本文選題：耦合歐拉-拉格朗日方法（CEL）　切入點(diǎn)：穿刺　出處：《天津大學(xué)》2014年碩士論文　論文類型：學(xué)位論文

【摘要】：自升式鉆井平臺(tái)在預(yù)壓期間容易發(fā)生“穿刺”事故，穿刺往往會(huì)對(duì)平臺(tái)造成巨大的危害甚至整個(gè)平臺(tái)的傾覆。目前，在實(shí)際工程中，關(guān)于穿刺是否發(fā)生SNAME規(guī)范和《海洋場(chǎng)井調(diào)查規(guī)范》等多采用地基極限承載力公式進(jìn)行評(píng)價(jià)。但是，海底地質(zhì)條件多種多樣，這些公式并不完全適用，因此，需要采用試驗(yàn)方法和有限元分析的方法解決穿刺問(wèn)題。 離心模型試驗(yàn)是一種模仿原位應(yīng)力場(chǎng)的有效的試驗(yàn)方法，它的優(yōu)勢(shì)在于通過(guò)提高徑向離心加速度，在一個(gè)縮小的模型箱里模擬樁靴的插入過(guò)程，得到與原位試驗(yàn)相同的應(yīng)力水平，是一種較為精確的模擬方法。根據(jù)本課題的需要，分別進(jìn)行了全模型和半模型離心模型試驗(yàn)。半模型離心模型試驗(yàn)結(jié)合PIV粒子圖像測(cè)速分析技術(shù)可以精確的得到樁靴在某一插深位置樁靴周圍土體的速度矢量圖，，從而得到土體的流動(dòng)機(jī)制和破壞模式。全模型試驗(yàn)得到荷載-插深曲線，通過(guò)不同插深位置的承載力分析，對(duì)穿刺發(fā)生可能性作出判斷。 由于離心模型試驗(yàn)耗資巨大，不易重復(fù)，因此，在離心模型試驗(yàn)的基礎(chǔ)上，采用ABAQUS有限元分析平臺(tái)進(jìn)行數(shù)值模擬。傳統(tǒng)的有限元模擬方法在研究樁靴插深之類的大變形問(wèn)題時(shí)，會(huì)因?yàn)榫W(wǎng)格變形過(guò)大造成計(jì)算不收斂，往往得不到計(jì)算結(jié)果。耦合的歐拉-拉格朗日方法（CEL）方法中地基土采用歐拉網(wǎng)格進(jìn)行模擬，將剛度大、變形微小的樁靴采用拉氏單元進(jìn)行模擬。這種方法可以完整的模擬動(dòng)態(tài)的插樁過(guò)程，解決計(jì)算過(guò)程中的大變形問(wèn)題。采用CEL方法模擬樁靴貫入成層土的過(guò)程，并用離心模型試驗(yàn)的結(jié)果對(duì)有限元分析進(jìn)行可靠性驗(yàn)證。 通過(guò)離心模型試驗(yàn)和CEL有限元分析模擬樁靴穿過(guò)多層粘土的過(guò)程得到以下結(jié)論： （1）SNAME推薦的理論計(jì)算方法的結(jié)果顯示中部硬層粘土上表層是可能發(fā)生穿刺的地方，兩種方法均未考慮硬層粘土對(duì)上下兩層軟粘土承載力的影響。 （2）通過(guò)PIV技術(shù)分析離心模型半模型試驗(yàn)得到的照片得到樁靴貫入三層粘土?xí)r不同插深的土體的速度矢量圖，說(shuō)明了樁靴穿過(guò)軟硬軟三層粘土?xí)r，當(dāng)樁靴靠近中部硬粘土層和穿過(guò)硬粘土層時(shí)均有可能發(fā)生穿刺的危險(xiǎn)。 （3）通過(guò)CEL有限元分析得到樁靴穿入成層粘土?xí)r土體的塑性區(qū)以及塑性區(qū)的深度隨樁靴插深變化的曲線。多層土承載顯現(xiàn)出與一般雙層土的插樁明顯的不同。硬層的存在對(duì)于地基承載力影響的大小和方式與硬層的厚度以及硬層的強(qiáng)度有關(guān)。
[Abstract]:During preloading, the jack-up drilling platform is prone to "puncture" accidents, which often cause great harm to the platform and even overturn the whole platform. At present, in actual engineering, As to whether the puncture occurs in SNAME Code and the Ocean Field well Survey Code, the formulas of ultimate bearing capacity of foundation are often used for evaluation. However, there are a variety of submarine geological conditions, and these formulas are not fully applicable, so, The method of test and finite element analysis is needed to solve the puncture problem. Centrifugal model test is an effective method to simulate in-situ stress field. Its advantage is to simulate the insertion process of pile boots in a reduced model box by increasing radial centrifugal acceleration. It is a more accurate simulation method to get the same stress level as the in-situ test. The semi-model centrifuge model test and semi-model centrifuge model test combined with PIV particle image velocimetry analysis technique can accurately obtain the velocity vector diagram of soil around the pile shoe in a certain inserted position. Thus the flow mechanism and failure mode of soil are obtained, and the load-depth curve is obtained by full-model test, and the possibility of puncture is judged by analyzing the bearing capacity of different insertion positions. Because the centrifugal model test is expensive and difficult to repeat, so, based on the centrifuge model test, ABAQUS finite element analysis platform is used for numerical simulation. When the traditional finite element simulation method is used to study the large deformation problems such as pile and boot depth, the calculation will not converge due to the large mesh deformation. In the coupled Euler-Lagrangian method (CEL), the foundation soil is simulated by Euler mesh, and the stiffness is large. The pile boots with small deformation can be simulated by Lagrangian element. This method can simulate the dynamic process of pile insertion and solve the problem of large deformation in the calculation process. CEL method is used to simulate the process of pile boots penetrating into layered soil. The reliability of finite element analysis is verified by the result of centrifugal model test. The following conclusions are obtained by centrifuge model test and CEL finite element analysis to simulate the process of pile boots passing through multilayer clay:. The results of the theoretical calculation method recommended by SNAME show that the upper surface layer of the middle hard clay is the place where the puncture may occur, and neither of the two methods takes into account the influence of the hard layer clay on the bearing capacity of the upper and lower layers of soft clay. (2) the velocity vector diagram of soil with different penetration depth was obtained by using PIV technique to analyze the semi-model test of centrifugal model. The results show that the pile shoe passes through soft and soft clay layers, and the velocity vector diagram of soil with different depth is obtained when the pile shoe penetrates into three layers of clay. When the pile boots are near the middle hard clay layer and through the hard clay layer, there is a danger of puncture. Through CEL finite element analysis, the curves of the plastic zone of soil and the depth of plastic zone varying with the depth of the pile shoe are obtained when the pile boots penetrate into the layered clay. The bearing capacity of the multi-layer soil is obviously different from that of the ordinary double-layer soil. The extent and mode of influence on the bearing capacity of foundation is related to the thickness of hard layer and the strength of hard layer.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：P751

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