Numerical Analysis Of Hydrodynamic Force On Free Spanning Submarine Pipeline Subjected To Earthquake

As an important component of the offshore oil and gas storage and transportation system, submarine pipelines are playing significant roles in the offshore exploitation and regarded as the lifelines of offshore oil and gas fields. The security production of the offshore oil and gas fields depends largely on the safe operation of the submarine pipelines. The Bohai Sea is a seismically active region in China. The combination of seismic loading and operation loadings is the critical case for the pipeline design laid in the region. The potential seismic risk is very severe. It is necessary and urgent that submarine pipelines in these areas be designed to resist earthquake ground motions. Since the characteristics of earthquake compared with wave and current are short duration, ample frequency content and high magnitude, interaction between pipeline and surrounded fluid under earthquakes differs from that under waves and currents. Thereby, the study on the hydrodynamic force models to simulate and simplify interacting model between pipeline and water subject to earthquakes has theoretical and practical meanings.The hydrodynamic forces on the free spanning submarine pipelines surrounded by sea water have been paid much attention by many researchers. Numerical simulation method is employed to analyze fluid field, hydrodynamic force and influential factors of free spanning submarine pipeline subjected to earthquake. The following parts of research have been carried out in this paper.(1) Based on theory of two-dimensional (2D) viscous and non-compressive fluid ADINA software is used to study fluid velocity of sea water subject to earthquake.(2) The hydrodynamic pressure on the surface of free spanning submarine pipeline subjected to earthquake is calculated on the base of computational fluid dynamics (CFD). The effects of input amplitudes and frequency of the seismic waves and span heights are considered.(3) To validate the proposed CFD method, model tests are conducted on an underwater shaking table. Experimental and numerical results are compared.(4) Based on Morison's equation, the drag coefficient CD and the inertial coefficient Cm related to earthquakes are obtained by the least square method. The effects of Re (Reynolds number), Kc (Keulegan-Carpenter number), water depth d and the gap ratio e/D on CD and CM are discussed. Above all, the study of hydrodynamic force on free spanning submarine pipeline subjected to earthquake suggests some conclusions for practical engineering.