【作者】 吕阳；

【导师】 杨庆； 王胤；

【作者基本信息】 大连理工大学 ， 岩土工程， 2015， 硕士

【摘要】 吸力式筒形基础在海洋工程中已获得越来越广泛的应用,其安装过程的数值模拟及理论研究对指导工程实践具有重要意义。在大型通用有限元软件ABAQUS平台上建立了二维轴对称模型,基于任意拉格朗日-欧拉算法(Arbitrary Lagrangian-Eulerian formulation, ALE)技术,解决了大变形网格畸变问题,成功模拟了黏性土中吸力筒的沉贯过程。在数值模型中通过编写子程序VUFIELD表达土体的不排水抗剪强度和弹性模量随土体深度变化。采用西澳大学的离心机试验数据及理论计算,对模型进行验证。利用已验证数值模型分析了不同吸力下沉贯阻力、土塞高度并讨论了筒壁摩擦特性对吸力筒沉贯的影响。数值计算结果表明,ALE技术能有效模拟吸力筒贯入过程,很好地解决了由于土体大变形而引起的网格畸变问题。贯入方式对贯入阻力影响很大,吸力式贯入阻力明显低于压力式贯入阻力。进一步研究发现,随着最终吸力值的增大,沉贯阻力会显著降低,土塞高度会显著提高。对吸力筒内壁摩擦特性的研究表明,内壁摩擦阻力是导致沉贯阻力改变的主要因素；相比吸力式贯入方式,压力式贯入受筒壁摩擦特性的影响更为显著。通过理论推导建立了吸力筒内壁摩擦力解析模型,并对沉贯过程中渗流作用对筒内壁摩擦阻力的影响进行了研究。从筒内土体微元段受力平衡的角度出发,充分考虑土体受力和变形状态以及渗流作用,推导了吸力筒贯入过程中土-筒摩擦应力计算的解析模型。并通过有限元程序ABAQUS建立吸力筒沉贯及土体渗流数值模型,对解析模型进行对比和验证。针对渗流速度、土-筒摩擦系数和筒体长径比进行了讨论分析。结果表明,渗流作用会显著降低土体的竖直有效应力,从而减小筒内壁摩擦阻力。通过对渗流速度的分析,发现应根据渗流速度判断渗流体系,从而合理选取不同渗流理论获得准确的筒内壁摩擦力结果。土-筒摩擦系数增大会造成土-筒法向正应力的增大,进而使得摩擦应力进一步增大。增大筒体长径比会增加土-筒摩擦应力,但筒内壁总摩擦力会随着筒长径比呈现倒抛物线的变化形式,存在最小值。由于理论推导是建立在筒内土体竖直有效应力沿径向均匀分布的假设基础上的,因而在使用该解析模型时,应考虑筒体长径比满足一定的限定条件。由于海洋工程问题的复杂性,以及试验研究的高成本和不确定性,通过本研究可以看出,数值模拟仍然是对海洋工程及其基础构筑物研究的有效方法。大变形有限元模拟技术对吸力筒的研究取得了一定的成功,但应得到进一步的改进,比如对于特殊土体采用合适的本构模型；提高ALE数值计算的速度等。数值模拟对吸力筒的研究还应进一步考虑土体微细观和特细观特性等。更多还原

【Abstract】 Suction bucket foundations are more and more widely used in ocean engineering, the numerical analysis and the theory research of the installation procedure is helpful to guide engineering practice.A two-dimensional axisymmetric model has been established on the finite element software ABAQUS with the help of the ALE (Arbitrary Lagrangian-Eulerian formulation) technique to simulate the penetration process of the suction bucket foundation in clay. The undrained shear strength of soil and elastic modulus are varied with depth of soil through the subroutine VUFIELD. A centrifuge test and theoretical calculation are used for FEM model validation. After the validation, the penetration resistance, the height of soil plug under different suctions and the bucket wall friction have been examined. Based on the numerical results, it is shown that the ALE technique is able to simulate the suction bucket penetration without mesh distortion problems. The installation method can play an important role on the penetration resistance, namely, the suction penetration reduces the resistance significantly than the purely jacked penetration. Through a further study, it is found that as the final suction increases, the soil plug height increases, while the penetration resistance reduces with increases of the final suction. The effect of internal friction on the bucket wall has been also investigated and a conclusion is drawn that internal friction has a significant contribution to the penetration resistance and the properties of soil-bucket wall friction give rise to bigger impact to the resistance when the purely jacketed penetration than the suction penetration.According to the soil micro yuan period of force equilibrium, fully considering the soil elastoplastic state and internal seepage effect, bucket wall friction stress theory formula was derived. And using the large finite element software ABAQUS to establish numerical model for verification. In view of the seepage velocity, bucket wall friction coefficient and the bucket length to diameter ratio perform parametric analysis. The results show that the seepage will significantly reduce the internal friction stress. The results of friction stress from different seepage theory are very different, reasonable selection of seepage theory based on seepage velocity is important. The increase of bucket wall friction coefficient can cause the increase of bucket wall normal stress which makes the friction stress increases further. Increasing the bucket length to diameter ratio can increase the bucket wall average friction stress. But the inner bucker wall total friction with the bucket length to diameter ratio presents inverted parabolic form of change. Too big or too small bucket length to diameter ratio will increase the error of the theoretical formula.Because of the complexity of the Marine engineering problems, as well as the high cost and uncertainty of experimental study, through this study it can be seen that the numerical simulation is still effective approaches to the study of ocean engineering and its the basic structures. Large deformation finite element simulation technology study of suction bucket has achieved some success, but it should be improved further. Such as using the more appropriate constitutive model to describe special soil. Improve the speed of the ALE numerical calculation. Numerical simulation study of soil suction bucket also should further consider the micro meso and mesoscopic.更多还原