由數值計算方法估算自升式風機安裝船之橫搖阻尼

ESTIMATION OF ROLL DAMPING FOR JACK-UP TURBINE INSTALLATION VESSELS BASED ON NUMERICAL CALCULATIONS

自升式風機安裝船在波浪中的運動反應性能，將影響船舶能否不受天候干擾如期執行任務。而且當定點執行任務時，橫搖運動則更加明顯。然而船舶橫搖運動的分析品質，高度取決於橫搖阻尼估算的準確性。橫搖阻尼的非線性特性乃源自流體的黏性、以及船殼及其附屬物周遭流體剝離（separation）及渦旋洩離（vortex shedding）等相關現象。自升式風機安裝船其較為方形剖面的線型與巨大的外伸樁腳，於橫搖運動時將產生大量黏性與渦流阻尼。為了探討此類具下放樁腳且於靜止無前進速度條件下作業船舶的橫搖阻尼特性，本文以流體動力計算的方法來計算模擬一自升式風機安裝船於靜水中的自然橫搖衰減運動。數值模擬乃以求解雷諾平均納維－斯托克斯方程（RANS方程）的Fluent軟體為計算工具，除了將模擬所得橫搖運動結果與之前的試驗結果進行比較，並觀察計算過程流場所呈現之剝離與渦旋洩離等現象。

Roll motion is a major concern of jack-up turbine installation vessels (TIV) because it has a direct impact on the downtime of the installation process owing to weather. The prediction of nonlinear roll motion of ships depends highly on the accurate estimation of roll damping. The nonlinear nature of roll damping arises from the viscous flow and the associated phenomenon of flow separation and vortex shedding around the ship hull and appendages. Sharp-cornered barge and long extracted legs of a TIV induce large viscous and eddy damping to the roll motion. To capture the roll characteristics with extracted legs in zero speed operational condition, CFD simulations of free roll decay of a TIV have been carried out in this project and results of time series of roll motions will be compared with those obtained from the previous experiments. In addition to comparing with the previous test results, the flow separations and vortex shedding from main hull and extracted legs during the calculation process have also been observed, and then try to analyze its influence on the roll damping. The numerical simulations will be carried out using the RANSE solver-Fluent. A good understanding of the viscous roll damping together with a validated software package that describes this, would cause the motion analysis to become more precise.