Methods for analysing wave slamming loads on truss structures used in offshore wind applications based on experimental data

Abstract

Offshore wind turbines installed in shallow water regions are subjected to highly varying hydrodynamic loads, also from plunging breaking waves. Many investigations have been made regarding the wave slamming forces acting on both vertical and inclined piles, on flat and sloping bottoms. However, very few studies have been carried out to study the slamming forces on truss structures. In this paper, the wave slamming loads on the truss structure are analysed based on the experimental studies carried out on a 1:8 truss model. The total force and the forces on local members were registered during the experiment. The total and local forces on the structure have been analysed using two different methods. The total slamming loads on the truss structure were analysed using the Empirical Mode Decomposition (EMD) method and for the local forces on the truss structure, the Frequency Response Function (FRF) method was used. The EMD method is based on time series decomposition of the measured force and the FRF method is on the hammer tests performed on the local force members during the experiments. The relative strengths and weaknesses of both the methods have been discussed and conclusions on optimum analysis method for those data set have been proposed. In addition, the slamming forces calculated from the measurements are compared with the values obtained using the existing force models.