【作者】 刘文玺；

【导师】 任慧龙；

【作者基本信息】 哈尔滨工程大学 ， 船舶与海洋结构物设计制造， 2009， 博士

【摘要】 本文以势流理论为基础,应用基于非均匀有理B样条(Non-Uniform Rational B-Spline,简称NURBS)的边界元法,在频域内,对船舶和海洋结构物的线性、二阶运动响应和波浪载荷进行计算；在时域内,结合浮体和系泊缆索的非线性响应计算方法,建立了浮体和系泊系统的耦合分析方法。首先建立了基于NURBS的边界元方法。对NURBS技术做了多方面的改进,并应用到复杂海洋浮体的构型和湿表面网格划分,结果表明,改进的NURBS技术,能够生成高质量的浮体外形和湿表面网格,而且效率很高。为应用扩展的边界积分方法去除不规则频率,在上述网格生成方法基础上,提出了进一步的网格改进措施。基于三维线性势流理论,应用基于NURBS的边界元法,在频域内建立了求解浮体线性运动响应和波浪载荷的理论模型,并采用扩展的边界积分方法消除不规则频率现象。对频域内海洋浮体的一阶运动响应、一阶波浪力进行了计算,并与模型试验结果进行了对比分析,验证了基于NURBS的边界元方法是一种计算精度、计算效率都较高的新型数值计算方法。对边界条件采用泰勒级数展开,通过摄动展开分离级数建立频域二阶边值问题,而且此边值问题的计算域是不随时间变化的。对二阶问题中自由面的积分项进行量阶分析,讨论了该项忽略与否对计算难度、计算结果精度等的影响。将基于NURBS的边界元方法应用到浮体频域二阶运动响应和波浪载荷的计算,并用谱分析法计算海洋浮体的漂移运动,通过与文献中相似计算的比较可以看出,本文二阶问题的计算方法是可靠的。用三维弹性梁理论将缆索模型化,并采用非线性有限元法对缆索的运动方程进行求解,得到了静态和动态问题中的缆索位移和张力响应,与文献值的对比表明,本文采用的缆索求解方法是有效的。在浮体和系泊系统的时域耦合分析中,研究并提出了一种预报浮体和系泊系统非线性运动响应和缆索张力的分析技术。考虑瞬时物面变化引起的各种非线性因素,在时域内建立浮体的非线性运动方程并求解。其中,入射波力和静恢复力按瞬时物面条件计算,辐射力和绕射力按浮体在瞬时平均湿表面为平衡位置做简谐振荡运动来计算。以三维弹性梁理论为基础,采用非线性有限元法对缆索进行计算。将浮体的分析方法和系泊缆索的分析方法结合,建立了浮体和系泊系统非线性运动响应和缆索张力的耦合计算方法。对系泊浮体的固有周期、各种工况下大幅非线性运动、缆索张力等进行了计算,并进行对比研究,可以看出,本文的方法既适用于缆索小变形条件下,也适用于缆索大变形条件下浮体与系泊系统的耦合动力分析。更多还原

【Abstract】 According to potential theory, by use of the boundary element method based on non-uniform rational B-spline (NURBS), the linear and second-order motion responses and wave loads of ship and ocean structure are calculated in frequency domain. By combining the calculating method of the nonlinear responses for floating structures and that for mooring lines, the coupled analysis method of floating body/mooring system is made in time domain:At first, the boundary element method based on NURBS is made. After developed in several aspects, NURBS technology is applied to construct complex ocean floating body and generate the wetted surface mesh, and the calculating results show that by the developing NURBS method, high quality mesh and floating body constructure can be obtained efficiently. Based on the above method for mesh, the further modifying method for mesh is applied for removing the irregular frequencies by the expanding boundary integral method.According to 3 dimension potential theory, by use of the boundary element method based on NURBS, the theory model for calculating motion response and wave loads of floating body is built and the irregular frequencies are removed by the expanding boundary integral method, In frequency domain, the linear motion response and wave loads are calculated and the results are compared with that from experiment. According to the comparison, it can be seen that the boundary element method based on NURBS is a new type of numerical method with high efficiency and accuracy.The boundary conditions are expanded by talor series, and then by perturbation expanding and separating series, the second order boundary value problems are built and the calculating domain for these problems does not change with the increasing time. Free surface integral term exists in the second order problem and by order analysis, it is analyzed that whether the term can be neglected or not and it’s influence on the calculating difficulty and the accuracy of the results. In frequency domain, by the boundary element method based on NURBS, the second order motion response and wave loads of floating body are calculated and the spectrum analysis method is applied to calculate the slow drift motion of floating body which is compared with the results from the similar calculation in literatures, and from the comparison, it can be drawn that the calculating methods for second order problem are reliable in this text.By the 3 dimension elastic beam theory, the calculating model for mooring lines is obtained and then the motion equations of the mooring lines are solved by nonlinear finite element method, so the displacement and tension response of the mooring lines are obtained in static and dynamic problem. The comparison between the results and that from literatures shows that the calculating method used in this text for mooring lines is highly efficient.In time domain analysis of the coupled floating body/mooring system, a coupled analysis technology is developed for the forecasting of nonlinear motion responses and wave loads of floating body and mooring system. Considering the nonlinear factors resulting from considering the changing of transient body wetted surface, the nonlinear motion equations are built and solved in time domain. The incident wave force and hydrostatic restoring are calculated in transient body surface condition, while the diffraction force and radiation forces are calculated on the assume that the floating body oscillates around the balance situation which is the transient body wetted surface. Based on 3 dimension elastic beam theory, the calculation is carried out for mooring lines by the nonlinear finite element method. Combining the analysis method for floating body and that for mooring lines, the coupled calculating method of nonlinear motion responses and mooring line tension for floating body and mooring lines is made. For the mooring floating body, all kinds of calculations are carried out, such as the natural periods, large amplitude nonlinear motion in all kinds of sea condition, mooring lines tension and so on, and at the same time comparisons among the results show that the analysis methods in this text are fit not only for small amplitude motion but also large amplitude motion in time domain.更多还原