由自由衰減試驗估算自升式風機安裝船之非線性橫搖阻尼

ESTIMATION OF NONLINEAR ROLL DAMPING FOR JACK-UP TURBINE INSTALLATION VESSELS FROM FREE DECAY TESTS

橫搖運動是自升式風機安裝船重要的性能，它將直接影響船舶能否不受天候干擾如期執行任務。為了能夠預估及預防大橫搖角及加速度發生，了解橫搖運動，特別是橫搖阻尼的物理原理是重要的。一般估算橫搖阻尼的經驗公式，如Ikeda方法，因是基於有限數量的船型而發展出來的，所以皆有其可適用範圍。具有較方形斷面且下放長尺寸樁腳的自升式風機安裝船，因偏離一般船形，可能就無法適用。為了獲取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運動特性，本計畫進行了靜水中的自然橫搖衰減的模型試驗。試驗中量測自然衰減的時間序橫搖運動量，並以三種方法進行分析，求得橫搖運動的線性及非線性阻尼係數值：Froude能量法、Faltinsen方法、以及不同橫搖振幅的類線性阻尼法。計算所得的阻尼係數值，代入相對應的自然橫搖運動方程式，然後以數值方法進行計算模擬。所模擬運動結果，分別與衰減試驗所量測的橫搖運動進行分析比較，進而探討各種分析方法的優劣。此研究目的，即針對自升式風機安裝船進行自然衰減試驗，希望藉由此試驗結果，進而獲得此類船舶的線性及非線性的橫搖阻尼係數；並且探討此類船舶各項參數，例如下放樁腳、啟始橫傾角度大小等，對於橫搖阻尼的影響，將可利於更加準確模擬此類船舶橫搖運動。

Roll motion is a major concern of jack-up turbine installation vessels because it has a direct impact on the downtime of the installation process owing to weather. To be able to predict or prevent large roll angles and accelerations, it is important to understand the physical principals of roll motion and especially roll damping. Empirical methods for prediction of roll damping, such as the Ikeda method, are also restricted in their use, as their development was based on a restricted number of hull shapes and may not be valid for such a TIV with sharp-cornered barges and long extracted legs. To capture the roll characteristics with extracted legs in zero speed operational condition, free decay model tests in calm water will be carried out in this project. Time series of roll motions will be measured for the free decay tests and linear and nonlinear roll damping coefficients will be analyzed using three methods: Froude energy method, Faltinsen method and linear damping for different amplitudes. The reliability will be confirmed by comparing the results from the numerical simulation of free roll motion equations represented by the fitted damping, and the free decay tests. 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.