Abstract

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 where the seabed is not included. The seabed effects are simply considered by exaggerating the explosive weight with an empirical factor. This paper tries to include the seabed in the simulation by using the Coupled Eulerian-Lagrangian (CEL) method. The effects of water, soil and the TNT are approached by using the Eulerian formulation with specified Equation of status (EOS). The steel pipe is approached by shell elements in a Lagrangian scheme. The strain rate effects on steel strength and failure strain 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 the Abaqus Explicit solver. Three offset distances (2.5 m, 5 m and 15 m) have been simulated. The simulation results are discussed in details with respect to the water, soil, TNT and pipeline deformations respectively. Additionally, the axial force is also discussed. It is shown that the present numerical model is able to capture the main characteristics of such a complicated physical process. The influence of the seabed has been shown explicitly in all the offset distances analyzed. The empirical factor method may give over-conservative results.

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