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  本文關(guān)鍵詞： 自升式平臺 波浪載荷 動力響應 疲勞分析　出處：《華南理工大學》2014年碩士論文　論文類型：學位論文

【摘要】：桁架式的自升式平臺，其自身柔性較大，在復雜多變的海洋環(huán)境載荷的作用下，平臺結(jié)構(gòu)動力響應明顯而復雜，特別是在波浪載荷這一主要控制載荷的長期作用下，平臺樁腿容易出現(xiàn)裂紋，甚至發(fā)生疲勞失效，因此，對自升式平臺樁腿進行動力響應研究和疲勞分析，并預測其疲勞壽命，對于自升式平臺的安全使用是非常必要的。 本文采用海洋工程專業(yè)軟件SACS，對自升式平臺樁腿進行動力響應和疲勞分析研究。首先，對作業(yè)工況進行模態(tài)分析，對比其固有頻率與波浪頻率，判斷其共振的可能性；然后，在此基礎(chǔ)上，進行平臺結(jié)構(gòu)的波浪動力響應分析；最后，考慮動力放大效應和應力集中的影響，采用直接確定性方法和動態(tài)譜分析方法進行平臺樁腿的疲勞壽命預測。 本文的主要工作如下： 1)闡述海洋環(huán)境載荷、疲勞分析的基本理論和方法，介紹基于SACS的疲勞分析流程等； 2)采用海洋工程軟件SACS建立自升式平臺的三維有限元模型，考慮樁-土非線性邊界條件的影響，，研究船體與樁腿結(jié)構(gòu)的連接方法以及采用弦桿模型的等效方法解決樁腿水動力問題，并對平臺樁腿結(jié)構(gòu)進行強度校核和樁基承載力校核；應用模態(tài)分析方法計算平臺的固有頻率，并與設(shè)計波浪頻率進行對比分析，判斷發(fā)生共振的可能性；另外，還對平臺結(jié)構(gòu)進行波浪動力響應分析，將波浪載荷下的動力響應與準靜態(tài)分析結(jié)果進行對比； 3)采用頻域分析方法中的直接確定性方法和譜分析方法分別對自升式平臺進行疲勞分析研究，并考慮結(jié)構(gòu)動力放大效應和應力集中系數(shù)的影響，對平臺樁腿進行疲勞壽命預測。采用直接確定性方法進行疲勞分析時，選取一年期波浪散布圖中發(fā)生頻次較高的24組波浪，進行平臺樁腿的疲勞壽命預測，疲勞壽命較短的區(qū)域集中在樁腿飛濺區(qū)的左舷位置及樁腿與主船體連接處；采用譜分析方法預測在波浪交變載荷作用下平臺的疲勞壽命時，以北海-BeryFrig地點處的一年期波浪散布圖為海況條件進行研究，通過計算應力傳遞函數(shù)，求得管節(jié)點的結(jié)構(gòu)響應譜密度函數(shù)，再根據(jù)S-N曲線和Miner線性累計損傷理論，求得平臺樁腿的疲勞壽命。通過分析上述兩種方法的計算結(jié)果可知，直接確定性方法的計算精度雖不如譜分析方法的計算精度高，但該方法計算簡單易行，在初步進行自升式平臺疲勞分析時，可先用直接確定性方法確定較為危險的管節(jié)點，再使用譜分析方法做進一步的疲勞分析，該方法的結(jié)果滿足海洋平臺疲勞分析的精度要求； 4)分別就S-N曲線的選擇、常見波浪譜密度（P-M譜等）、管節(jié)點應力集中系數(shù)SCF的計算方法以及波浪散布圖等因素對自升式平臺樁腿結(jié)構(gòu)譜疲勞分析結(jié)果的影響進行探討，并給出了合理的選擇范圍和方法。
[Abstract]:The truss self-lifting platform is flexible, and the dynamic response of the platform structure is obvious and complex under the complex and changeable marine environment load. Especially under the long-term action of wave load, the pile leg of platform is prone to crack and even fatigue failure. Therefore, the dynamic response and fatigue analysis of the platform pile leg are carried out. It is necessary to predict its fatigue life for the safe use of bootstrap platform. In this paper, the marine engineering professional software SACSS is used to analyze the dynamic response and fatigue of the pile leg of the jack-up platform. Firstly, the modal analysis is carried out to compare the natural frequency with the wave frequency. Judging the possibility of resonance; Then, on this basis, the wave dynamic response of the platform structure is analyzed. Finally, considering the effect of dynamic amplification and stress concentration, the direct deterministic method and dynamic spectrum analysis method are used to predict the fatigue life of the platform pile leg. The main work of this paper is as follows: 1) the basic theory and method of marine environmental load and fatigue analysis are introduced, and the fatigue analysis flow based on SACS is introduced. 2) the three-dimensional finite element model of jack-up platform is established by using marine engineering software SACS, and the influence of pile-soil nonlinear boundary condition is considered. The connection method between the hull and the pile leg structure and the equivalent method of the chord model are studied to solve the hydrodynamic problem of the pile leg, and the strength check and bearing capacity check of the platform pile leg structure are carried out. The natural frequency of the platform is calculated by using the modal analysis method, and compared with the design wave frequency, the possibility of resonance is judged. In addition, the wave dynamic response of the platform structure is analyzed, and the dynamic response under the wave load is compared with the quasi-static analysis results. 3) the direct deterministic method and spectral analysis method in frequency domain are used to analyze the fatigue of the jack-up platform, and the influence of dynamic amplification effect and stress concentration factor are considered. The fatigue life of platform pile leg is forecasted. When fatigue analysis is carried out by using direct deterministic method, 24 groups of waves with high frequency in the wave scatter map of one year are selected to predict the fatigue life of platform pile leg. The area with shorter fatigue life is concentrated in the port side position of the splashing zone of the pile leg and the joint between the pile leg and the main hull. In order to predict the fatigue life of the platform under the action of wave alternating load, the one-year wave dispersion map at Beihai BeryFrig site is used to study the sea condition when the spectrum analysis method is used. By calculating the stress transfer function, the structural response spectral density function of the tubular joints is obtained, and then according to the S-N curve and the Miner linear cumulative damage theory. The fatigue life of the platform pile leg is obtained. By analyzing the calculation results of the above two methods, it can be seen that the calculation accuracy of the direct deterministic method is not as high as that of the spectral analysis method, but this method is simple and feasible. In the initial fatigue analysis of jack-up platform, the more dangerous pipe joints can be determined by direct deterministic method, and then further fatigue analysis can be done by using spectrum analysis method. The results of this method can meet the precision requirements of offshore platform fatigue analysis. 4) the selection of S-N curve, the common wave spectrum density and P-M spectrum, etc. The calculation method of stress concentration factor (SCF) of pipe joints and the influence of wave scatter diagram on the spectrum fatigue analysis results of pile leg structure of jack-up platform are discussed, and the reasonable selection range and method are given.
【學位授予單位】：華南理工大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：P751

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本文編號：1482090