Numerical Analysis Of Submarine Landslides Impact On Pipeline

In ocean engineering, submarine pipeline is an important channel for the transmission of crude oil and natural gas. In general, pipeline is in state of laid on the seafloor in deep sea condition, but partly in state of suspended. Submarine pipeline plays an important role in the overall task of production in offshore oil and gas and is the main means of outward transport of oil and gas. with the more and more frequent and increasing number of the using of sea areas. Submarine rock and sediment slides the landslide under gravity. which may destroy the pipeline, oil platforms and other marine engineering facilities and buildings. It is one of the main reasons that the impact of submarine landslide causes the lose of submarine pipeline. In order to ensure the safe operation of the pipeline, it has important academic significance and engineering application value of submarine landslides on pipeline.In this paper, we mainly studied the stress analysis of submarine landslides on laid-on-seafloor pipeline, which used ANSYS CFX in simulating the impact process of landslide and adopted the Herschel Bulkley model landslide body, considering influence factors consist of different impact angle, mud content and impact velocity on the pipeline. At first, compared with the existing experimental study in order to verify the accuracy of the numerical simulation in this paper. Further, got the calculation formula of the normal drag coefficient CD-90 of the seabed surface pipeline in this paper, and the formula of the axial drag coefficient CD-0 under the laid-on condition, which included the effect of impact angle in special. The method to bearing capacity coefficient Np and axial frictional coefficient fa was gained according to the method of soil mechanics, and the method of fluid mechanics and soil mechanics methods was in a uniform representation. As a result, the load of the failure envelope of pipeline was given. At the same time, based on fluid mechanics and soil mechanics methods, the hybrid method suited better on describing the CFD simulation data and analysis drag coefficient.Three main factors which affect the pipeline were analyzed in this paper, that is, the distance from the seabed surface, the shape of the cross section along the impact direction and the roughness of the pipeline. By the simulation of submarine landslide on the pipeline from the seabed surface at different height, the relationship between the load and the height was obtained, and summarized the critical state conditions of suspended according to the result of pipeline in different distance, namely drag coefficient remained essentially constant from seabed pipeline more than this distance. At the same time, by the research of roughness on drag forces of pipeline, obtained that drag increased with the increase of surface roughness.Further, got the formula of drag and drag coefficient about the ratio of height to diameter (H/D), which was an important guiding to the problem in the real project.Cross section of submarine pipeline different impact angle will be different, section of the pipeline at 90 degrees is circular, but the section shape of pipeline at angle 15 degrees,30 degrees,45 degrees,60 degrees,75 degrees is oval. As the angle becomes smaller, the more obvious the properties of elliptic cross section are. The height width ratio was used to analyze the shape of elliptical cross section, and the stress rule of different section shape pipeline was obtained. For verifyng the correctness of the theory about the effect of impact section shape on the drag coefficient, the vertical tilt pipeline simulation realized elevation ellipse section shape of the impact, which was coincident with the force of the pipeline in the conclusion of the former study. Finally, got the formula between the drag force of the submarine pipeline and the nature of the impact cross section.The research work in this paper extended the existing research of submarine pipeline, enriched the calculated results of axial drag coefficient and normal drag coefficient under the different conditions of pipeline, also used a variety of methods in data analysis, ultimately the formula for estimating the impact force of debris flow on the submarine pipeline at different height from the seabed surface and influence factors of pipeline were derived.