Abstract
Abstract In offshore oil &gas production there is a large concentration of platforms in a limited area of the sea, with the consequent increase of vessel traffic in the region. Platform supply vessels (PSVs), shuttle tankers and maintenance and safety units operate very close to these production platforms, creating a propitious scenario for collisions. Thus, the risk of collision between vessels and platforms has significantly increased, causing concern from the point of view of life loss, material damage and marine environment degradation. It is important to adequately design the structures and to predict the effects of accidents on the involved vessels. In the structural analysis of collision, geometric and material nonlinearities must be considered, as well as the striking ship velocity, the vessels draft difference, among other variables. In this work, the collision of a platform supply vessel with a single-hull Floating Production Storage and Offloading (FPSO) platform is studied through numerical simulation using the ANSYS LS-DYNA computational system. Damage is locally characterized by the collision force on the FPSO hull and the depth of penetration (displacement). In addition, it is also shown the energy absorption capacity of each type of structural element for the collision scenarios studied and a criterion is proposed to determine which structural element group should receive more attention in the design phase in order to reduce the effects of a collision. Both the longitudinal strengths of the intact FPSO as well as the remainder after collision are evaluated by assessing the bending moment versus curvature curves. It is observed that a single-hull FPSO platform with the thicknesses of the structural elements maintained unchanged in the conversion of the original oil tanker (VLCC) shows a significant ultimate longitudinal strength even after collision of a larger support vessel at higher velocity than recommended by the IACS rule.
Highlights
The collision between ships, or a vessel with an offshore platform, is capable of compromising the stability and structural integrity of both structures, requiring withdrawal from operation for repair or even causing total loss
In the case of Ship collided by Platform supply vessels (PSVs) submitted to sagging (Figure 14) and hogging (Figure 15), there was not much variation in the ultimate bending moment for both cases when compared to the intact ship, but the post-collapse behavior was quite different
The bending moment versus curvature curve (Figure 14) in the event ship collided by PSV with initial velocity 7.2 m/s shows that near curvature 9.0x10-5m-1 there was loss of strength, and with an increasing curvature the momentum increases at low rate, and tends to remain constant starting at the curvature of 12x10-5 m-1 but with a bending moment lower than for an intact Floating Production Storage and Offloading (FPSO)
Summary
The collision between ships, or a vessel with an offshore platform, is capable of compromising the stability and structural integrity of both structures, requiring withdrawal from operation for repair or even causing total loss. Collision simulation models are important at the design stage to ensure that the most vulnerable structural parts to this type of accident can be properly dimensioned or protected These models are useful to analyse a damaged structure and to indicate which measures should be taken before permanent repair. The proposed methodology is able to estimate the local structural response indicating displacements, deformations, fracture of elements and absorbed energy in the impact It allows the prediction of the overall effect on the structure of the struck ship (FPSO) by comparing the longitudinal bending moment versus curvature, before and after the collision.
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