Intra-array wake meandering increases fatigue loading in downstream turbines and decreases farm total power output. In the case of floating offshore wind turbines (FOWTs), the motions of the floating substructure could have a non-neglectable contribution to wake meandering dynamics. This research experientially analyses the influence of imposed motions on the far-wake meandering of a FOWT. The study considers a 1:500 scaled porous disc representation of the 2 MW FLOATGEN system (BW Ideol) located off the coast of Le Croisic, France. A representative marine neutral atmospheric boundary layer is generated in a wind tunnel whilst monochromic and multi-frequency content three degrees of freedom (surge, heave, pitch) motion is imposed on the model tower. The stereoscopic particle image velocimetry (S-PIV) is then utilised to measure velocity vectors at a cross-section located at 8.125 D downstream of the model. No significant effect on the far-wake recovery in the velocity, turbulence and turbulent kinetic energy distribution is observed. However, the frequency characteristics of the imposed motions were observed in the far-wake meandering spectral content and streamwise characteristics of far-wake, such as normalised available power. While the frequency spectrum of the vertical oscillations showed more sensitivity to the three degrees of freedom (3DoF) imposed motion in all frequency ranges, the lateral oscillation was sensitive for the reduced frequency above 0.15. The monochromic motions with a reduced frequency of less than 0.15 also did not influence the far-wake centre distribution in both lateral and vertical directions. Regardless of reduced frequency, imposed motions show a strong effect on average power, in which the harmonic signature can distinguish in far-wake memory. This study provides an investigation, which its result could be beneficial to developing and examining wake models for offshore wind turbines, with a particular focus on the influence of FOWTs motions.

Ocean waves are complex, irregular, and random, making it difficult to produce definitive and repetitive time-series that represent oceans worldwide. Researchers have attempted to develop wave spectrum models for different oceans to create reliable wave time series for use in time-domain simulations of marine structures. Accurately estimating wave time-series is especially important in the analysing of wave energy converters (WECs) to assess the applied forces on the device and achieve a reliable estimation of the efficiency of the power take-off apparatus at the design stage. Therefore, there is a need for a set of low- and mid-fidelity tools and models to estimate the relation between the wave spectra discretisation and the correct correspondence exceedance probabilities of the wave time-series. The present study aims to respond to this fundamental necessity with a probabilistic and statistical approach. Initially, the whole logical process of time series generation with fitting risk-level analysis is formulated and interpreted. Then, a relationship between the produced artificial time-series and different probabilities of exceedance is developed. Finally, a logical relationship between the required precision of an artificial ocean time-series and the optimal level of design risk is developed and discussed. The findings provide a framework where generated time-series has a relation with the level of design risk.

There is a need for new numerical tools to capture the physics of floating offshore wind turbines (FOWTs) more accurately to refine engineering designs and reduce costs. The conventional measurement apparatuses in tank tests, including wave probes, velocity and current profilers, and Doppler sensors, are unable to provide a full 3D picture of velocity, pressure, turbulence, and vorticity profile. In tank tests, use of the underwater stereoscopic particle image velocimetry (SPIV) method to fully characterise the 3D flow field around floating wind platforms can overcome some of the limitations associated with classical measurement techniques and provide a rich source of validation data to advance high-fidelity numerical tools. The underwater SPIV method has been widely used for marine and offshore applications, including ship and propeller wakes, wave dynamics, and tidal stream turbines; however, to date, this technology has not seen widespread use for the hydrodynamic study of FOWTs. This paper provides a critical review of the suitability of underwater SPIV for analysing the hydrodynamics of FOWTs, reviews the challenges of using the method for FOWT tank test applications, and discusses the contributions the method can make to mitigating current research gaps in FOWT tank tests.

There is a need for new numerical tools to capture the physics of floating wind platforms more accurately to refine engineering designs and reduce costs. The conventional measurements apparatus in tank tests, including wave probs, velocity and current profiler, as well as doppler sensors, are unable to give a full 3D picture of velocity, pressure, and turbulence. In tank testing, the use of the underwater stereoscopic PIV method to fully characterise the 3D flow field around floating platforms can provide a rich source of validation data and overcome some of the limitations associated with more classical measurement techniques. This optical technique can be used to accurately measure the random and chaotic structure of turbulent flows around the floater. Moreover, the main characteristics of turbulence of the flow around the floater, such as rotationality, diffusivity, irregularity, as well as dissipation, can be extracted and studied. The underwater S-PIV method has been widely used for marine and offshore applications, including studies on ship and propeller wakes and tidal stream turbines; however, to date, this technology has not seen widespread use for the hydrodynamic study of floating offshore wind turbines. Therefore, in the current study, the key considerations for using S-PIV for this purpose are discussed; meanwhile, the related studies in the field of quantitative flow measurements are reviewed.