吸力筒贯入有限元模拟及内壁摩擦的理论研究
发布时间：2018-07-17 15:34
【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。
[Abstract]:Suction cylindrical foundation has been more and more widely used in marine engineering. Numerical simulation and theoretical study of its installation process are of great significance to guide engineering practice. Based on the Arbitrary Lagrangian-Eulerian formation (ale) technique, a two-dimensional axisymmetric model is established on the platform of Abaqus. The problem of large deformation mesh distortion is solved, and the sinking process of suction cylinder in clay is successfully simulated. In the numerical model, the undrained shear strength and elastic modulus of soil are expressed by the subprogram VUFIELD with the variation of soil depth. The model is verified by the centrifuge test data and theoretical calculation of the University of Western Australia. By using the verified numerical model, the penetration resistance of different suction sinking forces and the height of soil plug are analyzed and the influence of friction characteristics of cylinder wall on the penetration of suction cylinder is discussed. The numerical results show that ale technique can effectively simulate the penetration process of suction cylinder and solve the problem of grid distortion caused by large deformation of soil. The penetration resistance of suction type is obviously lower than that of pressure type. It is found that with the increase of the ultimate suction value, the penetration resistance decreases significantly and the plug height increases significantly. The study of friction characteristics of suction cylinder shows that the friction resistance of inner wall is the main factor leading to the change of sinking resistance, and the pressure penetration is more significantly affected by the friction characteristics of cylinder than the suction penetration. Based on the theoretical derivation, an analytical model of friction force on the inner wall of suction cylinder is established, and the influence of seepage on friction resistance of inner wall of suction cylinder is studied. From the point of view of the stress balance of the micro-element section of the soil in the tube, the stress and deformation state of the soil and the seepage flow are fully considered, and an analytical model for the calculation of the soil-tube friction stress in the process of suction cylinder penetration is derived. The numerical models of suction tube penetration and soil seepage are established by finite element program Abaqus, and the analytical model is compared and verified. The seepage velocity, the friction coefficient of soil-cylinder and the ratio of length to diameter are discussed and analyzed. The results show that the vertical effective stress of soil can be significantly reduced by seepage and thus the friction resistance of the inner wall of the cylinder will be reduced. Through the analysis of the seepage velocity, it is found that the seepage system should be judged according to the seepage velocity, and the accurate friction results of the inner wall of the cylinder can be obtained by reasonably selecting different seepage theories. The increase of the friction coefficient of soil-tube will cause the normal stress of soil-cylinder to increase, and further increase the frictional stress. Increasing the ratio of length to diameter of the tube increases the friction stress, but the total friction force of the inner wall of the cylinder changes in the form of inverted parabola with the ratio of length to diameter of the tube, and there is a minimum value. Since the theoretical derivation is based on the assumption that the vertical effective stress is uniformly distributed along the radial direction of the soil in the tube, the length to diameter ratio of the cylinder should be taken into account when the analytical model is used. Due to the complexity of ocean engineering problems and the high cost and uncertainty of experimental research, it can be seen from this study that numerical simulation is still an effective method for the study of ocean engineering and its infrastructure. The finite element simulation technique of large deformation has achieved some success in the study of suction cylinder, but it should be further improved, such as adopting appropriate constitutive model for special soil mass, increasing the speed of ale numerical calculation, and so on. The study of suction cylinder by numerical simulation should further consider the microcosmic and special mesoscopic characteristics of soil.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU476;P75
本文编号：2130114
[Abstract]:Suction cylindrical foundation has been more and more widely used in marine engineering. Numerical simulation and theoretical study of its installation process are of great significance to guide engineering practice. Based on the Arbitrary Lagrangian-Eulerian formation (ale) technique, a two-dimensional axisymmetric model is established on the platform of Abaqus. The problem of large deformation mesh distortion is solved, and the sinking process of suction cylinder in clay is successfully simulated. In the numerical model, the undrained shear strength and elastic modulus of soil are expressed by the subprogram VUFIELD with the variation of soil depth. The model is verified by the centrifuge test data and theoretical calculation of the University of Western Australia. By using the verified numerical model, the penetration resistance of different suction sinking forces and the height of soil plug are analyzed and the influence of friction characteristics of cylinder wall on the penetration of suction cylinder is discussed. The numerical results show that ale technique can effectively simulate the penetration process of suction cylinder and solve the problem of grid distortion caused by large deformation of soil. The penetration resistance of suction type is obviously lower than that of pressure type. It is found that with the increase of the ultimate suction value, the penetration resistance decreases significantly and the plug height increases significantly. The study of friction characteristics of suction cylinder shows that the friction resistance of inner wall is the main factor leading to the change of sinking resistance, and the pressure penetration is more significantly affected by the friction characteristics of cylinder than the suction penetration. Based on the theoretical derivation, an analytical model of friction force on the inner wall of suction cylinder is established, and the influence of seepage on friction resistance of inner wall of suction cylinder is studied. From the point of view of the stress balance of the micro-element section of the soil in the tube, the stress and deformation state of the soil and the seepage flow are fully considered, and an analytical model for the calculation of the soil-tube friction stress in the process of suction cylinder penetration is derived. The numerical models of suction tube penetration and soil seepage are established by finite element program Abaqus, and the analytical model is compared and verified. The seepage velocity, the friction coefficient of soil-cylinder and the ratio of length to diameter are discussed and analyzed. The results show that the vertical effective stress of soil can be significantly reduced by seepage and thus the friction resistance of the inner wall of the cylinder will be reduced. Through the analysis of the seepage velocity, it is found that the seepage system should be judged according to the seepage velocity, and the accurate friction results of the inner wall of the cylinder can be obtained by reasonably selecting different seepage theories. The increase of the friction coefficient of soil-tube will cause the normal stress of soil-cylinder to increase, and further increase the frictional stress. Increasing the ratio of length to diameter of the tube increases the friction stress, but the total friction force of the inner wall of the cylinder changes in the form of inverted parabola with the ratio of length to diameter of the tube, and there is a minimum value. Since the theoretical derivation is based on the assumption that the vertical effective stress is uniformly distributed along the radial direction of the soil in the tube, the length to diameter ratio of the cylinder should be taken into account when the analytical model is used. Due to the complexity of ocean engineering problems and the high cost and uncertainty of experimental research, it can be seen from this study that numerical simulation is still an effective method for the study of ocean engineering and its infrastructure. The finite element simulation technique of large deformation has achieved some success in the study of suction cylinder, but it should be further improved, such as adopting appropriate constitutive model for special soil mass, increasing the speed of ale numerical calculation, and so on. The study of suction cylinder by numerical simulation should further consider the microcosmic and special mesoscopic characteristics of soil.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU476;P75
【参考文献】
相关期刊论文 前3条
1 朱儒弟,高恒庆,马小兵,何生厚,王运安,洪学福;海上平台桶形基础模型压力压贯与负压沉贯试验研究[J];海岸工程;1999年01期
2 丁红岩,刘振勇,陈星;吸力锚土塞在粉质粘土中形成的模型试验研究[J];岩土工程学报;2001年04期
3 金书成;张永涛;杨炎华;黎冰;;饱和砂土地基中吸力式桶形基础水平承载力研究[J];岩土力学;2013年S1期
相关会议论文 前1条
1 童景盛;王胜利;敖运安;;侧压力系数研究与实践[A];第21届全国结构工程学术会议论文集第Ⅰ册[C];2012年
，本文编号：2130114
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