行功率譜估計。通過與原有的JONSWAP譜進行對比，可以看出仿真效果良好。在此基礎(chǔ)上，提出影響仿真結(jié)果和功率譜估計的幾個主要參數(shù)及其取值標準。 （2）根據(jù)不同波浪理論的適用范圍，選用Stokes二階波和線性波理論，結(jié)合線性化Morison方程，分別給出隨機波浪力的時域表達式。在此基礎(chǔ)上，利用MATLAB求解任意時刻作用在導(dǎo)管架平臺桿件上的隨機波浪力。運用有限元軟件ANSYS建立結(jié)構(gòu)有限元模型，通過施加隨機波浪力，對其進行瞬態(tài)動力分析，得到平臺各點的名義應(yīng)力時程。 （3）考慮到應(yīng)力集中系數(shù)對結(jié)構(gòu)疲勞損傷的影響，首先在ANSYS中利用SHELL63單元建立管節(jié)點的局部有限元模型，通過施加整體有限元模型中的位移邊界條件，求出各管節(jié)點的熱點應(yīng)力，從而得到熱點處的應(yīng)力集中系數(shù)。接著，運用雨流計數(shù)法統(tǒng)計出各熱點的應(yīng)力時程所對應(yīng)的等效應(yīng)力循環(huán)。最后，根據(jù)S-N曲線和Miner線性疲勞累積損傷理論，估算出各熱點的疲勞損傷度D和疲勞壽命N f。 （4）介紹了隨機疲勞載荷作用下考慮不確定因素的結(jié)構(gòu)疲勞損傷計算方法，給出結(jié)構(gòu)疲勞壽命的參數(shù)表達式。通過定義隨機變量來描述影響結(jié)構(gòu)疲勞壽命的幾種不確定因素，給出不確定因素下結(jié)構(gòu)的疲勞壽命可靠度計算公式。由此，可計算出該導(dǎo)管架平臺各點的疲勞壽命可靠度Pr和失效概率Pf。
[Abstract]:As the global climate changes, the marine environment becomes extremely complex. Especially in recent years, typhoon occurred frequently in coastal areas of China, and the typhoon storm surge brought severe test to the safety of offshore oil production platform. Under the action of high amplitude random wave force for a long time, it is easy to cause the fatigue problem of the structure. The influencing factors of fatigue life of structures are mostly uncertain. It is necessary to make a reasonable prediction of the fatigue life of structures based on the reliability theory. Stress amplitude and stress concentration factor are two important factors affecting fatigue life of structure. The fatigue behavior and reliability of the platform structure under random wave force were investigated by selecting the pipe joints at the bottom of the pile leg and the cross beam of each layer as the research object. In this paper, the fatigue reliability of a jacket platform under the action of storm surge is systematically studied. The main research contents include: 1) based on the two-dimensional model of random wave, the improved JONSWAP spectrum is used as ideal wave spectrum, and the numerical simulation of random wave in storm surge environment is realized by MATLAB programming. According to the basic principle of Welch algorithm, the power spectrum of the simulation results is estimated by using the pwelch function in MATLAB. By comparing with the original JONSWAP spectrum, we can see that the simulation effect is good. On this basis, several main parameters affecting simulation results and power spectrum estimation and their values are proposed. 2) according to the applicable range of different wave theories, Stokes's second-order wave theory and linear wave theory are selected, and the time-domain expressions of random wave forces are given in combination with linearized Morison equation. On this basis, the random wave force acting on the jacket platform member at any time is solved by MATLAB. The finite element model of the structure is established by using the finite element software ANSYS. By applying random wave force, the transient dynamic analysis is carried out, and the nominal stress time history of each point of the platform is obtained. Considering the effect of stress concentration factor on fatigue damage of structure, the local finite element model of pipe joint is established by using SHELL63 element in ANSYS. By applying the displacement boundary condition in the integral finite element model, the hot stress of each pipe joint is obtained. The stress concentration factor at the hot spot is obtained. Then, the equivalent stress cycles corresponding to the stress history of each hot spot are calculated by the rain flow counting method. Finally, according to S-N curve and Miner linear fatigue cumulative damage theory, the fatigue damage degree D and fatigue life N f of each hot spot are estimated. In this paper, the fatigue damage calculation method considering uncertain factors under random fatigue load is introduced, and the parameter expression of structure fatigue life is given. Several uncertain factors affecting the fatigue life of structures are described by defining random variables, and the formulas for calculating the reliability of fatigue life of structures under uncertain factors are given. Therefore, the fatigue life reliability and failure probability of the jacket platform can be calculated.
【學(xué)位授予單位】：江蘇科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：P742;TE952

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