着床式洋上風力発電基礎の局所洗掘と対策案に関する検討
着床式洋上風力基礎において洗掘対策施工の工期短縮が期待できる円盤型構造の対策工を提案し，その効果を確認するための水理模型実験を実施した。円盤型対策工単体では十分な洗掘抑制効果は得られなかったが，円盤型対策工と袋型根固材を併用することで，袋型根固材のみによる従来対策工法と同等の洗掘防止効果を得られることが確認できた。また三次元流体解析ツールOpenFOAM®を用いて固定床条件で実験再現解析を実施した結果，対策工周辺で流れの加速が確認され，このため対策工単体で十分な洗掘防止効果が得られなかったと推察された。
キーワード：洋上風力，洗掘対策工，水理実験，数値解析
＊１ 技術センター 社会基盤技術研究部 水理研究室
Study on Local Scour and Countermeasure around Pile Foundation of Offshore Windfarm
The foot protection bag (PB) is the most common technique for the reduction of the local scour around the monopiles of offshore windfarm facilities. However, it takes a lot of time to set all the PB around each monopile. In this study, the collar-type countermeasures for scour control were proposed, and the reduction of local scour was investigated in the movable bed experiments. The experiment results showed that sufficient local scour reduction was not achieved when the collar-type countermeasure alone was taken. However, use of both the collar-type countermeasure and PB sufficiently reduced the local scour and that its scour reduction effect was almost equivalent to that by the PB alone. The result of 3D numerical simulation under the fixed bed condition of the experiments indicated an increase in the water flow around the countermeasure works, which led to the estimation that this phenomenon was the reason implementation of the countermeasure alone failed to achieve the sufficient scour prevention effect.
Keywords: offshore windfarm, scour countermeasure, hydraulic experiment, numerical simulation
*1 Hydraulic Research Section, Infrastructure Technology Research Department, Taisei Advanced Center of Technology