汎用解析コードを用いた洋上風力浮体基礎の動揺解析手法の提案
浮体式洋上風力施設の浮体基礎の設計や施工計画では，浮体への流体力や係留索張力の検討など浮体の動揺解析が必要である。しかし，汎用的な動揺解析コードでは，施工の際の護岸係留時の解析手法や抗力係数の影響の考慮等の課題がある。本研究では，護岸係留浮体および沖合係留浮体を対象に，汎用的な動揺解析コードの適用性について検討した。護岸係留浮体の解析では，鏡像原理の適用が有効であるが，汎用的な動揺解析コードにはその機能は搭載されていない。そこで，汎用的な動揺解析コードでも鏡像条件を適用可能な手法を提案し，実験や護岸を直接モデル化した解析と比較することで，提案手法の妥当性を検証した。沖合係留浮体の検討では，浮体の自由減衰実験結果から同定した抗力係数を用いて再現解析を行うことで，汎用的な動揺解析コードにおいても実験結果を良好に再現可能であることを確認した。
キーワード：洋上風力，水理模型実験，動揺解析，係留，鏡像，抗力係数
＊１ 技術センター 社会基盤技術研究部 水理研究室
Motion Analysis of Floating Foundation of Offshore Wind Power Facility Using General Purpose Analysis Code
In the design of and construction planning for the floating foundation of an offshore wind power generation facility, it is necessary to analyze the motion of the floating structure. Forces acting on the floating structure, such as the hydrodynamic forces acting on it and the tension of the mooring cables, should be taken into consideration. In order to use general-purpose motion analysis codes, however, it is necessary to address some issues such as calculations associated with seawall-moored structures and the effects of drag coefficients. In this study, the applicability of a general-purpose motion analysis code to the analysis of seawall-moored and offshore floating structures is verified. When analyzing the motion of a seawall-moored floating structure, it is effective to apply the mirror model image principle, but a general-purpose motion analysis code generally does not have a mirror-image modeling function. In this study, we proposed a method to apply mirror-image conditions when using a general-purpose motion analysis code and verified the validity of the proposed method by comparing the results obtained by the proposed method with experimental results and analytical results obtained by direct modeling of seawalls. In the study of applicability to offshore floating structures, we confirmed that a general-purpose motion analysis code can be used to reproduce experimental results with good accuracy by using a drag coefficient calibrated based on the results of floating structure free-decay experiments.
Keywords: Offshore wind power facility, hydraulic model experiment, motion analysis, mooring, mirror model, drag coefficient
*1 Hydraulic Research Section, Infrastructure Technology Research Department, Taisei Advanced Center of Technology