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A Study of Sediment Motion On Seabed With Submarine Pipeline
Yang, Lipeng (College of Engineering, Ocean University of China) | Shi, Bing (College of Engineering, Ocean University of China) | Han, Yan (College of Engineering, Ocean University of China) | Wu, Jian (College of Engineering, Ocean University of China) | Sun, Xiufeng (College of Engineering, Ocean University of China)
ABSTRACT This paper investigates the pressure gradient between the contact points of submarine pipeline by studying the analytical formula of pressure distribution. The study condition is unidirectional current. On this basis, the formula of seepage velocity on the seabed is derived by using Darcy's law. Besides, the critical velocity of sediment incipient motion in the wake region is obtained by analyzing the forces of particles. Furthermore, the relation of scour hole depth and velocity is obtained according to the experiment data. Compared with experimental data, authors found that the formula results shows the variation regularity of seepage and the motional law of sand. INTRODUCTION With the development of ocean oil exploitation in recent years, submarine pipeline has become an important carrier which is extensively used to transport the oil from offshore to land. Because of the complicated ocean environment, the influence of many uncertain factors makes it very difficult to manage the underwater conditions. So the destruction of submarine pipeline have often occurred. The most important reason was that the pipeline was suspended owing to the scouring of seabed underneath the pipe. When the seepage velocity reached to critical value, the sediment starts to transport. That is the main reason for scouring. Therefore, the study of seepage velocity from which get the relationship between dynamic water pressure and seepage velocity is significant. It is the foundation for the further study of protection techniques, and will be of great value for engineering application and theory research. When the submarine pipeline is put on the seabed without a gap and covering, with the action of currents and waves local scour underneath the pipeline will happen. This part of dynamic water pressure will act on the seabed below the pipe and increase the seepage velocity.
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (0.69)
Experimental Study On the Function of Flexible Spoilers In Protecting Submarine Pipeline
Han, Yan (Engineering College, Ocean University of China) | Shi, Bing (Engineering College, Ocean University of China) | Yang, Lipeng (Engineering College, Ocean University of China) | Sun, Xiufeng (Engineering College, Ocean University of China) | Wu, Jian (Engineering College, Ocean University of China)
ABSTRACT When a pipeline is laid on a sediment bed, and subject to a current, the pressure difference between the upstream and the downstream of the pipe will induce a seepage flow underneath the pipe so that causing scour. The pressure difference is a main factor for the scour under pipelines. A new method to prevent the scour was proposed. Flexible spoilers were installed under the submarine pipeline to change the seepage flow field and pressure distribution, and reduce the pressure gradient between both sides of the pipeline. Experiment result shows that when the flexible spoilers reach or exceed a certain length, the pressure gradient is close to zero and the bottom scour almost disappears. INTRODUCTION The submarine pipeline is one of the most important oil transport tools in ocean oil exploitation. It is an indispensable component in offshore oil production systems. Because the ocean environment is very complicated, the influence of many uncertain factors makes it very difficult to lay and manage underwater condition. Along with the exploitation of deep ocean oil, the application of submarine pipeline has become increasingly widespread. Hence more and more attention is being paid to the erosion and destruction problems caused by ocean dynamics. The spoiler was proposed to install on the top of the pipe in order to make the pipe self-burial. However, they are not fit for the rocky seabed (because rocky span shoulders support parts of the pipeline and prevent it sinking, fatigue failure is easy to happen due to part of the pipeline suspending). So the flexible spoiler was proposed to install under the pipe. The flexible spoiler can cover the seabed so that to keep the seabed be eroded. 1 Research Status Li (Li et al., 1996) studied the net force acting on a seabed pipeline through physical model tests.
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (1.00)