深水柔性构件非线性动力响应研究

发布时间：2019-05-09 12:50

【摘要】：锚泊线和立管是海洋工程开发中的重要柔性构件,由于长度远远大于直径尺寸,在深水环境中极容易弯曲变形。其中,合成纤维锚泊缆材料的抗拉刚度小,轴向变形明显,同时具备了抗弯特性。针对这一问题,本文在轴向拉伸变形方面对经典细长杆模型进行改进,模拟在浮体运动中缆索的大位移、大转动、轴向大变形、弯曲大变形等几何非线性特征,解决已有的集中质量法、细长杆模型、非线性梁等理论只能计算大弯曲变形小轴向应变问题的局限性。同时,引入来自工业试验成果的Kim线性粘弹性模型和弹塑性P-y曲线海底土体刚度模型,提出与新细长杆模型相恰的数值计算方法,将只能模拟线弹性材料和弹性海底的经典细长杆理论拓展到材料非线性和边界非线性领域。最终,针对锚泊线和立管中出现的几何非线性、材料非线性和海底边界非线性等问题,基于细长杆理论发展新的杆元模型,并与三维间接时域法形成一种浮式系统的异步耦合计算方法。首先,研究轴向大变形的细长杆模型,并给出有限元数值计算方法。在轴向大变形的情况下,单元长度发生了明显改变,结构在参考构形和当前构形下的状态已经无法近似等同,这已经涉及到了有限变形的范畴,经典细长杆模型不再适用。因此,本文在经典细长杆模型基础上,从最基本的运动学和动力学层面重新研究应变、应力、曲率等各项因素对变形、平衡和运动的影响,通过拉伸变形前后结构点对点一一对应的假设,建立参量的变换关系,在有限元法的框架下建立大拉伸变形下的求解方法,以牛顿-拉斐逊法建立细长杆结构的静力平衡求解格式,通过显式的莫尔顿法形成细长杆结构的动力响应数值求解方法。利用大拉伸悬臂梁和强制运动的垂向梁算例,在大变形几何非线性方面进行静力平衡和动力响应计算验证。结果显示,本文所提的新细长杆模型具有较高的计算精度,具备处理轴向大拉伸和弯曲变形的能力。然后,研究由线弹特性、粘弹特性、泊松效应和结构内部阻尼等构成的非线性材料在细长杆模型中的实现方法。经典细长杆理论中只研究了适用于钢材的线弹性材料,然而合成纤维材料却不同,除了应变更大以外,还具有蠕变、松弛、应力应变滞回等特点,其非线性本构关系与几何非线性共同作用,极大地加重了合成纤维缆的分析难度。本文对Kim粘弹性模型的线性粘弹性本构关系进行了变换,并与泊松效应和结构内部阻尼形成材料本构方程,以拉力-应变的形式研究其在新细长杆模型中的实现方法,形成有限元求解格式,并通过特定的算例进行精确校核,证明这种计算方法的准确性。同时,在细长杆理论中研究弹塑性海底模型的计算方法。海底作为钢悬链线立管、悬链线式锚泊线分析中重要的边界条件,其土体刚度对结构的运动响应和应力分布有着直接的影响。经典细长杆模型采用线性弹簧模拟海床,但这不能反映真实的海床特性,因此,本文以从工业联合项目(JIP)实尺度试验中发展起来的弹塑性P-y曲线模型(土体反力-沉入深度曲线模型)为基础研究了海底土体刚度的非线性变化特征和数值实现方法,将小位移运动模型、大位移运动模型和运动反转模型,通过有限元法和梯形法给出在细长杆模型中的计算方法,解决结构在触地区域的受力响应问题。最后,根据细长杆模型的特点,发展一套缆索系统与浮体的异步耦合响应计算方法。目前,商业界已经形成了一些时域耦合分析计算程序,但在具体的耦合方式和如何提高计算效率等方面仍然有待进一步研究。本文采用新细长杆模型和三维间接时域法形成一种异步耦合分析方法,这种方法在频域内计算浮体运动相关水动力参数,变换到时域后,与新细长杆模型异步耦合,提高分析的准确度和计算效率,解决耦合过程中的浮体和缆索系统时间步长不一致的问题。通过FPSO单点锚泊系统案例,与AQWA软件进行对比分析说明这种方法可行。
[Abstract]:Mooring line and riser are an important flexible component in the development of ocean engineering, because the length is much larger than the diameter dimension, it is very easy to bend and deform in the deep water environment. In which, the tensile rigidity of the synthetic fiber anchoring cable material is small, the axial deformation is obvious, and the bending resistance property is also provided. In view of this problem, this paper improves the classical slender rod model in the aspect of axial tensile deformation, and simulates the geometric non-linear characteristics such as large displacement, large rotation, large axial deformation and large deformation of the cable in the movement of the floating body, and solves the existing concentrated mass method, the slender rod model, The nonlinear beam theory can only calculate the limitation of the small axial strain problem of large bending deformation. At the same time, by introducing the Kim linear viscoelastic model and the elastic-plastic P-y curve bottom soil mass stiffness model from the industrial test results, the numerical calculation method of the new slender rod model is proposed, The classical slender rod theory, which can only be used to simulate the elastic material of the line and the elastic seabed, is extended to the field of material non-linear and boundary non-linearity. In the end, the new rod-element model is developed based on the theory of the slender rod, and an asynchronous coupling method of the floating system is formed by the three-dimensional indirect time-domain method. First, the slender rod model with large axial deformation is studied, and the numerical method of the finite element method is given. In the case of large axial deformation, the unit length has changed significantly, the state of the structure in the reference configuration and the current configuration has not been nearly equal, which has been involved in the limited deformation category, and the classical slender rod model is no longer applicable. Therefore, on the basis of the classical slender rod model, the influence of various factors such as strain, stress and curvature on the deformation, balance and motion is re-studied from the most basic kinematics and dynamics, and the point-to-point one-to-one correspondence between the front and back structures of the deformation is adopted. The transformation relation of the parameters is established, and the solution method under the large-tensile deformation is established under the framework of the finite element method, the static equilibrium solution format of the slender rod structure is established by the Newton-Raphanson method, and the dynamic response numerical solution method of the slender rod structure is formed by the explicit Morton method. In this paper, a numerical example of vertical beam and forced motion is used to verify the static balance and dynamic response in the nonlinear aspect of large deformation geometry. The results show that the new slender rod model proposed in this paper has higher calculation accuracy, and has the ability to deal with axial large tensile and bending deformation. Then, the realization of nonlinear materials, such as line-elastic properties, viscoelastic properties, Poisson's effect, and internal damping of the structure, is studied. In the classical slender rod theory, only the linear elastic materials suitable for steel are studied, but the synthetic fiber materials are different. In addition to the large changes, the nonlinear constitutive relation and the geometric non-linear constitutive relation of the synthetic fiber material have the characteristics of creep, relaxation, stress-strain hysteresis and the like. And the analysis difficulty of the synthetic fiber cable is greatly increased. In this paper, the linear viscoelastic constitutive relation of the Kim viscoelastic model is transformed, and the constitutive equation of the material is formed by the Poisson effect and the internal damping of the structure. And the accuracy of the calculation method is proved by the specific example. At the same time, the calculation method of the elastic-plastic seabed model is studied in the theory of the slender rod. The sea floor is an important boundary condition in the analysis of the catenary riser and the catenary mooring line, and its soil stiffness has a direct effect on the motion response and the stress distribution of the structure. The classical slender rod model uses a linear spring to simulate the seabed, but this does not reflect the true sea-bed characteristics, so, Based on the elastic-plastic P-y curve model developed from the real-scale test of the industrial joint project (JIP), the nonlinear variation character and the numerical realization method of the stiffness of the seabed soil are studied, and the small-displacement motion model is obtained. In this paper, a large-displacement motion model and a motion inversion model are presented, and the calculation method in the slender rod model is given by the finite element method and the trapezoid method, and the stress response of the structure in the ground area is solved. Finally, based on the characteristics of the slender rod model, an asynchronous coupling response calculation method for a cable system and a floating body is developed. At present, the business community has formed some time-domain coupling analysis and calculation program, but still needs to be further studied in the specific coupling mode and how to improve the calculation efficiency. in this paper, an asynchronous coupling analysis method is formed by using a new slender rod model and a three-dimensional indirect time-domain method, And solves the problem that the time steps of the floating body and the cable system in the coupling process are not consistent. Through the case of FPSO single-point mooring system, the comparison and analysis with AQWA software show that this method is feasible.
【学位授予单位】：哈尔滨工程大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：P75

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