Dynamic response and performance of subsea sandwich pipelines with various interlayers subjected to underwater collision

Compared to single-layer pipelines, sandwich pipelines exhibit superior resistance to accidental collisions caused by falling objects. However, previous research has rarely examined sandwich pipelines with different interlayer materials under underwater collisions. This study developed an Arbitrary Lagrangian-Eulerian (ALE) based numerical model to predict the behavior of the sandwich pipe when subjected to complex underwater collision scenarios, considering the fluid-structure interaction (FSI) effects. Subsequently, comparative simulations were performed using the Lagrange method to evaluate its feasibility and accuracy. The results indicate a good agreement between the ALE and Lagrange models. A sensitivity analysis was conducted based on the Lagrange collision model, and investigated the effect of collision velocity, collision angle, seabed properties and interlayer medium on the responses of the sandwich pipeline including deformation, stress, and energy properties. It is concluded that increasing the collision angle, decreasing the collision velocity, and enhancing the seabed stiffness reduce pipeline damage. The inner pipe deformation was more sensitive to the density of the interlayer foam than the outer pipe. Additionally, the water-filled interlayer exhibited superior resistance to collision loads compared to the air-filled interlayer.