A Study on Dynamics of Flexible Marine Riser

本文提出了一种分析立管运动、剪力和力矩的数值方法。首先利用哈密顿原理推导出立管动力学的完全非线性运动方程，然后在适当的假设下线性化，以便于数值计算。本文提出了一种基于Galerkin法和Newmark-b法的立管动力学数值模拟方法。为了验证所开发的模拟方案的准确性，在不同的实验条件下，在实验水槽中进行了模型实验，实验中采用了高度灵活的立管模型。立管模型的顶端被强迫在没有波浪或电流的情况下进行简谐振荡。在立管轴线Z方向的5~6个垂直位置设置10~12个摄像头，每个垂直位置固定X-Y方向2个摄像机，即可测量立管的三维运动。一个摄像头可以跟踪三个CLO…可以同时检测到更多的Se点，并且可以检测到每个测量点的立管模型的斜率。在每个实验中，在立管模型的顶端安装了一个五分量称重传感器来测量模型所受的力和力矩。建立了一套完整、准确的试验系统，并对模型试验结果进行了多方面的分析和讨论。通过与受迫振动同方向的顺排运动与数值模拟结果的比较，证实了所开发的数值模拟方案能够准确地描述除极强运动范围外的立管顺行运动、力和力矩。在较高的振动频率和较大的振动幅度范围内，实验与模拟的差异在图形上是明显的，这可能是由于运动方程的线性化和小张力变化的假设，也可能是由于涡激振动的影响。最后一年，建立了“海洋立管涡激振动”的数值模拟方法，并与实验结果进行了对比，验证了该方法的准确性。较少

In this study, a numerical method is developed for analyzing the motion, shear force and moment of a riser. Firstly full nonlinear equations of motions for the riser dynamics are derived using 'Hamilton's principle' and then linearized under appropriate assumptions for convenience of the numerical work. A numerical simulation scheme for riser dynamics developed in this paper is based on the 'Galerkin method' and 'Newmark-b method'. For validating accuracy of the eveloped simulation scheme, model experiments are carried out in an experimental tank under various experimental conditions, Highly flexible riser models are used in these experiments. The top end of the riser model is forced to oscillate harmonically without wave or current. Ten to twelve CCD cameras are arranged at five to six vertical positions along the riser axis Z and at each vertical position two cameras are fixed in X-Y directions so that the three-dimensional riser motion can be measured. One camera can track three clo … More se points simultaneously and the slope of the riser model at each measured point can be detected. In each experiment, a five-component load cell is installed at the top end of the riser model to measure the force and moment exerted on the model. A comprehensive and accurate experimental system has been established.Results of model experiments are analyzed and discussed in various aspects. By comparing the results of the inline motion in the same direction as the forced oscillation with those of numerical simulations, it is confirmed that the developed numerical simulation scheme can describe accurately the riser inline motion, force and moment except in the range of extremely strong motion. In the range of high oscillation frequency and large oscillation amplitude, the discrepancy between experiments and simulations become visible in figures, which may be attributed to the linearization of the motion equations with the assumption of small tension variation or to the effects of vortex-induced vibration. They fall on the future work to be researched further.In the final year, the simulation method of "Vortex Induced Vibration of Marine Riser in Oscillating Flow" has been developed and its accuracy was confirmed by comparing with experiments. Less