Analytical solution to initial intrusion static equilibrium of steel catenary riser in touchdown zone on seabed based on nonlinear Pasternak foundation model

As the preferred riser system for deep-sea oil and gas resource extraction, steel catenary riser (SCR) has a large impact on the depth of burial and fatigue life of the pipeline in the touchdown zone due to its interaction with the seabed soil body. According to the nonlinear soil resistance-intrusion depth p-y curve of pipe soil interaction, it is simplified as a three segment linear elastic soil stiffness attenuation model, and the analytical solution of initial penetration static equilibrium of catenary riser on seabed is obtained based on the nonlinear Pasternak foundation model. Compared with three-dimensional finite element and five model test cases, it is found that conventional Winkler foundation model overestimates the pipeline vertical deformation and bending moment of soil, which verifies the rationality and applicability of the analytical solution based on nonlinear Pasternak foundation model; the increase of seabed shear strength So significantly improves the stiffness of three-stage linear elastic soil and reduces the pipeline vertical deformation. In addition, according to the changes of water depth H, riser laying angle x pipeline outer diameter D, pipeline elastic modulus E and material density p, the physical and mechanical properties of pipeline penetrating soil are compared and analyzed. The results show that with the increase of vertical pipe laying angle 2.; the pipeline vertical deformation will be reduced, while the bending moment and shear force will be increased. When the angle exceeds 82 degrees , it is prone to yield failure. With the increase of pipe outer diameter D, the soil vertical resistance, vertical deformation, bending moment and shear force in touchdown zone will be increased simultaneously. When the outer diameter exceeds 0.4 m, it is easy to yield. The larger the elastic modulus E is, the smaller the pipeline vertical deformation is, the greater the bending moment and shear force are, when the elastic modulus exceeds 275 GPa, it is easy to yield. When the density of pipeline material is higher, the pipeline vertical deformation is larger, the bending moment does not change obviously, but the shear force increases, and when the density exceeds 14 850 kg/m(3), it is easy to yield. The above conclusions can provide a theoretical basis for the preliminary design of catenary riser of offshore pipeline.