Research On The Buckling Instability Mechanism Of Deep-sea Pipeline Impacted By Dropped Objects,and The Prediction Of Oil Spill

In recent years,accidents of submarine pipeline failure and leakage often occur at home and abroad,while the third party damage has become one of the main causes.The mechanical behavior of pipeline structures under quasi-static and dynamic loads has attracted great attention from academia and engineering circles,where extensive research works have been carried out.However,few studies have been reported on the combined effect of impact load and deep water pressure at home and abroad,especially in the aspect of buckling instability for impacted pipelines suffering high external pressure.Therefore,it is of great theoretical significance and practical value to grasp the dynamic behavior characteristics of collision and buckling instability mechanism for deepsea pipelines through experimental,numerical and theoretical studies,as well as to predict the behavior of the underwater oil spill caused by the pipeline failure.The main research work in this paper is as follows:Firstly,a joint experimental research for pipeline of impact damage and high water pressure buckling was carried out,where full size submarine pipeline structure material for API X65 was selected as an object.Dynamic response and characteristic parameters of deformation and buckling instability are obtained.The main characteristics,basic phenomena and rules of pipeline impact damage are revealed.The conservatism of the calculation method in the evaluation of impact damage and ultimate bearing capacity of DNV specification are discussed by comparing tests results.Furthermore,LS-DYNA 3D is applied to simulate the dynamic response and buckling instability of experimental tube structures accurately based on the results of joint experiments.Then,the influence of impact contact form on damage deformation has been discussed,as well as the effect of ovality and geometric parameters of defect on buckling and collapse process.Secondly,numerical study is conducted on the dynamic response characteristics and buckling instability mechanism of pipelines under combined action of impact load and deepwater pressure.The influence of hydrostatic pressure on the impact response process of pipeline is analyzed,and the damage and failure characteristics of pipeline different from those without water pressure are found.Then,the sensitivity analysis of the impact resistance of the external pressured pipeline was carried out,and the failure modes and conditions of pipeline collision under different sensitivity parameters were discriminated.A critical failure pressure evaluation formula considering different failure mode of pipeline is put forward under the combined action of impact load and deep water pressure.Thirdly,a theoretical model of underwater oil spill and diffusion is established based on Lagrange integral method and particle tracking method,the docking particle calculation of the two stages of dynamic plume and advection diffusion is realized and the motion characteristics of the underwater oil particles are revealed.The reliability of the theoretical method is verified through the test data in various different conditions of leakage and water environmental.The influence of these sensitivity factors in the aspect of leakage and marine environment on the diffusion characteristics is analyzed quantitatively.Moreover,a visual software for forecasting the underwater oil spill is developed.In this paper,the dynamic response characteristics and buckling instability mechanism of deepsea pipeline structure under the combined action of impact load and deepwater pressure are preliminarily revealed.The critical failure water pressure evaluation formula for all failure mode of pipeline under combined action is proposed,which providing a new idea and method for the safety assessment and related research of the deepsea pipeline structure under the complex dynamic load.At the same time,the theory research for underwater oil spill and diffusion,and the developed visualization prediction software can also be applied to China’s offshore oil spill emergency prediction and guidance.