Effect of Horizontal Multidirectional Cyclic Loading on Piles in Sand: A Numerical Analysis

Orianne Jenck,Christophe Dano,Fabrice Emeriault,Armita Obaei

doi:10.3390/jmse9020235

Abstract

Foundations of offshore and nearshore wind energy production systems are subjected to multidirectional and cyclic loads, due to the combined action of wind and waves and in the particular case of mutualized anchor foundations for floating wind turbines, to the phase shift between the loads generated in the adjacent anchored turbines. This article presents a three-dimensional numerical model developed with FLAC3D to analyse the impact of the change in direction of the horizontal load during the cycles. The typical case of a 1.7 m diameter and 10 m-long pile founded in a dense homogeneous sand is considered. A specific procedure has been implemented to apply force-controlled cycles with a change in lateral load direction. The results are compared to mono-directional lateral cyclic loads with the same average and cyclic forces. The results of the parametric study highlight the effect of the average value and amplitude of the cyclic loading on the accumulation of pile head horizontal displacements during the cycles. When a multidirectional cyclic loading is applied, it also leads to an accumulation of the deviated horizontal displacements, and the resulting accumulated horizontal displacements are larger than for a mono-directional cyclic loading of the same amplitude.

Highlights

Wind power offers an interesting source of energy, leading to the current development of onshore, nearshore and offshore wind farms
There are several foundation concepts for offshore wind turbines, which depend on the loading, water depth and soil conditions: gravity-base; monopole, tripile, tripod, jacket or anchor for floating structures [1,2]
This study focuses on the case of piles as mutualized anchors for floating wind turbines, submitted to multidirectional lateral cyclic loads

Summary

Introduction

Wind power offers an interesting source of energy, leading to the current development of onshore, nearshore and offshore wind farms. Nearshore and offshore wind turbines benefit from a number of advantages such as limited visual impact, higher and more constant wind speed, and the possibility of using large capacity turbines, resulting in higher power generation. In the case of floating wind turbines, the structures are connected to the foundation system through several anchor lines and the cyclic load acts in multiple directions, due to the combined action of wind and waves. In the particular case of mutualized anchor foundations for floating wind turbines, the foundations are subjected to the phase shift between the loads generated in the adjacent anchored turbines. This study focuses on the case of piles as mutualized anchors for floating wind turbines, submitted to multidirectional lateral cyclic loads

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Conclusion