Experimental investigation of the wave slam and slap coefficients for array of non-circular section of offshore platforms

Abstract

The offshore platforms are generally designed with sufficient vertical clearance from the maximum predicted wave crest elevations. This vertical clearance is termed as 'air gap'. However, due to compelling reasons of hydrocarbon processes and also due to the increase in water levels due to climatic changes or seabed subsidence due to reservoir subsidence, the lower decks may become vulnerable to wave action due to reduction in air gap. The structural elements in the lower decks may become prone to wave-induced loads caused by high wave crests. The assessment of such wave-induced loads on the lower deck and supporting structures, especially in the existing platforms, becomes very essential for the continued safe operations. In the case of wave slamming on a structure, these supporting structural members will also be prone to large loads. Circular sections are commonly used for substructures due to their hydrodynamic efficiency; however, for deck structure, it is very common to use non-circular sections for supporting superstructure loads. The non-circular sections used in the lower decks get exposed to wave-induced loads. The imposed loads could be of higher magnitude compared with the circular sections due to the flat surface of the sections. A review of the literature indicates that the previous studies focused mainly on the circular sections and not much information is available on the non-circular shapes, especially in the case of wave slam and slap. The current study was focused on the measurement of wave-induced slam and slap loads on an array of non-circular sections in a laboratory wave flume and the estimation of force coefficient based on drag-based empirical equations. The studies revealed that the slam and slap coefficients for non-circular shapes are greater than those for circular shapes.

Numerical simulation of deterministic freak wave sequences and wave-structure interaction

“…Bennett et al (2013Bennett et al ( ,2014 experimentally produced a target abnormal wave within a random sea by utilising the optimisation technique, and investigated the influence of abnormal waves on a vessel travelling with different forward speed. Sekhar and Nallayarasu (2013) investigated wave slamming and air gap on non-circular offshore structures under predicted maximum wave crests which is due to extreme freak wave.…”