Abstract

This paper describes the validation of a novel wind turbine simulation tool based on an existing finite element offshore structural analysis solver that recently has been extended to simulate offshore wind turbines. Validation is focused on a jacket structure hosting a 5MW turbine, which is the reference model used in the international research project OC4 (Popko et al., 2012). Beginning with fundamental test cases, such as static equilibrium and eigen-analysis, the scenarios advance in complexity to include regular and random wave excitation, in conjunction with both steady and turbulent wind inflow. The new tool generates results which exhibit a close correlation with the OC4 benchmark data.

Introduction

Given the growing importance of offshore wind in the decarbonisation strategy of many countries, the requirement for validated numerical modelling tools to support detailed engineering design is now greater than ever before. Global offshore wind capacity totalled an impressive 29.1 GW at the end of 2019, accounting for 5% of total global wind capacity, and over 205 GW of additional offshore wind capacity is expected to come on stream over the next decade (Global Wind Energy Council, 2020). While floating wind has not yet reached commercial scale, independent estimates suggest that up to 10.7GW of floating wind is feasible by 2030 (Spearman et al., 2020). The exponential growth of offshore wind will naturally require a corresponding escalation in detailed engineering design studies, supported by trusted simulation software.

The modelling tool under consideration in this study is an engineering design software known as Flexcom (Wood, 2020). Traditionally used in offshore oil and gas, it offers a unique structural analysis solver incorporating a 3D hybrid beam-column element featuring fully coupled axial, torsional and bending deformation modes. Recently it has been combined with FAST (Jonkman, 2013), to enable it to perform fully coupled aero-hydro-structural simulation of offshore wind turbines (OWTs). FAST, an acronym for Fatigue, Aerodynamics, Structures, and Turbulence, is a numerical modelling tool for simulating the coupled dynamic response of wind turbines. Developed by the National Renewable Energy Laboratory (NREL), FAST joins aerodynamics models, hydrodynamics models for offshore structures, control and electrical system (servo) dynamics models, and structural (elastic) dynamics models to enable coupled nonlinear aero-hydro-servo-elastic simulation in the time domain. Software couplings have been developed between Flexcom and several of FAST's component modules, to enable the aero-hydro-structural simulation of horizontal-axis wind turbines. The new tool offers advantages for non-linear structural simulation via its innovative finite element solution technique, and detailed hydrodynamic modelling via its established and proven numerical models. The combination underlines the benefits of exploiting synergies between offshore oil and gas and offshore wind.

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