Japan aims to become one of the world’s leading producers of offshore wind energy, targeting 10 GW capacity by 2030 as part of its efforts in reaching net-zero emissions by 2050. But the global offshore wind sector is facing challenges such as high supply chain inflation and rising interest rates, and there is an urgent need to reduce both risk and cost in all phases of offshore wind farm development.

MTS is the first of its kind in Japan. It was initially developed by KU, Japan Weather Association (JWA) and RTI under a project led by a national research and development agency (NEDO) in 2023, followed by its transition to KU in April 2024. MTS provides test sites to verify accuracy of observation data measured by offshore wind measurement equipment to ultimately promote development of the renewable energy sector in Japan.

The FLS test site is exposed to high waves caused by extratropical cyclones and occasionally typhoons. A nearby vertical concrete breakwater complicates the wave field due to waves reflecting off the vertical face of the structure. RTI requested an accurate estimation of extreme wave conditions. The results had to be made available in limited time and pass thorough validation checks against measurements at the site. Traditional methods of acquiring such data can be both slow and expensive.

To quickly and accurately estimate the extreme wave conditions at the test site, the MIKE Metocean Simulator (MIKE MS) software was used to downscale a 45-years’ time series of the offshore wave conditions at the site. MIKE Metocean Simulator is a cloud-based wave modelling tool that enables marine infrastructure and offshore energy professionals to quickly assess wave conditions. The tool speeds up the modelling process by providing assisted meshing, automated boundary condition extraction and surrogate modelling techniques to provide accurate hindcast wave conditions. The tool does not require specialised wave modelling expertise.

Offshore wave conditions were taken from DHI’s Japan regional wave model. The resolution of the regional model allowed extraction of wave conditions close to the site, but it did not resolve the local bathymetry and breakwaters at the site. The MIKE Metocean Simulator was used to transform the offshore wave timeseries data to local data at the site. Wave reflection from the nearly fully reflective breakwater was also included in the model. The results were checked against results from a phase-resolving wave model MIKE 21 Boussinesq Waves, which provided additional confidence in using the MIKE Metocean Simulator.

The wave simulation showed that the wave pattern at the FLS site is highly affected by the wave reflection. The simulation was run over a few hours to obtain 45 years of metocean conditions at the site. The speed of the model runs allowed for the model setup to be adjusted and rerun several times to calibrate the model. Extreme metocean conditions for waves were established using DHI’s Extreme Value Analysis (EVA) toolbox. The calibrated results were validated against local test site measurements, and the validation confirmed the model’s accuracy.

The results clearly showed that the site is exposed to high waves, which is the key design parameter for the FLS mooring arrangement.

RTI quickly gained the detailed and accurate information on extreme metocean conditions needed to determine the optimal design of the Floating LiDAR System. The MIKE Metocean Simulator allowed results to be obtained faster and at lower cost than classic numerical modelling. The results thus contribute to eliminating risk and reducing cost in Japan’s transition to renewable energy and net-zero emissions.