ABSTRACT

This paper describes a new high-order composite numerical model designed for the efficient arbitrary-scale simulation of moored floating offshore bodies. The study focuses on static equilibrium and free decay of such structures, particularly a floating offshore wind turbine. The composite scheme models the linear or weakly-nonlinear motion in the time domain by solving the Cummins equations derived from Newton's 2nd law of motion. The mooring forces are acquired from a discontinuous Galerkin spectral element solver. The linear pseudo-impulsive radiation problems are modeled via a three-dimensional spectral element-based solver on an unstructured hybrid-configured mesh, ultimately providing accurate frequency-dependent added mass and damping coefficients. In this work, a numerical simulation of a moored model-scale floating offshore wind turbine is performed and compared with experimental measurements. The numerical experiments agree with the measurements and demonstrate that the model can be used for full-scale computations relevant to offshore engineering applications.

INTRODUCTION

Over the past decades, the importance and need for sustainable, renewable, and reliable energy resources has increased rapidly to cope with the climate crisis, and also – as seen recently – in response to political interest. Year by year, more ambitious targets are set to reduce net greenhouse gas emissions, where the current goal of the European Union is to cut the emissions by at least 55% (compared with 1990 levels) by 2030 and be completely neutral by 2050, European Commission (2022). The energy sector is indisputably the major contributor to this carbonation of the atmosphere and hereby, a key component towards a green energy transition.

In the quest to keep up with this desire, the offshore industry can be seen to play a principal role by having e.g., wind turbines, wave energy converters, dams, and so on, produce green non-fossil energy for society. Regarding wind turbines, a bottom-fixed installation technique is the most well-known approach, yielding requirements on the water depth, soil mechanics, scour protection, and much more. Another promising installation approach is to mount the wind turbines on floating offshore structures, which will allow for the establishment of floating offshore wind turbine (FOWT) farms in much greater depths and expand the energy potential of offshore wind.

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