Research On Ice-Soil-Pipeline Coupling Model Based On CEL Method

Submarine pipelines are important external transportation equipment for polar marine oil and gas development.Ice gouge has become one of the biggest factors affecting submarine pipelines in Arctic development.In order to ensure the safety of polar subsea pipelines during operation,the effects of ice gouge damage on pipelines in polar special environments must be assessed.In this paper,the mechanical response of the large deformation of the seabed to the pipeline caused by ice gouging is applied.The three-dimensional model of the ice gouging seabed is established by using the coupled large deformation simulation method based on the coupled Euler Lagrangian(CEL)method.The formation process of the ice gouge trench was analyzed using homogeneous soft clay,and the key factors affecting the numerical results were analyzed and selected.The results show that the mesh size of the Euler domain is greatly influenced in the numerical simulation,and the suitable ice keel loading velocity and soil constitutive model are selected.By comparing with the centrifugal experiment results and the PRISE engineering model,the feasibility of the CEL method for simulating the large deformation mechanism of the soil during the ice gouging process is verified.The key factors affecting soil deformation are studied.The results show that the ice gouge width has a certain influence on the vertical soil displacement.The PRISE soil displacement empirical formula predicts the horizontal soil deformation too much.When the attack angle is increased,the degree of soil deformation and the depth of disturbance are significantly reduced,and the soil deformation decreases with the increase of soil strength.The limitations of the PRISE engineering model for predicting soil deformation are further explained.Based on the finite element model of the above-mentioned ice gouging bed CEL method,the ice-soil-pipeline coupling model of the ice gouging submarine pipeline was further developed.The deformation mechanism and deformation process of the pipeline under ice gouging conditions are studied.It is indicated that the deformation path of the pipeline presents a circular path due to the flow around the soil.During the ice gouge,the displacement,stress and strain of the pipeline first increase and then decrease.By comparing the developed coupling model with the uncoupled model in current engineering practice,the computational error in the uncoupled model and the superiority of the current CEL coupled model are illustrated.The distribution of strain and the influence of main factors caused by ice gouge are discussed in detail.The results show that the increase of the depth of the gouge and the width of the gouge will increase the axial strain of the pipeline.An increase in the angle of attack,the depth of the pipeline,and the wall thickness of the pipeline will reduce the axial strain of the pipeline.The influence of soil strength on pipeline strain is nonlinear.An increase in the outer diameter of the pipeline will result in an increase in the axial strain of the pipeline,but the specific trend depends on the depth of the pipeline.Based on the strain-based pipeline design criterion and the established CEL coupling model,the design safety evaluation process of the submarine pipeline in the polar ice gouge area is given,and the practical application of the current CEL model is illustrated.The paper explores the complex nonlinear interaction mechanism between pipeline and soil caused by ice gouging and the strain mode of pipeline,revealing the complex and rich mechanical content contained in it,which has important theoretical value.It has important engineering significance for the safe service of polar seabed pipelines,and is in line with the major strategic needs of China's polar oil and gas development.