Numerical Simulation of a Subsea Pipeline Subjected to Near-Field Underwater Explosion Loads With the Coupled Eulerian-Lagrangian (CEL) Method

Abstract

Abstract An underwater unexploded ordnance (UXO) for example a mine filled with trinitrotoluene (also known as TNT), may present a potential threat to subsea structures. An explosion is a complicated physical phenomenon as it involves the interactions among water, seabed, the structure, and the explosive ordnance. The relevance of the paper is the need for removal of a large number of UXO on the Norwegian continental shelf during the installation of subsea pipelines. Numerical simulations have been used to calculate the effect of an explosion, but normally with an assumption of free explosion space. The seabed effects are simply considered by exaggerating the explosive weight with an empirical factor. This paper tries to include the real seabed effects in a near-field explosion underwater explosion events by using the Coupled Eulerian-Lagrangian (CEL) method. The effect of water, soil and the TNT are approached by using the Eulerian formulation with specified Equation of status (EOS). The Us-Up’s form of Mie-Gruneisen equation is used for the water and soil. The soil’s strength is described by linear Drucker-Prager yielding function. The Jones-Wilkins-Lee (JWL) equation of state is used for TNT. The steel is approached by shell elements in a Lagrangian scheme. The strain rate effects have been considered through the Cowper and Symonds equation. The coupling between Eulerian and Lagrangian formulation is done by the general contact features provided by Abaqus Explicit solver. The simulation results are discussed in details with respect to the water, soil and pipeline deformations respectively. Additionally, the axial force is also discussed. It is shown that the seabed plays an important role during the explosion and the empirical factor used to exaggerate the TNT mass is over-conservative. In the near-field explosion, the existence of soil may be beneficial to the pipeline’s damage. Global effects may be also triggered due to the large axial force generated during the explosion.