Nonlinear wave surface elevation around a multi-column offshore structure

Ren, Xiudi and Tao, Longbin and Liang, Yibo and Han, Duanfeng (2021) Nonlinear wave surface elevation around a multi-column offshore structure. Ocean Engineering, 238. 109757. ISSN 0029-8018 (

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Surface elevation around multiple column offshore structure is an important phenomenon crucial to air gap design of offshore platforms. This paper investigates the competing hydrodynamic phenomena, i.e., wave run-up of surface elevation rising along the column and near-trapping – the increase of surface elevation due to near-resonance among the columns. Both wave run-up and near-trapping have the characteristics of generating surface elevation peak and often impact the offshore structures with nonlinear wave loads and potentially cause slamming to platforms. With the free-surface Keulegan-Carpenter number Kc<O(1) and wave steepness H/L < 0.14 considered, the free surface amplitude primarily depends on the diffraction pattern caused by the multiple columns and potential theory is applicable. The wave run-up and near-trapping due to wave interaction with a platform consisting of four-square columns with different corner ratios are obtained by numerical simulations. It is found that the increasing corner ratio results in a lower wave run-up under 0° incident wave, but a higher wave run-up under 45° incident wave. For near-trapping among four columns, the peak surface elevation decreases with increasing corner ratio. Two mechanisms namely superposition and near-resonance resulting the peak surface elevation are examined in detail for wave interaction with multiple columns.