Abstract

A numerical model based on the scaled boundary finite-element method (SBFEM) was developed to address wave interaction with a tripile foundation. A monochromatic wave and parameters in terms of wave number and incident wave direction were systematically analyzed. Results show that the interaction of wave diffraction on individual piles of the tripile foundation can be ignored when the non- dimensional incident wave number ka≤0.15. However, pile group effect on wave diffraction around the foundation cannot be neglected when ka >0.15. As increases in ka, wave forces on each pile of the foundation fluctuate around the results of a monopile foundation. This study is expected to provide valuable information for the design of tripile foundations in offshore environments.

Introduction

Tripile foundations are a newly emerging supporting structure for offshore constructions (European Wind Energy Association, 2016), especially offshore wind turbines. They are well suited for water depth ranging from 25 m to 40 m. As shown in Fig.1, three piles of the tripile foundation are driven into the seabed and joined together at the top by a transition piece. Unlike traditional jackets or tripod foundations, tripile foundation is a three-legged jacked structure without any lateral or diagonal bracing. The tripile foundation has many advantages, such as simple design, improved stiffness and automated levelling process. In the past decade, a significant amount of research has been carried out by wind energy researchers and ocean engineers focusing on monopile (Damgaard, Ibsen, Andersen and Andersen, 2013; Oh, Kim and Lee, 2013; Li, Zhang and Guan, 2011), tripod (Lee, 2013), jacket (Zaaijer, 2006; Dong, Moan and Gao, 2011) and floating (Huang and Zhang, 2011; Lefebvre and Collu, 2012; Karimirad, 2013) offshore foundations. However, studies on tripile foundations are very limited in the literature. Tripile foundations certainly require more attention in terms of their design and safety analysis.

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