Nonlinear wave surface elevation around a multi-column offshore structure. (15th October 2021)

• Record Type: Journal Article
• Authors: Ren, Xiudi; Tao, Longbin; Liang, Yibo; Han, Duanfeng
• Is Part Of: Ocean engineering. Volume 238(2021)
• Publication Date: 2021-10-15
• Subjects: Free surface elevation -- Multi-column structure -- Nonlinear waves -- Slamming -- Near-trapping; Ocean engineering -- Periodicals; Ocean engineering; Periodicals; 620.4162
• DOI: 10.1016/j.oceaneng.2021.109757
• Languages: English
• ISSNs: 0029-8018

Abstract

Abstract: 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 K c < 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. Highlights: Increasing corner ratio of the four rounded-corner square columns results in lower wave run-ups under 0° incident wave, but higher wave run-ups under 45° incident wave. Both near-trapping and superposition of waves can lead to the peak of surface elevation. Near-trapping frequency model for multiple circular columns is demonstrated still effective for the four rounded-corner square columns. However, the peak surface elevation due to near-trapping reduces with increasing corner ratio. The impact of the column's corner ratio on the second-order component of the surface elevation is significantly larger than that on first-order component. A single peak surface elevation under 0° incident wave is attributed to superposition, while different peaks of surface elevation depending on scatting parameter under 45° incident wave are demonstrated due to near-trapping and superposition, respectively.