S型節能舵幾何之參數化設計及計算模擬

Abstract

舵的幾何形狀在船舶操縱性上扮演重要的角色。一個設計優良的節能舵不僅需提供足夠轉向力，更可以有效回收利用螺槳後方的旋向流場動能以改進推進效率。本研究以KRISO之貨櫃船(KCS)及其附屬之五葉螺槳(KP505)幾何模型為計算模擬之對象，該項幾何模型資料係針對計算比較之需要而公開發表的，另外以參數化方式設計S型節能舵置於船艉。數值模擬方法採用雷諾平均納維－斯托克斯方程式(RANS)求解整體流場，其中搭配適當的紊流模型以解析周圍流體作用於船體的阻力。螺槳旋轉產生向前推力則選用旋轉參考座標系之技術，模擬非穩態螺槳作動。將阻力與推進性能兩者計算結果與實驗值進行比較，顯示皆在合理範圍之內。參數化S型節能舵則以Rhinoceros之外掛程式Grasshopper做系統性參數化設計，共使用11個參數來定義節能舵之幾何造型。最後加入舵進行自推實驗模擬，並進一步分析整體節能效率。在最佳化計算中，則挑出設計變數─S型線扭轉中心點位置、S型線中三點斜率及最大拱高偏移量三個參數做最佳化設計。另外以創新之〝Pivot〞方法調整S型節能舵之各段面偏轉角度，並將此方法延伸為可控參數，計算不同船速下之最佳S型節能舵外型。

A rudder is a device used to maneuver a ship by redirecting the fluid past the hull, thus imparting a turning or yawing motion to the craft. The rudder for containerships operates behind the propeller and encounters non-uniform inflow. In additional to the lateral forces exerted by the foil sections, S-type rudders incorporate functions to retrieve the rotational momentum loss from the wake field of the propeller. In the presented research the KRISO containership (KCS) hull model and the five-blade propeller (KP505) were chosen. The ship equipped with a balanced streamlined rudder composed of NACA sections. The S-type rudder was modeled parametrically by adding cambers onto each foil section to adapt to the velocity field in the wake. The camber distribution was modeled by a cubic B-spline curve and assigned four geometrical parameters. A controllable pivot moving laterally and chordwisely was added to tune the overall angle of attack of the rudder. The innovative dual-pivot mechanism provides controls over the lateral forces for steering, but also the magnitudes of recovering energy in different operational conditions. The analysis was done by the RANS numerical methods with standard k-epsilon turbulence model. The moving reference frame (MRF) method was used to simulate the rotating propeller relative to the hull and rudder. The self-propulsion condition was achieved and agreed to experimental results. The geometric parameters for the rudder were studied systematically and the optimal combination was found that the drag force of the S-type rudder was reduced by 20%. The movements of the pivot proved to affect the efficacies of ship maneuvering as well as the energy saving.